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Fabrication and properties of extrusion-based 3D-printed hardmetal and cermet components
Abstract
Hardmetal and cermet bodies were printed by fused-filament fabrication (FFF) and composite-extrusion modelling (CEM) in an SDS (shaping – debinding – sintering) process. For FFF the filaments were prepared from hardmetal (WC-10Co) and cermet powder (Ti(C,N)-Co/Ni-based) and organic binder. The CEM feedstock consisted of WC-Co MIM powder. A 3D filament printer as well as a 3D printer working with a MIM granulate were employed to fabricate printed bodies by FFF and CEM, respectively. The solvent debinding process was performed in cyclohexane (FFF-printed bodies) or water (CEM-printed bodies). Thermal debinding of all parts was performed in a tube furnace up to a temperature of 800 °C. The pre-sintered parts were then subjected to vacuum sintering by application of conventional vacuum sintering profiles up to 1430 °C for hardmetals and up to 1480 °C for cermets. Dimensional and mass changes upon the various preparation steps as well as microstructure and porosity of the sintered bodies were investigated. While the microstructure is practically identical to that of conventionally prepared materials, some cavities were present from the printing process because of yet nonoptimised printing strategy. By change of printing strategy the cavities could be minimised or even avoided. The study shows that with the applied 3D extrusion-printing techniques, hardmetal and cermet components with innovative geometries are accessible.
... Since controlling the design parameters of single material extrusion process is easy, the properties of the composite can be tuned based on the requirement to obtain mutually exclusive properties. Singh The direct approach of fabricating MMCs using material extrusion process involves SDS (shaping-debinding-sintering) [108][109][110]. This process involves direct extrusion of MMCs including ceramic (WC, VC, TiC, TiN, Cr 3 C 2 ) and metals. ...
... This process involves direct extrusion of MMCs including ceramic (WC, VC, TiC, TiN, Cr 3 C 2 ) and metals. In this process, the feedstock consists of the hardphase carbides or nitrides and metals (Co, Fe, Ni) [108]. The unbound powders can be separated easily as in the case of binder jetting. ...
... shaping), polymer debinding is carried out either by solvent or thermal debinding process. Once, the binder is completely removed, the green part is sintered at appropriate temperature to form complex shaped MMC [108,109]. A similar approach is adopted in direct ink writing (DIW) process in which the ink is composed of mixture of metallic and ceramic powders dispensed through nozzle [111][112][113][114][115][116][117][118]. ...
... For the last ten years, there has been an increase in the research on AM with respect to tungsten carbide and cermets [4][5][6]. They have been tested with powder bed fusion (PBF) [7][8][9][10][11][12][13][14], binder jetting (BJT) [15][16][17], material extrusion (MEX) [18][19][20][21][22][23][24], and vat photopolymerization (VPP) [25]. Although they still underperform compared to the pressing and sintering method [26,27], they still possess advantages related to design freedom, which can justify the use of AM for certain applications. ...
... Currently, the AM technologies that show the best results for WC-Co and cermets, are BJT and MEX [15,16,18,19,21,37]. Both use organic binders to assist in the shaping step, and both are removed afterward by debinding. ...
... Suspension MEX allows for bigger solid loadings and sintered densities, but it has difficulty with overhang structures since it is a viscous paste [21,39]. The filament method is more versatile, but it induces a bigger macroscopic porosity due to the printing strategy used [18,19,23,37]. ...
Material extrusion (MEX) allows for the production of advanced cutting tools with new internal cooling systems, which are suitable for new machining equipment. To produce cutting tools via this process, hardmetal and cermet feedstock must be prepared for the extrusion of 3D printing filaments. After shaping the 3D object (green), debinding and sintering must be performed to achieve densification. Defects and microstructural heterogeneities were studied according to the powder material. The present study shows that, although MEX is a viable solution for hardmetals, it needs to produce homogeneous filaments for cermets. The WC-Co bulk microstructures versus hardness were similar to the ones that were measured with pressing and sintering. While cermet (Ti(CN)/WC-Ni/Co) microstructures were heterogeneous, their hardness, when compared with that from the pressing and sintering manufacturing process, decreased significantly.
... • Thermoplastic elastomer (TPE): TPE helps in achieving flexibility of filaments produced [41]. During 3D printing (AM) at high temperatures, TPE makes extruded filament properly bond with previous layers, which is also called tackiness [42]. ...
... Yimin et al. [31] prepared feedstock (pellets) after compounding in a rubber mixer for MIM of 17-4 PH stainless steel powder. Lengauer et al. [41] used counter-rotating rollers at a rotational speed of R = 60 rpm for compounding feedstock and ground in a cutting mill to pelletize it for filament extrusion. Thompson et al. [54] mixed their ingredients co-rotating twin screw extruder to J o u r n a l P r e -p r o o f Journal Pre-proof fabricate filaments of SS316L powder, and Li et al. [67] used a rotor internal mixer (roller mixer) for the same metal powder (SS316L) with different additives. ...
... Gloeckle et al. [32] used the piston-type extruder to fabricate desired filaments with D = 2.7 mm diameter. Lengauer et al. [41] used a high-pressure capillary rheometer to produce filaments of hard metal and cermet powders with a diameter of D = 1.75 mm at T = 200°C. Kurose et al. [57] also used a capillary rheometer to fabricate filaments with a barrel meter of D = 9.5 mm and a die of D = 1.75 mm. ...
Additive manufacturing (AM) is suitable for fabricating components made from expensive, highstrength metallic materials, which can be designed and created with minimal material waste during
the layer-upon-layer addition process. The development of new products has already made great
use of AM technology for prototyping. Today, components created by AM are used directly
in the finished product, and in some instances, AM components are used as spare parts across
numerous industries. However, the cost of currently available metal additive manufacturing (AM)
machines for metals based on selective laser melting and the cost of part manufacture is very high.
Furthermore, the processes used by these technologies produce waste metal powder, creating an
adverse effect on the environment. As a result, there is an increasing demand for new techniques
with environmental friendliness, high mass production rates, and low production costs. In light
of this, extrusion-based metal AM techniques, which utilize the fused filament fabrication (FFF)
approach, are a great alternative to the current laser-based metal AM solutions. The extrusionbased metal printing technique uses customized filaments with metal particles distributed in a
sacrificial polymeric binder. A FFF printer is utilized to 3D print the green part. The polymeric
binder is removed from the printed parts using a catalytic solvent or debinder (depending on the
step). The final metallic parts are obtained after the sintering stage. This article thoroughly
discusses all aspects of filament fabrication, AM of green parts, debinding, sintering, and postprocessing of green and sintered parts in extrusion-based metal AM.
... Various AM methods have been reported for the preparation of WC-Co, like Selective laser melting (SLM) [7], Laser engineering net shaping (LENS) [8], Binder jet printing (BJP) [9], Fused filament fabrication (FFF) [10] and 3D gel-printing (3DGP) [11]. Owing to the high melting point, decomposition of the carbides, and small carbon interval of WC-Co, it is rather difficult to obtain qualified samples with controlled morphology using laser powder bed fusion [7]. ...
... Cramer [13] prepared 3D WC-Co by BJP combined with Co infiltration, and dense parts were achieved with some residue carbon-deficient phases. Lengauer [10] showed an example for preparing WC-10Co and Ti(C,N)-based cermets by FFF, using filaments of the composites. 3DGP for WC-20Co was reported by Zhang [11], which was a method combined gel casting and direct ink writing (also called Robocasting). ...
Direct ink writing of 3D WC-Co with conformable green bodies was achieved benefiting from the highly flexible WC-Co paste with high solid loading. Rheology properties of the paste, microstructure of the 3D structure was investigated. Organic-based paste of WC-8Co with a high solid content of 91 wt% were prepared, which exhibited shear thinning behavior and had a high storage modulus, two key parameters for ensuring the smooth printing. After secondary molding, 3D WC-Co green bodies with overhanging structure and no cracks were confirmed through secondary treatment of twisting or bending. Sound 3D structures with uniform and dense microstructure were obtained after debinding and sintering in vacuum. This work showed a facile route for the fabrication of 3D bone cemented carbides by direct ink writing with flexible green bodies.
... These studies revealed improvements in powder dispersion and rheological behavior, accompanied by a slight increase in the viscosity of the feedstocks. Lengauer et al. [32] successfully printed, debinded, and sintered WC-10Co and Ti(C,N)-Co/Ni-based cermets using TPE as a soluble polymer and PP functionalized with maleic anhydride. They highlighted the need for optimized printing strategies to achieve defect-free microstructures, which aligns with Agarwala et al. [33] who developed printing strategies to rectify defects in Si3N4 and 17-4ph stainless steel (SS) printed by powder PFFF. ...
... All microstructures exhibit zones of carbon precipitation in the Co matrix, likely resulting from excess carbon originating from the degradation of the polymeric chains in the backbone, which reduces the measured density of the sintered samples. To address this issue, a reductive atmosphere in thermal debinding will be required to remove this excess carbon [32]. The WC particles in the sintered samples showcase typical faceted structures characteristic of liquid phase sintering [51] along with abnormal grain growth due to the absence of grain growth inhibitors. ...
This research explores the utilization of powder fused filament fabrication (PFFF) for producing tungsten carbide-cobalt (WC-10Co) hardmetals, focusing on binder formulations and their impact on extrusion force as well as the influence of printing variables on the green and sintered density of samples. By examining the interplay between various binder compositions and backbone contents, this study aims to enhance the mechanical properties of the sintered parts while reducing defects inherent in the printing process. Evidence suggests that formulated feedstocks affect the hardness of the sintered hardmetal—not due to microstructural changes but macrostructural responses such as macro defects introduced during printing, debinding, and sintering of samples. The results demonstrate the critical role of polypropylene grafted with maleic anhydride (PP-MA) content in improving part density and sintered hardness, indicating the need for tailored thermal debinding protocols tailored to each feedstock. This study provides insights into feedstock formulation for hardmetal PFFF, proposing a path toward refining manufacturing processes to achieve better quality and performance of 3D printed hardmetal components.
... Compared to FFF, the CEM process can also print green parts of highviscosity feedstocks due to the screw-based MEX [31]. As a result, high metal powder content can form relatively higher dense green parts, which makes post-processing less complex. ...
... CEM ExAM 225 machine (AIM3D GmbH, Germany) was utilized for 3D printing of the feedstock. It is a screw-based MEX printer with a heatable build platform of 255 × 255 × 255 mm 3 [28,31]. The CEM printer can directly extrude the granulate rather than the filament like the FFF printer, although the extruder axis movement works similarly for both printers. ...
... These studies revealed improvements in powder dispersion and rheological behavior, accompanied by a slight increase in the viscosity of the feedstocks. Lengauer, et al. [32] successfully printed, debinded, and sintered WC-10Co and Ti(C,N)-Co/Ni-based Cermets using TPE as a soluble polymer and PP functionalized with maleic anhydride. They highlighted the need for optimized printing strategies to achieve defect-free microstructures, which aligns with Agarwala et al. [33] who developed printing strategies to rectify defects in Si3N4 and 17-4ph stainless steel (SS) printed by FFF. ...
... All microstructures exhibit zones of carbon precipitation in the Co matrix, and this can be explained by carbon excess from the polymeric chains' degradation of the backbone, which reduces the measured density of the sintered samples. A reductive atmosphere in thermal debinding will be required to remove this excess carbon [32]. The WC particles in the sintered samples showcase typical faceted structures characteristic of Liquid Phase Sintering [44], along with abnormal grain growth due to the absence of grain growth inhibitors. ...
This research investigates the application of Fused Filament Fabrication (FFF) in producing WC-10Co hardmetals, focusing binder formulations and understanding its influence on extrusion force and the influence of printing variables on green density of the samples. By examining the interplay between different binder compositions and backbone contents, the study aims to enhance the mechanical properties of the sintered parts while reducing defects inherent in the printing process. Evidence suggested that formulated feedstocks influenced the hardness of the sintered hardmetal, not due to microstructural changes but to macrostructural responses like macro defects introduced during printing, debinding and sintering of the samples. The results demonstrate the critical role of PP-MA content in improving part density and sintered hardness, suggesting the need for specific thermal debinding protocols tailored to each feedstock. The study provides insights into the formulation of feedstocks for hardmetal FFF, proposing a path toward refining manufacturing processes for better quality and performance of 3D printed hardmetal components.
... Fig. 25. An indexable cutting insert with a looped cooling channel, produced by ceramic FDM process (a) CAD model, (b) As printed, (c) As sintered [57]. The characterization techniques discussed in this section are useful in identifying the required characteristics of the input feedstock and composite filaments. ...
... The composite filaments can also be used to print complex features. Lengauer et al. [57] printed an indexable cutting insert with a looped cooling channel from a filament made of WC-10 Co as a hard metal and Ti (C, N)-Co/Ni as a cermet powder and an organic binder as matrix as shown in Fig. 25. This cutting component can keep the thermal loads constant while saving money on coolants. ...
The usage of plastics has become an inherent part of human life due to low cost, light weight, flexibility and ease of production. The degradation time for plastics is one of the major concerns currently the world is facing. According to the United Nations Sustainability Development (UNSD), a major percentage of currently available plastic must be either recycled or reused for a sustainable ecosystem. In this systematic review a methodology is presented to recycle the discarded plastics, metal, and ceramic scrap for the fabrication of composite filaments for material extrusion based 3D printing. The capabilities and recent progress in material extrusion based metal additive manufacturing are reviewed to identify the potential recyclable resources. The sustainable and entrepreneurial opportunities for recyclable materials for composite filament fabrication are discussed. It is observed that the composite filament must contain a minimum of 40 vol% reinforcement infill to make the printed parts eligible for sintering. The applications of the material extrusion based metal and ceramic additive manufacturing are detailed. The limitations, future directions and the possible improvements are explained. From this comprehensive review, it is expected that the reader will attain a proficient understanding of the sustainable process involved in fabricating metal and ceramic particle filled polymer composite filaments.
... Another approach is to use multi-step additive manufacturing processes. Researchers use binder jetting (BJ) [9,[30][31][32][33][34][35][36][37][38][39][40], fused filament fabrication (FFF) [41], or 3D gel printing (3DGP) [42,43] to produce green parts, which are then sintered. Mixtures of cemented carbide powders and special flowable or fusible materials are used as raw mate-rials. ...
... Due to the lack of pressure, the density of powder compacts and sintered samples obtained by this method is lower than the density of powder compacts and samples obtained by conventional technology such as CP and metal injection molding. This also forces the use of pressure or raising the sintering temperature [28,[30][31][32]41,42]. ...
In this work, we propose the use of 3D printing to make molds for pressing cemented carbide compacts. The fused material extrusion technique was used to make solid molds from polylactide for pressing a rectangular standard sample and a square cutting insert. The densification of the WC-15Co powder mixture combined with rubber (2%) was studied at pressures ranging from 41 to 121 MPa in the obtained molds. A comparative analysis of the density of powder compacts and sintered products and their properties was performed against their analogs formed by pressing in a hardened steel mold at a pressure of 210 MPa. Increasing the pressure in the plastic molds from 41 to 121 MPa led to an increase in the relative density of powder compacts from 65% to 70%. The relative density of powder compacts (75%) obtained by the steel mold pressing at a pressure of 210 MPa was only 5% higher. The density of sintered samples increased from 99.22% to 99.5% when the molding pressure was increased, which was only 0.29% lower than the density obtained by steel mold pressing. The hardness (1130-1160 HV) and fracture toughness (23.1-24 MPa m 1/2) of samples produced in the plastic molds differed slightly from those produced in the steel molds (1170 HV and 24.4 MPa m 1/2). In terms of the hardness and fracture toughness combination, the samples obtained by this technique were superior to those obtained by the selective laser melting method and were comparable to the samples obtained by sintering of powder compacts produced by various 3D printing methods (binder jetting, 3D gel printing, material extrusion).
... AM technology has been applied to the aerospace, medical, automotive, and engineering industries due to its many advantages, such as the complexity of the parts it can create, short fabrication time, and repeatability. Powder extrusion additive manufacturing (PEM) is an indirect printing technology that relies on its extensive design freedom and cost-effectiveness over traditional AM technologies such as selective laser melting based on high-energy beams [31,32]. PEM takes place at low temperatures and printing does not involve melting of metal and ceramic powders, allowing for precise control of the gradient layer's thickness, composition, and uniformity. ...
Ti(C,N)-based cermets are crucial for high-speed cutting tools and other high-temperature applications, yet there remains a considerable gap in their preparation controllability, fracture strength, and toughness compared to cemented carbide. Despite numerous studies having focused on modifying the hardness and toughness of Ti(C,N)-based cermets by varying process parameters and chemical compositions, this research has used gradient Ti(C,N)-based cermets produced by powder extrusion additive manufacturing (PEM) technology, which is rare. This study developed the gradient structure layer by layer using PEM. The microstructure of the printed and sintered parts was studied, and the hardness, fracture toughness, and bending strength of the gradient material were analyzed. The gradient material demonstrates superior mechanical properties compared to traditional Ti(C,N)-based cermets, with a hardness of HV20, a fracture toughness of MPa·m1/2, and a bending strength of MPa. The research will assist researchers in assessing the potential application of PEM and broaden the application fields of gradient Ti(C,N)-based cermets.
... Single screw print heads were developed in the mid-2000s as an alternative to filament-based 3D printers. The technology finds applications in recycling [11,12], bio fabrication [13][14][15][16][17], low-cost metal and ceramic 3D printing [18,19], and personalized medicines [20]. However, in general, print heads based on single show limited process flexibility and mixing capacity. ...
This paper investigates the die swell phenomenon in material extrusion additive manufacturing (MEX-AM) using customized 3D printing equipment with a co-rotating vertical twin-screw extrusion unit (Co-TSE AM). In twin-screw-based MEX-AM, the output rate is independent of the screws’ rotational speed, and the complex die geometry impacts the thermomechanical behavior of the flow, thus affecting the die swell ratio (DSR). Towards exploring two premises, namely, influence of the Co-TSE AM die’s complex geometry and influence of the main extrusion parameters, this study estimated the shear rate in the screws and die analytically and designed experiments to evaluate the effects of screw rotational speed, output rate, and nozzle diameter on the DSR. Scanning electron microscopy (SEM) assessed filament morphology and surface texture. The main results show DSR averages between 1.28 and 1.67 and both output rate and nozzle diameter significantly influence DSR, whereas screw rotational speed has no significant impact on the thermomechanical environment affecting material swelling. Filament width and height are differently influenced by standoff distance and print platform speed. The study enhances the understanding of the way extrusion parameters affect die swell in twin-screw MEX-AM, contributing to improved control and quality in single-step additive manufacturing processes.
... On the other hand, as sinterbased routes are implemented following sequential and separated stages of geometrical shape formation and final consolidation by sintering, they are usually capable of achieving homogeneous two-phase microstructures; thus, it is aimed for the properties to be linked to the proper processing and compositions of hardmetals. Within this framework, two material delivery routes-binder jetting (BJT) [9][10][11][12][13][14][15] and material extrusion [16][17][18][19][20][21]-have emerged as the leading technologies for fabricating hardmetal parts. However, different from the latter, the former is the only one that has currently achieved maturity to fabricate hardmetal parts on a mass scale [7]. ...
Binder jetting additive manufacturing offers a promising route to produce complex geometries in cemented carbides (WC-Co), but it may introduce direction-dependent microstructural variations potentially affecting wear resistance. This study investigates the influence of printing direction on the sliding contact response of 3D-printed and subsequently sintered (BJT) WC-12%Co. Prismatic specimens were printed along two orientations and subjected to single and repetitive scratch tests on three orthogonal faces. The microstructure, Vickers and scratch hardness, and wear rate were analyzed. The results showed a heterogeneous microstructure consisting of a matrix of fine carbides where several large particles where embedded. It was different from the homogenous microstructural scenarios exhibited by conventionally pressed and sintered fine- and coarse-grained hardmetals, used as reference for comparison purposes. The influence of printing direction on either the microstructure or mechanical properties of BJT specimens was found to be negligible. Interestingly, BJT samples exhibited superior wear resistance than the reference hardmetals, even though the hardness levels were alike for all the studied hardmetal grades. Such behavior is attributed to the co-existence of coarse and fine carbides within the microstructure, combining the energy absorption capability of the former with the inherent strength of the latter. These findings, together with the intrinsic flexibility and versatility advantages associated with additive manufacturing, highlight the potential of BJT hardmetals to be used in applications where contact load bearing or wear resistance are critical design parameters. Finally, the effectiveness of implementing an iterative sliding contact test for evaluating wear behavior in cemented carbides was also validated.
... The method is also applied for metal or ceramic 3D printing by filling a thermoplastic material with high contents of metallic or ceramic powder (approx. 50 vol%) [16][17][18][19][20][21][22]. ...
Amines supported on porous solid materials have a high CO2 adsorption capacity and low regeneration temperature. However, the high amine load on such substrates and the substrate itself may lead to substantial pressure drop across the reactor. Herein, we compare the CO2 adsorption capacity and pressure drop of fumed silica powder to 3D-printed monolithic fumed silica structures, both functionalized by polyethylenimine (PEI), and find a drastically reduced pressure drop for 3D-printed substrates (0.01 bar vs. 0.76 bar) in the sorption bed with equal CO2 adsorption capacity. Furthermore, the effect of 3D-printing nozzle diameter and PEI loading on the adsorption capacity are investigated and the highest capacities (2.0 mmol/g at 25 °C with 5000 ppm CO2) are achieved with 0.4 mm nozzle size and 34 wt% PEI loading. These high capacities are achieved since the 3D printing and subsequent sintering (700 °C) of monolithic samples does not compromise the surface area of the fumed silica. Finally, the comparison between 3D-printed monoliths and extruded granulate of varying diameter reveals that the ordered channel system of 3D-printed structures is superior to randomly oriented granulate in terms of CO2 adsorption capacity.
... Single screw print heads were developed in the mid-2000s as an alternative to lament-based 3D printers. Furthermore, this technology nds application in recycling [11,12]; bio fabrication [13][14][15][16][17], lowcost metal and ceramic 3D printing [18,19] and personalized medicines [20]. However, generally, the print heads based on single screw, have limited process exibility and mixing capacity. ...
The study of die swell phenomenon in Material Extrusion Additive Manufacturing (MEX-AM) technologies holds great importance in order to maintain the control over the extruded beads diameter to ensure surface quality, dimensional precision, adhesion between adjacent beads (intra and inter), as well mechanical properties on manufactured parts. This paper addresses an experimental procedure to analyze the influence of extrusion parameters on the die swell phenomenon on extruded beads printed from a 3D customized equipment containing a customized co-rotating vertical twin-screw extrusion unit (Co-TSE AM). In this context, an analytical estimation of shear rate in the screws and die was performed; a design of experiments (DOE) was conducted to evaluate the influence of factors as of screw rotational speed (40 rpm and 80 rpm), output rate (20 g/h and 40 g/h), and nozzle diameter (0.4 mm and 0.6 mm) on the die swell ratio (DSR); and scanning electron microscopy (SEM) was employed to assess the morphology in the cross-sectional area of the beads, as well as qualitative aspects of surface texture. Additionally, print line experiments were conducted to examine the influence of platform speed and standoff distance on bead width and bead height. It was observed that the DSR average varied between 1.28 and 1.67. Output rate and nozzle diameter are the parameters that most strongly influence DSR. Screw rotational speed has not significant influence on the thermomechanical environment that influences material swelling. The bead width and bead height are differently influenced by the standoff distance and print platform speed.
... The component must be mixed properly to eliminate the risk of insufficient filament quality and deformation of product during printing. Both tiny batches and continuous mixing are possible(Cañadilla et al., 2022;Gonzalez-Gutierrez et al., 2018;Hertle et al., 2020;Lengauer et al., 2019; Strano et al., 2019b). Different mixers and grinders might be used in the initial arrangement. ...
Rapid prototyping to expensive items like sophisticated spare parts are just a few of the high-end products that can now be made using additive manufacturing (AM). The future of the manufacturing industry has been influenced by AM, which has advantages of lower material utilisation, geometric freedom, and production automation imaginable. With the rapid expansion of additive manufacturing (AM) applications, feedstock materials have undergone a significant transformation. These materials now include metals, composites, polymers, and ceramics. The development in metal feedstock material discoveries has made it possible to investigate the use of new AM methods. The very popular and economical material extrusion AM technique is fused filament fabrication (FFF). The article outlines the key concepts for FFF-based 3D printing of metal items. The process involves stacking filament that contains molten metal. Steel, ceramic, carbide, aluminium, and copper powders are utilised in the Metal Fused Filament Fabrication (MFFF) process. The powder particles need to be a particular size and form. The combination is then used to create filament. The preparation of the filament and the printing of the object are both covered in the paper. Analyses are done on the potential applications for MFFF technology. It has been shown that the technique holds great promise for various domains. The potential for further study in this field is also highlighted.
... Additive manufacturing (AM), also known as 3D printing, is regarded as one of the revolutionary technologies due to its low cost, short manufacturing cycles, and personalized customization of complex geometric parts [9]. Nowadays, additive manufacturing mainly includes digital light processing (DLP) [10,11], melt deposition manufacturing [12], selective laser sintering/selective laser melting [12], inkjet printing [13], and fused-filament fabrication [14], etc. Among those techniques, stereolithography is an additive manufacturing based on the preparation of slurry from resin monomers capable of photopolymerization reactions [15]. ...
Tungsten carbide-cobalt (WC-Co) cemented carbide has a wide range of application prospects in a wide range of industries because of its high strength, high hardness, excellent wear resistance, high temperature resistance, corrosion resistance, etc. Additive manufacturing (AM) makes it possible to fabricate geometrically complex tools compared to traditional manufacturing techniques. However, the preparation of high solid loading, superior stability, and optimal curing thickness of WC-Co cemented carbide slurry remains challenging for creating cemented carbide components with complex shapes via stereolithography. In this work, the dispensability, stability, and curing thickness of WC-Co cemented carbide slurry were systematically investigated. The suitable WC-Co (94-6wt.%) cemented carbide slurry for stereolithography was successfully achieved by ball milling under appropriate process parameters, and the complex-shaped WC-Co (94-6wt.%) cemented carbide green bodies were fabricated. This work aims to provide a reference for additive manufacturing of near-net-shape WC-Co cemented carbide parts by stereolithography.
... The second group includes multiple-step processes, in which forming and densification are performed at separate stages with different equipment. Namely, the most relevant are as follows: fused deposition modelling (FDM) [12,13], selective laser sintering (SLS) [14], in which the fusion occurs only in the polymer shells of the powders, and binder jetting additive manufacturing (BJAM) [15][16][17][18]. Multi-step processes combine the forming of a green-body with a subsequent thermal treatment (debinding-sintering) as in traditional powder metallurgy. ...
This study investigates the influence of different sinter-HIP temperatures and binder saturation levels on the microstructure and properties of WC-12Co cemented carbide, produced using binder jetting. The sinter-HIP process was performed at 1400 • C, 1460 • C, and 1500 • C and binder saturation levels of 60% and 75% were selected during printing. The binder saturation proved to affect the repeatability of the manufacturing process and the sturdiness of the green models. The increase of the sintering temperature from 1400°C to 1460°C is correlated with an increase in the density. Nonetheless, a further raise in temperature to 1500°C leads to significant grain coarsening without clear advantages in terms of porosity reduction. Both the transverse rupture strength and Vickers hardness increase when the sinter-HIP temperature rises from 1400°C to 1460°C, where the typical results for traditionally manufactured WC-12Co are met, with a comparable grain size. The transverse rupture strength and Vickers hardness then decrease for samples treated at 1500°C. Finally, potential issues in the manufacturing process are identified and correlated with the defects in the final components.
... Nevertheless, with the development of advanced materials combined with high performance, lightweight, and integration of structure and function, cermet with the complex-shaped structure attracts much attention. 20,21 Moreover, several net-shaping methods have been developed for the fabrication of fine cermets including gelcasting, 22 extrusion-based 3D printing, 23 and ceramic injection molding (CIM). 24 CIM is an innovative plastic shaping process that combines powder metallurgy technology with plastic injection molding, enabling the production of net-shaped components without additional processing. ...
Carbon‐free aluminum electrolysis is crucial for achieving the low‐carbon development and carbon neutrality in the future aluminum industry. NiFe2O4‐based cermet is the potential candidate of inert anode, benefiting from the satisfactory corrosion resistance and high‐temperature conductivity. Herein, complex‐shaped 25(Cu–20Ni)/(NiFe2O4–10NiO) cermets were fabricated via a plastic shaping method using the polyformaldehyde (POM)‐based granular feedstock. The feedstock showed uniform microstructure with evenly dispersed powders wrapped in polymers, which exhibited shear‐thinning behavior during molding. Roles of the feedstock with different powder loadings in the morphology and bending strength of the cermets were investigated. High‐precision gear parts exhibited no deformation, a high relative density over 98%. Investigation of different powder loadings revealed that parts prepared with a 56 vol% loading demonstrate the excellent performance, and possessed an impressive flexural strength of 178.4 MPa. This achievement provided a foundation for the future utilization of complex‐shaped inert anode material components in industrial applications.
... The most common indirect AM technology type is the MEX process, which uses high-filled filaments with metal powders as a starting material to create a final component shape instead of removing excess material. MEX has been tested in the production of complex-geometry parts from metals [16,17], ceramics [18,19], and cermets [20,21]. The metal extrusion technique follows the three-stage PDS (Printing-Debinding-Sintering) methodology. ...
Material extrusion is a suitable technology for the additive manufacturing of complex components from any family of materials. The processing of metallic parts involves a three-stage methodology known as PDS (Printing-Debinding-Sintering). In the printing stage, filaments made of metallic powder and a polymeric binder system are used. After printing, the binder must be removed, and the parts sintered to obtain densified metal components with the final properties. These last two stages, in particular sintering, require high temperatures, and are thus high-energy demanding processes. The use of the Concentrated Solar Energy (CSE) is increasingly the focus of research in materials science as it is a clean, non-polluting, renewable energy resource, which is highly efficient for high temperature materials processing. This is the first study to analyse the feasibility of using CSE in the thermal debinding and sintering stages in the production of metallic components via Printing-Debinding-Solar Sintering (PDSS) technology. The objective is to develop a new sustainable process for producing metallic components by combining additive manufacturing and solar energy. In this study, pure copper cylindrical parts were produced and sintered in a low-cost Fresnel lens. The results revealed that solar sintering occurred at lower temperature (975 °C) and much shorter time (∼1 h) than in the conventional process, enhancing the economic and environmental efficiency of the conventional manufacturing process.
... The development of hardmetal components through additive manufacturing has been extensively investigated for several years. Various additive manufacturing techniques have been researched, including the classic powder-bed fusion (PBF) processes [1][2][3][4][5][6][7][8], filamentbased methods (FFF, MEX) [9][10][11][12][13], suspension-based methods (VPP, MMJ) [14][15][16], and the promising powder-bed-based binder jetting (hereafter referred to as BJT according to DIN EN ISO/ASTM 52900; Additive manufacturing-General principles-Fundamentals and vocabulary (ISO/ASTM 52900:2021). Beuth Verlag GmbH: Berlin, Germany, 2022). ...
For several years, researchers have been exploring the use of the binder jetting powder-based additive manufacturing process to produce WC-Co hardmetals. Compared to other additive manufacturing processes, binder jetting has the potential for high-volume production. However, due to the powder-based approach, the resulting green bodies typically have low green density, limiting the achievable hardness and requiring higher Co content. Choosing the appropriate starting powder and post-processing can extend previous limitations and allow the selection of a suitable powder based on the application. This investigation focuses on exploring and evaluating the correlation between varying morphologies of WC-Co starting powders, their processability using the BJT method, and the resultant mechanical properties of sintered components.
... It is noteworthy that some materials, such as very soft or highly filled materials, pose significant challenges in converting them into filaments. To make metals and ceramics printable through MEX, a thermoplastic binder is blended with a significant amount of solid filler, typically exceeding 40 vol% of ceramic or metallic powder [19][20][21][22][23][24][25][26][27]. The high filling of the feedstock leads to additional challenges during printing, for example difficulties to print overhangs and bridges, layer-to-layer adhesion or clogging of the nozzle. ...
Aluminum die casting is a well-established industrial process for mass producing aluminum parts with complex shapes, but design restrictions exclude some features like undercuts and hollow structures from being produced with this method. Water-soluble casting molds offer a promising solution to overcome those restrains, for example by hot pressing of salt cores or 3D printing of NaCl molds. Presently, 3D printing techniques available for NaCl are limited to direct ink writing (DIW) and photopolymerization. This study presents an approach to prepare NaCl parts by thermoplastic material extrusion (MEX) 3D printing. Firstly, a 3D printable feedstock is developed consisting of an organic binder, which is usually used for ceramic injection molding, and sodium chloride (NaCl) salt crystals. Various molds are then printed on a granulate-fed MEX printer. After thermal debinding and sintering at 690 °C, the 3D printed parts consist of pure NaCl. Furthermore, the same NaCl feedstock is used for injection molding. The bending strength of 3D printed samples with and without post-treatment are measured and compared to injection molded test specimens. Finally, metal casting in 3D printed NaCl molds is shown with tin or aluminum and the metal demonstrator parts with complex geometries such as gyroid structures and turbine wheels are released by dissolving the NaCl molds in water.
... Qualitative and quantitative analysis of the pores in the green and sintered parts using micro-tomography confirmed that the optimized printing parameters were beneficial for the final microstructure. In addition, several researchers have also investigated the FDM process of other metallic or ceramic materials; for example, 316L [25][26][27], 17-4PH [28,29], copper [30,31], hardmetal [32], Ti6Al4V [33,34], tungsten heavy alloy [35], H13 [36], Al [37], 1.2083 steel [38], zirconia [39,40], etc. However, no studies on the FDM of 15-5PH stainless steel (15-5PH SS) materials were found in the available literature. ...
Metal FDM technology overcomes the problems of high cost, high energy consumption and high material requirements of traditional metal additive manufacturing by combining FDM and powder metallurgy and realizes the low-cost manufacturing of complex metal parts. In this work, 15-5PH stainless steel granules with a powder content of 90% and suitable for metal FDM were developed. The flowability and formability of the feedstock were investigated and the parts were printed. A two-step (solvent and thermal) debinding process is used to remove the binder from the green part. After being kept at 75 °C in cyclohexane for 24 h, the solvent debinding rate reached 98.7%. Following thermal debinding, the material’s weight decreased by slightly more than 10%. Sintering was conducted at 1300 °C, 1375 °C and 1390 °C in a hydrogen atmosphere. The results show that the shrinkage of the sintered components in the X-Y-Z direction remains quite consistent, with values ranging from 13.26% to 19.58% between 1300 °C and 1390 °C. After sintering at 1390 °C, the material exhibited a relative density of 95.83%, a hardness of 101.63 HRBW and a remarkable tensile strength of 770 MPa. This work realizes the production of metal parts using 15-5PH granules’ extrusion additive manufacturing, providing a method for the low-cost preparation of metal parts. And it provides a useful reference for the debinding and sintering process settings of metal FDM. In addition, it also enriches the selection range of materials for metal FDM.
... Industrial-ready binderbased AM technologies as Material Extrusion Additive Manufacturing (MEX) and Binder Jetting (BJ) have been starting to come an economic alternative to the powder-based technologies [1,2]. The extrusion-based processes allow to avoid raw material loss during the process and to avoid risks for human health due to the release of respirable small particles, because the metal powder is embedded in a filament [3]. Moreover, a lower initial investment for the equipment is required [4]. ...
Material Extrusion (MEX) is one of the most popular Additive Manufacturing technologies. Over the years, the material portfolio has expanded and nowadays, it covers metals such as stainless steels, copper and titanium alloys. The mechanical behaviour of metal parts realized by MEX is of great interest to understand both the potentialities and the limits of the technology. In the present work, a commercial filament of 17-4 PH stainless steel was used as feedstock material to realize four groups of bending specimens obtained by varying the printing direction and the infill line strategy. The main goal of the paper was to evaluate the effect of the above-mentioned factors on the flexural properties. With this purpose, a three-points bending test was performed and results were analysed using the one-way ANOVA approach. The density of the parts was also evaluated.
... Several metallic materials have been used so far with this process: stainless steels 316L [7][8][9][10][11][12][13][14][15] and 17-4PH [16][17][18][19][20][21]; titanium [22][23][24][25]; hard metals and tungsten [26,27]; and copper [28]. Beside metallic materials, ceramic powder [29] and combined ceramic and metal powder [30] can also be used in the feedstock of this process to produce ceramic and metal-ceramic composite parts. ...
... Consequently, only a few commercial feedstocks are available [18][19][20]. However, many researchers have used FFF for different metals such as hard metals [21], Fe [22,23], steel [24,25], copper (Cu) [23], Ti-Al-V [26,27], W-Cr [28], Ni-Ti [29], Mg-Al-Zn [30] along with various binder formulations. ...
The current study presents the effect of the backbone as an important binder component on the mechanical, rheological, and thermal properties of Aluminium (Al) alloy feedstocks. A thermoplastic elastomer (TPE) main binder component was blended with either polypropylene (PP), grafted-maleic anhydride-PP (PPMA), or grafted-maleic anhydride-PPwax (PPMAwax) plus PP, as the backbone. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were performed to investigate the thermal properties of binder systems and feedstocks. Fourier-transform infrared (FTIR) spectroscopy was used to study the chemical interaction between the binder and the Al alloy. After making feedstock filaments, tensile tests, scanning electron microscopy (SEM), and fused filament fabrication (FFF) printing were done. The results showed that although the PP printability was acceptable, the best mechanical properties and printed quality can be achieved by PPMA. TGA test showed that all binder systems in the feedstocks could be removed completely around 500 °C. From FTIR, the possibility of chemical reactions between Al alloy particles and maleic anhydride groups on the grafted PP backbone could explain the better dispersion of the mixture and higher mechanical properties. Tensile strength in PP samples was 3.4 MPa which was improved 1.8 times using PPMA as the backbone.
... Known for their elasticity and thermoplastic processing, these two materials have excellent mechanical properties and can bond to a variety of materials [30]. Application studies of TPE-based binders have shown good properties in FDMS [31][32]. Modified polyolefins often act as lubricants between the different components in the mixture and increase the compatibility between the different materials. ...
... After printing a "green" part, the polymer is removed from it by the active medium (debiding operation), and the resulting, so-called "brown" part is sintered in a high temperature vacuum furnace. The method does not impose strict requirements on the characteristics of powders and makes it possible to manufacture complex-shaped parts from various materials [19][20][21]. ...
The paper shows the possibility of synthesizing microparticles coated with nanoparticles by electric explosion of a wire made of Ti-6Al-4V alloy. Particles in which the core is a microparticle and the shell of a nanoparticle can provide effective sliding of the microparticles relative to each other and are promising for obtaining flowable metal-polymer compositions filled with powder up to 70 vol.%. Such compositions are promising feedstocks for the additive molding of complex metal parts, for example, customized implants from the Ti-6Al-4V alloy, by material extrusion. The article describes the properties of feedstock based on micro- and nanoparticles of the Ti-6Al-4V alloy, the microstructure and some mechanical properties of sintered samples. The structure, bending strength and Vickers hardness of additively formed samples sintered at a temperature of 1200 °C was investigated.
Additive manufacturing (AM) is a rapidly developing technical field that is becoming an irreplaceable tool to fabricate unique complex-shaped parts in aerospace, the automotive industry, medicine, and so on. One of the most promising directions for AM application is the design and production of multi-material components with different types of chemical, structural, and architectural gradients that also promote a breakthrough in bio-inspired approaches. At the moment there are a lot of different AM techniques involving various types of materials. This paper represents a review of extrusion-based AM techniques using metal-polymer composites for structural metal parts fabrication. These methods are significantly cheaper than powder bed fusion (PBF) and directed energy deposition (DED) techniques, though have a lower degree of part detail. Thus, they can be used for low-scale production of the parts that are not rentable to produce with PBF and DED. Multi-material structures application in machinery, main aspects of feedstock preparation, the subsequent steps of extrusion-based 3D printing, and the following treatment for manufacturing single-metallic and multi-metallic parts are considered. Main challenges and recommendations are also discussed. Multi-metallic extrusion-based 3D printing is just a nascent trend requiring further wide investigation, though even now it shows pretty interesting results.
Purpose
This study aims to develop a highly loaded filament with spherical metallic particles for fused filament fabrication (FFF) technology. The research focuses on optimizing powder loading, printing parameters and final processes, including debinding and sintering, to produce successful metal parts.
Design/methodology/approach
The optimal powder loading was identified by measuring mixing torque and viscosity at various temperatures. The filament was extruded, and printing parameters − particularly printing speed to ensure proper material flow − were optimized. Different filling patterns were also examined. After printing, the polymeric binder was removed and the parts were sintered to form the final metal components.
Findings
The optimal powder loading was determined to be 55 vol.%. The best surface quality was achieved with an optimized printing speed of 5 mm/s. Parts printed with various infill patterns were studied for differences in open, closed and total porosity, showing a strong link between porosity and infill pattern.
Originality/value
This comprehensive study provides new insights into manufacturing metal parts using FFF technology. It fills a gap in the literature regarding feedstock viscosity and shear rate in highly loaded metal filaments during FFF. Additionally, it uniquely examines the open, closed and total porosity of metal parts printed with different infill patterns.
Recently, the material extrusion (MEX) method, known for its straightforward and economical setup, has become a focal point in metal additive manufacturing. MEX enables the fabrication of precise 3D models by molding metal powders with resin, followed by debinding and sintering processes. Through material development, this method is expected to become more extensively applied for the development of various functional parts by materials and shape designated using topology optimization and lattice structures. This review covers the MEX process, including feedstock, equipment, materials, printing, debinding, sintering, and the physical properties of sintered parts.
Additive manufacturing (AM) has attracted huge attention for manufacturing metals, ceramics, highly filled composites, or virgin polymers. Of all the AM methods, material extrusion (MEX) stands out as one of the most widely employed AM methods on a global scale, specifically when dealing with thermoplastic polymers and composites, as this technique requires a very low initial investment and usage simplicity. This review extensively addresses the latest advancements in the field of MEX of feedstock made of polymers highly filled with metal particles. After developing a 3D model, the polymeric binder is removed from the 3D-printed component in a process called debinding. Furthermore, sintering is conducted at a temperature below the melting temperature of the metallic powder to obtain the fully densified solid component. The stages of MEX-based processing, which comprise the choice of powder, development of binder system, compounding, 3D printing, and post-treatment, i.e., debinding and sintering, are discussed. It is shown that both 3D printing and post-processing parameters are interconnected and interdependent factors, concurring in determining the resulting mechanical properties of the sintered metal. In particular, the polymeric binder, along with its removal, results to be one of the most critical factors in the success of the entire process. The mechanical properties of sintered components produced through MEX are generally inferior, compared with traditional techniques, as final MEX products are more porous.
Material extrusion additive manufacturing is of increased interest in producing materials with very high loadings of particles, specifically through the use of the direct ink write (DIW), or robocasting, technique and the use of highly loaded particle suspensions (HLS). Applications from biomedical composites to solid rocket propellants to powder metallurgy green bodies would benefit from the complex parts enabled by additive manufacturing but require very high particle contents during processing. This leads to very high viscosity fluids and challenges in flowing and curing the inks. In this comprehensive review, we examine the main components of designing an ink formulation and a DIW process: the ink rheology, the print mechanics and the solidification/post-processing. Our expanded discussion of these elements includes an introduction to the basics as well as the latest research in the field, so serves to both introduce a new practitioner and generate new ideas for those already working in the area. We finish with a discussion of two important applications and a perspective on the future directions of DIW for highly loaded particle materials.
All solid‐state batteries pave the way to safer batteries as they do not contain flammable components and allow potentially higher energy densities through the direct use of alkali metals as anode materials. However, the applicability of solid electrolytes is hindered by their slower diffusion kinetics and charge transfer processes compared to liquid electrolytes. The purpose of this study is to investigate the electrochemical performance of 3D printed ceramic electrolyte. Prepared filaments were printed with optimized parameters and the polymeric binders were subsequently removed by solvent/‐thermal debinding followed by a sintering process. The most reliable prints were performed with 58 vol % filled feedstock and the highest densities of sintered specimen were measured at a sintering temperature of 1100 °C with (94.27±0.37)% and (94.27±0.07)% for printed and pressed samples, respectively. The lowest impedances for 3D printed samples were measured for 1100 °C sintered specimen, yielding conductivities of (1.711±0.166)×10⁻⁴ S cm⁻¹ at 200 °C. Stripping/plating tests performed at 60 °C confirmed the feasibility of 3D printed electrolytes realized by Fused Filament Fabrication (FFF) for the application in solid‐state batteries.
Fused Filament Fabrication (FFF), also known under Stratasys' trademark name Fused Deposition Modelling (FDM) is a polymer-based additive manufacturing method and in wide use for the 3D-printing of polymer parts. When using a specially developed, highly filled metal/polymer feedstock (55 vol.%), FFF can also be applied as a shaping method for metallic green parts as an alternative to injection moulding in the MIM process. In this paper, the specific properties of sintered 316L (1.4404) steel parts, printed on a tailored Fused Filament Fabrication machine, then debinded and sintered as in the conventional MIM process, are discussed. An overview of the state-of-the-art of the equipment, respective processing parameters, currently achieved sinter shrinkage, densities and achievable surface quality are given.
Long lifetime, low wear and high dimensional accuracy are essential requirements for tools in the metal processing industry. High temperatures in the interaction zone between tool and component are harmful and lead to premature malfunction and imprecise processing results. To counteract these, cemented carbides are utilized with suitable properties in terms of stiffness and strength. Furthermore, the lubricants and coolants are used to reduce the temperature to a tolerable degree and to create suitable conditions for the machining. To guarantee an efficient fluid transport, tools include transport channels. These are difficult to achieve with conventional manufacturing methods. Additive manufacturing opens up new possibilities for implementing cavities with almost any shape. This paper presents the design of carbide cutter shafts and their manufacturing. The course and cross-section of channels are optimally designed for the requirements of the process zones to be cooled. The additive production by powder bed based laser sintering required a definition of the process parameters scanning speed, layer thickness and hatch distance that was adapted to the cemented carbide. This is supported by extensive materials characterization methods such as light and electron microscopy, qualitative and quantitative microstructure analysis and mechanical tests (bending strength, Young’s modulus, hardness, fracture toughness). The results are used to correlate process parameters, microstructure development and properties. The objective is to create a parameter set suitable to manufacture tungsten carbide cobalt hard metal parts with similar properties than conventionally produced hard metals. The cutter shafts produced by the additive process have a diameter of 16 mm and will be equipped with brazed cutting inserts in a further process step.
Additive manufacturing (AM) is the fabrication of real three-dimensional objects from metals, ceramics, or plastics by adding material, usually as layers. There are several variants of AM; among them material extrusion (ME) is one of the most versatile and widely used. In MEAM, molten or viscous materials are pushed through an orifice and are selectively deposited as strands to form stacked layers and subsequently a three-dimensional object. The commonly used
materials for MEAM are thermoplastic polymers and particulate composites; however, recently innovative formulations of highly-filled polymers (HP) with metals or ceramics have also been made available. MEAM with HP is an indirect process, which uses sacrificial polymeric binders to shape metallic and ceramic components. After removing the binder, the powder particles are fused together in a conventional sintering step. In this review the different types of MEAM techniques and relevant industrial approaches for the fabrication of metallic and ceramic components are described. The composition of certain HP binder systems and powders are presented; the methods of compounding and filament making HP are explained; the stages of shaping, debinding, and sintering are discussed; and finally a comparison of the parts produced via MEAM-HP with those produced
via other manufacturing techniques is presented.
The paper describes briefly the historical development and presents in more detail solidstate properties such as hardness, heat conductivity, thermal expansion and mechanical properties of titanium carbonitride Ti(C,N), the basis of the hard phase of cermets. The metallurgy of Ti(C,N)-based cermets with respect to microstructure formation during sintering and the impact on properties are presented in more detail. The various influences such as W and/or Mo content, Mo/W ratio, C content and C/N ratio, binder phase content and binder phase composition (Co/Ni), sintering time, dwell time, alloy state of powders and grain size were critically evaluated and are presented in form of fracture toughness vs. hardness graphs. A table gives a reference list on the study of these influences. TRS data on cermets were collected and summarised in a separate table, too.
The focus is put on grades which have the potential of being fabricated soon in industrial processes for production of cermet tools. Application examples for metal cutting, sawing and chip bonding are presented.
In two final sections recent modifications and achievements such as graded microstructures, multicomponent binder, and hybrid microstructures are also briefly presented together with an outlook on the future potential of cermet applications.
Fused Filament Fabrication (FFF) is one of the most commonly used polymer-based additive manufacturing techniques. FFF could be used to produce green parts with complex geometry out of feedstocks and after debinding and sintering a full metal or ceramic part is obtained. FFF machines, as the name implies, require the printing material to be in the shape of a filament. This represents a challenge for feedstocks since the addition of large amounts of particles greatly increase the viscosity of the molten suspension while making the solid filament very brittle. For the production of magnets by FFF a feedstock for magnetic powders, which shows the required flexibility and strength at the same time, and the necessary processing route was developed in the EU-funded project REProMag. Here the full route from the production of feedstocks via debinding and sintering to the characterisation of the resulting magnetic parts is shown.
Fused filament fabrication (FFF) is one of the most commonly used polymer-based additive manufacturing techniques. FFF could be used to shape parts with PIM feedstocks instead of injection moulding and after debinding and sintering obtain solid parts with complex geometry. Currently used PIM feedstocks do not necessarily meet the requirements of the majority of FFF machines available in the market, which rely on the use of flexible filaments. In this paper, the specific properties needed by the FFF feedstock materials are discussed. Different feedstocks with 316L steel powder at 55 vol.-% were characterized (viscosity and mechanical properties) and tested regarding the printability using a conventional FFF machine. Out of these experiments the most important requirements for printable PIM feedstocks are deduced.
There is an increased industry demand for Ti(C,N)-based cermets with improved material properties. One of the parameters which are supposed to influence these properties is the mean particle size of the Ti(C,N) powder used. In this study the effects of a newly developed submicron Ti(C,N) powder grade on the properties of Ti(C,N)-based cermets, including hardness, toughness and microstructure were investigated. The cermets showed only small differences with respect to outgassing upon sintering (investigated by MS-EGA) as well as shrinkage (dilatometry). Cermet formulations with submicron Ti(C,N) could be sintered under identical conditions as with fine Ti(C,N), yielding completely dense bodies of A00 porosity. From SEM and XRD investigations it was found that submicron Ti(C,N) powders cause accelerated diffusion and homogenisation of the microstructure leading to a substantially increased amount of outer rim phase, a higher amount of inverse grains and substantially finer and less Ti(C,N) cores. Upon using submicron Ti(C,N), hardness (HV10) is increased and in one grade the fracture toughness (Palmqvist–Shetty) is increased as well.
This article presents a study on the influence of selective laser melting (SLM) process on microstructure and property of a cemented carbide system containing high entropy alloy. Analysis along the building direction indicated variation of chemical composition and microstructure, and this was influenced by two effects, firstly the dilution effect due to elemental diffusion from the baseplate and secondly the elements evaporation caused by high-power laser. At the lower half of the specimen, high fraction of η-carbide formed near the level of baseplate, and there were chemical gradients of major binder elements along the building direction. At the upper half of the specimen, there were relatively less variation in chemical composition and more homogeneously distributed phases including WC, W2C, η-carbide and FCC metal binder. The hardness of the lower half specimen varied from 711.7 HV1 (bottom of the specimen) to 1178.6 HV1 at 1 mm height. For the upper half of the specimen, hardness values could range from 1306.8 HV1 to 1413.4 HV1 and fracture toughness varied from 9.74 MPa m1/2 to 13.29 MPa m1/2.
A study was carried out to evaluate the wear properties of Binder Jet 3D Printed (BJ3DP) WC-12% Co per the ASTM B611 and G65 test methods. The printed samples were sintered under a pressure of 1.83 MPa at 1485 °C for 5 min to achieve near theoretical densities. A dual WC grain size was observed in the microstructure of the sintered parts. The microstructure largely consists of 1.4–2.0 μm WC grains and clusters of coarse grains ranging in size up to ~ 20 μm in the Co matrix. The samples showed a volume loss of 140.48 ± 2.73 mm³during the B611 testing. The wear resistance of the samples was found to be superior to that of standard cemented carbides with similar amount of Co. The superior wear resistance is attributed to the dual grain size microstructure. The SEM micrographs of the wear surfaces after B611 testing showed the fragmentation and pull out of WC and substantial wear of the Co matrix. The G65 wear testing showed a volume loss of 3.67 ± 0.66 mm³. The SEM micrographs of the wear surfaces after the G65 testing showed wear occurring primarily in the Co matrix. The results from the present study confirm the feasibility of the BJ3DP process to fabricate WC-12%Co parts with superior wear resistance properties.
Cemented carbide is a difficult material to be processed by Additive Manufacturing (AM) necessitating the need for process chain development to overcome the limitations of AM. Selective Laser Sintering (SLS) is proven to be the best AM process for making a complex product, and has potential to help produce a defect-free cemented carbide product. Consequently, in the present work, SLS is selected for process chain development study. Optimized SLS parameters are obtained to process WC-17Co (cemented carbide), which are able to furnish products of appreciable dimensional accuracy containing various fine features. In order to further improve product properties and remove any deficiencies, heat treatment is selected as a post-processing, which is accomplished in a furnace by heating samples at various temperatures (400, 600, 800 and 1000 °C) for a fixed duration of 3 h and by letting them cool inside the furnace. Samples are subsequently characterized to determine their hardness, fracture toughness, microstructure, wear resistance, composition of various phases and types of compounds formed. It is found that a moderate heat treatment has beneficial effects as the treatment at 600 °C furnished better hardness and fracture toughness while at 400 °C gave the best wear resistance. It is concluded that the heat treatment can be included as a complementary processing technique for producing cemented carbides as it has helped achieve products having better mechanical and wear properties.
A study was carried out to evaluate the sintering densification, shrinkage and mechanical properties of WC-12%Co powders processed by binder jet 3D printing (BJ3DP). After debinding, vacuum sintering at 1435–1485 °C for 45 min yielded low sintered densities in the range of 13.1–13.5 g/cm³. Near theoretical densities of 14.1–14.2 g/cm³ were achieved by sintering the parts under a pressure of 1.83 MPa at 1485 °C for 5–30 min. Shrinkage in the range of 22.2–24.4% and 20.9–26.2% was observed in the parts sintered in vacuum and under pressure, respectively. The samples densified to near theoretical density showed hardness of 1256 HV30 and fracture toughness of 17 ± 1 MPa m1/2. The hardness and fracture toughness are in line with the properties of conventionally produced WC-12%Co with medium grain size. The results from the present study confirm the suitability of the binder jet 3D printing (BJ3DP) process to manufacture WC-Co parts with good mechanical properties.
3D gel-printing (3DGP) is a novel manufacturing technology, which builds a 3D component by depositing and gelating metal slurry layer by layer. In this paper, the hydroxyethyl methacrylate (HEMA) based slurries with WC-20Co solid loading of 47–56 vol% were directly formed by 3DGP and then sintered in a vacuum furnace. The WC-20Co slurries exhibited suitable fluidity and shear thinning behavior, which were beneficial for 3DGP forming process. The effects of 3DGP processing parameters, such as the internal diameter of print nozzle and filling rate, on the surface roughness and dimensional accuracy of as-printed green bodies were studied. The influence of solid loading on rheological property of WC-20Co slurry, green density, sintered density and mechanical properties of sintered samples were also investigated. The results show that the samples can be printed with good shape, appropriate precision and homogeneous microstructure. The sintered samples have good shape retention and uniform microstructure. The density, hardness and transverse rupture strength of the optimal sample were 13.55 g/cm³, HRA 87.7 and 2612.8 MPa, respectively. 3DGP has unique advantages in near-net forming for complex shape WC-20Co components.
Purpose
WC-Co is a well-known material for conventional tooling but is not yet commercially available for additive manufacturing. Processing it by selective laser sintering (SLS) will pave the way for its commercialization and adoption.
Design/methodology/approach
It is intended to optimize process parameters (laser power, hatch spacing, scan speed) by fabricating a bigger part (minimum size of 10 mm diameter and 5 mm height). Microstructural analysis, EDX and hardness testing is used to study effects of process parameters. Optimized parameter is ascertained after fabricating 49 samples in preliminary experiment, 27 samples in pre-final experiment and 9 samples in final experiment.
Findings
Higher laser power gives rise to cracks and depletion of cobalt while higher scan speed increases porosity. Higher hatch spacing is responsible for delamination and displacement of parts. Optimized parameters are 270 W laser power, 500 mm/s scan speed, 0.04 mm layer thickness, 0.04 mm hatch spacing (resulting in energy density of 216 J/mm3) and 200°C powder bed temperature. A part comprising of small hole of 2 mm diameter, thin cylindrical pin of 0.5 mm diameter and thin wall of 2 mm width bent up to 30° angle to the base plate is fabricated. In order to calculate laser energy density, a new equation is introduced which takes into account both beam diameter and hatch spacing unlike old equation does. In order to calculate laser energy density, a new equation is formulated which takes into account both beam diameter and hatch spacing unlike old equation does. WC was not completely melted as intended giving rise to partial melting-type binding mechanism. This justified the name SLS for process in place of SLM (Selective Laser Melting).
Research limitations/implications
Using all possible combination of parameters plus heating the part bed to maximum shows limitation of state-of-the-art commercial powder bed fusion machine for shaping hardmetal consisting of high amount of WC (83 wt. per cent).
Practical implications
The research shows that microfeatures could be fabricated using WC-Co which will herald renewed interest in investigating hardmetals using SLS for manufacturing complex hard tools, molds and wear-resistance parts.
Originality/value
This is the first time micro features are successfully fabricated using WC-Co without post-processing (infiltration, machining) and without the help of additional binding material (such as Cu, Ni, Fe).
Thermoplastic 3D printing (T3DP) is an Additive Manufacturing (AM) technology that cannot only be used for producing ceramic, metal or multi-material components, but for the Additive Manufacturing of hard metal or cemented carbide components, too. This is possible because the technology combines the precise deposition of small droplets of molten thermoplastic hard-metal-containing suspensions and an increasing viscosity resulting from a cooling process as curing mechanism. This paper demonstrates the suitability of the T3DP-process for the AM of hard metal compounds. Using WC-Co suspensions with a solid content of 67 vol%, single droplets were deposited and first components manufactured. After de-binding and sintering, completely dense samples were achieved. Zero porosity was determined in the microstructures analyzed by means of FESEM and optical microscopy.
A new hard tooling fabrication technique, named fused deposition of metals (FDMet), to fabricate prototype metal components was investigated. This fabrication is performed directly from a computer-aided design (CAD) file without using molds, dies, or similar tooling. The FDMet process is based on a patented fused deposition modeling (FDM) and fused deposition of ceramics process where a three-dimensional (3D) object is built from a 1.75-mm diameter metal filament fed into a heated extruder head capable of moving in the X–Y direction. The head extrudes controlled and continuous flow of material onto a fixtureless platform capable of moving in the Z-direction. The process from raw material to the final prototype is described. The post processing steps include binder removal of the polymer in the green part and sintering to densify the part. To demonstrate the capability of this technique, several standard samples and hard tooling components such as a wrench and lug fit were fabricated. The accuracy and reproducibility issues are discussed.
Structural ceramics by fused deposition of ceramics
- M K Agarwala
M.K. Agarwala, Structural ceramics by fused deposition of ceramics, Proc. Solid
Freeform Fabrication Symposium, 1995, pp. 1-8.
Process modelling for fused deposition of ceramics
- M A Yardimci
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