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The selective laser melting (SLM) test scheme.
Source publication
Due to the rapid melting and solidification mechanisms involved in selective laser melting (SLM), CoCrMo alloys fabricated by SLM differ from the cast form of the same alloy. In this study, the relationship between process parameters and the morphology and macromechanical properties of cobalt-chromium alloy micro-melting pools is discussed. By meas...
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Citations
... Various 3D printing technologies are available such as stereolithography (SLA), selective laser melting (SLM), selective laser sintering (SLS), direct metal laser-sintering (DMLS), fused deposition modelling (FDM), selective electron beam melting (SEBM) and inkjet printingStereolithography, direct metal laser-sintering and selective laser melting are commonly used additive 3D printing processes that can be used to produce RPD frameworks [11][12][13]. Cobalt-chromium alloy is the preferred material for RPDs manufactured via selective laser melting due to its ideal physical properties [14]. The physical properties of Co-Cr alloys fabricated by SLM for RPDs have higher hardness, better wear resistance, higher density and can withstand higher functional loads. ...
Background
The advent of digital technologies has introduced novel methods for RPD fabrication, potentially enhancing the fit compared to the conventional approaches. This systematic review aimed to evaluate the methods to assess the accuracy of fit and precision of the RPD framework fabricated using conventional and digital (3D printed and milled) methods.
Methods
A comprehensive literature search (Registration Number CRD42023459566) was conducted across different electronic databases like PubMed/MEDLINE, Embase, Scopus, Web of Science, and Google Scholar. Studies investigating RPD fit and precision assessment using various techniques (Visual inspection and pressing test using silicone impression material, 3D digital analyses using a software, light microscopy, digital microscope at 50x, superimposition method /surface matching software program, µCT on silicone specimens and direct measurements) in in-vitro studies were included. Data extraction and quality assessment were performed to evaluate the methodological rigour of the selected studies. A narrative synthesis of the findings was carried out to evaluate the methods to assess the accuracy of fit and precision of the RPD framework fabricated through conventional and digital methods due to heterogeneity in study variables.
Results
Out of 413 records, a total of 8 in-vitro studies were included in this review. The key findings of the review suggest that RPD fit accuracy varies across fabrication processes including conventional techniques, resin milling, selective laser melting (SLM), and digital superimposition. Resin milling with polyether ether ketone (PEEK) offers the best accuracy. Among the different methods used in assessing the fit accuracy of the RPD framework silicone-based fit evaluation and superimposition techniques/ surface matching are commonly used methods.
Conclusion
Both traditional (non-computerized) and computerized methods for the assessment of fit and precision of conventional and digital RPD frameworks are used commonly. But still, formulation of a standard method for fit assessment of RPDs is warranted. In future with further refinements, digital methods would completely outperform the traditional methods.
... To validate the model, the predicted width and depth of the melt bath were compared with the actual geometric characteristics of the fused single tracks. The effect of melting regimes on the quality of stent struts was assessed based on the factor analysis results [68,82]. Spatial accuracy is ensured by modeling, as a result of which the required dimensions of the elements of stent structures are determined. ...
Additive manufacturing of porous materials with a specific macrostructure and tunable mechanical properties is a state-of-the-art area of material science. Additive technologies are widely used in industry due to numerous advantages, including automation, reproducibility, and freedom of design. Selective laser melting (SLM) is one of the advanced techniques among 3D fabrication methods. It is widely used to produce various medical implants and devices including stents. It should be noticed that there is a lack of information on its application in stent production. The paper presents the technological aspects of CoCr stent SLM fabrication, including design of stents and development of regimes for their manufacturing. Physical, chemical, and technological properties of CoCr powder were initially determined. Parametric design of mesh stent models was adopted. A two-stage approach was developed to ensure dimensional accuracy and quality of stents. The first stage involves a development of the single-track fusion process. The second stage includes the stent manufacturing according to determined technological regimes. The single-track fusion process was simulated to assign laser synthesis parameters for stent fabrication. Melting bath temperature and laser regimes providing such conditions were determined. Twenty-seven SLM manufacturing regimes were realized. Dependence of single-tracks width and height on the laser power, exposition time, and point distance was revealed. The qualitative characteristics of tracks imitating the geometry of the stent struts as well as favorable and unfavorable fusion regimes were determined. The results of surface roughness regulating of the stents’ structural elements by various methods were analyzed. Thus, this two-staged approach can be considered as a fundamental approach for CoCr stent SLM fabrication.
... The importance of slow manufacturing and enhanced device quality cannot be overstated in the context of personalized medical devices. Li et al. [17] have shown that the graphite mould used in Spark Plasma Sintering (SPS) undergoes direct heating throughout the sintering process, leading to a notable improvement in thermal efficiency. Furthermore, any uniaxial pressure applied leads to plastic deformation of the particles, thereby promoting densification. ...
The present study investigates the impact of Mo and Nb on the characteristics of CoCr sintered alloys, with a specific focus on their potential for biomedical applications. Cobalt-chromium-based alloys (namely, Co-Cr-2.5Mo-2.5Nb, Co-Cr-3Mo-3Nb, and CoCr-3.5Mo-3.5Nb) were fabricated using sintering conditions comprising a heating rate of 200 °C/min, pressure of 50 MPa, temperature of 1100 °C, and a dwell period of 15 minutes. The findings indicated that the CoCr alloy, when supplemented with Mo and Nb, exhibited a singular-phase composition consisting mostly of a face-centered cubic (FCC) core comprised of gamma-Co, accompanied by a minor proportion of a hexagonal close-packed (HCP) solid solution matrix known as epsilon-Co, and interspersed with precipitates. The inclusion of Co-Cr-3Mo-3Nb alloy composition resulted in the highest relative density of 97.56% compared to other alloy compositions, indicating its optimum alloying properties. The Co-Cr-3Mo-3Nb alloy had the maximum polarization resistance of 522.52 Ω, indicating a strong resistance to corrosion. Additionally, it displayed the least corrosion rate of 1.5904 mm/year. The ternary alloy consisting of Co-Cr-3.5Mo-3.5Nb demonstrated superior resistance to the applied indentation stress, as shown by its minimal maximum penetration depth of 372.23 nm and the lowest average coefficient of friction (COF) values.
... The impact of irregularities on the mechanical properties of the manufactured material is well-documented in the literature [32,[34][35][36] and their contribution was quantified in Table 4. The results indicate that the presence of porosity varies significantly among the different test samples (p < 0.05). ...
This research investigates the impact of three process parameters of Laser Powder Bed Fusion (LPBF) - laser power, scanning speed, and base plate preheating temperature on the structure and mechanical properties of the EOS CoCr SP2 dental alloy. The LPBF process was used to fabricate dental Co-Cr alloy specimens for microstructural analysis and mechanical properties testing. Light and electron microscopy were used to determine microstructural parameters, including porosity, inclusions, and cracks. The material's chemical composition was analysed by EDS, while XRD and EBSD methods were used to determine the presence of microstructural phases and the crystallographic orientation of individual grains. The mechanical properties were evaluated through a static tensile test (Rp0.2, ε), a toughness test (KVa), and a three-point bending test to determine the flexural strength (Rms). In the microstructure, differences were observed that reflected statistically significant differences in mechanical properties (one-way analysis of variance (ANOVA) and Scheffé post hoc test (α = 0.05)) Using the base plate preheating temperature ϑp = 310 °C with a constant scanning speed v = 900 mm/s in combination with increasing laser power P from 160 W to 250 W the proportion of porosity decreased while the mechanical properties of toughness (KVa) and flexural strength (Rms) increase to maximum values.
... The impact of irregularities on the mechanical properties of the manufactured material is well-documented in the literature [32,[34][35][36] and their contribution was quantified in Table 4. The results indicate that the presence of porosity varies significantly among the different test samples (p < 0.05). ...
... In the case of crowns and bridges, the subsequent ceramic veneering of the metallic substructure necessitates the repeated firing of the different ceramic layers at temperatures over 900 • C [27]. ...
The aim of this work is to assess the crystalline structure modification of an SLM Co-Cr-W dental alloy, veneered with two different ceramics, by means of X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy, coupled with energy-dispersive spectroscopy (SEM-EDS). Ten identical plates were fabricated using SLM and were subsequently subjected to ceramic veneering. Following the repeated firing of the ceramic layers, carried out at temperatures exceeding 900 °C, new crystalline phases and variations in the crystallite sizes in the SLM Co-Cr-W dental alloy used for the substructure were detected via XRD. The two veneering ceramics showed significant differences in their behavior, beginning with the first firing, accompanied by structural changes. AFM micrographs and histograms of the surface heights over the whole scanned area of the samples showed that the surface of the Co-Cr-W dental alloy is strongly affected by the repeated firings necessitated by the ceramic firing process, a finding in accordance with the XRD results. The SEM investigation revealed that the different firing parameters had an impact on the alloy, the ceramic microstructure, and the surface quality. The differences in the chemical composition of the ceramics, highlighted by EDS, are reflected in their behavior. The crystalline alloy structure is influenced by the repeated firings of the ceramic layers.
... In recent years, Additive Manufacturing (AM) has attracted significant attention as a type of novel and continuously expanding technology [1,2]. Laser Powder Bed Fusion (LPBF), an additive manufacturing process, is widely used to manufacture orthopedic implants [3,4]. ...
... (Chengdu, China). This process was mainly the reaction of reducing agent and cobalt salt, and the equation of chemical reaction was shown in Equation (1). The plating solution and Al 2 O 3 powders were separated by centrifugation, and subsequently the powders were dried in a vacuum for 2 h to get Co-coated Al 2 O 3 composite powders. ...
In this study, we systematically examined the influence mechanisms of introduced cobalt coated alumina (Co-coated Al2O3) particles on the microstructure and properties of cobalt-chromium-molybdenum (CoCrMo) alloy printed by Laser Powder Bed Fusion (LPBF). The Co-coated Al2O3 composite powders with different density of cobalt coating were prepared by varying Al2O3 load from 1 g/150 mL to 2 g/150 mL during the electroless plating process. Then they were mixed with CoCrMo powders in the proportion of 1 wt.% and formed standard samples by LPBF technology. The results showed that the addition of Co-coated Al2O3 particles improved the friction performance of CoCrMo alloys significantly. The wear depth of CCM@2Al2O3 was only 2.18 μm and the wear volume of it was about 10% of pure CoCrMo alloy. The CoCrMo alloy introduced the Co-coated Al2O3 particles with a 1 g/150 mL Al2O3 load formed metal-ceramic bonding interface, which solved the problem of poor wettability between Al2O3 and matrix in LPBF process. Such CoCrMo alloy exhibited excellent tensile properties and the mean microhardness of it reached 379.9 ± 3.5 HV0.5.
... selective laser sintering (SLS) and selective laser melting (SLM) [4,[7][8][9][10][11]. Various alloys can be processed using Laser Powder Bed Fusion (L-PBF) processes, such as stainless steel, titanium, and cobalt alloys [12][13][14]. Among these, Co-Cr alloys have good versatility and durability, together with biocompatibility [15]. In general, these alloys are used to produce surgical tools and prostheses such as hip and knee replacements due to their excellent wear and corrosion resistance [16,17]. ...
... Besides cell geometry, the mechanical response of a lattice structure also depends on the material microstructure. In this regard, an additional peculiar aspect of the L-PBF process is the extremely rapid solidification rate [15]. This influences the microstructure significantly, as already pointed out in the literature. ...
Additive manufacturing research is continuously growing, and this field requires a full improvement of the capability and reliability of the processes involved. Of particular interest is the study of complex geometries production, such as lattice structures, which may have a potentially huge field of application, especially for biomedical products.
In this work, the powder bed fusion technique was utilized to manufacture lattice structures with defined building angles concerning the build platform. A biocompatible Co-Cr-Mo alloy was used. Three different types of elementary cell geometry were selected: Face Centered Cubic, Diagonal, and Diamond. These cells were applied to the radially oriented lattice structures to evaluate the influence of their orientation in relation to the sample and the build platform. Moreover, heat treatment was carried out to study its influence on microstructural properties and mechanical behavior. Microhardness was measured, and compressive tests were performed to detect load response and to analyse the fracture mechanisms of these structures.
The results show that the mechanical properties are highly influenced by the cell orientation in relation to the building direction and that the properties can be further tuned via HT. The favorable combination of mechanical properties and biocompatibility suggests that Co-Cr-Mo lattices may represent an optimal solution to produce customized metal implants.
... Furthermore, heat treatment reduces the presence of defects in the printed CCM that was evident from the analyzed microstructure. Wang et al. [51] optimized the process parameters of the SLM process for analyzing the relationship between the laser power, hatching spacing, and laser scanning speed. Totally 23 cobalt-chromium specimens were printed with different process parameters to identify the optimum parameter for the biomedical application. ...
... The obtained results (Yield strength of 735MPa and ultimate tensile strength of 1211MPa for the printed component) indicated higher mechanical properties than the previous studies. Wang et al. [51] analyzed the grain depth and width of the SLM printed Co-Cr alloy for estimating the mechanical properties. The process parameters are optimized to produce different grain sizes which influence the mechanical properties. ...
... (1) is used for estimating the proper laser energy density. [149] [105] 360 50 175 500 [106] 175 25 110 550 [66] 250 20 80 500-1000 [144] 310 50 130 8850 [145] 330 50 130 1200 360 50 130 1600 385 50 130 2000 100 30 120 556,311,280 [146] 150 30 80 700 [108] 140 30 50 900 [51] 180 30 50 900 220 30 50 900 260 30 50 900 300 30 50 900 180 30 50 700 180 30 50 900 180 30 50 1100 180 30 40 900 180 30 50 900 180 30 60 900 160 30 60 1100 160 30 50 1100 160 30 40 1100 160 30 60 700 160 30 50 700 160 30 40 700 200 30 60 1100 200 30 50 1100 200 30 40 1100 200 30 60 700 200 30 50 700 200 30 40 700 Figure 7. SEM images of printed sample. The image shows the presence of un-melted powder particles and void formation in the printed material. ...
Cobalt-chromium alloys and Ultra High Molecular Weight Polyethylene (UHMWPE) are widely used in total hip replacement due to their multifunctional properties such as high mechanical strength, hardness, fatigue, and tribological properties. The material has been more popular among researchers that pushing them to refine the multifunctional properties of materials by using different fabrication and postprocessing methods. Recent studies found that the Selective Laser Melting (SLM) technique of additive manufacturing (AM) shows a major response in changing the properties over the traditional methods, but there exist few problems while printing the cobalt-chromium alloys in SLM. However, it is hard to use cobalt-chromium alloys directly in the human body without post-processing stages such as post-heat treatment, surface modification, and Osseo-integration stage because it helps to improve the durability, reduce the ion elements release, wear debris, and promotes more adhesive strength between the tissue and stems. This review article explores the effects of process parameters on the SLM printed product and analyzes the post-processing stages to enhance the properties of printed components for total hip replacement. Furthermore, the solution for the problems and future research work are adequately discussed for restricting the ion element leaching of Cobalt-Chromium alloys
... The main properties of the cobalt-chromium alloy are shown in Table 2. The data presented in the table are taken from [49,50]. Band B 0.9 corresponds to laser-additive manufacturing of oxide ceramics at the ambient temperature T a with T max equal to the temperature of chemical decomposition (~2900 • C) [51][52][53][54][55]. T min should be chosen as high as possible because of the Arrhenius temperature dependence of the powder consolidation rate [56]. ...
A uniform distribution of power density (energy flux) in a stationary laser beam leads to a decrease in the overheating of the material in the center of the laser beam during laser powder bed fusion and a decrease in material losses due to its thermal ablation and chemical decomposition. The profile of the uniform cylindrical (flat-top) distribution of the laser beam power density was compared to the classical Gaussian mode (TEM00) and inverse Gaussian (donut) distribution (airy distribution of the first harmonic, TEM01* = TEM01 + TEM10). Calculation of the Péclet number, which is a similarity criterion characterizing the relationship between convective and molecular processes of heat transfer (convection to diffusion) in a material flow in the liquid phase, shows that the cylindrical (flat-top) distribution (TEM01* + TEM00 mode) is effective in a narrow temperature range. TEM00 shows the most effective result, and TEM01* is an intermediate in which evaporation losses decrease by 24% with increasing temperature and absolute laser bandwidth increases.
