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Effect of tungsten additions on the mechanical properties of Ti-6Al-4V
Abstract
The alloy Ti-6Al-4V was modified by addition of 10 wt.% tungsten through powder metallurgy. Depending on the initial W powder size, different materials were formed after powder densification: (i) “alloys” for fine (0.7 and 2 μm) W powders which were almost completely dissolved in the Ti-6Al-4V matrix; (ii) “alloyed composites” for intermediate (12 and <45 μm) W powders which were partially dissolved; (iii) and “composites” for coarse (<250 μm) W powders which were nearly un-dissolved. In all cases, tungsten strengthens Ti-6Al-4V, but much more so when dissolved in the matrix than as a second phase. Ductility was not affected by W additions for the fully-dissolved alloys, but was reduced in the case of composites with W particles, which exhibited fracture or pull-out from the matrix. Flaw sensitivity was apparent from strain hardening being much lower in tension than in compression, and from a much reduced ductility exhibited by one specimen with residual porosity.
... Previous studies have mainly investigated the effect of W on strengthening of titanium alloys [21][22][23][24][25]. For example, Frary et al. [21] and Choe et al. [22,23] showed that the addition of W to Ti and Ti-6Al-4V alloy significantly increased their strength, but at the expense of ductility, especially when some large W particles remained in the matrix. ...
... Previous studies have mainly investigated the effect of W on strengthening of titanium alloys [21][22][23][24][25]. For example, Frary et al. [21] and Choe et al. [22,23] showed that the addition of W to Ti and Ti-6Al-4V alloy significantly increased their strength, but at the expense of ductility, especially when some large W particles remained in the matrix. Similarly, Wang et al. [25] showed that the W addition could increase strength and ductility of Ti-6Al-4V alloy simultaneously, and the main strengthening mechanisms were fine grain strengthening and load transfer effect of undissolved W particles. ...
... Processing and microstructure AM processes, respectively. When alloyed with W, the etched Ti matrix shows an acicular structure due to the dissolution of W in the Ti matrix, which was previously reported and identified as a Widmanstätten α/β structure, with most of the W segregated in the β phase (Frary et al., 2003;Choe et al., 2005aChoe et al., , 2005b. The dissolution of W was anticipated to be fairly complete in the Ti-10W alloy fabricated by CHIP (Fig. 2a), given the W mean particle size of less than 1 mm (Frary et al., 2003;Choe et al., 2005a). ...
... When alloyed with W, the etched Ti matrix shows an acicular structure due to the dissolution of W in the Ti matrix, which was previously reported and identified as a Widmanstätten α/β structure, with most of the W segregated in the β phase (Frary et al., 2003;Choe et al., 2005aChoe et al., , 2005b. The dissolution of W was anticipated to be fairly complete in the Ti-10W alloy fabricated by CHIP (Fig. 2a), given the W mean particle size of less than 1 mm (Frary et al., 2003;Choe et al., 2005a). However, the degree of W dissolution was expected to be greater in the Ti-10W alloy fabricated by AM (Fig. 2b) owing to the nature of the liquidstate processing. ...
This study investigates and compares the microstructure, biocompatibility, and tribological properties of two different Ti-based composites, Ti-10W and Ti-7.5TiC-7.5W, with those of pure Ti for their potential use in biomedical applications. In particular, cold and hot isostatic-pressing and arc-melting methods were utilized and compared for the microstructure of the composites. Nano-scratch measurements and pin-on-disk wear tests were employed to understand their tribological behavior. As compared to pure Ti, Ti-10W and Ti-7.5TiC-7.5W showed significantly improved nano-scratch resistance (by 85 and 77%, respectively) and wear resistance (by 64 and 66%, respectively), in good agreement with hardness measurements. For biocompatibility examination, both microculture tetrazolium test (MTT) and water soluble tetrazolium (WST-1) test were used to quantify the cell viability of human osteoblasts and mouse fibroblasts on the materials. Both of the Ti-based composites showed acceptable biocompatibility in comparison with the pure Ti control.
... where E and E 0 are Young's modulus of foam and bulk materials with densities ρandρ 0 , respectively, using E 0 = 117 GPa and ρ 0 =4.43 g/cm 3 for Ti6Al4V [17]. The proportionality constant C including data of metals, rigid polymers, elasomers, and glasses has to be considered as 1 for titanium alloys [16]. ...
... where E and E 0 are Young's modulus of foam and bulk materials with densities and 0 , respectively, using E 0 = 117 GPa and 0 =4.43 g/cm 3 for Ti6Al4V [17]. The proportionality constant C including data of metals, rigid polymers, elasomers, and glasses has to be considered as 1 for titanium alloys [16]. ...
... The presence of W on the Tie6Ale4V alloy surface was believed to be the consequence of undissolved particles during the fabrication of the alloys via direct powder rolling technique. Although the undissolved coarse particles of W during the processing of Tie6Ale4V alloy reduce the strength and ductility of the alloy [32], there is no data on the influence of W on the electrochemical properties of titanium based alloys. ...
Great efforts have been made in fabricating Ti–6Al–4V alloys that can be used in the biomedical implants industry. The increasing interest in using fabricated Ti–6Al–4V alloys in industrial applications is mainly due to the properties of alloys which include good combination of mechanical and corrosion resistance. This study was aimed at evaluating the corrosion properties of the Ti–6Al–4V alloy fabricated via powder rolling technique under various simulated human body solutions. A three-electrode electrochemical cell was used to carry out corrosion studies at 37 °C where the fabricated Ti–6Al–4V was immersed in 3.5% NaCl (pH = 6.5) and two simulated human body fluids, namely; Hank's balanced salt solution (HBSS) and Ringers solution with the measured pH of 6.9 and 6.4 respectively. The electrochemical techniques used to investigate the corrosion studies included open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The fabricated Ti–6Al–4V alloy was characterized before and after the corrosion experiments via X-ray diffraction (XRD) and scanning electron microscope (SEM). The potentiodynamic polarization curves revealed a passivation phenomenon on the anodic domain indicating high corrosion resistance of Ti–6Al–4V alloy in all three electrolytes. The Ti–6Al–4V alloy exhibited the highest corrosion resistance when immersed in 3.5% NaCl with the estimated corrosion rate of 0.480 μm/yr. The excellent corrosion resistance of Ti–6Al–4V alloy was mainly due to the formation of an oxide film formed on the alloy surface as deduced from the EIS analysis. No corrosion products were detected by XRD analysis on the Ti–6Al–4V alloy surface immersed in all electrolytes which confirmed an excellent corrosion resistance property.
... Design and development of ceramic particle reinforced titanium matrix composites (TMCs) have been extensively studied, due to their superior wear resistance and increased mechanical properties when compared to unreinforced titanium alloys [1]. Among the titanium based alloys, aluminium and vanadium reinforcement (Ti-6Al-4V) is used in aircraft and turbines due to its heat treatment ability, adequate mechanical strength, and good corrosion resistance [2]. ...
The present investigation has been made to assess the influence of B4C reinforced with Ti-6Al-4V matrix prepared by powder metallurgy route. High energy ball milling was used to prepare the composites. Cylindrical preforms were prepared using suitable die set assembly. The green preforms were sintered in the muffle furnace at 900°C for 1 h. Further the preforms were cooled inside the furnace till the room temperature has attained. SEM with EDS mapping analysis was used to evaluate the morphology and elemental confirmation of the prepared composite. The density and hardness of the samples are determined using Archimedes principle and Rockwell hardness testing machine. The wear resistance of the samples was determined by employing a pin on disc apparatus. The hardness of the composites (Ti-6Al-4V/10B4C) was increased while comparing to the base material (Ti-6Al-4V) which is attributed to the presence of hard ceramic phase. Response Surface Methodology (RSM) five level central composite design approach was accustomed and it minimised the amount of experimental conditions and developed mathematical models among the key process parameters namely wt. % of B4C, applied load and sliding distances to forecast the abrasive response of Specific Wear Rate (SWR) and Coefficient of Friction (CoF). Analysis of variance was used to check the validity of the developed model. The optimum parameters of specific wear rate and coefficient of friction were identified.
... Novel amorphous Ti based metallic glasses Ti 75 Zr 10 Si 15 and Ti 60 Nb 15 Zr 10 Si 15 free of toxic materials were designed by Mariana Calin et al. and they evaluated thermal stability, glass forming ability, mechanical and corrosion properties [7]. The Ti-Zr--Cu-Pd metallic glass is greater in strength and lower in Youngs modulus when compared to Ti-6Al-4 V and showed corrosion resistance due to the formation of passive films which acts as a protective layer [15,16]. Ti 40 Zr 10 Cu 38 Pd 12 MG and Ti6-Al-4 V alloys were surface-modified by Blanquer et al. and examined adhesion of SaOS-2 cells, proliferation and differentiation by changing the topography of the specimen. ...
Biologically safe Ti-based quaternary Ti-Nb-Zr-Si thin film metallic glass (TFMG) was fabricated by sputtering on Titanium alloy (Ti6Al4V or Ti alloy) substrates. A preliminary assessment regarding glass forming ability, thermal stability and corrosion behavior was performed. The amorphous nature of the film is evidenced from the X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) and Selected Area Electron Diffraction (SAED) patterns. Ion scattering spectroscopy (ISS) and X-ray Photoelectron Spectroscopy (XPS) were used to analyse the chemical composition of surface which indicated oxygen on the top surface of the film and confirms the presence of Ti, Nb, Si, Zr without any other impurities. The surface morphology of the film showed a smooth surface as observed from scanning electron microscope (SEM) and atomic force microscope (AFM) analysis. It is found that the TFMG can sustain in the body-fluid, exhibiting superior corrosion resistance and electrochemical stability than the bare titanium. The cytotoxicity studies with L929 fibroblast cells showed that coatings were graded as zero and non-cytotoxic in nature. No hemolysis was observed on the coated surface indicating a better hemocompatibility. Assay using SaOS-2 bone cells showed good growth on the coated surfaces. The calcium assay showed that the SaOS-2 cells grown and differentiated on the control (Tissue Culture Polystyrene) TCPS surface had the highest mineral level. Higher alkaline phosphatase activity is obtained in SaOS-2 osteoblast cell cultures on TFMG than the control.
... Chen et al. [12,13] studied the cold compaction behaviour of Armstrong process Cp-Ti and Ti-6Al-4V powders in case of disk shape sintered products with three different aspect ratios, i.e., 0.5, 1, and 2. Behrens et al. [14] examined the incorporation of tool-die vibration on the mechanical properties of titanium P/M parts. Choe et al. [15,16] investigated the mechanical properties of Ti-6Al-4V alloys reinforced with W/TiC. Afrin et al. [17] reviewed the HA and Ti alloy interactions under various conditions. ...
The present work was undertaken to investigate and characterize the machining parameters (such as surface roughness, etc.) of uni-axially pressed commercially pure titanium sintered powder metallurgy components. Powder was uni-axially pressed at designated pressure of 840 MPa to form cylindrical samples and the green compacts were sintered at 0.001 mbar for about 4 h with sintering temperature varying from 1350 to 1450 °C. The influence of the sintering temperature, pulse-on and pulse-off time at wire-EDM on the surface roughness of the preforms has been investigated thoroughly. Experiments were conducted under different machining parameters in a CNC operated wire-cut EDM. The surface roughness of the machined surface was measured and critically analysed. The optimum surface roughness was achieved under the conditions of 6 μs pulse-on time, 9 μs pulse-off time and at sintering temperature of 1450 °C.
... W is completely miscible with β-Ti and no intermetallic compounds are formed in accordance with the Ti-W binary phase diagram 8) . In addition, Choe et al. examined the microstructure and mechanical properties of (Ti-6Al-4V)-10 mass% W produced by powder metallurgy 9) . The W particles were dissolved fully or partially in the Ti-6Al-4V matrix sintered above the β-transus depending on the W particle sizes. ...
A post-weld heat treatment process, that is, solution treatment and aging, was found to be effective in improving the fatigue strength of friction stir welded Ti-6Al-4V butt joints. The stir-zone microstructure was changed by friction stir welding, from an equiaxed-α structure to a lamellar structure, but equiaxed-α structure remained in the base metal. Subsequently, solution treatment and aging modified these microstructures to bimodal structures in both the stir zone and base metal. The hardness in the stir zone differed from the base metal after friction stir welding, but the difference was eliminated by solution treatment and aging. The fatigue strength of friction stir welded Ti-6Al-4V butt joints was successfully increased by solution treatment and aging, which was higher than that of the parent Ti-6Al-4V plate. This indicates that solution treatment and aging increases the fatigue strength of friction stir welded Ti-6Al-4V butt joints by the formation of similar bimodal structures in the stir zone and base metal, resulting in reduced stress concentration at these boundaries and retarded fatigue failure.
... Therefore, the Young's modulus was determined from the linear section of the stress-strain curve after this transient stage. The elastic moduli values obtained for the pure Ti and Ti-W foams were 2372 GPa and 2272 GPa, respectively, thus indicating that W alloying has negligible influence on Young's modulus, which is in agreement with a previous study where W dissolution in Ti matrix up to 10 wt% had little effect on the Young's modulus of Ti-10W alloy (Choe et al., 2005). On the other hand, the yield strength is more sensitive to W alloying because its value was much higher for the Ti-W foam ( $ 235 MPa) than for the pure Ti foam ($ 196 MPa). ...
Pure Ti and Ti-5%W foams were prepared via freeze casting. The porosity and grain size of both the materials were 32-33% and 15-17µm, respectively. The mechanical behavior of the foams was investigated by uniaxial compression up to a plastic strain of ~0.26. The Young׳s moduli of both foams were ~23GPa, which was in good agreement with the value expected from their porosity. The Young׳s moduli of the foams were similar to the elastic modulus of cortical bones, thereby eliminating the osteoporosis-causing stress-shielding effect. The addition of W increased the yield strength from ~196MPa to ~235MPa. The microstructure evolution in the grains during compression was studied using electron backscatter diffraction (EBSD) and X-ray line profile analysis (XLPA). After compression up to a plastic strain of ~0.26, the average dislocation densities increased to ~3.4×10(14)m(-2) and ~5.9×10(14)m(-2) in the Ti and Ti-W foams, respectively. The higher dislocation density in the Ti-W foam can be attributed to the pinning effect of the solute tungsten atoms on dislocations. The experimentally measured yield strength was in good agreement with the strength calculated from the dislocation density and porosity. This study demonstrated that the addition of W to Ti foam is beneficial for biomedical applications, because the compressive yield strength increased while its Young׳s modulus remained similar to that of cortical bones.
... The Ti-Zr-Cu-Pd alloys emerged as a new family of Ti-based metallic glasses in 2007, completely free from toxic elements (like Be or Ni), as an alternative to the previously investigated Ti-Cu-Ni-Zr-Be or Ti-Cu-Ni-Zr-Nb(Ta) bulk metallic glasses [4,5]. In terms of physical properties, the Ti-Zr-Cu-Pd bulk metallic glasses exhibit higher strength (almost twice) and lower Young's modulus than commercial Ti-6Al-4V [6]. The corrosion resistance of these materials is also very high, due to the formation of stable and protective passive films with enhanced Ti and Zr content [7]. ...
The use of biocompatible materials, including bulk metallic glasses (BMGs), for tissue regeneration and transplantation is increasing. The good mechanical and corrosion properties of Ti40Zr10Cu38Pd12 BMG and its previously described biocompatibility makes it a potential candidate for medical applications. However, it is known that surface properties like topography might play an important role in regulating cell adhesion, proliferation and differentiation. Thus, in the present study, Ti40Zr10Cu38Pd12 BMG and Ti6-Al-4V alloy were surface-modified electrochemically (nanomesh) or physically (microscratched) to investigate the effect of material topography on human osteoblasts cells (Saos-2) adhesion, proliferation and differentiation. For comparative purposes, the effect of mirror-like polished surfaces was also studied. Electrochemical treatments led to a highly interconnected hierarchical porous structure rich in oxides, which have been described to improve corrosion resistance, whereas microscratched surfaces showed a groove pattern with parallel trenches. Cell viability was higher than 96% for the three topographies tested and for both alloy compositions. In all cases, cells were able to adhere, proliferate and differentiate on the alloys, hence indicating that surface topography plays a minor role on these processes, although a clear cell orientation was observed on microscratched surfaces. Overall, our results provide further evidence that Ti40Zr10Cu38Pd12 BMG is an excellent candidate, in the present two topographies, for bone repair purposes.
... Indeed, it has been proved that addition of small quantities of tungsten nanoparticles greatly enhance the sinterability of otherwise micrometric tungsten, thus reducing the temperature required for sintering, and the final cost [15]. On the other hand, the use of tungsten nanoparticles has been used successfully to reinforce various materials, including metallic and intermetallic systems [16][17][18] or alumina [19]. Finally, tungsten nanoparticles have attractive reactivity and appropriate dimension for the synthesis of tungsten compounds nanoparticles, such as tungsten disulfide [20] used for its catalytic properties [21]. ...
Synthesis of tungsten nanopowders was studied using milling of micrometric tungsten, then using the WO3–Mg thermitic reaction, using SHS (Self-propagating High-temperature Synthesis), milling induced chemical reaction (MICR), and MASHS (Mechanically Activated SHS). Reactions are studied by measuring temperature and pressure inside the milling jar (during MICR), or by analyzing the temperature profile along the sample during the reaction propagation by infrared thermography (SHS, MASHS). After reaction, samples were analyzed by AFM or SEM, by XRD, and BET. MASHS seems to possess optimum conditions with a pre-milling before SHS of 10 min, which yielded the highest tungsten purity, together with a grain size corresponding to our aim.
... The yielding properties and the Young's modulus of ductile metals can depend on the direction of loading, i.e., they can show a directionality. The anisotropy or directionality can originate from microstructural changes, such as the formation of twin crystals under certain load states [6][7][8], or the formation of secondary martensite in austenitic steels (also d-ferrite, cf. Refs 9 and 10), which is an undesirable effect, e.g., with biomedical grade 316L stainless steels. ...
Compression testing of metal alloys is a basic procedure in material characterization and analysis. Though it follows many of the guidelines and physical considerations as tensile testing, in some respects compression testing implies more complexity, more difficulties, and, consequently, more possible causes for inaccuracy compared to tensile testing. Hence, compressive testing is applied much less than the standard tensile tests, unless the load case is requiring specific test data from compression, e.g., when brittle or cast alloys are applied. Ductile metals compressed to high strains require further consideration when the yield strength in compression, the compressive strength, or even the full flow curve for plasticity must be identified. A sophisticated test procedure for compression testing of ductile metals in the plasticity range has been developed and is presented. It allows the determination of elastic modulus, yield strength, and flow curve up to high strains. The procedure was evaluated with comparative tensile tests on identical specimens and with a round-robin test with a testing-machine manufacturer. Further considerations for compression testing and for the strain measurement are presented.
https://www.dora.lib4ri.ch/empa/islandora/object/empa:6972
... Volume 20 · Number 6 · 2014 · 541-550 E 0 ϭ 117 GPa for Ti6Al4V (Choe et al., 2005). The value C is confirmed by data for a variety of relative density and cellular structures that give the coefficients of Young's modulus (C AY ϭ 0.045) for armchair geometry and the coefficients of Young's modulus (C ZY ϭ0.052) for zigzag geometry, respectively. ...
Purpose
– The purpose of this paper is to fabricate cellular Ti6Al4V with carbon nanotube (CNT)-like structures by selective electron beam melting and study the resultant mechanical properties based on each respective geometry to provide fundamental information for optimizing molecular architectures and predicting the mechanical properties of cellular solids.
Design/methodology/approach
– Cellular Ti6Al4V with CNT-like zigzag and armchair structures are fabricated by selected electron beam melting. The microstructures and mechanical properties of these samples are evaluated utilizing scanning electron microscopy, synchrotron radiation X-ray and compressive tests.
Findings
– The mechanical properties of the cellular solids depend on the geometry of strut architectures. The armchair-structured Ti6Al4V samples exhibit Young’s modulus from 501.10 to 707.60 MPa and compressive strength from 8.73 to 13.45 MPa. The zigzag structured samples demonstrate Young’s modulus from 548.19 to 829.58 MPa and compressive strength from 9.32 to 16.21 MPa. The results suggest that the zigzag structure of the Ti6Al4V cellular solids can achieve improved mechanical properties and the mechanism for the enhanced mechanical properties in the zigzag structures was revealed.
Originality/value
– The results provide an innovative example for modulating the mechanical properties of cellular titanium by adjusting the unit cell geometry. The Ti6Al4V cellular solids with single-walled CNT-like structures could be used as light-weight construction components or filters in industries. The Ti6Al4V with multiwalled CNT-like structures could be used as new scaffolds for biomedical applications.
Bio-inspired mimicking natural structures generally duplicate the three dimensional “hard brick-and-soft mortar” structure that may overcome the intrinsic brittleness of the brick, resulting in an improved mechanical performance. Here for the first time, we proposed an anti-bioinspired strategy of designing metallic composite with soft bricks (pure Ti) confined by hard mortars (Ti6Al4V alloy). The three-dimensional minority of hard mortar (with a volume fraction of ∼14%) is fabricated by using selective laser melting (SLM), while the bricks are introduced by filling the pure titanium powders followed by the hot isostatic pressing. The resulting nacre-like structured composite reveals a distinct periodic distribution of “soft-brick” and “hard-mortar” domains by a well-bonded interface with a well-bonded interface between them. This unique composite structure exhibits a combination of high strength and high fracture toughness that both exceed the respective value calculated using the rule of mixtures (ROM). Three dimensional heterogenous plastic deformations between the two domains induce the mechanical incompatibility, which has been confirmed by the presence of higher density of geometrically necessary dislocations (GNDs) in front of the interface. The large amount of GNDs was believed primarily responsible for the extraordinary strengthening and toughening beyond the ROM. This novel strategy of designing artificial three dimensional “soft brick-and-hard mortar” structure could be further applied to other metals and alloys, shedding lights on the development of innovative heterogeneous materials relevant to industry.
Refractory metal particles can potentially be used to reinforce titanium matrix composites. In this research, a titanium matrix composite reinforced by 20 wt.% tungsten particles (20WP/Ti) was fabricated by powder metallurgy. The mechanical properties of 20WP/Ti were then evaluated over a broad strain rate range of 10⁻³–4×10³ s⁻¹. The microstructure of the composite consisted of W particle reinforcements, W diffusion regions, and an alloyed Ti matrix. The interdiffusion between W and Ti atoms produced broad diffusion regions and the Kirkendall effect. The W diffusion regions were a complex multiple-phase mixture of micron-sized β-Ti grains, nanoscale ω and α″-Ti phases and W nanoparticles. 20WP/Ti exhibited excellent mechanical properties due to the presence of multiple strengthening mechanisms including reinforcing phase strengthening, solid solution strengthening, and precipitation strengthening. The addition of W particle reinforcing phases suppressed the adiabatic shear sensitivity of the composite. When the strain rate exceeded 1400 s⁻¹, the dynamic strength of 20WP/Ti declined upon increasing the strain rate, attributing to a mass of Kirkendall pores and the thermal softening effect of the β-Ti phase in the W diffusion region at high strain rates.
W-containing Ti-6Al-4V alloys (W=0, 1, and 5 wt%) were fabricated by the powder injection molding process, and the corresponding effects of tungsten content on the mechanical properties and microstructure of the alloys were investigated. The alloy powders were sintered at 1200 °C and then hot-isostatically-pressed at 900 °C. The fabricated alloys were subjected to microstructural and chemical analyses, and tensile and nano-indentation tests. The yield strength and tensile strength proportionally increased as the W content was increased from 0 wt% to 5 wt%. Ductility was not affected by the addition of up to 5 wt% W due to its complete dissolution in the matrix. Higher W addition induced finer α/β lamellar microstructures and increased the β to α phase ratio. Moreover, the added W dissolved preferentially in the β phase by solid solution hardening, increasing the hardness of the β phase, which originally was significantly softer than the α phase. For the alloys containing up to 5 wt% W, the strengthening without ductility loss was attributed to the finer α/β lamellae and the volume increase in the β phase hardened by W. These results suggest that adding W to Ti-6Al-4V alloy is a promising method for developing Ti alloys with both high strength and toughness.
Ti–6Al–4V (TC4) alloy and Ti–6Al–4V-5 wt.%W (TC4-5%W) alloy were fabricated by spark plasma sintering (SPS). The crystalline structure and microstructure of both TC4 alloy and TC4-5%W alloy were confirmed using X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The XRD patterns suggested that a similar crystalline structure was formed in both of TC4 alloy with and without the W addition. SEM and TEM indicated that the dispersed W particles can refine the β grain, α colonies and coarsen the α laths by acting as the supernumerary nucleation sites for α laths during the β→α+β transformation process. Moreover, a comparative analysis of the mechanical properties of both TC4 and TC4-5%W alloys was obtained by the tensile tests, which is found that the W addition can increase the strength and ductility of TC4 alloy simultaneously. It is found that fine-grain strengthening is the dominant strengthening mechanism, which contributed 72% of the total strength increment. Meanwhile, the load-bearing effect also contributes to some of the total strength increments in this study. This study concluded that TC4 with W dispersed particles had a great potential to use as a novel Ti alloy with high strength and good ductility.
In this study Ti, Al, V and B4C powders were milled separately in ball mill for various time periods. The powder morphology was tested by particle size analysis (PSA), FTIR and SEM studies in every one hour interval. Finally the individual powders were mixed on a weight basis to produce novel Ti-6Al-4V-B4C composite precursor and fabricated compacts were heat treated at 900°C. The microstructural features and mechanical properties of the sintered compacts were ascertained by microhardness and SEM studies. It was observed that with increase in milling time and B4C reinforcement of 10 wt% yields a significant improvement of microhardness as well as homogeneous microstructure in the sintered composite.
The elastic moduli and acoustic loss behaviour of Ti-6Al-4V (wt.%) in the temperature range 5–298 K have been studied using Resonant Ultrasound Spectroscopy. A peak in the acoustic dissipation was observed at 160 K within the frequency range 250–1000 kHz. Analysis of the data acquired in this study, coupled with complementary data from the literature, showed that this was consistent with a Snoek-like relaxation process with an associated activation energy of 23 3 kJ mol. However, the loss peak was broader than would be expected for a Snoek-like relaxation, and the underlying process was shown to have a spread of relaxation times. It is suggested that this effect arises as a result of variations in the strain experienced by the phase due to different local microstructural constraint by the bounding secondary phase.
In order to improve the wear resistance of Ti-6Al-4V, different amounts of Si3N4 powder were added into the alloy powder and sintered at 1250°C. Porous titanium alloy with higher wear resistance was successfully fabricated. At sintering temperature, reaction took place and a new hard phase of Ti5Si3 formed. The mechanical properties of the fabricated alloys with different amounts of Si3N4 addition were investigated. The hardness of Ti-6Al-4V, which is the index of wear resistance, was increased by the addition of Si3N4. Amounts of Si3N4 addition have very significant influences on hardness and compressive strength. In present study, titanium alloy with 5 wt pct Si3N4 addition has 62% microhardness and 45% overall bulk hardness increase, respectively. In contrast, it has a 16.4% strength reduction. Wear resistance was evaluated by the weight loss during wear test. A new phase of Ti5Si3 was detected by electron probe microanalyzer (EPMA) and X-ray diffraction (XRD) method. The original Si3N4 decomposed during sintering and transformed into titanium silicide. Porous structure was achieved due to the sintering reaction.
Titanium and its alloys are currently considered as one of the most important metallic materials used in the biomedical applications, due to their excellent mechanical properties and superior biocompatibility. In the present study, a new effective method for fabricating high porosity titanium alloy scaffolds was developed. Porous Ti-6Al-4V scaffolds are successfully fabricated with porosities ranging from 30% to 70% using space-holder and powder sintering technique. Based on its acceptable properties, spherical carbamide particles with different diameters (0.56, 0.8, and 1 mm) were used as the space-holder material in the present investigation. The Ti-6Al-4V scaffolds porosity is characterized by using scanning electron microscopy. The results show that the scaffolds spherical-shaped pores are depending on the shape, size and distribution of the space-holder particles. This investigation shows that the present new manufacturing technique is promising to fabricate a controlled high porosity and high purity Ti-6Al-4V scaffolds for hard tissue replacement.
This paper reviews progress over the last five years in the field of laser surface modification of titanium alloys. The authors analyze the effect of new laser technologies and new materials as tools for improving surface properties—specifically, biocompatibility and resistance to wear, corrosion, and high temperatures. The authors discuss the effect of laser processing parameters on the microstructure and compare the results obtained by various researchers. Therefore, an overview of the difficulties involved in the laser processing of titanium is provided with a discussion of future prospects.
The effects of minor additions of Nb (2, 3 and 4 at%) to the Ti40Zr10Cu38Pd12 alloy are discussed in terms of microstructure, thermal behavior, mechanical properties and corrosion resistance. The addition of Nb promotes the formation of nanocrystals, i.e., from a completely amorphous structure (when no Nb is added) to a mainly crystalline structure (for a 4% of Nb addition). The glassy alloy exhibits large hardness, relatively low Young's modulus and excellent corrosion behavior, although the plasticity is rather limited. A significant increase in compressive plasticity (total strain over 13%) is achieved in the sample with 3% of Nb without compromising the strength. Young's modulus of the as-cast alloy (around 100 GPa, as determined from acoustic measurements) increases only slightly when disperse nanocrystallites are embedded in the amorphous matrix. Improvement of the corrosion performance, with delayed pitting corrosion, is also observed for 3% Nb addition.
In this work, the tensile properties of nanocrystalline Ti and bulk Ti processed by surface mechanical attrition treatment (SMAT) have been studied. The nanocrystalline Ti shows high strength which can be comparable to that of Ti–6Al–4V together with depressed plasticity. On the contrary, the strength of bulk Ti after SMAT is obviously improved with acceptable ductility and this new material has a potential biomedical application.
Residual stress induced by laser single pulse irradiation was analyzed using a dynamic finite element code, ABAQUS/Explicit. The effects of the magnitude and length of a surface pressure pulse having a circular top-hat shape on the final residual stress in Ti-6A1-4V were investigated. A high peak pressure and/or a long pulse duration was effective in generating large compressive residual stress deep beneath the surface. However, large tensile residual stress features occurred near the centre and edge of the laser spot on the surface for high pressure and/or long pulse durations due to a radial focusing effect. Use of shorter pulse durations avoided this. The peak pressure (3 GPa) required to induce a surface compressive residual stress across the whole area of the spot was slightly higher than the threshold pressure needed to plastically deform the surface.
7.5 mass% TiC and 7.5 mass% W powder blends were densified with Ti-6Al-4V blends by combined cold and hot isostatic pressing (CHIP) method to result in three types of composites with differing processing histories, namely hot isostatic pressing (HIPping), extrusion, and casting, which were compared with their monolithic counterparts. Tensile and microhardness tests, along with compressive testing, were carried out to investigate the mechanical properties of powder metallurgy (P/M) Ti-6Al-4V-7.5%TiC-7.5%W composites at ambient temperature. Dissolution of W powder in the Ti-6Al-4V matrix during consolidation seems to be limited by the presence of TiC particles, which can in turn influence mechanical properties of the composites. Cast Ti-6Al-4V-7.5%TiC-7.5%W composite exhibits superior hardness, yield strength, and tensile strength, with a decrease in ductility, compared to its monolithic counterpart and other composites.
In situ TiB2 particulate reinforced Fe-based composite was produced by vacuum induction melting (VIM) technique. The effect of tungsten element on the microstructure and tensile properties of the composite was investigated. The results show that the tungsten can dissolve into the TiB2 particulates and the segregation of TiB2 is reduced. Meanwhile, with the addition of 3.0wt.% tungsten, the composite is solid strengthened and an optimal tensile property can be obtained. The yield strength (YS), ultimate tensile strength (UTS) and elongation to rupture (Er) of the composite reach as high as 360MPa, 690MPa and 18.5%, respectively. The fracture morphologies also indicate that the addition of 3.0wt.% tungsten results in the increase of plastic fracture.
Ti–W alloys were produced via electrochemical reduction of TiO2–WO3 mixed oxide preforms in a pre-electrolysed, molten calcium chloride electrolyte at 1173K. Electrolysis voltages of 1500–3200mV were applied for times ranging from 6 to 24h across a graphite anode and Grade 2 commercial purity (CP) titanium cathodic current collector, which supported the ceramic precursors. Low-oxygen, homogeneous material was subsequently water washed and characterized to determine the level of residual species remaining from the reduction process, such as Cl and Ca. The microstructure (porosity and microchemistry) of the reduced material and microstructural examination of the mixed oxide feedstock (particle morphology, size and chemistry) were characterized using a field emission gun scanning electron microscope (FEG-SEM) with backscattered electron imaging (BSE) and X-ray energy dispersive spectrometry (X-EDS).
Y2O3-dispersed titanium with Y2O3 content ranging between 0.3 and 0.7 wt% was produced by an arc-melting technique starting from Ti and Y2O3. Compositional and microstructural characterization was performed by XRD, SEM and TEM for as-cast, forged and recrystallized samples. A uniform nanodispersion of Y2O3 particles with sizes <100 nm was found for all the alloys. These particles coarsened and tended to be aligned as the Y2O3 content rose and the alloy was forged, and their shape became more spherical after cold rolling and subsequent recrystallization. TEM observations also revealed that dislocations were pinned by Y2O3 particles. Tensile tests were performed at 298 K for forged alloys and at 298, 498 and 773 K for recrystallized alloys. The Y2O3 nanodispersion effectively strengthened these materials.
Ti6Al4V foams were fabricated by the spark plasma sintering (SPS) with post-heat treatment using a
blend of Ti6Al4V and sodium chloride powders. The microstructure and properties of the foams were
investigated by scanning electron microscopy, X-ray micro-CT, Synchrotron X-ray, compression test
and cell experiments. Results showed that the Ti6Al4V foams fabricated at 700 1C and 50 MPa in the SPS
cannot get high relative densities. These sintered foams were post-heat treated in a pressureless mode
of the SPS at 1100 1C for 5 min. This heat treatment is very effective to reduce the microporosity and to
densify the foam walls. Young’s modulus of the foams was in the range of 33.0–9.5 GPa and yield
strength ranged from 110.2 MPa to 43.0 MPa with porosity values from 44.7% to 70.0% obeying the
Gibson–Ashby models. The human osteoblast cell line MG-63 validated the cellular acceptance of the
foam surfaces. The pressureless SPS provides a new method for the heat treatment of metallic foams.
We demonstrate a powder metallurgy synthesis route for porous Ti–6Al–4V structures by consolidation of Ti–6Al–4V alloy powders and describe the influence of the processing conditions. Ti–6Al–4V foams with 50 vol% porosity having high strength were fabricated by low temperature solid state deformation at temperatures below 873 K. The open cellular structure consists of continuously connected Ti–6Al–4V struts and homogeneously distributed pores with nominal diameters between 10 and 50 µm and 150–500 µm length.
High frequency induction heating sintering method is used for sintering of the metal and ceramics powder. This technique has been used to produce high density compacts, containing as small grains as possible of powders. The alloy of Ti–6Al–4V was modified by addition of 2.5, 5, and 10 wt.% tungsten through powder metallurgy. Ti–6Al–4V/W was prepared by high-energy mechanical milling. The use of the high frequency induction heating sintering technique allows sintering to nearly full density at comparatively low temperatures and short holding times, and therefore suppressing grain growth. Different process parameters such as sintering temperature, and applied pressure have been investigated. The obtained compacts are characterized with respect to their densities, grain morphologies and pore distributions as well as hardness. Ti–6Al–4V/W powder precursors have been successfully compacted and consolidated to densities exceeding 98.8%. The maximum compressive strengths were obtained at sintering temperature 1000 °C for the samples containing 5% W, and at 1100 °C for the samples with 10% W. Maximum hardness was obtained 45 HRC at 1100 °C for 10% W.
Composites consisting of a Ti–W solid-solution-strengthened matrix reinforced with TiC particles are produced by powder metallurgy. TiC additions increase strength but reduce ductility and matrix microhardness. Composites with 7.5 wt.% TiC show some tensile ductility (3–7%) but those with 15 wt.% TiC are brittle in tension. They are however strong and ductile in compression: Ti–15W/15TiC (wt.%) has a compressive yield strength exceeding 1200 MPa. This composite also shows tensile crack growth rates which are considerably faster than for pure titanium (by a factor 2) or Ti–15W (by a factor 2–6) and a fracture toughness which remains relatively high as compared to Ti–15W (21 vs. ).
Tungsten-reinforced Ti and Ti–6Al–4V composites were fabricated by powder metallurgical techniques from Ti, W and Al–V powders. The microstructure of the composites consists of partially dissolved tungsten particles within an α/β titanium matrix containing tungsten in solid-solution. Yield and ultimate tensile strengths increase linearly with tungsten content in the range 0–15 wt.% W and decrease near-linearly with temperature in the range 25–540 °C. Ductility follows the opposite trend and is within technologically acceptable values, except for Ti/15W at 315 and 425 °C and Ti/10W at 540 °C which fractured near the ultimate stress value. The Ti–6Al–4V/10W composite shows the best combination of high strength and ductility at all temperatures. At ambient temperatures, Ti/10W exhibits a stress–strain curve very similar to Ti–6Al–4V (with a slight decrease in stiffness), while eliminating aluminum and vanadium alloy elements. Further improvements in mechanical properties of these non-equilibrium composites are likely to be achieved through optimized heat-treatments, which affect the matrix microstructure and the degree of dissolution of tungsten and thus the relative importance of matrix solid-solution strengthening and composite strengthening.
The corrosion susceptibility of Ti, Ti-6A1-4V and Ti-45Ni was studied in a buffered saline solution using anodic polarisation and electrochemical impedance measurements. Pitting potentials as low as + 250 mV(SCE) were recorded for Ti-45Ni and once initiated pits continued to propagate at potentials as low as -150 mV(SCE). It was possible to increase the pitting potential of Ti-45Ni to values greater than +800 mV(SCE) using a H2O2 surface treatment procedure; however, this surface modification process had no beneficial effect on the rate of pit repassivation. Impedance spectra, recorded under open-circuit conditions, were modelled using a dual oxide film model; a porous outer layer and an inner barrier oxide layer. The nature of this porous outer layer was found to depend on the nature of the electrode material and the presence of phosphate anions in the saline-buffered solution. The porous layers formed on Ti-45Ni and Ti-6Al-4V in the presence of phosphate anions had low resistances typically between 10 and 70 ohm cm2. Much higher porous layer resistances were recorded for Ti and also for Ti-45Ni and Ti-6Al-4V in the absence of the phosphate anions.
The release of metal ions from the Ti-15Zr-4Nb-4Ta alloy in pseudo body fluids was compared with those from Ti-6Al-4V and vanadium-free Ti-6Al-7Nb alloys widely used as implantable titanium alloys throughout the world, in order to choose an optimum acceleration solution for immersion testing. Bone plates, artificial hip joints of the cementless type and artificial tooth implants were experimentally fabricated using the Ti-15Zr-4Nb-4Ta alloy. The quantities of titanium ions released from the titanium alloys into phosphate-buffered saline, α-medium and fetal bovine serum were very small, and much lower than those released into 1.2 mass% L-cysteine, 0.05 mass%HCl and 1 mass% lactic acid solutions with lower pH values than the phosphate-buffered saline and α-medium. It was suggested that 1 mass% lactic acid solution was promising as an acceleration solution for immersion test. The quantities of titanium ions released from the Ti-15Zr-4Nb-4Ta alloy into fetal bovine serum, 1.2 mass% L-cysteine, 0.05 mass%HCl and 1 mass% lactic acid solutions were approximately 30% of those of titanium ions released from the Ti-6Al-4V alloy. The total quantity of zirconium, niobium and tantalum ions released from the Ti-15Zr-4Nb-4Ta alloy was much smaller than that of elements released from the Ti-6Al-4V and Ti-6Al-7Nb alloys. Bone plates, artificial hip joints and artificial tooth implants were successfully fabricated with the Ti-15Zr-4Nb-4Ta alloy using conventional manufacturing processes. The Ti-15Zr-4Nb-4Ta alloy with its excellent corrosion resistance is expected to become the preferential titanium alloy for implant applications in the future.
The chip process, combining cold and hot hydrostatic pressing, has been applied to the manufacture of metal matrix composites utilizing particulate reinforcements. These microcomposites demonstrate significant increase in the strength, modulus and use temperature of advanced structural alloys. This article describes the manufacture and properties of these MMCs with particular attention to the significant improvements in modulus and strength at both room and elevated temperatures.
Titanium has been increasingly applied to dental prostheses because of its biocompatibility. However, application remains limited, due to the low strength and poor wear resistance of unalloyed titanium. The purpose of this study is to evaluate the wear resistance of high-strength Ti–6Al–7Nb alloy castings for dental application. Test specimens were cast from commercially pure titanium (CP-Ti grades 2 and 3) and Ti–6Al–7Nb alloy ingots, and subjected to a wear test simulating the occlusal loading pattern. Wear resistance was evaluated by the weight loss during the test. Ti–6Al–7Nb alloy was found to exhibit lower weight loss than CP-Ti. Moreover, scanning electron microscopic (SEM) observation after the test revealed that the worn surface of Ti–6Al–7Nb alloy is much smoother than that of CP-Ti. These results indicate that Ti–6Al–7Nb alloy castings can be used to produce dental prostheses of improved wear resistance and mechanical strength.
In this paper is reported the results of a study aimed at establishing an understanding the role of particulate reinforcement on tensile deformation and fracture behavior of magnesium alloys discontinuously-reinforced with silicon carbide (SiC) particulates. An increase in particulate reinforcement content was observed to decrease ultimate tensile strength and ductility of the composite when compared to the unreinforced counterpart. Cracking of the individual and clusters of reinforcing particulates present in the microstructure dominated tensile fracture of the composite, on a microscopic scale. Final fracture occurred as a result of crack propagation through the matrix between particulate clusters. The fracture behavior of the composite is discussed in light of the concurrent and mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the metal matrix and the particulate reinforcement, nature of loading and local stress state.
The release of metal ions from the Ti-15Zr-4Nb-4Ta alloy in pseudo body fluids was compared with those from Ti-6Al-4V and vanadium-free Ti-6Al-7Nb alloys widely used as implantable titanium alloys throughout the world, in order to choose an optimum acceleration solution for immersion testing. Bone plates, artificial hip joints of the cementless type and artificial tooth implants were experimentally fabricated using the Ti-15Zr-4Nb-4Ta alloy. The quantities of titanium ions released from the titanium alloys into phosphate-buffered saline, alpha-medium and fetal bovine serum were very small, and much lower than those released into 1.2 mass% L-cysteine, 0.05 mass%HCl and 1 mass% lactic acid solutions with lower pH values than the phosphate-buffered saline and a-medium. It was suggested that I mass% lactic acid solution was promising as an acceleration solution for immersion test. The quantities of titanium ions released from the Ti-15Zr-4Nb-4Ta alloy into fetal bovine serum, 1.2 mass% L-cysteine, 0.05 mass%HCl and 1 mass% lactic acid solutions were approximately 30% of those of titanium ions released from the Ti-6Al-4V alloy. The total quantity of zirconium, niobium and tantalum ions released from the Ti-15Zr-4Nb-4Ta alloy was much smaller than that of elements released from the Ti-6Al-4V and Ti-6Al-7Nb alloys. Bone plates, artificial hip joints and artificial tooth implants were successfully fabricated with the Ti-15Zr-4Nb-4Ta alloy using conventional manufacturing processes. The Ti-15Zr-4Nb-4Ta alloy with its excellent corrosion resistance is expected to become the preferential titanium alloy for implant applications in the future.
The correlation between tensile and indentation behavior in particle-reinforced metal matrix composites (MMCs) was examined. The model composite system consists of a Al–Cu–Mg alloy matrix reinforced with SiC particles. The effects of particle size, particle volume fraction, and matrix aging characteristics on the interrelationship between tensile strength and macro-hardness were investigated. Experimental data indicated that, contrary to what has been documented for a variety of monolithic metals and alloys, a simple relationship between hardness and tensile strength does not exist for MMCs. While processing-induced particle fracture greatly reduces the tensile strength, it does not significantly affect the deformation under indentation loading. Even in composites where processing-induced fracture was nonexistent (due to relatively small particle size), no unique correspondence between tensile strength and hardness was observed. At very low matrix strengths, the composites exhibited similar tensile strengths but the hardness increased with increasing particle concentration. Fractographic analyses showed that particle fracture caused by tensile testing is independent of matrix strength. The lack of unique strength–hardness correlation is not due to the particle fracture-induced weakening during the tensile test. It is proposed that, under indentation loading, enhanced matrix flow that contributes to a localized increase in particle concentration directly below the indenter results in a significant overestimation of the overall composite strength by the hardness test. Micromechanical modeling using the finite element method was used to illustrate the proposed mechanisms under indentation loading and to justify the experimental findings.
Al 2024–SiC metal matrix composite (MMC) powders produced by centrifugal atomization were hot extruded to investigate the effect of clustering on their mechanical properties. Fracture toughness and tension tests were conducted on specimens reinforced with different volume fractions of SiC. A model was proposed to suggest that the strength of the MMCs could be estimated from the load transfer model approach that takes into consideration the extent of clustering. This model has been successful in predicting the experimentally observed strength and fracture toughness values of the Al 2024–SiC MMCs. On the basis of experimental observations, it is suggested that the strength of particulate-reinforced MMCs may be calculated from the relation: σy=σmVm+σr (Vr−Vc)−σrVc, where σ and V represent the yield strength and volume fraction, respectively, and the subscripts m, r, and c represent the matrix, reinforcement, and clusters, respectively.
The effect of the reinforcement spatial distribution on the mechanical behavior was investigated in model metal-matrix composites. Homogeneous microstructures were made up of a random dispersion of spheres. The inhomogeneous ones were idealized as an isotropic random dispersion of spherical regions—which represent the clusters—with the spherical reinforcements concentrated around the cluster center. The uniaxial tensile stress-strain curve was obtained by finite element analysis of three-dimensional multiparticle cubic unit cells, which stood as representative volume elements of each material, with periodic boundary conditions. The numerical simulations showed that the influence of reinforcement clustering on the macroscopic composite behavior was weak, but the average maximum principal stress in the spheres—and its standard deviation—were appreciably higher in the inhomogeneous materials than in the homogeneous ones (up to 12 and 60%, respectively). The fraction of broken spheres as a function of the applied strain were computed from experimental values of the Weibull parameters for the strength of the spheres, and the local stress computed in the simulations. It was found that the presence of clustering greatly increased (by a factor between 3 and 6) the fraction of broken spheres, leading to a major reduction of the composite flow stress and ductility.
In this research paper the tensile properties and fracture characteristics of aluminum alloy 2009 discontinuously reinforced with silicon carbide particulates (SiCp) are presented and discussed. The increased strength of the Al 2009/SiCp composite is attributed to the synergistic influences of residual stresses generated due to intrinsic differences in thermal expansion coefficients between the composite constituents, strengthening from constrained plastic flow and triaxiality in the ductile aluminum alloy metal matrix due to the presence of ceramic particle reinforcements. Fracture on a microscopic scale comprised of cracking of the individual and clusters of SiC particles present in the microstructure. Final fracture of the composite resulted from crack propagation through the matrix between the clusters of reinforcing SiC particles. The key mechanisms governing the tensile fracture process are elucidated.
In this study, comparative investigation of thermal oxidation treatment for Ti-6Al-4V was carried out to determine the optimum oxidation conditions for further evaluation of corrosion-wear performance. Characterization of modified surface layers was made by means of microscopic examinations, hardness measurements and X-ray diffraction analysis. Optimum oxidation condition was determined according to the results of accelerated corrosion tests made in 5m HCl solution The examined Ti-6Al-4V alloy exhibited excellent resistance to corrosion after oxidation at 600 degrees C for 60 h. This oxidation condition achieved 25 times higher wear resistance than the untreated alloy during reciprocating wear test conducted in a 0.9% NaCl solution.
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