Powder Metallurgy Titanium Research Articles

Impact-resistant titanium alloy with fine equiaxed structure fabricated by powder metallurgy

Although fine equiaxed structure benefits both strength and ductility in titanium alloys, it is often considered incompatible with high toughness, for its insufficient ability to deflect propagating cracks compared to coarse lamellar structure. This work reports an excellent combination of standard Charpy impact toughness (∼100 J) and yield strength (∼820 MPa) in a powder metallurgy titanium alloy with fine equiaxed structure (∼1.5 μm), wherein the β matrix exists as equiaxed nodules and fine ligaments for globularization of α grains. The impact curve divided with the “compliance changing rate” (CCR) method indicates that the energy consumed by crack propagation is dominant (∼82%) during the impact process. Fractographic and structural examinations indicate that multiple micro-voids nucleation near boundaries between fine β ligaments and α grains mitigates local stress concentration, and that coordinated deformation between equiaxed β nodules and α grains hinders crack propagation, which together enable the excellent combination of yield strength and impact toughness. Our work provides a new pathway for designing impact-resistant titanium alloys.

Mechanism of oxygen content on impact toughness of α + β powder metallurgy titanium alloy

Understanding the mechanism of oxygen on toughness of titanium alloys is crucial for popularizing powder metallurgy. In this work, the effect of oxygen content (1500, 3000 and 5000 ppm) on the impact toughness of powder metallurgically modified titanium alloys with fine equiaxed microstructures (∼1.5 μm) was systematically investigated. With increasing oxygen content, the c/a value of the α-phase lattice parameter increases to a maximum of 1.593 Å, and the hardness increases from 4.03 GPa to 5.05 GPa, resulting in an increase in strength of ∼150 MPa and a considerable decrease in the ability of the two phases to coordinate. The crack initiation energy is similar for different oxygen contents, whereas the crack propagation energy increases considerably with decreasing oxygen content; the impact energy of stable crack extension increases from 4 J to 13 J and 35 J, and the impact energy of unstable crack extension and crack collapse stages increases from zero to 14 J and 25 J, respectively, indicating that decreasing oxygen content can substantially improve the crack extension resistance. The activation of numerous dislocations within the two phases and the formation of subgranular boundaries at low oxygen contents promote the release of internal stresses in the grains, and simultaneously, the interfacial resistance to dislocation migration and the concentration of interfacial stresses are also reduced, which improves the coordination of the two-phase plastic deformation of the equiaxed microstructures; the crack extension paths in the impact process become more tortuous and finally achieve impact energies as high as 85–100 J.

Study on Multi-Objective Optimization of Milling Process of Powder Metallurgy Titanium Aluminum Alloys

Study on Multi-Objective Optimization of Milling Process of Powder Metallurgy Titanium Aluminum Alloys

Integrated high-performance and accurate shaping technology of low-cost powder metallurgy titanium alloys: A comprehensive review

Integrated high-performance and accurate shaping technology of low-cost powder metallurgy titanium alloys: A comprehensive review

Investigation of physical, chemical, and technological properties of titanium powder obtained by thermal dehydrogenation in vacuum

In recent times, there has been significant interest in powder metallurgy, driven primarily by the active development of additive manufacturing. Consequently, a pressing task is the development of methods for producing initial metal powders that are cost-effective while meeting high consumer standards. This research is a continuation of studies on titanium powders obtained through SHS hydrogenation and thermal dehydrogenation. The titanium hydride powders, previously obtained using SHS technology, were sieved, resulting in fractions that matched the granulometric composition of titanium powders of PTK, PTS, PTM, and PTOM grades. Subsequently, the titanium hydride powder samples underwent dehydrogenation through vacuum annealing in an electric resistance furnace. Throughout the dehydrogenation process, the kinetics of hydrogen release from the titanium powder were examined as a function of particle size. The macro- and microstructure, chemical composition, and technological properties of the dehydrogenated powders were thoroughly analyzed. It was determined that the titanium powder maintained its original polygonal fragmented shape after dehydrogenation. The average particle size decreased by 5–20 %, and “satellites” were observed on larger particles. Chemical analysis revealed that larger samples contained a higher level of residual hydrogen and gas impurities (Σ 0.77 wt. %) compared to finer powders (Σ 0.26 wt. %). Regarding the study of technological properties, the resulting powders exhibited the necessary characteristics for use in titanium powder metallurgy, with the exception of low flowability due to the particle shape and microstructural heterogeneity). In conclusion, this research has demonstrated the potential of the SHS hydrogenation and thermal dehydrogenation method in producing high-quality titanium powders.

New Powder Metallurgy Titanium Alloys with Built-In Antibacterial Capability

Amongst biomedical metallic materials, titanium alloys are normally used as structural permanent implants due to their favourable combination of mechanical properties and biocompatibility. However, commonly implanted titanium alloys are expensive and, unless purposely surface treated, generally cannot prevent surgical infections related to bacteria. Specifically, bacterial infection in biomedical protheses leads to inflammation, obstruction of the healing process, prevention of osteogenesis and, eventually, premature failure of the implant. This work therefore analysis the development of new ternary Ti-based alloys with built-in antibacterial capability as pathogenic bacterial infection occurring during surgery is a raising issue of metallic biomedical implants. The new Ti-based alloys were designed to be manufactured via powder metallurgy, which permits to successfully produce chemically homogeneous materials, key for a uniform antibacterial response, at lower cost. It is found that, primarily due to the stabilisation of the beta phase, the amount of the selected β stabilising alloying elements directly increases the mechanical performance and the antibacterial capability. Consequently, new ternary Ti-based alloys are promising candidates for structural prosthesis functionalised with antibacterial capability.

Achieving superior performance in powder-metallurgy near-β titanium alloy by combining hot rolling and rapid heat treatment followed by aging

Heat treatment plays an important role in tailoring the mechanical properties of powder-metallurgy (PM) titanium alloys. However, only limited work about the rapid heat treatment (RHT) of PM titanium alloys has been reported. In this work, RHT was applied to PM Ti–5Al–5Mo–5V–1Cr–1Fe alloy after hot rolling to study the evolution of its mechanical properties and the influence of residual pores on its properties. Through hot rolling and annealing, a fine and uniform α + β structure with few residual pores is obtained. During RHT, the primary α dissolves gradually and completes in the β region, and the β grains then grow, resulting in the continuous decrease in elongation after aging. Moreover, the tensile strength first increases and then decreases with increasing RHT temperature, owing to the increase in volume fraction of secondary α in α + β region and the β grain growth in β region. In contrast to the RHT of cast-and-wrought titanium, the negative influence of residual pores lowers the RHT temperature for obtaining the highest tensile strength to a temperature below the β-transus temperature. Despite the negative influence of the residual pores, retained primary α and fine β grains with fine secondary α inside contribute to achieving a good strength/ductility balance (1570 MPa and 6.1%, respectively). Additionally, although at higher cycles to failure, the negative influence of residual pores increases as it affects the crack initiation zone at the subsurface, the good resistance of secondary α to fatigue crack propagation still enhances the fatigue strength considerably (about 300 MPa). This work suggests a cost-effective strategy to produce titanium alloys with high performance.

Powder metallurgy of titanium alloys: A brief review

The powder metallurgy (PM) of titanium alloys has received more and more attention in structural and biomedical applications owing to its low cost, near-net-shape formability, and competitive mechanical properties compared with wrought titanium alloys. In this work, we present an overview of the state-of-the-art research on PM titanium alloys, including the basic fabricating processes, the typical microstructure, and the advanced mechanical properties obtained recently. Furthermore, we aim to discuss the different selection criteria so as to find the appropriate PM process (pressureless sintering, pressure-assisted sintering, or thermo-mechanical processes) for manufacturing a particular component with a defined set of material properties. Finally, the present manuscript raises some open and critical issues in the field of PM titanium alloy that remain unresolved but are critical for future research.

Damage behaviour and GTN parameter analysis of TC4 powder metallurgy titanium alloy during hot deformation

Damage behaviour and GTN parameter analysis of TC4 powder metallurgy titanium alloy during hot deformation

Achieving superior fatigue strength in a powder-metallurgy titanium alloy via in-situ globularization during hot isostatic pressing

Powder-metallurgy (PM) titanium alloys exhibit outstanding quasistatic-mechanical properties, but suffer from low fatigue performance, which severely limits their applications in aerospace. Here, we achieve a superior fatigue strength of 600 MPa in a near-α PM titanium alloy, using a two-step hot-isostatic-pressing scheme, during which more than 80 vol.% (volume fraction) randomly orientated equiaxed grains was obtained. The largely improved fatigue strength (∼ 25%) is mainly attributed to the in-situ globularization of the lamella-like microstructure, leading to higher crack nucleation resistance and lower growth rates of short cracks. The present findings offer a useful route for fabricating PM titanium alloys with high fatigue strengths.

A pathway to significantly improve the ductility of a high strength PM α+β titanium alloy by short GB α layers and refined αWGB colonies

An approach combing ball milling (BM) and thermomechanical consolidation of a TiH2 based composite powder was used to fabricate powder metallurgy (PM) α+β Ti–4Al–4Mo–4Sn-0.5Si (wt%) alloy. Compared with the coarse-grained alloy with the same composition fabricated by the traditional blended elemental (BE-PM) method, the alloy exhibited a low oxygen content of 0.27 wt% and much-refined β grains with average size of 21 μm owing to the unpassivated and refined powder and fast consolidation process. The fine-grained alloy exhibited an α/βt lamellar microstructure in combination with short grain boundary α (GB α) layers and small GB Widmanstätten α (αWGB) colonies, while the coarse-grained alloy was composed of a similar α/βt lamellar structure in combination with long and continuous GB α plates and large-sized αWGB colonies. βt represented a transformed β structure consisting of fine secondary α laths and residual β layers. It was worth noting that the fine-grained alloy exhibited both higher strength and drastically higher ductility than the coarse-grained alloy (yield strength: 1238 vs 1156 MPa; elongation to fracture: 15.4% vs 4.1%). The enhanced strength was ascribed to the width refinement of α plates and increased fraction of βt domains. The excellent ductility was attributed the refined αWGB colonies and short GB α layers with increased variety of crystal orientations, which relieved strain concentration at GB α phase and thus suppressed the crack nucleation and propagation along it. Therefore, a high density of <a> and <c+a> dislocations were successfully activated in the thin α plates to accommodate plastic deformation, leading to an excellent ductility. This work provides a new strategy to fabricate high strength PM titanium alloys with excellent ductility.

Effect of Alloying Elements on Strengthening Phase and Solidification Structure of Ti-Al-Mo-Zr Titanium Alloy

This paper mainly studies the composition of strengthening phase, characteristic precipitation temperature and composition range of strengthening phase in Ti-Al-Mo-Zr-Si medical titanium alloy, and the influence of element changes on the content and microstructure of strengthening phase. Promote the formulation of thermodynamic process of titanium alloy powder metallurgy, as well as the formulation of alloy hot working and solid solution aging process. In this paper, Panda thermodynamic software is used to calculate the multicomponent alloy thermodynamics and multicomponent phase diagram of titanium alloy materials. The effects of Al, Mo, Zr, Si and other elements on the precipitation of strengthening phase and the phase transformation content of solidification structure were obtained. It is found that the content of Mo is more than 2 wt.% β phase transition precipitation angle. Meanwhile, in order to avoid the excess of precipitates such as Mo5Si3 and M3Si, the content of Mo should be less than 4.6 wt.%. The content of Zr can be maintained at about 1.5 wt.%. If the aging precipitation of the material is considered, it can be controlled to be less than 2 wt.%. The content of this paper is the basis and improvement of titanium powder metallurgy technology and rapid prototyping technology.

Ductilization of fracture of a high strength interwoven α/βt structured PM titanium alloy by in-situ formed submicron Y2O3 particles

A method combining internal oxidation and thermomechanical consolidation of a composite powder with a trace amount of Y addition was used to fabricate powder metallurgy (PM) near-α Ti–6Al–2Sn–4Zr–2Mo−0.1Si−0.5Y (wt%) alloy, in which submicron Y2O3 particles were in-situ formed and distributed uniformly in the matrix to achieve a low oxygen content and an excellent combination of high tensile strength of 1242 MPa and excellent tensile ductility of 16.2%. The in-situ reaction of uniformly dispersed Y particles in the composite powders prepared by high-energy ball milling with the oxygen in the matrix to form submicron Y2O3 particles during powder consolidation can significantly scavenge oxygen in the matrix and eliminate the coarse grain boundary α layers. The Y2O3 particles also work as nucleants for heterogeneous nucleation of α grains in the prior β grains during cooling, thus promoting the formation of α plates with a larger number of orientation variations and a decrease of their aspect ratios in the interwoven α/βt microstructure consisting of fine α plates and β transformed structure (βt) domains, which is beneficial to suppress the initiation and rapid propagation of cracks during tensile deformation. It is demonstrated that with the high flow stress rendered by the ultrafine interwoven α/βt microstructure and oxygen scavenging effect of Y on the matrix, twinning across α/βt interfaces and decohesion between the submicron Y2O3 particles and matrix occur during tensile deformation. This further suppresses formation and propagation of microcracks often seen in the Y2O3 particle free PM near-α titanium alloy of the same composition in the same situation. It is believed that the twinning and decohesion of the interfaces between Y2O3 particles and matrix are responsible for the mitigation of strain localization needed for formation of microcracks, which is essential to maintain a good tensile ductility and allow the fracture to be totally ductilized.

The influence of tool quality on the machining of additive manufactured and powder metallurgy titanium alloys.

This study was carried out to investigate the impact the quality of the drill bits has on the machining behavior of additive manufacturing (AM) and powder metallurgy (PM) titanium alloys. Therefore, commercially available drill bits which typically reflect two extremes of drill bit quality were selected. The performance of coated carbide twist drills, typically recommended for the drilling of wrought titanium alloys was compared with that of high-speed steel (HSS) drills. The average torque value, specific cutting energy (SCE), and tool wear were used to evaluate the drilling performance of AM and PM titanium alloys. The results of drilling tests revealed the application of the coated carbide drill resulted in lower torque and SCE values, less flank wear, and lower build-up-edge (BUE) compared with the uncoated HSS drill bits for AM fabricated titanium alloys. However, the carbide drill appeared to offer negligible improvement over the uncoated HSS drill when employed with the PM fabricated titanium alloy. In spite of the improvement in the drilling performance offered by the carbide drills for the AM titanium alloy, TiB intermetallic particles (part of the AM titanium microstructure) contributed to the damage of the coated carbide drill which would limit the drill lifetime.

Advantages of Taguchi Method compared to Response Surface Methodology for achieving the Best Surface Finish in Wire Electrical Discharge Machining (WEDM)

Design of Experiments is a method to predict the optimum conditions of a process to reduce the time and number of experiments to be conducted with limited resources. In this paper, a comparative work on design and analysis of experiments between Taguchi method and response surface methodology is carried out in predicting the set of optimal conditions for obtaining the best surface roughness of commercially pure titanium powder metallurgy component using wire electrical discharge machining process. With surface roughness of the Titanium as the response and pulse on time, pulse off time, and sintering temperature of the wire electrical discharge machining process as the affecting factors, the optimum conditions for the surface roughness of the material have been predicted and analysed. Analysis of variance is used to identify the significant factors affecting the system. Both methods gave the same results and the Taguchi approach requires less number of experiments compared to response surface methodology and the predicted surface roughness of the components with the Taguchi method is 2.4 µm, whereas it is between 2.41-3.04 µm with the Response Surface Methodology. The factor Pulse on Time (N) shows a significant effect on the response of the system.

Quantitative Strengthening Evaluation of Powder Metallurgy Titanium Alloys with Substitutional Zr and Interstitial O Solutes via Homogenization Heat Treatment.

The decomposition behavior of ZrO2 particles and uniform distribution of Zr and O solutes were investigated by employing in situ scanning electron microscope-electron backscatter diffraction (SEM-EBSD) analysis and thermogravimetric-differential thermal analysis (TG-DTA) to optimize the process conditions in preparing Ti-Zr-O alloys from the pre-mixed pure Ti powder and ZrO2 particles. The extruded Ti-Zr-O alloys via homogenization and water-quenching treatment were found to have a uniform distribution of Zr and O solutes in the matrix and also showed a remarkable improvement in the mechanical properties, for example, the yield stress of Ti-3 wt.% ZrO2 sample (1144.5 MPa) is about 2.5 times more than the amount of yield stress of pure Ti (471.4 MPa). Furthermore, the oxygen solid-solution was dominant in the yield stress increment, and the experimental data agreed well with the calculation results estimated using the Hall-Petch equation and Labusch model.

Evaluation and parameter analysis of compaction equations applied to titanium powder

ABSTRACT Titanium is widely used in the fields of medicine, industry, and biological science due to its excellent properties. In addition, titanium powder metallurgy (PM) is widely used in production because it could considerably reduce the cost. The most critical step in PM is powder compaction. Thus, the compaction equation is highly important in the prediction and analysis of powder compaction process. In this paper, the experimental data of titanium hydride powder and hydrogenated-dehydrogenated titanium powder were fitted using different compaction equations, and all the equations could obtain a high fitting degree (R 2 > 0.99) and a small error. The linear compaction equation could distinguish the powder type and different particle size distribution forms in the same type of powder through fitting parameters. The nonlinear compaction fitting equation could also analyse the contribution of powder densification mechanism through parameter calculation.

Synthesis of Ti Powder from the Reduction of TiCl4 with Metal Hydrides in the H2 Atmosphere: Thermodynamic and Techno-Economic Analyses

Titanium hydride (TiH2) is one of the basic materials for titanium (Ti) powder metallurgy. A novel method was proposed to produce TiH2 from the reduction of titanium tetrachloride (TiCl4) with magnesium hydride (MgH2) in the hydrogen (H2) atmosphere. The primary approach of this process is to produce TiH2 at a low-temperature range through an efficient and energy-saving process for further titanium powder production. In this study, the thermodynamic assessment and technoeconomic analysis of the process were investigated. The results show that the formation of TiH2 is feasible at low temperatures, and the molar ratio between TiCl4 and metal hydride as a reductant material has a critical role in its formation. Moreover, it was found that the yield of TiH2 is slightly higher when CaH2 is used as a reductant agent. The calculated equilibrium composition diagrams show that when the molar ratio between TiCl4 and metal hydrides is greater than the stoichiometric amount, the TiCl3 phase also forms. With a further increase in this ratio to greater than 4, no TiH2 was formed, and TiCl3 was the dominant product. Furthermore, the technoeconomic study revealed that the highest return on investment was achieved for the production scale of 5 t/batch of Ti powder production, with a payback time of 2.54 years. The analysis shows that the application of metal hydrides for TiH2 production from TiCl4 is technically feasible and economically viable.

Mechanical property enhancement of high-plasticity powder metallurgy titanium with a high oxygen concentration

High-plasticity titanium materials with high oxygen content were prepared by powder metallurgy (PM) and hot rolling, using pure Ti and ZrO2 powder as raw materials. Completely dissolved oxygen and zirconium atoms resulted in the lattice constant change, thereby increasing the strength. Although the oxygen content was up to 0.56 wt% (much higher than the oxygen threshold of 0.33 wt%), PM Ti still exhibited high plasticity. The Ti-0.5 wt% ZrO2 sample (0.43 wt% O) had UTS of 737 MPa and EL. of 28%, while the Ti-1.0 wt% ZrO2 sample (0.56 wt% O) had UTS of 824 MPa and EL. of 15%. Compared to pure Ti, the addition of 0.5 wt% ZrO2 resulted in a noticeable increase in UTS (increased by 9%) and EL. (increased by 19%). The strength-ductility trade-off dilemma of PM Ti alloy was broken. The formation of fine and equiaxed dynamic recrystallized grains may be one of the reasons that increased the ductility. The reinforcement effect of ZrO2 was calculated as 146.7 MPa/wt% ZrO2.

Evolution of the Microstructure and Mechanical Properties of a Ti35Nb2Sn Alloy Post-Processed by Hot Isostatic Pressing for Biomedical Applications

The HIP post-processing step is required for developing next generation of advanced powder metallurgy titanium alloys for orthopedic and dental applications. The influence of the hot isostatic pressing (HIP) post-processing step on structural and phase changes, porosity healing, and mechanical strength in a powder metallurgy Ti35Nb2Sn alloy was studied. Powders were pressed at room temperature at 750 MPa, and then sintered at 1350 °C in a vacuum for 3 h. The standard HIP process at 1200 °C and 150 MPa for 3 h was performed to study its effect on a Ti35Nb2Sn powder metallurgy alloy. The influence of the HIP process and cold rate on the density, microstructure, quantity of interstitial elements, mechanical strength, and Young’s modulus was investigated. HIP post-processing for 2 h at 1200 °C and 150 MPa led to greater porosity reduction and a marked retention of the β phase at room temperature. The slow cooling rate during the HIP process affected phase stability, with a large amount of α”-phase precipitate, which decreased the titanium alloy’s yield strength.