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Ti-6554 (Ti-6Cr-5Mo-5V-4Al) alloy has attractive potential as a new structural material in the aviation field due to its excellent mechanical properties. However, it is expensive to manufacture, which can limit its application. Powder metallurgy (PM) is an economic technology to reduce the cost of titanium alloys. In this study, PM Ti-6554 alloy was prepared using irregular powder via vacuum sintering followed by forging. The influence of cooling rate (air cooling and water quenching) of as-forged sample on its microstructure was studied by scanning electron microscopy, electron backscatter diffraction and other analytical means. Experimental results showed that different cooling rates determined the structures of α and β phases. Compared with air-cooled sample, the water-quenched sample only had β phase microstructure without α phase precipitates. As-forged PM Ti-6554 alloy subjected to water quenching achieved ultimate tensile strength of 942 MPa and elongation of 20% and also had fine β grains of 10 μm. After solution treatment and aging, the sample exhibited high ultimate tensile strength (1211 MPa) and elongation (13.8%). Overall, PM Ti-6554 alloy possessed a good combination of high strength and reasonable ductility. This work marks a vital step forward in the application of high-performance PM Ti-6554 alloys. [ABSTRACT FROM AUTHOR]

High oxygen Ti6Al4V alloys are fabricated by vacuum sintering and hot rolling using hydrogenation-dehydrogenation Ti6Al4V powder and ZrO2 powder as raw materials. The complete dissolution of oxygen and zirconium atoms results in an increase in lattice constant and strength. As-rolled Ti64-ZrO2 sample exhibits a bimodal structure with a fine acicular α phase of around 1 μm. Ti64-0.75 ZrO2 alloy with equivalent oxygen content close to 0.6 wt.-% presents a good combination of the high tensile strength (1180.2 MPa) and sufficient elongation (7.3%). Therefore, the critical oxygen content for the ductile-to-brittle transition of powder metallurgy Ti6Al4V alloy can be improved by suitable preparation methods. The formation of a fine β transformation structure may be one of the reasons for maintaining sufficient ductility. [ABSTRACT FROM AUTHOR]

Although 3D printing of titanium alloys is often obtained by laser fusion deposition, its cost is relatively high. In this study, one light‐curing‐assisted technique is designed to print porous Ti6Al4V alloys via direct ink writing (DIW). For printing, titanium alloy slurry with 45 vol% solid content is prepared based on 1,6‐hexanediol diacrylate monomer‐trimethylolpropane triacrylate monomer (HDDA‐TMPTA) photosensitive system. In such a case, the extruded filament was in situ cured under the action of UV light irradiation in the printing process. The printed lattice sample has good surface performance without the observation of a collapse. After sintering, the shrinkage percentage is around 16% in the horizontal direction and 19% in the vertical direction. Surface morphology does not change significantly. Through comparative tests, it is found that the sintered samples have good microstructure and mechanical properties. When the filling rate is 50%, the compressive strength could reach 604.7 MPa and the flexural strength is 106.8 MPa. The feasibility of this new printing method to prepare titanium alloy parts are confirmed. [ABSTRACT FROM AUTHOR]

Cu Fe alloys with high iron content (Fe > 10 wt%) are a class of promising copper alloys with high strength and high conductivity. However, the strength and conductivity trade-off dilemma is a longstanding problem in the high iron content Cu Fe alloys owing to macro-segregation of iron particles and incomplete precipitation of solid solution iron atoms in the traditional casting process. We adopted a comprehensive strategy of designing the ultra-fine dual structures with fine copper grains and micro-nano iron particles, and adding phosphorus element to induce solid solution iron atoms precipitation to break through the above bottleneck. In this study, Cu 20Fe alloys with 0.05–1.0 wt% P were prepared through powder metallurgy process. The results showed that the addition of P promoted the precipitation of soluble Fe atoms, reduced oxygen content, and activated sintering. Ultimately, the strength and conductivity of cost-effective Cu 20Fe alloys were significantly improved. The annealed Cu 20Fe 0.1P alloys possess unprecedented comprehensive properties with 608 MPa tensile strength and 65.2% IACS electrical conductivity, which were 7.8% and 19.8% higher than the Cu 20Fe alloys, respectively. The annealed Cu 20Fe 1.0P alloys achieved 59.7% IACS electrical conductivity, increased by 10% compared to Cu 20Fe alloys. The results broke the conventional understanding that increasing P content deteriorated material properties. The influence of P on the microstructure and properties of powder metallurgy Cu 20Fe alloys was investigated in detail. These findings provide new insight into overcoming the dilemma of the inverted relationship between the strength and conductivity of copper alloys. • Simultaneous enhancement of the mechanical and electrical properties of Cu 20Fe alloys by introducing phosphorus. • The Cu 20Fe 0.1P alloys possess unprecedented comprehensive properties and property-costs. • The influence of P on the microstructure and properties of powder metallurgy Cu 20Fe alloys was investigated in detail. [ABSTRACT FROM AUTHOR]

In this work, copper ferroalloys (CFAs) with various Fe contents (5, 10 and 30 wt-%) were fabricated via the mechanical alloying and vacuum sintering method, followed by hot and cold rolling. Microstructure, mechanical, electrical and magnetic properties were investigated using scanning electron microscopy (SEM), X-Ray diffraction (XRD), tensile testing, four-point probe, vibration sample magnetometer and dc BH circuit tracer, respectively. The CFAs with homogenous and fine in-situ Fe particles prepared by powder metallurgy showed better performance compared with previously reported conventional casting. After annealing at 400°C, the cold-rolled CFA with 30 wt-% Fe had the tensile strength of 621 MPa, the electrical conductivity of 50.2% IACS, magnetic saturation strength (Ms) of 60.39 emu g−1 and coercivity (Hc) of 98.2 Oe, achieving a good combination of mechanical and functional properties. Relations between the microstructure and mechanical and functional properties are discussed in detail. [ABSTRACT FROM AUTHOR]

Powder metallurgy (PM) Ti6Al4V alloy was prepared from HDH alloy powder by vacuum pressureless sintering. To study its high-temperature deformation behaviour, isothermal compression testing was carried out with temperature range of 900–1050°C, strain rate range of 0.01–10 s−1, and compression ratio of 60%. Based on the hot deformation data, the corresponding constitutive equation and hot processing map were clarified. The deformation activation energy for PM Ti6Al4V alloy was 606.5 kJ mol−1. Its deformation instability zone was very small, locating in the range of 960∼990°C with strain rate >1 s−1. PM Ti6Al4V alloy had large hot working window and good hot workability. The ideal hot processing domain was at 970–990°C and 0.05–0.01 s−1. Besides, the domain at 1000–1040°C and 1–10 s−1 was also suitable for hot processing. This study proposed an effective guidance for the hot deformation (e.g. forging, extrusion, rolling) of PM Ti6Al4V alloy. [ABSTRACT FROM AUTHOR]

Simultaneous improvement of both the strength and electrical conductivity of Cu–Fe alloys (CFAs) through the conventional casting method is an extremely challenging task. In this study, an attempt was made to overcome this issue via preparing CFAs with ultrafine alloy powders embedded with nano Fe particles. Ultrafine CFA powders with various Fe contents ranging from 5 to 50 wt.% were synthesized by a novel rapid solidification route, namely, gas–water combined atomization (GWA) process. The alloy powders prepared via GWA were then processed by pressureless sintering, hot rolling, annealing, and cold rolling. The microstructure evolution, mechanical properties, and electrical conductivity of CFAs were comprehensively investigated. The average size of Cu grain and Fe particles in all sintered CFAs was smaller than 3 and 2 μm, respectively. The grains of sintered CFAs were obviously refined by the Fe particles, and the addition of Fe inhibited the formation of Cu twins. After rolling, the Fe particles elongated and became fibrous along the rolling direction. The degree of formation of fibrous Fe enhanced with the increase of Fe content. Cold-rolled CFAs with 5–50 wt% Fe exhibited the tensile strength of 560–1250 MPa and conductivity of 33–65% IACS, indicating that CFAs in this study achieved superior mechanical and electrical properties. The microstructure evolution and strengthening mechanisms of CFAs were described. These findings can provide new insights into the powder metallurgy manufacturing of high-performance CFAs. • Ultrafine CFA powders were prepared by gas-water combined atomization. • The average size of Fe particles and grains of sintered CFAs was 2–3 μm. • Cold-rolled CFAs achieved superior mechanical and electrical properties. [ABSTRACT FROM AUTHOR]

Powder metallurgy Cu-30Fe alloy was prepared by mechanical alloying, pressureless sintering, and rolling processes. The alloy microstructure and physical properties affected by rolling were studied. The Fe particles were small and uniformly distributed in the Cu matrix. The average Fe particle size in the sintered state was 1 µm, and particles had subspherical or irregular shapes. The Fe particles became elongated, tadpole-shaped, and spindle-shaped as a result of rolling. At the same time, the Cu grains were elongated and refined, while the Cu grains near the Fe particles were finer as a result of the coordinated deformation of the soft Cu and hard Fe phases. After annealing at 400 °C, the cold-rolled Cu-30Fe alloy had 620 MPa tensile strength, 10% elongation, and 50% IACS electrical conductivity, achieving a good combination of mechanical and functional properties. The coordinated deformation behavior and grain refinement mechanisms of both Cu and Fe phases due to rolling were described, along with the microstructure and physical properties evolution. • Cu-30Fe alloys with Fe particles were fabricated by powder metallurgy and rolling. • Grain refinement mechanisms of Cu and Fe phases due to rolling were described. • Microstructure and physical properties of Cu-30Fe alloys were studied. • Cu-30Fe has 620 MPa tensile strength, 10% elongation, 50%IACS electrical conductivity. [ABSTRACT FROM AUTHOR]

Preparing high relative density γ-TiAl alloy by pressure-less sintering at low-cost has always been a challenge. Therefore, a new kind of non-spherical pre-alloyed TiAl powder was prepared by the reaction of TiH2 powder and Al powder at 800 °C to fabricate high-density Ti-48Al alloy via pressure-less sintering. The oxygen content was controlled to below 1800 ppm by using coarse Al powder (~120 μm). The sintered densities ranged from 92.1% to 97.5% with sintering temperature varying from 1300 °C to 1450 °C. The microstructure of the sintered compact was greatly influenced by the sintering temperature. The as-sintered samples had a near-γ structure at 1350 °C, a duplex structure at 1400 °C, and a nearly lamellar structure at 1450 °C. To achieve full densification, non-capsule hot isostatic pressing was performed on the 1350 °C and 1400 °C sintered samples. As a result, high compressive strengths of 2241 MPa and 1931MPa were obtained, which were higher than the existing Ti-48Al alloys. [ABSTRACT FROM AUTHOR]

Powder metallurgy methods such as additive manufacturing are often employed to fabricate bulk refractory alloys with high-melting temperature, nevertheless, it still remains a challenge to produce high-quality refractory high-entropy alloy (RHEAs) powders. In this work, we found that hydrogen absorption can embrittle the NbTaTiZr RHEA and promote intragranular fracture due to segregation of hydrogen atoms at grain boundaries. Synergistic effects of the hydrogenation temperature and time on the pulverization behavior of the NbTaTiZr RHEA were investigated, and the relation between grain sizes in the original ingots and particle sizes in the pulverized powders was explored. The present findings not only provide a highly efficient approach to produce high-quality powders of alloys with high-melting points, but also shed light into understanding hydrogen embrittlement of RHEAs. • The RHEA was easily pulverized after hydrogenation. • The particle size distributions of the pulverized powders matched those of the grain sizes. • An orderly transition from grains to powders was established. [ABSTRACT FROM AUTHOR]

After high-temperature forging and rapidly cooling, the microstructure evolution and spheroidization mechanism of powder metallurgy Ti-6Al-4 V alloy have been clarified. The spheroidization process is divided into two asynchronous stages. The initial stage is primarily characterized by the initial shearing and twisting of GBα grain boundaries, as well as the deformation of lamellar structure. Subsequently, the fragmentation of original GBα grain boundaries and the fracture of intra-granular α lamellae are observed. This process is accompanied by grain twisting and substructure formation, especially the division of lamellae through interface splitting and the segregation of local chemical elements. The differential accumulation of elements around the fractured and twisted grains suggests that element segregation and interfacial energy play a significant role in microstructure evolution. Therefore, the static spheroidization process largely depends on the formation and evolution of dislocation substructures, and the reduction of interfacial energy may be a key factor driving this process. These findings provide a theoretical basis for manufacturing metals with specific anisotropic properties by controlling microstructure evolution. [Display omitted] • Dynamic recrystallization drives microstructural changes in Ti64 alloy forging. • GBα and internal spheroidization are related to crystal rotation asynchronously. • Elemental segregation affects the occurrence of grain boundary spheroidization. • Increased activity of pyramidal slip systems reveals anisotropy in hcp metals. [ABSTRACT FROM AUTHOR]

• ELI Ti-6Al-4V alloys with 0.07 wt% O are produced by sintering HDH powder. • O content of powder exposed to the air is proportional to its specific surface area. • Fine near-equiaxed α of 20 µm is obtained by vacuum sintering and capsule-free HIP. Ti alloys produced from HDH powder have suffered from high O/N interstitials content. In the present study, a whole well-protected process from Ti sponge to as-sintered materials is adopted, and thus the lowest O/N contents of as-sintered materials are 0.07 wt% and 0.018 wt%, within the specification of Grade F-23 (Ti-6Al-4V ELI) according to ASTM B988-13. The passivation law of powder and its compact has also been studied in detail. Subsequently, sintering experiment indicates fine ELI powder has an excellent sinterability. A relative density over 96% can be obtained by sintering at 1100 °C. Capsule-free HIP post-sintering is performed to achieve full density and obtain fine and near-equiaxed α grain at the same time. The as-HIPped sample has better comprehensive mechanical properties, with strength exceeding 970 MPa and elongation exceeding 16.4%. [ABSTRACT FROM AUTHOR]

TiAl-based alloy is an excellent high-temperature structural material, but poor hot workability has been the bottleneck hindering its development. In this study, we take into account the hot workability and mechanical properties of Ti-48Al alloy through microstructure adjustment. Powder metallurgy Ti-48Al alloy prepared by vacuum sintering is used as the raw material, which has a near-γ microstructure composed of equiaxed grains. Although the composition is simple, the alloy achieves high mechanical properties after forging with 75 % deformation. Controlling the forging temperature to 1300 °C can make the microstructure transform into a duplex structure composed of γ/α2 lamellar colonies and γ equiaxed grains. As-forged alloy has an ultimate tensile strength of 650 ± 17 MPa and a yield strength of 644 ± 16 MPa at room temperature. It still maintains high strength at high temperature, with ultimate tensile strength of 684 ± 19 MPa at 500 °C, 700 ± 19 MPa at 700 °C, and 320 ± 10 MPa at 900 °C. In addition, the alloy has good ductility with elongation of 58.2% due to dynamic recrystallization at 900 °C. • Mechanical property is significantly improved by forging with simple composition. • The alloy has ultrafine equiaxed grain of 2.45 µm and lamellar spacing of 20–50 nm. • Duplex microstructure without remnant lamellae forms in PM Ti-48Al alloy. • Ti-48Al alloy exhibits great plasticity of 58.2 % at 900 °C. [ABSTRACT FROM AUTHOR]

The short communication presents a synergistical reinforced Ti–48Al alloy with multiple Ti–Al intermetallic compounds which was prepared with irregular pre-alloyed powders by vacuum sintering at low temperature (1250°C). With simple composition, this alloy has tensile and yield strength of 593 ± 8 MPa and 435 ± 5 MPa at room temperature, and more than 510 MPa and 490 MPa at 700°C, reached the level of Ti–Al alloys with complex composition. • Ti–48Al alloy is synergistically reinforced by multiple intermetallic compounds. • Nano-sized and submicron-sized intermediate phases form and refine grain growth. • Low sintering temperature avoids the decomposition of formed intermetallic phases. • Mechanical properties significantly improve while alloy composition is simplified. [ABSTRACT FROM AUTHOR]

Poor sinterability of powder metallurgy TiAl-based alloy is an important factor that restricts its industrial production. In this paper, we improve the sinterability of Ti-48Al alloy by adding Co element. In such case, the relative density of Ti–48Al based alloy sintered at 1250 ℃ increases from 82.6% to 96% with an increase of Co content from 0 to 1.5 at%. The densification improvement is caused by liquid TiAl 2 Co phase, which is formed at 1230 ℃. Then, uniform and fine near-γ microstructure is obtained, and the grain size increases with the increasing of Co content. More than 70% of grains in the Ti-48Al-0.5Co alloy are smaller than 2 µm. Overall, Ti-48Al-0.5Co alloy has better comprehensive performance, with compressive strength of 2533 MPa, yield strength of 683 MPa and fracture strain of 29.5%. [Display omitted] • High-density Ti-48Al alloy with Co addition is prepared using irregular powder. • Liquid TiAl 2 Co phase is formed to promote densification sintering. • Sintering temperature of Co-added TiAl alloy is reduced by 50 ℃. • More than 70% of grains in the Ti-48Al-0.5Co alloy are smaller than 2 µm. • Ti-48Al-0.5Co has superior compressive and yield strengths of 2533 MPa and 683 MPa. [ABSTRACT FROM AUTHOR]

In this study, in-situ tensile deformation behavior of powder metallurgy (PM) Ti6Al4V alloys was investigated to analyze the crack initiation and propagation. Accordingly, the fracture mechanisms of the as-sintered and forged PM alloys were summarized. At the initial stage of plastic deformation, cracks appeared in the stress concentration area of pores in the as-sintered Ti6Al4V alloy, and the crack propagation direction was along the phase boundary. Due to the existence of pores, early fracture was obtained, resulting in low elongation of 6.3%. After forging, the crack initiation occurred between α lamellar structure, and the propagation direction was along the lamellar direction. The fine lamellar structure in different directions in the forged PM Ti6Al4V alloy can hinder the crack propagation, thus improving the plasticity. As a result, better comprehensive mechanical performance was obtained in the forged sample, with UTS of 960 MPa, YS of 850 MPa, and EL of 16%. • In-situ tensile deformation behavior of PM Ti6Al4V alloys was studied. • Porosity was the main reason for the crack initiation and propagation. • The driving force of fracture was normal stress in the sintered sample. • Fine α lamellae with different orientations hindered the crack propagation. • The driving force of fracture was shear stress in the forged sample. [ABSTRACT FROM AUTHOR]