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Powder metallurgy (PM) offers cost-effective potential for manufacturing titanium and titanium alloys. High oxygen content on titanium powder surface is a key problem affecting the mechanical properties of PM Ti alloys. Therefore, this study proposes a chloro-deoxidation method to reduce the oxygen content of titanium powder via introducing stannous chloride (SnCl2) into titanium powder. In the sintering process, SnCl2 reacts with the surface oxide on titanium powder to remove the oxide film, and thus forms gas TiClxOy escaping from Ti matrix, resulting in the decrease of oxygen content. With ~ 2.5 wt.% SnCl2 addition, the oxygen content reduces from 0.6 wt.% to 0.5 wt.%. Accordingly, the elongation of as-sintered Ti-SnCl2 sample significantly increases from 4.8% to 11% (increasing by 129%), while the tensile strength decreases from 815 MPa to 788 MPa. After HIP treatment, the elongation increases from 11% to 13%, and the strength is about 765 MPa. Although same Sn content (5 wt.%) is added in Ti samples, Ti-SnCl2 sample shows higher elongation value of 9.4% compared to Ti-Sn sample (3.6%), due to lower oxygen content. [ABSTRACT FROM AUTHOR]

The effects of solution-aging treatment on microstructure and mechanical properties of powder metallurgy (PM) Ti-6554 titanium alloy were investigated. PM Ti-6554 titanium alloy can achieve a good balance between strength and ductility after solution treatment at 810°C/30 min with furnace cooling and aging treatment at 520°C/6 h. Accordingly, the ultimate tensile strength, yield strength and elongation were 1360 MPa, 1323 MPa and 9.0%, respectively. The alloy had smaller α phase grain size (~ 0.69 μm), and its volume fraction was 73%. When the solution temperature increased from 810°C to 850°C, the ultimate tensile strength increased to 1601 MPa, the yield strength increased to 1543 MPa, and the elongation reduced to 3.5%. Microstructure results showed that the grain size of α phase gradually increased, while the volume fraction of α phase showed the opposite trend. When the solution temperature remained constant, slower cooling rate was beneficial to increase the alloy strength and maintain the strength-plasticity matching. [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]

In this study, phosphorus-containing Fe-5 wt.% Si silicon steel sheet was prepared by powder loose sintering followed by hot rolling. Defect-free sheet with high P content was achieved. The study found that P effects on sintering promotion and processing deterioration were significantly suppressed by the presence of Si in steel. Appropriate P content would significantly improve the mechanical and magnetic properties of the sample. Under a comprehensive consideration, P content of 0.3-0.5 wt.% was suitable for silicon steel. Compared with P-free silicon steel, with 0.3 wt.% P addition, the tensile strength of silicon steel increased from 521 MPa to 680 MPa. As to the magnetic performance, the sample with 0.5 wt.% P had B8 of 1370.5 mT, and W10/50 0f 1.16 W·kg−1, while those for P-free sample were 1332.3 mT, and 1.46 W·kg−1, respectively. FeP phase with special morphology would be precipitated in samples with P addition. [ABSTRACT FROM AUTHOR]

Powder metallurgy high-silicon steel strip (Fe–6.5 wt-% Si) was prepared by directly sintering followed by rolling using gas atomised powder with low oxygen content. Due to its poor formability, the gas atomised powder was directly sintered with something heavy of 1 kg overlaid on powder top. The relative density of sintered samples was about 94.1% and the porosity was 5.9%. The pore pinning effect prevented the formation of extremely large grains during sintering, which was beneficial for subsequent rolling. The grain size was controlled in the range of 100–300 μm. After cold rolling, a large number of sub-grain boundaries and deformation bands were generated, which increased the strength to 1190 MPa. It was worth noting that these two would disappear after annealing. Instead, ordered B2 and D03 phases were formed, and the texture of high-silicon steel was mainly {100}<110>. A low iron loss W10/50 value of 0.55 W kg−1 was achieved. [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]

In this study, a novel W and TiO2 synergistic strengthened copper matrix nanocomposite was prepared by a powder metallurgy route with a mechano-chemical method and subsequent consolidation. Nano-sized W and TiO2 particles in the composite powder were fabricated by solid-phase reaction during the mechanical alloying procedure. The average sizes of W and TiO2 particles were only 51 and 171 nm, far finer than single-phase particle-strengthened composites. It was found that the nanoparticles effectively resisted the grain coarsening in the copper matrix, containing the grains with an average size of 350 nm. The ultimate tensile strength and electrical conductivity of the copper composite are 520 MPa and 74 IACS%, achieve an ideal trade-off between them. The observations suggested that the nanoparticles were highly uniformly dispersed in the copper matrix, and the particle coarsening was restrained as the results of the interaction effects between W and TiO2 nanoparticles. [ABSTRACT FROM AUTHOR]

In this paper, powder metallurgy (PM) H13 steels were investigated based on the characterisation of water atomised H13 powders. Vacuum sintering was carried out from 1150 to 1265°C for sintering densification. The relative density of the as-sintered sample reached to 95% and mechanical properties were released above 1200°C. To eliminate the residual pores, subsequent forging was performed. The relative density increased to above 99%. As the concentration of Si elements on the powder surface was higher than the nominal composition, there was Si segregation in the form of silicon oxides (1–3 μm). Although oxide particles such as SiO2 were inevitable, the mechanical performance of PM H13 steels was still comparable to that of ingot metallurgy products. The tempered PM H13 steels exhibited high tensile strength of 1460 MPa in YS, 1737 MPa in UTS and 8.7% in elongation. Besides, the impact toughness was as high as 14.7 J cm−2. [ABSTRACT FROM AUTHOR]

In this paper, the microstructural evolution, precipitation behavior and mechanical properties of 2195 Al-Li alloys prepared by powder metallurgy (PM) combined with hot extrusion were investigated systematically. The results show that the deformation of PM 2195 Al-Li alloys during hot extrusion is dominated by the coupling of dynamic recovery with continuous dynamic recrystallization. The homogeneously distributed needle-like T 1 phase is precipitated in the matrix after T6 treatment. The T6-treated sample exhibits a perfect combination of strength and ductility, that is, ultimate tensile strength of 662 MPa, yield strength of 617 MPa and uniform elongation of 6.6 %. The strengthening of heat-treated alloys originates from densification, work hardening, grain refinement and precipitation strengthening. It is noted that the precipitation strengthening of T 1 phase is the dominant mechanism. Therefore, this work should suggest a strategy for developing novel Al-Li alloys with excellent mechanical properties. • The 2195 Al-Li alloys were successfully prepared by powder metallurgy and hot extrusion. • The tensile strength, yield strength and elongation of the 2195 Al-Li alloy were 662 MPa, 617 MPa and 6.6 %, respectively. • Mechanical properties of the alloy were enhanced by densification, work hardening, grain refinement and precipitation. • The precipitation strengthening of T 1 phase is the dominant mechanism. [ABSTRACT FROM AUTHOR]

Microstructure evolution and variations in mechanical properties of Al-Al2O3 nanocomposite produced by powder metallurgy were investigated and compared with commercially pure aluminum (Al-1050) after furnace annealing. Fine gas-atomized Al powder compacts were first sintered in flowing nitrogen, subsequently consolidated into wires by rotary swaging and eventually annealed at 300 and 500 °C for 24 h each. Scanning and transmission electron microscopy with energy-dispersive spectroscopy was utilized to document the microstructure evolution. Rotary swaging was proven to lead to a marked decrease in grain size. After heavy swaging to true deformation degree of φ = 6 and annealing at 500 °C, obvious recrystallization was observed at Al-1050’s existing grain boundaries and the crystals began to grow perpendicular to the flow direction. In the Al-Al2O3 nanocomposite, fabricated from d50 = 6 μm Al powder, recrystallization partially occurred, while grains were still extremely fine. Due to the dual role of fine-grained Al2O3 dispersion strengthening, the nanocomposite showed improved mechanical performance in terms of tensile strength, approximately twice higher than Al-1050 after annealing at 500 °C. [ABSTRACT FROM AUTHOR]

In this paper, Al-8.3Zn-2.3Mg-2.5Cu alloys with different oxygen contents were prepared through complex techniques including blending or ball milling, cold isostatic pressing, vacuum sintering, hot extrusion, and heat treatment, and their microstructure and mechanical properties were investigated. For the samples containing 0.15 wt% and 0.33 wt% oxygen, the sintered density values are 99.1% and 98.7% of the theoretical density, and the corresponding average grain sizes are 5.60 μm and 4.83 μm. After heat treatment, the average grain sizes of the samples with 0.15 wt% oxygen subjected to the extrusion ratios of 4:1, 9:1, and 17:1 are 5.17 μm, 4.28 μm and 3.83 μm, respectively, and the corresponding yield strengths are 607 MPa, 615 MPa, and 621 MPa. Moreover, the {111}<112> deformation texture changes to {001}<001> and {001}<111> recrystallization textures. In contrast, for the extruded sample (9:1 extrusion ratio) with 0.33 wt% oxygen, the grains are finer, and static recrystallization barely occurs with little variation in texture after heat treatment. This is due to the increase in content of thermostable γ-Al 2 O 3 particles. Accordingly, the sample with high oxygen content exhibits excellent comprehensive mechanical properties with the ultimate tensile strength of 719 MPa, yield strength of 690 MPa, and elongation of 11.5%. Regarding the strengthening mechanism, apart from the common precipitation strengthening, the contributions of dislocation strengthening and grain boundary strengthening are greater in the 0.33 wt% oxygen alloy than in the 0.15 wt% oxygen alloy. This is due to the pinning effect of γ-Al 2 O 3 particles on dislocations and grain boundaries. • The oxygen content of powder was increased by ball milling. • The effects of extrusion ratios on mechanical properties of Al–Zn–Mg–Cu alloys. • Static recrystallization was suppressed by thermostable γ–Al 2 O 3 particles. • Ultrahigh strength and toughness of Al–Zn–Mg–Cu alloy were obtained by fine grains, γ–Al 2 O 3 particles and precipitates. [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]

Al matrix composite reinforced by hexagonal boron nitride (h-BN) with nearly full densification was successfully fabricated by the semi-solid powder metallurgy technique. The h-BN/Al composites were synthesized with elemental pure Al powder size of d 50 =35, 12 and 2 μm. The powder morphology and the structural characteristics of the composites were analyzed using X-ray diffraction, scanning and transmission electron microscopy. The density, Brinell hardness and compressive behavior of the samples were characterized. Density measurement of the Al composites revealed that the composite densification can be effectively promoted by plenty of embedded liquid phase under pressure. Composites prepared using Al powder with varying granularity showed different grain characteristics, and in situ recrystallization occurred inside the original grains with 35 μm Al powder. A sharp interface consisting of Al/Al 2 O 3 /h-BN was present in the composites. Both the compressive strength and the fracture strain of the investigated composites increased with the decrease of the Al powder size, along with the Brinell hardness. The composite with 2 μm Al powder exhibited the highest relative density (99.3%), Brinell harness (HB 128), compressive strength (763 MPa) and fracture strain (0.299). [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]

In this work, Al-Zn-Mg-Cu powders containing 0.15 and 0.33 wt % oxygen were utilized to prepare high-strength aluminum alloys through the process of cold isostatic pressing, sintering, hot extrusion, and heat treatment. Microstructural and mechanical properties at elevated temperatures of 250, 350, and 450 °C were investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and high-temperature tensile tests. Results showed that the tensile strengths of the obtained Al-Zn-Mg-Cu alloys with 0.15 wt % oxygen were 185, 46, and 18 MPa at 250, 350, and 450 °C, respectively. When the oxygen content of Al-Zn-Mg-Cu alloy rose to 0.33 wt %, the tensile strengths at the corresponding temperature reached up to 205, 68, and 25 MPa, respectively. The excellent high-temperature performance could be attributed to double hindrance to dislocation motion and grain boundary migration by a large amount of nano γ-Al2O3 created by the in-creased oxygen, thereby resulting in fine grains even at high temperatures. [ABSTRACT FROM AUTHOR]

The high thermal stability of pure Al conductors is an urgent requirement for their applications in power transmission lines. Powder metallurgy (PM) Al conductor was produced in this work from Al powder with a low oxygen content (~0.1 wt%), followed by cold isostatic pressing, sintering, hot extrusion, and cold drawing. The microstructure evolution, mechanical properties and electrical conductivity of hot-extruded rods and cold-drawn wires before and after annealing at 300 °C and 500 °C were investigated. The γ-Al 2 O 3 nanoparticles located primarily at high angle grain boundaries promote the stabilization of Al grains, resulting in enhanced annealing strength (89 MPa), almost twice higher than commercial pure Al (45 MPa). Fine grains and texture play a significant role in the overall strength (160 MPa) of PM Al conductors. One interesting finding is that the electrical conductivity of cold-drawn wires (60.2% IACS) is higher than the hot-extruded rods (58.7% IACS) due to the beneficial evolution of initial Al 2 O 3 film and grain boundaries. The compatibility of documented strength-structure Hall-Petch relation was discussed. Optimal properties (172 MPa ultimate tensile strength and 60.2% IACS electrical conductivity) were obtained through cold drawing. These results push forward the potential application of PM Al in heat resistant conductors. [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]

High-plasticity in-situ TiB/Ti matrix composites (TMCs) are fabricated by in-situ reaction between Ti and ZrB 2 powder during vacuum sintering followed by hot rolling. Uniform microstructure is observed in the TMCs with obvious grain refinement. Compared with pure titanium, the mean grain size of Ti-2.0 wt% ZrB 2 composite significantly decreases from 50.7 µm to 17.5 µm, decreasing by 65%. Accordingly, Ti-2.0 ZrB 2 composite displays outstanding mechanical properties of 734.6 MPa in ultimate tensile strength, 579.0 MPa in yield strength, 21.4% in elongation, while these values of pure Ti are 632.4 MPa, 507.0 MPa, and 14.2%, respectively. The strength improvement of TMCs can be mainly attributed to five parts: grain refinement, solid solution strengthening, load transfer mechanism, CTE mismatch between TiB and Ti matrix and the dislocation substructure hardening. Among them, dislocation substructure hardening (more than 50% of the total improvement) takes the dominant position in strength increment in the as-rolled TiB/Ti matrix composites. [Display omitted] • In-situ TiB/Ti composites were synthesized by ZrB 2 additive via PM process. • Obvious grain refinement is found with grain size decreasing from 51 µm to 16 µm. • TiB/Ti composites show a balanced combination of good strength and high ductility. • Ti-2 wt% ZrB 2 sample has UTS of 734 MPa, YS of 579 MPa and EL. of 21%. • Strength increment caused by dislocation substructure hardening is ranged from 47.2 MPa to 116.6 MPa. [ABSTRACT FROM AUTHOR]

• High-plasticity PM Ti material with high O content is prepared with ZrO 2 addition. • The strength-ductility trade-off dilemma of PM titanium alloy is broken. • Ti-1.0 wt% ZrO 2 sample (0.56 wt% O) has UTS of 824 MPa and EL. of 15%. • Zr and O atoms fully dissolve in the Ti matrix, leading to lattice constant change. • The strengthen effect of ZrO 2 is calculated as 146.7 MPa/wt% ZrO 2. [Display omitted] High-plasticity titanium materials with high oxygen content were prepared by powder metallurgy (PM) and hot rolling, using pure Ti and ZrO 2 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% ZrO 2 sample (0.43 wt% O) had UTS of 737 MPa and EL. of 28%, while the Ti-1.0 wt% ZrO 2 sample (0.56 wt% O) had UTS of 824 MPa and EL. of 15%. Compared to pure Ti, the addition of 0.5 wt% ZrO 2 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 ZrO 2 was calculated as 146.7 MPa/wt% ZrO 2. [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]

Powder metallurgy in-situ TiB/Ti6Al4V composites with good mechanical properties are fabricated by vacuum sintering using high-oxygen HDH Ti6Al4V and CaB 6 powders. CaB 6 can not only be used as a boron source, but also synthesize Ca-Ti-O ternary compounds with solid solution oxygen in titanium matrix. Therefore, it has a purification effect on oxygen scavenging, and the relative density of TiB/Ti6Al4V composites can exceed 99%. The interface between titanium matrix and TiB is semi-coherent. Good interfacial adhesion, high density, and reduced oxygen content make the composite material exhibit higher ductility. Although the equivalent oxygen content for Ti6Al4V-0.1CaB 6 composite material is about 0.57 wt%, the elongation still reaches 9.5%, which is 57.4% higher than that of CaB 6 -free sample. Besides, the ultimate tensile strength reaches 1015.6 MPa, and the yield strength is 932.0 MPa. [Display omitted] • In-situ TiB strengthened Ti64 material is prepared via adding CaB 6 in HDH powders. • CaB 6 reacts with solid dissolved oxygen in Ti matrix to form ternary oxides. • The formation of TiB can significantly refine the matrix structure. • CaB 6 acts as an effective oxygen scavenger to reduce oxygen content in matrix. • Ti64-0.1CaB 6 has good ductility of 9.5% although its [O] e content is 0.57 wt%. [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 hot deformation behavior and microstructural evolution of powder metallurgy (PM) Ti-6Al-4V are investigated using the Arrhenius constitutive model, hot processing map, microstructure observation, and hot deformation mechanism analysis. The optimal processing parameters obtained from the hot processing map are 1323–1423 K at 0.1–1 s−1, and 1423–1523 K at 1–10 s−1. Hot deformation in β region is attractive for PM Ti-6Al-4V. The dominant hot deformation mechanism of PM Ti-6Al-4V is dynamic recrystallization (DRX) in the (α + β) and β regions. Continuous dynamic recrystallization (CDRX) is the dominant mechanism in the (α + β) region. The combination of CDRX and discontinuous dynamic recrystallization (DDRX) is the preferred mechanism in the β region. The power-dissipation efficiency is affected by DRX, which consumes dislocations and refines the microstructure. Specific hot working parameters for thermomechanical processing (TMP) of PM Ti-6Al-4V are identified. [Display omitted] • Proper hot working parameters for the thermomechanical processing are identified. • Hot deformation of PM Ti-6Al-4V was more effective in the β region than in the (α + β) region. • Undesired microstructure and hot working parameters have been addressed. • The dominant hot deformation mechanism is dynamic recrystallization. [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]