Search

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]

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]