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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 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]

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]

• 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]

Abstract High-quality Ti 2 AlNb alloys were prepared from blended elemental powders via cold isostatic pressing and pressureless vacuum sintering. When sintered at 1200 °C, the Ti-23Al-17Nb alloy attained a very high relative density (98.7%) and low contents of interstitials (0.1 wt% O, 0.03 wt% N and 0.005 wt% H). Three crystalline phases – B2, α 2 , and orthorhombic (O) – were observed in a fine and homogeneous microstructure in the sintered samples. The fine microstructure and low interstitials account for the good mechanical properties achieved: approximately 941 MPa of ultimate tensile strength, 862 MPa of yield strength and 11.7% of elongation. Highlights • Ti-23Al-17Nb with high relative density (98.7%) was prepared by vacuum sintering from blend elemental powder. • The as-sintered Ti-23Al-17Nb has low interstitials, about 0.1 wt% of O, 0.03 wt% of N and 0.005 wt% of H. • The mechanical properties of as-sintered Ti-23Al-17Nb is about 941 MPa in UTS, 862 MPa in YS and 11.7% in elongation. [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, 3D gel printing based on a low molecular mass organic gel system was employed to fabricate complex-shaped Ta parts. As opposed to a polymeric gel system, this system was initiated by heat transition. To obtain suitable printing slurry with 62 vol% solid content, 2.5 wt% resin was introduced to improve green body strength and 0.55 wt% oleic acid was added to modify the viscosity. As a result, the printed samples had relatively good surface quality without defects or pores observed on the surface. Ta particles were closely bound by dibenzylidene sorbitol (DBS) gelators. After sintering, a uniform shrinkage was obtained with a shrinkage of 11%, but the surface quality of the as sintered samples was improved. Sintering decreased the surface roughness from 4.0 μm to 2.8 μm. Besides, the as-sintered Ta samples had a relatively dense and homogenous microstructure. The relative density of the as-sintered sample was about 98%. Therefore, 3D gel printing is a promising method to prepare complex-shaped Ta parts with minimal material waste. Unlabelled Image • Ta parts with a relative density of about 98% was prepared by 3D gel printing. • Low molecular mass organic gel system was introduced in to 3D gel printing. • The printed Ta parts had good surface quality and high dimensional accuracy. • One promising method was proposed to prepare complex-shaped Ta parts. [ABSTRACT FROM AUTHOR]