Microstructure and Mechanical Properties of Ti-6Al-4V Rods Fabricated by Powder Compact Extrusion of TiH 2 /Al 60 V 40 P
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INTRODUCTION
TI-6AL-4V (wt pct) alloy is the most popular titanium alloy due to its excellent strength-to-density ratio, high ductility, good corrosion resistance, and biocompatibility, and thus a workhorse alloy used in various fields such as automotive, chemical engineering, aerospace, and biomedical industries.[1–4] However, owing to its inherent affinity to oxygen, high buy-to-fly ratio in making the final parts, and difficulty in machining, the production costs of Ti-6Al-4V alloy components and structural members are high, being unaffordable for a wide range of engineering
YIFEI LUO, YUEHUANG XIE, WEI ZENG, and JIAMIAO LIANG, are with the Shanghai Key Lab of Advanced Hightemperature Materials and Precision Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. Contact e-mail: [email protected] DELIANG ZHANG is with the Shanghai Key Lab of Advanced Hightemperature Materials and Precision Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University and also with the Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang 110819, P.R. China. Contact e-mail: [email protected] Manuscript submitted September 10, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
applications where titanium alloys are highly desirable from the points of view of mechanical properties and density. In this sense, both the price of raw materials and the wastage during machining need to be reduced. Powder metallurgy, as a near-net shape forming method, can minimize the material wastage and cost of machining. Compared with pre-alloyed powders, the blended elemental or intermetallic powders are cost-effective, thus reducing the costs of raw materials.[3] The production time associated with conventional powder sintering, forging, and casting is typically several hours, and this leads to low productivity and high cost.[5] Recently, it has been reported that titanium and titanium alloy powders can be rapidly consolidated by the combination of cold compaction, induction heating and sintering, and hot extrusion.[6–8] Zheng et al.[7] fabricated nearly fully dense Ti extrusion rods by powder compact extrusion, and the whole process took less than 15 minutes. For powder compact extrusion, pre-alloyed Ti-6Al-4V or hydride-dehydride (HDH) Ti powders were usually used as raw materials.[5,6,8,9] TiH2 powder is the intermediate product for producing HDH Ti powder, so using TiH2 powder instead of HDH Ti powder as the starting material can reduce the costs further.[7,10] Besides the costs advantage, the hydrogen-accelerated Ti diffusion induces lowering of the a/b
transus temperature and helps to achieve high density and homogeneous microstructure during sintering, producing sintered Ti-6Al-4V alloy with mechanical properties comparable with those of wrought Ti-6Al-4V alloy.[7,11] In addition, complete dehydrogenation of TiH2 can be achieved by vacuum annealing, making
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