On a Testing Methodology for the Mechanical Property Assessment of a New Low-Cost Titanium Alloy Derived from Synthetic
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idespread use of titanium alloys is mainly inhibited by the high cost of the production of titanium alloy components. This costly upstream extraction and multistage processing route have resulted in the restriction of high strength titanium alloys mainly to the aerospace sector.[1] Titanium’s unique blend of properties such as high strength-to-weight ratio, corrosion resistance, and biocompatibility make it an attractive material for many commercial applications. However, without a step change in the economics of titanium production, the super-metal will be confined to the aerospace industry and niche applications in markets such as the defence and automotive industries.
L.L. BENSON, L.A. BENSON MARSHALL, N.S. WESTON, and M. JACKSON are with the Department of Material Science and Engineering, The University Of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK. Contact e-mail: [email protected] I. MELLOR is with the Metalysis, Materials Discovery Centre, Unit 4 R-Evolution@TheAMP, Brindley Way, Catcliffe, Rotherham, S60 5FS, UK. Manuscript submitted June 2, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
One long-term solution is the production of titanium metal components entirely in the solid state via the combination of electrochemical extraction (Metalysis FFC process)[2] to directly produce a titanium alloy powder and subsequent consolidation via near net shaping technologies. Solid-state consolidation techniques such as the use of field assisted sintering technology (FAST) in conjunction with hot forging are capable of producing shaped metal components with full densities and wrought properties from a powder feedstock.[3] Titanium is currently extracted via the Kroll process, a discontinuous metallothermic reduction process, which involves the reduction of TiCl4 by Mg to produce a titanium metal sponge. Master alloys are added to the Kroll sponge, before compaction and welding into an electrode for melting. Vacuum arc melting requires multiple re-melts to produce homogeneous ingots, particularly in the case of alloying additions such as Fe or Mn, which are prone to segregation.[4] After melting, ingots are subject to multistep hot forging and heat treatments to refine the grain structure and homogenize the chemistry in the billet. Finally, significant wastage is endured during expensive machining of titanium alloys, with some critical aerospace titanium alloy parts having a reported buy-to-fly ratio of 40-to-1.[5] Although powder can be produced from Kroll sponge via additional procedures such as hydride dehydride processing, plasma rotating electrode process (PREP) or gas atomization (GA), these are expensive powder production routes that reduce the cost effectiveness of using near net shape powder metallurgy (PM). Hence, producing titanium alloy powder directly via the solid-state FFC extraction process, followed by downstream solid-state consolidation using FAST and hot forging (‘‘FAST-forge’’[3]) to near net shape, will significantly reduce the cost of titanium alloy components. Cost r
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