On a Testing Methodology for the Mechanical Property Assessment of a New Low-Cost Titanium Alloy Derived from Synthetic Rutile

Metallurgical and Materials Transactions A, Sep 2017

Mechanical property data of a low-cost titanium alloy derived directly from synthetic rutile is reported. A small-scale testing approach comprising consolidation via field-assisted sintering technology, followed by axisymmetric compression testing, has been designed to yield mechanical property data from small quantities of titanium alloy powder. To validate this approach and provide a benchmark, Ti-6Al-4V powder has been processed using the same methodology and compared with material property data generated from thermo-physical simulation software. Compressive yield strength and strain to failure of the synthetic rutile-derived titanium alloy were revealed to be similar to that of Ti-6Al-4V.

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On a Testing Methodology for the Mechanical Property Assessment of a New Low-Cost Titanium Alloy Derived from Synthetic Rutile

On a Testing Methodology for the Mechanical Property Assessment of a New Low-Cost Titanium Alloy Derived from Synthetic Rutile L.L. BENSON 0 L.A. BENSON MARSHALL 0 N.S. WESTON 0 I. MELLOR 0 M. JACKSON 0 0 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 Mechanical property data of a low-cost titanium alloy derived directly from synthetic rutile is reported. A small-scale testing approach comprising consolidation via field-assisted sintering technology, followed by axisymmetric compression testing, has been designed to yield mechanical property data from small quantities of titanium alloy powder. To validate this approach and provide a benchmark, Ti-6Al-4V powder has been processed using the same methodology and compared with material property data generated from thermo-physical simulation software. Compressive yield strength and strain to failure of the synthetic rutile-derived titanium alloy were revealed to be similar to that of Ti-6Al-4V. - Widespread 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. 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 reductions are achieved by directly producing an alloy powder, reducing the number of multistep forging and heat treatment steps, and minimizing both wastage and machining. Further, as the entire production route is conducted in the solid state, melting procedures can be eliminated entirely. It is generally the melting stage in which most defects in titanium alloys originate and so its removal has additional benefit.[ 6 ] Further cost advantages can be made by utilizing synthetic rutile (SR) as a feedstock to the FFC process. SR is derived from the iron-rich titanium ore, ilmenite (FeTiO3), and as such contains a range of alloying elements, principally iron. Following reduction of SR an a + b type titanium alloy is produced, without the cost of alloying additions.[ 7 ] Hence, the use of SR as a feedstock is notably cost-effective, as not only are feedstock costs reduced, but the dependency on master alloy additions further downstream is reduced or eliminated. As the utilization of a synthetic rutile feedstock within a production route entirely in the solid state is a particularly lucrative operation, this paper assesses the mechanical properties of a synthetic rutile-derived titanium alloy (3.9 w (...truncated)


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L. L. Benson, L. A. Benson Marshall, N. S. Weston, I. Mellor, M. Jackson. On a Testing Methodology for the Mechanical Property Assessment of a New Low-Cost Titanium Alloy Derived from Synthetic Rutile, Metallurgical and Materials Transactions A, 2017, pp. 5228-5232, Volume 48, Issue 11, DOI: 10.1007/s11661-017-4333-1