Design of titanium alloy for efficient sintering to low porosity

Few Ti alloys have been designed for ease of sintering. This paper considers the design of alloys for processing using the mixed elemental technique, in which powders are mixed, cold pressed in a die to near net shape and sintered under vacuum at high temperature. The authors describe steps in the process of developing a Ti–Ni–Sn alloy, able to be sintered to near full density at a sintering temperature as low as 1100°C without requiring unusually fine powder or high compaction pressure. Higher sintering temperature allows the Ni content of the alloy to be reduced, but swelling of the alloy probably imposes an upper limit on practical sintering temperature. The increase in green density, and hence sintered density, conferred by Sn in Ti–Sn alloys, and the increase in sintered density due to the high diffusivity of Ni in Ti–Ni alloys, are combined in Ti–Ni–Sn alloys.