Effect of Fe addition on sintering behaviour of titanium powder

Abstract

The effect of iron on the sintering behaviour of titanium powder was investigated from two aspects: (1) diffusional homogenisation of iron; (2) densification of Ti-5Fe alloy. Under the present process conditions (heating rate of 5 K min^-1 and iron content 5 wt-%), iron dissolved into the titanium matrix thoroughly before the first eutectic temperature; potential liquid phase did not appear. The addition of iron enhances the sinterability of titanium alloys because the mobility of titanium atoms is accelerated by the rapid diffusion of iron. Most sintering shrinkage is achieved during the heating stage from 950 to 1250°C. Based on the diffusion creep mechanism of Nabarro-Hering, the result can be explained as a combination of the diffusion coefficient D and inherent local sintering stress σ, and the dissolution of iron in titanium is expected to reduce the creep strength of the Ti matrix at high temperatures due to its very fast diffusion rate. The effect of iron on the microstructure of Ti-5Fe alloy is also discussed. The formation of a Widmanstättenlike microstructure in Ti-5Fe alloy can be attributed to a β stabilising effect and a high diffusion rate of iron during furnace cooling.