Creating Ti–Fe α/β Alloys by Diffusion‐Driven Solid‐State Processing

Some alloys are difficult to make by ingot metallurgy. Here, the potential for making alloys by hot isostatic pressing (HIPing) and homogenising powder mixtures is explored for Ti–Fe. Iron is an effective and cost-effective β stabiliser but gives rise to segregation issues during solidification. Exploiting the fact that Fe diffusion through Ti is fast, Fe and Ti powders are co-HIPed at, and homogenised at, only 800°C in order to create an α+β microstructure based on small prior β grains. The evolution of phase composition and elemental distribution during homogenisation has been tracked quantitatively in 3D by X-ray computed tomography and in 2D by energy dispersive spectroscopy and electron backscatter diffraction. The final homogenised microstructure consists of fine α Ti laths separated by β ligaments with a prior β grain size of only 80 μm, free of TiFe intermetallics with no indication of a grain boundary α constituent. Kirkendall pore formation was observed during homogenisation heat treatment due to the fast diffusion of Fe in Ti. This study shows the potential of HIP processing followed by homogenisation heat treatment as a novel solid-state manufacturing route for difficult-to-cast alloys.