Effects of V Addition on the Microstructure and Mechanical Properties of a PM Ti–4Al–3Cu–2Fe Alloy

The effects of an addition of 4 wt pct V on the mechanical properties and microstructure of a Ti–4Al–3Cu–2Fe (wt pct) alloy manufactured by extrusion of compacts of TiH₂/Al/Cu/Fe powder blend followed by vacuum annealing were investigated. It was found that the V addition changed the microstructure of the alloy from lamellar structure to basket-wave structure, increased the volume fraction of β phase from 47 to 53 pct, and reduced the average α lamella thickness significantly from 4.0 to 1.5 μm. Surprisingly, these compositional and microstructural changes cause only a small increase of the yield stress (from 1132 to 1151 MPa) and elongation to fracture (from 6.1 to 6.5 pct), but the strain hardening rate of the alloys are substantially enhanced over a narrow strain range of 0.9-1.7 pct, leading to a clear increase of the ultimate tensile strength from 1184 to 1252 MPa. The main mechanism for the microstructural changes caused by the V addition is the enhanced stabilization of β phase by V atoms and the growth restriction of α lamellae by V partitioning between α and β phases. The enhancement of strain hardening rate can be attributed to the enhance the number density of the α/β interfaces associated with the decrease of the α lamella thickness and which provides more effective barriers for the movement of dislocations.