Hot-deformation behaviour of α+β Ti-Al-V-Fe experimental alloys

Abstract

To reduce the cost of metallic alloys the first approach considered is to substitute expensive alloying elements with inexpensive elements that fulfil similar functions. The second approach is to optimise the microstructure and mechanical properties of the alloys by adjusting processing conditions. Iron, a cheap β-stabilising element in titanium alloys, was added to partially substitute vanadium in experimental Ti-6Al-xV-yFe alloys (where x = 1-4, y = 0-3 and x+y = 4). Unlike other studies where vanadium was totally replaced by iron, in this work partial substitution of V by 1-3 wt % Fe was made to limit the possibility of forming intermetallic phases in the alloys. The experimental alloys were produced by vacuum arc melting and the small ingots were machined to produce plane strain compression samples for hot isothermal testing on a Gleeble 3500. The tests were done at a temperature of 900°C, strain rate of 1s−1 and total strains of 0.6 and 1.2, under plane strain conditions. The microstructures of the as-cast and deformed samples were analysed using optical and scanning electron microscopy (SEM) to assess the deformation mechanisms. The flow stress curves showed that the as-cast Ti-6Al-4V had a higher resistance to deformation than the iron-added experimental alloys. The amount of total strain had a significant effect on the flow behaviour of the alloys. Microscopy showed that deformation bands were more prominent in the deformed Ti-6Al-4V alloy than in the deformed Ti-Al-V-Fe alloys. SEM images revealed rotation and bending of α-laths in the deformed experimental Ti-Al-V-Fe alloys. The low resistance to deformation observed in the experimental alloys at 900°C was sensitive to the higher ratio of iron to vanadium.