The influence of Fe-40Ti intermetallic master alloy additions on the sintering behaviour of Ti-2.5Fe

The sintering behaviour of Ti-2.5 wt% Fe was investigated to help in the development of new, lower cost titanium alloys and powder metallurgy production methods. In contrast to previous studies of blended elemental (BE) Ti-Fe mixtures, the present work focused on introducing the iron (Fe) as a Fe-40 wt% Ti master alloy (MA). Under certain conditions, BE mixtures were previously found to exhibit rapid swelling and an exothermic reaction near the first eutectic temperature of 1085 °C due to intermetallic formation. Under similar conditions, the MA mixtures studied here underwent only melting since the additions were already in intermetallic form. However, as with the BE mixtures, coarse MA mixtures (d50 = 50-90 μm) resulted in additional large porosity due to liquid formation as well as microstructural inhomogeneity during sintering. Introducing a pre-eutectic hold to the sintering cycle nearly eliminated any liquid formation, but additional coarse porosity was still present due to imbalanced diffusion of Fe into Ti. The use of fine MA particles (d50 = 20-25 μm) was found to eliminate incipient melting and coarse porosity and resulted in improved homogeneity. Only small differences in final sintered density were observed between unalloyed Ti and the Ti-2.5Fe mixtures with BE or MA additions. However, alloys with higher Fe concentrations may result in more noticeable differences in densification behaviour.