The effect of a small addition of boron on the sintering densification, microstructure and mechanical properties of powder metallurgy Ti-7Ni alloy

The effect of a small addition of boron (B) on the sintering, sintered microstructure and mechanical properties of a Ti-7Ni alloy (wt.%) compacted from -100 mesh hydride-dehydride (HDH) Ti powder has been investigated systematically. An addition of ≥0.62%B to the Ti-7Ni alloy resulted in fast, near full-densification (≥99% relative density) within 15 min at 1200 °C, compared to 95.6% relative density obtained after 120 min at 1200 °C without B, compacted at 400 MPa in both cases. In addition, the pre-eutectoid α phase changed from long parallel α-laths (up to ∼500 μm) to near-equiaxed α-Ti throughout the microstructure with an addition of ≥0.31%B. Elemental B was found to be more effective than TiB as a sintering aid for Ti-7Ni. A small addition of B increased both the tensile strength and yield strength of Ti-7Ni but at the expense of tensile ductility. The mechanisms behind each of these observations were discussed