Enhanced Powder Sintering of Near-Equiatomic NiTi Shape-Memory Alloys Using Ca Reductant Vapor.

Abstract An alternative powder metallurgical process (called VPCR process) for the fabrication of single-phase NiTi shape-memory alloys is presented. It is based on a vapor phase metallothermic reduction operating during the NiTi compound formation. This process allows to achieve high chemical homogeneity. It is effective not only for obtaining homogeneous near-equiatomic NiTi without undesirable oxides (Ti4Ni2Ox) and carbonitrides (TiC1−xNx), but also avoids the formation of other Ni–Ti intermetallics such as Ti2Ni, Ni4Ti3 and Ni3Ti. Furthermore, the produced near-equiatomic NiTi (Ti-50.2 at.% Ni) exhibits improved shape-memory effects associated with the reversible B2 ↔ B19′ transformation.