Mechanically alloyed Ni50Ti50 and its transformation by thermal treatments

Amorphous powders have been obtained by mechanical alloying (MA) equiatomic powder mixtures of nickel and titanium. The amorphous phase thus formed decomposes upon heating first into the cubic B2 NiTi intermetallic compound; however, further heating promotes the precipitation of the intermetallics Ni₃Ti and NiTi₂. These transformations are shown to occur also in mechanically ground (MG) NiTi wire, but not in this same material exempted from ball-milling processing. It is suggested that this unique behaviour is brought about by the particular structural features of the MA or MG powders, which promote the otherwise sluggish decomposition of B2 NiTi.