Electron microscopy studies of the “Premartensitic” transformations in an aged Ti-51 at%Ni shape memory alloy

“Premartensitic” transformations in an aged Ti-51at%Ni shape memory alloy have been studied by means of electrical resistance measurements, and electron diffraction and microscopy. On aging at 500°C or below following solution treatment, premartensitic transitions appear in Ti-51at%Ni. The appearance of the premartensitic transitions is attributable to the formation of Ti₃Ni₄ precipitates. Crystallographic and morphological aspects of the premartensitic transitions in specimens aged under several conditions are described in detail. The premartensitic behavior of the present aged specimens is essentially the same as that of the ternary TiNiFe [8–10] and TiNiAl alloys [16].