Lattice constant, elastic modulus and electrical resistivity of Ni 50Ti 50− xAl x

Abstract

Measurements of the lattice constant, the elastic modulus and the electrical resistivity were carried out for Ni 50Ti 50 − x Al x ( x ⩽ 3) alloys in order to investigate the effect of addition of aluminium to a NiTi alloy. At room temperature, the aluminium-containing NiTi alloy has the CsCl structure, from which Ti 2Ni precipitates. Each phase forms a solid solution with aluminium. When the aluminium content is increased to 2 at.%, the lattice constant of NiTi decreases while the elastic modulus increases. At higher aluminium content, the lattice constant and the elastic modulus remain practically unchanged. The elastic anomaly was confirmed at temperatures ranging from 293 to 373 K, the elastic modulus showing a positive temperature coefficient. Although the thermal cycle dependence of the transformation behaviour and the elastic anomaly in the CsCl structure for the Ni 50Ti 50 − x Al x alloys resemble those of binary NiTi, the aluminium addition emphasizes the premartensitic phenomenon and drastically expands the temperature region of the transformation.