On the Martensitic Transformation in TiNi

The structural transformation of the CsCl-type compound TiNi has been investigated by X-ray-diffraction, calorimetric, and metallographic methods. The transition is a first-order one, with a latent heat of 370 ± 20 cal/g-atom. It occurs rapidly and with small hysteresis in bulk material, the transition temperature varying with composition within the range 48–52 at.-%nickel, and its martensitic character was confirmed by metallographic and electron-microscope observations. The martensite (low-temperature) structure is probably of low symmetry. There is some evidence that different transition products are formed on either side of the stoichiometry. Oxygen level significantly affects the transition behaviour.