Influence of the microstructure on the resulting 18R martensitic transformation of polycrystalline CuAlZn thin films obtained by sputtering and reactive annealing

We report the influence of the microstructure on the martensitic transformation in polycrystalline CuZnAl thin films with 18R structure. The films are grown in two steps. First, CuAl thin films are obtained by DC sputtering. Second, the Zn is introduced in the CuAl thin films by the annealing them together with a bulk CuZnAl reference. The crystalline structure of the films was analyzed by X-ray diffraction and transmission electron microscopy. The martensitic transformation temperature was measured by electrical transport using conventional four probe geometry. It was observed that temperatures above 973 K are necessary for zincification of the samples to occur. The resulting martensitic transformation and its hysteresis (barrier for the transformation) depend on the grain size, topology and films thickness.