Crack propagating and stress-promoted the precipitate of Ni3Ti in NiTi thin films

Abstract

This study investigated the stress-induced crack propagation and precipitation in Ti-51.45at.%Ni thin films. Tensile tests were carried out on CSS-44100 electron universal testing machine. The strain rate was 1.1?10-4 s-1. The surface micrographs of the NiTi thin film were obtained using scanning electron microscopy (SEM). The precipitates were determined by X-ray diffraction (XRD) experiments (D8 GADDS). The results showed that a series of parallel cracks grew in the film and the cracks were equally spaced. The fracture toughness of the film was estimated, c K I =0.96MPa?m1/2. The minimum crack spacing was about 87ím. The stress-strain curve can be divided into two stages. The first linear stage corresponded to the elastic deformation of the parent phase. In the following stage, the serrations were considered to be the stress relaxation due to the cracks propagating and the precipitate grain transformation. During tension the (102) peak intensity of Ni3Ti phase increased with elongation increased. The precipitate orientation was same. © (2010) Trans Tech Publications, Switzerland.