Papers by Author: Y.M. Wang

Abstract: This study has investigated the cracking of Ti-51.45at.%Ni thin films deposited on Cu substrate. An analysis is presented that relates the crack spacing and the Vickers microhardness values to the strain in the film. Tensile tests are carried out on CSS-44100 electron universal testing machine. The strain rate is 1.1 × 10-4 s-1. The average crack spacing is obtained using scanning electron microscopy (SEM). The Vickers microhardness values are determined by Everone MH-6 microhardness tests. The results have showed that a series of parallel cracks grew in the film and the cracks are equally spaced. The minimum crack spacing is about 87 μm. The mean crack spacing is dependent on the tensile strain in the film. The crack spacing decreases as the film elongation increases. The Vickers microhardness values increase as the film elongation increases.

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, =0.96MPa∙m1/2. The minimum crack spacing was about . 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.

Abstract: Ti-51.45at.%Ni thin films were deposited onto copper substrates by magnetron sputtering. The copper substrates were pre-punched into dog-bone specimens with 4.5mm×30mm(gauge portion) ×35µm( thickness). The substrate temperature was about 673K. The thin films were about 20µm thick. The as-deposited films were first solution treated at 1073K for 1h, and then aged at 773K for 30min. The grain size was estimated to be 1.5µm from scanning electron microscopy micrographs. Tensile tests were carried out on CSS-44100 electron universal test-machine. The strain rate was 1.1×10-4 s-1. The stress-strain curves of the free-standing film were obtained from the experimental stress-strain curves of copper substrate together with the thin film adherent to the substrate compared with the curves of copper substrate without film. The Hall-Patch coefficient was calculated, k=205Mpa.µm1/2. It seems that the Hall-Patch coefficient decreases with increasing film thickness. The experimental results showed that a series of parallel cracks grew in a concerted fashion across the thin film and the cracks were equally spaced. The cracks were more closely spaced if the film stress was increased. The fracture toughness of the film was estimated, c KΙ =0.96MPa·m1/2. Therefore, the minimum crack spacing is predicted by the film stress given.