Host: The Japan Society of Mechanical Engineers
Name : International Conference on Advanced Technology in Experimental Mechanics 2019
Date : October 07, 2019 - October 11, 2019
In this study, the Bulge Test was used to investigate the mechanical properties and residual stress of TiNi shape memory alloy film under different post-annealing temperature.Ti-60 at%Ni thin films with thickness of 600nm were deposited on silicon nitride with and without chromium interlayer. Static and dynamic mechanical properties of these films were investigated by bulge test and using SEM, XRD for internal structure and crystalline phase orientation. Figure 1 shows the experimental setup. It was found that the Ti-Ni film has the lowest residual stress and the highest Young’s modulus with the adhesion of chromium interlayer. The addition of chromium interlayer between film and silicon nitride introduces R phase transformation in room temperature. Microstructure analysis revealed that the surface trenches will be significantly reduced when the film with chromium interlayer, which indicates that chromium interlayer can minimize the stress evolution during film deposition. Thermal cycling stress evolution test results showed that chromium interlayer has the function of buffering TiNi and SiNx thermal mismatch. In addition, the thermal cycling bulge test method was used to measure the thermal expansion coefficient of unknown films. Also, the fatigue test showed that the interlayer layer of Cr can enhance the fatigue strength of TiNi films. The fatigue test showed the fatigue resistance of TiNi film. The relationship between the change of the microstructure and the crystalline phase and the mechanical properties was observed by SEM and XRD. From the results of SEM and XRD analysis, we can observe that as the annealing temperature increases, the Ti atoms on the surface of the TiNi film annealed in the atmosphere easily form a brittle layer of TiO2 with oxygen, while annealing under high vacuum and in N2 environment can effectively avoid the surface of the TiNi film oxidized, and the condition under high vacuum environment had the best effect, and the degree of crystallization is obviously superior to other conditions. In the results of the bulge test. We can find that as the annealed temperature increase, the residual stress decreases obviously, and the Young's modulus increases. The results of SEM and XRD analysis can determine that the formation of precipitates such as TiO2 and Ti3Ni4 on the surface as the annealing temperature increases. The R phase was introduced into the austenite matrix, which leads to an increase in the Young's modulus of the TiNi film. In the fatigue test, the residual stress released after fatigue decreases as the annealing temperature increases. The FWHM changes are analyzed by XRD, and the TiNi film is judged to be at The first stage of fatigue shows good fatigue resistance.
