| TiNi alloys and pure titanium have received a great deal of attractions in recent years because of their fascinating properties. Especially,the TiNi thin film is wildly used in micro-electromechanical systems as its shape memory effect. Besides, pure titanium is frequently used in aerospace and nuclear industriesas as the important components. And the pure nickel is usually used as the middle layer of titanium and other materals(the stainless steel) to bond them together. So, in this study we fabricate the homogeneous TiNi thin films and block Ti/Ni diffusion couple and analysis the interdiffudion behavior of Ti-Ni system for obtaining the low cost TiNi thin film and deeply investigating factors influencing the interdiffusion of Ti/Ni.Firstly, the prepared sandwiched Ni/Ti/Ni films by chemical nickelplating method is used to fabricate the TiNi thin films by vacuum diffusion technology, and the method has relatively lower cost. The thin film are parapared by changing the diffusion time and temperature and the homogeneous is successfully fabricated at 1173 K for 4h. Meanwhile the interface energy and Gibbs free energy are calculated, and we also study the formation sequence of the intermetallics in Ti-Ni systems by the combination of the calculated and experimental results. The analysis result indicates that the TiNi3 and Ti2 Ni nucleate firstly, and then the TiNi nucleates.Secondly, the Ti/Ni diffusion couple is fabricated with pure Ti and pure Ni by hot pressing technology. In process of hot pressing, we strictly control the hot pressing parameters, including diffusion temperature(1023K,1073 K and 1123K),diffusion time(30min,60 min and 90min),pressure(5MPa, 10 MPa, 15 MPa and 20MPa),surface roughness(the surfaces grounded by 280# or1000# grit SiC paper,or polished by 0.05μm silicon latex particles). The effect of diffusion temperature and time on the interface microstructure and the result shows the diffusion layers become more and more coherent with the increasing temperature and time. Meanwhile we also investigate the influence of pressure and surface roughness on interface microstructure and poriperties of the joints. The result indicates the voids on the interface decrease in scale and quantity, and the mechanical property increases with the decreasing surface roughness. Besides, with the increasing pressure, the interface becomes tighter and tighter, while the diffusion layer increases first and then decreases. |
