Study On Preparation Of Ti-Ni Alloy Films By Unbalanced Magnetron Sputtering And Its Mechanical Properties

Since the 1960s, Ti-Ni alloys have been developed as shape memory alloy due to their excellent shape memory effect. However, during the past two decades, TiNi alloys'wear resistance has attracted more and more attention. In recent years, using TiNi thin film to improve wear resistance of materials has become an updated research area. For Ti-Ni thin film, its structure and propertie are sensitive to composition, therefore, it is necessary to study the preparation condition to precisely control the composition of the film. The mechanisms responsible for the tribological performance of Ti-Ni film could be revealed through investigation to microstructure, phase transition temperature, surface morphology and mechanical properties of films with different composition. These fundamental studies are beneficial to promote the application of TiNi films as wear resistant material. In this paper, the Ti-Ni alloy films with 45.4at.%, 46.8at.%, 49.7at, 51.3at.% and 53.3at.% Ti content were prepared using closed field unbalanced magnetron sputtering process. The composition, surface morphology and phase structure of the films were tested by EDXA, FSEM, AFM and XRD, respectively. Meanwhile, the phase transition temperature, micro-hardness and elastic modulus were analyzed by DSC, nano-indenter and the other instruments. In addition, three types of transition layer were designed for film of 49.7at.% Ti content. Bonding strength, friction coefficient and wear rate were tested by automatic scratch tester and ball-disc wear tester. Finally, the mechanism of tribological behavior for Ti-Ni thin films was discussed.Through the above research and analysis, the main conclusions are obtained as follows:1. The optimum process parameters for the preparation of Ti-Ni alloy thin film with nearly equal atomic ratio is: argon flows ~ 30sccm, bias ~ 60V, Ti-Ni alloy target current ~ 6A, Ti target current ~ 3A.2. With the increase of Ti content, Ms temperature of Ti-Ni alloy films increases firstly and then tends to keep stable, the maximum occurs at nearly equal atomic ratio; the surface roughness of Ti-Ni alloy thin films decreases at first and then increases, the minimum occurs also at the nearly equal atomic ratio.3. For the same load, the micro-hardness and elastic modulus firstly increase and then decrease with the increase of Ti content; Under different loads, they have no obvious change. The pseudo-elastic recovery rateηof the films is independent of applied load, it increases firstly and then decreases as the Ti content increases.4. Friction coefficient of the Ti-Ni alloy film is smaller than that of TC4 substrate material. Wear rate of the film is an order of magnitude lower than the substrate, and wear track is also narrower.In summary, the improvement in tribological properties of Ti-Ni thin films is mainly related to its super-elastic transformation , and the superb strain-hardening , hot hardness and anti-fatigue properties also possibly contribute to the wear resistance. Besides, composition, phase structure and the other factors also affect the super-elastic of TiNi thin films.