| Summary: | 碩士 === 逢甲大學 === 材料科學研究所 === 86 === TiNi intermetallic compound with pseudoelasticity and erosion and corrosion resistance could be potentially applied to sliding wear, rolling fatigue, corrosion, or erosion environment. The TiNi is however expensive. Thin film coating of TiNi will enable the usage of low cost materials such as polain steel to the above application. Thus a study on the TiNI coating is required.
A cathodic arc plasma ion plating process was used to deopsit TiNi films on plain steel. In the exoperimental, plain steel were use as substrates. Substrates bias voltage, working pressure and target composition were changed to reveal the effect on microstructure of the deposited films.
Observations of the surface topography and cross sectional morphology on the deposited films were carried out by suing SEM. XRD and TEM were used to characterize microstructure. EDS was used to identify elemental composition of the deposited films. DSC measurement was used to obtain the transformation temperature of the deposited films.
Experimental results show that the crystallinity of deposited films were strongly dependent upon coating paraceters. Dre to the higher migration ability of surface adatoms, high substrate bias voltage facilitate the higher crystallinity of the deposited films. Growth rate of the deposited films decreases from 20 μm/hr to 4 μm/hr when negatively bias substrate voltage increases from 0 V to 800 V.
By evaluating working pressures, The better crystallinity of the deposited film with lower groeth rate 6μm/hr can be obtained when working pressure decrease from 400 mtorr to 200 mtorr. This again benefit from the higher adatom mobility when working pressure is low. However, the lower working pressure can caused frequent are decease and fail to grow film.
By adjusting the target composition, positive dependence on the film composition is found. However, the deposited films suffer a decrease in Ti composition of 5~10 at%. This may be attributed to the low atomic weight and high chemical activity of titanium atom which may be either easily scattered or oxidized during flight to the substrates.
The crystallinity of the deposited film is also found to be higher when the Ti-rich target composition in used. This may caused by the back sputtering effect when the growing films submitted by a rich nickel ionbombardment. The measure phases in the deposited film characterized by TEM are B2 and B19 with minor phase TiNi3 when target composition Ti50Ni50 is used. It turns out to be Ti2Ni as the minor phase when target composition Ti60Ni40 is used.
DSC measurement shows that the transformation temperaturs of the deposited film increase from 193.6K to 276K when target composition increase from Ti 50% to Ti 60% . This is far below the bulk TiNi reported and can be attributed to the high defect structure of the deposited films.
As a result of this study, well defined crystallinity and adjustable composition of the deposited films can be obtained by suitable controll of the coating parameters.
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