Study On Preparation And Tribological Performance Of Plasma Surface Ni Alloy On Pore Titanium

Titanium and its alloys have been extensively applied in aerospace、 automobile and biological industries, due to their low density, high specific strength and good corrosion resistance. However, titanium and its alloys are sensitive to adhesive wear and fretting wear, because of the low hardness and heat conductivity. Therefore, the insufficient tribological performance has become a major obstacle in the practical applications of titanium alloys. In this study, the plasma surface alloying technique is employed to improve the wear resistance of pure titanium.It has been reported that as an alloying element, Nickle can enhance the mechnical strenth and abrasive wear resistance. The equal atomic ratio TiNi alloy possesses good toughness, extensibility and outstanding tribological performance. Besides, the Ti-rich Ti2Ni precipitation phase will further increase the hardness and wear resistance of the alloy. In this paper, a TiNi aloyed layer was prepared on the surface of pure titanium, with the purpose of improving its tribological performance.The parameters of the processing were optimized. The composition distribution, micro-structure, phase structure, and micro-hardness of alloyed layer in the optimum parameter were investigated. The dry sliding friction of Ni alloyed layer was investigated by using of pin-on-disc tribometer. The influences of different parameters were reflected in their tribological performances. Fretting wear behavior of Ni alloyed layer was studied in SRV-IV fretting wear tester, which was made in the company of optimol in Germany. The influences of loads, frequencies and amplitudes on wear processes of Ni alloyed layer were analyzed. The wear mechanisms of the different wear tests were also investigated.The main results are as follows:1. The optimum of processing parameters are:workpiece voltage600-800V, cathode voltage450-550V, working pressures35Pa, processing temperature810℃, holding time3h, distance between source and cathode18mm.2. Ni alloyed layers were dense and uniform, with depth up to30μm approximately. The highest and average content of Ni were about43at%, and30at%respectively. The micro-hardness of the layer was up to570HV, nearly twice as the untreated pure titanium. The X ray diffraction revealed the formation of Ti2Ni, TiNi, Ti within the Ni alloyed layer.3. The dry sliding tribological performances was optimal in the typical parameters. By contrast to pure titanium, the Ni alloyed layer possessed lower friction coefficient and better abrasion resistance. The friction and wear mechanism of the Ni alloyed layer was almost adhesive wear, but the untreated titanium mainly displayed abrasive wear, accompanying with adhesive wear and oxidative wear.4. In the fretting wear process, the Ni alloyed layer of the typical process presented lower friction coefficient and better resistance to fretting wear, and the friction and wear mechanism was adhesive wear. As contrast, the friction and wear mechanism of the untreated titanium was abrasive wear, accompanying with adhesive wear and the features of fatigue damage.5. The friction coefficient of the Ni alloyed layer gradually increased with the increase of loads. The circumstances were similar to the increase of wear rates and amplitude.