Study On Tribological Behavior Of Nickle Based High Temperature Self-Lubricating Composites

High temperature self-lubricating composites have been widely used in some tribology system owing to their extraordinary tribological properties at elevated temperatures. Some solid lubricants were commonly incorporated into composites materials to improve their tribological properties at high temperatures, but their applications were limited by the temperature and oxidation at high temperatures.SrSO₄ and Ag have been proved to be effective high temperature solid lubricant. In this paper, SrSO₄ and Ag were used as additives in high temperature alloy so as to prepare nickel based high temperature composites with excellent tribological properties over a wide range of temperatures.In this paper, SrSO₄ was prepared by chemical precipitation method, and SrSO₄ and Ag were used as high temperature solid lubricant to incorporate into nickel based high temperature alloy to improve tribological properties. XRD, SEM, TEM, XPS and high temperature friction and wear tester were used to investigate the microstructure, mechanical properties and tribological behavior of the composites.The influence of addiction of SrSO₄ and Ag to the tribological properties of the composites were discussed and the related self-lubricating mechanisms over a wide range of temperatures were clarified.Ni-Cr high temperature alloy was successfully fabricated by spark plasma sintering method. The friction coefficients of Ni-Cr alloy at room temperature, 200?,400? and 600? are 0.5, 0.49, 0.41 and 0.41, respectively. The corresponding wear rates are 2.77×10-4mm3/?Nm?, 3.2×10-4mm3/?Nm?, 1.3×10-4mm3/?Nm? and2.53×10-4mm3/?Nm?, respectively.Nanoscale tablet-like SrSO₄ was prepared by chemical precipitation method.Ni-based composites containing different amount of SrSO₄ were fabricated by spark plasma sintering method. The results indicated that the addition of SrSO₄ can significantly improve the tribological properties of composites at elevated tempretures. Ni Cr-10 SrSO₄ composites exhibited satisfactory mechanical properties and tribological properties at elevated temperatures. The friction coefficients of Ni Cr-10 SrSO₄ at 400? and 600? are 0.32 and 0.20, respectively. The corresponding wear rates are 1.44×10-5mm3/?Nm? and 2.4×10-5mm3/?Nm?.Ni Cr-10 SrSO₄ composite exhibited satisfactory tribological properties at elevatedtemperature due to the formation of the lubricating film containing oxides?Ni O and Cr2O3?, SrSO₄ and Sr Cr O4 on the contact surface.Ni Cr-SrSO₄-Ag composites containing 10 wt.%SrSO₄ and different amount of Ag have been successfully fabricated by spark plasma sintering method. The results indicated that the addiction of Ag can obviously reduce the friction coefficient of composites at moderate temperatures. However, the addition of Ag increase the friction coefficient of composites at 400 and 600?, 0.41 and 0.30, respectively. The increasing adding amount of Ag can not significantly decrease the friction coefficient,but can decrease the wear rates at a wide range of temperatures. Ni Cr-10 SrSO₄-20 Ag composites exhibited satisfactory mechanical properties and tribological properties at a wide range of temperatures. The friction coefficients of Ni Cr-10 SrSO₄-20 Ag at room temperature and 600? are 0.38 and 0.29, respectively. The corresponding wear rates are 3.32×10-4mm3/?Nm? and 1.60×10-5mm3/?Nm?. Ni Cr-10 SrSO₄-20 Ag composite exhibited satisfactory tribological properties at elevated temperature due to the formation of synergistic lubricating film containing oxides?Ni O, Cr2O3 and Ag2O?, SrSO₄, Sr Cr O4 and molten Ag particles on the contact surface.