Influence Mechanism Of Strontium Sulfate On Tribological Properties Of Nickel Matrix Composites

Aiming at the problem of high-temperature wear between moving parts in high-tech fields such as aerospace,nuclear engineering and military industries,based on the view of in-situ reinforced phase and lubricating phase derived from the tribochemical reaction,through the composition regulation of Ni,Mo and Sr Mo O₄,the in-situ Ni based composites containing Sr Mo O₄and Sr₂Ni Mo O₆were prepared in the oxygen-deficient environment originated from the decomposition of SrSO₄during the vacuum hot pressing sintering process.The effects of SrSO₄content on phase composition,microstructure,hardness and wide temperature tribological properties of Ni-20wt%Mo(N20M)alloy were systematically investigated.On the condition of optimized SrSO₄content.the influence of Mo content on the tribological properties of sintered composites over a wide temperature range was discussed to reveal the formation mechanism and evolution law of the friction layer composed of the in-situ phases and tribochemical reaction products and clarify the friction and wear mechanism of composites at different temperatures.The main conclusions were as follows:1.For N20M-SrSO₄ composites,during the vacuum hot-press sintering process,the formation of the oxygen-deficient environment derived from the decomposition of SrSO₄led to the oxidation of Ni and Mo,then Sr₂Ni Mo O₆was detected in the sintered composites by the solid reaction between Ni O,Mo O₃and Sr O.With the increase in the content of SrSO₄,Sr Mo O₄also appeared in the sintered composites.2.With the increase of the oxygen partial pressure in the oxygen-deficient environment,more pores appeared between the components of N20M-SrSO₄composites,which resulted in a distinct decrease in microhardness.Compared with the tribological properties of N20M alloy over a wide temperature range,the N20M-5SrSO₄composite exhibited low friction coefficient and wear rate(0.26 and 1.32×10^-5mm³/Nm,respectively)at 800?,which was attributed to the formation of synergistic lubrication film on the wear surface consisting of Sr₂Ni Mo O₆,Sr Mo O₄and oxides(Ni O,?-Mo O₃,?-Ni Mo O₄and?-Ni Mo O₄).3.The variation of Mo content in the N20M-5SrSO₄ composite led to the formation of Sr₂Ni Mo O₆,Sr Mo O₄and Sr O.At the room temperature,the satisfactory tribological properties were due to the synergistic lubrication effect of Sr₂Ni Mo O₆and Sr Mo O₄on the worn surface.Compared with N5M-5SrSO₄composite at 800?,the synergistic lubrication film composed of Sr₂Ni Mo O₆,Sr Mo O₄and oxides(Ni O,?-Mo O₃,?-Ni Mo O₄and?-Ni Mo O₄)was formed on the worn surface of N10M-5SrSO₄and N15M-5SrSO₄composites,which played an important role in the decrease in the friction coefficient and wear rate.The N15M-5SrSO₄composite exhibited good tribological properties at room temperatures and 800?.