Reaction Mechanism and Synthesis of Ni₃Al–MoS₂ Matrix Self-Lubricating Composites Using Ni, Al, and MoS₂ Powders

The reactions between MoS₂ and several metallic powders, including Ni, Al, and Ni₃Al, were studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The DSC results revealed that MoS₂ started to react with Ni and Al at 630 and 560 °C, respectively, but did not react with Ni₃Al even at 1200 °C. The XRD results indicated that the reaction products of MoS₂ and Ni were a series of new sulfides and molybdenum compounds, including Ni₃S₂, Ni₇S₆, and Ni₄Mo, and those of MoS₂ and Al were Al₂S₃ and various aluminides. Additionally, the compositions of the products varied with the reaction temperature. Because these new sulfides did not possess self-lubricating properties, the consumption of MoS₂ should be avoided. According to these reactions, a synthetic route for the Ni₃Al/MoS₂ composite using Ni, Al, and MoS₂ composite powders was proposed and demonstrated. During the synthesis process, the composite powders were first compressed under a pressure of 180 MPa. The resulting green compacts were heated to 500 °C with a heating rate of 20 °C/min, and then to 530 °C with a heating rate of 1 °C/min. The holding time at 530 °C was 4 h. The phase composition and microstructure of the as-synthesized composite were studied by XRD and SEM. The results showed that MoS₂ remained stable during the synthesis process. Friction and wear tests demonstrated that the composite exhibited good self-lubricating properties with a low friction coefficient of about 0.2 and a small wear rate of 1.04 × 10^{− 5} mm³ N^{− 1} m^{− 1}.