Lubrication behavior of Ni–Cr-based alloys containing MoS2 at high temperature

Ni–Cr-based alloys with excellent self-lubricating property in a wide temperature range were prepared by powder metallurgical hot pressing of alloyed Ni–Cr powder, Mo, Al, Ti, B and various proportions of MoS2 powder. The effects of MoS2 on some mechanical and tribological properties of the alloys when rubbing with W18Cr4V high-speed steel were investigated in the temperature range of 20–600°C. The results show that the anti-bending strength of the alloy decreases with addition of MoS2, and the tribological properties of the alloy were improved by adding MoS2. The best comprehensive properties of mechanics and tribology were obtained when the amount of MoS2 in the alloy is up to 10 wt.%. XRD analysis shows that the alloy was mainly composed of Ni-based solid solution, Ni3Al, CrxSy, MoS2 and Mo2S3. The selective transfer of oxides between rubbing pairs occurs in the friction process at 600°C. The glaze layer is formed on the oxide film at worn surface of the alloy during high temperature friction process. The hardness of the glaze and oxide film is higher than that of the matrix alloy, which accounts for the wear resistance of the alloy at high temperature. The synergistic action of oxides and residual sulfides in the wear surface and wear debris at high temperature is responsible for reduction of friction.