Influence of composition and microstructure on the tribological property of SPS sintered MCrAlY alloys at elevated temperatures

In order to explore the mechanical and tribological properties of high-temperature alloy materials, the present study aims to investigate the synthesis, microstructure, composition, mechanical and tribological properties of high-temperature monolithic MCrAlY (M = Ni or NiCo) alloys. The alloys were prepared by spark plasma sintering technique. The microstructure and composition were studied by Scanning Electron Microscopy and X-ray diffractometry. The tribological properties of Ni-based alloys were tested by friction tester against Si3N4 balls at elevated temperatures. The results showed that the NiCrAlY alloy was composed of γ-Ni(Cr) solid solution, β-NiAl, and γ′-Ni3Al with little CrAl. The NiCoCrAlY alloy was consisted of γ-Ni(Cr/Co) solid solution, β-NiAl and γ′-Ni3Al. The hardness of NiCrAlY alloy was higher than that of NiCoCrAlY alloy. However, its flexural strength was lower than the NiCoCrAlY alloy. The more uniform microstructure of NiCoCrAlY alloy along with the evenly dispersed fine reinforced phases and the less pores defects contributed to the higher flexural strength. The μs and WRs of NiCrAlY and NiCoCrAlY alloys increased firstly to reach the highest value at 200 and 400 °C, and then declined with the temperature increasing to 800 °C. The WRs of NiCrAlY were lower than that of NiCoCrAlY for all the temperatures. Adhesive wear dominated the wear mechanism of NiCrAlY/Si3N4 tribo-pair, while abrasive wear was the main wear mechanism for NiCoCrAlY/Si3N4 tribo-pair. At high temperature, oxidation of worn surfaces to a certain extent decreased the wear for both the tribo-pairs. The higher hardness of NiCrAlY may contributed to the lower wear than NiCoCrAlY.