Effects of Ag2Mo2O7 nano-shapes on the mechanical and tribological properties of NiAl intermetallic compound over a wide temperature range

Ag2Mo2O7 has attracted considerable interest as excellent high-temperature solid lubricant. The effect of Ag2Mo2O7 nano-shape on the mechanical and tribological performances of NiAl-Ag2Mo2O7 composites was investigated in the study. Ag2Mo2O7 with three different shapes (nanowires, nanorods, and nanoparticles) were prepared by hydrothermal method. The synthesized Ag2Mo2O7 completely decomposes to Ag and MoO3 during sintering of NiAl-Ag2Mo2O7 composites. The decomposed Ag and MoO3 can improve the microhardness of the composites due to the grain refinement and enhancement of strain strength. In particular, Ag2Mo2O7 nanowires can increase the hardness of NiAl by 27%. With the specific decreasing of surface area of Ag2Mo2O7, the friction coefficients of the composites slightly decrease over a wide temperature range. Moreover, Ag2Mo2O7 could be obtained again by a high-temperature tribochemical reaction at 800 °C. The tribo-layer comprising NiO, MoO3, NiMoO4, and Ag2Mo2O7 renderes excellent tribological performances to the composites at 800 °C. Especially for the composite with addition of Ag2Mo2O7 nanoparticles, the friction coefficient and wear rate could be as low as 0.27 and 4.6 × 10−6 mm3/Nm respectively.