High temperature tribological properties of NiAl-Ag2Mo2O7 composite coatings prepared by spark plasma sintering

NiAl-Ag2Mo2O7 composite coatings were prepared with different contents of Ag2Mo2O7 (0-15 wt%) by spark plasma sintering (SPS) technology, in which Ag2Mo2O7 was synthesized through hydrothermal method. The mechanical and tribological properties of the composite coatings were investigated from room temperature (RT) to 800 degrees C, and the corresponding lubrication mechanisms were also revealed. The results show that Ag2Mo2O7 is decomposed into Ag, MoO3 and Mo2C phases during sintering process. NA10 (NiAl-10wt%Ag2Mo2O7) presents excellent tribological properties, especially at 800 degrees C, the friction coefficient and wear rate reach the lowest value of 0.29 and 6.15 x 10(-5) mm(3)/(N center dot m), respectively. The significant improvement of tribological properties is attributed to the formation of a synergistic lubricating glaze layer composed of NiO, NiMoO4, Ag2MoO4 and Ag2Mo2O7 by tribo-chemical reaction on the worn surface.