Mechanical properties and tribological behaviors of Ni (5Al)-Al2O3-MoS2-Ag composite coatings at various temperatures

Abstract

Given the ongoing demand for self-lubricating metal matrix coatings, Ni(5Al)-Al2O3-MoS2-Ag composite coatings were developed and evaluated in this study. For this purpose, Al2O3, MoS2, and Ag at various contents as hard wear-resistant and solid lubricants phases, respectively, were embedded in Ni (5Al) matrix. Wet-milling process along with spray drying were successfully employed for producing composite granules with a rather uniform distribution of reinforcements which were appropriate for plasma spraying. After the plasma spraying of the agglomerated powders, phase composition, microstructure and mechanical properties were investigated, along with the tribological behaviors of the coatings from room to 600 °C. The formation of NiAl2O4 spinel, NiO, and Ni3S2 during the milling and plasma spraying affected the mechanical and tribological behaviors of the coatings. Furthermore, the decomposition of MoS2 to MoO3 and oxidation of Ni at high temperatures altered the tribological behaviors of the coatings. The best frictional behaviors at all temperatures were obtained for Ni(5Al)- 20 wt% Al2O3–15 wt% MoS2–5 wt% Ag coating thanks to its optimized content of Ag, MoS2, and Al2O3.