Microstructure and Wear-Resistance of Nano-Al2O3 Doped Co-Alloy-Based Composite Coating Produced by Laser Cladding

Cobalt-based composite coatings doped with nano-Al_2O_3 were prepared on Ni-based superalloy substrate by laser-cladding of a CO_2 laser. The microstructures of the coatings were analyzed by means of optical microscopy, scanning electron microscopy, and transmission electron microscopy, while the elemental composition and phase composition of the composite coating were determined by means of X-ray diffraction and energy dispersive X-ray analysis. Moreover, the microhardness of the coatings were measured, while the friction and wear behaviors of the composite coatings sliding against 9CrSi alloy in a block-on-ring configuration were evaluated on an MM-200 test rig. The worn surface morphologies of the composite coatings were also observed by means of scanning electron microscopy. It was found that the incorporation of the nano- Al_2O_3 particulates contributed to increasing the microhardness and wear-resistance of the laser-cladded composite coating, which was attributed to the dispersive strengthening effect and fine-crystalline strengthening effect of the nano-particulates. However, with the increase of the nano-Al_2O_3 amount in the composite coating, the nano-particulates would agglomerate and act as entrapped impurities of decreased bonding strength with the Co-alloy matrix, which led to the decrease in the wear-resistance of the coating. The composite coatings were characterized by scuffing, adhesion, and spalling as they slid against the 9CrSi alloy. Specifically, the enhanced adhesion and spalling of the composite coating with a higher content of nano-Al_2O_3 corresponded to its poorer wear-resistance, though it had a relatively larger microhardness.