High Temperature Tribological Characterisation of Laser Nitrided Nickel-Based Superalloy

The surface of a nickel-based superalloy used for air-borne gas turbine application was laser nitrided to improve the tribological properties. An optimal laser power and scanning speed was derived to avoid any possible variation in elemental composition of the treated surface. The metallurgical modification over the treated surfaces was studied along the cross-section through microstructural characterisation to understand the refining mechanism and possible nitriding. The coarse grains present over the base material surface reoriented to fine equiaxed grains under lower power and higher interaction time. The grains were refined with higher scanning power and lower interaction time. The higher thermal gradient and cooling rate combination attributed to the refining mechanism. Further increase in the laser power resulted in the formation of columnar grains at the treated depth. The presence of nitride species was observed over the treated surface, which improved the microhardness. All laser treated samples were subjected to wear analysis at ambient and high temperature. The treated pin surface exhibited a combination of adhesive and abrasive wear mechanism. A significant reduction in wear rate was observed for samples treated with high power and lower interaction time.