Experimental study on the effect of minimum quantity lubrication on the grinding surface/subsurface of nickel-based single-crystal superalloys

Nickel-based single-crystal superalloys are widely used in aerospace and industrial gas turbine blades due to their excellent material properties. However, these alloys are also known for their difficulty in machining due to their superior physical properties. To improve the surface quality of machined parts, this study investigates the effects of different grinding conditions (dry grinding, flood, minimum quantity lubrication (MQL)) on the surface morphology, grinding-induced damage layer, and subsurface microstructure of nickel-based single-crystal superalloys. The experiments show that under MQL conditions, as the wheel speed increases, the grinding marks become more uniform, surface micro-defects decrease, and surface quality improves. A comparison of the thickness of the grinding-induced damage layer (D) obtained from dry grinding, flood, and MQL reveals that MQL cooling is more effective in reducing the damage layer thickness of nickel-based single-crystal superalloys compared to flood cooling. With an increase in wheel speed from 15 to 35 m/s, the thickness of the subsurface damage layer reduced from 14.2 to 11.4 µm using emulsion cooling and from 12.8 to 9.1 µm using MQL cooling. Unlike dry grinding, the use of grinding fluid significantly impacts the subsurface microstructure of the alloy, effectively suppressing work hardening and reducing the thickness of the grinding-induced damage layer, thereby improving the surface quality. It has important theoretical and practical significance to improve the quality of grinding surface.