Modelling and experimental analysis of subsurface damage in low-temperature nano-lubrication grinding

Cooling and lubrication performance played an important role in improving the surface integrity of binderless tungsten carbide (WC) with high hardness and low fracture toughness during the mechanical grinding process. Although relevant efforts have been made to predict the subsurface damage (SSD) of hard and brittle materials, most of the existing SSD depth prediction models were based on the room temperature condition without considering the thermal characteristics of lubricants. To fill this gap, this study presented a low temperature nano-lubrication method to enhance the machinability of WC and established a theoretical model of grinding-induced SSD in WC, where the relationship between SSD depth and the ground surface roughness of maximum height S_z was developed considering the temperature effect under various cooling and lubrication environments. Experimental results show that using low temperature air at -20 °C in combination with mixed nano-lubricant of MoS₂/Fe₃O₄ at ratio 1:2 effectively improved surface integrity of WC, achieving minimum values of arithmetical mean height S_a, maximum height S_z, and SSD depth of 12 nm, 85 nm, and 5.5 µm, respectively. The established SSD depth model was validated with a prediction error of less than 10 %, enabling accurate assessment of SSD during ultra-precision grinding of WC under different cooling and lubrication environments.