Surface integrity deterioration by the volcano-like craters eruption during pulse laser polishing of NAK80 tool steel

Laser polishing has emerged as a critical quality control technique in the manufacturing of precision components, establishing itself as a leading surface processing technology in recent years. This study investigated the effects of heterogeneous impurities on the outcomes of laser polishing (LP) by conducting a pulse laser polishing (PLP) experiment on the NAK80 steel surface. The integrity of the resulting surface was evaluated based on morphology, surface profiles, and roughness. The influence of variations in laser parameters on the polished surface morphology was analyzed, and the challenges associated with minimizing surface roughness were summarized. Additionally, the elemental composition, chemical species, and distribution of surface craters formed during PLP were systematically characterized, with the mechanisms underlying the formation of these craters were explored. The results demonstrate that the utilization of optimal polishing parameters resulted in a substantial decrease in surface roughness, with the average roughness Ra diminishing from an initial value of 1.375 μm to 0.229 μm, representing an 83.3 % reduction. Nevertheless, the existence of surface craters, primarily attributed to low-melting-point impurities such as aluminum particles, posed a significant challenge to further minimizing surface roughness. The investigation demonstrated that both the density and dimensions of these craters were affected by the laser pulse frequency and duration. Specifically, higher pulse frequencies correlated with an increased density of craters, while extended pulse durations resulted in larger crater sizes accompanied by a decrease in density. The research concludes that the formation of surface craters during PLP is a result of the interplay between laser parameters and intrinsic properties of NAK80 steel. It is recommended that efforts to minimize low-melting-point impurities are crucial for optimizing the PLP process and achieving the desired level of surface smoothness. These findings carry substantial implications for the field of precision tool manufacturing, as the attainment of ultra-smooth surfaces is essential for enhancing both performance and durability.