Boron nitride-reinforced SS316 composite: influence of laser processing parameters on microstructure and wear resistance

Abstract

Using laser surface modification, coatings of stainless steel 316 (SS316) alloy with 5 weight % hexagonal boron nitride (BN) were processed and then subjected to various tests to determine whether altering surface chemistry and microstructures via laser passes could enhance the mechanical performance of the coating. X-ray diffraction (XRD), scanning electron microscopy, Vickers hardness, and wear tests were used to characterize the coatings. It was hypothesized that the introduction of BN and modifying microstructures would influence hardness and wear resistance. The substrate was used as a control with a hardness of 178 ± 13 HV and a wear rate of 2.30 ± 0.04 × 10−4 mm3/Nm. The addition of laser passes on the substrate slightly reduced wear rates while increasing hardness values by at least 12%. However, the addition of 5 wt% BN with no laser passes increased surface hardness by 85% to 329 ± 17 HV and reduced the wear rate by 38% to 1.43 ± 0.02 × 10−4 m3/Nm. Modifying the composite’s surface with one additional laser pass increased the surface hardness by 78% to 316 ± 6 HV and decreased the wear rate by 51% to 1.13 ± 0.01 × 10−4 mm3/Nm. Two laser passes increased the composite’s surface hardness by 71% to 304 ± 6 HV and decreased the wear rate by 55% to 1.04 ± 0.02 × 10−4 mm3/Nm. Grain sizes were smaller in the coating when compared to the substrate and exhibited congruency at the coating–substrate interface. XRD analysis confirmed a major phase of austenitic stainless steel in the coating while containing a small amount of minor phase hexagonal BN. Our results indicate that both BN reinforcement and laser processing parameters can positively influence surface properties of these structures.