Microstructural characterization and wear resistance of boride-reinforced steel coatings produced by Selective Laser Melting (SLM)

Abstract Surface engineering is an effective method to extend the lifespan of carbon steels submitted to severe wear degradation. In this work, the surface of a low carbon steel (AISI 1020) was protected by a boron-modified stainless steel coating produced by selective laser melting (SLM). Commercial precursors such as 2205 duplex stainless steel and ferrous-alloy (Fe-B) were used to produce boron-modified steel powders by two different routes: i) gas atomization, and ii) gas atomization followed by mechanical milling of large particles (to reduce the particles’ size and to add a solid lubricant – hexagonal boron nitride, h-BN). Thick coatings (200 – 600 μm) metallurgically bonded to the substrate were produced with reduced dilution, characterized by refined, hard and rigid borides homogeneously distributed within the predominant ferritic matrix. The boron-modified steel coatings were hard (~800 HV0.5) and wear-resistant, since the specific wear rate was ~4.5 × 10−5 mm3·N−1·m−1, much inferior to that of the soft (~120 HV0.5) AISI 1020 substrate (~1.8 × 10−3 mm3·N−1·m−1). Although recognized as solid-lubrificant, the coating produced by powder containing h-BN additions did not exhibit reduced coefficient of friction. Given the high temperatures achieved during SLM process, the h-BN may decompose, being the remaining content insufficient to enable the formation of an effective lubrificating layer. The present work contributes to widespread the use of SLM to produce wear-resistant protective coatings using boride-reinforced stainless steels.