Multi-component boron and niobium coating on M2 high speed steel processed by powder metallurgy

A multi-component boron and niobium coating can improve properties compared to conventional boron coating. A thicker layer of boron diffusion could be formed, providing a support layer of higher mechanical strength for the hard layer. The objective of this research is to develop a boron and niobium-based coating on the high-speed steel M2 produced by powder metallurgy (P/M). Firstly, calculations by ThermoCalc® were made to estimate parameters of niobium boronizing. Secondly, thermochemical treatments by pack cementation were carried out, in stages and also simultaneously. Microstructures, phases, hardness, roughness, wear resistance and coefficient of friction of the coatings were investigated. Finally, coatings composed of niobium carbides or niobium borides and iron borides, measuring more than 3000 HV0.025 of hardness was obtained by niobium‑boron based treatments. However, the best wear resistance was conferred in the boronizing coating.The authors would like to acknowledge financial support to the Ph.D. student from FAPESC, under the studentship number 0951801-0-01, from CAPES for Sandwich Doctorate, BEX 9676/11-2. Also, they would like to thank the UC3M and UDESC universities, where this investigation was performed