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

Abstract

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.