Feasibility of preparing Mo2FeB2-based cermet coating by electrospark deposition on high speed steel

• An attempt was made to gain Mo2FeB2-based cermet coating by electrospark deposition.
• The coating is dense, and metallurgically bonded to the substrate.
• Mo2FeB2 and ferrite of the electrode turn into amorphous and ultra-fine martensite.
• Phase contents and grain size of the coating were estimated by Rietveld method.
• The peak hardness of the coating is 1282.5 HV0.05, the substrate is greatly enhanced.

In this study, Mo2FeB2-based cermet coating has been attempted to produce by electrospark deposition (ESD) process on a high speed steel substrate. Microstructural morphology, elementary distribution, phase constitute, microhardness, and wear resistance of the coating were investigated by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), microhardness measurement and tribological test. The SEM and EPMA results show that the coating is dense, metallurgically bonded to the substrate, and has an average thickness of 48.1 μm. Moreover, a discernible composition transition zone appeared between the coating and the substrate. The XRD patterns reveal a microstructural transformation from Mo2FeB2 phase and binder phase (ferrite) of the cermet to amorphous phase and martensitic phase of the coating during the deposition, and the martensitic phase has nanocrystalline structure (31.7 nm). Such microstructure of the coating results in higher microhardness, lower friction coefficient, and better wear resistance than the high speed steel substrate. The main wear types for the coating are abrasive wear and fatigue wear.