Influence of molybdenum on the microstructure and properties of a FeCrBSi alloy coating deposited by plasma transferred arc hardfacing

FeCrBSi alloy powders without and with 2-6 wt.% Mo (Mo-free and Mo-added, respectively) were deposited on a plain steel using plasma transferred arc (PTA) hardfacing. The effects of Mo addition on the microstructure and properties of the FeCrBSi alloy coating were investigated by X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) attachment, transmission electron microscopy (TEM), Vickers hardness tester, hydraulic universal testing machine, dry sand abrasion test (DSAT) and water quenching method. The results show that the Mo-free coating consists of γ (Fe, Ni), M7(C, B)3, and (Fe, Cr)2B phases. Adding Mo leads to the formation of M23(C, B)6, Mo2(B, C) and Fe3Mo3(C, B) phases, except for those phases existed in the Mo-free coating. The twinning with 101¯ twinning plane is observed in the orthorhombic M7(C, B)3 (M = Fe, Cr, Mo) phase. A hypoeutectic microstructure can be seen in the Mo-free and 2 wt.% Mo-added coatings. Increasing Mo addition to 4 wt.% and 6 wt.%, a hypereutectic microstructure can be obtained. The microstructure of the Mo-free coating can be refined after adding 2-6 wt.% Mo. The finest microstructure can be obtained in the 4 wt.% Mo-added coating. Adding Mo in the FeCrBSi alloy coating can increase its abrasive wear resistance that has no direct relation with H/E or H3/E2 because brittle fracture occurred occasionally in the abrasive wear test. The thermal shock resistance of the Mo-free coating can be improved after adding 2-6 wt.% Mo. The best abrasive wear resistance and thermal shock resistance can be received in the 4 wt.% Mo-added coating.