Microstructure and wear resistance of Mo coating deposited by plasma transferred arc process

To improve the wear resistance of a C45E4 steel substrate, a Mo coating was deposited by plasma transferred arc (PTA) process. The phase and microstructure of the coating were characterized by X-ray diffraction (XRD), optical microscope (OM), scanning electron microscopy equipped with an energy dispersive spectrometer (SEM-EDS) and transmission electron microscopy (TEM), respectively. The hardness and wear resistance were investigated by Vickers hardness and pin-on-disk wear testers. It was found that the metastable Fe63Mo37, Fe solid solution, Fe7Mo6, and a certain amount of amorphous phases co-existed in the as-deposited Mo coating. The peritectic coupled growth in Fe-Mo alloys was observed. Based on the undercooling and eutectic growth theory, the possibility of the Fe63Mo37/α-Fess peritectic coupled growth has been discussed. The microhardness was much higher than that of the C45E4 steel substrate. The results showed that the coating exhibited higher wear resistance ascribed to the high hardness phases and low-friction MoO3 film on the worn surface of the coating under dry sliding wear test against ZrO2 disc at room temperature.