Effects of molybdenum on the microstructure and wear resistance of nickel-based hardfacing alloys investigated using Rietveld method

The nickel-based hardfacing alloys with different Mo contents have been deposited on Q235-carbon steel using a plasma transferred arc (PTA) welding machine. The effects of Mo on the microstructure and wear resistance properties of the nickel-based hardfacing alloys were investigated using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). More detailed information about the crystallographic structure and phase compositions of the deposited coatings was obtained with the application of Rietveld refinement method to analyze XRD spectra. It was found that the addition of Mo did not lead to a change in phase compositions. Furthermore, it can also be seen that the relative contents of the total Cr-rich compounds increased from 36 wt.% to 45 wt.%, though the M23C6 type carbide increased but the relative contents of the M7C3 type carbide decreased with the increasing of Mo contents from 0 wt.% to 6 wt.%. The component segregation, which existed in the Mo-free coating, decreased gradually then disappeared finally with the increasing of Mo contents. The morphology of Cr-rich compounds observed in the interdendritic region changed from plate-like to net-like, as well as the refinement of Ni-rich dendrites because of the addition of Mo. The wear resistance increased but the microhardness decreased with the increasing of Mo contents from 0 wt.% to 6 wt.%. The microstructural change and phase contents variation were responsible for the improvement of the mechanical properties such as wear resistance of the Mo-modified nickel-based hardfacing alloy.