The effect of Mo content in plasma-sprayed Mo-NiCrBSi coating on the tribological behavior

NiCrBSi is a material popularly used as a hard thermal sprayed coating. The coating performs well as a wear resistant coating under low stress. At higher stress in metal-to-metal sliding wear condition, however, the NiCrBSi starts to experience surface deformation, which will inevitably lead to seizure as the stress increases. In order to improve the tribological properties of the NiCrBSi plasma-sprayed coating, Mo is added to the coating to reduce the friction between the coating and other metal contacting surface, thus, improving its dry sliding wear resistance. In this study, various amounts of Mo were mixed with NiCrBSi at 0, 25, 50, 75 and 100 wt.%. The powders were sprayed using an air plasma spraying technique onto stainless steel samples to form coatings, which were ground to achieve flat surfaces and a thickness of 350–400 μm. The mechanical properties of the coatings were determined. The coating samples were then tested using a reciprocation ball-on-flat tribometer. It was found that as the Mo/NiCrBSi ratio increases, the wear mechanism changes. Coatings containing 75%Mo and 25%NiCrBSi exhibit the highest wear depths corresponding to the cracking of the thin NiCrBSi splats. On the other hand, coatings containing 25%Mo and 75%NiCrBSi possess the lowest wear depths with no surface cracks. The presence of Mo covering the coating surface hinders the metal seizure between NiCrBSi and steel counter surface.