Impact wear performances of Cr 3C 2NiCr coatings by plasma and HVOF spraying

Abstract

Three kinds of Cr 3C 225%NiCr coatings prepared by APS-Ar H 2 , APS-Ar He and HVOF spraying, respectively, have been studied with a self-made impact wear rig. The wear resistant performances of Cr 3C 225%NiCr coatings were tested under different impact stress. The wear losses and worn surface profiles are measured, and the corresponding wear mechanisms were studied with Scanning Electronic Microscope (SEM). It is found that wear resistance of Cr 3C 225%NiCr coatings under different impact conditions increases in the order of APS-Ar H 2 APS-Ar He and HVOF spraying. The HVOF sprayed Cr 3C 225%NiCr coatings show the best impact wear resistance due to the denser structure and fewer defects. The wear mechanisms of Cr 3C 225%NiCr coatings under impact condition is impact fatigue, which consists of two wear processes of plastic smearing and breaking-off. The plastic smearing produces plastic deformation of the thin layer in the outer coatings and then causes microcracks in the near subsurface due to stress accumulation. There are horizontal and perpendicular microcracks. The former commonly nucleate from the boundary of lamellae, while the latter may occur from the sub-microcracks inside lamellae. The propagating and merging of both horizontal and perpendicular microcracks finally give rise to the breaking-off of coatings. The cohesive defects such as stratification, porosity and microcracks in the lamellae have much effects on the wear resistance of coatings.