IMPACT-WEAR PERFORMANCES OF CR3C2-NICR COATINGS BY PLASMA AND HVOF SPRAYING

Three kinds of Cr3Cr2-25%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 Cr3C2-25%NiCr coa tings were tested under different impact stress. The wear losses and w orn surface profiles an measured, and the corresponding wear mechanism s were studied with Scanning Electronic Microscope (SEM). It is found that wear resistance of Cr3C2-25%NiCr coatings under different impact conditions increases in the order of APS-Ar/H-2 APS-Ar/He and HVOF spr aying. The HVOF sprayed Cr(3)C(2)25%NiCr coatings show the best impact wear resistance due to the denser structure and fewer defects. The we ar mechanisms of Cr3C2-25%NiCr coatings under impact condition is impa ct fatigue, which consists of two wear processes of plastic smearing a nd breaking-off. The plastic smearing produces plastic deformation of the thin layer in the outer coatings and then causes microcracks in th e near subsurface due to stress accumulation. There are horizontal and perpendicular microcracks. The former commonly nucleate from the boun dary of lamellae, while the latter may occur from the sub-microcracks inside lamellae. The propagating and merging of both horizontal and pe rpendicular microcracks finally give rise to the breaking-off of coati ngs. The cohesive defects such as stratification, porosity and microcr acks in the lamellae have much effects on the wear resistance of coati ngs.