Failure Analysis of a Chromium Plating Layer on a Piston Rod Surface and the Study of Ni-Based Composite Coating with Nb Addition by Laser Cladding

The failure of a chromium plating layer on the surface piston rod was analyzed, and an Ni-based alloy mixed with niobium (Nb) composite coating investigated by means stereomicroscopy, metallographic microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Vickers hardness testing, wear testing. results show that penetrating cracks were present in layer. Subsequently, corrosion intensified, resulting bubbling, cracking, peeling cladding presented structure morphology planar crystalline at bottom, dendritic middle, equiaxial top. solidification parameters, which derived from simulation results, confirmed ratios between temperature gradient (G) speed (S) decreased, values cooling speeds increased bottom to top With increase Nb content, became gradually refined uniformly dense. mainly composed ?-Ni, Cr23C6, Cr7C3, NbC, Ni3Nb. NbC could be formed situ itself four forms: particles, dendrites, polyhedrals, networks. microhardness 15% added enhanced 400 HV0.2, resistance thereof 11.14 times higher than substrate. After had aged for 16 h, peak intensities Cr23C6 Cr7C3 significantly increased, volume fraction granular 1.67% 2.54%. 580 better