The effects of heat treatment on microstructure and erosion properties of laser surface-clad Ni-base alloy

The effects of heal treatment on the microstructure, microhardness and resi stance to erosion of laser surface-clad Ni alloy on a 0.2% C martensitic st ainless steel were investigated by means of scanning electron microscopy, X -ray diffraction, energy dispersive X-ray analysis, microhardness testing a nd erosion testing. The hardness of the stainless steel increased from 230 HV to 500-700 HV on applying a laser surface-clad Ni-base alloy, and heat t reatment enabled the microhardness of the clad layer to be further increase d to 850-1120 HV. Under the conditions of a water solution with a quartz sa nd slurry containing H2SO4 and NaCl, 7 m s(-1) nominal test speed, and 45 d egrees test angle, the erosion properties of the stainless steel were impro ved by the laser-clad Ni-base alloy. After applying heat treatment to the c lad layer, a further improvement in erosion resistance was achieved. The er osion rates of the surface alloy layer with and without heat treatment were reduced by factors of about 9 and 2 as against that of the stainless steel substrate, respectively. It is suggested that the marked improvement in er osion is closely related to the cladding layer being strengthened owing to the increase of coating hardness, formation of a more ductile structure, an d precipitation of M23B6 borides produced by heat treatment. (C) 1999 Elsev ier Science S.A. All right reserved.