Effects of laser remelting on microstructural characteristics of Ni-WC composite coatings produced by laser hot wire cladding

Abstract

The work presented in this paper focused on the effects of laser remelting with varied laser energy densities from 800 J/mm to 1400 J/mm on the phase transformation and microstructural characteristics in the tungsten carbide nickel-based matrix composite (Ni-WC) tracks obtained by laser hot wire cladding. The microstructures of the as-deposited tracks fabricated by laser hot-wire deposition were mainly composed of spherical residual carbons, eutectic Ni/Ni3B, retained WC/W2C particles and the granular in situ W2C particles formed in the interdendritic regions of primary (Ni,Fe) dendrites. When the low laser energy densities of 800 J/mm and 1000 J/mm were applied, the dispersive W2C particles in the as-deposited tracks were dissolved, and the WC particles were successfully in situ synthesized and uniformly distributed in the remelted tracks. When the laser energy density was increased to 1200 J/mm, the feather-like M6C(Ni2W4C) carbides homogeneously precipitated in the remelted tracks. When the laser energy density was further increased to 1400 J/mm, the dissolution degree of the ex-situ WC/W2C particles was significantly increased, resulting in a remelted track with a relative low volume fraction of retained ceramic particles and a high dilution ratio of the base metal. In addition, the dendritic M6C(Fe3W3C) carbides were precipitated around the retained particles, and the eutectic M6C(Fe3W3C) carbides in the herringbone morphology were uniformly distributed in the matrix of the track remelted by a high laser energy density of 1400 J/mm. These experimental results confirmed that the homogenization of the in situ synthesized reinforcements in the tracks could be well realized by laser hot wire cladding and the subsequent laser remelting. The coatings remelted by the low energy densities (800 J/mm and 1000 J/mm) possessed higher wear resistance than that of the as-deposited coating, but the wear performance of the remelted coatings was decreased when the laser energy densities were increased to 1200 J/mm and 1400 J/mm.