Microstructural characterization of WCp reinforced Ni-Cr-B-Si-C composite coatings

30 vol.% WCp reinforced Ni-Cr-B-Si-C composite coatings were deposited on A1SI1045 steel by laser cladding. The typical microstructures and the phases present in the coatings were investigated using scanning and transmission electron microscopies. It was found that WC particulates partially dissolved on the surface of the particulates in the melt pool during the laser cladding. Upon cooling, the bar-like alpha-W2C, blocky beta-W2C and quadrilateral eta(1)M(6)-C carbides were formed from the laser-generated melt pool, and the final eutectic reaction resulted in the formation of gamma-Ni + Ni3B lamellar eutectic. The rapidly solidified microstructure of the laser melt is composed of gamma-Ni+Ni3B lamellar eutectic in which bar-like alpha-W2C, blocky beta-W2C and quadrilateral eta(1)-M6C carbides are distributed. The coating thus consists not only of thermodynamically stable, but also of metastable phases. The presence of the latter can be attributed to the nonequilibrium solidification arisen from the high cooling rates involved during the processing. (C) 1999 Elsevier Science S.A. All rights reserved.