Investigation on the microstructure and cracking susceptibility of laser-clad V2O5 /NiCrBSiC alloy coatings

The effect of V2O5 on the refinement of microstructures and the reduction of cracking susceptibility of laser-clad NiCrBSiC hardfacing coatings are investigated. It is shown that high volume fraction and inhomogeneous distribution of the coarse brittle phases of chromium borides and carbides in NiCrBSiC layer are the dominating origins for hot cracks. The addition of V2O5 has an apparent effect on enhancing the toughness, refining the microstructure and reducing the cracking sensitivity of the coating. This is attributed to the generation of vanadium borides and carbides. The vanadium borides generate prior to and consequently inhibit the formation of chromium borides during rapid solidification because of lower standard free energy of formation of the former. They also restrain the growth of chromium carbides and make them distribute homogeneously. The reasons for crack initiation and distribution are discussed based on the microstructures of the cladding layers. It is demonstrated that the generation of cracks is determined by the microstructure of the cladding layers and the occurrence of cracking is governed by heat stress.