Microstructural characterization of laser-clad TiCp-reinforced Ni-Cr-B-Si-C composite coatings on steel

A continuous-wave CO2 laser was used to clad a TiC particle-reinforced Ni-Cr-B-Si-C composite coating on to an AISI 1045 steel substrate. The microstructure of the clad was investigated by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It was found that partial dissolution of the TiC occurred on melting, and epitaxial growth of the remaining particles takes place by the precipitation of TiC upon cooling. This epitaxial TiC layer has an additional alloying effect by using elements such as chromium and silicon from the matrix, The pushing of TiC particles (TiCp) by the solidification front causes them to be unequally spaced. Besides the TiCp, the microstructure of the coating is a mixture of feather-like colonies and a small amount of (gamma-Ni+M32C6) eutectic. The feather-like colonies consist of CrB laths distributed in a gamma-Ni solid solution and grow radially from the TIC particles because of the large difference between the thermal properties of TiC and the Ni-Cr-B-Si-C matrix alloy. (C) 1999 Elsevier Science S.A. All rights reserved.