Microstructure characteristics of ZrC-reinforced composite coating produced by laser cladding

In the present work, metal-matrix composites layers reinforced by various sizes ZrC0.7 particles were formed by laser single and overlapping cladding on a medium carbon steel, which are in situ synthesized by laser melting of precursor mixtures of Fe-based alloy powders and Zirconium powder using a 3 kW continuous wave CO2 laser. A high quality coating free of cracks and porosities was obtained. Excellent bonding between the coating and the medium carbon steel substrate was ensured by the strong metallurgical bonding. The chemical compositions, surface morphology, microstructure, interface structure and the distribution of the ZrC0.7 particles of the clad layers were analyzed by Optical microscopy, field emission scanning electron microscopy with associated energy dispersive X-ray spectroscopy, X-ray diffractometry, and metallography computer analysis system. The microstructure consists typically of dendrites/cells, interdendritic eutectic and dispersed ZrC0.7 particles. The in situ ZrC0.7 particles are distributed within dendrite and interdendritic regions owing to the trapping effect of the advancing solid-liquid interfaces. The average volume fractions of in situ ZrC0.7 particles are less than 1.96% for the single clad layer, and vary from 2.2 to 3.84% for the overlapping layers respectively. The martensite (M) transformation went with the rapid cooling processes also. The microhardness profile across the cross-section of the single clad layer varies from HV0.2 1000 to 1200. The microstructure of the interface between the clad layer and the substrate is martensite, which shows that there is good metallurgical bonding. The sizes and amounts of ZrC0.7 particles in overlapping layers are larger and more than that of laser single clad layer. (C) 2002 Elsevier Science B.V All rights reserved.