Electron microscopy study of reaction layers between single-crystal WC particle and Ti-6Al-4V after laser melt injection

Laser melt injection of single-crystal WC particles (WCp) into Ti-6Al-4V was demonstrated to produce functionally graded materials (FGMs). A detailed electron microscopy examination was performed to study the microstructure of the FGMs. A thermal simulation experiment was designed to clarify the existing controversy about the formation of the W2C reaction layer. Twinning deformation occurred in the W2C layer can explain the absence of orientation relationships between the W2C layer and the parent phase WC during solid-phase transformation. A new W layer with a thickness of 200-300 nm at the WCp/Ti reaction zones is found. As a diffusion barrier, this W layer can Suppress further dissolution of WCp and inhibit interfacial reactions. Although particle cracking is still the main failure mechanism, the tensile strength of the composites is increased by at least 17% when granular WCp is used instead of single-crystal WCp. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.