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 (WC_p) 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 WC_p/Ti reaction zones is found. As a diffusion barrier, this W layer can suppress further dissolution of WC_p 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 WC_p is used instead of single-crystal WC_p.