Laser melt injection of monocrystalline WC particles into Ti-6AL-4V

The laser melt injection (LMI) process was used to produce WC particles (WC_p) reinforced Ti-6Al-4V metal matrix composites (MMCs). In particular monocrystalline WC_p were used as injection particles to avoid the intercrystalline cracking often observed in granular or cast WC_p reinforced MMCs. WC_p were injected into the extended part of the melt pool just behind the laser beam to prevent WC_p from excessive dissolution. Moreover, different parameters were applied, and the processing window of LMI was obtained. The produced MMCs layers were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). A graded distribution of WC_p along the depth direction of the MMCs layer is observed. In addition, some new phases such as TiC and W₂C can be found in the MMCs layer. TiC decreases both in quantity and size with the distance from the surface to the bottom of the MMCs layer, and a graded microstructure of TiC in the matrix is also achieved. Two types of reaction layers around WC_p are observed, namely an irregular reaction layer and a cellular reaction layer. The composition of the neighbouring melt pool plays a critical role in the growth and subsequent morphology of reaction layers around WC_p.