Tungsten carbide phase transformation under non-equilibrium solidification of high intensity pulsed ion and electron beams

Abstract

The WC-13Ni cemented carbides irradiated by high-intensity pulsed ion beam (HIPIB, 300 keV, 2–6 J/cm2, 70 ns) and high-intensity pulsed electron beam (HIPEB, 127 keV, 3–34 J/cm2, 180 ns) have been investigated by using scanning electron microscopy, surface profilometer and X-ray diffraction in order to explore the mechanisms of phase transformation. It was found that in both cases beams irradiation with higher energy density resulted in obvious surface remelting and phase transformation from WC to WC1-x, expect that W2C was also found for HIPEB-irradiated samples. However, surface morphology differed greatly in the two cases, HIPIB irradiation induced significant selective ablation of nickel binder, forming a wavy surface of “hill-valley” topography, whereas HIPEB irradiation caused notable surface melting but with less selective ablation, forming a flatter surface with occurrence of apparent cracks and blow holes. The formation of WC1-x phase during the process of beams irradiation should be attributed to the reaction ablation of carbon in the WC and the eutectic reaction at ∼2995 K, while the formation of W2C phase was resulted from the eutectic reaction at ∼2925 K and WC1-x decomposition during the more longer melting process of HIPEB irradiation.