Microstructural evolution and its correlation with hardening of WC-Ni cemented carbides irradiated by high-intensity pulsed ion beam

Abstract

Modification of WC-Ni cemented carbides was studied by using high-intensity pulsed ion beam (HIPIB) irradiation. Surface hardening can be achieved for all the HIPIB-irradiated surfaces but of different degree at ion current density of 50–300A/cm2 up to 10 shots. Thermal and dynamic process of remelting and ablation under HIPIB irradiation led to significant changes in surface morphology, phase structures and composition of the irradiated surfaces. Gradual transitions to remelting densification, selective ablation of Ni binder and phase transformation from hexagonal α-WC to cubic non-stoichiometric β-WC1−x were found by adjusting the irradiation intensity and shot number, explaining the hardness enhancement of cemented carbides. It is revealed that the densification with defects healing and the lower binder content can significantly enhance the hardness whereas occurrence of the metastable non-stoichiometric phase and limited surface cracking may slightly lower the hardness. The parameter-dependent variation of surface hardening degree is thus attributed to single or multiple contributions from remelting densification, binder removal and phase transformation. It is demonstrated by the HIPIB processing that mechanical properties of WC based cemented carbides may be effectively improved by decreasing the binder phase content and enhancing the bonding strength between carbide grain and binder with less defect density.