Surface Modification Of WC-Ni Hard Alloy By High-Intensity Pulsed Ion Beam Irradiation

Irradiation experiments on WC-Ni hard alloy by high-intensity pulsed ion beam (HIPIB) is performed in TEMP-6 apparatus. The effect of HIPIB irradiation on properties of WC-Ni hard alloy was studied with relation to surface morphology, surface roughness, phase structure, composition, microhardness and wear resistance. The mechanism of modification on WC-Ni irradiated by HIPIB was subsequently discussed.The WC-13i hard alloy irradiated by HIPIB was performed at ion current densities of 100-300 A/cm2 up to 10 shots. At 100 A/cm2, remelting and ablation on the surface was weak and a slight surface roughening was observed with increasing the shot number. No new phase could be detected on the surface irradiated at 1 shot, but some cubic phase WC1-x was formed at 10 shots. The new phase formation at 10 shots thus led to a certain decrease in the surface hardness as compared to that of less shot number. At the ion current densities higher than 100 A/cm2, the surface remelting on hard alloy and the ablation of Ni binder was enhanced significantly, leading to formation of a more compact surface layer with low Ni binder content. Simultaneously, the WC phase in the surface layer transformed into cubic WC1-x phase, and the content of the new phase was increased with increasing the shot number. Densification of remelted top layer and selective ablation of Ni phase led to the considerable surface hardening on the irradiated hard alloy, as increasing the shot number. In addition, the surface was apparently roughened at larger shot number. Wear resistance of irradiated WC-13Ni hard alloy was characterized by using a block-on-cylinder type wear test machine under dry friction condition with a normal load of 10 kg and a sliding speed of 0.47 m/s. The specific wear rate of HIPIB irradiated WC-13Ni hard alloy was reduced as increasing shot number. The specific wear rate of original hard alloy sample was 1.2×10-6 mm3/Nm, and the wear rate for the sample irradiated by 5 shots decreased to 44% of the original one, and further down to 30% at 10 shots. The improved wear resistance of WC-13Ni hard alloy is mainly attributed to the surface hardening by HIPIB irradiation.