Effects and influence of Y2O3 addition on the microstructure and mechanical properties of binderless tungsten carbide fabricated by spark plasma sintering

Abstract

The chemical activation pretreatment was executed on the WC powder and the WC-Y2O3 composite powder was prepared by the chemical liquid mixing method. The binderless tungsten carbide with varied amounts of Y2O3 (0–4wt%) was produced by spark plasma sintering (SPS) at 1400–1700°C with an applied pressure of 45MPa. The effects of Y2O3 addition and the sintering temperature on the densification, microstructure and mechanical properties of the sintered sample were investigated. The results demonstrated that the addition of Y2O3 was of significant influence on the sintering densification and mechanical properties of the binderless tungsten carbide. When the sintering temperature and sintering pressure were 1600°C and 45MPa respectively, the Vickers hardness and the fracture toughness of the WC-1wt% Y2O3 increased by 46% and 40% compared to the pure WC binderless tungsten carbide. As the Y2O3 content increased further, the fracture toughness displayed a slight increase, whereas the Vickers hardness decreased highly. The sub carbide phase W2C was observed when the Y2O3 content exceeded 2wt% and increased with the increase of the Y2O3 content. Abnormal grain growth occurred when the Y2O3 content was 4wt%. As the sintering temperature increased from 1400°C to 1600°C, the relative density and mechanical properties of the WC-1wt% Y2O3 increased remarkably. When the sintering temperature was 1600°C, the binderless tungsten carbide WC-1wt%Y2O3 was obtained with the relative density of 99.7%, the Vickers hardness value of 2420kg·mm−2 and the fracture toughness of 10.5MPa·m1/2. When the sintering temperature was further increased to 1700°C, the sub-carbide W2C was formed and the fracture toughness apparently decreased.