Performance gradient distribution of (Ti,W)C cermet by skin effects of high-frequency spark plasma sintering

A (Ti,W)C cermet with graded properties was prepared using high-frequency spark plasma sintering (HF-SPS). The effects of the sintering process on the microstructure and mechanical properties of the prepared cermet material were studied, and the densification behavior of the material was analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Owing to the skin effect and pulse current discharge in HF-SPS, the experimental results showed different sintering effects, as indicated by the current density difference between the surface layer and bulk. On one hand, the surface-layer grains were larger, the metal phase was concentrated, and the hardness was high; however, the bulk grains were smaller, the metal phase was uniformly distributed, and the strength and toughness were high, causing the material to account for the higher hardness of the surface layer and the bulk strength and toughness. The skin effect of pulse direct current was key for the performance gradient distribution, whereas increases in the current density and sintering temperature decreased the skin effect. In general, the Joule heat effect was more significant, leading to abnormal grain growth.