Ultrafine binderless WC-based cemented carbides with varied amounts of AlN nano-powder fabricated by spark plasma sintering

Abstract

Ultrafine binderless WC-based cemented carbides with varied amounts of AlN nano-powder (0–16wt.%) were fabricated by spark plasma sintering at 1600°C under a pressure of 50MPa with the assistance of VC and TaC as WC grain growth inhibitors. The densification behavior, phase composition, microstructure and mechanical properties of the as-prepared samples were investigated. During sintering, rapid sample shrinkage started at about 1050°C and ended at about 1550°C. X-ray diffraction analysis revealed that an appropriate addition amount of AlN nano-powder would be of help to limit the formation of W2C phase and promote the formation of solid solution phase of (V,W)C2 during sintering. As the added fraction of AlN nano-powder increased, the relative density of the samples initially increased and then decreased, reaching its maximum of about 99.6% when 3–5wt.% AlN nano-powder was added. Scanning electron microscopy examination indicated that the average size of WC grains in the samples was about 0.7μm and with increasing added fraction of AlN nano-powder, the abnormal growth of WC grains was suppressed and their sizes were somewhat reduced. Both the sample hardness and flexural strength first increased and then decreased with increasing added fraction of AlN nano-powder, reaching the maximum hardness of about 2400 HV10 with 3wt.% AlN nano-powder and maximum flexural strength of about 1250MPa with 5wt.% AlN nano-powder, respectively. However, the fracture toughness slightly decreased from 7.5 to 6.3MPa·m1/2 with increasing added fraction of AlN nano-powder.