The grain growth and boundary evolution of extra-coarse-grained cemented carbides by pressureless sintering of ball-milling-mixed WC with Co at different temperature

Highlights: • Extra coarse WC-10Co powders were mixed by mildly ball milling method. • Extra-coarse-grained WC-10Co cemented carbides were acquired. • Optimal mechanical properties were obtained at sintering temperature of 1450 °C. • Enhanced coarse grains and low energy boundaries are beneficial to properties. • Defective structures generated at low/overtop temperature deteriorate properties. Recently, the fabrication of the extra-coarse-grained WC-Co cemented carbide has aroused wide interests for useful applications as mining bits or shield cutting tools. In this study, extra-coarse-grained WC-10Co cemented carbides were sintered using ball-milling-mixed composite powders, and the inner relationship of mechanical properties with microstructural evolution was investigated systematically. The average particle size of mixed WC-10Co powders decreased rapidly from about 20 μm to 2 μm by extending milling time from 3 h to 12 h, and then kept stable at about 1 μm with increasing ball milling time further. After sintering of the mildly ball-milled WC-10Co composite powders at 1350 °C, the average grain size of WC (d_WC) was measured to be located at about 6.3 μm. With increasing sintering temperature to 1450 °C, the d_WC increased to about 7.3 μm, where transverse rupture strength (TRS) and impact toughness were both enhanced due to the increased density. On the other hand, the coarse grain growth may enhance the grain and boundary strength through precipitation of fine grains and substantial low energy boundaries, although WC contiguity is increased. Here, fracture features of cemented carbide through a tortuous path by cobalt deformation and obstruction of coarse grain contribute to the higher destructive resistance. However, with increasing temperature to 1475 °C, the increase of WC aggregation structure, WC grain boundaries with decreased low energy boundaries and locked micro-pores may contribute to deteriorative mechanical properties.