Investigation of microstructure and mechanical properties at low and high temperatures of WC-6 wt% Co

The correlations of the microstructure, room temperature hardness and toughness, and high temperature compressive stress and strain of a series of WC-6 wt% Co materials with grain sizes at sub-micrometer ranges (<0.30 mu m) have been investigated. It is found that the average size and size distribution of WC grains play a critical role in both room temperature and high temperature (600 and 800 degrees C) properties. Furthermore, the maximum compressive stresses at 600 and 800 degrees C increase with increasing the room temperature hardness and decreasing grain sizes. However, the fracture strain in compression at 600 and 800 degrees C cannot be predicted from the room temperature toughness. This absence of a relationship is attributed to the facts that the fracture strain of compressive tests at high temperatures is dictated by significant plastic flow of the Co phase, whereas the toughness at room temperature is controlled by crack propagation with little plasticity. In general, small grain sizes (at similar to 0.20 mu m) with or without a bi-modal grain size distribution are beneficial to the maximum compressive stress and fracture strain at 600 and 800 degrees C. In contrast, grain sizes at similar to 0.27 mu m with a bi-modal grain size distribution are good for room temperature toughness, but offer inferior high temperature compressive stresses and fracture stains. Thus, the design of the microstructure at a fixed Co composition depends on the intended applications. (C) 2016 Elsevier Ltd. All rights reserved.