The role of tungsten in the Co binder: Effects on WC grain size and hcp-fcc Co in the binder phase

Recent advances in microscopy techniques have made possible the quantitative examination of the Co binder phase in WC-Co cemented carbides [1]. The composition of the binder phase is of interest with respect to applications where fracture toughness and fatigue are particularly important. A previous work has observed that the hcp/fcc ratio can change with fatigue and applied stress [2]. This work is part of a wider study examining the role of Co mean free path, mean WC grain diameter (d(WC)) and composition on the hcp-fcc content on the Co binder phase extracted from a wide range of WC-Co samples with an average d(WC) of 0.6 mu m < d(WC) < 10 mu m and Co content from 6 wt.% to 25 wt.%. This paper aims to study the effect of carbon composition on three 10 wt.% Co grades with target d(WC) 0.8 mu m < d(WC) <6 mu m. The concentration of W in the Co was monitored by examining the binder magnetic saturation (BMS). Samples with a variety of Co M-sat values through the WC-Co pseudo-binary phase field were studied. The effects on grain size, Co distribution, physical properties and hcp content with varying W content were examined. Experimental results show that lower BMS resulting from dissolved tungsten in the binder has a negative exponential correlation with hcp abundance for grades with d(WC)< 1.5 mu m. A significant abundance of hcp was associated with a more diffuse large scale fcc-fcc structure of the binder phase, which has been associated with improved crack deflection [14]. This work belongs to the Special Issue of the International Conference on the Science of Hard Materials (ICSHM10). (C) 2014 Elsevier Ltd. All rights reserved.