Effects of Al2O3–ZrO2 content on the densification, microstructure, and mechanical properties of cemented tungsten carbides

Abstract

In order to prepare cobalt-free cemented carbide by liquid phase sintering, various contents of Al2O3–ZrO2 by eutectic ratio were utilized as binders for tungsten carbides. The effects of Al2O3–ZrO2 content on the densification, microstructure, mechanical properties, and interfacial characteristics of these binderless tungsten carbides were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high–resolution transmission electron microscopy, and mechanical properties tests. The fully dense WC toughened by Al2O3–ZrO2 composite powders could be consolidated through spark plasma sintering at 1600 °C. The results indicated that a small amount of eutectic Al2O3–ZrO2 binder phase (up to 3 wt%) would aggregate, increasing the contact chance of WC particles and eventually leading to abnormal growth of WC grains. When the Al2O3–ZrO2 content increases to 6.0 wt%, the abnormal growth of WC particles was inhibited by the pinning effect of the well-distributed second phase. The mean grain size of WC decreased with the increasing amount of Al2O3–ZrO2 content, while the mean grain size of Al2O3–ZrO2 colony increased. The temperature corresponding to the maximum shrinkage rate of densification process decreased with increasing Al2O3–ZrO2 content. In general, with the increase of the eutectic ceramic content, the hardness of the composite decreased and the indentation fracture toughness increased. The toughening mechanisms include crack deflection, crack bridging and t– to m–ZrO2 phase transformation toughening. The WC–Al2O3–ZrO2 composites show maximum toughness of approximately 10.5 MPa m1/2 and hardness value of 22.29 GPa, respectively.