Microstructure and Mechanical Properties of Ultra-Fine WC-10Co Cemented Carbides with Cr3C2 and NbC: Experimental Investigation Supported by Thermodynamic Calculation

In this work, Cr3C2 and NbC grain-growth inhibitors are added simultaneously to control the grain growth of ultrafine WC-10 wt.% Co cemented carbides. Several ultra-fine WC-10 wt.% Co cemented carbides with various contents of Cr and Nb are designed and fabricated by a hybrid approach of thermodynamic calculations and key experiments. According to thermodynamic calculation, the maximum additions of Cr and Nb are 0.65 and 0.4 wt.%, respectively, in order to avoid the appearance of detrimental phases M7C3 and (Nb,W)C. The present experiments reveal that the density, transverse rupture strength, hardness and fracture toughness of WC-10 wt.% Co cemented carbides are improved significantly with the addition of Cr3C2 and NbC below the maximum solubility in the binder phase. However, excessive Cr3C2 and NbC lead to the formation of M7C3 as well as coarse (Nb,W)C grains, which deteriorates the mechanical properties. The correlation between composition, microstructure, and mechanical properties is discussed from experimental and phase assemblage points of view.