Effect of NbC content on microstructure and mechanical properties of W-NbC composites

Abstract

W-NbC composites with up to 40vol% NbC were prepared by hot-pressing at 2200°C under a pressure of 30MPa. The effects of NbC content on the microstructure and mechanical properties of the W-NbC composites were investigated. A (Nb, W)C solid solution was detected at the NbC/W interface, and W2C phase formed in the composites. A core/shell structure was found in the composites as the NbC content is 10–20vol%, attributed to the undissolved NbC and the newly formed (Nb, W)C solid solution. A (W, Nb) solid solution precipitated from the supersaturated (Nb, W)C1−x as rods or spheres as the NbC content is 30–40vol%. The crystallographic orientation relationship at (W, Nb) and (Nb, W)C interfaces were detected: (110) (W,Nb)∥(2‾00) (Nb, W)C, [1‾11] (W,Nb)∥[001] (Nb, W)C. The flexural strength and fracture toughness of composites first increased and then decreased with NbC content increasing, reaching maximum values of 1050MPa and 13.6MPa·m1/2, respectively, at a NbC content of 20vol%. The strengthening mechanisms of composites are grain refining strengthening and solid solution strengthening. Nevertheless, NbC particle clusters, defects within the NbC particles and (W, Nb)ss precipitates in (Nb, W)C1−x decrease the strength and toughness of composites.