Effect of La₂O₃ additions on microstructure and mechanical properties of Ti (C,N)-WC-Mo₂C-Ni-Co cermets

Abstract

Rare earth elements were considered alternative additives beneficial to the TiCN based cermets, but their effect with high content Mo₂C has not been thoroughly investigated. In this study, Ti(C, N)-WC-Mo₂C-Cr₃C₂-Ni-Co cermets containing 12 wt.% Mo₂C doped with different contents of La₂O₃ were prepared by vacuum hot-press sintering at 1500 °C. Parametrical analysis on La₂O₃ addition (0, 0.5 wt.%, 1.0 wt.%, 1.5 wt.%, and 2.0 wt.%) was conducted, in terms of microstructure and mechanical properties of Ti(C, N) based cermets. Experimental results show that when the content of La₂O₃ increases from 0 to 1.0 wt.%, the ratio of core phase increases while the ratio of brittle rim phase decreases. Nanostructure is formed on the grain boundary of ceramic phase, which effectively inhibits the abnormal growth of rim structures. This can thin the brittle shell, coarsen the core phase, and refine the grains, thus improving its mechanical properties, including hardness and fracture toughness. When the addition amount of La₂O₃ increases from 1.5 wt.% to 2.0 wt.%, it will aggregate to form larger particles of about 100 nm, which sharply reduces its mechanical properties. The optimal La₂O₃ addition is 1.0 wt.%, in which Ti(C,N)-based cermets show the optimal comprehensive mechanical properties: the Vickers hardness and fracture toughness are 16.55 GPa and 6.14 MPa·m^1/2, respectively. This work provides further knowledge about the effect of rare earth on the core-rim structure and mechanical properties of Ti(C,N)-based cermets with high Mo₂C contents.

Keywords

Ti(C,N)-based cermets / earth elements / La₂O₃ / core-rim structure / fracture toughness

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