Influence of coarse TiCN content on the morphology and mechanical properties of ultrafine TiCN-based cermets

In this study, TiCN-based cermets with duel grain structure were prepared by long time milling of the microsized raw powders. The effects of coarse TiCN content on the microstructure and mechanical properties of ultrafine TiCN-based cermets were investigated. Results showed that the addition of coarse TiCN powders in ultrafine composite mixture could increase the compact density, but also resulted in increased closed pores in cermets. Coarse TiCN particles would accelerate the dissolution and precipitation reaction of the fine powders, forming more bright cores or thick inner rims on the fine TiCN grains. Grain size of the cermets gradually increased with higher coarse TiCN content. When the coarse content was more than 30%, abnormal growth of TiCN grains occurred via the coalescence of TiCN particles. Mechanical properties of the cermets were firstly increased within 10 or 20% coarse TiCN, then decreased sharply with further increasing the coarse powders. Highest strength (1940 MPa) and toughness (11.67 MPa·m1/2) were achieved with 10% coarse TiCN. Coarse ceramic grains with thick rims exhibit brittleness, deteriorating the final properties of the cermets.