Microstructure and tribological properties of reactive hot pressed TiN-TiB2 composites incorporated with or without MoSi2 from room temperature to 800 °C

TiN-TiB2 composites incorporated with or without MoSi2 have been prepared by the reactive hot pressing method, using Ti, BN or MoSi2 powders as the starting materials. The influence of MoSi2 addition on tribological properties of TiN-TiB2 composites have been evaluated by using a ball-on-disk friction and wear tester in sliding against alumina ball from room temperature to 800 °C. The wear performance depends mainly upon temperature as well as the applied load. At room temperature and 10 N load, the TiN-TiB2 ceramic has a wear rate of 1.6×10-6 mm3 N-1 m-1, however, the TiN-TiB2-MoSi2 composite exhibits a wear rate of 1.5×10-4 mm3 N-1 m-1 under identical wear condition. At room temperature, the material removal of composites results from brittle fracture and abrasive wear during wear tests. The addition of MoSi2 can improve the oxidation resistance of TiN-TiB2 ceramic at high temperatures as it oxidizes to produce a protective SiO2 layer, which forms an effective barrier layer to restrain from further oxidation. At 800 °C and 10 N load, the wear rate of TiN-TiB2-MoSi2 composite is 1.7×10-6 mm3 N-1 m-1, which is only one fifth as much as the TiN-TiB2 ceramic. The low wear rate of TiN-TiB2-MoSi2 composite at 800 °C is attributed to high oxidation resistance, the formation of dense SiO2 scale and self-healing of microcracks.