Four-point bending of a molybdenum-free titanium carbonitride cermer

Hard-phase powders of Ti(C_0.3N_0.7) + TaC + WC were mixed and compacted using a uniaxial press at 180 MPa and then heat treated in nitrogen partial pressure at 1800°C for 12 h to undergo a pre-sintering solid-solution treatment. The treated compacts were pulverized using a planetary ball mill, mixed with metallic binders Ni and Co and then sintered at 1550°C, 1600°C, 1650°C for 0.5 h up to 4 h. The sintered cermet samples were tested under four-point bending at room temperature and at elevated temperatures of between 800°C to 1000°C. It was found that the best sintering conditions for the cermet under study was 1550°C for 2 h, further increase in sintering temperature and/or time bringing about a decrease in flexural strength. The four-point bending strength (modulus of rupture) of this cermet is 594.6 MPa at room temperature and 573.6 MPa at 1000°C. After a dip from the room temperature, the bending strength increases with testing temperature from 800°C to 1000°C. At room temperature the fracture surface shows mainly a trans-granular feature whilst at elevated temperature the fracture is mainly of inter-granular nature.