4-POINT BENDING OF A MOLYBDENUM-FREE TITANIUM CARBONITRIDE CERMET

Hard-phase powders of Ti(C0.3N0.7) + TaC + WC were mixed and compacted using a uniaxial press at 180 MPa and then heat treated in nitrogen p artial pressure at 1800 degrees 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 s intered at 1550 degrees C, 1600 degrees C, 1650 degrees C for 0.5 h up to 4 h. The sintered cermet samples were tested under four-point bend ing at room temperature and at elevated temperatures of between 800 de grees C to 1000 degrees C. It was found that the best sintering condit ions for the cermet under study was 1550 degrees C for 2 h, further in crease in sintering temperature and/or time bringing about a decrease in flexural strength. The four-point bending strength (modulus of rupt ure) of this cermet is 594.6 MPa at room temperature and 573.6 MPa at 1000 degrees C. After a dip from the room temperature, the bending str ength increases with testing temperature from 800 degrees C to 1000 de grees C. At room temperature the fracture surface shows mainly a trans -granular feature whilst at elevated temperature the fracture is mainl y of inter-granular nature.