The crack-healing and strength recovery mechanisms for the new developed Ti(C,N)-TiSi2-WC composite ceramic tool materials with crack-healing ability

Because the ceramic tool life will be reduced due to the crack growth, it is necessary to develop the new ceramic tools with crack-healing ability for improving the ceramic tool life. Ti(C,N)-TiSi2-WC composite ceramic tools were fabricated by vacuum hot pressing sintering technology. The Vickers hardness tester was used to prefabricate cracks with different lengths. The crack-healing abilities of materials were researched by air and vacuum heat treatments. The effects of different healing conditions on crack-healing behaviors were investigated based on the strength recovery and microstructure of crack morphology. The healing conditions included healing temperature, healing time, crack length and healing atmosphere. It could be found that the surface cracks were entirely healed after air heat treatment, but locally healed after vacuum heat treatment. After air heating at 800 °C for 90 min, the restoration ratio of flexural strength of the crack-healed samples returned to 109.02% compared to that of the smooth specimen. The strength of the crack-healed specimen would be fully recovered when the crack length was less than 400 μm. After vacuum heating at 1000 °C for 60 min, the recovery of the flexural strength of the crack-healed samples returned to 49.73%. X-ray diffraction and scanning electron microscope technology were used to analyze compositions and microstructure of crack-healed specimens. In the air atmosphere, the liquid filling of SiO2 and TiO2 and crack closure caused by WSi2 and MoSi2 were confirmed as the crack-healing mechanisms. SiO2 and TiO2 were produced by high temperature oxidation reaction of TiSi2 and WSi2. WiS2 and MoSi2 were new phases formed during sintering and heat treatment, and their formation could be explained by thermodynamically feasible reactions. In the vacuum atmosphere, local filling of the crack with silicide solid solutions such as WSi2, MoSi2 and NiSi was the main crack-healing mechanism.