Degradation of strength properties and its fracture behaviour of TiB2-TiC-based composite ceramic cutting tool materials at the high temperature

• Composite containing SiC has room-temperature strength of 800 MPa and retained 75% at 900 °C.
• SiC additive makes a greater contribution to high-temperature strength of composite than MoSi2.
• Composite without SiC exhibits plastic deformation and its strength degrades quickly at 900 °C.
• Composite containing SiC fails almost without any plastic deformation, and its strength degradation velocity is delayed.
• The improved high-temperature strength is ascribed to the pinning of sliding grain boundary rather than grain refinement.

Strength retention is important for tool materials at high temperature because cutting temperature in machining is ranged from room temperature to 1000 °C. A study examining the strength properties and fracture behaviour of TiB2-TiC-based composite ceramic cutting tool materials is presented at different temperatures. MoSi2 and SiC additives are considered to investigate their effects on the density, microstructure, strength and failure mechanism of composites. It is found that the addition of SiC contributed more to the high-temperature strength of composites than MoSi2, but it did not improve the room-temperature strength, despite grain refinement. The TBAVS8 composite has a flexural strength of 800 MPa at room temperature and can retain 75% at 900 °C. At room temperature, the fracture behaviour of composites was dominated by the strong bonding of the Ni binder phase. At high temperatures, the softer Ni binder phase was pinned, and its sliding was inhibited by SiC particles, which decelerated the strength degradation.