MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Ti₃SiC₂ CERAMICS

Dense layered material Ti₃SiC₂ was fabricated by hot-pressed TiH₂, Si and C powders. The Vickers indentations were made at loads of 0.5~30 kg to measure hardness. The results show that the hardness decreased with the increasing of loads. At the load of 30 kg, the hardness value was stable to 4 GPa. Most importantly, no indentation cracks were observed even at 30 kg load. This property should be due to the multiply energy absorbing-grain delamination, crack deflection, grain deformation, et al. The flexural strength and fracture toughness were 270 MPa and 6.8 MPa·m^1/2, respectively, by means of the three point bending test and single edge notched beam test. The fracture surfaces show the obvious layered nature in the observation of scanning electron microscope (SEM). Larger Ti₃SiC₂ grains are prone to delamination and intragranular fracture, but smaller grains are more easily pulled out. Crack propagation is parallel to the basal plane of Ti₃SiC₂ resulting in the grain delamination. Crack propagation will be deflected inner of grains when it is normal to the basal plane, and the crack propagation path was prolonged and the spreading energy was dissipated. The morphology of the crack propagation path is similar to that of synthetic multilayered composites. The main mechanisms of improving fracture toughness are crack deflection, crack pinning, grain pull out, and grain delamination. Moreover, the authors found the samples for the single edge notched beam (SENB) test without breaking pieces after unloading. The feature indicates that Ti₃SiC₂ is a damage tolerance material and has plastic property like as the ductile metals at the room temperature.