层状Ti3SiC2陶瓷的组织结构及力学性能

利用热压烧结TiH₂,Si和C粉获得了致密度大于98%的层状Ti₃SiC₂陶瓷。利用压痕法,在不同的载荷下测定了材料的维氏硬度, 发现其硬度值随载荷的增加而降低,在最大载荷30kg时,硬度值为4GPa。压痕对角线没有发现径向裂纹的出现。 这归因于多重能量吸收机制——颗粒的层裂、裂纹的扩展、颗粒的变形等。利用三点弯曲法和单边切口梁法测定了材料的强度和韧性分别为270MPa和6.8MPa·m1/2。Ti₃SiC₂材料的断口表现出明显的层状性质,大颗粒易于发生层裂和穿晶断裂,小颗粒易被拔出。当裂纹沿平行于Ti₃SiC₂基面的方向扩展造成颗粒的层裂,当裂纹沿垂直于基面的方向扩展时,裂纹穿过颗粒的同时,在颗粒内部发生偏转,使裂纹的扩展路径增加。裂纹的扩展路径类似人们根据仿生结构设计的层状复合材料。裂纹在颗粒内的多次偏转、裂纹钉扎以及颗粒的层裂和拔出等是材料韧性提高的主要原因。此外,在室温下得到的荷载-位移曲线,说明Ti₃SiC₂材料不象其它陶瓷材料的脆性断裂,而是具有金属一样的塑性。

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·m1/2, 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.