Effect of Crack Length on Strength Recovery of Silicon-Carbide-Whisker-Reinforced Silicon Nitride Upon Healing Treatment

A silicon carbide whisker (SiCw) reinforced silicon nitride (Si3N4) composite ceramic was selected to study the crack-healing performance. Pre-cracks of various length were introduced on the tensile side of specimens by Vickers hardness tester. The crack-healing performance as a function of heating temperature and crack dimension, as well as the crack-healing mechanism were investigated. The optimal heat treatment temperature for crack-healing of Si3N4/SiCw is 1200–1300 °C. The treatment allows complete healing of a crack of 200 μm after heat treated at 1300 °C, and achievement of a substantial strength recovery for pre-cracked specimens even with much longer cracks (1200 μm). Crack closure and strength recovery of the pre-cracked specimen were considered to be triggered by the creation of SiO2, liquid aluminosilicate glass and silicon yttrium oxide by the oxidation reaction as filling mechanism during heat treatment.

Influence of the crack area on the crack-healing performance of silicon carbide whisker reinforced silicon nitride composite

The crack healing properties of Si3N4 composite ceramic reinforced by SiC whiskers (Si3N4/SiCw) was studied. Six kinds of pre-cracks were introduced on the center of the tensile side of the specimens, and the relationship between the crack area and crack healing properties was studied. The results show that the healing effect of strength recovery is similar with that of smooth specimens for pre-cracked specimens with crack depth less than 60 μm. As for the propagated crack and the central through crack, the strength recovery rapidly decreases due to the increase of crack depth. It could be concluded that it is difficult to heal pre-cracked specimens with the crack depth over 90 μm. The main reason is considered to be that the melted glass phase blocked in the surface, and prevented the oxidation reaction in the inner of crack.

Wear Behavior of Graphene-Reinforced Alumina–Silicon Carbide Whisker Nanocomposite

In the present work, the tribological properties of graphene-reinforced Al2O3-SiCw ceramic nanocomposites fabricated by spark plasma sintering were studied against alumina ball. Compared with pure ceramic, the wear resistance of these nanocomposites was approximately two times higher regardless of the applied load. It was confirmed by Raman spectroscopy that the main factor for the improvement of the wear resistance of the Al2O3-SiCw/Graphene materials was related to the formation of protecting tribolayer on worn surfaces, which leads to enough lubrication to reduce both the friction coefficient, and wear rate.