| The research on crack healing behavior of structure ceramics has been a hot field for the past decade. It has been found that Si3N4, Al2O3, SiC, mullite have crack healing ability to a certain degree. One of the reasons for crack healing of ceramic materials is oxidation reactant filling, e.g., silicon oxide filling as a major cause for crack healing in SiC.To improve the toughness of ceramics, SiC particulates or whiskers were used as reinforcements in the composites, e.g. Al2O3/SiC, mullite/SiC, Si3N4/SiC, etc. However, the limited reports about crack healing behavior of Si3N4/SiC whisker composite only concerned with short surface cracks. Moreover, there is little research on effects of crack width or depth on crack healing behavior.In this paper, the optimal temperature of heat treatment for crack healing in Si3N4/SiC whisker composite and the effects of crack dimension on crack healing behavior were investigated.According to the crack healing effect of specimens with 3 Vickers indents after heat treated at 1000,1100,1200,1300 "C for 1 h, it could be inferred that the optimal heat treatment temperature of Si3N4/SiC whisker composite is 1200-1300℃.Cracked specimens with 3,5,15,22 Vickers indents were heat treated at 1300 "C for 1 h using an electric furnace. There was similar crack healing effect on strength for specimens with different number of indents.Specimens with 22 Vickers indents were subjected to three points bending load of 250N for 2 h to extend the crack. Besides, the straight-through crack was introduced into the specimens with 15 Vickers indents by single edge pre-crack beam method.The relationship between bending strength and logarithm of crack area was near linear and parabolic in the original and heat-treated specimens, respectively. The experimental results could be explained by the oxidation diffusion-controlled model and oxidation filling model according oxidation kinetics. |
PDF Full Text Request