Observation of fatigue damage process in SiC fiber-reinforced Ti-15-3 composite at high temperature

摘要

Unnotched SiC (SCS-6) fiber-reinforced Ti-15-3 alloy compositeis subjected to a tension-tension fatigue test in a vacuum of2×10 –3 Pa at 293 and 823 K with a frequency of 2 Hz and R=0.1.Direct observation of the damage evolution process during thetest is carried out by scanning electron microscopy (SEM). Testtemperature dependent and independent fatigue damage behaviorsare observed. The early stage fiber fractures observed at thepolished surface are not influenced by the testtemperature;however, matrix crack initiation and propagationbehaviors differ greatly with temperature. The evolution ofinterface wear damage also differs with temperature, becomingmore severe at 823 K, and the interface wear damage zoneincreases with the increase of the number of fatigue cycles. Themacroscopic fatigue damage appears as a modulus reductionassociated with interface sliding, matrix crack propagation,and plastic deformation of the matrix. The deformation zone ofthe composite tested at 823 K spreads more than that at 293 K.The fatigue life of the composite tested at 823K is longer thanthat at 293K. This behavior is related to the difference inspread of the damage zone in the matrix.