<italic>In situ</italic> observation of high temperature tensile creep damage and fracture mechanism of 2D C/SiC composites

The fracture morphology of the specimens is observed using a scanning electron microscope， and the failure modes of the 2D C/SiC composites under the action of tensile creep and fracture are investigated and analyzed. The crack extension process of the 2D C/SiC composites under the action of tensile creep is observed using the home-built high-temperature tensile creep tester and the in-situ crack extension observation system. The fracture process and failure mode of 2D C/SiC composites under tensile creep are investigated and studied. The experimental results show that the creep rupture time of 2D C/SiC composite without notch is greater than 8000 s at 1000 ℃/50 MPa， the steady state creep rate is 5.11×10-8-1.36×10-7 s-1. The existence of the notch shortens the steady state creep stage significantly， and the creep time is shortened by about 2000 s， and the steady state creep rate increases to 2.0 × 10-7 s-1. The two stages of decelerated creep and steady state creep are the key features of the tensile creep curves of 2D C/SiC composites at 1000 ℃/50 MPa. Crack expansion is mainly concentrated in the late stage of steady state creep phase， where the carbon fiber will rapidly undergo oxidation reaction in the high temperature environment and micro-cracks sprout in the matrix. When the specimen internal micro-crack saturation will produce macro-cracks， macro-cracks connected to the internal pores of the material to form a coherent expansion path， resulting in the rapid expansion of cracks， crack expansion caused by fiber blocking led to cracks occur many times the deflection of the creep specimen macroscopic fracture is jagged， and there are a large number of fibers pulled out.