Research On High Temperature Stability Of Mechanical Properties Of SiC/SiC Composites

Due to its high specific modulus,high specific strength and high temperature resistance,SiC/SiC composite has become an important candidate material for the hot components of aero engine of the new generation.However,the composition,structure and properties of SiC/SiC composites will change under the high temperature environment for a long time.Therefore,exploring the high temperature stability of SiC/SiC materials under high temperature and anaerobic environment will provide important references for further research on the performance changes of aero-engine under the actual combustion environment.X ray diffractometer(XRD),scanning electron microscopy(SEM)with energy spectrum analyzer(EDS)were used to observe and analyze the crystal structure,surface and tensile fracture of fiber and composite before and after high temperature treatment.In this paper,SiC/SiC composites were treated at 1200~1500℃ for 50 hours under argon protection environment.Then the tensile strength of the fibers before and after high temperature treatment were measured by a self-built single fiber tensile test system,and the distribution of fiber strength was obtained.The tensile strength of small SiC/SiC composites were measured by Electronic Tension Microscope(ETM).And the stress-strain response curves were obtained.The changes of cracks under different tensile stress levels were observed and counted by a self-built ceramic matrix composite(CMCs)crack real-time observation system.Based on the shear lag model,the relationship between the theoretical values of the slope of the initial segement,the slope,the intercept of the second linear segment of the axial tensile stress-strain curve and the mesoscopic parameters was established.The micro-mechanical parameters were identified by comparing the the theoretical values with the experimental values.Finally,a one-dimensional strength model of CMCs was established to describe the mesoscopic damage modes of unidirectional CMCs during axial tension,which includes matrix cracking,interfacial debonding,slipping and fiber failure.The component parameters of the materials which were treated at different temperatures were taken into the strength model.And the stress-strain curves and tensile strength of the materials were predicted.The predicted results fit well with the experimental results,which is proved that the strength model in this paper is reasonable.