1100℃水氧环境下Mini-SiCf/BN/SiC的基体/界面/纤维一体化氧化机制OA

SiCf/SiC composites exhibit advantages such as high-temperature resistance,oxidation resistance and high strength,making them a"star"candidate material in the field of aerospace thermal protection.Under operational conditions,these materials are subjected to prolonged multiple coupled fields such as heat,water and oxygen,exhibiting complex failure mechanisms and damage evolution patterns.This study investigated the integrated oxidation mechanism of the matrix/interface/fiber in Mini-SiCf/BN/SiC composites under cyclic oxidation at 1100℃in a water-oxygen coupled environment by using multi-scale macro/micro characterization techniques.The results showed that during the initial oxidation stage,an amorphous SiO2 glass layer with relatively smooth morphology formed on the material surface.However,with an increase in crystallinity,localized spallation occurred in the oxide layer,causing the surface roughness to initial decrease and subsequent increase.X-ray microscope results showed that numerous micro-defects were generated within the material after cyclic oxidation,and the number of defects increased by orders of magnitude(about 107 fold).Majority of these micro-defects were mainly distributed on the matrix surface,and the oxidation products played a certain filling role in these defects.The tensile strength showed no significant variation before((328.47±32.84)MPa)and after((343.27±35.71)MPa)cyclic oxidation,indicating continued effectiveness of the synergistic toughening mechanism of"strong matrix-weak interface".These observations indicate that an integrated oxidation protection mechanism involving matrix,interface and fiber exists in the Mini-SiCf/BN/SiC,which is predicated on the filling of defects by SiO2 and borosilicate glass generated by its interface layer and adjacent matrix with fibers in the direction parallel to the fiber axis.Dynamic"outer porous sacrificial layer-middle dense SiO2-inner SiC matrix"is a three-dimensional protective barrier of the matrix in the direction perpendicular to the fiber axis.This dual-protection system substantially alleviates material degradation under cyclic thermal water oxidative conditions.