高温热处理对国产KD-SA型SiC纤维组成结构与力学性能的影响

Effect of Heat Treatment on Composition,Microstructure and Mechanical Property of Domestic KD-SA SiC Fibers

高结晶近化学计量比SA型SiC纤维以其优异的耐温性,在新一代航空发动机和高超声速飞行器等领域得到广泛应用。对比国产第二代SiC纤维(F-Ⅱ),本工作研究了第三代SA型SiC纤维(F-Ⅲ)高温热处理前后的微观结构演变和拉伸强度及断裂行为。结果表明, F-Ⅲ纤维主要由β-SiC晶粒(~200 nm)和少量游离碳组成, F-Ⅱ纤维则由β-SiC晶粒(~5 nm)、游离碳和SiCxOy无定形相组成。与F-Ⅱ纤维相比, F-Ⅲ纤维具有更大的晶粒尺寸与孔隙,室温下的拉伸强度较低。但经1800℃热处理后, F-Ⅲ纤维结构和强度基本保持不变,而F-Ⅱ纤维由于发生了SiC_(x)O_(y)相的分解和晶粒长大,强度明显降低。SA型SiC纤维的耐高温性能优异,可归因于纤维组成结构上的高结晶、大晶粒和低碳氧含量。

Polycrystalline near stoichiometric SA type SiC fibers have a prospective application in the fields of the new generation aero engine and hypersonic vehicles due to their excellent temperature resistance.In this work,microstructure evolution,tensile strength as well as fracture behavior of the second-generation domestic F-II SiC and the third-generation SA(F-III)SiC fibers before and after heat treatment were studied.The results showed that F-III fiber was mainly composed ofβ-SiC grains(~200 nm)and a small amount of free carbon,while F-II fiber was composed ofβ-SiC grains(~5 nm),free carbon and amorphous SiC_(x)O_(y) phase.Compared with the F-II fiber,the F-III fiber showed lower tensile strength at room temperature,owing to their larger grain size and pores.However,after heat treatment at 1800℃,the structure and strength of F-III fiber remained almost unchanged,while the strength of F-II fiber decreased sharply due to decomposition of SiC_(x)O_(y) phase and grain growth.The excellent high temperature resistance of SA type fiber could be attributed to high crystallinity,large grain size,low carbon and oxygen content in microstructure and composition.