용융침투법을 이용한 섬유강화복합소재 제조 시 다양한 탄화규소섬유 적용에 따른 공정적용성에 관한 연구

Abstract

탄화규소(SiC)는 열안정성, 내산화성 등 초고온세라믹 재료로 사용함에 있어 우수한 특성을 가지고 있다. 그러나 단일 세라믹스가 갖는 취성파괴와 신뢰성문제로 인해 산업응용에 많은 제약이 따른다. 이에 따라 단일상의 구조세라믹은 인성향상을 중요하게 여긴다. 탄화규소섬유강화 탄화규소 복합재료는 일반적으로 단일 탄화규소 세라믹재료보다 더 높은 파괴인성을 보이고, 동시에 우수한 탄화규소 고유 특성을 지니고 있다. 섬유 강화 세라믹 복합소재의 제조 방법 중 용융 실리콘 침투법(LSI)은 낮은 제조단가 및 형상화의 용이함 등 많은 장점이 있다. 이에 따라 탄화규소 섬유의 LSI 공정 적용가능성을 확인하기 위하여 결정도와 산소 함량이 다른 세 가지 탄화규소 섬유(Tyranno-SA, LoxM, Tyranno-S)를 이용하여 탄화규소섬유강화 탄화규소 복합소재(SiCf/SiC composites)를 제작했다. LSI공정을 통해 제조된 복합소재는 2% 미만의 기공률로 치밀화 되었지만, 결정도와 산소 함량에 따라 3점 굽힘 강도 값은 큰 차이를 나타냈다. 이는 LSI공정의 높은 온도에 노출 시 비정질구조 SiOC상의 결정화로 인한 섬유의 수축 및 열처리 과정에서 섬유 내에 잔존하는 다량의 산소와 탄소로 구성된 매트릭스의 반응으로 인한 미세구조의 차이로 판단된다. 이는 SEM, XRD 및 TEM 분석을 통해 섬유별 공정온도에서의 변화로 확인하였다.| SiC have excellent properties for use in ultra high temperature ceramic (UHTC) materials because of their heat-stability, oxidation resistance at high temperature. however, they are brittle as monolithic state, resulting in relatively low reliability as structural components and limiting its widespread applications. Therefore the major concern in utilizing ceramics as structural materials is improving toughness. SiCf/SiC composites usually exhibit higher fracture toughness than SiC ceramics. At the same time the excellent intrinsic features of SiC ceramics are retained. Liquid Silicon Infiltration, which is one of the methods of producing fiber reinforced ceramic composites, has many advantages such as low fabrication cost and good shape formability. Consequently, in order to confirm LSI process feasibility of SiC fiber, SiCf/SiC composites were fabricated using three types of SiC fibers (Tyranno-SA, LoxM, Tyranno-S) with different crystallinity and oxygen content. Composites that were fabricated with LSI process were well densified by less than 2% of porosity, but showed an obvious difference in 3-point bending strength according to crystallinity and oxygen content. When composites in LSI process was exposed to a high temperature, crystallization and microstructure change were occurred in amorphous SiOC phase in SiC fiber. Fiber shrinkage also observed during LSI process that caused from reaction in fiber and between fiber and matrix. These were confirmed by with changes of process temperature SEM, XRD and TEM analyses.; SiC have excellent properties for use in ultra high temperature ceramic (UHTC) materials because of their heat-stability, oxidation resistance at high temperature. however, they are brittle as monolithic state, resulting in relatively low reliability as structural components and limiting its widespread applications. Therefore the major concern in utilizing ceramics as structural materials is improving toughness. SiCf/SiC composites usually exhibit higher fracture toughness than SiC ceramics. At the same time the excellent intrinsic features of SiC ceramics are retained. Liquid Silicon Infiltration, which is one of the methods of producing fiber reinforced ceramic composites, has many advantages such as low fabrication cost and good shape formability. Consequently, in order to confirm LSI process feasibility of SiC fiber, SiCf/SiC composites were fabricated using three types of SiC fibers (Tyranno-SA, LoxM, Tyranno-S) with different crystallinity and oxygen content. Composites that were fabricated with LSI process were well densified by less than 2% of porosity, but showed an obvious difference in 3-point bending strength according to crystallinity and oxygen content. When composites in LSI process was exposed to a high temperature, crystallization and microstructure change were occurred in amorphous SiOC phase in SiC fiber. Fiber shrinkage also observed during LSI process that caused from reaction in fiber and between fiber and matrix. These were confirmed by with changes of process temperature SEM, XRD and TEM analyses.