PROCESSING AND PERFORMANCE OF CFCCs USING VACUUM ASSISTED RESIN TRANSFER MOLDING AND BLACKGLAS~(TM) PRECERAMIC POLYMER PYROLYSIS

摘要

Vacuum assisted resin transfer molding (VARTM)used in conjunction with preceramic polymer pyrolysis proposesto be a cost effective method to manufacture continuous fiberceramic composites (CFCCs) of complex geometry. Inpreceramic polymer technology, a polymer is used as a startingmaterial, i.e., precursor, and hence conventional polymermanufacturing techniques, like VARTM, can be used tofabricate tubes that upon reinfiltration/pyrolysis cycle yieldceramic matrix composites (CMCs). In this research, four CMCtubes were fabricated using this technique. Total VARTMmanufacturing time averaged 15 minutes for each tube. Thematrix material used was Blackglas~(TM). Two differentceramic fibers were used as reinforcements: Carbon coatedNicalon~(TM) in form of woven fabric, and boron nitridecoated Nextel in form of braided textile. For each fiber/matrixcombination, two VARTM techniques were used. One techniquemold, and the other technique was the use of vacuum onlywithout the injection pressure, where resin flows due to (a)gravity, (b) capillary effects, and (c) vacuum assistance. Eight toten pyrolysis cycles were necessary to reach a convergence byweight. Nicalon~(TM)/Blackglas~(TM) CFCC tubes of goodquality with 2-6% porosity, 44-56% fiber volume fraction, and2.26-2.30 g/cm~3 reached convergence by weight in about tendays. Nextel/Blackglas~(TM) tubes of good quality with 4-5%porosity, 72-75% fiber volume fraction, and 2.28-2.32 g/cm~3converged by weight in eight days. The mechanical performanceof the components was evaluated at room and high temperaturesusing a C-Ring test. Scanning Electron Microscopy(SEM) wasemployed to study the microstructure of the finished partsbefore and after mechanical testing. A comparison betweenparts manufactured by the two VARTH techniques, that is withand without injection pressure; shows that the without injectionpressure technique offers a promising method to produce tubularCMCs in terms of lower manufacturing costs, part uniformity,and enhanced mechanical properties. Boron nitride coatingperforms better at high temperature compared with carbon-coating. Also, a combination of boron nitride coating and atextile braided architecture of fiber perform in the mold provedto enhance the performance of the manufactured CFCCs significantly.