Homogeneity and flexural properties of SiC/SiC composites prepared by CVI method

Several SiC/SiC composites reinforced with either Nicalon-CG or Hi-Nicalon fibers were fabricated by chemical vapor infiltration (CVI) process. Two kinds of reactant gases, methyltrichlorosilane (MTS) and ethyltrichlorosilane (ETS), were used as the source gases for SiC matrix. The space homogeneities of the composites were investigated with statistic density measurements and microstructure examinations. The flexural properties were studied using three-point bending tests. About 35 bending tests were conducted for each composite and the effects of the space homogeneity were studied using the Weibull distribution analysis. High-density composite with the highest individual bending specimen density of 2.85 Mg/m3 was obtained. Hi-Nicalon/SiC composite prepared with MTS showed a Weibull modulus of 7.43 with average fracture strength of 665 MPa. Similar situation was observed for the Hi-Nicalon/SiC composite prepared with ETS. The Nicalon-CG/SiC composite showed lower fracture strengths with much lower Weibull modulus of 2.08.