Mechanical behavior of silicon carbide fiber-reinforced strontium aluminosilicate glass-ceramic composites

Unidirectional CVD SiC fiber-reinforced SrO . Al2O3 . 2SiO(2) (SAS) glass-ceramic matrix composites have been fabricated by hot pressing. Both carbon-rich surface coated SCS-6 and uncoated SCS-0 fibers were used as reinforcements. Monoclinic celsian, SrAl2Si2O8, was the only crystalline phase observed in the matrix from X-ray diffraction. During three point flexure testing of composites, a test span to thickness ratio of greater than or equal to 25 was necessary to avoid delamination. Strong and tough SCS-6/SAS composites having a first matrix cracking stress of similar to 300 MPa and an ultimate strength of similar to 825 MPa were fabricated. No chemical reaction between the SCS-6 fibers and the matrix was observed after high temperature processing. The SCS-0/SAS composite, having a fiber volume fraction of 0.24, exhibited a first matrix cracking stress of similar to 231 +/- 20 MPa and ultimate strength of 265 +/- 17 MPa indicating a somewhat limited improvement over the monolithic material. From fiber push-out tests, the fiber/matrix debonding stress (tau(debond)) and frictional sliding stress (tau(friction)) in the SCS-6/SAS system were evaluated to be similar to 6.7 +/- 2.3 and 4.3 +/- 0.6 MPa, respectively, indicating a weak interface. However, for the SCS-0/SAS composite, somewhat higher values of similar to 17.5 +/- 2.7 MPa for tau(debond) and 11.3 +/- 1.6 MPa for tau(friction) respectively, were observed; some of the fibers were strongly bonded to the matrix and could not be pushed out. Examination of fracture surfaces revealed limited short pull-out lengths of SCS-0 fibers. The applicability of theoretical models in predicting the values of first matrix cracking stress and ultimate strength of these composites has been investigated. (C) 1997 Elsevier Science S.A.