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

Abstract

Unidirectional CVD SiC fiber-reinforced SrO·Al 2O 3·2SiO 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, SrAl 2Si 2O 8, 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 ≥25 was necessary to avoid delamination. Strong and tough SCS-6/SAS composites having a first matrix cracking stress of ∼300 MPa and an ultimate strength of ∼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 ∼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 ( τ debond) and frictional sliding stress ( τ friction) in the SCS-6/SAS system were evaluated to be ∼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 ∼17.5±2.7 MPa for τ debond and 11.3±1.6 MPa for τ 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.