Effect of Oxidation Heat Treatments on the Mechanical Behavior of a Si-C-O-Fiber-Reinforced Magnesium Aluminosilicate

Oxidized magnesium aluminosilicate composites reinforced with Si-C-O (Nicalon) fiber have been found to retain their as-received flexural strength. The elastic moduli of the oxidized composites exhibited an increase for samples oxidized at 1000°C and a decrease at higher temperatures. Densification of the matrix may increase the elastic modulus of composites oxidized at 1000°C, whereas cracks in the matrix and at the fiber-matrix interfaces may be responsible for the low elastic moduli of composites oxidized at higher temperatures. The interfacial friction stresses were high at or near the edges and low in the interior of the oxidized samples. As a result, the oxidized composites failed by fiber fracture on the surface, followed by delamination and fiber pullout in the interior.