CARBON COATED ALUMINA FIBER GLASS MATRIX COMPOSITES

Carbon coated alumina fiber reinforced borosilicate glass composites were fabricated by slurry infiltration and hot-pressing. For fiber contents of 20 vol.%, composite strengths of 118 and 263 MPa were observed for uncoated and carbon coated composites respectively. Fiber pull-out was observed in fracture surfaces only for carbon coated composites, and pull-out lengths were approximately 30-60 μm. The fiber/matrix interface was studied to characterize the interfacial frictional stress. Direct measurements by indentation were compared with calculated values based on pull-out lengths and fiber strengths. Direct indentation measurements gave interfacial frictional stress values of 100 MPa, which were reduced by as much as 40% after a correction for Poisson's ratio effects. Values calculated from pull-out lengths suggested a value of 63-84 MPa, in good agreement with direct measurements. Elastic modulus and thermal expansion measurements confirmed the debonded character of the carbon coated fiber/matrix interface. © 1989.