Mechanism of Degradation of Mechanical Properties of Metal Matrix Composite due to Interfacial Reaction

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In order to describe the degradation due to interfacial reaction and coating treatment in mechanical properties of metallic composites, the influence of reaction layer on room and high temperature strength of alumina fiber-reinforced aluminium composite, and mechanical interaction between coating(or reaction)layer and fiber were studied experimentally and theoretically.(A)In alumina/aluminium composite, a metallic compound CuAl_2 was formed by addition of copper element into matrix. This compound fractured in an early stage of deformation, forming crack on fiber surface, which reduced fiber strength. This phenomenon was described in a quantitative manner by calculation of energy release rate of fiber at crack-tip. On the other hand, at high temperatures, the compound behaved plastically, which decreased energy release rate, resulting in high strength of fiber. At very high temperatures, the softening of matrik caused reduction in strength of composite due to increase in critical length.(B)A new calculation method was proposed to describe the strength of fiber with coating layer. With this method, the influence of difference in elastic properties between coating layer and fiber on strength of fiber was well described. This method is useful to design the-coating treatment. The application of this method revealed that the high modulus-type carbon fiber has critical energy release rate of 3 J/m^2 and the high strength-type one 2 J/m^2 This is the first finding in this field.