EFFECT OF SIC VOLUME FRACTION AND PARTICLE-SIZE ON THE FATIGUE RESISTANCE OF A 2080-AL SICP COMPOSITE/

The effect of SIC volume fraction and particle size on the fatigue beh avior of 2080 Al was investigated. Matrix microstructure in the compos ite and the unreinforced alloy was held relatively constant by the int roduction of a deformation stage prior to aging. It was found that inc reasing volume fraction and decreasing particle size resulted in an in crease in fatigue resistance. Mechanisms responsible for this behavior are described in terms of load transfer from the matrix to the high s tiffness reinforcement, increasing obstacles for dislocation motion in the form of S' precipitates, and the decrease in strain localization with decreasing reinforcement interparticle spacing as a result of red uced particle size. Microplasticity was also observed in the composite , in the form of stress-strain hysteresis loops, and is related to str ess concentrations at the poles of the reinforcement. Finally, interme tallic inclusions in the matrix acted as fatigue crack initiation site s. The effect of inclusion size and location on fatigue life of the co mposites is discussed.