Isothermal and Nonisothermal Fatigue Behavior of a Metal Matrix Composite

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Abstract
The isothermal and nonisothermal fatigue resistance of a metal matrix com posite (MMC) consisting of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) matrix reinforced by 33 v/o continuous SiC fibers was investigated. The fibers were nominally oriented parallel to the specimen axis. Isothermal fatigue tests were performed in air at 300 and 550°C. In non isothermal fatigue tests, each load excursion at 300°C or 550°C was preceded by a tem perature excursion from 300 to 550°C at zero load. The MMC had good isothermal fatigue resistance at 300 and 550°C at low cyclic stresses, with fatigue cracks initiating from fiber-matrix interfaces and foil laminations. At high cyclic stresses, stress relaxation in the matrix reduced isothermal composite fatigue resistance at 550°C. Nonisothermal fatigue loading substantially degraded composite fatigue resistance. This degradation was produced by a thermomechanical fatigue damage mechanism associated with the fiber-matrix interfaces.