Thermal stresses in metal matrix composites studied by internal friction

Abstract

Thermal stresses in metal matrix composites (MMC) can induce plastic deformation and damage accumulation in the region close to the reinforcements. In this connection, Al-4% Cu-based MMC reinforced with 10, 20 and 30% Al 2O 3 short fibres were characterized by internal friction (IF) measurements. As a function of the temperature, a maximum of damping has been observed in the composites at ca 150 K during cooling. This maximum is absent in the corresponding unreinforced AlCu alloy. The maximum is attributed to the generation and motion of dislocations produced by high thermal stresses at metal-fibre interfaces. The height of the maximum is found to be an index of the extent of relaxation of thermal stresses by the plastic deformation of the metal matrix. IF measurements have allowed us to identify whether plastic flow in the matrix or damage accumulation at matrix-fibre interfaces take place for different composites.