Creep Characteristics of Metal Matrix Composites

Abstract

Creep is the slow, plastic deformation of materials at elevated temperatures and a constant applied stress or load. Metals creep faster as the temperature or stress increases. This creep is the consequence of various deformation mechanisms, which in turn are the result of different microstructures. The deformation behavior is influenced, for example, by the presence of solute atoms, intermetallic precipitates, grain sizes, twins in the microstructure, different dislocation densities as a result of deformation processes or different thermal expansions, or dispersoids introduced into the metal matrix by different processes. These dispersoids, in turn, can influence the factors mentioned above which influence creep deformation. Thus, the creep resistance of metals can be altered with reinforcing components. The minimum creep rate is often used as a measure of the creep resistance of metallic materials. It corresponds to the minimum of the first derivative of the creep curve, which is located in the secondary area of this curve. The lower the minimum creep rate, the more resistant is the material against creep. This is usually correct, but not always. This article describes the influence of reinforcing components on the microstructure and thus on the creep properties of metal matrix composites. Examples are given for fiber- and particle-reinforced composites whose reinforcing components are arranged in different concentrations, sizes, and orientations in the composite material and influence the creep resistance of the composite material.