Mechanisms of creep crack growth in 1 wt% antimony-copper: Implications for fracture parameters

Abstract

A copper alloy with 1% (by weight) antimony was used as a model material and tested at 400°C to study the mechanisms of creep crack growth. At this temperature, the creep deformation in this material was dominated by secondary and tertiary creep. The expression for estimating C t (a crack tip parameter for creep conditions) in a compact type specimen used for testing was modified to include tertiary creep deformation. Extensive damage characterization was conducted on tested creep crack growth specimens using optical metallography and scanning electron microscopy. The following observations were derived from the test results. The creep crack growth rates correlated with C t only when intense cavitation damage was restricted to a region approximately 1.3 mm in size near the crack tip and no crack branching occurred. It was observed that the average diameter, areal density, and percent of grain boundary area cavitated decreased as function of distance from the crack tip. From these results it is argued that simultaneous nucleation and growth of cavities occur on grain boundary facets during the creep crack growth process. Percent grain boundary area cavitated is proposed as the most reasonable measure of creep damage. The critical amount of damage for crack extension appears to depend on the magnitude of the C t parameter.