Creep cavitation in metals

Abstract

This review concisely describes the state-of-the-art of the understanding of cavity, or r-type void, formation during stages I and II (primary and secondary) creep in polycrystalline metals and alloys, particularly at elevated temperatures. These cavities can directly lead to Stage III, or tertiary, creep and the eventual failure of metals. There have been, in the past, a variety of creep fracture reviews that omitted important developments relevant to creep cavitation or are less than balanced in their discussions of conflicting ideas or theories regarding various aspects of cavity nucleation and growth. This concise, comprehensive, review discusses all of the important developments over the past several decades relating to both the nucleation and growth of cavities. The nucleation section discusses the details and limitations of the approaches based on “classic” nucleation theory, slip-induced nucleation as well as grain boundary sliding effects. Growth is discussed starting from the Hull–Rimmer diffusion controlled cavity growth (DCCG) model. This will be followed by refinements to DCCG by others. Next, there will be a discussion of plastic cavity growth and diffusion-plasticity coupling theories. This will be followed by the particularly important development of constrained cavity growth, initially proposed by Dyson, and probably under-appreciated. Other growth effects by grain boundary sliding will also be discussed. All of these mechanisms will be compared with their predictions in terms of creep fracture phenomenology such as the Monkman–Grant relationship. Finally, there will be a discussion of creep crack propagation by cavitation ahead of the crack tip.