Cavity growth mechanism maps

Abstract

Cavity growth and shrinkage are of great technological and scientific interest in many areas of physical metallurgy. Small cavities, of diameter 10 ..mu..m or often much less, occur during creep deformation, during the later stages of sintering and as a result of radiation damage. They may arise as a side effect of ion implantation, or this technique may be used to produce them for experimental purposes. Similarly, quenching has been used to introduce and then study the behaviour of voids. The term ''cavity'' covers a whole spectrum of defects, which may or may not contain gas. There will be a gas pressure which exactly balances the surface tension forces of the gas/solid interface and a cavity containing gas at this pressure is usually said to be an ''equilibrium bubble''. If the cavity contains more gas than this it is an overpressurised bubble and if it contains less it is strictly an underpressurised bubble. The limiting case of an empty cavity is clearly a ''void'' but in practice this term is often applied to any underpressurised bubble. Most cavities are thought to contain at least a small amount of gas, since it is generally agreed that a few gas atoms aremore » necessary for the nucleation of even a ''void''. Other sources of gas within cavities are ion implantation (for example resulting from alpha particle bombardment) and the trapping of air (or other gas) during the closure of porosity in the early stages of sintering. There may also, at elevated temperatures, be a vapour pressure component in the total gas content of the cavities.« less