Nucleation and growth instabilities of precipitates induced under irradiation

Abstract The effect of ageing and of high-temperature neutron irradiation on the microstructure in titanium-containing austenitic steels was investigated by transmission electron microscopy. During irradiation at 840 K, two completely new precipitate morphologies were created: firstly, star-shaped precipitates with long thin protrusions into the six 〈100〉 directions and, secondly, nail-shaped precipitates which were nucleated in a crystal orientation different from the common cube-on-cube precipitate—matrix orientation relationship and which break the basic twofold crystal symmetry by their singular shape. Microdiffraction analysis showed that the two new precipitate variants are MC-type carbides. Common to both is one-dimensional growth along 〈100〉 directions. In aged specimens a high resistance against equilibration of MC precipitate shapes was observed. Nucleation and growth anomalies are discussed.