A comparison between calculated and observed elastically induced precipitate shape transitions in a Cu-2 At. Pct Co alloy

Elastic and interfacial energy calculations have been performed for misfitting spherical-, cuboidal-, octahedral-, and tetrakaidecahal-shaped precipitates in a face-centered cubic (fcc) matrix ac- counting to first order for the difference in elastic constants between precipitate and matrix phases. The energy calculations predict a number of possible precipitate shape transitions with increasing particle size, depending upon the material parameters and anisotropy of the interfacial energy. Predicted shape transitions were compared with experimentally observed transitions of coherent, Co-rich precipitates in a low volume fraction Cu-2 at. pct Co alloy. The predicted octahedron-to-tetrakaidecahedron transition was not observed. Rather, the corners of the octa- hedra were observed to become progressively more rounded with increasing particle size. Pos- sible sources of disagreement between calculations and experiment are discussed. formerly with the Department of Materials Science and Engineering, Carnegie Mellon University.