TEM characterization of invariant line interfaces and structural ledges in a Mo-Si alloy

摘要

Two distinct <1(bar 1)0> lath morphologies of Mo(sub 5)Si(sub 3) precipitates observed in MoSi(sub 2) differ in their cross-sectional shape and lattice orientation. Type I laths exhibit a rectangular cross section, with interfaces parallel to low-index planes, while Type II laths are parallelogram-shaped, with their major interface at 13(degree) to the Type I precipitate. The corresponding orientation relationships differ by a 1.8(degree) rotation around the lath axis. In this study, the difference between the two characteristic morphologies and orientation relationships is shown to be the formation of an invariant line strain for Type II precipitates. On an atomic scale, both interfaces have a terrace and ledge structure but differ in the stacking sequence of interfacial ledges associated with partial dislocations. The structural unit model and the invariant line model predict identical interface geometries which agree closely with the observations.