APPLICATION OF THE INVARIANT LINE MODEL FOR BCC/HCP COUPLES - A CRITERION BASED ON SURFACE VARIATIONS

The problem of the physical meaning of the invariant line, which is generally encountered during precipitation reactions involving b.c.c./h.c.p. couples, is reconsidered. The applicability of various criterions for the selection of a specific invariant line and for the precipitate morphology in these systems is tested in view of the experimental data available. It is shown that energetic considerations are not sufficient to account for the experimental results whereas criterions based on consideration of surface variations are in good agreement with observations.