THE ROLE OF STRUCTURAL LEDGES AT PHASE BOUNDARIES .3. FCC-BCC INTERFACES IN KURDJUMOV-SACHS ORIENTATION

The ledge mode of misfit accommodation is extended to {111} f.c.c. par allel-to {110} b.c.c. interfaces with the Kurdjumov-Sachs (KS) orienta tion relationship. As with the Nishiyama-Wassermann (NW) relationship the geometric quantities are uniquely related by the misfit ratio r of atomic diameters. A rigid lattice analysis shows that the driving for ces for a KS orientation relationship are significantly larger than th ose for the NW-x and even more so than those for the NW-y relationship s. The rigid analysis also predicts that the terrace width which satis fies the periodicity conditions for a stepped interface are well withi n the terrace widths which allow significant energy gains. The models developed for the NW analysis are modified for KS configurations and e mployed to sum energies for the terrace patches, tilt misfit dislocati ons and the riser interface energy. Comparing this energy with that of a planar interphase boundary comprised of only misfit compensating di slocations shows that a stepped interphase boundary is energetically f avored at r values near and greater than r(KS) but less than r(NW-y).