OMEGA PHASE IN A ZR-25 AT DEGREES TI ALLOY

Dark field electron microscopy showed that the as-quenched ω phase was distributed as equiaxed particles ∼10 Å in diameter in rows along 〈111〉β∥〈0001〉ω with a minimum interparticle spacing of 15 Å. These observations as well as the analysis of selected area diffraction patterns confirmed the suggestion of Silcock et al.(5) and Bagaryatskii et al. (6) that there were four orientations of the as-quenched ω phase. Diffraction studies showed the presence in reciprocal space of {111} planes of diffuse intensity, which were related to the 〈111〉 row morphology. The 101̄0ω and 202̄0ω reflections were shown to result from double diffraction in as-quenched alloys and to be real in aged alloys. A transformation mechanism was suggested in which the bcc structure becomes metastable relative to 〈111〉 longitudinal displacement waves which initiate the b.c.c. → ω transition. © 1969.