The Formation of the Omega Phase in Ti-Nb Alloys.

摘要

The as-quenched and the aged form of the omega phase in Ti-Nb alloys was examined using high resolution dark field electron microscopy and diffraction. The as-quenched omega morphology was shown to be based upon (111) rows of equiaxed particles which are 12-20 A in diameter and spaced 20-22 A apart. After short aging times the (111) row length increased,and eventually the isolated rows were replaced by clusters of rows. With continued aging the clusters increased in size and evolved into an ellipsoidal shape. The as-quenched Ti-18at. pct. Nb alloy exhibited sharp omega reflections and (111) planes of diffuse intensity in reciprocal space As the Nb content of the alloy increased the omega reflections broadened,and in alloys containing 34at. pct. Nb or more,the 0001and 0002omega reflections were shifted toward each other along an (0001) direction. The forbidden (10(-1)0) and (20(-2)0) omega reflections were shown to be real in aged alloys,indicating that the aged form of the omega phase is ordered. (Author)