Contributed by Carl Boehlert of Alfred University
John Bingert of Los Alamos National Laboratory
OIM data obtained from a longitudinal section of a Ti-26Al-27Nb(at.%) rod produced by local induction-float-zone melting (IFZM). The IFZM process was intended to grow a single crystal of the lower-temperature orthorhombic phase from the parent body-centered cubic (BCC) structure, which formed upon solidification. The rod did not consist of a single crystal of the orthorhombic phase (O), but rather fine O laths precipitated from the parent BCC with some retained BCC phase present.
The map is colored to highlight the 6 resolvable O variants. The horizontal direction in the map and pole figures corresponds to the longitudinal rod direction. Using this map, the areal fractions of the variants were measured and the values ranged between 0.13-0.20. Thus no variant dominated the nucleation and/or growth events during the very slow transformation (i.e. the IFZM process lasted 5 days) from the parent BCC. This indicates the difficulty in growing large O single crystals.
"Microstructure, tensile, and creep behavior of O+BCCTi2AlNb alloys processed using induction- float-zone melting" C.J. Boehlert and J.F. Bingert, Journal of Materials Processing Technology, 117, 400-408 (2001).