Characterization of C11(b)/C40 lamellae in a MoSi2-15mol%TaSi2 alloy

The crystallography of the lamellar structure composed of the tetragonal C1 1(b) phase and the hexagonal C40 phase which is similar to the well-known T iAl/Ti3Al lamellae was investigated by means of transmission electron micro scopy in a MoSi2-15mol%TaSi2 pseudo-binary alloy after homogenized at 1400 degreesC for 168 h. It was found that the orientation relationship between C11(b) and C40 phases obeys the coincidence of the equivalent hexagonal ato mic planes for the two phases. Three distinct variants of this orientation relationship were identified by electron diffraction. 1/3 < 2 (1) over bar( 1) over bar0] Dislocations prevail in the C11(b)/C40 interfaces to accommod ate the lattice misfit between the two phases. On the other hand, networks of < 100] and < 110] dislocations dominate the C11(b)/C11(b) boundaries. < 100] and < 110] dislocations are also present within C11(b) variant plates while 1/3 < 2 (1) over bar(1) over bar0] and 1/3 < 2 (1) over bar(1) over b ar3] dislocations are frequently observed in C40 phase. Significance of the 1/3 < 2 (1) over bar(1) over bar3] c-component dislocations for improvemen t of the plasticity of C40 phase has been discussed. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.