2001 Volume 42 Issue 7 Pages 1349-1355
The phase stability of molybdenum disilicide (MoSi2, C11b structure) relative to other phases, C40 and C54 phases, in the pseudo-binary systems of MoSi2 and other types of disilicides of transition metals including Cr, V, Nb, Ta and Ti was investigated by establishing the MoSi2–TSi2 (T=Cr, V, Nb, Ta, Ti) pseudo-binary phase diagrams. It was found that V, Nb, Ta and Ti which substitute for Mo in MoSi2 strongly stabilize the C40 phase while Cr only shows a weak C40 structure-stabilizing effect. The phase stability was also discussed on the basis of geometrical change in the three phases when composition varies. Change in lattice parameter of each phase indicated that phase stability of C11b, C40 and C54 structures greatly depend on the relative stacking spacing of the equivalent hexagonal atomic plane for the three structures. Based on the results of phase diagram investigation, the present work attempted to design a C11b/C40 lamellar microstructure. Existence of the equivalent hexagonal stacking atomic plane among C11b, C40 and C54 phases makes it possible to design a coherent C11b/C40 two-phase microstructure. Assuming the equivalent atomic planes in C11b and C40 phases coincide with each other, high lattice coherency between C11b and C40 phases is available in MoSi2–CrSi2 system with a lattice misfit of less than 0.5% and in the other four systems with a misfit of 1.3 to 2.7%. A lamellar microstructure was observed in MoSi2–TaSi2 and MoSi2–NbSi2 systems but no lamellar microstructures were obtained in MoSi2–CrSi2, MoSi2–VSi2 and MoSi2–TiSi2 systems.