Ps. Frankwicz et Jh. Perepezko, PHASE-STABILITY OF MOSI2 IN THE C11(B) AND C40 STRUCTURES AT HIGH-TEMPERATURES, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 246(1-2), 1998, pp. 199-206
The phase equilibrium of molybdenum disilicide in are melt and plasma
spray processed samples has been investigated in order to define the p
hase relationship between alpha-MoSi2 (C11(b) structure) and beta-MoSi
2 (C40 structure) phases. The analysis of solidification microstructur
es and X-ray diffraction patterns of are melt processed MoSi2-based al
loys indicates solidification takes place by primary alpha-MoSi2. Reta
ined Rho-MoSi2 phase in plasma spray processed powders exhibits an irr
eversible transformation to alpha-MoSi2, at T approximate to 1110 K, w
ith an exothermic enthalpy of transformation of Delta Hbeta-alpha = 0.
9 +/- 0.1 kJ g-atom(-1) atom during heating from room temperature at 0
.5 K s(-1). The Mo-Si and MoSi2-TiSi2 equilibria phase diagrams have b
een used to derive the upper bound of the metastable melting point of
the beta-MoSi2 phase T-m(beta) approximate to 2299 K, which is below t
he experimentally measured melting point of MoSi2 (T-m = 2303 K). The
phase stability analysis indicates that the beta-MoSi2 phase is a meta
stable phase relative to alpha-MoSi2 at temperatures below the congrue
nt melting point. (C) 1998 Elsevier Science S.A. All rights reserved.