PHASE-STABILITY OF MOSI2 IN THE C11(B) AND C40 STRUCTURES AT HIGH-TEMPERATURES

Citation
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
Citations number
54
Categorie Soggetti
Material Science
ISSN journal
09215093
Volume
246
Issue
1-2
Year of publication
1998
Pages
199 - 206
Database
ISI
SICI code
0921-5093(1998)246:1-2<199:POMITC>2.0.ZU;2-J
Abstract
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.