Фазовая диаграмма системы Al-Cr

К оглавлению: Другие диаграммы (Others phase diargams)

Al-Cr (Aluminum-Chromium) J.L. Murray The assessed phase diagram for the Al-Cr system is based on the work of [63Kos] , with review of the data of [81Bro] and [81Ten]. The assessed peritectic temperature is based on the data of [60Zol]. The assessed Al-rich phase boundaries were constructed by thermodynamic calculation. The optimized Gibbs energies agree well with both the phase diagram and thermodynamic data, so the phase boundaries can be reliably extrapolated to lower or higher temperatures. [81Bro] and [81Ten] showed that alloys previously identified as single-phase ( Cr) are two-phase (Cr) + X admixtures. This is not surprising, because [63Kos] reported a very narrow and nearly vertical two-phase field between (Cr) and AlCr2. [81Bro] and [81Ten] constructed the phase boundaries reproduced in the assessed diagram showing X as an additional stable equilibrium phase. It is also possible that at stable equilibrium, the two-phase (Cr) + AlCr2 field is broad and that X precipitates as a metastable phase in the supersaturated (Cr) solution. An analogy would be w phase precipitation in supersaturated bcc (bTi) alloys that at equilibrium are in the cph (aTi) + bcc (bTi) two-phase field. Depending on alloy composition, superheat, and cooling rate, rapid solidification of Al-rich alloys can result in suppression of peritectic reactions, in formation of supersaturated solid solution, or in formation of the metastable icosahedral i phase. In alloys quenched at cooling rates on the order of 500 K/s from either the single-phase liquid field or from a two-phase L + compound phase field, equilibrium peritectic reactions are suppressed or delayed. Thus, Al11Cr2 and/ or Al4Cr may be found in alloys that at equilibrium would contain only (Al) + Al7Cr [66Ess, 70Var, 70Ven1, 70Ven2, 71Ich]. The solubility extension in Al-Cr is one of the greatest obtainable in Al- transition metal systems; it is about 3 at.% Cr in melt-spun ribbons [86Ben], but can be as much as 5 to 6 at.% Cr in samples solidified at the highest rates, e.g., by the gun technique. Beyond the maximum supersaturation, primary Al7Cr and decomposition in the solid by discontinuous precipitation leading to two coexisting solid solutions and an intermetallic have been observed [65Bur, 76War, 86Ben]. Other studies of supersaturation as a function of cooling rate, supercooling, and composition include [52Fal], [68Bur], [70Ble], and [71Ich]. Icosahedral i phase has been reported in as-melt spun ribbons containing 8 to 13 at.% Cr [85Dun, 86Ben, 88Zha]; i phase of approximate composition 20 at.% Cr has also been reported to occur as a result of solid-state decomposition of the amorphous phase in coevaporated films [86Lil]. According to [86Ben, 88Zha], i phase is replaced by Al7Cr after annealing above 350 C; according to [ 85Dun], it is replaced by Al11Cr2. 37Bra: A.J. Bradley and S.S. Lu, J. Inst. Met., 60, 319-337 (1937). 52Fal: G. Falkenhagen and W. Hofmann, Z. Metallkd., 43, 69-81 (1952). 60Zol: H. Zoller, Schweiz. Arch. Angew. Wiss. Tech., 26, 478-491 (1960). 63Kos: W. Koster, E. Wachtel, and K. Grube, Z. Metallkd., 54, 393-401 (1963). 65Bur: L.M. Burov and A.A. Yakunin, Zh. Fiz. Khim., 39(8), 1927-1931 (1965) in Russian; TR: Russ. J. Phys. Chem., 39(8), 1022-1025 (1965). 65Ess: P. Esslinger, Z. Metallkd., 57, 12-19 (1966). 68Bur: L.M. Burov and A.A. Yakunin, Zh. Fiz. Khim., 42(4), 1028-1029 (1968) in Russian; TR: Russ. J. Phys. Chem., 42(4) 540-541 (1968). 70Ble: J. Bletry, J. Phys. Chem. Solids, 31, 1263-1272 (1970). 70Var: N.I. Varich and R.B. Lyukevich, Russ. Metall., (4), 58-60 (1970). 70Ven1: R.D. Vengrenovich and V.I. Psarev, Russ. Metall., (5), 138-142 (1970). 70Ven2: R.D. Vengrenovich and V.I. Psarev, Phys. Met. Metallogr. (USSR), 29, 93-99 (1970). 71Ich: R. Ichikawa, T. Ohashi, and T. Ikeda, J. Jpn. Inst. Met., 34, 929-935 ( 1971); see also Trans. Jpn. Inst. Met., 12, 280-284 (1971). 75Ohn: T. Ohnishi, Y. Nakatani, and K. Okabayashi, Bull. Univ. Osaka Prefect., 24, 183-191 (1975). 76War: H. Warlimont, W. Zingg, and P. Furrer, Mater. Sci. Eng., 23, 101-105 ( 1976). 77Vis: J.W. Visser, Acta Crystallogr., B33, 316 (1977). 81Bro: F.J.A. Den Broeder, G. Van Tenderloo, S. Amelinckx, J. Hornstra, R. DeRidder, J. Van Landuyt, and J.J. Van Daal, Phys. Status Solidi (a), 67, 233- 248 (1981). 81Ten: G. Van Tenderloo, F.J.A. Den Broeder, S. Amelinckx, R. DeRidder, J. Van Landuyt, and J.J. Van Daal, Phys. Status Solidi (a), 67, 217-232 (1981). 85Dun: R.A. Dunlap and K. Dini, Can. J. Phys., 1267-1269 (1985). 86Ben: L. Bendersky, R.J. Schaefer, F.S. Biancaniello, and D. Shechtman, J. Mater. Sci., 21, 1889-1896 (1986). 86Lil: D.A. Lilienfeld, M. Nastasi, H.H. Johnson, D.G. Ast, and J.W. Mayer, J. Mater. Res., 1, 237-242 (1986). 88Zha: H. Zhang, D.H. Wang, and K.H. Kuo, Phys. Rev. B, 37, 6220-6225 (1988). Submitted to the APD Program. Complete evaluation contains 8 figures, 5 tables, and 43 references. Special Points of the Al-Cr System