Фазовая диаграмма системы Cr-N

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Cr-N (Chromium-Nitrogen) M. Venkatraman and J.P. Neumann The assessed Cr-N phase diagram is a composite based on several investigations [67Sch, 70Mil, 70Sve, 72Mil, 73Kot, 83Ish]. The system is characterized by complete miscibility in the liquid state and the presence of two intermediate phases, Cr2N and CrN, in the solid state. The phase boundaries involving the liquid state are in part speculative; further experimental work is needed to establish them more accurately. The temperature (1640 C) and composition (13.4 at.% H) of the eutectic reaction L = (Cr) + Cr2N are from [70Sve]. The uncertainty of these values is estimated to be с30 C and с1 at.% N, respectively. The two liquidus points at 1700 C on both sides of the eutectic are based on the solubility measurement of N in liquid Cr by [83Ish]; they correspond to the isobars log P(N2)/bar = -1 and 0. The solidus curves are drawn so that a match between the isobars in the liquid and solid states is obtained. In contrast to the liquid state, the phase boundaries in the solid state are generally well established. The solubility of N in (Cr) in equilibrium with Cr2N above 900 C (~1200 K) is given by log (at.% N) = 4.36 - 7100/T (1200 to 1700 K) [57Cap, 67Sch, 71Mil]. Extrapolation of this equation to the adopted eutectic temperature of 1640 C yields a value of ~4.4 at.% N for the solubility of N in (Cr) at the eutectic. According to [79Tsu], the solubility of N in (Cr) near the eutectic temperature has a value of 5.7 at.% N. The solubility of N in (Cr) below 900 C has been determined by means of chemical analysis [57Cap], internal friction [65Kle], and electrical resistivity [72Pri] measurements. The data reveal a higher solubility than the one obtained by extrapolation of the solubility equation given above. [57Cap] and [65Kle] suggested that the equilibrium solubility of N in (Cr) drops to about 100 mass ppm at 900 C; this is of the same order of magnitude as the total interstitial impurity content (C, H, N, O) of the Cr used in the studies, 30 mass ppm [72Pri], 100 mass ppm [57Cap], and 200 mass ppm [65Kle]. It is also possible that at these low concentrations lattice defects such as dislocations or grain boundaries affect the solubility. The existence of the two intermediate phases Cr2N and CrN is firmly established. However, the nitride Cr3N2 reported by [08Hen] was probably a mixture of Cr2N and CrN. The adopted stability field of Cr2N is based on the data of [67Sch], [70Mil], [ 72Mil], and [73Kot]. The Cr-rich phase boundary varies strongly with temperature. Extrapolation of this phase boundary to the eutectic temperature of 1640 C yields ~18 at.% N for the solubility; this value is adopted in the assessed diagram. The N-rich phase boundary of Cr2N, which lies at approximately 32.6 с 0.3 at.% N, has a very slight temperature dependence. According to [70Mil], [72Mil], and [73Kot], the N solubility increases with decreasing temperature from 32.8 at.% N [70Mil, 72Mil] and 32.3 at.% N [73Kot] at ~1100 C to 32.9 at.% N [70Mil, 72Mil] and 32.4 at.% N [73Kot] at ~900 C. It may reach the stoichiometric composition 33.3 at.% N at lower temperatures. The congruent melting point of Cr2N, ~1800 C, is speculative. The homogeneity range of CrN, in contrast to Cr2N, is very narrow; it extends probably from 49.5 to 50.0 at.% N. [70Mil], [72Mil], and [73Kot] indicate that the phase boundary shifts with increasing temperature toward lower N concentrations; however, the absolute values differ by about 0.5 at.% N. The formation of Cr2N and CrN by bombardment of thin films of Cr with N+2 ions was reported by [79Bel]. Chromium azide, Cr(N3)3, has not been prepared in pure form, only in aqueous solution [62Gme]. It is highly explosive and probably stable only at elevated N2-pressures. Using levitation melting, the density of liquid Cr-N alloys containing 0 to 14 at.% N was measured from 1900 to 2100 C [78Tsu]. The density of the liquid alloys decreases with increasing temperature and increasing N concentration. An amorphous modification of Cr2N was prepared by [47Sch] by thermal decomposition of chromium amide, Cr(NH2)3. [79Tsu] and [83Ish] reported that the solubility of N in liquid Cr obeys Sieverts' law up to ~5 at.% N or P(N2) = 0.05 to 0.10 bar. The 0.1 and 0.01 bar isobars shown in the assessed diagram are based on the detailed investigation by [83Ish]. According to [83Ish], the N2-pressure at the eutectic, L = (Cr) + Cr2N, has a value of P = 0.24 bar. The equilibrium pressure corresponding to the N-rich phase boundary of CrN has not been determined, but [70Bro] indicates that the pressure reaches 1 bar at approximately 1150 K (850 to 900 C). According to [70Bro], Cr2N is not ferromagnetic in the temperature range 85 to 500 K. CrN undergoes a paramagnetic-antiferromagnetic first-order transition below room temperature. The N‚el temperature varies from 276 K at 49.5 at.% N to 286 K at 49.9 at.% N [70Bro]. 08Hen: G.G. Henderson and J.C. Galletly, J. Soc. Chem. Ind. London, 27, 387- 389 (1908). 29Bli: R. Blix, Z. Phys. Chem. B, 3, 229-239 (1929) in German. 30Bla: F.C. Blake and J.O. Lord, Phys. Rev., 35, 660 (1930). 34Eri: S. Eriksson, Jernkontorets Ann., 118, 530-543 (1934) in Swedish. 40Bri: R.M. Brick and J.A. Creevy, AIME Tech. Publ. No. 1165, Vol. 7, 1-10 ( 1940). 47Sch: O. Schmitz-Dumont, G. Broja, and H.F. Piepenbrink, Z. Anorg. Chem., 254, 329-342 (1947) in German. 49Hum: W. Hume-Rothery and W.B. Pearson, J. Inst. Met., 76, 718-725 (1949-1950) . 50Moz: V.S. Mozgovoi and A.M. Samarin, Dokl. Akad. Nauk SSSR, 74, 729-732 ( 1950) in Russian. 51Kie: R. Kiessling and Y.H. Liu, J. Met., 3, 639-642 (1951). 57Cap: D. Caplan, M.J. Fraser, and A.A. Burr, Ductile Chromium and Its Alloys, Chap. 16, American Society for Metals, Metals Park, OH, 196-215 (1957). 60Cor: L.M. Corliss, N. Elliott, and J.M. Hastings, Phys. Rev., 117(4), 929- 935 (1960). 62Gme: Gmelins Handbuch der Anorganishchen Chemie, 8th ed., Chrom, Part B52, 157-163 (1962) in German. 65Kle: M.J. Klein and A.H. Claver, Trans. Metall. Soc. AIME, 233, 1771-1776 ( 1965). 66Ark: V.I. Arkharov, L.M. Katano, V.N. Konev, and G.V. Samsonov, Uch. Zap. Ural. Gos. Univ., (50) 79-86 (1966) in Russian. 66Kot: H. Kotsch and G. Putsky, Abh. Dtsch. Akad. Wiss. Berlin, Kl. Math. Phys. Tech., 1, 249-252 (1966) in German. 67Kie: R. Kieffer, P. Ettmayer, and T. Dubsky, Z. Metallkd., 58, 560-564 (1967) in German. 67Sch: K. Schwerdfeger, Trans. AIME, 239, 1432-1438 (1967). 70Bro: J.D. Browne, P.R. Liddell, R. Street, and T. Mills, Phys. Status Solidi (a), 1, 715-723 (1970). 70Mil: T. Mills, J. Less-Common Met., 22(4), 373-381 (1970). 70Sve: V.N. Svechnikov, G.F. Kobzenko, V.G. Ivanchenko, and E.L. Martynchuk, Dop. Akad. Nauk Ukr. RSR, A, Fiz.-Mat. Tekh., 32(9), 833-837 (1970) in Ukrainian. 71Mil: T. Mills, J. Less-Common Met., 23, 317-324 (1971). 71Nas: M. Nasr-Eddine and E.F. Bertaut, Solid State Commun., 9, 717-723 (1971) in French. 72Mil: T. Mills, J. Less-Common Met., 26(2), 223-234 (1972). 72Pri: D. Prioux and J. Bigot, C.R. Hebd. S‚ances Akad. Sci., Ser. C, 275(18), 1025-1028 (1972) in French. 73Kot:. A. Kotlar, M. Achour, and M. Dode, Rev. Chim. Miner., 10(4), 651-659 ( 1973) in French. 77Aiv: M.I. Aivazov and T.V. Rezchikova, Zh. Neorg. Khim., 22(2), 458-463 ( 1977) in Russian; TR: Russ. J. Inorg. Chem., 22(2), 250-253 (1977). 78Tsu: Y. Tsu, K. Takano, S. Watanabe, and Y. Shiraishi, Tohoku Diagaku Senko Seiren Kenkyu Sho Iho, 34(2), 131-143 (1978) in Japanese. 79Bel: I.M. Belyi, F.F. Komarov, V.S. Tishkov, and V.M. Yankovskii, Fiz. Khim. Obrab. Mater., (1), 48-53 (1979) in Russian. 79Tsu: Y. Tsu, T. Saito, and Y. Sakuma, Nippon Kinzoku Gakkaishi, 43(2), 71-80 (1979) in Japanese. 83Ish: F. Ishii, Y. Iguchi, and S. Ban-Ya, Tetsu to Hagane, 69(8), 913-920 ( 1983) in Japanese. Submitted to the APD Program. Complete evaluation contains 4 figures, 5 tables, and 91 references. 1