Фазовая диаграмма системы Hf-N

К оглавлению: Другие диаграммы (Others phase diargams)

Hf-N (Hafnium-Nitrogen) H. Okamoto The assessed phase diagram for the Hf-N system is based on limited information available from the literature. The equilibrium phases are NaCl-type HfN and two stacking variants, Hf3N2 and Hf4N3, consisting of aHf and HfN. Additional stable stackings may be found in the Hf-rich side of the diagram. No information is available on the N-rich side. Addition of N stabilizes aHf and increases the b = a transformation temperature of Hf with a slope of 83.6 с 10.1 C/at.% [64Kri]. Assuming that the heat of the allotropic transformation of Hf is 5910 J/mol [83Cha], the van't Hoff relationship predicts that the initial slope of the (bHf) solvus is about 180 C/at.%. The (aHf) solid solution with 27 at.% N melts peritectically at 2910 C [69Boo]. The maximum solubility of N in (aHf) at 1700 C is 29 at.% [61Rud]. The Hf-N and Hf-C diagrams are similar [60Now], and the L = (bHf) + (aHf) eutectic transition temperature is 1910 C [80Fro]. The melting point of HfN was placed at 3310 [35Ruf] or 3000 C [60Now]. In reasonable agreement, the congruent melting point of HfN was reported to be 3387 C at 49 at.% N [69Boo]. [76Ero] detected the melting point of HfN at 4050 C, which is substantially different from earlier reports. The value of [ 69Boo] is tentatively shown in the assessed diagram, but a decisive investigation clearly is needed. According to [61Rud], Hf2N is in equilibrium with HfN. More detailed subsequent investigations [70Rud] clarified that the Hf-rich side of this range consists of two stable stacking variants, Hf3N2 and Hf4N3. They are unstable above ~2000 and ~2300 C, respectively. According to [80Fro], the eutectoid decomposition temperature of "Hf2N" is 1970 C. Each variant may have some homogeneity range, because a single-phase specimen was obtained at an off-stoichiometric composition. Furthermore, Hf4N3 may be unstable at low temperatures, because [73Bil] showed that Hf3N2, not Hf4N3, is in equilibrium with HfN at 800 to 1200 C. According to [70Rud], an infinite number of stacking variants, consisting of close-packed aHf and HfN, are conceivable. Therefore, it is possible that additional stacking variants exist at compositions and temperatures that have not been investigated to date, or in alloys that have been heat treated long enough to reach true equilibrium. The superconducting transition temperature of HfN is higher at a low N concentration [66Gio]. The highest temperature observed was 8.7 K at the lowest N concentration. A 52.8 at.% N alloy is not superconducting at 2.0 K [ 66Gio]. 35Ruf: O. Ruff, Congr. Chim. Ind., 15th Congr., Bruxelles, 68 (1935); quoted in [Hansen]. 53Gla: F.W. Glaser, D. Moskowitz, and B. Post, Trans. AIME, 197(9), 1119-1120 ( 1953). 60Now: H. Nowotny, H. Braun, and F. Benesovsky, Radex-Rundsch., 6, 367-372 ( 1960). 61Rud: E. Rudy and F. Benesovsky, Monatsh. Chem., 92(2), 415-441 (1961) in German. 64Kri: N.H. Krikorian and T.C. Wallace, J. Electrochem. Soc., 111, 1431-1433 ( 1964). 66Gio: A.L. Giorgi, E.G. Sklarz, and T.C. Wallace, U.S. At. Energy Comm., LA- DC-8022 (1966). 67Str: M.E. Straumanis and C.A. Faunce, Z. Anorg. Allg. Chem., 353, 329-336 ( 1967) in German. 69Boo: P. Booker and C.E. Brukl, U.S. Air Force Tech. Rep., AFML-TR-69-117, Part VI (1969). 70Rud: E. Rudy, Metall. Trans., 1(5), 1249 (1970). 76Ero: M.A. Eron'yan, R.G. Averbe, and I.N. Danisina, Teplofiz. Vys. Temp., 14, 398-399 (1976) in Russian; TR: High Temp., 14, 359-360 (1976). 79Lit: V.F. Litvinenko, A.S. Bolgar, O.P. Kulik, and O.T. Khorpyakov, Zh. Fiz. Khim., 53(2), 318-321 (1979) in Russian; TR: Russ. J. Phys. Chem., 53(2), 178- 179 (1979). 80Fro: E. Fromm and T.E. Gebkhard, Metallurgy, Moscow, 712 (1980) in Russian; quoted in [86Bar]. 83Cha: M.W. Chase, Bull. Alloy Phase Diagrams, 4(1), 123-124 (1983). 86Bar: O.M. Barabash and Yu.N. Koval, Crystal Structure of Metals and Alloys, Naukova Dumka, Kiev (1986) in Russian. Published in Bull. Alloy Phase Diagrams, 11(2), Apr 1990. Complete evaluation contains 1 figure, 2 tables, and 22 references. 1