Фазовая диаграмма системы Nb-Zr

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Nb-Zr (Niobium-Zirconium) J.P. Abriata and J.C. Bolcich Only partial agreement exists in the literature regarding quantitative description of the Zr-Nb phase boundaries, possibly due to the extreme sluggishness of the solid-state reactions, as well as to the high sensitivity of the phase diagram to oxygen contamination. The (bZr) + (bNb) miscibility gap, as well as the temperature of the (bZr) = ( aZr) + (bNb) monotectoid reaction, is based on the work of [72Fle]. Only rough agreement exists regarding the composition of (bZr) and (bNb) at the monotectoid reaction. Wide discrepancies exist regarding the solubility of Nb in (aZr). The solubility of Nb in (aZr) is accepted as 0.6 at.% Nb in the temperature range of the monotectoid reaction [72Eff]. Contamination with oxygen appears to increase the solubility of Nb in (aZr). [70Rab] observed that alloying Zr with Nb reduced the value of the pressure at which the w phase first became noticeable. The cph martensitic phase a› forms athermally during rapid quenching from the b phase to room temperature. Generally, upon quenching, alloys with less than 7 wt.% Nb transform almost completely to a›; alloys between 7 and 7.5 wt.% Nb contain a› in metastable coexistence with quenched b and metastable w. Beyond 7.5 wt.% Nb, a› is not observed. For very high cooling rates, the martensitic transformation has been shown to exist also in pure Zr itself. The martensite start temperature decreases linearly with increasing Nb content. It appears to be independent of cooling rates, or oxygen impurity content, or the prior b-phase solution treatment temperatures and times. Two types of martensite morphologies have been observed. A portion of the coherent spinodal was determined experimentally by [74Fle]. Metastable equilibrium states containing variants of the stable w phase have been produced by rapid quenching to room temperature from the b phase ( athermal wa), isothermal aging below 500 C (isothermal wiso), and high- pressure treatments (wpr). 70Rab: A.G. Rabinkin, L.A. Klishanova, and L.N. Pronina, Problems of Superconducting Materials, 141 (1970) in Russian. 72Eff: P. Van Effenterre, Report CEA-R-4330, Atomic Energy Commission, Saclay, France (1972) in French. 72Fle: P.E.J. Flewitt, J. Appl. Crystallogr., 5, 423 (1972). 74Fle: P.E.J. Flewitt, Acta Metall., 22, 47 (1974). Published in Bull. Alloy Phase Diagrams, 3(1), Jun 1982. Complete evaluation contains 10 figures, 5 tables, and 67 references. 1