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Further studies on the nickel–aluminium system. I. β‐NiAl and δ‐Ni 2 Al 3 phase fields
Author(s) -
Taylor A.,
Doyle N. J.
Publication year - 1972
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889872009203
Subject(s) - nial , nickel , materials science , lattice constant , aluminium , stoichiometry , atom (system on chip) , crystallography , intermetallic , valence electron , lattice (music) , electron , condensed matter physics , metallurgy , chemistry , alloy , physics , diffraction , quantum mechanics , computer science , acoustics , optics , embedded system
New lattice parameter and density results have been obtained for alloys in the β‐NiAl and 6‐Ni 2 Al 3 phase fields of the nickel–aluminium system. The lattice parameter of the β‐NiAl phase (CsCl‐type) falls linearly from 2.8870 Å at 50 at.% Ni to 2.8618 Å at 66. at.% Ni, with 2.00 atoms per unit cell. On the other hand, the lattice parameter on the Al‐rich side of NiAl falls linearly from 2.8870 Å to 2.8652 Å, while the number of atoms per unit cell falls from 2.00 to 1.817 by the creation of vacancies in normally nickel sites. The trigonal 6‐Ni 2 Al 3 phase‐structure, which is essentially an extension of cubic β‐NiAl, but with every third plane of nickel atoms perpendicular to the trigonal axis missing, shows a minimum in the a and c spacings at stoichiometric Ni 2 Al 3 . Density measurements indicate that the vacancies formed by the missing planes are progressively filled as nickel is added to Ni 2 Al 3 , but that a substitutional solid solution is formed on the aluminium‐rich side of stoichiometric Ni 2 Al 3 with aluminium replacing nickel atom by atom. In the NiAl phase, the number of valence electrons increases from 2.28 per unit cell at 61.9 at.% Ni to 3.00 at stoichiometric NiAl, and remains constant at 3.00 as the vacancies form until Ni 2 Al 3 is reached, at which stage the number of vacancies will have reached a maximum when there are only 1.67 atoms per pseudo‐cubic cell. The number of electrons per pseudo‐cubic unit cell then begins to rise and reaches the phase boundary value of 3.12 at 37.6 at.% Ni.