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Further studies on the nickel–aluminum system. II. Vacancy filling in β and δ‐phase alloys by compression at high temperatures
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/s0021889872009215
Subject(s) - vacancy defect , nial , materials science , aluminium , nickel , alloy , atom (system on chip) , lattice constant , phase (matter) , condensed matter physics , atomic radius , lattice (music) , metallurgy , intermetallic , crystallography , chemistry , diffraction , physics , organic chemistry , computer science , acoustics , embedded system , optics
The combined action of pressure and temperature on aluminium‐rich alloys in the β‐NiAl field produces an increase in density and lattice parameter as a result of vacancy‐filling. Thus at 43.7 (4) at.% Ni, a pressure of 78 kbar at 1000 °C will increase the density of the alloy from 5.16 to 5.37, with a concomitant increase in lattice parameter from 2.8593 to 2.8712 Å and an increase in atoms/unit cell from 1.77 (5) to 1.87 (7). Similar density changes and increases in atoms/unit cell occur in the trigonal δ‐Ni 2 Al 3 phase structure, but in alloys on the aluminium‐rich side of stoichiometric Ni 2 Al 3 vacancy‐filling can actually lead to a reduction in both the a and c parameters. This may result from promoting electrons in the 3 d shell of nickel into the conduction band, thereby reducing the nickel atom radius.