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The Effect of Phase Change on the Mechanical Properties of Cobalt Near Its Transformation Temperature
Author(s) -
Kamel B.,
Halim K.
Publication year - 1966
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.19660150104
Subject(s) - materials science , creep , thermodynamics , climb , dislocation , activation energy , phase (matter) , vacancy defect , cobalt , phase transition , condensed matter physics , hardening (computing) , work hardening , diffusion , work (physics) , crystallography , chemistry , composite material , physics , metallurgy , microstructure , organic chemistry , layer (electronics)
The phase transformation of cobalt is studied from observations of the changes in the work‐hardening, creep and fracture characteristics of cobalt near its critical temperature. The parabolic work‐hardening coefficient, X p , is found to be about four times greater for the h.c.p. than for the f.c.c. phase at the same temperature. However, the temperature coefficient of X p remains fairly constant over the phase change and has an average value of about −0.0027 deg −1 . In the presence of the two phases simultaneously during the transition stage, this thermal coefficient is increased by an order of magnitude. The phase transition is exhibited as a change in slope of the curve of the logarithm of steady state creep versus the reciprocal of the absolute temperature. Dislocation climb controlling of the steady state creep is activated by 5.6 eV in the h.c.p. phase, which is comparable with double the activation energy for self diffusion. This is attributed to the fact the height of an elementary jog in the hexagonal structure is twice an interatomic spacing. In the cubic phase, the climb process requires only 2.0 eV which is smaller than that for self diffusion by nearly double the vacancy‐dislocation binding energy.