Vs. Okovit et La. Chirkina, EFFECT OF DISLOCATION SHAPE-MEMORY IN BCC AND FCC METALS AFTER SMALL DEFORMATIONS AT 4,2 K, Fizika nizkih temperatur, 19(10), 1993, pp. 1111-1116
The effect of dislocation shape memory Is studied experimentally al 4.
2-300 K on niobium, iron, nickel and copper samples after their torsio
nal deformation from 0.1 to 0.4 % at 4.2 K. after the above mode of de
formation, the effect of dislocation shape memory Is observed both in
bcc and in fee metals, but its intensity and temperature are dependent
on the defect structure formed during the low-temperature deformation
and on the friction forces of the crystalline lattice. The degree of
the shape restoration is much higher hi bcc metals than in fee ones. I
t is found that the shape restoration in bcc metals has three stages.
In fcc metals the presence of the dislocation shape memory sad its ext
ent are dependent on the energy of stacking defects (SDE): In low SDE
metals (e.g., Cu) the shape restoration proceeds in two stages; in hig
h SDE metals (e.g., NI) no shape restoration is observed. Physical mec
hanisms accounting for the stages of dislocation shape memory are prop
osed. The temperature dependences of the shape restoration rates and t
he mechanical properties of Nb, Fe, Cu and Ni are compared. It is assu
med that the character of changes in the thermally activated dislocati
on shape memory may serve a criterion of bcc metal liability to brittl
e fracture at low temperature-deformation.