The features of the creep deformation of γ-single phase single crystals with the
composition of Ni-20mass%Cr are characterized by the extended transient stage, which consists of
Stage I and Stage II. In the Stage I, the creep rate just after loading remains unchanged, while the
creep rate decreases continuously in Stage II.
In the single crystals except for the single crystals with the stress axis of [001] and [1,
–
11], the
predominant creep deformation using the primary slip plane continues. By this deformation, the
cross section of specimen turns to elliptical in shape. However, in the single crystals with the
angle between stress axis and primary slip plane (111) is more than 45°, the deformation using the
primary slip plane does not continue, as a result, the duration of Stage II turn to shorter one. The
single crystal with the stress axis of [011] has the largest angle of 55°.
In this study, the deformation manner during transient stage of single crystal with the stress axis
of [011] orientation is investigated from the two viewpoints. The first one is to clarify the change
in deformation manner with decreasing the stress. As a result, with decreasing the stress, the Stage
I become clear and strain during Stage I and Stage II become small, furthermore, the decreasing
ratio of creep rate with definite strain becomes larger. While, the second viewpoint is to
investigate the change in crystallographic orientation of the [011] single crystals with creep
deformation using the inverse pole figure obtained by the EBSD method. As a result, at the stress
of 29.4 MPa, the spot of stress axis turns from the [011]-[1,
–
11] line to the <1,
–
01> direction.
While, at the stress of 19.6 MPa, the stress axis moves for the [1,
–
11] pole along the [011]-[1,
–
11]
line from the [011] pole. And, it is noteworthy that the spot widely spread from the [011] pole
during transient stage. This indicates the large distortion in the primary slip plane and the
evidence of heterogeneous deformation.
Ferroelectricity and Phase Transitions in Pyridinium Periodate Single Crystal