Deformation Twin in Single Crystals of a 3% Vanadium-Iron Alloy

Abstract

Observations were made on deformation twins in single crystals of a 3% vanadium-iron alloy which were deformed in compression along the [1̄10] direction at -195°C. In most twin bands, a narrow but straight line (`midrib') is seen to run along the longitudinal direction. Electron microscope observations show that the thickness of such a `midrib' is less than 100 Å and also, near the midrib, a considerably high density of dislocations is located. The midrib runs straight without being disturbed by sub-boundaries, where twin bands are always constricted. Besides such `constrictions', `indentations' are frequently observed in a twin band, which are interpreted as regions left untwinned locally in the growth process of thickness because of the presence of isolated obstacles. These observations may suggest that a deformation twin is formed by the following two processes. A very thin twin plate less than 100 Å in thickness is first formed dynamically, and then the thickness of the twin increases with increasing stress, forming constrictions or indentations at the place of obstacles such as sub-boundaries, pre-cipitates, or pre-existing dislocations.