Helical dislocations produced by low temperature thermocycling in a Ti-Al Alloy

By transmission electron microscopy (TEM), the structural state of a Ti–Al alloy subjected to low temperature thermocycling from 300 to 77 K has been investigated. As the result of this observation, helical dislocations were revealed with the density 109 cm−3. These were generated mainly by grain boundaries or subboundaries. Their formation is thought to be associated with thermomechanical stresses arising during thermocycling. Thermomechanical stresses at the interface of neighbouring grains, estimated with making allowance for the anisotropy of the linear expansion coefficient, appeared to be about 7 kg/mm2. It is assumed that helical dislocation formation is one of the ways in which local internal stresses are relieved. [Russian text ignored]