Effect of mono-tension and biaxial tension on microstructure and stress corrosion cracking of Alloy 690TT

The grain boundary misorientation and dislocation structure for Alloy 690TT under mono-tension and biaxial tension at room temperature was investigated by using electron backscatter diffraction technique (EBSD) and transmission electron microscopy (TEM). The strain amplitudes for mono-axial tension were X3%, X5%, X7% and X9% respectively, and biaxial tension followed X3%, X5%, Y3%, X7%, Y7%, X9%, and Y9% tensile strains. The results showed that the mono-tension could decrease the amount of Σ3 twin boundaries, increased the amount of the low angle boundary and random grain boundary. The biaxial tension recovered some random boundaries partially back to Σ3 boundaries. Tension strains in Y direction restricted the decease of Σ3 boundaries. For the mono-tension specimen the dislocation had high energy pile-ups structure and for the biaxial tension specimen had low energy tangle structure. According to mechanochemical effect theory, the biaxial tension could retard stress corrosion cracking of Alloy 690TT.