Effects of antiphase domains on dislocation motion in Ti₃Al single crystals deformed by prism slip

Abstract

To shed light on the enormous dependence of the critical resolved shear stress (CRSS) for prism slip of Ti₃Al on antiphase domain (APD) size, which was found in a previous study, morphologies and configurations of dislocations in crystals with various APD sizes were examined by transmission electron microscopy (TEM). Contrary to models in previous works, dislocation had a wavy or winding morphology depending on , the average APD size. Also, unpaired dislocations were observed in the APD structure with an approximately smaller than 100 nm, whereas superpartial dislocation pairs were observed in coarser APD structures. Based on these observations we propose a new model of dislocation motion in relatively coarse APDs. The model relies on a detailed theoretical investigation of the interaction of dislocations with differently oriented antiphase domain boundaries (APDBs). In the model, dislocations move by bowing out between APDBs that are inclined from their Burgers vector, b, because dislocation motion is interfered by APDBs inclined from b but they can move easily through APDBs parallel to b. As this process is reminiscent of the classical Orowan mechanism, the model is designated an “Orowan-like model”. For relatively coarse APD structures with larger than approximately 100 nm, the dependence of the CRSS on the APD size derived from this model agrees with that measured experimentally. Also, the mechanism of uncoupling of superpartial dislocation pairs is suggested considering dislocation motion shearing APDBs inclined from b.

Acknowledgements

This work was supported by a Grant-in-Aid for Scientific Research Development from the Ministry of Education, Culture, Sports, Science and Technology of Japan. This work was also supported by “Priority Assistance of the Formation of Worldwide Renowned Centers of Research–The 21st Century COE Program (Project: Center of Excellence for Advanced Structural and Functional Materials Design)” from the Ministry of Education, Sports, Culture, Science and Technology of Japan. The authors thank Professor H. Mori and Dr. E. Taguchi of the Ultra High Voltage Electron Microscope Center of Osaka University for their help in TEM observation.