One-dimensional migration of interstitial clusters in SUS316L and its model alloys at elevated temperatures

Abstract

For self-interstitial atom (SIA) clusters in various concentrated alloys, one-dimensional (1D) migration is induced by electron irradiation around 300 K. But at elevated temperatures, the 1D migration frequency decreases to less than one-tenth of that around 300 K in iron-based bcc alloys. In this study, we examined mechanisms of 1D migration at elevated temperatures using in situ observation of SUS316L and its model alloys with high-voltage electron microscopy. First, for elevated temperatures, we examined the effects of annealing and short-term electron irradiation of SIA clusters on their subsequent 1D migration. In annealed SUS316L, 1D migration was suppressed and then recovered by prolonged irradiation at 300 K. In high-purity model alloy Fe-18Cr-13Ni, annealing or irradiation had no effect. Addition of carbon or oxygen to the model alloy suppressed 1D migration after annealing. Manganese and silicon did not suppress 1D migration after annealing but after short-term electron irradiation. The suppression was attributable to the pinning of SIA clusters by segregated solute elements, and the recovery was to the dissolution of the segregation by interatomic mixing under electron irradiation. Next, we examined 1D migration of SIA clusters in SUS316L under continuous electron irradiation at elevated temperatures. The 1D migration frequency at 673 K was proportional to the irradiation intensity. It was as high as half of that at 300 K. We proposed that 1D migration is controlled by the competition of two effects: induction of 1D migration by interatomic mixing and suppression by solute segregation.

Keywords:

• point defects
• irradiation effects
• electron irradiation
• dislocation loops
• in situ observation
• high-voltage electron microscope
• radiation-induced segregation
• strain ageing

Acknowledgements

We are grateful to Mrs E. Aoyagi and Y. Hayasaka of the High Voltage Electron Microscopy Center at Tohoku University, and to Mrs S. Ohta, H. Oosaki, and S. Takakuwa of JEOL Ltd for technical support in the electron irradiation experiments at Tohoku University and Nagoya University, respectively. We also thank Dr T. Ashino and Mr H. Shimada of the Analytical Research Core for Advanced Materials, Institute for Materials Research, Tohoku University for impurity analysis of the specimens.

Additional information

Funding

This work was supported in part by a Grant-in-Aid for Scientific Research number [grant number 21560868] of the Ministry of Education, Culture, Sports, Science, and Technology of Japan (MEXT); and ‘Collaborative Research Station of High-Voltage Electron Microscopy (MEXT)’ and ‘Advanced Characterization Nanotechnology Platform, Nanotechnology Platform Program (MEXT)’ of the High Voltage Electron Microscope Laboratory at Nagoya University.