Dislocation Loop Formation and Growth under In Situ Laser and/or Electron Irradiation
Vacancies and interstitial atoms are primary lattice (point) defects that cause observable microstructural changes, such as the formation of dislocation loops and voids in crystalline solids. These defects' diffusion properties determine the phase stability and environmental resistibility of macroscopic materials under ambient conditions. Although in situ methods have been proposed for measuring the diffusion energy of point defects, direct measurement has been limited. In this study, we propose an alternative in situ method to measure the activation energy for vacancy migration under laser irradiation using a pulsed laser beam from a laser-equipped high-voltage electron microscope (laser-HVEM). We made in situ observations that revealed the formation and growth of vacancy dislocation loops in an austenitic stainless steel during laser irradiation. These loops continued to grow when thermal annealing was performed after laser irradiation at the same temperature. We anticipate that laser-HVEM will provide a new method for investigating lattice defects.
Point defect interactions and growth of dislocation loops
A direct method of determining the effective measure of the interaction of point defects with dislocation loops is proposed. A system of partial differential rate equations for loop growth is formulated and is solved by a numerical method. An in-situ HVEM irradiation experiment was conducted to study growth kinetics of dislocation loops in Ni at 450/sup 0/C. It is found from systematic variations of the vacancy migration energy, E/sub v//sup m/, and the preference factor of dislocation loops for self-interstitials, delta/sub i/, that delta/sub i/ = 0.06 and E/sub v//sup m/ = 1.2 eV together yield reasonable agreement between the theoretical model and the experimental observations.
A quantitative study of the dose and impurity dependence of the defect concentrations remaining in molybdenum after 4 MeV electron irradiation at (77°K)
Abstract Experimental measurements using resistivity techniques to follow the increase of defect concentration with electron irradiation dose were made on high purity molybdenum and molybdenum doped with nitrogen to two different levels. The marked dependence of defect concentration on impurity can be satisfactorily explained by the Walker model (1) which assumes that the interstitial defect is mobile at the irradiation temperature and that the retention of the interstitial depends on it being trapped at an impurity sink rather than annihilated at a vacancy. It appears therefore that the interstitial defect is mobile in molybdenum at 77°K. This result is in direct contrast to that of de Jong and Afman (1) who deduced from their work that the interstitial did not become mobile until Stage III, Evidence is presented to show that their results are in fact compatible with the Walker model and the implication of the present work on Stage III annealing in molybdenum is discussed.