Characterization of Irradiated Microstructure by X-Ray Diffraction Line Profile Analysis
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CHANGES in the properties of materials by irradiation are of great technological interest. The structural materials used in the core of the nuclear reactors experience significant changes during operation due to the change in the microstructure, phase distributions, dimensions, electrical properties, magnetic properties, and corrosion[1,2] under a severe radiation environment. Keeping the technological interests in view, several studies have been carried out on the problems of simulating fission and fusion neutron damage with light and heavy ions.[3–7] Extensive studies have also been carried out on the nuclear structural materials[8,9] on the response of the light and heavy particle irradiation and consequent defect production and microstructural evolution. In the early stages of the projectile trajectory, the collision sequences are widely spaced,[10] giving a distribution of single vacancies and interstitials. Toward the end of the projectile trajectory, the distance between the collisions decreases to the interatomic distance. This generates a large number of primary knock-on atoms (PKA) causing a highly localized production of vacancies and interstitials; hence, the distribution of vacancies and interstitials within the damaged regions is nonuniform.[11] The presence of substitutional and interstitial impurities can conceivably result in a change of the total A. SARKAR, Postdoctoral Fellow, is with the Laboratory of Texture and Related Studies, Department of Materials Engineering, Indian Institute of Science, Bangalore 560-012, India. P. MUKHERJEE and P. BARAT, Scientific Officers, are with the Variable Energy Cyclotron Centre, Kolkata 700064, India. Contact e-mail: pbarat@ veccal.ernet.in This article is based on a presentation given in the symposium entitled ‘‘Materials Behavior: Far from Equilibrium’’ as part of the Golden Jubilee Celebration of Bhabha Atomic Research Centre, which occurred December 15–16, 2006 in Mumbai, India. Article published online January 26, 2008 1602—VOLUME 39A, JULY 2008
amount of damage at a given dose by two mechanisms as follows: (a) replacement collision sequences may be terminated and the defect production rate will decrease by the enhancement of mutual recombination; and (b) the trapping of point defects may result in the retention of point defect clusters that might otherwise be lost by mutual recombination on migration to sinks.[2,12] These result in an overall change of the microstructure, forming vacancy clusters, dislocation loops or small domains, immobile clusters of self interstitials, etc.[2,13] The irradiation-induced defect clusters play a major role in governing the mechanical properties of the structural materials. The structural materials used inside the nuclear reactors are in cold-worked and heat-treated conditions. The damage accumulation and the microstructural evolution during irradiation affect the in-reactor behavior, particularly irradiation creep and irradiation growth, which finally determine the structural integrity of these materials during service. T
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