Articles written in Pramana – Journal of Physics
Volume 12 Issue 3 March 1979 pp 275-289 Solids
Evaluation of irradiation-induced creep rate: application to the vacancy dislocation loop contribution
K Krishan V Balakrishnan S K Ray
Irradiation (as in a nuclear reactor) drastically affects the defect structure and its time evolution in a material, and induces new creep mechanisms in it. We present a formalism to evaluate the contribution to creep owing to such mechanisms. Beginning with the phenomenological constitutive relation for the strain appropriate to a given mechanism, we put in simple statistical considerations to derive an expression for the corresponding creep rate. This formal expression is in terms of the defect production rate and a non-equilibrium probability distribution function involving the pertinent properties of the defect type concerned. A convenient approximation scheme for practical calculations is employed, that also makes contact with standard rate theory and provides a proper interpretation for the variables occurring there. As an illustration, we evaluate the contribution to irradiation-induced creep from the orientation-dependent shrinkage of vacancy dislocation loops in an applied stress field. The circumstances inducing transient and non-transient creep are clarified and a numerical estimate is given for the latter component.
Volume 12 Issue 6 June 1979 pp 607-629 Solids
Effect of irradiation at low doses and incubation of voids within the rate theory approach
The evolution of defects in a material under irradiation is studied at low doses (∼5 dpa or less) using rate equations. It is shown that as a function of temperature at a critical value
Volume 15 Issue 2 August 1980 pp 189-205 Solid State Physics
Lattice static properties of vacancy clusters and interstitials in hcp magnesium: Computer simulation studies
H K Sahu S Srinivasan K Krishan
Computer simulation studies have been made to investigate the static properties of mono-, di- and tri-vacancy clusters and of self-interstitials in hcp magnesium in different configurations. Three interatomic potentials have been chosen for which the results have been compared. A crystallite containing about 1500 atoms and a model with the interatomic interaction extending upto the fourth neighbour distance have been used. Relaxation field, defect relaxation and formation energies, strength dipole tensors and relative changes in volume in the above defects have been computed and our final results compared with those of earlier workers. The formation energies of the defects are highly sensitive to the choice of the potential whose detailed structure guides the nature of relaxation and the dipole tensors. Calculations have been done for octahedral, tetrahedral and dumb-bell interstitials of which the last is found to be the most stable.
Volume 24 Issue 1-2 January 1985 pp 361-381 Solid State Physics And Materials Science
Radiation-induced structural changes in alloys
Development of alloys for reliable performance in extreme radiation environments is vital for the viability of advanced nuclear reactor systems. Over the past decade, there has been a considerable growth in our understanding of the basic processes of radiation damage, the nature of the induced defects, their interaction and migration, and the influence of these on the mechanical behaviour of metals. This understanding has however come mainly from studies in pure metals and dilute alloys, and there are difficulties when applying these concepts to concentrated alloys, particularly of technological interest. The present article, which attempts to bridge this gap, discusses recent research developments and some of the emerging new concepts as applicable to alloy systems. Interstitialcy transport; percolation effects in defect migration; short range and long range ordering and restructuring of alloys; defects and damage behaviour of metallic glasses; synergetic processes and phase instabilities; and finally, swelling, irradiation creep and ductility behaviour of alloy systems are the topics discussed.
Volume 39 Issue 2 August 1992 pp 117-130
Solid state effects during deuterium implantation into copper and titanium
H K Sahu M C Valsakumar B Panigrahi K G M Nair K Krishan
Results of neutron counting experiments during deuterium implantation into titanium and copper are reported. Models for neutron yield have been developed by taking into account different solid state effects like energy degradation of incident ions, energy dependent d-d fusion cross section and diffusion of implanted deuterium possibly influenced by surface desorption and formation of metal deuterides. The asymptotic time dependence of the neutron yield during implantation has been compared with the experimental results. Using these results, solid state processes that might occur during deuterium implantation into these metals are inferred.
Volume 97, 2023
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