Ion Beam & Computer Simulation Section

Defect & Radiation Damage

Understanding basic processes of radiation damage phenomenon of irradiated materials on qualitative as well as quantitative level requires a great deal of sophistication in modeling at atomic scale. Radiation damage is a multiscale phenomenon. The scope of experiments is very limited by both the size and timescale of cascades. This is why people are so keen to handle the situation by computer experiments in “virtual material laboratory”. Different modeling techniques e.g. atomistic or continuum or rate theory based approaches are used for handling different length and time scales.

Formation and stability of Y-Ti-O nanoclusters in bcc Fe: An ab initio study

Nanostructured ferritic alloys derive their strength from the dispersion of oxidenanoclusters in ferritic matrix. Our abinitio density-functional theory calculations show core/shell structure for these nanoclusters. Strong binding of Y, Ti, O clusters in bcc Fe in presence of vacancy leads to enrichment of these elements at the core of nanocluster and repulsive interaction of Cr with Y and Ti resultsin the depletion of Cr in the core of nanocluster. The binding energy of the defect clusters increase when we replace Ti with Zr, which could lead to finer dispersion of nanoclusters resulting in improved performance of ferritic alloys.

Defect generation and evolution in Fe: Molycular Dynamics  calculation

We are using atomistic modeling for studying generation of primary knock-on atom (PKA) and corresponding defect evolution in model materials. We employ here semiempirical potential based molecular dynamics (MD) approach for iron (Fe). Reliability of such calculations depends on the effectiveness of the empirical potential to describe the equilibrium and nonequilibrium properties of the model material. For generating such potential we require various experimental data and ab-initiodata where experimental data are not available. We performed density functional theory (DFT) based calculations for materials like iron, nickel, chromium and calculated various properties like equilibrium lattice parameter, bulk modulus, defect formation energy, binding energy etc. These data are important inputs for modeling a good potential for such materials. The development of such potentials is one of the ongoing activities. We are also working on the modeling for truthful representation of actual situation of radiation damage

The cascade of defects is generated in a small region around the PKA position and its spatial position and extent depends on the PKA energy. In general, we can assume that most part of the materials is unaffected and a highly disordered region is created around depending on PKA direction and energy. Therefore, it is most important to do the pattern recognition of such highly disordered region. We are also working on developing a code for structural pattern recognition of defects.  For this we are employing mainly voronoi tessellation and cluster analysis based approach. This study will enable us to have an idea about number of defects as a function of PKA energy and time. This will also help us to have an idea of cascade structure. Our aim is to correlate the cascade size and structure with some experimentally available data for the model material.