ATOMISTIC SIMULATIONS TO STUDY EFFECT OF HE BUBBLE ON THERMAL AND MECHANICAL PROPERTIES OF NICKEL

Abstract

Growing cities, the rise in population and the desire for a comfortable modern lifestyle has skyrocketed the demand for energy. Today, this has given rise to the fear of an energy crisis. To combat this problem, most countries rely heavily on power from coal and natural gas. This has resulted in increasing CO2 emissions, which are responsible for global warming. The issues such as rising air pollution, limited land area and large variations in wind and sunlight make nuclear energy the most attractive option to overcome the shortage of energy in a sustainable way. Although nuclear energy is the most viable and widely accepted option for green energy in most parts of the world, major issues faced are safe nuclear waste disposal and safety during plant operations. Both issues can be tackled by continuous innovations and studies in the field of nuclear materials. The presence of severe conditions acting in tandem in a nuclear reactor, such as radiation of varying energy, high temperature, highly corrosive environments and the combination of mechanical and thermal stresses, makes this task challenging. In order to understand the failure phenomenon due to irradiation, it is required to replicate the working environment of the nuclear power plant. This poses time, spatial and cost concerns. The post-irradiation handling of samples is hazardous as well as cumbersome, which compromises the experimental results. Atomistic simulations are capable of capturing radiation damage occurring in a time frame of picoseconds and also predicting the mechanical response of materials accurately. Therefore, atomistic simulations are chosen to study the effect of helium bubbles on the mechanical, and thermal behaviour of single and bi-crystals of nickel. Initially, molecular dynamics (MD) and statics-based simulations were carried out to study the effect of helium bubbles on defect dynamics and tensile/shear deformation in Ni crystal. The onset of plastic deformation has been quantified as a function of the orientation of slip planes with shear force and configuration of helium nanobubbles. It was predicted from the atomistic simulations that concentration of helium atoms in the bubble is more detrimental for the mechanical strength of the nickel crystal than the size of the bubble. In the next phase, MD-based simulations were performed to study the effect of helium bubbles on crack tip behaviour in a Ni crystal. Simulations were performed after aligning the crack plane with varied principal planes of fcc crystal. Deformation was found to be governed by dislocations, twinning, and stacking faults emanating due to the placement of helium bubbles in front of the crack tips or from the surface of the crack plane.