Effect of helium on thermal transport properties in single- and bi-crystals of Ni: a study based on molecular dynamics

Nuclear structures are prone to irradiation-induced defects that make them susceptible to alternation in mechanical and thermal properties. The transmutation of Ni to insoluble He atoms is considered to be responsible for the embrittlement of Ni. Helium bubbles are deemed responsible for the deterioration of mechanical and thermal properties of the Ni crystal, and this should be studied in detail to predict the lifespan of ageing nuclear structures. The aim of this article is to study the effect of helium on the thermal transport phenomenon in single- and bi-crystals of Ni. Molecular dynamics-based simulations in conjunction with a hybrid force field are performed to study the effect of a helium bubble on the thermal transport phenomenon in Ni crystals. These simulations are further extended to study the impact of symmetrical tilt grain boundaries (STGB) in conjunction with the doping of helium atoms on the thermal transport phenomenon in bi-crystal Ni. The effect of helium concentration in the bubble significantly alters the thermal transport in single-crystal Ni. The STGB configuration also introduces interfacial thermal resistance as a function of the misorientation angle. The helium-doped grain boundaries further increase the resistance to phonon movement and increase Kapitza resistance. The increase in Kapitza resistance is more dominant in higher misorientation angle grain boundaries.