ATOMISTIC SIMULATIONS OF HYDROGEN EMBRITTLEMENT IN PALLADIUM

Abstract

Palladium hydrogen system has unique catalytic activities and up to 1:1 hydrogen adsorption capability. It is studied in the context of hydrogen embrittlement, which is a subset of stress corrosion cracking, with classical molecular dynamics techniques. Hydrogen embrittlement is a long lasting metallurgical challenge due to its intractability and unpredictability.

First, the thermomechanical properties are studied parametrically in a wide range of hydrogen concentration and temperature, serving a database for hierarchical multiscale simulations and constitutive models in mechanics. To quantitatively describe the kinetics of hydrogen segregation at crack tips, anisotropic diffusion properties are investigated under tensile/compressive loads in both elastic and plastic regions at different temperature and hydrogen concentration. Meanwhile, vacancy concentration as a function of strain is also studied in the same circumstances to quantitatively study the super abundant vacancy phenomenon and how it could initiate hydrogen embrittlement. Further, hydrogen interactions with coherent twin boundary is simulated at finite temperature. The local strength of twin boundary with hydrogen is estimated by molecular dynamics nanoindentation. At last, the heterogeneous nucleation mechanisms of defects under the influence of hydrogen content in single crystal pillars with different growth orientations are investigated to reveal the slip versus twin competition in plastic deformation. In short, a wide range of interesting topics are rigorously explored in the realm of atomistic hydrogen embrittlement.