An Investigation of Hydrogen Impacts on the Ductile-Brittle Transition by Nanoindentation

Abstract

Understanding mechanical properties is essential for material reliability in almost all industrial applications. While materials have been mechanically investigated and standards exist at the bulk scale, this is not the case when relevant material dimensions change to the order of microns to nanometers. The material property trends observed at the bulk scale do not necessarily apply at the small-scale. As industries and laboratories develop products with small components, the need for small scale testing and property mapping has increased drastically. Throughout this work, the impact of hydrogen on the mechanical properties was investigated in three systems: Sc, Si, and Ni. First, Sc films were deuterium charged and the resulting scandium deuteride (ScD2) films, used in applications for neutron generation, are examined. Fracture, elastic, and plastic properties are defined for films and micropillars milled into the films. Size, impurity, and substrate effects are discussed. The subsequent sections examine the mechanical properties and dislocation dynamics of single crystal Ni and Si specimens. Hardness, elastic modulus, fracture toughness, and activation volumes for dislocation motion are determined and discussed for samples with and without thermal gas-hydrogen charging. Hydrogen is shown to decrease fracture toughness as well as effect stresses and activation volumes measured in strain rate jump tests, particularly in Si samples. Together, these results indicate hydrogen charging causes a decrease in dislocation velocity, supporting a hydrogen enhanced decohesion mechanism in Si at this small scale.