The Role of Grain Boundary Structure and Chemistry in Materials Failure

The project investigated the local mechanical behavior of metal grain boundaries with and without the influence of a segregated alloy element, specifically in the Fe-C alloy system. Local deformation was carried out using nano-indentation with varying indentation-grain boundary geometry and strain rate. Stress relaxation under constant load and strain rate response to stress jumps were used to determine activation energy, activation volume and athermal stress as a function of grain boundary chemistry. The primary accomplishments of the project were (i) resolving the action of the proposed Ashby mechanism of grain boundary hardening from the action of the accepted Hall-Petch mechanism (ii) revealed the relationship between grain boundary chemistry, activation energy and athermal stress.