Resumen:

When metals are exposed to hydrogen (H)-rich environments, they may lose ductility and fail catastrophically without showing any sign of damage. This problem is known as hydrogen embrittlement (HE). Over the last few decades, extensive research on HE has shown that hydrogen-assisted cracking is a microstructure-sensitive phenomenon. The causes behind crack initiation, however, remain elusive to this day. We used in situ tensile straining experiments to investigate the role of H in crack initiation in a widely used structural material, nickel-based alloy 725. In our experiments, we varied different hydrogen charging conditions, which are representative of a range of applications: electrochemical charging and high temperature thermal charging. We found fundamentally different crack initiation mechanisms in both scenarios. In electrochemically charged samples, cracks initiate at regions which experience localized slip if the hydrogen content is low, or more ubiquitously at higher concentrations, but always on the sample surface. Conversely, thermal charging leads to a predominance of secondary cracks in the sample interior. We ascribe these differences to the variance in internal hydrogen distribution and, possibly, to the degree of confinement on crack tip plasticity. Comprehending these mechanisms is pivotal for making reliable lifetime predictions of components operating in H-rich environments, and paves the way for future development of novel, HE-resistant alloys.

Breve Biografía:

Mengying Liu es profesora asistente de ingeniería en la Universidad Washington and Lee. Sus principales intereses de investigación se centran en la degradación ambiental de materiales metálicos. Esto incluye proyectos específicos sobre fragilización por hidrógeno de aleaciones basadas en Ni y corrosión localizada de Ni puro. Liu emplea técnicas como la microscopía electrónica de barrido y la correlación de imágenes digitales para explorar la relación estructura-propiedades de estos materiales. Tiene un doctorado. en Ciencia e Ingeniería de Materiales de la Universidad Texas A&M y una licenciatura en ingeniería de la Universidad de Tianjin en China. Liu es premiada por la Asociación Estadounidense de Mujeres Universitarias y es conocida por su pasión por orientar a estudiantes y fomentar su crecimiento, tanto académica como personalmente.