Atomistic Deformation Mechanisms in Advanced Structural Materials
Twinning in Hexagonal Close-Packed Alloys
Deformation twinning impacts the mechanical properties of a material by influencing its strength, work hardening, ductility, and toughness. Twinning plays an important role in the mechanical behavior in hexagonal-close-packed (HCP) materials, where the number of operative dislocation slip systems is limited. The study of twin nucleation and growth in HCP materials is of broad interest in the field of structural metals and alloys. By using density functional theory theory and molecular dynamics simulations, the kinetics and thermodynamics of twinning behaviors can be investigated.
Dislocation Climb and Cross-Slip Kinetics
Fundamental understanding of mechanical behavior of materials beyond the initial yield point is crucial for a variety of structural applications. This requires elucidation of the kinetics of various processes involving dislocations, which are defects that govern deformation in metals.
Dislocation climb is a mechanism fundamental to high temperature deformation processes, annealing of quenched-in defects, and irradiated defect absorption in metals. In FCC metals, the dislocation climb process can be slower than expected from diffusion kinetics due to limited jog availability. Using a dislocation climb theory informed by atomistic calculations, we have shown that the climb efficiency of a straight edge dislocation in FCC metals is low until high homologous temperatures are reached (especially if the stacking fault energy is low). The results of this work are anticipated to be an important contribution for alloy design and mesoscale modeling centered around creep.
This research is sponsored by the Office of Naval Research.