On cyclical phase transformations in driven alloy systems
Document Type
Conference Proceeding
Publication Date
5-2008
Department
Department of Materials Science and Engineering
Abstract
Cyclical phase transformations occurring in driven materials syntheses such as ball milling are described in terms of a free energy minimization process of participant phases. The oscillatory flow behavior of metals with low stacking fault energies during hot working is taken as a prototype in which a ductile crystalline phase sustains undulation in its free energy, due to the alternate succession of work-hardening and work-softening mechanisms. A time-dependent, oscillatory free energy function is then obtained by solving a delay differential equation (DDE), which accounts for a time lag due to diffusion. To understand cyclical transitions on an atomistic scale, work is extended to molecular dynamics simulations. Under shear deformation, a two-dimensional nanocrystal shows cyclical transitions between an equilibrium rhombus and a nonequilibrium square phase. Three-dimensional simulations show crystalline-to-glass transitions at high strain rates, but very high shear strain rates are found to lead to a latticelike network structure in the plane perpendicular to the shear direction, with strings of atoms parallel to the shear direction.
Publication Title
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Recommended Citation
Lee, J.
(2008).
On cyclical phase transformations in driven alloy systems.
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science,
39 A(5), 964-975.
http://doi.org/10.1007/s11661-007-9379-z
Retrieved from: https://digitalcommons.mtu.edu/michigantech-p/5058