Thermodynamics and Kinetics of Structural Transformations in Metal and Ceramic Systems

Rutgers University New Brunswick, New Brunswick NJ

Investigators

Abstract

This award supports theoretical and computational research and education on the 3-dimensional evolution of strain-generating complex structures formed in diffusional and diffusionless transformations as well as of the evolution of defects, e.g. dislocations and cracks, formed in plastic deformation and fracture. In spite of an apparent diversity of these problems, there is a profound commonality among them: they present different aspects of the problem of self-organization of a multi-mode complex system with a long-range strain-induced anisotropic interaction. The Phase Field Microelasticity model developed by the PI together with 3-dimensional computer simulations will be used to investigate complex microstructures to elucidate the mechanisms controlling their evolution in technologically important systems. The relative role played by thermodynamics, crystallographic symmetry, microelasticity, and kinetics in microstructure evolution will be investigated to provide insight into mechanisms of thermal stability of microstructure, to predict the morphology and evolution rate, and to help establish the optimal processing parameters to yield microstructures that provide the best mechanical properties. Three groups of problems of scientific and engineering interest for advanced materials will be addressed. The first group, related to mechanisms controlling coherent decomposition in cubic systems with several structural variants of ordered intermetallics, includes investigating the formation of coherent two-phase microstructures with a very complex morphology (e.g., the chessboard microstructure in Co-Pt and other alloys) via precipitation of multi-variant ordered intermetallics from a transient congruently ordered phase, and investigating the formation of a multi-phase coherent microstructure involving more than two phases. The second group of problems involves the response of the martensite to applied stress in crystallographically and elastically inhomogeneous systems. This group includes the study of martensitic transformations involving dislocation plasticity. Stress-accommodating dislocations drastically affect the morphology of martensitic crystals; they are responsible for irreversible plastic deformation, which are detrimental to the Shape Memory Effect. The study of stress-induced martensitic transformation generated by advancing cracks in transforming inclusions is also included in this group. Of particular interest is the heterogeneous nucleation of the martensite followed by the rearrangement of its domains in the crack tip zones as well as the effect of this rearrangement on the development of the crack system. The corresponding stress-strain curve will be simulated. The third group of problems involves coherent diffusional and martensitic phase transformations near free surfaces. The study of these phenomena becomes possible because of the availability of a new theoretical approach developed with NSF support. Effective software that will enable realistic simulations of multiple processes simultaneously occurring in complex materials systems will be developed. The code will be distributed to researchers in the field. The galleries of virtual experiments, simulation animations and movies will be collected for public education in materials science and engineering. This activity will also enable more students to participate in advanced interdisciplinary research. There are additional broader impacts in the education of undergraduate and graduate students. %%% This award supports theoretical and computational research and education on the evolution of strain-generating complex structures formed in diffusional and diffusionless transformations as well as of the evolution of defects, e.g. dislocations and cracks, formed in plastic deformation and fracture. The Phase Field Microelasticity model developed by the PI together with 3-dimensional computer simulations will be used to investigate complex microstructures to elucidate the mechanisms controlling their evolution in technologically important systems. Microstructure plays an important role in determining mechanical properties of materials and in materials processing. Research focuses on three problem areas: The first is related to mechanisms controlling coherent decomposition in cubic systems with several structural variants of ordered intermetallics; The second is related to the response of martensite to applied stress in crystallographically and elastically inhomogeneous systems; The third involves coherent diffusional and martensitic phase transformations near free surfaces. Effective software that will enable realistic simulations of multiple processes simultaneously occurring in complex materials systems will be developed. The code will be distributed to researchers in the field. The galleries of virtual experiments, simulation animations and movies will be collected for public education in materials science and engineering. This activity will also enable more students to participate in advanced interdisciplinary research. There are additional broader impacts in the education of undergraduate and graduate students. ***