MSE Seminar Series: Alexander Roytburd, UMD
Friday, August 31, 2018
2108 Chem/Nuc (bldg #90)
Speaker: Alexander L. Roytburd, MSE Professor Emeritus at UMD
Title: Past and Future of Elastic Domains in Thermodynamics of Crystalline Materials
In this talk, Dr. Roytburd will present the development on the Thermodynamics of Phase Transformations and Deformations in Crystalline materials for 60 years, starting with the middle of the last century. At that time the thermodynamics of solid materials was just Chemical Thermodynamics constructing temperature-composition diagrams for liquid-solid transformation of multicomponent system. The classical thermo-mechanical aspect of the thermodynamics had been presented only by Clausius-Clapeyron relation between the temperature and pressure of the liquid-solid transformation. Consideration of the same problems for solid-state transformations was doubtful due to plastic relaxation of unavoidable internal stress which makes these transformations irreversible. The exceptional ones were only some martensitic transformations demonstrating reversible growth of martensite crystals inside of the initial phase and their reversible deformation. It was explained by special character of deformation in martensitic phase-twinning. In 1968, Roytburd proposed alternative explanation for the internal structure of a martensitic phase as a collection of domains formed by different orientational variants of the martensite phase. Since these domains remove internal stresses and decrees the elastic energy, he called them “elastic domains” - similar to electric domains in ferroelectrics and magnetic domains in ferromagnetics. However, in real bulk materials with defects, domain relaxation often lost competition to dislocation one. Then, he proposed the polydomain formation at transformations in epitaxial films, which have more perfect crystal structure, but the experimental support of this theory didn’t come until 1988. Since the first observation of polydomain epitaxial films, hundreds of papers, including numerous with Dr. Roytburd’s participation have been published. The new perspective object of thermodynamics study becomes nanocrystals, rod and plate, consisting of single-domain phases. The analysis of phase transformation in nanorods and nanoplates under stress and strain results in constriction temperature – stress and temperature-strain diagrams which are very similar to diagrams of binary and multicomponent solutions. This new thermodynamic approach will be presented in the book Thermodynamics of Single Crystalline Materials (Springer, 2019).