The John Cahn Memorial Symposium: Session II
Sponsored by: TMS Materials Processing and Manufacturing Division
Program Organizers: James Warren, National Institute of Standards and Technology; W. Craig Carter, MIT; Carol Handwerker, Purdue University; Yuri Mishin, George Mason University
Wednesday 2:00 PM
March 1, 2017
Location: San Diego Convention Ctr
Session Chair: Carol Handwerker, Purdue University; Yuri Mishin, George Mason University
2:00 PM Invited
Beyond the Gorsky Effect – Exploring Larché-Cahn Open System Elasticity in Experiment: Shan Shi1; Jörg Weissmüller2; 1Helmholtz-Zentrum Geesthacht; 2Hamburg University of Technology
With their Linear Theory of Thermochemical Equilibrium of Solids under Stress  and with later extensions, John Cahn and Francis Larché established a fundamental link between solid mechanics and the thermodynamics of multicomponent systems. Well in the 20th century each of the two fields was mature, and interactions between alloy chemistry and stress were acknowledged and understood in individual instances, yet it was only with the Larché-Cahn theory that a general joint description was presented. In view of the role of that theory as a key achievement of 20th century thermodynamics, it is amazing that little, if any, direct experimental demonstrations of its power have been reported. Arguably the most closely related phenomenon of experimental interest is the Gorsky effect, a transport of solute stimulated by cyclic applied stress. Internal friction experiments which exploit the Gorsky effect for measuring diffusion parameters have been of interest to the field of hydrogen diffusion in metals. Yet, the opportunities of probing the quasi-static elastic constants in open systems and of possibly even tuning the elastic response of materials based on the predictions by Larché and Cahn appear to have so far been largely overlooked. The talk will discuss experimental approaches that explore the ramifications of mobile solute on the elastic response of solids, confirming the impact of the Larché-Cahn theory for materials behavior.
2:30 PM Invited
Phase Transition and Anomalous Diffusion in Metastable β Ti-Mo: Srinivasan Srivilliputhur1; Niraj Gupta1; Srikumar Banerjee1; 1University of North Texas
Dr. John Cahn made seminal contributions to structural phase transformations that are ubiquitous in nature and fundamental to modern materials science. For example, the nature of ω phase formation and its subsequent transformation to the thermodynamically stable α phase upon annealing has been extensively studied experimentally for over 50 years using many of the fundamental principles discovered by Dr. Cahn. Yet, several significant questions about the atomistic mechanisms remain. In this tribute to him we present our results on the formation of hexagonal omega phase at the nanoscale by quenching prototypical beta titanium-molybdenum binary alloys. We address the following important questions using ab-initio methods: (i) How does an optimum level of molybdenum stabilize the ω phase? Can ω transform to the α-phase in the crystal bulk or only at high-energy regions such as grain boundaries. Furthermore, can atomic configurations within ω particles act as embryos for nucleation of the α phase? (ii) Experiments reveal that many ω forming alloys exhibit anomalous (non-Arrhenius) diffusion behavior. What is the atomistic mechanism responsible for such anomalous diffusion? Importantly, how does temperature and concentration of beta stabilizing elements influence anomalous diffusion? (* Funded by the National Science Foundation)
3:00 PM Invited
How Some Quasicrystals Might Grow: Jean Taylor1; 1Rutgers University and Courant Institute, NYU
Questions about how quasicrystals might self-assemble have been raised ever since their discovery. Overlapping clusters have been used to describe quasicrystal structures; how might they be related to growth? For Tsai-type quasicrystals, a subcluster of the RTH cluster used for their description may perhaps occur in the liquid, similar to the icosahedral clusters that Frank proposed may exist in single-component liquids. If so, then two such subclusters coming together would produce the overlap region between two RTH clusters, and the addition of a third subcluster would provide the combination of overlapping and face-to-face junctions that are seen in all of the Tsai-type quasicrystals and their periodic approximants. Stoichiometry alone would then determine whether the crystal growing around this large nucleus would be periodic or quasiperiodic.
3:30 PM Break
3:50 PM Invited
John Cahn and Aesthetics of Materials: Leonid Bendersky1; 1NIST
John always had fascination with aesthetics and symmetry of materials, which was in part inherited from his mentor Cyril Smith. This fascination was reflected not only in his beautiful equations, but also throughout his career learning about and predicting well-organized shapes, defects, and structures. John always had a kin interest in experiment and in interaction with experimentalists. Naturally, the aesthetics and underlying laws of the icosahedral phase discovered by his friend Danny Shechtman enchanted him; he got deeply involved in quasicrystal’s research for many years. My association with John was mainly related to quasicrystals: whenever I was lucky to discover by electron microscopy something new, John was always of great support. I am happy to present a few examples of my collaboration with John that are related to the celebrated icosahedral symmetry: (1) work on crystalline aggregates with icosahedral symmetry; (2) work on special grain boundaries based on local symmetries; and (3) work on highly ordered noncrystalline metallic phase coined by John the Q-phase.
4:20 PM Invited
Quasi-history of Quasi-crystallinity: Olivier Hardouin Duparc1; 1Ecole Polytechnique
John Cahn contributed to the birth of quasicrystals because he believed in the observations made by Dan Shechtman about the existence of an icosahedral metallic phase with long-range orientational order up to the point of writing with Shechtman, Ilan Blech and Denis Gratias a paper which was successfully submited to Physical Review Letters. Under the sign of the icosahedron I’ll start with Plato’s physical chemistry in his Timeaus, to Kepler’s 1595 planetary model and to the invention of the mathematical quasiperiodic functions in order to illustrate some relations between mathematics and physics which do not have to be simple.
4:50 PM Invited
John Cahn's Boss, Really?: Lyle Schwartz1; 1Courtesy Professor at the University of South Florida
From my earliest days, when I met John who was visiting John Hilliard at Northwestern where I was a grad student, until now, his influences on my life and career were profound. I marveled at his deep understanding of the subjects I was struggling with, used his results in work that underlay a major segment of my and my student’s own work, and sought his advice as my career advanced. How could I ever imagine that one day he would be influential in the move that brought me to the National Bureau of Standards and made me “John Cahn’s Boss”. In this talk I’ll trace the path of our interaction during those forty years and hope to add just a bit of personal information about this giant of our field.
5:20 PM Concluding Comments