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Meeting 2021 TMS Annual Meeting & Exhibition
Symposium Continuous Phase Transformations
Presentation Title Thermodynamics of the Invar Transition: Phonons vs. Magnetism
Author(s) Stefan Lohaus, Pedro Guzman, Brent Fultz
On-Site Speaker (Planned) Stefan Lohaus
Abstract Scope The invar effect, where the volume remains unchanged with increasing temperatures, is characterized by a continuous magneto-volume transition with competing thermodynamic effects. A change in magnetism from a ferromagnetic high spin state to a low spin state with temperature or pressure is accompanied by a decrease in volume, which counteracts the usual thermal expansion. For a fundamental thermodynamic understanding of this effect, the interaction between phonons, electrons and their spins was investigated. We performed nuclear inelastic X-ray scattering and synchrotron Mössbauer experiments at several pressure and temperature conditions across the invar transition, to measure the phonon spectrum and the magnetic evolution in Ni-Fe invar. These experiments allow us to quantify the vibrational and magnetic entropies and investigate their effect on the free energy of invar. The magnetic and vibrational entropies have opposing effects on the phase transition, helping to explain the unchanging volume and the thermodynamics behind the invar effect.
Proceedings Inclusion? Planned:


Cluster Variation Model of Phase Behavior in Heusler-forming Alloy Systems
Competitive Partitioning and Decomposition Evolution in Nanocrystalline Alloys
Cross-Slip and Work-Hardening in Short-Range Ordered FCC Alloys
Effect of Bulk and Local Phase Transformation on Deformation Mechanisms
Interfacial Spinodals
Intrinsic Phase Stability and Continuous Phase Transformations in TiAlZrN Ultra-hard Nitride Coatings
Magnetically Driven Short-range Order in the CrCoNi System
Microstructural Engineering of Ni-based Superalloys Processed by Conventional and Additive Manufacturing
Phase-field Modelling of Transformation Pathways and Microstructural Evolution in MPEAs (Multi Principle Element Alloys)
Phase Competition in the Two Steps Continuous Phase Transformation during Solidification of Terbium
Short-range Clustering and Ordering Evolution of Ni-22Cr-13Mo Alloy
Structural Transformations Driven by Irradiation in the High Defect Density Limit
Study of Precipitation Behavior of High-Cr Ni-based Filler Metals Using In-situ S/TEM
Thermodynamics of the Invar Transition: Phonons vs. Magnetism

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