The Role of Surface-Energy on Texture Development in Rare-Earth-Free Auxetic and Magnetostrictive Materials Alison B. Flatau, University of Maryland College Park, DMR Fig. 1: Calculations of total grain boundary and surface energies as a function of matrix grain radius (r m ) for normal grain growth, NGG, (n=1) and abnormal grain growth, AGG, (n  10 ) of (011) grain with the ratio (n) of abnormal grain to matrix grain size of 10~100.  Total interface energy model calculations  Experimental results on abnormal grain growth (AGG) Fig. 2: Surface energy relative to that of clean surface (k=  hkl /  o hkl ) needed for single crystal growth in varying sample thicknesses. The relative surface energy of each crystal surface plane (k  o hkl ) is incorporated into the total interface energy model as each  hkl can be replaced by k  o hkl, where  o hkl is for a clean surface. Fig. 3: (011) single grain growth (right) as if a single crystal from primary recrystallized sample with random oriented small grains (left) through annealing of Fe- Ga based alloy sheets under a sulfur atmosphere.  Research Goals 1) Discovery of new rare-earth-free iron-based alloys with auxetic and magnetostrictive properties and of new processes for selective development of their crystallographic texture by controlling surface energy. 2) Understanding of the mechanisms that lead to abnormal grain growth (AGG) with a preferred texture/grain orientation in polycrystalline metals, by including surface energy in thermodynamic models. 3) Use of first principle calculations to optimize selection of candidate alloys (with Prof. R. Wu, Collaborator at UCI).  Significant Findings 1)A total interface energy model for Fe-Ga system can be used to quantify the dominant driving force for AGG in terms of both surface and GB energies as a function of matrix grain size (Fig. 1). 2)From the model calculations, we can determine the regimes of single crystal growth (f hkl =1.0) with varying thickness (Fig. 2). Expect model applicability extends to thin film and thin foil materials down to the nano scale. 3)AGG as if a single crystal occurs after primary recrystallization demonstrated through control of surface energy using anneal under a sulfur atmospheres (Fig. 3).  Technical and Scientific Impact This is a significant contribution to understanding of AGG phenomena related to the role of surface energy in metallic materials. This work will provide lead and rare-earth-free alternatives to expensive single crystal materials by allowing massive and low-cost production of single-crystal-like materials for applications of magnetostrictive sensors, actuators, structural auxetics, etc.

The Role of Surface-Energy on Texture Development in Rare-Earth-Free Auxetic and Magnetostrictive Materials Alison B. Flatau, University of Maryland College Park, DMR High school interns, John (Left) and Angela (Right), stacking tetrakaidecahedron unit grains to understand grain growth phenomena. A new Ph.D. student, Michael, being trained in the use of an AFM system as well as SEM and EBSD systems.  Education and Training A new Ph.D. student, Michael, joined this program since April 2014, and is being trained in the use of an Atomic Force Microscopy (AFM) as well as Electron BackScatter Diffraction (EBSD) system in a Scanning Electron Microscope (SEM) to analyze grain boundary structures. High school students, Angela and John, have worked in our laboratory as a summer internship (Jun-July 2014). They had hands-on-experience working on magnetostrictive sample preparation, bonding of strain gauge, and measurement of strain. Furthermore, they made stacking tetrakaidecahedron unit grains to understand grain growth phenomena and to calculate interface area incorporated into total interface energy models Dr. Na (co-PI) developed.  Broader Impact A paper titled “The magnetostrictive Alfenol whisker sensor performance and sensitivity to whisker thickness” will be published at IEEE Transactions on Magnetics in November A paper titled “Prediction of solid-state single crystal growth beyond abnormal grain growth”, will be submitted to Nature Materials.