In-Situ Investigation of Grain Boundary Mobility and Character in Aluminum Alloys in the Presence of a Stored Energy Dri
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N6.5.1
In-Situ Investigation of Grain Boundary Mobility and Character in Aluminum Alloys in the Presence of a Stored Energy Driving Force Mitra L. Taheri1, Anthony D. Rollett1, and Hasso Weiland2 1
Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15232, USA 2
Alcoa Technical Center, Alcoa Center, PA 15609, USA
ABSTRACT This paper investigates the effect of solute in Al alloys on grain boundary character and mobility based on experiments in which individual boundaries migrate under a stored energy driving pressure acquired from prior plastic strain; among those studied are Zr, Fe and Si. A compensation effect is noted for both alloys studied with respect to both temperature and solute content. As supported by the literature, boundaries exhibit a maximum mobility for a 3839º misorientation in initial annealing experiments; this mobility maximum is asymmetric with a sharp cutoff below 38-39º but a more gradual decrease at misorientations beyond 40º. The presence of a minimum at 38-39º is found at both higher temperatures and higher solute concentrations. A shift in texture dependency with solute and temperature is also observed. This transition from a local mobility maximum to a minimum is discussed within the context of recent developments in solute drag theory. INTRODUCTION Due to their pronounced effect on the behavior and use of alloys, impurities have long been a subject of interest when studying microstructural development in materials, especially the effect of composition on recrystallization kinetics. All commercially significant alloys have substantial levels of solute that affect the migration of grain boundaries during recrystallization, namely a ‘solute drag effect’ [1]. Only a small amount of experimental data has been collected with respect to solute drag effects, all of which was performed within a Scanning Electron Microscope in conjunction with the use of Electron Backscattered Diffraction [2-7]. These methods allow for the observation of solute effects on kinetics [7, 10] as well as in differences in growth mechanisms of particular boundary types [2-5]. Correlations have been noted between the pre-factor and the effective activation enthalpy when the temperature dependence of the mobility is expressed as an Arrhenius relationship [3, 4].The quantification of the effect of individual solutes, however, (e.g., not grouped together as one contributing impurity concentration) remains as relatively unexplored territory. The current literature suggests a preference for boundary types depending on temperature and solute content [4-6], suggesting a compensation effect; this paper further explores the effect of both temperature and solute on boundary character and mobility during recrystallization. The observations in these experiments suggest that stored energy driving forces produce similar anisotropic behavior to those carried out under a curvature driving force.
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EXPERIMENTAL The mobility of individual grain boundaries during recrystallization was stud
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