Bridging Simulations and Experiments in Microstructure Evolution M. C. Demirel, 1,2,3 A. P. Kuprat, 2 D. C. George, 2 and A. D. Rollett 3 1 Materials Science and Technology, MST-8, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 2 Theoretical Division, T-1, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 3 Carnegie Mellon University, Department of Materials Science & Engineering, Pittsburgh, Pennsylvania 15213 (Received 28 May 2002; published 9 January 2003) We demonstrate the importance of anisotropic interface properties in microstructure evolution by comparing computed evolved microstructures to final experimental microstructures of 5170 grains in 19 thin aluminum foil samples. This is the first time that a direct experimental validation of simulation has been performed at the level of individual grains. We observe that simulated microstructures using curvature-driven grain boundary motion and anisotropic interface properties agree well with experi- mentally evolved microstructures, whereas agreement is poor when isotropic properties are used. DOI: 10.1103/PhysRevLett.90.016106 PACS numbers: 68.35.–p, 68.37.Hk, 68.55.Jk, 81.40.–z This paper seeks to extend previous statistical compari- sons of predicted and experimentally observed grain boundary network evolution by demonstrating agreement at the scale of individual grains, provided that the anisot- ropy of interfacial energy and mobility is included. With very few exceptions [1], only statistical comparisons have been made such as determining the exponent in the power-law relationship between average radius and time. In addition to this general aim, we consider coarsening in networks of low angle grain boundaries (subgrains), which has been the subject of some controversy. Some authors have postulated that the interfaces are essentially sessile because they are themselves networks of lattice dislocations and that coarsening occurs by rotation of individual subgrains [2,3]. Rotation is driven by minimi- zation of interfacial energy and tends to eliminate the misorientation between certain pairs of adjacent grains, thus causing coalescence and coarsening to occur. Gleiter, on the other hand, showed that low angle grain boundaries migrate under curvature driving forces just as observed for high angle grain boundaries [4]. Clearly, both mecha- nisms are feasible for coarsening of subgrain networks, and so it is of some importance to determine which one is applicable to real materials. Since the torque that drives grain rotation is supralinear in (inverse) grain size, it is reasonable to expect that curvature-driven migration dominates at the large grain sizes observed in this ex- periment whereas rotation should dominate in nanoscale grain sizes. We have previously shown a strong agreement between small-scale grain growth experiments and anisotropic three-dimensional simulations [5] obtained from elec- tron backscatter diffraction (EBSD) measurements [6]. Using the same technique, we obtained data for 5170 grains from 19 thin aluminum foil samples with colum- nar grain structure (thereby avoiding serial section- ing) and compared our computational results with experiments. Our simulation model uses curvature-driven motion implemented by GRAIN3D [7], a three-dimensional, gradient-weighted moving finite elements code. We as- sume that the grain boundary motion is proportional to the local mean curvature of the interface, v n  ; (1) where v n is the normal velocity of the interface,  is the grain boundary mobility, and  is the interface energy per unit area.  is the sum of principal curvatures, i.e., twice the mean curvature; in these simulations, the cur- vature is equal to the curvature observed in the plane. The interfaces are represented as piecewise linear. For details of the simulation method, the reader should refer to Ref. [7]. The interfacial anisotropy is based on a previous deter- mination of grain boundary energy, , and mobility, , from a statistical/multiscale analysis of triple junction geometry and crystallography in aluminum [8–10], and the result for energy is in very good agreement with the Read-Shockley model [11] as expected. In the highly textured, columnar grain structure aluminum foil we investigated, most interfaces are low angle boundaries (misorientation <15  ). The grain boundary mobility is low for small misorientations but undergoes a sharp transition to high mobilities between 10  and 15  in misorientation which is in agreement with the literature [12–14]. For our simulations, we assume that all high angle grain boundaries ( > 15  ) have the same values of energy and mobility. The occurrence of high angle boundaries is very low in this material, which means that only a small error is introduced by this assumption. This experiment permitted a verification of curvature-driven interface motion [4], as compared with the competing mechanism of grain rotation [3] leading to coalescence [2]. We found a standard deviation of 0:98  in misorien- tation angle between the initial and final experimental PHYSICAL REVIEW LETTERS week ending 10 JANUARY 2003 VOLUME 90, NUMBER 1 016106-1 0031-9007= 03=90(1)=016106(4)$20.00  2003 The American Physical Society 016106-1