This study reveals the development of texture and microstructure that occurs during friction stir welding of two aluminum alloys. Friction stir welds of single crystal aluminum and 2195 aluminum were investigated using a stop-action technique, where the microstructure surrounding the tool was preserved by immediately quenching the weld end upon completion. Plan view sections of these weld terminations reveal that slight variations in the crystallographic orientation within the base material have different susceptibilities to the shear deformation produced by the rotating tool. Similarly, the misorientations generated during subgrain development can also induce variations in the lattice rotation rate. The divergent orientations that develop can have different susceptibilities to both rotation and grain subdivision. Lattice rotations continue until achieving a readily-sheared orientation, after which no further rotation is observed. The final texture that develops near the tool corresponds to the B and (B) over bar components of the simple shear texture. In the 2195 alloy, the deposited weld also exhibits a simple shear texture, but it varies with a periodicity of the tool advance per revolution between a pure B/(B) over bar component and a mixture of the B/(B) over bar and C components. Thus, the development of textures ahead of the tool can be correlated directly to the increasing temperature and shear deformation of those regions, while the periodic texture variations of the deposited weld indicate a systematically varying component in the friction stir welding process.

A method to incorporate grain size effects into crystal plasticity is presented. The classical Hall-Petch equation inaccurately predicts the macroscopic yield strength for materials with non-equiaxed grains or materials that contain unequal grain size distributions. These deficiencies can be overcome by incorporating both grain size and orientation characteristics into crystal plasticity theory. Homogenization relationships based on a viscoplastic Taylor-like approach are introduced along with a new function, the grain size and orientation distribution function (GSODF). Estimates of the GSODF for high purity alpha-titanium are recovered through orientation imaging microscopy coupled with chord length measurements. A comparison between the new method and the traditional viscoplastic Taylor approach is made by evaluating yield surface plots.

Examples of texture evolution occurring during annealing of low alloyed Zr sheets submitted to different cold rolling schedules with a moderate thickness reduction (40 and 50\%) are presented here. It is shown that the stability or the texture during primary recrystallisation previously reported for cold rolled Zirconium and Titanium(1-3) is not a general rule. The differences in texture evolution behavior exposed here are linked to the various deformation microstructures which exhibit distinctive heterogeneity distributions. In the case of 40\% cross rolling there is little fragmentation, which induces an oriented nucleation, whereas transverse rolling creates heterogeneous microstructures which favor the abnormal growth of subgrains with specific orientation.

Various tools are useful in the design of materials from texture and related higher order structure statistics. This paper presents recent results in two key areas - homogenization methods linking the material structure to its properties, and reconstruction techniques that produce material realizations from the statistics. Homogenization techniques that are based upon material statistics captured by correlation functions have been available for several decades. With recent increases in computational power, and with the added efficiencies of spectral methods, attention has returned to these methods as viable inputs to multiscale models. One such method that involves a more complex integration scheme than the typical Kroner-type approach, is the strong contrast formulation pioneered by Brown, and more recently developed by Torquato. In this paper we utilize spectral techniques to apply the strong contrast formulation to the computationally demanding case of polycrystalline materials, and discuss the potential benefits to material design. Another important capability in the statistical modeling, analysis and design of materials involves the reconstruction of statistical data in order to recover detailed realizations that can be used in deterministic models. Popular reconstruction techniques such as simulated annealing take large amounts of computational power and time to create relatively small realizations. Recent work, based upon image analysis methods, has resulted in dramatic increases in speed. These advances in reconstruction capabilities are presented and some of the issues inherent in the approach are discussed as they relate to material design.

Recrystallization textures were investigated in thin layers of both pure Cu and alloyed Cu combined with Nb in roll-bonded composites. Texture analysis using X-ray revealed that Cube orientation was the dominant texture component after recrystallization in rolled monolithic pure Cu whereas 2 1 5 < 2 1 1 > and B/S were the dominant components for the recrystallized alloyed Cu. In the composites, however, the rolling texture is retained during annealing in both the pure Cu and the alloyed Cu layers when the layer thickness enters the sub-micron regime. This is attributed to the nucleation and growth of recrystallizing grains being impeded via a reduction in recrystallization driving pressure and the grain boundary movement and growth being limited due to the layer thickness effect. A new term- confined recrystallization was also introduced to describe more accurately the morphological evolution observed within the sub-micron thick layers after annealing and highlights the contrast to either simple recovery or continuous recrystallization.

We have measured and reconstructed via forward modeling a small volume of microstructure of high purity, well annealed nickel using high energy x-ray diffraction microscopy (HEDM). Statistical distributions characterizing grain orientations, intra-granular misorientations, and nearest neighbor grain misorientations are extracted. Results are consistent with recent electron backscatter diffraction measurements. Peaks in the grain neighbor misorientation angle distribution at 60 degrees (Sigma 3) and 39 degrees (Sigma 9) have resolution limited widths of approximate to 0.14 degree FWHM. The analysis demonstrates that HEDM can recover grain and grain boundary statistics comparable to OIM volume measurements; more extensive data sets will lead to full, five parameter grain boundary character distributions. Due to its non-destructive nature, HEDM can then watch, both statistically and through tracking of individual grains and boundaries, the evolution of such distributions with processing of the sample.

Four crystal plasticity codes, the viscoplastic Material Point Simulator (MPS) developed at Cornell and the ViscoPlastic Self-Consistent code (VPSC7b) developed at LANL, and two elastic-viscoplastic codes developed at Drexel University, were employed to calculate deformation textures and mechanical properties of model polycrystalline specimens by simulating isochoric. free upsetting. Uniaxial compression of a model sample with a starting random texture of 5000 grains was carried out at a constant true strain rate of 0.001/s to a true strain of 1.0 with 0.02 strain increments. Material properties simulated a face-centered cubic (FCC) alloy, Type 304 Stainless Steel, and a hexagonal close-packed (HCP) material, unalloyed Ti. Both non-hardening and linear hardening conditions were investigated. Different strain-rate sensitivities simulated deformation conditions appropriate to ambient and elevated temperature conditions. All codes permitted use of the Taylor homogenization hypothesis, resulting in an upper bound for the mechanical properties. All codes produce essentially identical results for the same input material, homogenization hypothesis and deformation conditions. For comparison, one alternative homogenization hypothesis to model grain interactions was examined for each of the MPS and VPSC7b codes.

Samples of AA 6022 were deformed at different temperatures, strain and strain rates through channel die compression. Deformed samples, though quenched immediately after deformation, had both deformed grains/bands and recrystallized grains. Using a simple criterion of grain size and in-grain misorientation developments, respective deformed and recrystallized regions could be distinguished. Deformation temperature/strain rate, or the so-called Zener-Holloman (Z) parameter, had clear effects on the deformed microstructure in terms of orientation stability or textural changes and in terms of in-grain misorientation developments. These, in turn, strongly affected the associated recrystallization behavior including relative contributions from particle stimulated nucleation and contributions from deformed grains/bands of different ideal orientations.