A methodology for measuring and modeling crystallographic texture gradients in processed alloys

The explicit representation of internal material structure in alloy processing and in-service performance simulations is becoming increasingly prevalent. This paper presents a methodology for characterizing and representing a spatially-varying orientation distribution function (ODF) that can be used in processing and performance simulations for alloys containing texture gradients. We use thick AA 7050 aluminum plate, which is known to contain texture gradients, as a case study to demonstrate the methodology, which employs a finite element representation of the ODF initialized using individual lattice orientation measurements taken using the electron backscatter pattern (EBSP) technique. As expected, we find that the texture varies significantly through the plate thickness. We use the ODF to examine the effect of the varying texture on the resulting yield strength distribution as embodied by the average Taylor factor. We find that the predicted yield strength anisotropy is different at different locations through the thickness of the plate. We examine the optimal number of orientation measurements necessary for determining the ODF in the presence of this texture gradient. We find that as we increase the number of orientations, the ODF quickly becomes stable but eventually starts to change under the influence of the texture gradient. We also investigate spatial interpolation of the ODF using the finite element representation. We find that, as with finite element representations of other fields, interpolation accuracy depends on the variation of the field variable and the discretization of the domain. In this case, gradients in both physical space and orientation space affect the accuracy of the interpolation. Finally, the effects of the texture gradient on the mechanical response of the material is demonstrated by employing the ODFs taken from various locations through the thickness of the plate in polycrystal plasticity simulations of uniaxial tension and plane strain compression.