Deformation induced grain rotations in single crystal tantalum

Validation studies of crystal plasticity fi nite element models typically compare model predictions of strain fi elds withexperimental measurements; often ignored are the grain rotations predicted by the model. Accurate predictions ofcrystallographic rotations are necessary for trustworthy predictions of strain fi elds, deformed texture, and failure.This is especially important for body centered cubic (BCC) metals because the exact nature of BCC slip is stillunder debate [1]. Orientation changes caused by deformation in BCC materials have been predicted by models[2], but little experimental data exists that can confi rm or contradict these predictions. To further complicate thesituation, there are indications that grain rotations follow different paths in different BCC metals (e.g., Mo and Ta).This study presents experimental measurements of grain rotations in single crystal Ta resulting from quasistaticdeformation using multiple techniques. In one set of experiments, single crystal specimens are loaded using an insitu load frame within a scanning electron microscope. Crystallographic rotation is directly observed by repeatedEBSD measurements at several load levels. In other experiments, grain orientations (measured by X-ray diffrac-tion and/or EBSD) are compared before and after loading to specifi c strain levels. Full-fi eld measurements ofstrain are made during loading to relate orientation changes to local deformation behavior. These grain rotationmeasurements are compared to predictions from a BCC crystal plasticity model [3] to examine the effects of modelchoices. Ultimately, these experiment-model comparisons should improve crystal plasticity model predictions ofre-orientations and strains, not only for single crystals, but for polycrystals as well. Sandia National Laboratories isa multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of LockheedMartin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contractDE-AC04-94AL85000. REFERENCES[1] Weinberger, C.R., Boyce, B.L., Battaile, C.C. International Materials Reviews. 2013, 58,296-314.[2] Weinberger, C.R., Battaile, C.C., Buchheit, T.E., Holm, E.A. Int. J. Plast. 2012, 37, 16-30.[3] Lim, H., Carroll, J.D., Battaile, C.C., Buchheit, T.E., Boyce, B.L., Weinberger, C.R. Int J.Plast. (in review).