Description
Shear localization is often a failure mechanism in materials subjected to high strain rate deformation. It is generally accepted that the microstructure evolution during deformation and the resulting heterogeneities strongly influence the development of these shear bands. However, current crystal plasticity models fail to effectively capture the heterogeneous plastic deformation. One critical missing piece in these models is the information on the development of local mechanical heterogeneities during deformation. Consideration of local microstructure evolution through electron back scattered diffraction (EBSD) measurements constitutes only one aspect of the characterization of a deformed material. Another equally important attribute, which is somewhat difficult to capture, is the change in local mechanical properties at the submicron length scale. With the recent advances in spherical nanoindentation data analysis, there is now an unprecedented opportunity to obtain insights into the change in local mechanical properties during deformation in materials at submicron length scales. In this study, we quantify the evolution of microstructure and local mechanical properties in tantalum under dynamic loading conditions, to capture the structure–property correlations at the submicron length scale, with an aim to gain insights into failure mechanisms in these materials. A split Hopkinson pressure bar is used to dynamically (strain rates ~103) impart predetermined levels of strain into high purity tantalum samples. Insights into the structure–property relationships in these samples will be obtained by combining local mechanical property information captured using spherical nanoindentation with complimentary structure information at the indentation site obtained using EBSD. As a first step, the orientation dependence of the indentation yield strength in tantalum in the fully annealed condition (negligible dislocation density) will be mapped. This yield contour has tremendous value in studies on deformed polycrystalline samples. When characterizing deformed samples (appreciable dislocation content, nonuniformly distributed in the sample), the yield contours will be used to reliably de-couple the contributions to the local indentation yield strength from the local crystal lattice orientation and the local dislocation density. Thus, local dislocation density variation within deformed samples, as a function of orientation, grain boundaries, and triple junctions will be established. This constitutes an extremely powerful dataset from which insights into the local mechanical properties of various structural constituents at a submicron length scale will be extracted. This information can in turn be used to determine the contribution of individual features to the local as well as overall (macroscale) performance of the material. Specifically, this study will provide an understanding of the evolution of local structure and mechanical properties during high strain-rate deformation of tantalum, in particular effects of orientation and individual grain boundaries on the development of mechanical heterogeneities within the deformed microstructure. This study will also serve to establish an initial, comparative basis for future studies focused on quantifying the strength of damaged tantalum.
Recommended Citation
Vachhani, S., Mara, N., Livescu, V., & Cerreta, E. (2014). Evolution of local mechanical behavior during high strain rate deformation of tantalum. In A. Bajaj, P. Zavattieri, M. Koslowski, & T. Siegmund (Eds.). Proceedings of the Society of Engineering Science 51st Annual Technical Meeting, October 1-3, 2014 , West Lafayette: Purdue University Libraries Scholarly Publishing Services, 2014. https://docs.lib.purdue.edu/ses2014/mss/mmemb/6
Evolution of local mechanical behavior during high strain rate deformation of tantalum
Shear localization is often a failure mechanism in materials subjected to high strain rate deformation. It is generally accepted that the microstructure evolution during deformation and the resulting heterogeneities strongly influence the development of these shear bands. However, current crystal plasticity models fail to effectively capture the heterogeneous plastic deformation. One critical missing piece in these models is the information on the development of local mechanical heterogeneities during deformation. Consideration of local microstructure evolution through electron back scattered diffraction (EBSD) measurements constitutes only one aspect of the characterization of a deformed material. Another equally important attribute, which is somewhat difficult to capture, is the change in local mechanical properties at the submicron length scale. With the recent advances in spherical nanoindentation data analysis, there is now an unprecedented opportunity to obtain insights into the change in local mechanical properties during deformation in materials at submicron length scales. In this study, we quantify the evolution of microstructure and local mechanical properties in tantalum under dynamic loading conditions, to capture the structure–property correlations at the submicron length scale, with an aim to gain insights into failure mechanisms in these materials. A split Hopkinson pressure bar is used to dynamically (strain rates ~103) impart predetermined levels of strain into high purity tantalum samples. Insights into the structure–property relationships in these samples will be obtained by combining local mechanical property information captured using spherical nanoindentation with complimentary structure information at the indentation site obtained using EBSD. As a first step, the orientation dependence of the indentation yield strength in tantalum in the fully annealed condition (negligible dislocation density) will be mapped. This yield contour has tremendous value in studies on deformed polycrystalline samples. When characterizing deformed samples (appreciable dislocation content, nonuniformly distributed in the sample), the yield contours will be used to reliably de-couple the contributions to the local indentation yield strength from the local crystal lattice orientation and the local dislocation density. Thus, local dislocation density variation within deformed samples, as a function of orientation, grain boundaries, and triple junctions will be established. This constitutes an extremely powerful dataset from which insights into the local mechanical properties of various structural constituents at a submicron length scale will be extracted. This information can in turn be used to determine the contribution of individual features to the local as well as overall (macroscale) performance of the material. Specifically, this study will provide an understanding of the evolution of local structure and mechanical properties during high strain-rate deformation of tantalum, in particular effects of orientation and individual grain boundaries on the development of mechanical heterogeneities within the deformed microstructure. This study will also serve to establish an initial, comparative basis for future studies focused on quantifying the strength of damaged tantalum.