Grain boundaries play an important role in the overall mechanical performance of metals and alloys; however, isolating the effects of individual grain boundaries remains rather challenging experimentally. In this work, wire-feed, electron beam additively manufactured tantalum is studied under shock loading conditions generating incipient spall damage. Three grain boundaries aligned parallel to the shock direction were isolated inside a single sample. Postmortem metallography showed voids preferentially appeared on two of the three grain boundaries which had high misorientation angles > 30° compared to the third grain boundary with a relatively lower misorientation angle < 10°. Nanoindentation in grain boundary regions for both pyramidal and spherical tips showed characteristically different strain hardening trends for each grain boundary. Significant local strain hardening is present on both sides of one high angle grain boundary, while strain softening is captured at the other high angle grain boundary. A negligible trend of either hardening or softening is shown in the vicinity of the single low angle grain boundary. This leads to the conclusion that the trend of strain hardening/softening in grain boundary regions is not monotonically correlated to the susceptibility of specific grain boundaries to an increased propensity for void damage.
Bibliographical noteFunding Information:
The authors acknowledge funding from the Laboratory Directed Exploratory Research (LDRD) program at Los Alamos National Laboratory (LANL), USA. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science user facility operated for the U.S. Department of Energy (DOE) Office of Science, USA. Los Alamos National Laboratory, an affirmative action equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy , USA under DE-AC52-06NA25396 . We wish to thank Roberta Beal, Veronica Livescu, and Rodney McCabe of LANL for their insight into metallographic and microscopy endeavors.
- Dynamic deformation
- Electron microscopy
- Grains and interfaces
- Stress/strain measurements