Mechanical characterization of grain boundaries using nanoindentation

•Nanoindentation is effective in mechanically probing grain boundary regions.•Grain boundary pop-ins provide insights into dislocation transmission across grain boundaries.•Hardness estimates do not reliably capture subtle changes in mechanical responses.•Reliable and consistent stress–strain curves can be obtained using spherical nanoindentation.•Indentation techniques can quantify the different roles of grain boundaries.

Grain boundaries and other mesoscale interfaces play an important role in controlling macroscale mechanical properties of various hierarchical materials needed for advanced technologies. Recent enhancements in both instrumentation and data analyses protocols have demonstrated the tremendous potential of nanoindentation as a high-throughput technique for robust and quantitative assessment of the mechanical role of these mesoscale interfaces. These new protocols are geared to address some of the most critical gaps impeding the efforts aimed at the accelerated and cost-effective design and development of new and improved materials. This review summarizes recent advances and identifies specific research directions that are likely to produce the maximum benefit and impact in these pursuits.