S.P. Bhusare; A. Lambai; J. Schwiedrzik; J. Michler; B.L. Boyce; G. Mohanty
Materials & Design 260 (2025) 115067
This study presents the development of nanoindentation stress relaxation testing as a robust method for
extracting deformation activation parameters in materials. Using an in-situ, displacement-controlled nano
indenter, stress relaxation tests were conducted on nanocrystalline (nc) nickel (Ni) with Berkovich, cube-corner,
and spherical tips. Results showed good agreement with uniaxial micropillar compression relaxation tests per
formed on the same sample, demonstrating the reliability of the testing protocol and data analysis methodology.
The apparent and effective activation volumes were comparable, indicating minimal changes in deformation
substructure during indentation relaxation. Effective activation volumes averaged 8.11 ± 3.3 b3 for indentation
and 5.91 ± 0.8 b3 for micropillar compression, with corresponding strain rate sensitivity exponents (m) of 0.028
± 0.002 and 0.028 ± 0.001, respectively. These consistent values underscore the reliability of the indentation-
based approach for probing transient plasticity. Additional tests on single-crystal (sx) Ni and chromium (Cr)
revealed strong and weak strain dependence of activation volume, respectively. Overall, this work establishes
nanoindentation stress relaxation as a promising technique for investigating size effects and transient plasticity
mechanisms in metals.