Some critical experiments on the strain-rate sensitivity of nanocrystalline nickel

• Published in: Acta materialia 2003-10, Vol.51 (17), p.5159-5172
• Main Authors: Schwaiger, R, Moser, B, Dao, M, Chollacoop, N, Suresh, S
• Format: Article
• Language: English
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Metals. Metallurgy; Nanocrystalline materials; Nanoindentation; Nanoscale materials and structures: fabrication and characterization; Nickel; Physics; Strain-rate dependence; Tension test
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/S1359-6454(03)00365-3

Systematic experiments have been performed to investigate the rate sensitivity of deformation in fully dense nanocrystalline Ni using two different experimental techniques: depth-sensing indentation and tensile testing. Results from both types of tests reveal that the strain-rate sensitivity is a strong function of grain size. Specifically microcrystalline and ultra-fine crystalline pure Ni, with grain size range of >1 μm and 100–1000 nm, respectively, exhibit essentially rate-independent plastic flow over the range 3×10 −4 to 3×10 −1 s −1, whereas nanocrystalline pure Ni with a grain size of approximately 40 nm, exhibits marked rate sensitivity over the same range. A simple computational model, predicated on the premise that a rate-sensitive grain-boundary affected zone exists, is shown to explain the observed effect of grain size on the rate-dependent plastic response.