Layer Thickness-Dependent Hardness and Strain Rate Sensitivity of Cu-Al/Al Nanostructured Multilayers

doi:10.1007/s40195-016-0372-7

Abstract

Abstract:

Cu-Al/Al nanostructured metallic multilayers with Al layer thickness h _Al varying from 5 to 100 nm were prepared, and their mechanical properties and deformation behaviors were studied by nanoindentation testing. The results showed that the hardness increased drastically with decreasing h _Al down to about 20 nm, whereafter the hardness reached a plateau that approaches the hardness of the alloyed Cu-Al monolithic thin films. The strain rate sensitivity (SRS, m), however, decreased monotonically with reducing h _Al. The layer thickness-dependent strengthening mechanisms were discussed, and it was revealed that the alloyed Cu-Al nanolayers dominated at h _Al ≤ 20 nm, while the crystalline Al nanolayers dominated at h _Al > 20 nm. The plastic deformation was mainly related to the ductile Al nanolayers, which was responsible for the monotonic evolution of SRS with h _Al. In addition, the h _Al-dependent hardness and SRS were quantitatively modeled in light of the strengthening mechanisms at different length scales.

Key words: Nanostructured, films, Cu-Al/Al, multilayers, Hardness, Strain, rate, sensitivity, Layer, thickness, dependence

Ya-Qiang Wang, Zhao-Qi Hou, Jin-Yu Zhang, Xiao-Qing Liang, Gang Liu, Guo-Jun Zhang, Jun Sun. Layer Thickness-Dependent Hardness and Strain Rate Sensitivity of Cu-Al/Al Nanostructured Multilayers[J]. Acta Metallurgica Sinica (English Letters), 2016, 29(2): 156-162.

Figures/Tables 6

Fig. 1 XRD patterns for the Cu-Al/Al NMMs with different thicknesses of Al layer hAl

Fig. 2 Representative TEM a, HRTEM b images of as-deposited Cu-Al/Al NMMs with h Al of 50 nm. The SAED inset in a exhibits the strong Cu (111), Cu (200) and Al (111), Al (200) texture. Fast Fourier transform (FFT) from two interest regions RI (in the Cu-Al layer) and RII (in the Al layer) in b indicate the fcc crystalline structure

Fig. 3 a Typically EDX mapping analysis of the Cu-Al/Al NMMs with h Al of 50 nm, b, c show the uniform distribution of constituent elements

Fig. 4 Representative load-depth curves of Cu-Al/Al NMMs with h Al of 20 nm at different strain rates a, all the Cu-Al/Al NMMs at strain rate of 0.1 s-1 b

Fig. 5 Dependence of nanoindentation hardness on h Al for Cu-Al/Al NMMs (upper part) and Cu/Al multilayers (bottom part) [8]

Fig. 6 a Representative logH versus log ε˙ε˙ plots of Cu-Al/Al NMMs with different h Al, b experimental results of the strain rate sensitivity m as a function of h Al for the Cu-Al/Al NMMs

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