Fig. 1. Typical BF (a) and DF (b) TEM images of the as-deposited ng Ni-14.2Mo. Insets in (a) and (b) are the corresponding SAED pattern and histogram of grain size distribution, respectively, exhibiting randomly orientated tiny grains and homogeneous grain size distribution.

Fig. 2. (a) Microhardness (H) at different holding time for the ng Ni-14.2Mo at RT and LNT, where circles and squares are the experimental data, the dotted lines are the corresponding fitting lines with Eq. (3). (b) Variation of strain rate against holding time of ng Ni-14.2Mo. (c) Logarithmic plots of hardness as a function of indentation strain rate ε˙ for the ng Ni-14.2Mo at RT and LNT. Strain rate sensitivity m was estimated from the slope of the linear fit.

Fig. 3. DF images of ng Ni-14.2Mo taken underneath the indented surface (indicated by the black dashed lines) at RT (a) and LNT (b), respectively. Insets in (a) and (b) are the corresponding histograms of grain size distribution respectively. The cumulative area fractions of grains versus grain size in the subsurface layer of ng Ni-14.2Mo sample before and after microhardness test at RT and LNT are shown in (c). Clearly, very little grain coarsening occurred at LNT.

Fig. 4. Cross-sectional BF (a) and DF (b) TEM images of ng Ni-14.2Mo after microhardness test at LNT. Inset in (a) is the SAED pattern where a slight texture is observed. Two parallel red dashed lines in the enlarged BF (c) and DF (d) TEM images outline a shear band. Black dashed lines in (a, c) and white dashed lines in (b, d) designate the indented surface. Inset in (d) is the corresponding cumulative area fraction of grains against grain size. (e) HRTEM image taken from a shear band. (f) Enlarged image of area “A” as outlined in (e), where multiple parallel stacking faults are observed.