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The rate sensitivity and plastic deformation of nanocrystalline tantalum films at nanoscale.

Cao Z, She Q, Huang Y, Meng X - Nanoscale Res Lett (2011)

Bottom Line: Nanoindentation creep and loading rate change tests were employed to examine the rate sensitivity (m) and hardness of nanocrystalline tetragonal Ta films.Experimental results suggested that the m increased with the decrease of feature scale, such as grain size and indent depth.The magnitude of m is much less than the corresponding grain boundary (GB) sliding deformation with m of 0.5.

View Article: PubMed Central - HTML - PubMed

Affiliation: National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, People's Republic of China. mengxk@nju.edu.cn.

ABSTRACT
Nanoindentation creep and loading rate change tests were employed to examine the rate sensitivity (m) and hardness of nanocrystalline tetragonal Ta films. Experimental results suggested that the m increased with the decrease of feature scale, such as grain size and indent depth. The magnitude of m is much less than the corresponding grain boundary (GB) sliding deformation with m of 0.5. Hardness softening behavior was observed for smaller grain size, which supports the GB sliding mechanism. The rate-controlling deformation was interpreted by the GB-mediated processes involving atomic diffusion and the generation of dislocation at GB.

No MeSH data available.


Related in: MedlinePlus

Load-depth curves at different loading rates for the Ta films with different d; a d = 10 nm and b d = 20 nm.
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Figure 2: Load-depth curves at different loading rates for the Ta films with different d; a d = 10 nm and b d = 20 nm.

Mentions: It is useful to obtain the effect of strain/loading rate on the mechanical response in revealing the deformation mechanism of NC metals. The variations of load-depth curves of NC Ta films of d = 10 and 20 nm with loading rate change are shown, respectively, in Figure 2a,b. Five different loading rates were performed for the rate change testing. With the increased loading rate, in both cases as shown in Figure 2a, b, a higher indentation force is required to impose the same displacement. The influence of loading rate on mechanical response becomes more remarkable for Ta films with a smaller d of 10 nm. This suggests that the reduced d can enhance the rate sensitivity of NC Ta films. The applied indentation forces become much lower for a smaller d at a given depth, which means Ta film with d of 10 nm is of lower hardness. The hardness is determined by means of the Oliver-Pharr method [20]. The inset in Figure 3 shows the change of Young's moduli (E) with the strain rate. It is found that E is directly proportional to d. As a result, E increases with d. These values are slightly smaller than that of NC tetragonal Ta film with larger d of 32.3 nm reported by Zhang et al. [18]. It is believed that the stiffness of GB is lower than that of grain interior. The decreased E may be associated with the increased GB volume corresponding to decreasing d [21,22]. In addition, as strain rate increases, E increase in Ta films. The rate-sensitive modulus is contrary to that of NC Au films reported by Jonnalagadda et al. [23]. The elastic deformation usually encompasses both elastic and anelastic behaviors, where the anelastic behavior arising from atomic reconfigurations is time dependent on a much longer scale, i.e., rate-dependent behavior [24]. The GB-mediated process involving atomic diffusion and dislocation generation results in the anelastic behavior, which should be responsible for the rate-sensitive modulus.


The rate sensitivity and plastic deformation of nanocrystalline tantalum films at nanoscale.

Cao Z, She Q, Huang Y, Meng X - Nanoscale Res Lett (2011)

Load-depth curves at different loading rates for the Ta films with different d; a d = 10 nm and b d = 20 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211239&req=5

Figure 2: Load-depth curves at different loading rates for the Ta films with different d; a d = 10 nm and b d = 20 nm.
Mentions: It is useful to obtain the effect of strain/loading rate on the mechanical response in revealing the deformation mechanism of NC metals. The variations of load-depth curves of NC Ta films of d = 10 and 20 nm with loading rate change are shown, respectively, in Figure 2a,b. Five different loading rates were performed for the rate change testing. With the increased loading rate, in both cases as shown in Figure 2a, b, a higher indentation force is required to impose the same displacement. The influence of loading rate on mechanical response becomes more remarkable for Ta films with a smaller d of 10 nm. This suggests that the reduced d can enhance the rate sensitivity of NC Ta films. The applied indentation forces become much lower for a smaller d at a given depth, which means Ta film with d of 10 nm is of lower hardness. The hardness is determined by means of the Oliver-Pharr method [20]. The inset in Figure 3 shows the change of Young's moduli (E) with the strain rate. It is found that E is directly proportional to d. As a result, E increases with d. These values are slightly smaller than that of NC tetragonal Ta film with larger d of 32.3 nm reported by Zhang et al. [18]. It is believed that the stiffness of GB is lower than that of grain interior. The decreased E may be associated with the increased GB volume corresponding to decreasing d [21,22]. In addition, as strain rate increases, E increase in Ta films. The rate-sensitive modulus is contrary to that of NC Au films reported by Jonnalagadda et al. [23]. The elastic deformation usually encompasses both elastic and anelastic behaviors, where the anelastic behavior arising from atomic reconfigurations is time dependent on a much longer scale, i.e., rate-dependent behavior [24]. The GB-mediated process involving atomic diffusion and dislocation generation results in the anelastic behavior, which should be responsible for the rate-sensitive modulus.

Bottom Line: Nanoindentation creep and loading rate change tests were employed to examine the rate sensitivity (m) and hardness of nanocrystalline tetragonal Ta films.Experimental results suggested that the m increased with the decrease of feature scale, such as grain size and indent depth.The magnitude of m is much less than the corresponding grain boundary (GB) sliding deformation with m of 0.5.

View Article: PubMed Central - HTML - PubMed

Affiliation: National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, People's Republic of China. mengxk@nju.edu.cn.

ABSTRACT
Nanoindentation creep and loading rate change tests were employed to examine the rate sensitivity (m) and hardness of nanocrystalline tetragonal Ta films. Experimental results suggested that the m increased with the decrease of feature scale, such as grain size and indent depth. The magnitude of m is much less than the corresponding grain boundary (GB) sliding deformation with m of 0.5. Hardness softening behavior was observed for smaller grain size, which supports the GB sliding mechanism. The rate-controlling deformation was interpreted by the GB-mediated processes involving atomic diffusion and the generation of dislocation at GB.

No MeSH data available.


Related in: MedlinePlus