**8. Conclusions**

The effect of grain size on the superplastic deformation of metallic materials was studied. There were different combination of deformation mechanisms, accommodation mechanism, and rate-controlling mechanisms that governed the superplastic deformation which depends on the grain size, temperature, and strain rate. The following conclusions were obtained based on the detail study.


**111**

**Author details**

Chennai, India

and Ch. Srinivasa Rakesh

provided the original work is properly cited.

\*Address all correspondence to: edjay@iitm.ac.in

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Department of Engineering Design, Indian Institute of Technology Madras,

Allavikutty Raja, Rengaswamy Jayaganthan\*, Abhishek Tiwari

*Effect of Grain Size on Superplastic Deformation of Metallic Materials*

• The kinetics of nano-grained deformation is different from that of their

higher-scale grain sizes. The deformation mechanism in nano-grain structure is also GBS, but its accommodation by slip becomes difficult. The piled-up dislocations give rise to different accommodation mechanisms, namely, nanotwins, emission of Shockley partials, and stress-induced atomic shuffling.

• In materials with mixed grain size microstructure, the microstructure evolution during deformation needs to favor CDRX in the coarse-grained region in order to exhibit superior superplastic elongation—else finer-grained region

*DOI: http://dx.doi.org/10.5772/intechopen.86017*

controls the deformation.

*Effect of Grain Size on Superplastic Deformation of Metallic Materials DOI: http://dx.doi.org/10.5772/intechopen.86017*

*Aluminium Alloys and Composites*

superplastic elongation in Al alloys which was not present in the AZ91 Mg alloy. However, elongation of more than 600% and strain-rate sensitivity of more than 0.5 in FFG material confirmed that friction stir processed AZ91 behave superplasti-

*IPF maps of deformed samples with tensile axis parallel to process direction (parallel to X-axis shown above)* 

*in its IPF map and (b) grain boundary misorientation distribution of as-cast material showing predominant* 

The effect of grain size on the superplastic deformation of metallic materials was studied. There were different combination of deformation mechanisms, accommodation mechanism, and rate-controlling mechanisms that governed the superplastic deformation which depends on the grain size, temperature, and strain rate. The

• The maximum elongation obtained by coarse-grained microstructure was between 500 and 800%. Solute-drag creep controlled by diffusion and GBS preceded by CDRV/CDRX was the deformation mechanisms in the coarse-

• In fine-grained materials, GBS dominated the deformation mechanism. The accommodation mechanism could be either by "glide and climb" or by diffusion. If diffusion is the accommodation mechanism, it can be divided either by grain boundary diffusion or lattice diffusion which depends on the required

• In UFG regime most of the materials exhibited either low-temperature superplasticity or high-strain-rate superplasticity. The mechanism in both cases is

mostly observed to be GBS accommodated by dislocation slip.

s<sup>−</sup><sup>1</sup>

*; (a) AC material with highlighted (yellow) extension twins indicated by arrows* 

due to dynamic grain

cally at temperature of 350°C and strain rate of 5 × 10<sup>−</sup><sup>4</sup>

*tensile twin population around 86.3°, (c) HFG, (d) SFG, and (e) FFG [88].*

following conclusions were obtained based on the detail study.

growth can be observed from the **Figure 11(e)**.

grained microstructure.

activation energy.

**8. Conclusions**

**Figure 11.**

*at a strain rate of 5 × 10–4 s<sup>−</sup><sup>1</sup>*

**110**

