Recent advances in using severe plastic deformation for the processing of nanomaterials

The grain size is an important structural parameter in polycrystalline materials contributing to the strength of the material and the ability to achieve a superplastic forming capability. Grain refinement is especially important because small grains lead to stronger materials and they provide more opportunities for attaining superplastic flow. Traditionally, the grain size was modified through the use of various thermo-mechanical treatments but this had a significant limitation because it was not possible to produce materials with grain sizes smaller than a few micrometers. The situation has changed over the last forty years with the demonstration that much smaller grain sizes may be produced by processing through the application of severe plastic deformation (SPD) where a high strain is imposed without causing any significant change in the overall dimensions of the sample. This report summarizes the principles of the main SPD processing techniques and then demonstrates the significance of producing submicrometer grain sizes.