Quantitative in situ TEM Studies

Understanding the relationship between the microstructure and mechanical properties is an essential step in improving the performance of materials. In situ TEM experiments allow direct visualization of the microstructural evolution during deformation. Thus, one can identify the microscopic deformation mechanisms and how they change with the microstructure. However, most in situ TEM studies are qualitative in nature, i.e., the  stress-strain response is not measured during deformation, and hence one cannot directly correlate the  macroscopic behavior to the microscopic mechanisms.

We overcome this limitation through the use of MEMS based tensile testing stages that are TEM compatible and have built-in stress and strain gauges. Thus, we can measure the stress-strain response while simultaneously visualizing the microstructural changes induced by the deformation. Our quantitative in situ experiments have revealed the presence of extended microplasticity and the mechanism of early bauschinger effect in NC metals.

Our current efforts in this area are oriented towards quantifying the effect of beam irradiation on the stress-strain response of nanoscale thin films during in situ deformation. We are also interested in studying the phase transformation in shape memory alloys using this technique.

Quantitative in situ TEM straining of a 225 nm thick Al film. The TEM micrographs show the microstructure at different stages of deformation

Related Publications

1. J. Rajagopalan, C. Rentenberger, P. H. Karnthaler, G. Dehm and M. T. A. Saif, “In situ TEM study of microplasticity and Bauschinger effect in nanocrystalline metals,” Acta Materialia 58, 4772-4782, 2010 (pdf)

2. J. Rajagopalan, J. H. Han, and M. T. A. Saif, “Plastic deformation recovery in freestanding nanocrystalline aluminum and gold thin films,” Science 315, 1831-1834, 2007 (pdf)

3. J. Rajagopalan, J. H. Han and M. T. A. Saif, “Bauschinger effect in unpassivated freestanding nanoscale metal films,” Scripta Materialia 59, 734-737, 2008 (pdf)

4. J. Rajagopalan and M. T. A. Saif, “Effect of microstructural heterogeneity on the mechanical behavior of nanocrystalline metal films,” Journal of Materials Research 26, 2826-2832, 2011 (pdf)

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