The Woodruff School

SUMMARY

Materials enabling most advanced technologies exhibit hierarchical structure, where important features at different length scales contribute to the overall properties/performance of a material. In many engineering applications, prolonged exposures to high temperatures of components lead to significant internal microstructure evolution on multiple length scales and is accompanied by degradation in overall material properties. As an example, steel components in industrial gas turbines undergo multiscale microstructural evolution in form of graphitization (formation of secondary graphite particles) and spheroidization (coarsening of lamellar cementite structure within pearlite grains), which are reported to decrease the overall yield strength.
The central goal of this work is to explore experimentally the correlations between the multiresolution mechanical responses of a material that are mediated by the details of the material structure. Specifically, we will explore experimentally the relations between the mechanical responses of microscale constituents in ferrite-pearlite steels measured in nanoindentation to the overall (bulk) properties of the material measured in microindentation. Furthermore, in collaboration with an industry partner, this work will be carried out on small volumes of material excised as shallow scoops from operating gas turbines at various thermal histories that correspond to varying degrees of graphitization and spheroidization. This challenge is addressed in multiple tasks. First, we extend and apply spherical indentation stress-strain protocols to multiresolution mechanical evaluation of the steel scoops obtained from the industry partner. The indentation protocols will be applied to microscale constituents (ferrite, pearlite, graphite) and also to mesoscale measurements. Second, we develop and employ image acquisition and analyses protocols to document the salient information on the material microstructure. This includes a new segmentation framework combined with previously developed quantification protocols based on 2-point spatial correlations and principal component analyses. Third, all of the indentation and microstructure information is then utilized in different homogenization theories to evaluate critically their relative accuracies.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Almambet Iskakov

TIME:	Tuesday, February 18, 2020, 9:00 a.m.

PLACE:	College of Computing, 053

TITLE:	Experimental correlation of microstructure and properties in structural alloys through image analyses and multiresolution indentation

COMMITTEE:	Dr. Surya R. Kalidindi, Chair (ME) Dr. Hamid Garmestani (MSE) Dr. David McDowell (ME) Dr. Richard W. Neu (ME) Dr. Sudhir Rajagopalan (Siemens)

SUMMARY Materials enabling most advanced technologies exhibit hierarchical structure, where important features at different length scales contribute to the overall properties/performance of a material. In many engineering applications, prolonged exposures to high temperatures of components lead to significant internal microstructure evolution on multiple length scales and is accompanied by degradation in overall material properties. As an example, steel components in industrial gas turbines undergo multiscale microstructural evolution in form of graphitization (formation of secondary graphite particles) and spheroidization (coarsening of lamellar cementite structure within pearlite grains), which are reported to decrease the overall yield strength. The central goal of this work is to explore experimentally the correlations between the multiresolution mechanical responses of a material that are mediated by the details of the material structure. Specifically, we will explore experimentally the relations between the mechanical responses of microscale constituents in ferrite-pearlite steels measured in nanoindentation to the overall (bulk) properties of the material measured in microindentation. Furthermore, in collaboration with an industry partner, this work will be carried out on small volumes of material excised as shallow scoops from operating gas turbines at various thermal histories that correspond to varying degrees of graphitization and spheroidization. This challenge is addressed in multiple tasks. First, we extend and apply spherical indentation stress-strain protocols to multiresolution mechanical evaluation of the steel scoops obtained from the industry partner. The indentation protocols will be applied to microscale constituents (ferrite, pearlite, graphite) and also to mesoscale measurements. Second, we develop and employ image acquisition and analyses protocols to document the salient information on the material microstructure. This includes a new segmentation framework combined with previously developed quantification protocols based on 2-point spatial correlations and principal component analyses. Third, all of the indentation and microstructure information is then utilized in different homogenization theories to evaluate critically their relative accuracies.