Local Strain Development and Property Variability in B2 Intermetallics

摘要

The overall objective of this research program was to develop a quantitative understanding of the relationship of straining processes at the scale of microstructure to macroscopic mechanical properties of structural materials. To accomplish this, experimental high-resolution displacement mapping techniques for analysis of strains at the micron scale were developed and validated. Strain accumulation and its relationship to microstructural features in several variants of the B2 intermetallic RuAl were investigated. Significant heterogeneity of straining was observed within individual grains and among neighboring grains in all materials studied. The scale of strain heterogeneity was influenced by grain size and the presence of second phases along grain boundaries. Grain to grain strain distributions developed early in the straining process and strain maps revealed self-similar straining patterns during progressive loading. The relationship between grain-scale strains and deformation mechanisms was studied via dislocation substructure analysis with 'targeted' removal of TEM foils with a focused ion beam system. The strain mapping tool proved useful for the identification of active slip systems in the intermetallic RuAl system. Finally, high resolution EBSD analysis of lattice orientations in samples with strong gradients within strain maps demonstrated that these gradients could not be attributed to the presence of geometrically necessary dislocations.