The mechanical performance of engineering alloys is greatly influenced by their microstructure and the micromechanics when the material is loaded to plasticity. To date, our understanding of early-stage plasticity, the resulting work hardening, and eventual material failure are still limiting our ability to predict life of components with great accuracy. Therefore, it is necessary to understand the intricate mechanisms governing the deformation behaviour of these alloys, which is crucial for optimising their performance. In our research, we are aiming to analyse the deformation mechanism to quantify plastic strain, where the link between Geometrically Necessary Dislocations (GND), Statistically Stored Dislocation (SSD) and slip system activity needs to be established to enable more accurate modelling predictions. 

In recent years, in-situ deformation techniques, including Scanning Electron Microscopy (SEM) with Electron Backscatter Diffraction (EBSD) and High Resolution Digitial Image Correlation (HR-DIC), have improved dramatically with the development of a fully integrated systems enabling fully automated scans over long durations.

Here, we compared the deformation of aged Inconel 718 (IN718) with a grain size of 30 μm containing g' and g'' strengthening precipitates, solution-treated IN718 at 1000 ℃ and 1040 ℃ with grain sizes of 30 μm and 140 μm without strengthening precipitates, and Inconel 690 (IN690) with a grain size of 120 μm without precipitates. The GND density was calculated by the Weighted Burgers Vector (WBV) method [1]. The presence of precipitates can lead to a higher GND density increase rate. Additionally, a higher GND density increase rate corresponds to a higher work-hardening rate. The combination of EBSD and HR-DIC maps shows that the precipitates can lead to higher localised deformation, where aged IN718 displays highly localized regions with high dislocation density and high local strain, whereas the alloys without precipitates show more uniform dislocation densities and local strain across the grains. Moreover, the areas with high local strain are mainly near twin boundary and areas with high GND density are near twin boundary and grain boundary.

[1] Wheeler, J. et al. The weighted Burgers vector: A new quantity for constraining dislocation densities and types using electron backscatter diffraction on 2D sections through crystalline materials. https://doi.org/10.1111/j.1365-2818.2009.03136.x