Leveraging automated SEM based insitu mechanical testing to analyse heterogeneous strain accumulation in additively manufactured alloy-alloy composites

3D printed alloy-alloy composites could provide weight and cost savings by tailoring material properties within the continuum of a manufactured component. However, the safety case for implementation is yet to be made, so a better understanding of the development of local plasticity, leading to failure is required. Performing mechanical testing in an SEM provides insight into localised phenomena in materials during deformation so is ideally suited to help make this case. Recent developments introducing automation has increased temporal resolution, area of interest and/or sample throughput to what isn't feasible using manual collection. Achieved by taking advantage of running outside of working hours, since no user is required to track the ROI, refocus the system and change load state.

In this work, two titanium alloy-alloy composites consisting of Ti-6Al-4V and other high performance alloys were wire arc additively manufactured and subjected to automated tensile deformation within the SEM. These samples present an interesting problem for insitu studies since the scale and degree of heterogeneity is uniquely large. Consequently, a large-scale study was performed by correlating the band contrast of sequentially collected multiregion EBSD maps covering the entire gauge section of the sample. The strain maps possess a resolution sitting between etched-optical and SEM-speckled correlated images of microstructures, providing information on strain localisation in clusters of grains but not grain interiors. This resolution is sufficient to identify “strain hotspots” relevant for a higher resolution investigation and since data was collected by EBSD, information on the development of misorientation with increased plastic deformation is retained. A follow-up study was performed at high-resolution, utilising correlated images of high mass nanoparticles to observe and quantify slip behaviour within individual grains at the interface of two material property fronts. An orientation map collected prior to application of the pattern allows linking plasticity to the underlying microstructure.