EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Ti6Al4V is a workhorse aerospace alloy also finding applications in the automobile, biomedical and corrosion industry due to its high specific strength, good corrosion resistance, biocompatibility, and fracture toughness. Ti6Al4V has high fracture toughness but damage micro-mechanisms during the fracture are still unexplored. In the present investigation, samples with three different microstructures namely equiaxed, Widmänstatten and additively manufactured Widmänstatten microstructure were subjected to mode I fracture toughness testing using 3 point bending setup on a universal testing machine with 2D digital image correlation facility. The additive manufactured sample with Widmänstatten microstructure shows the highest KIC value while the equiaxed conventional sample shows the lowest value. The conventional widmänstatten microstructure specimen had almost comparable fracture toughness value to the additively manufactured sample. Crack tortuosity and strain evolution at the crack tip was traced at two different length scales by 2D digital image correlation at the mesoscale and electron back scatter diffraction as along with SEM imaging at the micro-scale. The cracks nucleated at the notch tip and propagated in different directions depending on the microstructure. Asymmetric strain evolution at the notch tip for widmänstatten microstructures was observed by digital image correlation due to different lath orientations. Additive manufactured sample showed the highest strain at the notch tip before failure at mesoscale as measured by DIC accompanied with higher mean value of kernel average misorientation measured from EBSD. The relationship between mesoscopic and microscopic deformation characteristics in terms of operation of slip and twin systems as well as different microstructural features like grain size, lath and colony size is expected to provide vital information on the damage micro-mechanisms. Crystal plasticity fast Fourier transform based DAMASK software will be employed to decipher the micro-mechanisms of deformation and damage for different initial microstructures in Ti6Al4V.