The use of compact specimens to determine fracture toughness anisotropy of Ti–6Al–4V additively manufactured for repair

Abstract

The use of compact specimens to determine the fracture toughness anisotropy of Ti–6Al–4V additively manufactured for repair by directed energy deposition (DED) technique via thin was thoroughly investigated by microstructure examination and fracture toughness test. One characteristic of DED is the anisotropy of the microstructure due to local heating and the build direction. The specimens were originally part of an additively manufactured repair study where AM material was added to an already existing mild heat treated wrought Ti–6Al–4V bar. To understand the intrinsic anisotropy of fracture toughness in the AM build, small size specimens were machined from the halved AM and wrought Ti of the repaired specimens. The crack mouth opening displacements were measured using digital image correlation (DIC). The mechanical testing was supported with direct current potential drop (DCPD) to monitor the formation and growth of cracks. To gain insights into failure mechanisms and microscopic characteristics, polished sections and fractured surfaces were examined. The measured fracture toughness of DED AM samples were compared with wrought annealed Ti–6Al–4V in relations to the microstructure features. Hence, the fracture toughness of the DED specimens depended on orientation with the orientation of the notch perpendicular to the build layer possessing higher fracture toughness. The fracture toughness of DED AM specimens with the notch configuration perpendicular to the build layers were found slightly higher than the wrought Ti–6Al–4V, respectively.