Anisotropic tensile behavior of Ti–6Al–4V components fabricated with directed energy deposition additive manufacturing

• Published in: Acta materialia Vol. 87; pp. 309 - 320
• Main Authors: Carroll, Beth E., Palmer, Todd A., Beese, Allison M.
• Format: Journal Article
• Language: English
• Published: 01.04.2015
• Subjects: Additives; Anisotropy; Deposition; Ductility; Mechanical properties; Three dimensional; Titanium base alloys; Ultimate tensile strength
• ISSN: 1359-6454
• DOI: 10.1016/j.actamat.2014.12.054

The present work investigates the anisotropic mechanical properties of a Ti-6Al-4V three-dimensional cruciform component fabricated using a directed energy deposition additive manufacturing (AM) process. The mechanical properties of the component in longitudinal and transverse orientations with respect to the build layers were measured under uniaxial tension. While the average ultimate tensile strength of 1060MPa in both directions agrees well with prior studies on AM Ti-6Al-4V, the achieved elongations of 11% and 14% along the longitudinal and transverse directions, respectively, are higher. The enhanced ductility is partially attributed to the lack of pores present in these components. The anisotropy in ductility is attributed to the columnar prior- beta grain morphology and the presence of grain boundary alpha , which serves as a path along which damage can preferentially accumulate, leading to fracture. In addition, the effect of oxygen on the strength and ductility of the component was studied. The findings indicate that a combined effect of an increase of 0.0124wt.% oxygen and a decrease in alpha -lath width due to differential cooling at different heights within the component resulted in an increase of ultimate and yield strengths without a significant loss of ductility. Furthermore, this study demonstrates that quasi-static uniaxial tensile mechanical properties similar to those of wrought Ti-6Al-4V can be produced in an AM component without the need for post-processing heat treatments.