Effect of defects on environment-assisted fracture (EAF) behavior of Ti–6Al–4V alloy fabricated by direct energy deposition (DED)

Abstract

Environment-assisted fracture (EAF) behavior of direct energy deposition (DED) Ti–6Al–4V (Ti64) specimen was investigated using a slow strain rate test (SSRT) method in air and 3.5% NaCl solution under controlled potentials, where the susceptibility to EAF was described by the reduction in tensile elongation (RTE) with exposure to aggressive environment. It was found that RTE value of DED Ti64 specimen was approximately 4 times greater than that of conventional manufacturing (CM) counterpart. The fractographic analysis on DED Ti64 specimen tested in 3.5% NaCl solution suggested that crack-like discontinuity was instantly formed from corrosion damages by merging into band-like lack of fusion (LOF) near the surface. Since LOFs were developed perpendicular to build direction (BD), the RTE value of DED Ti64 specimen with tensile direction (TD) perpendicular to BD was approximately 4 times lower than those with TD parallel to BD. Excellent correlation between the area fraction of LOF and the RTE was observed, indicating that LOFs were responsible for high susceptibility to EAF of DED Ti64 specimen in Cl− bearing environment.

Keywords

• Ti–6Al–4V
• Direct energy deposition
• Environment-assisted fracture
• 3.5% NaCl solution