Comparative study on fatigue crack propagation behavior of Ti–6Al–4V products made by DED (direct energy deposition) and L-PBF (laser-powder bed fusion) process

Abstract

The fatigue crack propagation (FCP) behavior of L-PBF (laser-powder bed fusion) and DED (direct energy deposition) Ti–6Al–4V (Ti64) specimens with different crack directions (CDs) were studied in air and 3.5% NaCl solution under controlled potential, and the results were compared to that of CM (conventional manufacturing) Ti64 specimen. Among the specimens tested, L-PBF Ti64 specimen showed the lowest resistance to FCP, followed by DED and CM Ti64 specimens. The effect of CD with respect to building direction (BD) was negligible on the FCP behavior of L-PBF and DED Ti64 specimens. The micrographic and fractographic analyses suggested that refined microstructure was responsible for the FCP behavior of L-PBF and DED Ti64 specimens. L-PBF and DED Ti64 specimens were susceptible to EAFCP (environment-assisted FCP) in 3.5% NaCl solution, while the sensitivity was not as significant as that of CM counterpart. The sensitivity to EAFCP of L-PBF and DED Ti64 specimens was related to crack bifurcation, rather than intrinsic environmental degradation in Cl− bearing environment.

Keywords

• Ti–6Al–4V
• Direct energy deposition
• Laser-powder bed fusion
• Fatigue crack propagation
• NaCl solution