Environment-Assisted Fatigue Crack Propagation (EAFCP) Behavior of Ti64 Alloy Fabricated by Direct Energy Deposition (DED) Process

Abstract

Environment-assisted fatigue crack propagation (EAFCP) behavior of as-built and beta-annealed Ti64 specimens manufactured by direct energy deposition (DED) process was examined in air and 3.5 pct NaCl solution under an anodic applied potential of E-corr + 0.05 V-SCE. As-built DED Ti64 specimen was found to be susceptible to EAFCP in 3.5 pct NaCl solution, and beta anneal did not decrease the sensitivity to EAFCP. It was suggested that Cl- bearing environment tended to decrease the tendency for crack bifurcation during EAFCP of DED Ti64 specimen, because of local corrosion damage at boundaries between alpha and beta phases. Since crack bifurcation increases the resistance to fatigue crack propagation (FCP) by reducing effective increment K (stress intensity factor range) at the tip of crack, the FCP rates of DED Ti64 specimen increased in 3.5 pct NaCl solution.