Effect of microstructure on fatigue crack growth of wire arc additive manufactured Ti–6Al–4V

Abstract

In the present paper, the effect of microstructure on fatigue crack growth (FCG) behavior of wire arc additive manufactured (WAAMed) Ti–6Al–4V was investigated. The fatigue crack growth rate (FCGR) in WAAMed sample with heat-treated was lower than that in the forged sample. The 1050-AA (1050 °C/2h/air cooling (AA)+550 °C/4h/air cooling (AC)) sample showed the lowest FCGR because of its highest ΔKT (18.01 MPa m1/2), while the forged sample exhibited the highest FCGR because of its lowest ΔKT (13.3 MPa m1/2). The larger the plastic zone (rp) at the crack tip, the higher values of the stress intensity factor transition factor (ΔKT), the lower FCGR in the sample. In addition, the sample with continuous grain boundary α (αGB) or discontinuous αGB showed different FCG behavior and its mechanisms were discussed. For the sample with continuous grain boundary α (αGB), the crack in the horizontal sample (H-sample) passed through the continuous αGB and grew along with basket-weave microstructure and colony microstructure, while the crack in the vertical sample (V-sample) grew along with basket-weave microstructure. Therefore, the FCGR in these samples showed anisotropy. For the sample with discontinuous αGB, the crack in the H-sample and the V-sample passed through the discontinuous αGB and grew along with colony microstructure or basket-weave microstructure. The two samples showed the same FCG behavior, which indicated that there was no anisotropy.