The effect of residual stress on the fracture toughness of Ti–6Al–4V produced by laser-based powder bed fusion

Abstract

Laser powder bed fusion (LPBF) imposes steep thermal gradients, resulting in distortion and the formation of significant residual stresses, which often precipitate in-situ cracking at support interfaces and sharp geometric features. To isolate their influence on structural integrity, we combined fracture mechanics testing with residual stress evaluation on as-built compact tension specimens printed in two orthogonal orientations. The experimentally measured apparent stress-intensity factor was deconvolved into mechanical and residual-stress components, yielding a residual-stress-free fracture toughness (KICeff). Apparent fracture toughness (KIC) ranged from 25 to 35 MPa m1/2, whereas KICeff increased to 45–52 MPa m1/2. Residual stresses, therefore, depress the material’s residual-stress-free resistance by up to ~ 50% and accentuate orientation-dependent anisotropy. The framework presented offers a route for quantifying process-induced toughness degradation in LPBF alloys.