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 ( $${K}_{ICeff}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>K</mml:mi> <mml:mrow> <mml:mi>ICeff</mml:mi> </mml:mrow> </mml:msub> </mml:math> ). Apparent fracture toughness ( $${K}_{IC})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>K</mml:mi> <mml:mrow> <mml:mi>IC</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> ranged from 25 to 35 MPa m 1/2 , whereas $${K}_{ICeff}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>K</mml:mi> <mml:mrow> <mml:mi>ICeff</mml:mi> </mml:mrow> </mml:msub> </mml:math> increased to 45–52 MPa m 1/2 . 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.