Residual stress and cracking are major problems in 3D-printed metal part manufacturing. Casting, welding, cold forming and machining processes induce residual stresses sometimes resulting in cracked components. Residual tensile stresses can cause warping or distortions and decrease fatigue strength. Stress relief heat treatments can be applied to parts to remove the residual stress, but part distortion and cracking can occur during this process. Mechanical peening, laser peening and ultrasonic peening can impart residual compressive surface stress in a part, which enhances fatigue properties.High residual tensile stresses can cause cracks in components. Segregation, liquation and shrinkage can occur during AM with melting and solidification steps. Liquation occurs because the lower melting constituents in an alloy solidify first, separating out during solidification. Upon reheating, these liquated regions can cause liquation cracks, usually in the partially melted zone (PMZ) outside the weld pool.
Shrinkage from the liquid to solid volume change can cause solidification cracks, usually in the center of a weld or casting. Liquation and solidification cracking are more likely to occur in weld- or plasma arc-based additive processes where a hotter and larger melt pool heating forms.