Many Ni-based alloys are susceptible to different weld cracking phenomena that can be sensitive to alloy chemistry. During the solidification of weld metal, the alloying elements segregate to either the liquid or the solid and cause local composition differences. Segregation of aluminum (Al), titanium (Ti), and/or niobium (Nb) causes local variances in gamma prime (γ′) and gamma double prime (γ″) precipitation kinetics and volume fractions, leading to a loss of creep strength. Depending on alloy chemistry, this segregation can also cause formation of low melting point eutectics, which can then cause solidification cracking. The extent of segregation can be predicted using the Scheil Solidification Simulation Calculator included in Thermo-Calc.
This figure shows the segregation across a hypothetical dendrite for Alloy 718. Nb, Mo, and Ti segregate heavily to the dendrite boundary, which will have an impact on the local precipitation behavior.