An analytical algorithm to predict weldability of precipitation-strengthened nickel-base superalloys

A new mathematical-solidification-weldability model has been developed to obtain the optimum chemical composition in the γ-Ti–Al–Nb precipitation-strengthened nickel-base superalloys, in which, the best resistance to hot cracking be achieved. To solve the weldability model, SEM microphotographs and EDAX analysis extracted from microstructure of the welds and phase diagrams were used as model data inputs. The relation between the segregating elements versus the retained weld liquid, and as well as, solidification path of welds (L → γ) were attained. The model is able to predict the brittleness temperature range (BTR) and the extent of weld mushy zone as a direct criterion of weldability determination. For the weld type A (alloy Inconel 718), formation of secondary phases or eutectics is too probable. In case of weld type B (alloy Udimet 500), formation of secondary phases enriched in Ti in the interdendritic locations can be anticipated. The BTRs and the size of mushy zones for welds type A, B and C (65 wt% alloy 500 + 35 wt% alloy 718) have been calculated. The solidification-weldability model showed that weld type C with dilution level of 65% and the ratio Nb/(Ti + Al) = 0.53 has the best weldability among the dilutions studied and can be offered as a new-weldable nickel-base superalloy.