A COMBINED SOLUBILITY PRODUCT NEW PHACOMP APPROACH FOR ESTIMATING TEMPERATURES OF SECONDARY SOLIDIFICATION REACTIONS IN SUPERALLOY WELD METALS CONTAINING NB AND C

Solubility data are combined with the new PHACOMP calculation procedur e and solute redistribution equations to propose a simple method for e stimating temperatures of the secondary solidification reactions that occur in superalloy weld metals. The variation in the primary solid co mposition with temperature is calculated with the Scheil equation for substitutional elements, while the lever law is used for C. The calcul ated compositions are used to determine the temperature-dependent vari ation in the solubility parameter and the metal d-level parameter, whi ch is used in the new PHACOMP routine. The solubility parameter and me tal d-level profiles are compared to temperature-dependent critical va lues to predict temperatures of secondary solidification transformatio ns involving carbides and topologically close-packed phases such as La ves. The general approach is applied to experimental Ni-base and Fe-ba se alloys containing systematic variations in Nb, Si, and C. The proce dure correctly predicts formation of the NbC phase prior to the Laves phase and reveals the effect of nominal alloy content on reaction temp erature. Calculated reaction temperatures are in reasonable agreement with experimentally measured values, particularly when considering the relatively large range of material constants that are needed to make the calculations.