Abstract
A method is proposed for calculating the variation in fraction liquid with distance in the mushy zone as an aid to determining the effect of alloy additions on solidification cracking susceptibility. The model combines the general liquidus equation of a multicomponent system, solute redistribution relations, and temperature gradient information. Calculations are presented for a range of niobium bearing superalloys and the results were found to reveal important relations between alloy composition, variation in fraction liquid with distance in the mushy zone, and cracking susceptibility as measured by the Varestraint test. In particular, the results directly show that the addition of carbon to these alloys is generally beneficial because it reduces the size of the crack susceptible mushy zone and limits the amount of terminal liquid available for the low temperature L → γ + Laves reaction. The modelling results and experimental data are also used to describe the influence of other alloy additions.
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