Modelling mushy zones in welds of multicomponent alloys: implications for solidification cracking

A method is proposed Sol calculating the variation in fraction liquid with distance in the mushy zone as art aid to determining the effect of alloy ad ditions on solidification cracking susceptibility. The model combines the g eneral liquidus equation of a multicomponent system, solute redistribution relations, and temperature gradient information. Calculations are presented Sor a range of niobium bearing superalloys and the results were found to r eveal important relations between alloy composition, variation in fraction liquid with distance in the mushy zone, and cracking susceptibility as meas ured 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 Sor the low temperature L-->gamma+Laves reacti on. The modelling results and experimental data are also used to describe r ite influence of other alloy additions.