Two dimensional microstructural model of the liquid evolution between the matrix and NbC particles on grain boundaries was presented to make the mechanism of grain boundary liquation clear during laser welding of Inconel 718 alloy. The constitutional liquation mechanism was adopted as the basic liquation mechanism of second particles.
The numerical analysis of local melting of NbC under welding thermal cycle was divided into three stages such as solution stage, liquation stage and solidification stage. The first of solution stage corresponds to that NbC particles dissolved into matrix during heating process. The second of liquation stage corresponds to that liquation takes place between the matrix and NbC particles and liquid infiltrates along the grain boundary also during heating process. Finally the third of solidification stage corresponds to that liquid phase on grain boundary solidifies during cooling process. During this work, a local equilibrium between the solid and liquid phase was assumed and the compositions at interface were calculated by Thermo-Calc using Ni-DATA as a database.
The numerical results suggest that a liquid begin to appear between the particle of NbC and matrix at a temperature of 1439 K and as the temperature increases, the volume of liquid increases. Meanwhile, the liquid infiltrates along grain boundary during heating.
