Modeling and simulation of weld solidification cracking part II

Abstract

Several advanced alloy systems are susceptible to weld solidification cracking. One example is nickel-based superalloys, which are commonly used in critical applications such as aerospace engines and nuclear power plants. Weld solidification cracking is often expensive to repair, and if not repaired, can lead to catastrophic failure. This study, presented in three papers, presents an approach for simulating weld solidification cracking applicable to large-scale components. The results from finite element simulation of welding are post-processed and combined with models of metallurgy, as well as the behavior of the liquid film between the grain boundaries, in order to estimate the risk of crack initiation. The first paper in this study describes the crack criterion for crack initiation in a grain boundary liquid film. The second paper describes the model for computing the pressure and the thickness of the grain boundary liquid film, which are required to evaluate the crack criterion in paper 1. The third and final paper describes the application of the model to Varestraint tests of Alloy 718. The derived model can fairly well predict crack locations, crack orientations, and crack widths for the Varestraint tests. The importance of liquid permeability and strain localization for the predicted crack susceptibility in Varestraint tests is shown.

Modeling and simulation of weld solidification cracking part III

“…In order to calibrate and evaluate the WSC model, which was developed in parts I and II of this study, on Varestraint tests of alloy 718, the temperature field and macroscopic strain fields of the Varestraint tests must be known. These fields are used to calculate the GBLF pressure (see part II [13]), which in turn is used to compute the crack initiation length (see part 1 [12]). In this study, the temperature and macroscopic mechanical strain fields were obtained from a finite element computational welding mechanics (CWM) model of the Varestraint test.…”

“…A major challenge with this crack criterion is its depends on the GBLF pressure and the GBLF thickness at the location where it is evaluated. These quantities are determined from the macroscopic mechanical strains and temperature fields of the weld by a model presented in part II of this study [13]. In this paper, the third in the series, we evaluate the crack criterion from part I on Varestraint tests of the nickel-based superalloy alloy 718.…”

A numerical model for simulating the effect of strain rate on eutectic band thickness

“…Because the GBLF is weaker than the grain clusters, deformations that occur during the solidification can strongly localize in the GBLF. This has been discussed by the authors in their previous work on solidification cracking [4].…”

“…This is the same approach that the authors were using when they were modeling solidification cracking in the FZ of a TIG weld. More information about this can be found in [4,5].…”

“…This large misorientation gives rise to an "unstructured" GBLF; that is, the GBLF is thicker than a GBLF associated with a small misorientation. Moreover, even though the opposing secondary primary dendrite arms of a GBLF with a high misorientation come into contact, a significant amount of undercooling may be required to fuse them together [4,6,7]. However, if the misorientation angle is small, the dendrite arms can fuse with no undercooling.…”