Physically based modeling of hot cracks in welded nickel based superalloys

Important results from the project

A state of the art crack model for both solidification and HAZ liquation cracking has been developed. The model takes several factors that are known to affect these cracks into account, such as: grain size, gas concentration, solidification interval, amount of eutectic phase, and strain localisation. The core of the model is a crack criteria where hot cracks are assumed to be initiate from pores in liquid between grains, a phenomena that has been demonstrated in experiments. The model has been validated and have produced good results. The model is a tool to reducing the risk of hot cracks.

Expected long term effects

Since it is now possible to simulate both solidification and HAZ liquation cracking, the welding process of aircraft engine components can be optimized at an early stage. Thereby the risk of these types of cracks is reduced. The technology itself is physically based, and is therefore not limited to a specific welding method or material. The project has led to new knowledge at both LTU and GKN and has opened up for technology dissemination in general and provided opportunities for increased competitiveness at GKN. The project has produced a graduated doctor in the research field.

Approach and implementation

The work has been run as a doctoral project at LTU, where a PhD candidate has been responsible for the main work. The project is a continuation of a NFFP6 project focused on hot cracks that occurred in the part of the weld where the material had been completely molten. In this project the focus area has been expanded to include the HAZ zone around the weld. A method for evaluating the risk of cracking has also been developed. The work has been extensive and has led to a new groundbreaking model that can be used to evaluate how a weld crack arise and how the welding process is affected by various factors.