Welding and heat treatment of Nickel based superalloys

Purpose and goal

A numerical model that indicates the risk of welding hot cracks to appear in nickel-based superalloys has been developed. The core of the model is a physically based cracking criterion where hot cracks are believed to be initiated from pores in fluid films between grains, a phenomenon that has been observed in in-situ experiments. An index is calculated, as the ratio of the negative pressure of the fluid to the critical negative pressure required for the surface tension of the pore to hold it together. The model has been validated with good results and is used to reduce the risk of hot cracking.

Expected results and effects

It is now possible to simulate hot cracking. The welding process of jet engine components can therefore be optimized at an early stage, so that the risk of thermal cracking is reduced. This is a large improvement. The model takes important factors such as grain cluster formations and dendritic distances into account. Simulation of hot cracks can also be a powerful tool that facilitates the introduction of new alloys, and when replacing cast components with welded components that are cheaper to produce.

Planned approach and implementation

The work has been conducted as a PhD project at LTU. One PhD student has been responsible for the main part of the research work. The project was initiated with a literature study that gave information about what had already been done in the field. It also indicated an appropriate direction for the project. The work then focused on how cracks develop during welding and how to calculate the risk of cracking. The work has been extensive and has led to a groundbreaking model that has gained inspiration from the foundry technology.