Research on cracks in cast superalloys

News and results from the project LCF and TMF crack growth in cast nickel-based superalloys, KME-702.

Today, there is a growing demand for gasturbines for cyclical operation. These turbines are needed as a complement to the intermittent energy sources such as solar and wind power, which cannot be regulated in the same way as a gasturbine. Since gasturbines have traditionally been designed for base loads, a change in operating conditions, such as more start stop-cycles, will lead to an increased risk for damage and failure. In addition, the requirements for fuel flexibility also increases, which means that new and more corrosion-resistant materials and coatings must be introduced.

In this project, we have investigated crack growth during thermomechanical fatigue in two different types of cast nickel-based alloys for turbine blades. One of them is a newly developed alloy specially designed for industrial gas turbines to meet the challenges described above. As the alloy is a so-called single crystal, completely without grain boundaries, crack growth differs significantly from conventional materials. Among other things, these materials show two distinctly different modes of crack propagation behaviour as the crack under certain load and temperature conditions changes to a crystallographic failure mode. In the project, this behaviour has been mapped for a variety of temperature and load conditions.

The results from material studies and mechanical testing have been used to develop a new calculation methodology and new fracture mechanics parameters for crack growth in material for gas turbine blades. To verify the new test and calculation methods developed within the project, a more traditional conventionally cast nickel base alloy has also been studied.

Results from the project are already implemented by Siemens Industrial Turbomachinery in their development of new turbines focusing on fuel flexibility and cyclical operation.

PhD students, project participants and project leader of project from left to right in the picture above:
Christian Busse, PhD student LiU
Frans Palmert, Industrial PhD student Siemens & LiU
Daniel Leidermark, Supervisor
Johan Moverar, Supervisor & Project leader

Participating companies:
Siemens Industrial Turbomachinery AB, Finspång

To the project-site here!