Research project

The aim of the project is a better fundamental understanding of the influence of coatings on the thermo-mechanical fatigue performance of coated turbine blade materials. The investigations can be subdivided into two parts: stress response and life during thermo-mechanical fatigue (TMF) testing and the characterization of the microstructure of the coating.
The materials to be examined are two platinum-modified aluminide coatings with different microstructures: one is a single-phase coating, the other one a two-phase coating. The substrate material is the monocrystalline nickelbase-superalloy CMSX-6. Uncoated substrate material is also studied as a reference material. The TMF-tests concentrate on one type of cycle representing typical loads exerted on turbine blades under service conditions. Turbine blades in the first stages of the turbine must be protected by a coating against oxidation and corrosion. On the other hand, the coatings tend to lead to a reduced TMF life of the material.
Crack initiation is observed to occur at the surface of the coating. Due to the intermetallic nature of the main constituents of the coatings, the cracks tend to be brittle and spread early during the TMF life, if a sufficiently high load is experienced. Thus, the coating generally results in a decrease in TMF life.
In the present investigations, the effects of the coating characteristics (microstructure, Al-content, element distribution, crystallographic orientation, etc.) on the TMF behaviour are investigated with the aim to provide guidelines for the development of new, more ductile coatings.