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Ni-base superalloys for land-based gas turbines and aero engines

For more than a decade, the single crystal Ni-base superalloys are widely applied for turbine components in advanced jet engines.

Crack formation in uncoated Ni- cast alloy specimen after Out-of-Phase TMF- loadingCrack formation in uncoated Ni- cast alloy specimen after Out-of-Phase TMF- loading

Nowadays, these materials are also employed in stationary gas turbines for electric power generation or in combined cycle gas turbines in spite of the distinctly larger size of turbine blades comparing to the jet engines.

The research work of the department “Materials Mechanics” in this area covers characterization of deformation behavior of the alloys (also depending on the crystal orientation) under isothermal and thermomechanical fatigue loadings as well as the microstructure development aspects especially with respect to the precipitation strengthening.

Furthermore, the high temperature components such as first stage turbine blades experience a complex thermal and mechanical loading during service and must be protected with metallic corrosion protective coatings. These coatings with typical composition MCrAlY (M=Ni und/oder Co) form a dense protective alumina scale, which has a slow growth rate and adheres well to the coating. However, corrosion protective coatings affect the fatigue lifetime of turbine blade and may in some cases reduce it. The main reason for that is the low ductility of the coating at low temperatures causing accelerated crack development under tensile stresses applied.

Within the Collaborative Research Program supported by the German Federal Ministry of Economy and Technology (BMWI) the influence of two oxidation protection coating systems, i.e. a MCrAlY single layer and a MCrAlY/NiAl - duplex coating on the damage mechanisms and lifetime of the Ni-base superalloy under TMF loading was investigated. Based on the results obtained a TMF-lifetime prediction model will be developed using coatings fracture strain approach.

Accelerated crack propagation into the substrate in case of no branching effect at the MCrAlY-layer/substrate interface in duplex-coated specimen (batch II) under Out-of-Phase TMF- loadingAccelerated crack propagation into the substrate in case of no branching effect at the MCrAlY-layer/substrate interface in duplex-coated specimen (batch II) under Out-of-Phase TMF- loading


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