5 Werkstofftechnik
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The multi-phase approach has proven to widen the application properties of high entropy alloys. After a decade of testing different alloys in the Al-Co-Cr-Cu-Fe-Ni-Ti family the Al10Co25Cr8Fe15Ni36Ti6 was found to be a solid base for more fine-tuned microstructural optimization. Following the example of superalloys, the Al10Co25Cr8Fe15Ni36Ti6 alloy aims for a γ/γ' microstructures in order to guarantee a good microstructural stability at high temperatures. The shape and volume fraction of the γ' particles is known to influence the mechanical properties of superalloys, and they do so in the high entropy family as well [1]. Shape, misfit and creep properties of several modified versions of the Al10Co25Cr8Fe15Ni36Ti6 alloy are compared and discussed in this talk.
Trace elements W and Hf have different influence on the microstructure and the mechanical properties when added to the Al10Co25Cr8Fe15Ni36Ti6 compositionally complex alloy. The addition of both can thus merge both element’s beneficial influences when combined with the appropriate heat treatment: Hf enhances the cubicity of the γ’ particles in the γ matrix while the W reduces the negative influence of the Heusler phase: this phase can be completely dissolved when W is present in the alloy.
Early Material Damage in Equimolar CrMnFeCoNi in Mixed Oxidizing/Sulfiding Hot Gas Atmosphere
(2022)
The challenges to use more varied fuels at medium and high temperatures above 500 °C need to be addressed by tuning the materials towards a better resistance against increased corrosion. As a first step the corrosion processes need to be better understood, especially in the case of the unavoidable and highly corrosive sulfur-based gases. In this work oxidation/sulfidation of an equimolar CrMnFeCoNi high entropy alloy is studied at an early stage after hot gas exposure at 600 °C for 6 h in 0.5% SO2 and 99.5% Ar. The oxidation process is studied by means of x-ray diffraction, scanning and transmission electron microscopy and supported by thermodynamic calculations. It is found that the sulfur does not enter the bulk material but interacts mainly with the fast-diffusing manganese at grain boundary triple junctions at the alloy surface. Sub-micrometer scaled Cr-S-O rich phases close to the grain boundaries complete the sulfur-based phase formation. The grains are covered in different Fe, Mn and Cr based spinels and other oxides.