TY - BOOK

T1 - Evaluation of Microstructure and Mechanical Properties of a Precipitation Strengthened Compositionally Complex Alloy

AU - Biermair, Florian

N1 - no embargo

PY - 2023

Y1 - 2023

N2 - The aim of the present work is to gain new insights into promising alloy compositions as well as processing routes and conditions for an optimum microstructure and corresponding properties of precipitation strengthened compositionally complex alloys based on the concept of high entropy alloys. Such alloys have already shown promise as potential candidates for high temperature structural applications. The motivation to study such alloys in detail is that they potentially achieve similar long term mechanical properties as modern metallic materials for high temperature structural applications, but at even higher temperatures than the conventional ones. Finally, it is intended to achieve higher operating temperatures and, thus, higher efficiency in turbines for aviation and power generation. For this purpose, a promising representative of precipitation strengthened compositionally complex alloys with a high entropic matrix phase was selected from the literature. Corresponding test samples were manufactured in industrially relevant sizes applying different methods (with slight chemical variations) and investigated with respect to the evolution of phases and mechanical properties along the processing route using advanced techniques. In addition, density functional theory (DFT) calculations were performed in cooperation with partners for the matrix phase in different process states to predict relevant properties. The main results are: The test alloys can be effectively homogenized at 1150°C without leaving harmful phases in the alloy. Precipitation studies revealed very fast nucleation of the ¿¿-phase, even when quenched with water from solution annealing temperature, and slow coarsening kinetics of the precipitated phase were observed during aging. Prediction of the yield strength by state-of-the-art models is in good agreement with the experiment, but an increased APB energy in the precipitates compared to the predicted value can be suggested. Experimental results indicate the alloy's promising high temperature compressive yield strength, especially for the cast alloy after a two-step deformation process, showing the great potential of this alloy for applications at increased temperatures. Additionally, high thermodynamic stability and good mechanical properties in the matrix phase of the alloy can be expected from computational results for formation energy, Young¿s modulus or critical resolved shear stress.

AB - The aim of the present work is to gain new insights into promising alloy compositions as well as processing routes and conditions for an optimum microstructure and corresponding properties of precipitation strengthened compositionally complex alloys based on the concept of high entropy alloys. Such alloys have already shown promise as potential candidates for high temperature structural applications. The motivation to study such alloys in detail is that they potentially achieve similar long term mechanical properties as modern metallic materials for high temperature structural applications, but at even higher temperatures than the conventional ones. Finally, it is intended to achieve higher operating temperatures and, thus, higher efficiency in turbines for aviation and power generation. For this purpose, a promising representative of precipitation strengthened compositionally complex alloys with a high entropic matrix phase was selected from the literature. Corresponding test samples were manufactured in industrially relevant sizes applying different methods (with slight chemical variations) and investigated with respect to the evolution of phases and mechanical properties along the processing route using advanced techniques. In addition, density functional theory (DFT) calculations were performed in cooperation with partners for the matrix phase in different process states to predict relevant properties. The main results are: The test alloys can be effectively homogenized at 1150°C without leaving harmful phases in the alloy. Precipitation studies revealed very fast nucleation of the ¿¿-phase, even when quenched with water from solution annealing temperature, and slow coarsening kinetics of the precipitated phase were observed during aging. Prediction of the yield strength by state-of-the-art models is in good agreement with the experiment, but an increased APB energy in the precipitates compared to the predicted value can be suggested. Experimental results indicate the alloy's promising high temperature compressive yield strength, especially for the cast alloy after a two-step deformation process, showing the great potential of this alloy for applications at increased temperatures. Additionally, high thermodynamic stability and good mechanical properties in the matrix phase of the alloy can be expected from computational results for formation energy, Young¿s modulus or critical resolved shear stress.

KW - compositionally complex alloy

KW - precipitation strengthening

KW - microstructure

KW - mechanical properties

KW - yield strength prediction

KW - komplex zusammengesetzte Legierung

KW - Ausscheidungshärtung

KW - Mikrostruktur

KW - mechanische Eigenschaften

KW - Fließgrenzenvorhersage

M3 - Doctoral Thesis

ER -