TY - THES

T1 - Correlation of process conditions, microstructure and mechanical properties of magnetron sputtered equiatomic CrMnFeNiCo alloys

AU - Baumegger, Walter

N1 - embargoed until null

PY - 2021

Y1 - 2021

N2 - Phase decomposition and formation of second-phase precipitates in CrMnFeCoNi high-entropy alloys are important phenomena, which are worth studying in detail as any thermal instability of the alloys significantly affects their overall properties. In order to avoid deterioration of the mechanical properties of the CrMnFeCoNi alloy during operation at elevated temperatures, the understanding of the microstructure and temperature dependencies on the precipitation kinetics is essential. In this study, a CrMnFeCoNi alloy with an equiatomic composition was synthesized by physical vapor deposition at various temperatures ranging from 50 to 450°C, forming a complex multilayer architecture. The growth of each sublayer corresponded to a specific temperature for which phase (in)stability has been reported. By this cross-sectional combinatorial approach, fast screening of microstructure- and temperature-dependent precipitation was possible, giving insights into the optimum process conditions and microstructure of thermally stable CrMnFeCoNi alloys. It was found that while no precipitates formed at temperatures below 200°C, a pronounced precipitation took place above this temperature, and the size and volume fraction of the precipitates scaled with the grain size. Furthermore, in order to relate the microstructure and properties of the alloys synthesized at various temperatures, selected sublayers of the multilayer architecture were grown as a single-layers and characterized by X-ray diffraction and nanoindentation. The results revealed that the mechanical properties of the alloy strongly depend on the alloy microstructure as the presence of the precipitates affects the deformation of the alloy upon loading.

AB - Phase decomposition and formation of second-phase precipitates in CrMnFeCoNi high-entropy alloys are important phenomena, which are worth studying in detail as any thermal instability of the alloys significantly affects their overall properties. In order to avoid deterioration of the mechanical properties of the CrMnFeCoNi alloy during operation at elevated temperatures, the understanding of the microstructure and temperature dependencies on the precipitation kinetics is essential. In this study, a CrMnFeCoNi alloy with an equiatomic composition was synthesized by physical vapor deposition at various temperatures ranging from 50 to 450°C, forming a complex multilayer architecture. The growth of each sublayer corresponded to a specific temperature for which phase (in)stability has been reported. By this cross-sectional combinatorial approach, fast screening of microstructure- and temperature-dependent precipitation was possible, giving insights into the optimum process conditions and microstructure of thermally stable CrMnFeCoNi alloys. It was found that while no precipitates formed at temperatures below 200°C, a pronounced precipitation took place above this temperature, and the size and volume fraction of the precipitates scaled with the grain size. Furthermore, in order to relate the microstructure and properties of the alloys synthesized at various temperatures, selected sublayers of the multilayer architecture were grown as a single-layers and characterized by X-ray diffraction and nanoindentation. The results revealed that the mechanical properties of the alloy strongly depend on the alloy microstructure as the presence of the precipitates affects the deformation of the alloy upon loading.

KW - Hoch-Entropie Legierungen

KW - CrMnFeCoNi Legierung

KW - thermische Stabilität

KW - Ausscheidung

KW - Struktur-Eigenschafts-Beziehungen

KW - Magnetronsputtern

KW - Dünnschichten

KW - High-Entropy alloys

KW - CrMnFeCoNi alloy

KW - thermal stability

KW - precipitation

KW - structure-property relations

KW - magnetron sputtering

KW - thin films

M3 - Master's Thesis

ER -