TY - THES

T1 - A laboratory total scattering approach for studying short-range order in a novel precipitation-strengthened compositionally complex alloy

AU - Bauer, Nicolas Erwin

N1 - no embargo

PY - 2024

Y1 - 2024

N2 - Precipitation-strengthened compositionally complex alloys (CCAs), which are derived from the novel material class of high-entropy alloys (HEAs), show high potential for demanding high strength high temperature applications, but some of their properties such as serrated plastic flow are peculiar. The local ordering phenomenon termed short-range order (SRO) of different elements such as Ni and Ti may explain these peculiar properties. One method for studying such local phenomena that has risen to remarkable importance over the past few years is X-ray total scattering (XTS), or pair distribution function (PDF) analysis. In the present thesis, first, a robust laboratory approach for PDF analysis devised at Materials Center Leoben Forschung GmbH (MCL) is presented and applied to Ni powder. The generated laboratory PDF data of Ni is then validated against benchmark data generated with high-energy synchrotron radiation as well as data from literature. The second aim of the present thesis is the investigation of ordering phenomena, in particular SRO, in a Ni 11 wt.% Ti binary alloy and a precipitation-strengthened CCA manufactured at MCL using the total scattering approach. Using Rietveld refinement and PDF refinement of both laboratory and synchrotron data in combination with scanning electron microscopy (SEM) and energy-dispersive X ray spectroscopy (EDX), the evolution of ¿¿ precipitation in the CCA is investigated in detail. The findings indicate that in the most rapidly quenched states of the CCA, early stages of ¿¿ precipitation can be observed in the form of SRO, extending over only a few nanometers and acting as a precursor for subsequent ¿¿ formation. In PDF analysis of laboratory and synchrotron data, indirect evidence of the transition from SRO to long-range ordered (LRO) ¿¿ precipitation in the investigated CCA is found. Hence, the present thesis proves that the presented laboratory total scattering approach is a valuable tool for investigating the local atomic structure in polycrystalline materials of varying chemical complexity up to CCAs.

AB - Precipitation-strengthened compositionally complex alloys (CCAs), which are derived from the novel material class of high-entropy alloys (HEAs), show high potential for demanding high strength high temperature applications, but some of their properties such as serrated plastic flow are peculiar. The local ordering phenomenon termed short-range order (SRO) of different elements such as Ni and Ti may explain these peculiar properties. One method for studying such local phenomena that has risen to remarkable importance over the past few years is X-ray total scattering (XTS), or pair distribution function (PDF) analysis. In the present thesis, first, a robust laboratory approach for PDF analysis devised at Materials Center Leoben Forschung GmbH (MCL) is presented and applied to Ni powder. The generated laboratory PDF data of Ni is then validated against benchmark data generated with high-energy synchrotron radiation as well as data from literature. The second aim of the present thesis is the investigation of ordering phenomena, in particular SRO, in a Ni 11 wt.% Ti binary alloy and a precipitation-strengthened CCA manufactured at MCL using the total scattering approach. Using Rietveld refinement and PDF refinement of both laboratory and synchrotron data in combination with scanning electron microscopy (SEM) and energy-dispersive X ray spectroscopy (EDX), the evolution of ¿¿ precipitation in the CCA is investigated in detail. The findings indicate that in the most rapidly quenched states of the CCA, early stages of ¿¿ precipitation can be observed in the form of SRO, extending over only a few nanometers and acting as a precursor for subsequent ¿¿ formation. In PDF analysis of laboratory and synchrotron data, indirect evidence of the transition from SRO to long-range ordered (LRO) ¿¿ precipitation in the investigated CCA is found. Hence, the present thesis proves that the presented laboratory total scattering approach is a valuable tool for investigating the local atomic structure in polycrystalline materials of varying chemical complexity up to CCAs.

KW - Chemisch komplexe Legierung

KW - Nahordnung

KW - lokale atomare Struktur

KW - totale Röntgenstreuung

KW - Paarverteilungsfunktion

KW - Labor-Ansatz

KW - ¿¿-Ausscheidung

KW - Compositionally complex alloy

KW - short-range order

KW - local atomic structure

KW - X-ray total scattering

KW - pair distribution function

KW - laboratory approach

KW - ¿¿ precipitation

U2 - 10.34901/mul.pub.2024.078

DO - 10.34901/mul.pub.2024.078

M3 - Master's Thesis

ER -