Graded steel microstructures by laser powder bed fusion for increased material efficiency

Abstract: This thesis presents a comprehensive investigation into functionally graded microstructures (FGMi) generated by Laser Powder Bed Fusion (L-PBF) in order to enhance material efficiency. Novel approaches in process parameter development, thermal measurement and microstructural analysis are introduced and build the foundation for generating tailored FGMi. The investigations are executed on low alloy steel 30CrMoNb5-2. The main objective of the study is to build a framework and explore the potential of FGMi generated by L-PBF for kinetic energy absorption. This is achieved by addressing specific sub-targets, including choosing a concept of micro-gradation, selecting a suitable alloy, estimating sustainability potential, establishing an approach for developing L-PBF process parameters, generating FGMi through local in-situ heat-treatment, measuring the thermal history, analyzing the resulting microstructure and exploring limitations and performance of FGMi implemented into lattice structures. The investigation begins by exploring the concept of micro-gradations, focusing on variations in exposure parameters to impact grain size or phase composition. Low alloy steels are found to be the most promising material due to their favorable processability, mechanical properties, and potential for creating complex phase steels through the integration of ductile phases. The sustainability potential of FGMi by L-PBF is estimated, considering resource consumption and the impact of exposure parameter changes on manufacturing efficiency. Based on single laser track experiments and a design of experiment approach, a universal approach for the development of initial L-PBF process parameters is synthesized. A double exposure approach is presented, enabling in-situ heat-treatments in order to generate FGMi of increased material performance. This approach provides increased parameter flexibility in order to impact the resulting microstructure, while avoiding increased porosity. The thermal loads resulting from single laser tracks as well as consecutive laser tracks is analyzed using pyrometry. A novel EBSD based IQ analysis is employed to analyze the different states of tempered martensite resulting from in-situ heat treatments. The limitations and potential of FGMi within lattice structures are investigated, revealing that the 30CrMoNb5-2 alloy does not result in unwanted scale effects like other alloys, due to its higher thermal conductivity. The research addresses a significant gap in tailoring FGMi through process parameter variations and their realization in lattice structures. It lays the foundation for further application-oriented experiments by demonstrating the controlled in-situ heat treatment's potential without impacting porosity. Additionally, it introduces measurement capabilities to quantify thermal loads within L-PBF and resulting microstructures. Overall, this work contributes to the advancement of tailored FGMi in bulk material and lattice structures, enhancing material efficiency for kinetic energy absorption applications

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Albert-Ludwigs-Universität Freiburg, Dissertation, 2025

Klassifikation und Themen

• Schlagwort: Mikrostruktur ; Selektives Laserschmelzen ; Stahl ; Funktioneller Gradientenwerkstoff ; Laserbearbeitung ; Rapid Prototyping ; Rapid Prototyping ; Funktioneller Gradientenwerkstoff ; Niedriglegierter Stahl ; Elektronenrückstreubeugung ; Pyrometrie ; Selektives Laserschmelzen

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2025
• Urheber: Pfaff, Aron
• Beteiligte Personen und Organisationen: Balle, Frank ; Albert-Ludwigs-Universität Freiburg ; Ernst-Mach-Institut ; Albert-Ludwigs-Universität Freiburg. Institut für Nachhaltige Technische Systeme ; Walter und Ingeborg Herrmann Professur für Leistungsultraschall und Technische Funktionswerkstoffe (EFM) ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Weitere Informationen

• DOI: 10.6094/UNIFR/262215
• URN: urn:nbn:de:bsz:25-freidok-2622155
• Rechteinformation: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 15.08.2025, 07:38 MESZ