Open Access

In the SimuCrown project, ageing mechanisms within the crown-cement-tooth complex (CCTC) are investigated, with a focus on high-resolution structural characterisation. Although dental crowns are widely used indirect restorations worldwide, links between clinical complications such as debonding, fractures and time-dependent cement degradation remain insufficiently understood. To address this, we employ high-resolution X-ray µCT and synchrotron X-ray refraction radiography (SXRR) to identify microstructural ageing processes which are inaccessible with conventional imaging. CCTCs subjected to controlled chewing simulation are examined using SXRR to detect structural alterations, interfacial defects, and the progression of damage within the cement layer and neighbouring materials. Our research explores crack initiation, pore evolution, and interfacial integrity using SXRR, capturing degradation phenomena across multiple time scales. By integrating synchrotron imaging with functional ageing simulation and computational modelling, the SimuCrown project offers a robust framework for evaluating the long-term performance of dental restorations. The outcomes contribute to the optimisation of materials and cementation approaches aimed at improving the clinical durability of dental restorations.

Inconel 718 (IN718) is the most commonly used nickel-based superalloy for high-temperature structural applications due to its remarkable strength, as well as its resistance to creep, fatigue, and corrosion up to 650 °C. This study investigated the room- and high-temperature (650 °C) tensile and low-cycle-fatigue (LCF) behavior of IN718 produced by laser powder bed fusion (PBF-LB/M). A bidirectional scanning strategy with 90° rotation after each layer and a four-step heat treatment was applied, and the results were compared to the conventional wrought material. The hierarchical microstructure after heat treatment was characterized on different length scales using microscopic methods. Distinct microstructural characteristics generated during the PBF-LB/M process, such as grain size and morphology, and the periodically graded arrangement of stacked columnar grains interspersed with regions of elongated grains aligned with the build direction, are largely preserved following the applied heat treatment. Additionally, the heat treatment reduces microsegregation and dislocation density associated with the cellular structure, promoting a more uniform precipitation of γ’/γ’’ strengthening phases. At both room and elevated temperatures, the elastic and yield properties of the PBF-LB/M material are comparable to those of the wrought variant. However, the additively manufactured material shows slightly reduced tensile strength, ductility, and strain hardening capability. As a result, it exhibits slightly lower inelastic strain under LCF conditions at both temperatures. While the fatigue life of the PBF-LB/M material is slightly lower than that of the wrought alloy at room temperature, it is vice versa at 650 °C. Both materials demonstrate cyclic softening behavior, which becomes more pronounced at the higher test temperature. Crack propagation is primarily influenced by grain orientation, morphology, and the presence of δ phase at grain boundaries. Under LCF loading at both room and elevated temperatures, multiple crack initiation sites are observed on the surfaces of PBF-LB/M specimens. In microstructurally heterogeneous regions, pronounced crack branching and deflection occur, suggesting that crack paths are shaped by sharp micromechanical gradients and localized clusters of grains with ⟨001⟩ orientation, which are favored for crack growth. The tendency of the PBF-LB/M material to exhibit systematic crack branching and deflection results in irregular crack fronts and mixed-mode propagation behavior. This crack path complexity contributes to additional energy dissipation during fatigue loading. Consequently, despite the relatively large average grain size and a pronounced formation of slip bands, the fatigue life at room temperature approaches that of the wrought material.

Die zunehmende Einführung von KI-gestützten und anderen digitalen Assistenzsystemen in der zerstörungsfreien Prüfung (ZfP) eröffnet erhebliche Potenziale zur Steigerung von Effizienz, Qualität und Zuverlässigkeit von Prüfaussagen. Gleichzeitig verändert sie die Rolle des Prüfpersonals grundlegend und stellt neue Anforderungen an die Gestaltung der Mensch-Maschine-Interaktion (MMI), die für eine sichere, akzeptierte und nachhaltige Umsetzung entscheidend sind. Der DGZfP-Unterausschuss „Mensch-Maschine-Interaktion (UA MMI)“ im Fachausschuss „ZfP 4.0“ adressiert diese Fragestellungen in einem umfassenden Empfehlungspapier zur menschengerechten Einführung von KI- und anderen Assistenztechnologien in der ZfP. Auf Basis einer ZfP-Community-weiten Umfrage sowie aktueller Forschung werden fünf zentrale Herausforderungen identifiziert: (1) Vertrauen und Akzeptanz, (2) Qualifikation und Kompetenzentwicklung, (3) Kognitive Belastung und Interaktionsgestaltung, (4) Zuverlässigkeit und Leistungsbewertung sowie (5) Verantwortung, Ethik und Datenqualität Das Merkblatt formuliert darauf aufbauend praxisnahe Handlungsempfehlungen für die Gestaltung und Nutzung von Assistenzsystemen entlang des Lebenszyklus – von der Entwicklung über die Einführung bis zum Betrieb. Zentrale Aspekte sind menschenzentrierte Systemgestaltung, ergonomische und gebrauchstaugliche Schnittstellen, erklärbare KI, Mensch-KI-Teaming, Steigerung des Vertrauens und der Akzeptanz, gezielter Kompetenzaufbau sowie die ganzheitliche Bewertung der Zuverlässigkeit des Mensch-Maschine-Systems. Ziel des Beitrags ist es, das Bewusstsein für die zentrale Rolle der Mensch-Maschine-Interaktion in der ZfP 4.0 zu schärfen und einen strukturierten Orientierungsrahmen bereitzustellen. Dieser soll Organisationen dabei unterstützen, Assistenzsysteme verantwortungsvoll, zuverlässig und akzeptiert in die Praxis zu integrieren – mit dem Menschen als dauerhaft verantwortlicher Akteur im Prüfprozess.

In metal additive manufacturing, stainless steel 316L has become a benchmark for studying and understanding microstructure-property relationships. However, for a wider acceptance in safety-relevant applications, more data and a better understanding are still required. This study investigates the impact of a non-recrystallization heat treatment at 900 ◦C for 1 h on the creep properties of a nearly fully dense PBF-LB/M/316L variant that had previously undergone a heat treatment at 450 ◦C for 4 h. Creep tests at 600 ◦C and 225 MPa until rupture and until reaching the minimum creep rate were carried out. A comparison with the 450 ◦C/4 h heat treated PBFLB/M/316L variant and a hot-rolled 316L was performed. The evolution of the microstructure, the damage characteristics, and the tensile properties were characterized using XCT, SEM, EBSD, TEM, and room temperature tensile tests on miniaturized test pieces. The heat treatment increased the creep rupture time, the minimum creep rate, and the creep ductility of the alloy. The creep ductility exceeded that of a hot-rolled 316L benchmark variant. The increased creep rupture time and ductility are mainly due to the contributions of the secondary and tertiary creep stages. The results of the investigations performed in the state at the minimum creep rate further demonstrate the deterministic role of the cell structure and related dislocation substructure in determining creep strength. The volume fraction of microcracks decreased in the 900 ◦C/1 h heat treated condition, although the underlying creep microcrack formation mechanism remained unchanged for the two PBF-LB/M/316L heat treated conditions. This reduction in microcracking is attributed to the enhanced deformation capacity during tertiary creep, which was accompanied by inhomogeneous texture evolution.

The goal of this work is to provide a deeper understanding of the high-temperature fatigue properties of this alloy. For that purpose, a comparison of the mechanical properties, fatigue lives, and fatigue crack initiation mechanisms at room temperature, 300°C, 650°C, and 750°C has been conducted. This approach enabled the determination of the fatigue behavior of VDM 780 at elevated temperature.