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- High entropy alloy (1)
- Hochentropie Legierung (1)
- Machining (1)
- Medium entropy alloy (1)
- Mediumentropie Legierung (1)
- Rührreibschweißen (1)
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Organisationseinheit der BAM
High Entropy Alloys (HEAs) are a recent class of materials. In contrast to conventional alloys, HEAs consist of five alloying elements in equiatomic equilibrium. The high entropy effect is due, among other things, to the increased configuration entropy, which promotes solid solution formation. Many HEAs have enormous application potential due to excellent structural property combinations from very low to high temperatures. For the introduction of HEAs in real components, however, the question of the applicability of machining production technologies for component manufacture is of central importance. This has so far received Little attention in global materials research. Reliable and safe processing is essential for the demand of economical component production for potential areas of application, e.g. in power plant technology.
For metals, milling is the standard machining process. This article presents the results of machining analyses. It focuses on the surface integrity resulting from the milling process on a Co20Cr20Fe20Mn20Ni20-HEA. For this purpose, investigations were carried out using ball nose end milling tools for conventional milling process in comparison to an innovative hybrid process available at BAM Berlin, Ultrasonic-Assisted Milling (USAM). USAM promises a lower Degradation of the surface properties due to lower loads on the workpiece surface during machining.
For this purpose, basic milling parameters (cutting speed and tooth feed) were systematically varied and cutting forces were measured during the milling experiments. The subsequent Analysis of these forces allows an understanding of the mechanical loads acting on the tool and component surface. These loads cause topographical, mechanical and microstructural influences on the surface and consequently on the surface integrity. For their characterization, light and scanning electron microscopy were used, and the roughness and residual stresses via X-ray diffraction were measured. The results indicate significant advantages using USAM, especially due to reduced cutting forces compared to the conventional milling process. This causes lower mechanical loads on the tool and surface, combined with lower tensile residual stresses on and below the surface, and ultimately results in a significantly enhanced surface integrity.
Hoch- und Mittelentropie-Legierungen (engl. High/Medium Entropy Alloys–HEA/MEA) sind relativ neue Werkstoffklassen. Im Gegensatz zu herkömmlichen Le-gierungen bestehen HEA aus fünf bzw. MEA aus drei oder vier Legierungselementen im äquiatomaren Gleichgewicht. Viele HEA weisen aufgrund hervorragender struktu-reller Eigenschaftskombinationen von sehr tiefen bis zu hohen Temperaturen enor-mes Anwendungspotential auf. Die Anwendung für reale Bauteile stellt jedoch die zentrale Frage der Eignung für die fügetechnische Verarbeitung. Dieser Aspekt findet in der weltweiten Materialforschung bisher kaum Beachtung. Anforderungen an die zuverlässige und sichere fügetechnische Verarbeitung dieser Werkstoffe sind von wesentlicher Bedeutung hinsichtlich wirtschaftlicher Bauteilfertigung für spätere po-tenzielle Anwendungsbereiche, bspw. in der Energietechnik. Das Rührreibschweißen (engl. Friction Stir Welding–FSW) stellt hierbei einen vielversprechenden Fügepro-zess dar, dessen Hauptvorteil in der Schweißprozesstemperatur unterhalb der Schmelztemperatur der zu fügenden Werkstoffe liegt. Dies bedingt die Vermeidung der Ausbildung von harten, versprödenden intermetallischen Phasen, wie sie z. B. beim konventionellen Schmelzschweißen von Eisen-Aluminium-Verbindungen auf-treten. Die vorliegende Arbeit stellt grundlegende Untersuchungen zur Schweißbar-keit einer CoCrFeMnNi-Legierung (HEA) und einer CoCrNi-Legierung (MEA) mit dem FSW-Prozess vor. Die Versuchsschweißungen werden mittels mikroskopischer Analysen hinsichtlich des Schweißnahtaufbaus sowie Schweißnahtfehlern charakte-risiert. FSW zeigt sich als grundlegend geeignet zur Verbindungsschweißung der HEA bzw. MEA. Anhand dieser Ergebnisse kann eine weitere Bewertung der Schweißbar-keit erfolgen.
Medium and High Entropy Alloys (MEA/HEA) are recently developed material classes, providing manifold applications, e.g., due to extraordinary structural properties. In that connection, the machinability as important issue for the processing of these materials was not in the scientific focus. This study focusses on experimental analysis of milling process conditions including ultrasonic assisted milling (USAM) and their effects on the resulting surface integrity of equiatomic CoCrFeNi-MEA specimens. For that reason, milling parameters (cutting speed, feed per cutting edge) were systematically varied for both conventional milling and USAM. The surface integrity was analyzed in terms of topography, defects, and residual stresses. Especially USAM leads to a decrease of occurring cutting forces and, hence, to an improvement of the surface integrity. Beneficial effects were observed in terms of lower tensile residual stresses at high cutting speed and feed per cutting edge.