TY - JOUR A1 - Rhode, Michael A1 - Erxleben, Kjell A1 - Richter, Tim A1 - Schroepfer, Dirk A1 - Mente, Tobias A1 - Michael, Thomas T1 - Local mechanical properties of dissimilar metal TIG welded joints of CoCrFeMnNi high entropy alloy and AISI 304 austenitic steel JF - Welding in the World N2 - Multiple principal element alloys encompass the well-known high entropy alloys (HEA). The alloy system represents a new class of materials consisting of at least three alloying elements, each containing 5 to 35 at.%. Thus, this alloying concept differs fundamentally from conventional materials such as steel or nickel alloys. For this purpose, the alloying elements are specifically selected, the microstructures are adjusted in a single-phase and, in some cases, multi-phase manner. In particular, conflicting goals, such as the trade-off between strength and ductility in conventional steels, are overcome. However, in the last 20 years, the focus has been on material synthesis. With the increase in available material quantities, the focus is now on processing issues such as joining and welding processes. The weldability of HEAs has received very little attention so far. The experience with dissimilar metal welds is completely lacking but is essential for the application of these materials in combination with conventional materials. The present study presents comprehensive experimental results on the weldability of an equimolar CoCrFeMnNi-HEA in cold-rolled and heat-treated condition, which was joined by tungsten inert gas welding to an austenitic steel AISI 304. The mechanical properties of the dissimilar metal welds were characterized by cross-weld tensile samples, whereas the local deformation in the weld of the different welding zones was measured by digital image correlation. In accordance with the respective initial HEA condition (cold-rolled vs. heat-treated), the local strain behavior was divergent and influenced the global mechanical properties of both DMW types. Nonetheless, the experiments provided proof in principle of the weldability for dissimilar joints of the CoCrFeMnNi-HEA welded to conventional materials like austenitic stainless steels ensuring a corresponding capability for mechanical loading. This allows further considerations on the application of these innovative materials. KW - TIG welding KW - High-entropy alloys KW - Mechanical properties KW - Dissimilar metal weld PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-595775 DO - https://doi.org/10.1007/s40194-024-01718-4 SN - 0043-2288 SP - 1 EP - 11 PB - Springer Science and Business Media LLC AN - OPUS4-59577 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Buzolin, R. H. A1 - Richter, Tim A1 - Pixner, F. A1 - Rhode, Michael A1 - Schroepfer, Dirk A1 - Enzinger, N. T1 - Microstructure characterisation of multi-principal element alloys welds produced by electron beam welding JF - Materials and design N2 - This work explores the feasibility of producing bead-on-plate welds of a CrCoNi medium entropy alloy and a CrMnFeCoNi high entropy alloy using electron beam welding. The alloys were welded in two states: one in an as-cold-rolled condition and the other in an annealed condition. In addition, the materials are welded with two different parameters. The FCC microstructure of the welds is investigated using scanning electron microscopy assisted by energy-dispersive X-ray spectroscopy and electron-backscattered diffraction. The impact of the weld on the microstructure is discussed. The heat-affected zone is negligible for the annealed condition of both medium and high entropy alloys since there is no driving force for recrystallisation and the exposure time to high temperature is insufficient for grain coarsening. The texture formed in the fusion zone is also discussed and compared to the texture in the base metal and the heat-affected zone. Although the grain growth along the (100) crystallographic direction is preferential in all cases, the crystallographic texture type differs from each weld. Higher hardness values are measured in the medium entropy alloy’s base metal and fusion zone than in the high entropy alloy. KW - Multi-principal element alloy KW - Electron backscattered diffraction KW - Electron beam welding KW - High-entropy alloy KW - Microstructure characterization PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-568129 DO - https://doi.org/10.1016/j.matdes.2023.111609 SN - 1873-4197 VL - 225 SP - 1 EP - 14 PB - Elsevier Science CY - Amsterdam [u.a.] AN - OPUS4-56812 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Buzolin, R.H. A1 - Richter, Tim A1 - Pixner, F. A1 - Rhode, Michael A1 - Schroepfer, Dirk A1 - Enzinger, N. T1 - Microstructure and texture characterisation of friction stir welded CoCrNi and CoCrFeMnNi multi-principle element alloys JF - Materials Today Communications N2 - This work investigates the microstructure formed in friction stir welds of FCC alloys, focused on two multiprincipal alloys: a CoCrFeMnNi high-entropy alloy (HEA) and a CoCrNi medium-entropy alloy (MEA). A commercial stainless steel AISI 304 is used for comparison. The largest nugget was formed in the MEA, while the smallest was formed in the HEA. Grain refinement occurs in the stirred zone in all welds. Discontinuous dynamic recrystallisation is the predominant restoration mechanism during friction stir welding of the three investigated alloys. A sharp decrement in the Σ3 boundary fraction occurs in the stirred zone of the AISI 304 and HEA welds, while comparable values with the base metal are found for the MEA weld. The peak in the maximum index of crystallographic texture is observed on the advancing side of the stirred zone of the AISI 304 weld. A strong <001> θ-fibre texture is formed in the advancing side of the nugget in the AISI 304 from a well-established {123} <634> S-type texture in the base metal. Multiple crystallographic texture components without specific fibres are identified in most regions of the welds, indicating the complex shear path history during friction stir welding. KW - Microstructure KW - Multiple principal element alloy KW - Friction stir welding KW - Electron backscattered diffraction KW - Crystallographic texture PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-572987 DO - https://doi.org/10.1016/j.mtcomm.2023.105870 VL - 35 SP - 1 EP - 14 PB - Elsevier Ltd. CY - Amsterdam (NL) AN - OPUS4-57298 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Delgado Arroyo, Diego A1 - Richter, Tim A1 - Schroepfer, Dirk A1 - Boerner, Andreas A1 - Rhode, Michael A1 - Lindner, T. A1 - Preuß, B. A1 - Lampke, T. T1 - Influence of Milling Conditions on AlxCoCrFeNiMoy Multi-Principal-Element Alloys JF - Coatings N2 - Multi-Principal-Element or High-Entropy Alloys (MPEAs/HEAs) have gained increasing interest in the past two decades largely due to their outstanding properties such as superior mechanical strength and corrosion resistance. However, research studies on their processability are still scarce. This work assesses the effect of different machining conditions on the machinability of these novel alloys, with the objective of advancing the introduction of MPEA systems into industrial applications. The present study focuses on the experimental analysis of finish-milling conditions and their effects on the milling process and resulting surface finish of CoCrFeNi, Al0.3CoCrFeNi and Al0.3CoCrFeNiMo0.2 alloys fabricated via Spark Plasma Sintering. Ball-nose-end milling experiments have been carried out various milling parameters such as cutting speed, feed per cutting edge, and ultrasonic assistance. In situ measurements of cutting forces and temperature on the tool edge were performed during the experiments, and surface finish and tool wear were analyzed afterwards. The results exhibited decreasing cutting forces by means of low feed per cutting edge and reduced process temperatures at low cutting speed, with the use of ultrasonic-assisted milling. It was shown that the machinability of these modern alloys through conventional, as well as modern machining methods such as ultrasonic-assisted milling, is viable, and common theories in machining can be transferred to these novel MPEAs. KW - Multi-principal element alloys KW - Finish milling KW - Spark plasma sintering KW - Ultrasonic-assisted milling KW - Microstructure characterization PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-572990 DO - https://doi.org/10.3390/coatings13030662 VL - 13 IS - 3 SP - 1 EP - 18 PB - MDPI (Multidisciplinary Digital Publishing Institute) CY - Basel (CH) AN - OPUS4-57299 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schroepfer, Dirk A1 - Rhode, Michael A1 - Erxleben, Kjell A1 - Richter, Tim T1 - Local mechanical properties of TIG dissimilar metal welded CoCrFeMnNi high-entropy alloy to austenitic steel AISI 304 N2 - Multiple principal element alloys (MPEA) encompass the well-known high entropy alloys (HEAs). MPEA/HEA represent a new class of materials consisting of at least three alloying elements, each containing 5 to 35 at.-%. This alloying concept thus differs fundamentally from conventional materials such as steel or nickel alloys. For this purpose, the alloying elements are specifically selected, and the microstructures are adjusted in a single-phase and, in some cases, multi-phase manner. In particular, conflicting goals, such as the trade-off between strength and ductility in conventional steels, are overcome. In the last 20 years, however, the focus has been on material synthesis. With the increase in available material quantities, the focus is now on pro-cessing issues such as joining and welding processes. The weldability of MPEA has received very little atten-tion so far. Experience with dissimilar metal welds (DMWs) is completely lacking but is essential for the appli-cation of these materials in combination with conventional materials. The present study presents, comprehen-sive experimental results on the weldability of MPEA-DMWs. For that purpose, a Co20Cr20Fe20Mn20Ni20 HEA in cold-rolled and heat-treated condition was joined by means of tungsten inert gas welding (TIG) with the austenitic Cr-Ni steel AISI 304. The DMWs resulted in interesting mechanical properties. They were obtained by instrumented tensile tests as well as the local deformation in the weld area by using digital image correlation (DIC) technique. A significant softening in the heat-affected zone (HAZ) of the MPEAs as well as a slightly reduced tensile strength with a significant decrease of the elongation at fracture were found. The experiments provided proof in principle of the weldability of the MPEAs for DMWs with conventional materials that ensure a corresponding capability for mechanical loading. This allows further considerations on the application of these innovative materials. T2 - IIW Annual Assembly, Meeting of Commission C-II CY - Singapore DA - 18.07.2023 KW - High-entropy alloy KW - Welding KW - Microstructure KW - Mechanical properties KW - Dissimilar metal weld PY - 2023 AN - OPUS4-57978 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Richter, Tim A1 - Schroepfer, Dirk A1 - Rhode, Michael A1 - Boerner, Andreas A1 - Saliwan Neumann, Romeo A1 - Schneider, M. A1 - Laplanche, G. T1 - Influence of machining on the surface integrity of high- and medium-entropy alloys JF - Materials Chemistry and Physics N2 - High- and medium-entropy alloys (HEAs) are a quite new class of materials. They have a high potential for applications from low to high temperatures due to the excellent combination of their structural properties. Concerning their application as components; processing properties, such as machinability, have hardly been investigated so far. Hence, machinability analyses with a focus on the influence of the milling process and its basic parameters (cutting speed, feed per cutting edge) on the resulting surface integrity of specimens from an equiatomic high- (CoCrFeMnNi) and a medium- (CoCrNi) entropy alloy have been carried out. A highly innovative milling process with ultrasonic assistance (USAM) was compared to conventional milling processes. Recent studies have shown that USAM has a high potential to significantly reduce the mechanical load on the tool and workpiece surface during milling. In this study, the basic machining and ultrasonic parameters were systematically varied. After machining, the surface integrity of the alloys was analyzed in terms of topography, defects, subsurface damage, and residual stresses. It was observed that USAM reduces the cutting forces and increases the surface integrity in terms of lower tensile residual stresses and defect density near the surfaces for the CoCrFeMnNi alloy. It was shown that the cutting forces and the metallurgical influence in the sub surface region are reduced by increasing the cutting speed and reducing the feed rate per cutting edge. With the CoCrNi alloy, the tool revealed severe wear. As a result, for this alloy no influence of the parameters on the machinability could be determined. KW - High Entropy Alloy KW - Medium Entropy Alloys KW - Ultrasonic assited machining PY - 2022 DO - https://doi.org/10.1016/j.matchemphys.2021.125271 SN - 0254-0584 VL - 275 SP - 125271 PB - Elsevier B.V. AN - OPUS4-53606 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Richter, Tim A1 - Diese, Marcel A1 - Rhode, Michael A1 - Schroepfer, Dirk A1 - Richter, Tim T1 - Characterization of cracking phenomena in TIG welds of high and medium entropy alloy N2 - Multi-element systems with defined entropy (HEA - High Entropy Alloy or MEA - Medium Entropy Alloy) are rather new material concepts that are becoming increasingly important in materials research and development. Some HEA systems show significantly improved properties or combinations of properties, e.g., the overcome of the trade-off between high strength and ductility. Thus, the synthesis, the resulting microstructures, and properties of HEA have been primarily investigated so far. In addition, processing is crucial to achieve a transfer of potential HEA/MEA materials to real applications, e.g. highly stressed components. Since fusion welding is the most important joining process for metals, it is of vital importance to investigate the weldability of these materials. However, this has rarely been the subject of research up to date. For that reason, in this work the weldability depending on the surface preparation of a CoCrFeMnNi-HEA and a CoCrNi-MEA for TIG welding is investigated. The fusion welding of longer plates is described here for the first time for the CoCrNi alloy. The welds of both materials showed distinct formation of cracks in the heat affected zone (HAZ). Optical and scanning electron microscopy analysis clearly confirmed an intergranular fracture topography. But based on the results, the crack mechanism cannot be conclusively clarified as either a liquid metal embrittlement (LME) or hot cracking like liquid film separation occurred. T2 - 2nd International Conference on Advanced Joining Processes CY - Online meeting DA - 21.10.2021 KW - High Entropy Alloy KW - TIG welding KW - Cracking PY - 2021 AN - OPUS4-53607 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael A1 - Kromm, Arne A1 - Schroepfer, Dirk A1 - Steger, J. A1 - Kannengießer, Thomas ED - Seefeldt, M. T1 - Residual stress formation in component related stress relief cracking tests of a welded creep-resistant steel T2 - RESIDUAL STRESSES 2018, ECRS-10 N2 - Submerged arc welded (SAW) components of creep-resistant low-alloyed Cr-Mo-V steels are used for thick-walled heavy petrochemical reactors (wall-thickness up to 475 mm) as well as employed in construction of modern high-efficient fossil fired power plants. These large components are accompanied by significant restraints during welding fabrication, especially at positions of different thicknesses like welding of nozzles. As a result, residual stresses occur, playing a domi-nant role concerning so-called stress relief cracking (SRC) typically during post weld heat treat-ment (PWHT). Besides specific metallurgical factors (like secondary hardening due to re-precipitation), high tensile residual stresses are a considerable influence factor on SRC. For the assessment of SRC susceptibility of certain materials mostly mechanical tests are applied which are isolated from the welding process. Conclusions regarding the influence of mechanical factors are rare so far. The present research follows an approach to reproduce loads, which occur during welding of real thick-walled components scaled to laboratory conditions by using tests designed on different measures. A large-scale slit specimen giving a high restraint in 3 dimensions by high stiffness was compared to a medium-scale multi-pass welding U-profile specimen showing a high degree of restraint in longitudinal direction and a small-scale TIG-re-melted specimen. The small-scale specimens were additionally subjected to mechanical bending to induce loads that are found during fabrication on the real-scale in heavy components. Results show for all three cases compa-rable high tensile residual stresses up to yield strength with high gradients in the weld metal and the heat affected zone. Those high tensile stresses can be significant for cracking during further PWHT. T2 - European Conference on Residual Stresses 2018 - ECRS-10 CY - Leuven, Belgium DA - 11.09.2018 KW - Welding KW - Residual stresses KW - Stress Relief Cracking (SRC) KW - Creep-resistant steel KW - Post Weld Heat Treatment (PWHT) PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-459683 SN - 978-1-9452-9188-3 SN - 978-1-9452-9189-0 DO - https://doi.org/10.21741/9781945291890-29 SN - 2474-395X SN - 2474-3941 VL - 6 SP - 185 EP - 190 PB - Materials Research Forum LLC CY - Millersville, PA, USA AN - OPUS4-45968 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -