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 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 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-595775 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 - CONF A1 - Richter, Tim A1 - Erxleben, Kjell A1 - Rhode, Michael A1 - Schroepfer, Dirk T1 - Local mechanical properties of TIG dissimilar metal welded high entropy alloy with austenitic steel AISI 304 N2 - High entropy alloys (HEA) are a new class of materials that have been investigated since the early 2000s and offer great potential to replace conventional alloys. However, since they sometimes have significant contents of expensive alloying elements such as Co or Ni, their use is only conceivable in highly stressed areas of components. For this purpose, the weldability with conventional alloys such as high-alloy austenitic steels must be investigated. In addition to the resulting microstructure, the mechanical properties are also fundamental for the usability of HEAs in DMWs. For this purpose, TIG welds of CoCrFeMnNi HEA (cold rolled and recrystallized state) with AISI 304 austenitic steel are investigated. These mechanical properties are analyzed in this work by means of tensile tests and local hardness measurement. The local strain behavior of the welded joints is also characterized by means of Digital Image Correlation (DIC). The results of the local hardness measurement show a clear influence of the initial condition of the HEA on the HAZ. Thus, the HEA in the cold-rolled condition shows a clear softening because of recrystallization processes in the HAZ. On the other hand, there is no influence on the hardness of the weld metal, which is approx. 200 HV0.1 in both cases. The tensile tests show a consistent failure of the weld in the weld metal. However, regardless of the HEA condition, strengths in the range of the recrystallized HEA (RM ~ 550–600 MPa) are achieved, although with significantly reduced fracture elongations. T2 - IIW Intermediate Meeting of Commission II-A CY - Garching, Germany DA - 06.03.2023 KW - High-entropy alloy KW - Welding KW - Dissimilar metal weld (DMW) joint KW - Mechanical properties KW - Digital image correlation PY - 2023 AN - OPUS4-57108 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 - Dissimilar metal joints of multiple principal element alloys friction stir welded to conventional austenitic steel 304 N2 - Multiple principal element alloys (MPEA) represent a class of materials consisting of at least three alloying elements, each with 5 to 35 atomic %. The MPEAs encompass the so-called high-entropy (HEA) and medium-entropy alloys (MEAs) and are fundamentally different from conventional materials like the Fe-based steel. Within the last 20 years, highly innovative MPEA with individually adjustable properties for industrial applications were identified. However, the focus has been on pure material synthesis. With the increase in available material quantities, the focus is now on processing issues such as joining and welding. In that connection, the weldability of MPEAs has received very little attention so far and experience in dissimilar metal welds (DMWs) is lacking so far but. The present study summarizes comprehensive experimental results on the weldability of MPEA-DMWs and their resulting microstructure. For this purpose, two equiatomic MPEAs, CoCrFeMnNi (HEA) and CoCrNi (MEA) in cold-rolled and annealed conditions were joined by solid-state friction stir welding (FSW) to an austenitic stainless steel 316L. The DMWs showed very interesting microstructure features. In addition, the mechanical-technological properties were obtained by instrumented tensile tests, and the local straining was determined in-situ by digital image correlation (DIC). A significant influence of the FSW processing on the mechanical performance was identified,in terms of the formation of FSW-specific defects like whitebands or tunnel defects. The experiments proofed the general (but currently limited) FS weldability of the MPEAs to conventional austenitic steel grade AISI 304. This enables targeted further considerations of these highly innovative MPEAs. T2 - AJP 2023: 3rd International Conference on Advanced Joining Processes 2023 CY - Braga, Portugal DA - 19.10.2023 KW - Multi-principal element alloys KW - Friction stir welding KW - Dissimilar metal weld (DMW) joint KW - Mechanical properties KW - Digital image correlation (DIC) PY - 2023 AN - OPUS4-58678 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 - CONF A1 - Rhode, Michael A1 - Nietzke, Jonathan A1 - Konert, Florian A1 - Sobol, Oded A1 - Böllinghaus, Thomas A1 - Merz, Benjamin T1 - Hollow specimens as simplified approach for testing metallic materials under high pressure hydrogen development and utilization N2 - The hydrogen economy requires large-scale storage and transportation options like long-distance transmission pipelines. The applied materials (typically steels) must be carefully tested under different conditions (pressure, temperature, impact of impurities, etc.) for their suitability and service with hydrogen. In combination with mechanical load, as occurs in every gas network, hydrogen can induce degradation of the mechanical properties and promote finally resulting in embrittlement, i.e., the formation of cracks. The conventional testing procedures consist of autoclaves in which samples are strained under pressurized hydrogen. The test apparatus requires large amounts of hydrogen and thus a high level of safety and costs. In very specific cases, these tests might be replaced by simplified electrochemical charging. However, these test alternatives raise several questions regarding the equivalency of both testing scenarios. In the early 1980’s the idea of a so-called hollow tensile sample raised and was reinitiated 2021 in ISO TC 164 by T. Ogata (NIMS, Japan) and further developed (e.g. by Fraunhofer IWM, Germany). The idea was: the sample itself represents the autoclave instead of charging a sample from outside. For that reason, a hole is drilled through the sample and the inner surface is pressurized by hydrogen gas during the mechanical testing. Indeed, this represents the main advantage as no expensive pressure-resistant autoclave equipment for large H-volumes is necessary, which significantly reduces the safety-related issues and thus the high costs. In the following, we show recent activities at BAM Berlin on adaption of the hollow-specimen technique for slow strain rate testing (SSRT). The current research activities are focussed on macroscopic influences like the sample geometry, minimum necessary dimensions, and microscopic influences e.g., on the surface by the processing method (drill hole quality and geometric precision) as well as the gas pressure effect (mechanical deformation of surface in different media). T2 - FEMS EUROMAT 2023 CY - Frankfurt a. M., Germany DA - 04.09.2023 KW - Hydrogen KW - Hollow tensile specimen KW - High-pressure KW - Mechanical properties KW - Testing PY - 2023 AN - OPUS4-58220 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael A1 - Schröder, Nina A1 - Kannengießer, Thomas T1 - Microalloying influence on precipitation behavior and mechanical properties of welded high strength structural steels N2 - Microalloying elements, such as Nb and Ti, are essential for the targeted mechanical strength of quenched and tempered, high-strength fine-grained structural steels with a nominal yield strength ≥ 690 MPa. Current specifications for chemical composition only provide upper limits for manufacturers. But even small deviations in the alloying route can have a drastic effect on the mechanical properties. Thus, an adequate prediction of the weldability and the integrity of the welded joint becomes difficult or even impossible due to the varying composition and, hence, the microstructures. Undesirable side effects are the possible softening of the heat-affected zone (HAZ) as well as the opposite effect of hardening. Against this background, different microalloying routes with varying Ti and Nb contents are systematically investigated for the first time on specially designed lab-cast alloys. The basis of each alloy route was the common S690QL in terms of both the chemical composition as well as the heat treatment. To investigate the weldability, three-layer welds were performed using metal active gas welding (MAG) and critical microstructural areas with high softening/hardening were identified. The scope was here on the identification of phase transformations during cooling and on the respective metallurgical precipitation behavior. Isothermal and non-isothermal phase calculations were performed using Thermo-Calc® and showed that the prediction of the non-equilibrium precipitation characteristics during welding is not trivial, especially for this relatively complex chemical composition. The mechanical properties of the welded joints were identified by both Charpy tests (toughness) and tensile tests (strain and strength). During the test, the local straining behavior of the welded joints, was identified using a digital image correlation (DIC) system, see Figure 1. Despite the generally good weldability of the materials, the results show a significant influence of the microalloying route as well as the welding heat input on the different precipitation kinetics. T2 - FEMS EUROMAT 2023 CY - Frankfurt a. M., Germany DA - 04.09.2023 KW - High-strength KW - Steel KW - Mechanical properties KW - Welding KW - Thoughness PY - 2023 AN - OPUS4-58221 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael A1 - Erxleben, Kjell A1 - Richter, Tim A1 - Schroepfer, Dirk A1 - Michael, Thomas T1 - Dissimilar metal TIG weld joints of multiple principal element alloys (MPEA) to austenitic steel 304 N2 - Multi-element alloys (MPEA - Multiple Principal Element Alloys) represent a new class of materials consisting of at least three alloying elements, each with 5 to 35 atomic %. This material class includes high-entropy alloys (HEA, with n ≥ 4 elements). The underlying alloying concept differs fundamentally from conventional materials such as the Fe-based steel. 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. The aim is to identify highly innovative MPEA with individually adjustable properties for industrial applications. In the last 20 years, however, the focus has been on pure material synthesis. With the increase in available material quantities, the focus is on processing issues such as joining and welding processes. In that connection, the weldability of MPEAs has received very little attention so far. Experience with dissimilar metal welds (DMWs) is completely lacking but is essential for the application of these materials if joint to conventional materials. This study presents selected experimental results on the weldability of MPEA-DMWs and the resulting microstructures. For this purpose, the equiatomic CoCrFeMnNi (HEA) was investigated in cold-rolled (CR) and heat-treated (HT) condition and joined by tungsten inert gas (TIG) welding to an austenitic stainless steel 304. The DMWs showed defect-free conditions (no lack of fusion, cracks and so on), whereas the cold-rolling increases the microhardness. The global mechanical properties were obtained by instrumented tensile tests of cross-weld samples and showed sufficient yield and tensile strength comparable to that of the individual base materials (BM). The local strain conditions were determined by digital image correlation and showed the highest local strains to occur in the intermixed weld metal. Indeed, the preferred fracture location of the cross-weld tensile samples was in the weld metal. Finally, the experiments proofed the weldability of the MPEAs to conventional 304. This enables targeted further considerations for example as structural materials. T2 - FEMS EUROMAT 2023 CY - Frankfurt a. M., Germany DA - 04.09.2023 KW - Multi-principal element alloys KW - TIG welding KW - Dissimilar metal weld (DMW) joint KW - Microstructure KW - Mechanical properties KW - Digital Image Correlation (DIC) PY - 2023 AN - OPUS4-58222 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Manzoni, Anna Maria A1 - Rhode, Michael A1 - Erxleben, Kjell A1 - Richter, Tim A1 - Schroepfer, Dirk T1 - Mechanical performance and integrity of tungsten inert gas (TIG) welded CoCrFeMnNi high entropy alloy with austenitic steel AISI 304 N2 - High entropy alloys (HEA) are a new class of materials that have been investigated since the early 2000s and offer great potential to replace conventional alloys. However, since they sometimes have significant contents of expensive alloying elements such as Co or Ni, their use is only conceivable in highly stressed areas of components. For this purpose, the weldability with conventional alloys such as high-alloy austenitic steels must be investigated. In addition to the resulting microstructure, the mechanical properties are also fundamental for the usability of HEAs in DMWs. For this purpose, TIG welds of CoCrFeMnNi HEA (cold rolled and recrystallized state) with AISI 304 austenitic steel are investigated. These mechanical properties are analyzed in this work by means of tensile tests and local hardness measurement. The local strain behavior of the welded joints is also characterized by means of Digital Image Correlation (DIC). The results of the local hardness measurement show a clear influence of the initial condition of the HEA on the HAZ. Thus, the HEA in the cold-rolled condition shows a clear softening because of recrystallization processes in the HAZ. On the other hand, there is no influence on the hardness of the weld metal, which is approx. 200 HV0.1 in both cases. The tensile tests show a consistent failure of the weld in the weld metal. However, regardless of the HEA condition, strengths in the range of the recrystallized HEA (RM ~ 550–600 MPa) are achieved, although with significantly reduced fracture elongations. T2 - International Conference on High-Entropy Materials (ICHEM 2023) CY - Knoxville, TN, USA DA - 18.06.2023 KW - Multi-principal element alloys KW - Welding KW - Mechanical properties KW - Dissimilar metal weld KW - Digital image correlation PY - 2023 AN - OPUS4-57713 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rhode, Michael A1 - Nietzke, Jonathan A1 - Richter, Tim A1 - Mente, Tobias A1 - Mayr, P A1 - Nitsche, A T1 - Hydrogen effect on mechanical properties and cracking of creep‑resistant 9% Cr P92 steel and P91 weld metal N2 - Martensitic 9% Cr steels like P91 and P92 can show an increased susceptibility to delayed hydrogen-assisted cracking. The focus of this study was the microstructure and heat treatment efect on the mechanical properties of P92 base material and P91 multi-layer weld metal in both as-welded and post weld heat treated (PWHT) condition. Tensile tests with hydrogen free reference samples and electrochemically hydrogen charged samples were carried out; the mechanical properties were assessed and supported by detailed fractographic analysis. Finally, a hydrogen and microstructure-dependent fracture criterion is established. All investigated microstructures showed a hydrogen-infuenced degradation of the mechanical properties compared to the hydrogen-free reference samples. The as-welded martensitic P91 weld metal had the highest degree of degradation in the presence of hydrogen. The P91 PWHT weld metal and the P92 base material had comparable properties. From that point of view, a signifcantly increased risk for hydrogen-assisted cold cracking during welding fabrication of P91 weld joints must be considered before any heat treatment is conducted. T2 - IIW Annual Assembly, Meeting of Commission IX-C CY - Tokyo, Japan DA - 16.07.2022 KW - Creep-resisting materials KW - Welding KW - Hydrogen assisted cracking KW - Hydrogen embrittlement KW - Mechanical properties PY - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-564070 SN - 0043-2288 SP - 1 EP - 12 PB - Springer Nature CY - Basel (CH) AN - OPUS4-56407 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Richter, Tim A1 - Rhode, Michael A1 - Nietzke, Jonathan A1 - Mente, Tobias A1 - Mayr, P. A1 - Nitsche, A. T1 - Hydrogen embrittlement and mechanical properties of 9 % Cr P92 steel and P91 weld metal N2 - Martensitic 9 %-Cr steels like P91 and P92 can show an increased susceptibility to delayed hydrogen assisted cracking. The focus of this study was the microstructure and heat treatment effect on the mechanical properties of P92 base material and P91 multi-layer weld metal in both as-welded and post weld heat treated (PWHT) condition. Tensile tests with hydrogen free reference samples and electrochemically hydrogen charged samples were carried out, the mechanical properties were assessed and supported by dedicated fractographic analysis. In addition, hydrogen and microstructure dependent fracture criteria were calculated. All investigated microstructures showed a hydrogen influenced degradation of the mechanical properties compared to the hydrogen free reference samples. In that connection, the as welded martensitic P91 weld metal had the highest degree of degradation in presence of hydrogen. The P91 PWHT weld metal and the P92 base material had comparable properties. From that point of view, a significantly increased risk for hydrogen assisted cold cracking during welding fabrication of P91 weld joints must be considered before any heat treatment is conducted. T2 - IIW Annual Assembly, Meeting of Commission IX-C CY - Tokyo, Japan DA - 21.07.2022 KW - Creep-resistant steel KW - Mechanical properties KW - Hydrogen assisted cracking KW - Weld joint KW - Degradation PY - 2022 AN - OPUS4-55462 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -