In this project, we work on a generic solution to design advanced high-entropy alloys (HEAs) with enhanced magnetic properties. By overturning the concept of stabilizing solid solutions in HEAs, we propose to render the massive solid solutions metastable and trigger spinodal decomposition. The motivation for starting from the HEA for this approach is to provide the chemical degrees of freedom required to tailor spinodal behaviour using multiple components.
Magnetic properties of the Fe15Co15Ni20Mn20Cu30 HEA samples in different processing conditions. a, b) Temperature dependence of magnetization of the homogenized a) and 600 oC / 240 h annealed b) HEA samples after zero-field cooling in applied magnetic fields of 50-0.05 T and after a 0.5 T field cooling in an applied magnetic field of 0.01 T. c) Hysteresis loops investigated up to 2 T of the HEA with different annealing time at 300 K. d) Experimental Curie temperatures as a function of annealing time. The morphological evolution of the alloy’s nanostructure as a function of annealing time is shown in terms of APT reconstructions of volume portions with dimensions of 40×40×200 nm3. The APT reconstructions also show 50 at. % iso-composition surfaces of Cu. e) DFT calculated Curie temperatures as a function of annealing time. The blue shaded area indicates the impact of strain induced volume dilatation on the Curie temperature, i.e., the difference between the Curie temperature calculated for a hypothetical free-standing unconstrained single-phase bulk-like Fe-Co alloy and that for the experimentally measured strained volume of the same region in the HEA. For the 6 h and 24 h annealed samples, light blue squares and spheres indicate the Curie temperature values calculated for compositions corresponding to three different APT tips while the final value is the arithmetic mean over the three compositions. The oval shapes for these two annealing times mark the fluctuations in the Curie temperatures that occur due to the scatter in local composition among the different APT specimens.
Magnetic properties of the Fe15Co15Ni20Mn20Cu30 HEA samples in different processing conditions. a, b) Temperature dependence of magnetization of the homogenized a) and 600 oC / 240 h annealed b) HEA samples after zero-field cooling in applied magnetic fields of 50-0.05 T and after a 0.5 T field cooling in an applied magnetic field of 0.01 T. c) Hysteresis loops investigated up to 2 T of the HEA with different annealing time at 300 K. d) Experimental Curie temperatures as a function of annealing time. The morphological evolution of the alloy’s nanostructure as a function of annealing time is shown in terms of APT reconstructions of volume portions with dimensions of 40×40×200 nm3. The APT reconstructions also show 50 at. % iso-composition surfaces of Cu. e) DFT calculated Curie temperatures as a function of annealing time. The blue shaded area indicates the impact of strain induced volume dilatation on the Curie temperature, i.e., the difference between the Curie temperature calculated for a hypothetical free-standing unconstrained single-phase bulk-like Fe-Co alloy and that for the experimentally measured strained volume of the same region in the HEA. For the 6 h and 24 h annealed samples, light blue squares and spheres indicate the Curie temperature values calculated for compositions corresponding to three different APT tips while the final value is the arithmetic mean over the three compositions. The oval shapes for these two annealing times mark the fluctuations in the Curie temperatures that occur due to the scatter in local composition among the different APT specimens.
Since its first emergence in 2004, the HEA concept has aimed at stabilizing single- or dual-phase multi-element solid solutions through high mixing entropy. Here, we change this strategy and render such massive solid solutions metastable, to trigger spinodal decomposition for improving the alloys’ magnetic properties. The motivation for starting from a HEA for this approach is to provide the chemical degrees of freedom required to tailor spinodal behavior using multiple components. The key idea is to form Fe-Co enriched regions which have an expanded volume (relative to unconstrained Fe-Co), due to coherency constraints imposed by the surrounding HEA matrix. As demonstrated by theory and experiments, this leads to improved magnetic properties of the decomposed alloy relative to the original solid solution matrix. In a prototype magnetic FeCoNiMnCu HEA, we show that the modulated structures, achieved by spinodal decomposition, lead to an increase of the Curie temperature by 48% and a simultaneous increase of magnetization by 70% at ambient temperature as compared to the homogenized single-phase reference alloy.
Future technology challenges will no longer be simply addressed by today's materials and processing solutions, which are often based on trial and error. Instead, guidance will be attained from correlative experimental and theoretical research bridging all length scales.
Within the EU project „ADVANCE - Sophisticated experiments and optimisation to advance an existing CALPHAD database for next generation TiAl alloys”, MPIE collaborated with Thermocalc-Software AB, Stockholm, Montanuniversität Leoben and Helmholtz-Zentrum Hereon, Geesthacht. At MPIE the focus lay on the production and heat treatments of model alloys…
The promising mechanical properties of metallic glasses (MG) such as high hardness, yield strength, and toughness [1] are desirable to exploit for structural applications. Monolithic MGs lack grains and grain boundaries; thus, the mechanical properties of MGs are depending on the chemistry as well as processing and testing conditions. However…
Scandium-containing aluminium alloys are currently attracting interest as candidates for high-performance aerospace structural materials due to their outstanding combination of strength, ductility and corrosion resistance. Strengthening is achieved by precipitation of Al3Sc-particles upon ageing heat treatment.
In this project, we aim to synthetize novel ZrCu thin film metallic glasses (TFMGs) with controlled composition and nanostructure, investigating the relationship with the mechanical behavior and focusing on the nanometre scale deformation mechanisms. Moreover, we aim to study the mechanical properties of films with complex architectures such as…
Wear-related energy loss and component damage, including friction and remanufacturing of components that failed by surface contacts, has an incredible cost. While high-strength materials generally have low wear rates, homogeneous deformation behaviour and the accommodation of plastic strain without cracking or localised brittle fracture are also…
Multiple Exciton Generation (MEG) is a promising pathway towards surpassing the Shockley-Queisser limit in solar energy conversion efficiency, where an incoming photon creates a high energy exciton, which then decays into multiple excitons.
In this project, we aim to design novel NiCoCr-based medium entropy alloys (MEAs) and further enhance their mechanical properties by tuning the multiscale heterogeneous composite structures. This is being achieved by alloying of varying elements in the NiCoCr matrix and appropriate thermal-mechanical processing.
