Konrad Chrzan

This study investigates the microstructural evolution as well as the mechanical and soft-magnetic properties of as-cast AlCoCuFeNi-based high-entropy alloys (HEAs) with varying aluminium and copper contents. The alloys were produced using a cost-effective casting method that involved melting in an open crucible under a protective argon atmosphere, with mechanical stirring to improve chemical homogeneity. The results demonstrate that aluminium content strongly governs phase stability, atomic ordering, and elemental segregation. Increasing Al concentration drives structural transitions from a face-centred cubic (FCC) matrix containing nanoscale L1₂ precipitates to an ordered L1₂ structure and finally to a multiphase FCC + BCC system with pronounced Cu segregation. These changes significantly influence performance. Alloys with lower Al content exhibit the best soft-magnetic properties and high compressive ductility (~60%), whereas the equiatomic alloy shows the highest yield strength (~1060 MPa) but limited ductility and reduced magnetic performance. The findings highlight the key role of compositional tuning and atomic ordering in controlling structure–property relationships in AlCoCuFeNi-based HEAs.

This study investigates the microstructural evolution as well as the mechanical and soft-magnetic properties of as-cast AlCoCuFeNi-based high-entropy alloys (HEAs) with varying aluminium and copper contents. The alloys were produced using a cost-effective casting method that involved melting in an open crucible under a protective argon atmosphere, with mechanical stirring to improve chemical homogeneity. The results demonstrate that aluminium content strongly governs phase stability, atomic ordering, and elemental segregation. Increasing Al concentration drives structural transitions from a face-centred cubic (FCC) matrix containing nanoscale L1₂ precipitates to an ordered L1₂ structure and finally to a multiphase FCC + BCC system with pronounced Cu segregation. These changes significantly influence performance. Alloys with lower Al content exhibit the best soft-magnetic properties and high compressive ductility (~60%), whereas the equiatomic alloy shows the highest yield strength (~1060 MPa) but limited ductility and reduced magnetic performance. The findings highlight the key role of compositional tuning and atomic ordering in controlling structure–property relationships in AlCoCuFeNi-based HEAs.

Three variants of high-entropy alloys (HEAs) from the AlCoCuFeNi group, containing different amounts of Al and Cu, were developed and produced via induction melting and casting into ceramic moulds. The ingots were homogenized at 1000 °C for 10 h. Analyses revealed that variations in Al and Cu concentrations led to significant changes in the material’s microstructure, hardness, strength, and impact strength. In the equiatomic variant, differential scanning calorimetry revealed a peak associated with the phase transformation, indicating that this alloy’s microstructure consists of two distinct phases. In contrast, when the concentrations of Al and Cu are reduced, a single-phase microstructure is observed. The equiatomic variant (used as a reference) is characterized by its hardness and brittleness, exhibiting slight ductility, with a tensile strength of 80 MPa, a hardness of 400 HV5, and an impact strength of 1.9 J/cm². However, with adjusted Al contents of 1/2 and Cu contents of 1/4, the alloy displays exceptional strength combined with good plasticity, achieving a tensile strength of up to 450 MPa with 60% elongation, and an impact strength of 215 J/cm². The non-equiatomic variants exhibit a comparatively more straightforward microstructure and enhanced ductility, which may facilitate easier processing of these alloys. Fractography investigation revealed a ductile mode of fracture in the samples.

The results of tribological tests carried out on two novel high-entropy alloys (HEAs) from the AlCoCuFeNi group are described in this study. Research was carried out using a Miller machine (ASTM G75 standard) in an abrasive slurry environment, which contained SiC and water in a 1:1 ratio. The results obtained showed a higher rate of abrasive wear in the material designated as D3 (total weight loss in D3-1.6g compared to 1.1g in the D5 alloy), characterised by a homogeneous microstructure and hardness of 186 HV5. The second dual phase alloy, designated D5, was characterised by a lower rate of abrasive wear. In this alloy, the appearance of the second phase precipitates, evenly distributed throughout the entire volume, with higher hardness (760 HV0,01) and in a content of approximately 65% has led to a decrease in wear. The different wear resistances of the tested materials are due to differences in the hardness of the phases that constitute the microstructure of the tested alloys and the interaction of hard abrasive particles with the tested material. This has a direct impact on the plastic nature of the deformation in the upper layers of the samples. A characteristic system of linear grooves and protrusions, visible on surface profiles, was observed on the surfaces tested. Small local defects were also observed as a result of hammering and subsequent removal of hard SiC abrasive particles from the alloys tested or, in the case of the D5 alloy, additional removal of precipitates of the harder phase from the matrix.

The article presents the developed IT solutions supporting the material and technological conversion process in terms of the possibility of using the casting technology of selected alloys to produce products previously manufactured with the use of other methods and materials. The solutions are based on artificial intelligence, machine learning and statistical methods. The prototype module of the information and decision-making system allows for a preliminary assessment of the feasibility of this type of procedure. Currently, the selection of the method of manufacturing a product is based on the knowledge and experience of the technologist and constructor. In the described approach, this process is supported by the proprietary module of the information and decision-making system, which, based on the accumulated knowledge, allows for an initial assessment of the feasibility of a selected element in a given technology. It allows taking into account a large number of intuitive factors, as well as recording expert knowledge with the use of formal languages. Additionally, the possibility of searching for and collecting data on innovative solutions, supplying the knowledge base, should be taken into account. The developed and applied models should allow for the effective use and representation of knowledge expressed in linguistic form. In this solution, it is important to use methods that support the selection of parameters for the production of casting. The type, number and characteristics of data have an impact on the effectiveness of solutions in terms of classification and prediction of data and the relationships detected.

The as-cast microstructure, alloying element segregation, solidification behavior, and thermal stability of model superalloys based on Inconel 740 with various Al/Ti ratios (0.7, 1.5, 3.4) and Ta (2.0, 3.0, 4.0 wt%) concentrations were investigated via ThermoCalc simulations, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, dilatometry, and differential scanning calorimetry. The solidification of the superalloys began with the formation of primary γ dendrites, followed by MC carbides. The type of subsequently formed phases depended on the superalloys’ initial Al/Ti ratio and Ta concentration. The results obtained from solidification simulations were compared to the obtained microstructures. For all castings, the dendritic regions consisted of fine γ′ precipitates, with their size mainly depending on the initial Al/Ti ratio, whereas in the interdendritic spaces, (Nb, Ta, Ti)C carbides and Nb-rich Laves phase precipitates were present. In high Al/Ti ratio superalloys, β-NiAl precipitates, strengthened by η and α-Cr phases, were observed. Based on dilatometric results, the dissolution of γ′ precipitates was accompanied by a substantial increase in the coefficient of thermal expansion. The end of the dilatation effect took place around the γ′ solvus temperature, as determined via calorimetry. Moreover, the bulk solidus temperature was preceded by the dissolution of the Laves phase, which may be accompanied by local melting.