Rafał Babilas

In this work, a series of novel high-entropy alloys CoCrFeNiSiV_x (x = 0.25; 0.5; 0.75; 1.0) with an intermetallic compound structure was proposed. The effect of vanadium addition on the structure, as well as selected mechanical and corrosion properties, was investigated. In the case of the CoCrFeNiSiV_0.25 alloy, the structural analysis revealed the formation of a dual-phase structure consisting of Fe_1.812V_0.907Si_0.906-type and Fe₅Ni₃Si₂-type intermetallic phases. The increase in vanadium concentration results in the crystallization of one Fe_1.812V_0.907Si_0.906 intermetallic phase detected by the X-ray diffraction method. The increase in vanadium content had a beneficial influence on the corrosion resistance of CoCrFeNiSiV_x alloys in 3.5% NaCl. The CoCrFeNiSiV alloy exhibited the lowest corrosion current density of 0.17 μA/cm² and the highest corrosion potential of −0.228 V. The hardness of the alloys investigated increased with vanadium content, reaching 1006 HV for the equimolar alloy. In turn, the lowest friction coefficient of 0.63 ± 0.06 was obtained for the CoCrFeNiSiV_0.75 alloy. The abrasive, fatigue, and oxidative wear were identified as the main wear mechanisms.

This paper presents the results of research on the structure and properties of the AlCoFeNiTiB high-entropy alloy (HEA) obtained by two casting methods. Microstructural studies confirmed the formation of the BCC, TiB₂, and L2₁ phases in the alloy, both in the as-cast state and in the form of plates. Mössbauer spectroscopy showed that in the AlCoFeNiTiB alloy, the iron atoms were mainly distributed in the BCC structure. The paramagnetic properties of the alloys at room temperature were also observed. SEM images revealed the presence of a spinodal decomopsition in the tested alloy in both the ingot and plate forms. Increasing the cooling rate from the liquid state had a positive effect on the corrosion resistance of the alloy in environments of 3.5 and 5 pct NaCl solution. The AlCoFeNiTiB plate in the more aggressive environment showed the best corrosion resistance (polarization resistance of 58.6 kΩcm², corrosion current density of 0.31 μA/cm² and the lowest weight loss of 0.0076 mm/year). The results of the electrochemical impedance spectroscopy (EIS) study indicated the beneficial effect of higher cooling rate on the protective abilities of the oxide and hydroxide layer which forms on the alloys surface. The hardness of the rapidly cooled plates (685 HV1) was slightly higher than the hardness of the more slowly cooled ingots (648 HV1), which is likely due to the refinement of the alloy’s microstructure and, consequently, the occurrence of fine grain strengthening. The AlCoFeNiTiB HEA ingot and plate, as well as the AlCoFeNiTi HEA, were described by the same average value of the friction coefficient (0.69); however, the surface morphology of the wear tracks showed a beneficial effect of the TiB₂ phase and the increased cooling rate.

In this work, CoCrFeNiNb_x (x = 0.25, 0.45 and 0.65) high entropy alloys were prepared by two different methods to determine the effect of cooling rate and the niobium content on the structure and properties of ingots and plates. The structure was investigated extensively using X-ray diffraction, scanning electron microscopy, and Mössbauer spectroscopy. The results confirmed the dual-phase structure, consisting of the FCC solid solution and the Laves phase. The increase in niobium content changed the microstructure from hypoeutectic (x = 0.25 and 0.45) to hypereutectic (x = 0.65). The high cooling rate during solidification from the liquid state enabled the formation of ultrafine eutectic structures with an average lamellae thickness of only 130 ± 9 nm in the CoCrFeNiNb_0.65 plate. The corrosion behaviour of the alloys was studied in solutions of 3.5% NaCl and 3.5% NaCl + H₃BO₃. The beneficial effect of increasing the niobium content in as-cast CoCrFeNiNb_x alloys on the corrosion resistance was confirmed in both environments. Furthermore, the alloys solidified with a higher cooling rate exhibited a lower corrosion susceptibility in the 3.5% NaCl solution. The results of the EIS study indicated that a higher content of niobium contributed to the formation of a more stable and compact passivation layer. The hardness of the CoCrFeNiNb_x alloys increased with a higher niobium content, achieving the highest value of 669 HV₁ for the CoCrFeNiNb_0.65 plate. The increase in the cooling rate positively affected the tribological properties of the CoCrFeNiNb_x alloys, contributing to the decrease in the friction coefficient for the CoCrFeNiNb_0.25 and CoCrFeNiNb_0.45 plates.

Medium-entropy alloys (MEAs) exhibit properties comparable or even superior to high-entropy alloys (HEAs). Due to their very good resistance in thermomechanical conditions and corrosive environments and unique electrical and magnetic properties, medium-entropy alloys are good candidates for coating applications. One of the most economically effective methods of producing metallic coatings is electrodeposition. In this work, the structure of an electrodeposited CoFeNi medium-entropy alloy coating on a copper substrate from a metal chlorides solution (FeCl₂ ∙ 4H₂O + CoCl₂ ∙ 6H₂O + NiCl₂ ∙ 6H₂O) with the addition of boric acid (H₃BO₃) was investigated. The coating was characterized by a nanocrystalline structure identified by transmission electron microscopy examination and X-ray diffraction methods. Based on XRD and TEM, the face-centered cubic (FCC) phase of the CoFeNi MEA coating was identified. The high corrosion resistance of the MEA coating in a 3.5% NaCl environment at 25 °C was confirmed by electrochemical tests.

The influence of copper addition on the structure and selected properties of AlCoCrFeNiSi_0.5Cu_x high-entropy alloys is described. Slowly cooled ingots were prepared by induction melting, and the samples in the form of plates were obtained by pressure casting. The conducted structural studies confirmed the presence of BCC/B2 phase. Microsegregation in the ingots was associated with the formation of intermetallic Cr₃Si and Fe₅Si₃ phases. An increase in the cooling rate stopped segregation by reducing the mobility of Cr and Si. The hyperfine magnetic field distributions indicated the formation of the BCC Fe(Co,Ni,Si,Cr) solid solution for alloys in the form of plates. The lowest corrosion-current density (0.04 μA/cm²) in 3.5%-NaCl solution was obtained for the plate with the lowest copper content. The dominated aluminum surface states for the post-corrosive plates highlighted the binding energies of Al₂O₃. A tendency of reduced coercivity with increased copper content was observed. The positive effect of copper addition on wear resistance was confirmed for the AlCoCrFeNiSi_0.5Cu_0.1 alloy.

Magnesium-based materials are an interesting solution in terms of medical applications. Alloys that are hard to obtain via standard means may be manufactured via mechanical alloying (MA), which allows the production of materials with complex a chemical composition and non-equilibrium structures. This work aimed to investigate materials obtained by the MA process for 5, 8, 13, and 20 h in terms of their phase composition and changes during heating. The results of thermal XRD analysis were in the temperature range between 25 and 360 °C, which revealed MgZn₂, PrZn₁₁, Ca₂Mg₅Zn₁₃, and Ca phases as well as α-Mg and α-Zn solid solution. The structural analysis features the powder morphology of the analyzed samples, showing cold-welding and fracturing processes leading to their homogenization, which is supported by the EDS results. The base Mg-Zn-Ca alloy was modified by different additions, but a thorough analysis of the influence of praseodymium on its thermal properties has not yet been performed. We chose to focus on Pr addition because it belongs to low-toxicity rare earth metals, which is an essential feature of biomaterials. Also, the Ca₂Mg₅Zn₁₃ phase is not fully known, as there are no crystallographic data (hkl). Therefore, the investigation is important and scientifically justified.

Zirconium-based alloys are highly regarded by the research community for their exceptional corrosion resistance, thermal stability, and mechanical properties. In our work, we investigated two newly developed alloys, Zr_42.42Cu_41.18Al_9.35Ag_7.05 and Zr_46.81Cu_35.44Al_10.09Ag_7.66, in the form of ingots and ribbons. In the course of our investigation, we conducted a comprehensive structural and thermal analysis. In addition, an examination of the corrosion activity encompassing electrochemical studies and an analysis of the corrosion mechanisms was carried out. To further evaluate the performance of the materials, tests of their mechanical properties were performed, including microhardness and resistance to abrasive wear. Structural analysis showed that both alloys studied had a multiphase, crystalline structure with intermetallic phases. The samples in the form of ribbons showed improved corrosion resistance compared to that of the ingots. The ingot containing a higher content of copper Zr_42.42Cu_41.18Al_9.35Ag_7.05 was characterized by better corrosion resistance, while showing lower average hardness and a higher degree of abrasive wear based on SEM observations after pin-on-disc tests.