Łukasz Rogal

This study investigates how surface modification of commercially pure magnesium influences the formation, microstructure, and long-term protective performance of phosphate conversion coatings (PCCs). An iron-free Surface Mechanical Attrition Treatment (SMAT) setup using zirconium dioxide balls of two diameters was employed to generate substantially different surface roughness while maintaining comparable subsurface modification, providing an experimental basis for isolating the effects of surface topography on PCC formation. PCCs were deposited on SMAT-treated and as-polished substrates and characterized using complementary microscopic, spectroscopic, and electrochemical techniques. The comparable subsurface modification but distinct surface topographies indicate that differences in PCC formation cannot be attributed solely to subsurface deformation. Instead, surface topography appears to influence coating nucleation and subsequent growth, with consequences for corrosion protection. SMAT pretreatment resulted in thinner, more uniform coatings composed of finer phosphate crystals. In contrast, coatings formed on polished substrates were more than twice as thick and exhibited inferior long-term corrosion performance, whereas those on SMAT-treated substrates remained highly stable throughout 28 days of immersion in 0.9 wt.% NaCl solution. These findings demonstrate that controlling magnesium surface state prior to phosphating enables tailoring of conversion coating structure and long-term protective performance.

The phase stability, crystal structure, and melting of Nb have been examined under high pressure shock compression to 365 GPa using ultrafast x-ray diffraction measurements on two x-ray free electron laser facilities. On compression, Nb remains stable in the bcc phase up to 220 GPa, with coexistence of bcc-Nb and liquid from 249 to 298 GPa, and complete melting at 301 GPa, with melt identified by diffuse liquid diffraction. Melting initiates at higher pressure than expected based on theoretical predictions, and the data consistently excludes the presence of other suggested phases of Nb at these pressures, including and hcp, thereby resolving the long-standing structural discrepancy. Singh-type strength analysis provides experimental evidence for a change in sign of the elastic anisotropy parameter at 121 GPa, consistent with the previously reported heat-induced hardening to heat-induced softening transition in Nb.

High-entropy Ti ₄₀ Zr ₂₀ Nb ₂₀ Hf ₅ Ta ₁₅ (at%) alloy was melted under a high nitrogen pressure (40 bar) using an inductive cold crucible, yielding a nitrogen-saturated alloy. The as-cast microstructure is complex, comprising nitride dendrites enriched in Ti, Zr, and Hf that occupy approximately 48% of the volume. These dendrites are surrounded by an interdendritic body-centered cubic solid solution matrix enriched in Nb and Ta. Additionally, two distinct nitride phases, such as (ZrHf)N and (TiZrHf)N, form needle-like precipitates within the interdendritic regions. The nitrogen-saturated alloy exhibits a compressive strength of 2159 MPa with negligible plastic deformation, and a hardness of HV (684 ± 6). This strength is significantly higher than that of the precursor alloy, primarily due to the reinforcing effect of the dendritic nitrides and the fine precipitates in the interdendritic matrix. Ab initio density functional theory calculations confirm the stability or metastability of the experimentally identified nitride phases. The overall phase constitution and segregation are governed primarily by strong metal–nitrogen chemical interactions (enthalpy), while configurational entropy mainly contributes to chemical disorder within the individual phases.

This study presents zirconium-based conversion coatings formed on AlSi11Cu2(Fe) cast alloy, with emphasis on determining optimum application conditions for use in an industrial setting. Controlled application procedures enabled formation of an amorphous ZrO₂·mH₂O (m < 2) layer ~100 nm thick. The coating nucleates on silicon particles at almost double the thickness as it does on the aluminum matrix due to micro-galvanic coupling. A 5 wt.% NaCl corrosion test showed a corrosion rate of 6.55×10⁻⁷ mm·y⁻¹ for the 10 min conversion coating deposition process, which is an enhancement by three orders of magnitude compared to bare metal. The mechanisms involve selective anodic dissolution of aluminum and cathodic activation on silicon sites. The conversion coating demonstrates strong adhesion to subsequent powder coating, and provides adequate protection from corrosion in saline environments. This research demonstrates an environmentally friendly alternative to chromate processing for high-silicon casting alloys.

In this work, we have performed experimental measurements and analysis of the annealing effect in the temperature range of 100°C-900°C on the magnetic field-induced bending phenomenon of Heusler alloys with the nominal composition of Ni50Mn30Ga18Cu2. The annealing process resulted in an increase of the average grain size. Annealing also affected the magnetic field-induced bending effect, increasing the maximum value of the obtained normalized deflection by about six-fold. However, this effect occurred in the case of ribbons annealed at higher temperatures, i.e. above 500°C. Annealing also led to a reduction in the magnetic field value required to activate the magnetic field-induced bending effect. The annealing process in the range from 500°C to 900°C affected both the amplitude and the maximum value of the normalized deflection. The presented results demonstrate that through heat-treatment the functional properties of the analyzed Ni-Mn-Ga-Cu ribbons, obtained by the melt spinning method, can be effectively optimized.

The Cu₄₃Zr₄₃Ag₇Al₇ alloy was obtained in an amorphous form through inert gas spray forming, followed by separation using a tower cyclone gas separator. The resulting spherical particles were about 11 μm in size. The consolidation of the powder was carried out using two distinct methods. First, Spark Plasma Sintering (SPS) was performed under a pressure of 35 MPa at two temperatures: 750°C and 900°C. Second, the High-Pressure High-Temperature (HPHT) method was applied, utilizing a toroidal-type Bridgman apparatus at about 560°C under a pressure of 7.8 GPa. In both processes, the consolidation duration was one minute. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) analyses revealed distinct differences in the crystallization behavior of the alloy. SPS processing led to complete crystallization, resulting in the formation of Zr₂Cu, Ag₂Al, and Cu₁₀Zr₇ crystalline phases. In contrast, the HPHT method significantly delayed crystallization, with only nanocrystalline nuclei observed within the amorphous matrix. Additionally, the application of high pressure in the HPHT process resulted in lower porosity and higher hardness compared to the SPS method.

In this study, the microstructure and catalytic potential of two Al-Ni-Fe alloys synthesised through a melt-spinning process with compositions selected to favour quasicrystalline phase formation were investigated. Microstructural and chemical analyses performed using X-ray diffraction, scanning and transmission electron microscopy methods revealed complex morphology and multiphase composition for both alloys. The presence of a decagonal quasicrystalline phase in both materials and additional crystalline phases occurring along the grain boundaries was confirmed. The catalytic potential of alloys was explored in the phenylacetylene hydrogenation reaction. The Al70Ni15Fe15 catalyst demonstrated catalytic activity with over 90% phenylacetylene conversion and selectivity to styrene exceeding 50% for styrene production under mild reaction conditions, and Al71.5Ni23.5Fe5 alloy provided the substrate conversion of 46% and selectivity over 50%. The presented results provide insight into the experimental verification of the properties of the new sustainable catalyst solutions.

The microstructure-properties relationship of the low-alloy, high-carbon nanostructured bainitic steel obtained by heat treatment, including austenitization and cooling followed by isothermal nanobainitic transformation at 280℃ for 72 h, was investigated. Detailed characterization of the obtained microstructure was performed using light optical, scanning, and transmission electron microscopy. These analyses reveals that the microstructure of tested nanobainitic steel consists of bainitic ferrite lath with an average size of 84 ± 21 nm and retained austenite with two different morphologies: (i) thin films with an average size of 64 ± 19 nm and (ii) blocks with a size of a few micrometers. The carbon concentrations in the film-type retained austenite and blocks of retained austenite were determined through X-ray synchrotron radiation diffraction analysis. The concentrations are 1.81 ± 0.09 wt.% and 1.39 ± 0.06 wt.%, respectively. The total amount of retained austenite in the microstructure is 48.0 ± 1.8 vol.%, and the dominant crystallographic orientation relationships between the microstructure constituents were determined to be Nishiyama-Wassermann. The minor K-S relationship was also recognized from the SEM/EBSD results. Tensile strength of the nanostructured steel was tested, and yield strength was found to be high. At an elongation of 7.2%, the tensile strength reached a significant level, while the average hardness was 490 ± 7 HV.