Fe-rich Phases Research Articles

Microstructure Evolution and Mechanical Properties of Extruded AlSiCuFeMnYb Alloy

This study investigates the impact of varying extrusion ratios on the microstructure and mechanical properties of AlSiCuFeMnYb alloy. Following hot extrusion, significant enhancements are observed in the microstructure of the cast rare earth aluminium alloy. Within the cross-sectional microstructure, the α-Al phase is reduced in size, and its dendritic morphology is eliminated. The morphology of the eutectic Si phase transitions from long strips to short rods, fine fibres, or granular forms. Similarly, the Fe-rich phase changes from a coarse skeletal and flat noodle shape to small strips and short skeletal forms resembling Chinese characters. The CuAl2 phase evolves from large blocks to smaller blocks and granular forms, while the Yb (Ytterbium)-rich rare earth phase shifts from large blocks to smaller, more uniformly distributed blocks. In the longitudinal section, the structure aligns into strips along the extrusion direction, with the spacing between these strips decreasing as the extrusion ratio increases. At an extrusion ratio of 22.56, the alloy demonstrates superior mechanical properties with a tensile strength of 325.50 MPa, a yield strength of 254.44 MPa, a hardness of 143.90 HV, and an elongation of 15.47%. These represent improvements of 27.8%, 36.5%, 38.9%, and 236.4%, respectively, compared with the as-cast rare earth alloy. In addition, the fracture surface of the extruded rare earth alloy exhibits obvious ductile fracture characteristics. Additionally, the alloy undergoes dynamic recrystallisation and dislocation entanglement during hot extrusion. The emergence of a twinned Si phase and a dynamically precipitated nanoscale CuAl2 phase are critical for enhancing deformation strengthening, modification strengthening, and dynamic precipitation strengthening of the extruded alloys.

Redistribution of Nb and other alloying elements in Nb-doped Zr alloy under high dose ion irradiation

ABSTRACT To understand the microstructural changes in Nb-doped zirconium alloy cladding at high irradiation doses, the Mitsubishi Developed Alloy (MDA) cladding was ion- irradiated up to 40 dpa at 400 ◦ C and the distribution of alloying elements was in- vestigated using atom probe tomography (APT) and scanning transmission electron microscopy and energy dispersive X-ray spectroscopy (STEM-EDS). APT analysis revealed two types of Nb nanoclusters with different Nb contents after the ion irradia- tion. The Nb concentration in the matrix decreased significantly with ion irradiation up to 10 dpa and then decreased slowly to 40 dpa. STEM-EDS analysis estimated that the secondary phase precipitates (SPPs) of Zr(Fe,Cr,Nb)2 and Zr(Fe,Cr)2 were formed before the ion irradiation. Although Fe, Cr, and Nb were dissolved from the SPPs during the ion irradiation, these alloying elements still remained in the SPPs after 40 dpa irradiation. Other Fe-Cr nanoclusters, Nb-rich phase, and Fe-rich phase were also formed during the ion irradiation. These radiation-induced precip- itates were observed until after 40 dpa irradiation and were expected to be stable under irradiation conditions.

Tailoring phase transformation pathways to enhance magnetic performance in Ga-doped sintered Nd-Fe-B magnets

The RE6Fe13Ga phase (RE, Rare Earth) exhibits tremendous promise for achieving high-performance magnets. However, the challenge of controlling its formation and distribution hinders improvements in coercivity and squareness of Ga-doped magnets. In this study, we present a strategy to regulate the chemical composition of the RE-rich phase (0–9 at.% Cu, without Ga) and subsequently modify the phase transformation pathways of the RE6Fe13Ga phase in Ga-doped magnets by incorporating a Pr-rich Ga-Cu-containing aiding alloy. Remarkable magnetic performance was achieved, with values of Br=13.36 kGs, μ0Hcj=20.82 kOe, (BH)max=43.75 MGOe, and μ0Hk90/μ0Hcj=0.99. Through quantitative analysis of chemical and structural properties and phase fractions at grain boundary (GB) triple junctions, we elucidate the phase transformation pathways in the magnets. The reaction between amorphous RE-Ga-rich phases and the matrix phases, along with partial consumption of the RE-rich phases with the Mn2O3-type structure (space group Ia3¯), led to the formation of the RE6Fe13Ga phase, accompanied by the presence of an amorphous Fe-rich transitional phase sharing a similar chemical composition. The gradual and partial involvement of the RE-rich phase improved the melt's wettability and delayed the formation of the RE6Fe13Ga phase. Consequently, a uniform microstructure was achieved, establishing the conditions for high magnetic performance. Thin metallic GBs and thick RE-rich, amorphous Fe-rich, and RE6Fe13Ga GBs were formed in the magnet. The former ensured squareness, while the sufficient coverage of the latter contributed to exceptional coercivity. The Pr-rich aiding alloy induces chemical heterogeneity, reinforcing the magnetic properties. This study advances our understanding of phase transformation pathways in Ga-doped magnets and introduces an effective approach for achieving high-performance magnets.

Microstructure and mechanical properties of non-heat-treated Al–8Si-0.2Mg-0.5Mn alloy inoculated by Al–Nb–B refiner

Al–Nb–B refiner has been considered as an alternative to Al–Ti–B refiner for hypoeutectic Al–Si alloys due to Si-poisoning effect. In this paper, the effects of Al–Nb–B and Al–Ti–B refiner on the microstructure and mechanical properties in indirect squeeze casting Al–8Si-0.2Mg-0.5Mn alloy were compared. Results show that the grain sizes in the edge chilling layer, segregation band, and the center region of the Al–Nb–B refined alloys were refined by 13.9%, 12.5%, and 17.6% compared to Al–Ti–B refined alloys, respectively. The yield strength, tensile strength, and elongation of Al–Nb–B inoculated alloys were superior to those of the unrefined alloys and Al–Ti–B inoculated alloys. The coexistence of NbAl3 and NbB2 particles in the Al–Nb–B refiner exhibited excellent anti Si-poisoning capability. They significantly decreased the grain size and uniformly distributed the eutectic Si particles and Fe-rich phases, resulting in an increase in the yield strength of the alloy by 16.1% compared to the Al–Ti–B inoculated alloy. The distribution of iron-rich phases in the segregation band was affected by the inoculation. The size of α-Al15(Fe, Mn)3Si2 phase in Al–Ti–B inoculated alloys was refined, and the number significantly increased, resulting in a decrease in tensile strength of 12.82 MPa. In the Al–Nb–B inoculated alloys, the size and number of α-Al15(Fe, Mn)3Si2 phase decreased, and the δ-Al4FeSi2 phase increased, which effectively improved the fracture toughness and ductility. In addition, with the increase in grain refinement (from unrefined to Al–Ti–B to Al–Nb–B inoculated alloy), the fracture behavior changed from trans-granular fracture to intergranular fracture, improving the fracture toughness.

Effect of Ni content on 475°C embrittlement of directed energy deposited duplex stainless steel using a laser beam and wire feedstock

Duplex stainless steel (DSS), specifically the 2209 grade, is increasingly employed in additive manufacturing, particularly in processes like directed energy deposition using a laser beam with wire (DED-LB/w). However, a significant challenge arises when DSS faces brittleness within the temperature range of 250–500 °C. This study employs advanced characterization techniques, including atom probe tomography (APT) and transmission electron microscopy (TEM), to investigate DSS embrittlement after aging at 400 °C for up to 1000 h. The hardness analysis revealed that the higher Ni content in DED-LB/w-fabricated DSS cylinder promotes the age hardening compared to 2205 wrought DSS plate. Furthermore, APT and TEM demonstrated that, alongside the decomposition of ferrite into Fe-rich (α) and Cr-rich (αʹ) phases, clustering of Ni, Mn, and Si atoms contributes to the embrittlement. Although the Ni-Mn-Si-rich clusters could suggest nucleation of G-phase, the G-phase crystal structure was not observed by TEM. This might be attributed to the short aging time or limitations in the characterization technique. This work underscores the impact of characterization techniques on the measurement of spinodal decomposition, with APT providing capability of detecting nanometer sized clusters. By elucidating the complexities of 475 °C-embrittlement in DED-LB/w DSS, this study offers valuable insights for industrial applications and a deeper understanding of age hardening in duplex DSSs under specific manufacturing conditions.

Effect of cooling rates and Fe contents on microstructure evolution of Al-Cu-Mn-Mg-Fe-Si alloys

During the solidification process, the recycled Al-Cu alloys form coarse Fe-rich phases, which seriously deteriorate the mechanical properties of the alloy. The study employed optical microscope (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and synchrotron X-ray imaging to investigate the impact of cooling rate and Fe contents on the growth of Fe-rich phases, Al2Cu, and pores in recycled Al-Cu-Mn-Mg-Fe-Si alloys under synergistic effect ultrasonic melt processing (USMP) and Al-Ti-B. USMP can homogenize the distribution of TiB2 particles and provides more nucleation sites for the formation of Fe-rich phases. Under the synergistic effect of USMP and Al-Ti-B, increasing the cooling rate,the volume fractions of Fe-rich phases in 0.7FeUB (0.7 wt%Fe + USMP + Al-Ti-B) and 1.2FeUB (1.2 wt%Fe + USMP + Al-Ti-B) alloys decreased from 8.92% and 16.52% to 8.03% and 14.73%, respectively. The volume fraction of Al2Cu increased from 4.06% and 3.13% to 4.37% and 3.54%, respectively. Furthermore, the three-dimensional (3D) morphology of Fe-rich phases and Al2Cu became more compact and uniform. The volume fraction of pores in the 1.2FeUB alloy decreased from 0.412% to 0.072%. In-situ synchrotron X-ray radiography revealed that increasing cooling rates led to increased nucleation undercooling of primary α-Al and Fe-rich phases. These phenomena can be attributed to the combined effects of ultrasonic cavitation, ultrasonic streaming, and an increased cooling rate. These factors serve to homogenize the alloy composition, ensure uniform distribution of TiB2 particles, inhibit element diffusion, reduce solute segregation, and ultimately lead to the refinement of the grain size, α-Al, Fe-rich phases, and Al2Cu, while also inhibiting pore growth.

Mechanisms of phase decomposition in a non-equimolar CrFeMnNi alloy during thermal aging

While high entropy alloys and multi principal element alloys have been largely studied and developed as single solid solutions, fewer investigations have focused on phase transformations in these multicomponent alloys. This study reports on the aging behavior at 500 °C of a non-equimolar CrFeMnNi alloy. The results unveil a complex evolution, leading to complete decomposition into three main phases, namely an L10 NiMn phase, an FCC Fe-rich phase, and a BCC Cr-rich phase. The intricate microstructure is achieved in stages through continuous precipitation of L10 Ni-Mn nanoscale precipitates, which are progressively overtaken by a sweeping discontinuous front involving the co-precipitation of the L10 NiMn and BCC Cr-rich phases in addition to the parent FCC Fe-rich phase. Furthermore, the Cr-rich phase initially forms with metastable compositions leading to further precipitation of Fe-rich precipitates within the Cr-rich region behind the transformation front. Understanding these transformation pathways through metastable states emphasizes the potential for expanding the range of achievable properties through deliberate microstructure tailoring of multi principal element alloys.

Influence of minor Mg/Ca/Nb/Ag addition on the morphology and microstructure of Fe-rich phase in powder metallurgy Cu[sbnd]10Fe alloy

The effect of Mg/Ca/Nb/Ag alloying on the morphology and microstructure of powder metallurgy Cu10Fe alloy was investigated systemically in this work. Alloying of Ca reduces the size of Fe-rich particles, while alloying of Mg/Nb/Ag increases the Fe-rich particles. This is attributed to the different roles of various alloying elements on the liquid-phase separation behaviors as well as diffusion of Fe atoms during the solidification. Coarse size spherical Fe-rich particles with a face centered cubic structure are observed in CuFe alloys bearing Mg/Ag/Nb, whilst the alloying of Ca favors the formation of fine spherical Fe-rich particles with a body centered cubic structure. The factor governing the morphology is found to be interfacial energy for CuFe alloys containing Mg/Ag/Nb and elastic energy for Cu-Fe-Ca alloy, respectively. Coarse size Fe-rich particles are hard to deform during subsequent rolling, but the fine Fe-rich particles can co-deform with Cu matrix. This study could provide a detailed picture regarding the influence of various alloying element types on the size, morphology, and lattice structure of Fe phase of CuFe alloy.

3D characteristics and growth behavior of Fe-rich phases in Al−Si−Fe−Mn alloys during melt holding

The morphological evolution and growth behavior of Fe-rich phases in the Al−7.0Si−1.0Fe−1.2Mn alloy during melt holding were studied using scanning/transmission electron microscopy, thermodynamic calculations and synchrotron X-ray imaging. The results show that with a decrease in holding temperature, the Fe-rich phase underwent a morphological transformation from coarse star-like and polygonal structures to fine Chinese-script and coupled structures consisting of Chinese-script and polygonal shapes. The 3D structure of the star-like phase was composed of multibranched primary phases and irregular secondary phases; the coupled structure was composed of polyhedrons and dendrites; the Chinese-script phase was composed of dendrites. When the holding temperature was decreased, the number and volume fraction of Fe-rich phases were significantly reduced. A similar trend was also obtained for the largest volume particles and their connectivity. In situ synchrotron X-ray radiography results indicated that two types of primary Fe-rich phases were formed during the solidification process, and the smaller phase that remained in the melt could act as nucleation sites for the formation of the coupled eutectic structures.

Insight into the Fe-rich phases strengthening mechanisms of non-heat-treatable Al-Mg-Mn-Fe-Cu alloys

This paper examines the effect of Fe addition on the microstructure characterized by scanning electron microscopy/electron backscattered diffraction, neutron diffraction, and synchrotron X-ray tomography and the mechanical properties of Al-Mg-Mn-Fe-Cu alloys. The findings reveal that the microstructures of the alloys consisted of an Al matrix, Al6(FeMn), and Al2CuMg phase particles. The addition of Fe significantly increased the yield strength (YS), and ultimate tensile strength (UTS) of the alloys, while reducing elongation. The transformation of the 3D morphology of the Al6(FeMn) phase from separated and fine particles with Chinese-script morphology to interconnected rod-like structure as Fe content increased from 0.1 % to 0.8 %. This strengthening effect was attributed to the slip lines being blocked at the vicinity of the interconnected Fe-rich phase, leading to grain rotation and dislocation density increment around the Fe-rich phase, ultimately improving the strength of the alloys. However, the Fe-rich phases and Al2CuMg phases were found to be prone to cracking under tensile stress, resulting in decreased elongation of the alloys. This study provides a potential application in the design and manufacturing of new non-heat-treatable Al alloys for the automotive industry.

Dependence of the Structural and Magnetic Properties on the Growth Sequence in Heterostructures Designed by YbFeO3 and BaFe12O19.

The structure and the chemical composition of individual layers as well as of interfaces belonging to the two heterostructures M1 (BaFe12O19/YbFeO3/YSZ) and M2 (YbFeO3/BaFe12O19/YSZ) grown by pulsed laser deposition on yttria-stabilized zirconia (YSZ) substrates are deeply characterized by using a combination of methods such as high-resolution X-ray diffraction, transmission electron microscopy (TEM), and atomic-resolution scanning TEM with energy-dispersive X-ray spectroscopy. The temperature-dependent magnetic properties demonstrate two distinct heterostructures with different coercivity, anisotropy fields, and first anisotropy constants, which are related to the defect concentrations within the individual layers and to the degree of intermixing at the interface. The heterostructure with the stacking order BaFe12O19/YbFeO3, i.e., M1, exhibits a distinctive interface without any chemical intermixture, while an Fe-rich crystalline phase is observed in M2 both in atomic-resolution EDX maps and in mass density profiles. Additionally, M1 shows high c-axis orientation, which induces a higher anisotropy constant K1 as well as a larger coercivity due to a high number of phase boundaries. Despite the existence of a canted antiferromagnetic/ferromagnetic combination (T < 140 K), both heterostructures M1 and M2 do not reveal any detectable exchange bias at T = 50 K. Additionally, compressive residual strain on the BaM layer is found to be suppressing the ferromagnetism, thus reducing the Curie temperature (Tc) in the case of M1. These findings suggest that M1 (BaFe12O19/YbFeO3/YSZ) is suitable for magnetic storage applications.

Effects of Fe content on the 3D morphology of Fe-rich phases and mechanical properties of cast Al-Mg-Si alloy

Fe is a common impurity element in recycled aluminum scraps, and adjusting Fe content can effectively promote the effective utilization of recycled aluminum. In this study, Al-Mg-Si-Mn-Fe alloys with different Fe contents were prepared by adding various percentage of aluminum scraps. Synchrotron X-ray tomography technology was used to study the morphological evolution of Fe-rich phases and corresponding effect on mechanical properties of studied alloys. The results showed that as the Fe content increased, the 3D morphology of Fe-rich phases changed from fine Chinese-script and needle-like shapes to coarse Chinese-script structure. Their 3D morphology was mainly composed of thin platelets and curved branches. The increase in Fe content did not significantly change the 3D structure of Fe-rich phases, but increased the volume fraction of large Fe-rich phases. When the Fe content reached 0.35 %, the maximum volume and the number of branches of individual phases increased by 182.9 % and 142.2 %, respectively, compared with the 0.2Fe alloy. With the increase of Fe content, the ductility of alloys gradually decreased, especially when the Fe content exceeded 0.25 %. The Fe content had a small effect on the liquidus temperature of alloys, but it changed the initial formation temperature and type of Fe-rich phases. When the Fe content exceeded 0.32 %, it promoted the formation of β-Fe phase, which may be the main reason for the significant decrease in ductility of studied alloys with higher Fe content.

Evolution behavior of Fe and Fe-rich phases in high-Fe concentration Al-Si-Mg alloy with Mn, Cr, and Co alloyed

In this work, we report the evolution behavior of Fe and Fe-rich phases in the high-Fe concentration recycled Al-Si-Mg aluminum melt with and without alloying elements (Mn, Cr, Co) introduced. Firstly, the thermodynamic calculations reveal that the addition of Mn, Cr, and Co could improve the nucleation temperature of the Fe-rich phase. Moreover, four solidified ingots for Al-10Si-0.5Mg-1Fe alloy(base alloy) and the base alloy with 1.3 wt% Mn, 0.8 wt% Cr, and 0.8 wt% Co added, respectively, were prepared by holding the melt for 30 min at 610 ℃ after all the raw materials were fully melted. Microstructure examination revealed that the addition of Co resulted in the formation of the needle-like Fe-rich phase, which further leads to a poor settling effect and low iron removal efficiency. In contrast, the addition of Mn and Cr favors converting β-AlFeSi into α-AlFeMnSi, and forming the Chinese script and fish-bone Fe-rich phase. The size of the Fe-rich phase formed after adding Cr is smaller, while the residual Fe content after adding Mn is less. Also, the sludge phase at the bottom of the ingot presents a polygonal shape and long rod shape after adding Mn and Cr, respectively. Further, the Mn alloying increases the particle size of the sludge, while Cr refines the sludge phase and increases the aspect ratio (length/width ratio) of the sludge. Particularly, for Al-Si-Mg alloy with 1.0% Fe content, the superior mechanical properties are obtained by adding 0.8 wt% Cr, and the tensile strength reaches 136 MPa. After adding 1.3 wt% Mn, the Fe content of the upper section is reduced to 0.37 wt%, and the Fe removal rate achieves 63%. The obtained results provide some guidelines for achieving high iron separation efficiency in recycled aluminum-silicon alloy melts.

Effect of heat treatment temperature on microstructure and electrochemical behavior of additive-manufactured AlCoCrFeNi high entropy alloy

In this paper, a high-entropy AlCoCrFeNi alloy were prepared using laser melting deposition (LMD) and the effect of heat treatment on their microstructure and corrosion resistance was studied. XRD, OM, SEM, EDS, EBSD and electrochemical tests were used to investigate the structure, microstructure, and corrosion resistance. The LMD and LMD-500 °C samples showed a single BCC phase structure. After the temperature was increased to 800 °C, a small amount of a Cr-rich and Fe-rich FCC phase and σ phase precipitated at the grain boundaries, Al and Ni were enriched within the crystals. At 1100 °C, the σ phase disappeared, and the FCC phase content increased from 1.4% to 5.2%. The average grain size was the largest at 500 °C, reaching 31.29 μm. In 3.5% NaCl solution, the LMD-500 °C sample showed a high self-corrosion potential and the lowest corrosion current density; the polarization resistance (Rp) and charge transfer resistance (Rct) were 5.266 × 105 Ω∙cm2 and 1.248 × 108 Ω∙cm2, respectively, with the shallowest surface corrosion and the best corrosion resistance. In 0.5 mol/L NaOH solution, there were only a few corrosion holes in the samples before and after the heat treatment, and all the samples showed a good corrosion resistance. In 0.5 mol/L H2SO4 solution, with the increase of temperature, the Cr, Al and other elements underwent intensified segregation. The corrosion resistance gradually improved, the Rp and the Rct was 2.785 × 102 Ω∙cm2 and 7.569 × 103 Ω∙cm2, respectively, at 1100 °C, providing the best corrosion resistance.

Effect of laser beam incidence angle on weld formation mechanism and corrosion resistance of T2 copper/304 stainless steel

Over the last 20 years, industry interest in copper has increased. Its application in the petrochemical, automotive, and nuclear power industries highlights the need for new research directions especially in the joining of copper to other metals. In this work, lap joint of 304 stainless steel and T2 copper precoated with Cu–Mn–Ni filler metal was performed by laser brazing. The aim of this study is to characterize the influence of laser beam incidence angle on the welded joint forming mode, microstructure, elements diffusion and corrosion resistance. According to the findings, the joint is classified as a welded joint when the laser beam incidence angle is 80°, and as a welded-brazed joint when it’s 90°, 70°, or 60°. The microstructure is mainly composed of Cu-rich and Fe-rich phases, Mn in the Cu-rich phase aggregation and Cr in the Fe-rich phase aggregation. In the fusion zone (FZ) the content of less than 50% of the liquid will be in the form of supersaturated droplets in the matrix of the other side. The local corrosion pair that the copper steel matrix and liquid drop produce in the FZ speeds up the dissolution of the Cu-rich phase, which effected corrosion resistance of the joint.

Stable hydrogen and oxygen isotope geochemistry of Fe3+-rich, interstratified clay minerals from seafloor hydrothermal sites

Chemical and structural complexities in interstratified clay minerals arising from mineral transformations and evolving formation conditions should be recorded in their stable isotope signatures. This paper examines the controls on the stable hydrogen and oxygen isotope compositions of Fe3+-rich, glauconite-nontronite, talc-nontronite and talc-saponite from submarine hydrothermal sites, with a focus on the Red Sea Atlantis II Deep. Values of δ18O became less positive in the order nontronite > glauconite-nontronite > talc-nontronite > talc-saponite, yielding oxygen isotope temperatures ranging from ∼40 °C for nontronite to ∼135–300 °C for talc-saponite. These clay minerals have low δ2H, ranging from −145 to −127‰ for talc-nontronite, −135‰ for nontronite, −129 to −85‰ for glauconite-nontronite, and −95 to −59‰ for talc-saponite. The clay mineral-water hydrogen isotope fractionation is strongly affected by Fe3+ content, with increasing structural Fe3+ causing progressive weakening of O-H bonds. The large ionic radius and high charge of Fe3+ cause it to be more poorly shielded by surrounding oxygen from hydroxyl hydrogen relative to other octahedral or tetrahedral cations. The resulting lengthening of O-H bonds favours 1H over 2H. Our results confirm that Fe-rich phases, such as nontronite-glauconite, are produced at the lowest temperatures and Mg-rich phases, such as talc-saponite, are formed at the highest temperatures in seafloor hydrothermal environments. Evolving fluid chemistry and fluid pathways during clay mineral formation are also important. Glauconite layer formation from precursor nontronite likely occurred during diagenesis; redox changes causing Fe-reduction and an increase in layer charge facilitated interlayer K-fixation. Talc-saponite compositions vary with temperature and fluid chemistry, forming at variable sediment depths depending on access to the hottest hydrothermal fluids.

Role of aging temperature on thermal stability of Co-free Cr0.8FeMn1.3Ni1.3 high-entropy alloy: Decomposition and embrittlement at intermediate temperatures

This study prepared a reduced activation single-phase Co-free Cr0.8FeMn1.3Ni1.3 high-entropy alloy (HEA) through arc melting, which exhibits great potential as a radiation-resistant material. The microstructural evolution and mechanical property changes of the alloy after prolonged aging at temperatures of 300, 500, and 700 °C were systematically studied using scanning and transmission electron microscopy (SEM/TEM/STEM) and electron probe microanalysis (EPMA) techniques. The results reveal that the alloy forms a single-phase FCC solid solution following cold deformation and subsequent recrystallization annealing. After prolonged aging at 300 °C for 1500 h, the microstructure of the alloy remains stable, maintaining a single-phase structure with minimal changes in mechanical properties. After aging at 500 °C for 1500 h, the alloy undergoes complex phase decomposition, giving rise to tetragonal σ-FeCr and L10-NiMn phases, along with minor amounts of Cr-rich BCC and Fe-rich FCC phases. During this stage, the interfaces between σ-FeCr and L10-NiMn phases undergo amorphization, leading to room-temperature embrittlement of the alloy. Following aging at 700 °C for 1500 h, the alloy precipitates the Cr-rich BCC phase, forming a dual-phase microstructure, resulting in increased tensile strength and reduced ductility. This study discloses the thermal stability of Cr0.8FeMn1.3Ni1.3 HEA through extended aging at 300 °C and 500–700 °C for up to 300 h, simultaneously providing reference values for evaluating the stability of other HEA systems. The occurrence of complex phase decomposition significantly impacts the mechanical properties of HEAs, necessitating cautious evaluation of their application potential.

Supergene mineral assemblage from sediments affected by contact and hydrothermal metamorphism, locality Dobrá – Staré Město near Frýdek-Místek (Czech Republic)

At locality Dobrá – Staré Město, series of outcrops occur on both banks of the Morávka River. The river cuts through the sediments on the tectonic contact between the Silesian and Subsilesian units of the Outer Western Carpathians. Clayey facies of the Hradiště Formation (Early Cretaceous, Valanginian to Aptian) contains numerous tectonic fragments reaching hundreds meters in size of strongly altered (carbonatized, smectitized) subaquatic volcanic rocks of the Teschenite Association. These volcanic rocks are dominated by fine-grained to aphanitic rocks, possibly of both effusive and intrusive origin. The host sediments affected by the contact metamorphism (contact adinole) also occur. Framboidal pyrite is abundant in majority of sediments of the studied area, giving rise to efflorescences of gypsum, baryte, celestine, and a mineral of alunite group (Figure 1). A more varied assemblage of supergene minerals was recognized on a small rock outcrop at GPS coordinates N 49° 39.992’ E 018° 23.810’ (Figure 2), where it developed relatively recently after the big floods in 2010 that washed away the previous mineralization. During the first years, only gypsum crusts were detectable, while in 2023, we recognized 4 macroscopic and 5 microscopic minerals forming thin botryoidal crusts. These crusts show faint zoning, with gooey, gel-like X-ray amorphous material in the humid upper part , middle zone with abundant fibroferrite and the lower part dominated by gypsum. Gypsum forms well-developed, but frequently corroded crystals with various habitus (Figure 4A, B). Fibroferrite is present as fibrous aggregates with individual crystals of up to ca. 100–150 µm long and &lt;1 µm thick (Figure 4C). It forms directly from the gel-like substance (Figure 4D). Rhombohedral crystals and rossete aggregates of hydroniumjarosite vary from 2 µm to 5 µm in size (Figure 4E), but the most common are dust-like coatings on rock fissures with particle size &lt;1 µm. Rusty coatings of schwertmannite (Figure 4F), in some places accompanied by gypsum, with Fe/S at. % ratios near 4–5 are common. In some cases, the Al/Fe at. % ratio exceed 1, which might indicate presence of yet undescribed Al-analogue of schwertmannite, ill-defined alumogel, or an amorphous precursor of aluminite. Presence of ferrihydrite is possible but not confirmed. The above-mentioned Fe-rich phases are frequently accompanied by diplobacilli-shaped bacteria (Figure 4F). Slavíkite, pickeringite-halotrichite, alunogen, copiapite group mineral, hexahydrite, and melanterite (Figure 5) were also recognized by EDS and PXRD. Slavíkite and copiapite group minerals seem to be alteration products of fibroferrite. Unit-cell parameters refined from the X-ray powder diffraction are presented for all recognized phases (Table 1). Surprisingly, secondary sulfates are present on the metasediments with abundant calcite (Figure 3), which should serve as a neutralization buffer. The reason is the restricted amount of calcite available on the rock fissure surfaces, and water infiltration partially blocked by newly-formed gypsum. The albite in contact adinole (Figure 3) is unaffected by the acid rock drainage, since Na ions are not present in significant quantities in supergene phases. Since there is still enough available unaltered pyrite, we expect a shift towards more stable mineral assemblage in future. The limited amount of secondary sulfates does not present any significant harm to the environment.

Influence of Fe content on the microstructure and mechanical properties of Al-7Si-0.7Mg-2.8Fe alloy processed by laser powder bed fusion

Iron contamination is a major concern in aluminum alloys recycling. It is considered the main deleterious contamination due to its low solubility in the aluminum matrix leading to the formation of Fe-rich intermetallic phases with platelet-like morphology, which act as stress risers deteriorating the mechanical properties. This paper investigates the effect of Fe contamination in the microstructure and mechanical properties of Al–7Si-0.7Mg-2.8Fe alloy processed by Laser Powder Bed Fusion (LPBF). Microstructure characterization was carried out by Optical Microscopy (OM), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscope (TEM). The mechanical characterization was performed by Vickers microhardness and tensile tests. The LPBF sample was analyzed in two directions, vertical and horizontal. The results show that the LPBF process provided a microstructural refinement and reduction of the aspect ratio of α-AlFeSi phase and silicon particles, leading to a strong improvement in mechanical properties when compared to the Fe-contaminated as-cast Al–7Si-0.7Mg-2.8Fe alloy.

Thermodynamic Study of the Influence of Mn on the Precipitation of Fe-Rich Phase in Al-Si Alloy

Thermodynamic Study of the Influence of Mn on the Precipitation of Fe-Rich Phase in Al-Si Alloy