Fe-rich Phases Research Articles

Effect of B4C nanoparticles addition on the refinement of Fe-rich phase in ZL108 alloy

Refining effect of B4C nanoparticles in ZL108 alloy on Fe-rich phase was studied in this work. It was observed that B4C nanoparticles apparently refines the size of the Fe-rich phases and partially transforms Fe-rich phases morphology from hollow polyhedron to petal-like shape. The DSC results show that B4C nanoparticles does not affect the initial nucleation temperature of the Fe-rich phase. However, the addition of B4C nanoparticles to ZL108 alloy inhibits the growth of Fe-rich phase. The TEM results confirm that the addition of B4C nanoparticles alters the lattice parameter of Fe-rich phase due to incorporation of C atoms, thereby suppressing the growth of the Fe-rich phase and ultimately leading to its refinement. From the perspective of fracture behavior, the addition of B4C nanoparticles remarkably reduces the stress concentration of Fe-rich phase, and the elongation of the alloy increases by 25.3%. These findings provide a new perspective for further research and development to refine Fe-rich phase.

High temperature co-processing of stainless-steel slag and red mud: Towards a selective Cr immobilization and harmless treatment

Stainless-steel slag and red mud are bulk metallurgical wastes, which are difficult to reuse due to the complex composition and high environmental risk. To realize their harmless and resource utilization, a collaborative treatment of the stainless-steel slag (AOD slag) and red mud at high temperature was proposed in this study. The influence of the stainless-steel slag to red mud ratio on spinel phase precipitation and crystallization, Cr enrichment and immobilization in the mixed slags were systematically investigated. The results demonstrated that when the stainless-steel slag to red mud ratio was 6:4, the enrichment degree of Cr in spinel phase was 94.12 wt%, and the precipitation amount of spinel reached the highest, 20.98 wt%. In this case, only small amounts of other mineral phases existed, the crystal particle size of spinel phase was larger, and the self-wrapped spinel phases were formed in the stage of cooling. The outer Cr-poor spinel could avoid the abrasion and erosion of the inner Cr-rich spinel in the subsequent physical separation process, thus reducing the risk of Cr6+ dissolution. In the toxic leaching test, the total Cr concentration leached from the mixed slag (stainless-steel slag to red mud ratio was 6:4) was far lower than the national leaching concentration limit of Cr-related ions. The Cr and Fe-rich spinel phases separated from the mixed slag of stainless-steel slag and red mud can be used as the raw material for the production of stainless steel, while the residual Cr-poor slag rich in Ca, Si and Al can be applied in the field of construction.

Effect of pre-aging on mechanical reinforcement of the Cu–Fe–Nb composites

Pre-aging treatment was demonstrated to significantly enhance the mechanical properties of Cu–10Fe–1Nb (wt.%) composites. Specifically, after rolling and aging at 400 °C for 8 h, the microhardness, tensile strength, and elongation of the pre-aged samples reached 163 HV, 559 MPa, and 11.2%, respectively. The refinement of Fe-rich phases in pre-aged samples was primarily attributed to the increased shear strain between the Fe-rich phases and the matrix, which was driven by the precipitation-strengthening effect induced by pre-aging. Additionally, the matrix of the pre-aged samples suffered significant refinement as dynamic recovery and recrystallization of the matrix were suppressed during the rolling process, forming a high-density dislocation structure that greatly enhances the work-hardening effect. The main contribution to strength improvement in the Cu–10Fe–1Nb composites was identified as precipitation strengthening, refinement strengthening, and work hardening. Moreover, compared with the sample without pre-aging treatment, the refinement strengthening and work hardening effects of pre-aged samples exhibited substantial improvements, with increment of 49 MPa and 21 MPa, respectively.

Effect of current on the tribological behavior of Cu-Fe-P immiscible alloy produced by laser powder bed fusion

Cu-based immiscible alloys have significant potential application value in the field of electrical contacts. This study investigated the tribological behavior of Cu-Fe-P immiscible alloys produced via laser powder bed fusion (LPBF) under current-carrying conditions. The alloys consist of softer ε-Cu phase and harder Fe-rich phases. The Fe-rich phase acts as a protective reinforcement during current-carrying friction and wear tests, improving the wear resistance of the alloy. With the increasing current, the coefficient of friction initially rose and then decreased, whereas the wear rate showed a gradual increase. At low currents (0, 2, 3 and 5 A), mechanical wear predominantly governs the wear mechanism. As the current increases, the mechanical wear gradually transitions from adhesive wear to abrasive wear, accompanied by weak oxidative wear. At higher currents (7 A and 10 A), the wear mechanism is dominated by arc erosion wear and oxidative wear. Notably, when the current exceeded 2 A, an oxide film consisting of CuO, Fe2O3, and Fe3O4 formed, enhancing the frictional properties of the alloy. Once the current surpassed 5 A, the arc discharge occurred at high currents, forming molten phases and arc erosion pits on the worn surface of the Cu-Fe-P immiscible alloy.

Design of explosively welded Fe–Al multilayer laminated composite pipes: A critical microscopy analysis of stand-off distance and post-weld heat treatment effects on interface properties

This study examined the microstructure and mechanical properties of explosively welded (EXW) Fe–Al multilayer laminated composite pipes, specifically SS321/AA1050/AA5083, with varying stand-off distances (SD) and post-weld heat treatments (PWHT). Findings revealed that higher collision forces at higher-SD produced a wavy interface with finer grains at the AA1050/AA5083 interface. In contrast, lower-SD yielded a smooth, flat interface. At the SS321/AA1050 interface, collision energy resulted in the formation of an uneven composite reaction layer comprising multiple intermetallics. Analysis of the SS321/AA1050 interface revealed that an increase in the PWHT temperature results in diffusion toward the reaction layer, transforming the unevenly Al-rich and Fe-rich phases into a uniform Al85(Fe,Cr,Ni)15 solid solution. The increase in the fraction of this phase made the reaction layer more brittle. At the AA1050/AA5083 interface, PWHT at higher temperatures caused a significant hardness decline extending further from the interface in samples with higher-SD. On the SS321 side of the laminated composite, higher SD resulted in higher kernel average misorientation (KAM) and increased hardness. Despite a decrease in hardness after PWHT at 350 °C, the hardness gradient from the matrix to the interface in laminates with higher SD remained relatively unaffected, whereas the lower SD counterparts experienced a noticeable stress relief.

Effect of alloying elements on coexisting phases and microstructure of M174 heat-resistant aluminum alloy

Abstract This article mainly focuses on high-power density diesel engine piston alloys, with the main component system being M174 heat-resistant aluminum alloy. On this basis, the main heat-resistant alloying elements Cu, Ni, and Fe were optimized and designed. This article is based on Thermo-Calc thermodynamic software, and comprehensively calculates and analyzes the multi-component alloy equilibrium phase diagram and Scheil non-equilibrium solidification of Al-(4-6)Cu-(1.5-3)Ni-(0.7-1.1Fe)-12.5Si-0.85Mg (mt.%) heat-resistant aluminum alloy system. Through the orthogonal experimental method of alloy composition, the phase distribution and microstructure composition of different alloy compositions are obtained. Research has found that Fe-rich phases such as Al5FeSi and Al9FeNi, as well as Ni-rich phases such as A13CuNi, A17Cu4Ni, and Al3Ni, are the main heat-resistant phases of the alloy in the temperature range of 350°C-420°C, providing important support for the high-temperature mechanical properties and creep damage resistance of piston aluminum alloy. At the same time, this article further studies the solidification history and microstructure precipitation of alloys. Fe-rich heat-resistant phases such as Al5FeSi and Al9FeNi have a higher solidification sequence. As primary and secondary phases, it is easy to generate coarse solidified structures. The organizational content is sensitive to the alloy composition. A13CuNi and A17Cu4Ni mainly precipitate in a multi-component eutectic structure, with layered and petal-shaped morphologies. The research results of this article have important theoretical significance and application value for the optimization design of high-power density piston aluminum alloy composition and the coordinated control of multi-phase structure.

Microstructure and mechanical properties of CP780 steel - 7075 aluminum alloy laser welded joint assisted by rotating magnetic field

Abstract This study uses a rotating magnetic field for laser welding on 1 mm thick CP780 high-strength steel and 1.5 mm thick 7075 aluminum alloy. The effects of different welding parameters (B = 0 mT, B = 65 mT with V = 0°/s, B = 65 mT with V = 10°/s) on the morphology, microstructure, and tensile properties of welded joints are analyzed. At B = 0 mT, the weld shape is V-shaped, with the intermetallic compounds primarily consisting of needle-like brittle Al-rich (Fe, Si)Al2 phase and fewer granular ductile Fe-rich (Fe, Si)Al phase, resulting in poor mechanical properties. With the application of the rotating magnetic field, the laser energy becomes more concentrated, forming a ‘T’ shape weld. The rotating magnetic field (B = 65 mT with V = 10°/s) generates a constantly changing Lorentz force, promoting molten pool flow and enhancing Fe diffusion within the weld. This process reduces needle-like brittle Al-rich (Fe, Si)Al2 phase and increases granular ductile Fe-rich (Fe, Si)Al phase. It also accelerates the weld cooling rate and inhibits the reaction time and grain growth of intermetallic compounds, thereby reducing the thickness and content of the intermediate transition layer and significantly improving mechanical properties. A comprehensive comparison shows that the best mechanical properties are achieved at B = 65 mT with V = 10°/s. This study offers new insights and a theoretical foundation for achieving cost-effective, high-performance welded joints in advanced high-strength steel and high-strength aluminum alloy for automobiles, thereby facilitating lightweight vehicle development.

3D morphological evolution of the Fe-Rich phase and mechanical properties of the recyclable A356 alloy

Efficient utilisation of recycled aluminium promotes low-carbon and green manufacturing in the aluminium industry. However, the low tolerance of Al for Fe content limits its application. The morphological evolution of the Fe-rich phase and the mechanical properties of recycled A356 alloys with varying Fe contents were investigated using optical microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), synchrotron radiation X-ray computed tomography (SRXCT), and Thermo-Calc thermodynamic calculations. The results show that with increasing Fe content, the morphology of the Fe-rich phase transformed from fine-granular and short rod-like structures into coarse needle-like and Chinese-script. In three dimensions (3D), the larger Fe-rich phases displayed a multibranched structure composed of rod-like and plate-like phases rather than a single morphology. Notably, at an Fe content of 0.4 %, the Fe-rich phases presented Chinese-script and short rod-like shapes in sections but did not significantly change the 3D morphology or type of the Fe-rich phase. However, the Fe-rich phases in the 0.4 %Fe alloy exhibited higher thickness and sphericity, which improved the ductility of the alloy. Thermodynamic calculations indicate that the initial formation temperature of the Fe-rich phase in the 0.4 % Fe alloy overlaps with that of the Al-Si eutectic reaction, which is referred to as the critical Fe content. At the critical Fe content, the ternary eutectic reaction of Al-Si-(AlFeSi) suppressed the rapid growth of the Fe-rich phase and mitigated their negative impact on ductility.

High-performance Co-free dual-phase perovskite positrodes for protonic ceramic cells: Zn and Ni-doped BaCe0.2Fe0.8O3-δ system

Protonic ceramic cells (PCCs) can convert the energy between electricity and fuels efficiently, and are attracting increasing attention. However, the development of PCCs is restricted by the lack of proper positrode materials. In this work, we report a Co-free system with a nominal composition of BaCe0.2Fe0.8O3-δ, which is composed of a Fe-rich matrix phase decorated with Ce-rich nanoparticles. The performance of such a dual-phase positrode system is further improved by doping Zn and/or Ni to increase bulk and surficial concentration of oxygen vacancies. The hydration reaction and surficial adsorption of oxygen species are thereby promoted, benefitting the oxygen reduction reaction. The Ni and Zn co-doped composition Ba(Ce0.2Fe0.8)0.85(Ni0.5Zn0.5)0.15O3-δ exhibits lower polarization resistance than the pristine and singly doped systems, enabling the fuel cells to show high peak power densities of 400, 721, and 828 mW cm−2 at 550, 600, and 650 °C, respectively.

Mechanism of Fe-rich phase supercooling induced by CDS process to regulating microstructure and strengthen properties of Al-Si-Fe alloy

Excessive iron in aluminum alloys forms compounds that weaken their strength and workability. Therefore, controlling the morphology of the Fe-rich phase is vital for developing strong, high-quality aluminum alloys. This research explores the controlled diffusion solidification (CDS) process, an innovative approach designed to optimize the morphology and distribution of the Fe-rich phase, thereby enhancing the alloy properties beyond what conventional methods can achieve. Specifically, the CDS process uniquely modifies the solidification behavior of the alloy, suppressing the growth of the primary Fe-rich phase and enhancing the overall properties. This demonstrating the ability of process to refine microstructural characteristics effectively. The experimental results confirm the presence of primary Si and Al3Fe in the CDS process samples. Consequently, the nucleation of Al3Fe in the precursor alloy leads to the concentration of Fe solutes reduce, impeding the nucleation and growth of the primary Fe-rich phase during the subsequent solidification process. The key factors are temperature difference between two mixed alloy and mass ratio of precursor alloys. The mass ratio influences the precipitation sequence of the precursor alloys, while the difference of temperature and concentration induces the undercooling necessary for nucleation. The study reveals that an optimal mass ratio of 4:1 in the CDS process achieves the best mechanical properties with a 73.78 % increase in ultimate tensile strength (UTS) and a 107.77 % increase in elongation (UL) compared to conventional casting. The findings provide a theoretical basis for controlling the Fe-rich phase evolution, significantly augmenting the performance of Al-Si-Fe alloys. The findings not only enhancing the optimizing fundamental reactions in the CDS process for other alloy systems but also enriching the broader field of materials science.

Separation and extraction of iron resources from hazardous electric arc furnace (EAF) steel slag: Aggregation of Fe-rich layers, magnetic separation, powder characterization

China's electric arc furnace (EAF) slag reserves are huge, the problems of EAF slag resource application need to be solved urgently. In this study, high temperature holding and slow cooling treatment were used to treat the slag. The phase and structure of the slag were analysed by means of X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. To analyse the migration pattern of iron elements and to study the interaction between EAF slag basicity and magnetic separation efficiency. The results show that, there is an obvious layering phenomenon during the cooling slag, and the top layer is the Fe-rich layer. The slow cooling treatment makes the Fe-rich phase grow sufficiently and improves the dissociation efficiency of the Fe-rich phase in the crushing process. As the basicity increases, the thickness of the iron-rich layer gradually decreases and the iron element is transferred to the RO phase, while the concentrate yield decreases. Multi-stage wet weak magnetic separation of treatment slag resulted in the highest concentrate yield of 49.05 % at an basicity of 1, with a T.Fe content of 56.711 %, and 70.32 % of the iron component entering the concentrate. The concentrate can be returned to the steelmaking process instead of the charge, and the tailings can be used to make high value-added products.

Optimizing the Morphology and Solidification Behavior of Fe-Rich Phases in Eutectic Al-Si-Based Alloys with Different Fe Contents by Adding Mn Elements.

A high Fe content easily produces Fe-rich phases with a harmful morphology, resulting in a huge detrimental effect on the properties and recycling ability of Al-Si alloys. Therefore, finding ways to effectively transform Fe-rich phases to form a beneficial phase or shape is of great significance. Accordingly, Al-Si-based alloys with Fe contents ranging from 0.1 wt.% to 2.0 wt.% were modified by different Mn additions. Moreover, experiments combined with simulations were utilized to comprehensively analyze the mechanism of Mn on the morphology and microstructural evolution of Fe-rich phases from different perspectives. The current findings determine that adding different Fe contents changes the phase-transition reactions in alloys. Without Mn, and by increasing the Fe content from 0.1 wt.% to 2.0 wt.%, the Fe-rich phases gradually convert from a skeleton-shaped α-Al8Fe2Si (<0.25 wt.%) to β-Al9Fe2Si2 with a fibrous (0.5 wt.%), needle-like (1.0 wt.%) and plate-like shape without curvatures (2.0 wt.%). The maximum length and mean aspect ratio increase from 12.01 μm to 655.66 μm and from 1.96 to 84.05, while the mean curvature decreases from 8.66 × 10-2 μm-1 to 8.25 × 10-4 μm-1. The addition of 0.35 wt.% Mn promotes a new Chinese-character and petal-shaped α-Al15(FeMn)3Si2, with an atomic ratio of Fe and Mn of 1:1 when the Fe content is lower than 0.5 wt.%, while it transforms to β-Al15(FeMn)3Si2 with an atomic ratio of 5:1, presenting as a refined plate-like shape with a certain curvature, as the Fe content increases to 2.0 wt.%. Mn alters the phase reactions and increases the threshold of the Fe content required for β-Al15(FeMn)3Si2, limiting the formation and growth of them simultaneously in time and space. The enrichment of Mn atoms and solute diffusion at the growth front of β-Al15(FeMn)3Si2, as well as the strong atomic-binding ability, can deflect the growth direction of β-Al15(FeMn)3Si2 for it to have a certain curvature. Additionally, the enriched Mn atoms easily form α-Al15(FeMn)3Si2 and cause the long β-Al15(FeMn)3Si2 to be broken and refined to further reduce the damages caused to the alloy's performance. Ultimately, the maximum length and mean aspect ratio can be effectively reduced to 46.2% and 42.0%, respectively, while the mean curvature can be noticeably increased by 3.27 times with the addition of Mn.

Tailoring thermal conductivity and microstructure of Al–Fe alloys by addition of Sc2O3 and variable cooling rates

Al–Fe alloy is a kind of high thermal conductivity alloy, which are widely utilized in the communication and automobile industries. The thermal conductivity is greatly affected by the morphology, size, and distribution of iron-rich intermetallic phases (Fe-rich phases), pores, and Al grains. The evolution of microstructure and thermal conductivity of Al–Fe alloys by adding Sc2O3 particles and adjusting cooling rates are systematically studied by optical and scanning electron microscopy, and synchrotron X-ray imaging. The results show that Sc2O3 addition reduces the size and increases the number of primary Fe-rich phases, while increasing the grain size of Al matrix. The Sc2O3 promote their nucleation of primary Fe-rich phases and partial Sc solutes inhibit their growth, resulting in the improvement of thermal conductivity and mechanical properties. The remaining Sc2O3 particles have large lattice misfit with Al, led to the formation of coarsen size Al. The highest thermal conductivity is 214 W/(m·K) in the alloy with Sc2O3 and slow cooling rate. Sc2O3 addition increase the thermal conductivity of the studied alloys, i.e., an increment of 3 W/(m K) (by 1.1 %) at slow cooling rate by and an increment of 11 W/(m K) (by 6.2 %) at fast cooling rate. This study provides a new strategy to improving thermal conductivity of Al alloy for both academia and industry.

Operando study of the dynamic evolution of multiple Fe-rich intermetallics of an Al recycled alloy in solidification by synchrotron X-ray and machine learning

Using synchrotron X-ray diffraction, tomography and machine-learning enabled phase segmentation strategy, we have studied under operando conditions the nucleation, co-growth and dynamic interplays among the dendritic and multiple intermetallic phases of a typical recycled Al alloy (Al5Cu1.5Fe1Si, wt.%) in solidification with and without ultrasound. The research has revealed and elucidated the underlying mechanisms that drive the formation of the very complex and convoluted Fe-rich phases with rhombic dodecahedron and 3D skeleton networks (the so-called Chinese-script type morphology). Through statistical microstructural analyses and numerical modelling of the ultrasound melt processing, the research has demonstrated that a short period of ultrasound processing of just 7 s in the liquid state is able to reduce the average size of the α-Al dendrites and the Fe-containing intermetallic phases by ∼5 times compared to the cases without ultrasound. For the first time, this work has revealed fully the nucleation and growth dynamics of the convoluted morphology of the Fe-containing intermetallic phases in 4D domain. The research has also demonstrated clearly the beneficial effects of applying ultrasound to control the Fe phases' morphology in recycled Al alloys and it is one of the most effective and green processing strategies.

Identification of nano-sized precipitates in CLAM steel induced by 3.5 MeV Fe13+ ion irradiation

Nano-sized precipitate phases in normalized-and-tempered CLAM steel (HEAT-0912) before and after 3.5 MeV Fe13+ ion irradiation at 400 °C to 0.61, 1.29 and 2.77 dpa were studied using transmission electron microscope and high-resolution transmission electron microscope. Six types of nanoprecipitate phases based on Cr23C6, TaC, Ta3C2, VC, Cr7C3, and V2C were identified in unirradiated steel. During irradiation, a large number of nanoprecipitates uniformly distributed in the matrix occurred, and the number density of nanoprecipitates initially increased and subsequently decreased with increasing the irradiation dose. Nanoscale Cr-rich M23C6, V-rich MX and M2X phases but no nanoscale phases based on TaC, Ta3C2 and Cr7C3 were identified in the steel irradiated up to 2.77 dpa. After irradiation, five types of irradiation-induced nanoscale new phases were identified in the irradiated steel. These include Fe-rich M3X2 (Cr3C2 types I and II) carbonitrides with the same simple orthorhombic lattice and totally different lattice parameters (approximately a/b/c = 1.146/0.552/0.2821 nm and 0.285/0.925/0.696 nm), Fe-rich M2C, M3C and M5C2 carbides, but the occurrence of which under irradiation varied with the irradiation dose. Fe-rich M3X2 (Cr3C2 type I) and Fe-rich M5C2 phases were identified in the steel irradiated up to 1.29 dpa and only to 2.77 dpa, respectively. Fe-rich M2C and M3C in addition to Fe-rich M3X2 (Cr3C2 type II) phases were identified in the steel irradiated up to 2.77 dpa. The irradiation-induced Fe-rich M3X2 (Cr3C2 type I & II), M5C2 and M2C precipitates appear to be identified, for the first time, in reduced activation ferritic/martensitic steels including CLAM steel. The formation mechanism of these irradiation-induced precipitate phases is also discussed.

Co-, Ni- and Fe-rich grain-boundary phases enhance creep resistance in θ′-strengthened Al-Cu alloys

Microstructural evolution and creep response were investigated in the cast Al-5.0Cu-0.3Mn-0.2Zr (wt.%) alloy with and without addition of slow-diffusing, intermetallic-forming elements Fe, Ni, or Co. Baseline Al-5.0Cu-0.3Mn-0.2Zr alloy exhibits high creep resistance at 300 °C, up to ∼75 MPa, which is attributed to high-aspect-ratio, intragranular θ′-Al2Cu precipitates that effectively suppress dislocation climb. However, θ′-Al2Cu precipitate-free zones form along grain boundaries upon heat treatment, whose extent is amplified during subsequent creep. Such weak regions experience dislocation creep, leading to strain localization and acceleration of grain-boundary sliding. Adding Ni and Co, individually or in combination, leads to the formation of grain-boundary precipitates (Al9Co2, Al3Ni2) which are resistant to coarsening, thus suppressing the formation of θ′-Al2Cu precipitate-free zones. This microstructure provides high creep resistance at stresses up to 75–80 MPa, with strain rates much lower than in unmodified Al-5.0Cu-0.3Mn-0.2Zr. Adding Fe, which results in extensive decoration of grain boundaries with coarsening-resistant Al7Cu2Fe, and then increasing the Cu content to compensate for the Cu loss to this new phase, leads to a new Al-7.4Cu-1.6Fe-0.3Mn-0.2Zr alloy with creep resistance at 300 °C that surpasses known cast aluminum alloys. Adding Fe to improve the creep resistance of Al-Cu alloys is both cost-effective and sustainable. Our findings offer guidelines applicable to various alloy systems on controlling the evolution of precipitate-free zones and its ensuing effects on creep deformation.

Towards optimizing cooling rate, microstructure, and compressive strength in rapidly solidified Cu–20Fe alloy

There is currently interest in the development new Cu–Fe alloys with higher Fe content (>5 wt%), a low-cost element. In order to improve electrical, thermal and mechanical properties, there is a need to decrease the size of the Fe-rich phase and improve its distribution, whose possibilities rely on adding alloying third elements and heat treatments. However, the prospect of controlling the size of the phase through dendritic spacing control by means of rapid solidification processes may be feasible and deserves to be explored, as is the case in the present study. The following methods were employed to evaluate the round stepped cast samples of the Cu-20 wt% Fe alloy: centrifugal casting in a Cu mold, optical microscopy, CALPHAD, Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), X-ray Diffraction (XRD), Vickers hardness, and compressive tests, in samples corresponding to different coarsening microstructures. Finally, dendritic growth is modelled using the Kirkwood equation. The results demonstrate a promising processing route with control of the secondary dendrite arm spacing (SDAS), whose methodology and modeling can serve as a basis for other alternative processes with the Cu–Fe alloys, allowing suitable size and distribution of Fe phase to be attained. It is further demonstrated that the Kirkwood model is able to match experimental SDAS in both slowly and rapidly solidified Cu–Fe samples. While Fe (BCC) is expected to increase strength, this is only slightly observed in the hardness results for smaller SDAS, as the loads are more superficial. In the case of compressive yield strength, SDAS in the observed range (1.4 μm–2.2 μm) is found to have no effect.

Sunflower-like eutectic solidification in gas atomized Al0.3CrFeNiTi0.3 medium-entropy alloy powders: A comprehensive microstructural study

The addition of larger atomic size elements, such as Al and Ti, to CrFeNi medium-entropy alloys (MEAs) offers a strategic approach to overcome the strength-ductility trade-off. This study focuses on examining the morphological, solidification, phase, and elemental characteristics of Al0.3CrFeNiTi0.3 feedstock powders produced through gas atomization (GA). The rapid cooling rate inherent in GA results in sunflower-like eutectic solidification. This structure exhibits firstly solidified Cr-rich BCC phases filled with cuboidal-shaped L21-type precipitates, each measuring up to ∼20 nm. Their peripheral regions display outward and radial growth of L21 and Fe-rich BCC eutectic phases, while FCC phase develops at the remaining sites. Intermediate B2 layers between BCC and L21 phases are considered as kinetic buffers, which enhance the interfacial stability. The size and shapes of powders determine their cooling rates, leading to a transition from comparably large sunflower-like eutectic structures to finer equiaxed grains alongside reduced elemental segregation with decreasing powder size. Nano-hardness measurements demonstrate superior mechanical strength in the peripheral regions due to the higher volume fraction of the L21 phase and its optimal interfacial coherency with the Fe-rich BCC phase. Furthermore, the slightly higher concentrations of Al and Ti in Fe-rich BCC phase (compared to the Cr-rich BCC phase) induce a better lattice distortion effect.

Unveiling the Refinement Effect of the Coarse Fe-Rich Phase in Al-Si-Fe Alloy under Controlled Diffusion Solidification Treatments

Unveiling the Refinement Effect of the Coarse Fe-Rich Phase in Al-Si-Fe Alloy under Controlled Diffusion Solidification Treatments

Friction stir welding of as-cast and pre-aged Al–Si–Zn–Mg–Fe alloy: Microstructure, mechanical and corrosion properties

Al–Si–Zn–Mg–Fe alloy in as-cast and artificially aged (T6) conditions was friction stir-welded with a traveling speed of 200 mm/min and a rotation speed of 800 rpm. Their microstructure, mechanical and corrosion properties were investigated. α-Al, Si, Mg2Si, MgZn2 and Fe-rich phase were detected in the as-cast and pre-aged Al–Si–Zn–Mg–Fe before and after FSW. The secondary phases in pre-aged Al–Si–Zn–Mg–Fe after FSW are slightly more than those in the as-cast Al–Si–Zn–Mg–Fe after FSW. For the pre-aged Al–Si–Zn–Mg–Fe after FSW, the grains are refined and the dislocation density decreases. Hardness of the pre-aged Al–Si–Zn–Mg–Fe is higher than that of the as-cast one, whereas the hardness of weld nugget zones (NZs) of the both FSWed Al–Si–Zn–Mg–Fe joints is lower than their base materials, and the strength coefficients of both FSWed joints of the as-cast and pre-aged Al–Si–Zn–Mg–Fe are 0.82 and 0.9 respectively. The ultimate tensile strength (UTS) and yield strength (YS) of the pre-aged Al–Si–Zn–Mg–Fe after FSW (UTS = 208.86 MPa and YS = 156.72 MPa) is about 35% higher than that of as-cast Al–Si–Zn–Mg–Fe after FSW (UTS = 159.4 MPa and YS = 112.06 MPa) mainly due to the smaller grain size and more precipitates in the former. The corrosion resistance (CR) of the FSWed joint of the pre-aged Al–Si–Zn–Mg–Fe is the highest, owing to the most refined grain size, highest HAGBs, lowest KAM, increase in the close-packed {111} (α-Al) texture, dispersed particles of secondary phases, followed by the pre-aged Al–Si–Zn–Mg–Fe and then the FSWed joint of the as-cast Al–Si–Zn–Mg–Fe, and the as-cast one is the lowest.