Intermetallic Research Articles

Impact of Mg on the Feeding Ability of Cast Al–Si7–Mg(0_0.2_0.4_0.6) Alloys

The demand for high-performance Al–Si casting alloys is driven by their mechanical properties, making them popular in automotive, aerospace, and engineering industries. These alloys, especially hypoeutectic Al–Si–Mg, offer benefits like high fluidity, low thermal expansion, and good corrosion resistance. Silicon and magnesium primarily define their microstructure and mechanical properties. Silicon enhances fluidity, while magnesium improves strength and fatigue resistance. However, challenges like shrinkage porosity persist during solidification. Understanding solidification feeding regions is crucial, influenced by factors such as chemical composition, solidification characteristics, and casting design. This study investigates magnesium’s influence on feeding ability in hypoeutectic Al–Si7–Mg alloys through experimental tests. Increasing magnesium content from 0% to 0.6% affects the interdendritic and burst feeding regions. This could impact shrinkage porosity formation. The “Sand Hourglass” test results indicate a rise in porosity levels with higher magnesium content, which is linked to the narrowing of interdendritic channels and the formation of magnesium-rich intermetallic compounds. These changes hinder the liquid metal flow, worsening shrinkage porosity. Therefore, magnesium’s role in expanding the interdendritic region is a key factor in developing porosity in cast hypoeutectic Al–Si7–Mg alloys. This study highlights that porosity levels increase from 0% in magnesium-free Al–Si7 to 0.84% in Al–Si7–Mg0.6, underscoring magnesium’s significant impact on the occurrence of porosity in these alloys.

Morphological Characterization and Tribological Properties of TiCoNi Alloy Coatings on Ti–6Al–4V Alloy via Laser Deposition

The goal of this work is to improve the Ti–6Al–4V alloy's hardness and tribological behavior. Coaxial laser surface cladding was used to develop intermetallic layers of nickel (Ni), cobalt (Co), and titanium (Ti). Laser power of 900 W, beam spot size of 3 mm, powder feed rate of 1.0 g/min, and gas flow rate of 1.2 L/min are the optimized parameters used for laser depositions. The laser scan speeds were adjusted between 0.6 and 1.2 m/min. Investigations were conducted into the effects of powder admixture and laser parameters on the fabricated coatings' microstructure, tribological behavior and hardness. X-ray diffractometry (XRD), energy dispersive spectroscopy (EDS) with Scanning electron microscopy (SEM) was employed for the characterization of the microstructural evolution and phase identification, respectively. Additionally, the tribological experiment was conducted via UMT-2 –CETR reciprocating tribometer, and the coatings’ micro-hardness characteristics were examined using EmcoTEST DURASCAN. The micrographs exhibit no signs of porousness, cracks, or stress introduction, according to the results. For every manufactured sample, good metallurgical adhesion was obtained. By comparing the hardness of the ternary coating (Co–Ni–10Ti deposited at a scan speed of 1.2 m/min, with a hardness of 980 HV) to the substrate (Ti–6Al–4V, with a hardness of 330 HV), a hardness increase of approximately 2.96 times was observed. Furthermore, the Co–Ni–10Ti coating, deposited at a scan speed of 1.2 m/min, demonstrated a 51.1% reduction in the coefficient of friction (COF) compared to the base alloy, indicating superior anti-wear performance. The enhanced properties are attributed to the formation of hard intermetallic compounds such as Ti–Co, Co2Ti, Al5Co2, and Ni3Ti, along with their uniform distribution and finely tuned grain sizes.

Two-Dimensional Correlation Spectroscopy (2D-COS) Tracking of the Formation of Selected Transition Metal Compounds Cu(II) and Cd(II) With Cinchonine and Their Impact on Model Components of Erythrocytes.

Cinchonine is a quinoline alkaloid known for its antimalarial properties. Due to the advantages of using compounds of metal ions with alkaloids, a copper(II) compound with cinchonine was synthesized, and, for comparative purposes, a cadmium(II) compound with cinchonine. During the synthesis, the emerging interactions between the metal ion and cinchonine were studied. After crystallization, it was examined how the obtained compounds would interact with the model blood component, hematoporphyrin IX. Ultraviolet-visible (UV-Vis) spectroscopy, Raman spectroscopy, and attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) were used in the study. In the case of monitoring the synthesis, the best method turned out to be UV-Vis spectroscopy, combined with the possibility of two-dimensional correlation spectroscopy (2D-COS), which enabled the identification of peaks characteristic of the interactions of the cinchonine quinoline ring with metal ions. In turn, the obtained Raman spectra showed shifts of individual bands and changes in their intensity, and 2D-COS showed the sequence of formation of individual interactions, which confirmed the formation of cinchonine compounds with metals. ATR FT-IR also allowed us to compare the spectra of the substrates used in the synthesis with the crystallized compounds and thus confirm the formation of the expected compounds. Bands characteristic of π-π-stacking interactions between the quinoline ring and the tetrapyrrole ring of hematoporphyrin IX were also observed. Observed interaction with a model blood component may be important when designing drugs for antimalarial therapy.

Quantum embedding method with transformer neural network quantum states for strongly correlated materials

The neural-network quantum states (NNQS) method is rapidly emerging as a powerful tool in quantum mechanisms. While significant advancements have been achieved in simulating simple molecules using NNQS, the ab initio simulation of complex solid-state materials remains challenging. Here in this work, we have adopted the periodic density matrix embedding theory to extend the NNQS method to deal with complex solid-state systems. Our approach notably reduces the computational problem size while maintaining high accuracy. We have validated the accuracy and efficiency of our method against traditional methodologies and experimental data in extended systems, and have investigated the magnetic ordering and charge density wave state in transition metal compounds. The findings from our research indicate that the integration of quantum embedding with intuitive chemical fragmentation can significantly enhance the NNQS simulation of realistic materials.

Interfacial evolution in Cr/Mo-coated Zr alloys near the Mo-Zr eutectoid temperature

This study investigates the interfacial evolution of Cr/Mo-coated Zr alloys near the Mo-Zr eutectoid temperature, from the viewpoints of microstructure and chemical composition and with the joint application of XRD, TEM and EDS analyses. The experimental findings highlight significant changes in microstructure and diffusion behavior associated with the Mo-Zr eutectoid reaction. In the as-fabricated specimen, it is noted that introducing a Mo-intermediate layer results in the formation of an amorphous Cr layer at the Cr/Mo interface. In the case of the annealing temperature below the Mo-Zr eutectoid reaction, Mo interlayer effectively impedes the diffusion between Cr and Zr, thereby suppressing the formation of intermetallic compounds. However, the diffusion barrier function of Mo interlayer deteriorates when the temperature exceeds the eutectoid point, with the presence of four distinct diffusion zones, including α-Zr, β-Zr, the intermetallic compound Zr(Mo,Cr,Fe)₂, and the Mo layer containing fine Zr(Mo,Cr,Fe)2 particles. These findings underscore the critical role of Mo-interlayer in influencing the structural stability and intermetallic compound formation in Cr/Mo-coated Zr alloys, not only at the temperature regime around the eutectic reaction, but also at the temperature regime around the eutectoid reaction, which is of great necessity for the practical applications of accident tolerant fuel cladding under high temperature environment.

Anisotropic corrosion behavior of laser-based direct energy deposited H13 steel in molten ADC12 aluminum alloy

The immersion corrosion experiment of laser-based direct energy deposited H13 steel in ADC12 aluminum alloy melt was conducted to evaluate the demands for corrosion resistance after mold repair. The effect of the anisotropic microstructure of the deposited H13 steel on corrosion behavior was elucidated by characterizing the microstructure before and after corrosion. The results show that the microstructural heterogeneity affects the initiation, development and stabilization process of corrosion. Corrosion tends to initiate near the heat-affected zone due to the heterogeneous distribution of grain size, carbides, and dislocation density. Planes with weak microstructural heterogeneity are less likely to develop cracks in the intermetallic compounds (IMCs) layer during the corrosion development stage, thus exhibiting a slower corrosion rate. The IMCs layer of plane with weak microstructural heterogeneity stabilizes more quickly during the corrosion stabilization stage. The plane perpendicular to the build direction exhibits the highest corrosion resistance due to fewer corrosion initiation locations and the weakest microstructural heterogeneity. Furthermore, the composite structure of carbide core + Si phase shell, generated during corrosion, contributes to improving localized corrosion resistance. This study provides insights into understanding the influence of the heterogeneous microstructure from additive manufacturing on the reaction-diffusion process and offers guidance on direction selection when preparing components for applications in contact with aluminum melts using additive manufacturing techniques.

Synthesis and physical properties of Sm2PdGe3 in a context of RE2PdGe3 family

In this study, we present the crystallographic and magnetic characterization of a new intermetallic compound Sm2PdGe3, which was synthetized by a two stage method employing an eutectic alloy. The investigations carried out exhibited, that Sm2PdGe3 crystallize in AlB2-type structure with lattice parameters a = 4.2189(1) Å and c = 4.1031(2) Å. This compound can be classified as a cluster-glass with a spin freezing temperature Tf = 10.5 K. Furthermore, there were carried out the analysis of the role of the rare earth (RE) elements on the structural parameters of RE2PdGe3 and draw a correlation between the RE radius and the unit cell parameters. We show that a deviation from the ideal 1:3 Pd:Ge ratio is necessary to synthesize RE2PdGe3 with smaller RE elements.

Effect of Ta/Ni dual-interlayer on the microstructure and properties of high strength titanium alloy and steel composite plate

The combination of ultra-high-strength Ti-6Al-4V (TC4) titanium alloy and 30CrNiMoNb (6211) steel was achieved by adding Ta/Ni dual-interlayer and rolling at 950 °C through welding a symmetrical blank sleeve with a vacuum electron beam. In order to unveil the metallurgical bonding mechanism and the interfacial structure, SEM, XRD, and compression-shear performance tests were used. The results revealed the presence of thin-film brittle TiC, TiFe, and TiFe2 compounds at the TC4/6211 interface, resulting in an increased risk of interface mismatch and brittle fracture along the matrix phase interface, and the average interfacial bonding strength was tested at 323 MPa.In contrast, the TC4-Ta interface and the 6211-Ni interface in the TC4/Ta/Ni/6211 composite plate displayed good solid solution formation. The strengthening mechanism of the Ta/Ni dual-interlayer interfacial bonding was analyzed using selected area electron diffraction (SAED), revealing that the Ta-Ni diffusion region consisted of Ni3Ta and Ni2Ta. The addition of the Ta/Ni dual-interlayer prevented the aggregation of Ti and Fe atoms to form Ti-Fe compounds. The malleable intermetallic compounds of Ni3Ta and Ni2Ta effectively coordinated deformation, leading to an average interfacial bonding strength of 469 MPa, which was 45.2 % higher than the composite plate without Ta/Ni dual-interlayer.

Prototyping Ti2Cu intermetallic grain growth heterogeneously in Ti6Al4V matrix through laser additive manufacturing

The Ti2Cu intermetallics compound possessing an ability to release Cu2+ ions has promising antibacterial properties. This research integrates experimental and computational techniques to delve into the interfacial intermetallic (IMC) formation within the Ti6Al4V/Cu system. Heat transfer analysis is performed to numerically outline the thermal history within the microstructure during laser surface alloying (power = 1000 W and scan speed = 200 mm/s), while the phase field method is employed to describe the Ti2Cu IMC grain growth in the Ti6Al4V matrix. As the IMC and the matrix phases respectively have free energy minima of -68.52 and -61.35 kJ/mol at Taverage=1250.0 K, the growth of Ti2Cu IMC grains at the Ti6Al4V matrix located around the depth of 5 μm from the top surface is thermodynamically favorable. Laser processing can cause the nucleation of IMC precipitates of irregular sizes and curvature profiles, in which case the curvature driven effects between the adjacent grains can additionally affect their growth kinetics. Furthermore, microbiological assays underscore the superior antibacterial efficacy of the Ti6Al4V+Ti2Cu heterostructures as compared to the control (Ti6Al4V) counterpart.

Reaction mechanisms and mechanical properties of SiCf/SiC composite and GH536 superalloy joints using CoFeNiCrMn high-entropy alloy filler

To meet the service conditions and strength requirements of turbine stator blades and the inner and outer rings of aero engine casings, CoFeNiCrMn high-entropy alloy filler was used to braze SiCf/SiC/GH536 joints. This study investigated the effects of holding time on the joints' microstructure and mechanical properties. Key phases identified in the welded joints include MoNiSi, FCC, and Cr23C6 near the composites, with brittle Ni3Si and Fe2Si intermetallic compounds forming due to filler diffusion. Optimal brazing parameters were found to be 1220 °C for 30 min with a shear strength of 64.28 MPa. The study also highlighted that increased holding time at the same temperature enhances diffusion at the joint, increasing brittle intermetallic compounds, initially improving shear strength, which then declines. Microstructural and fracture morphology analyses revealed that insufficient insulation time leads to poor welding and stress concentration at pores, causing cracks. Excessive insulation time results in joint fractures due to the brittleness of Ni3Si and Fe2Si intermetallic. Thus, joint shear strength correlates with welding quality and intermetallic compound distribution.

Особенности тонкой структуры Ni-Al покрытий, полученных методом HV-APS

Introduction. Development of Ni-Al intermetallic compounds is one of the priority directions of modern machine building. Due to such characteristics as high heat resistance, high temperature strength, and low density, nickel aluminides are used as functional coatings in the aerospace industry. The main methods of Ni-Al coating surfacing are High-Velocity Oxygen-Fuel and High-Velocity Air-Fuel spraying (HVOF and HVAF), atmospheric plasma spraying (APS) and its modification such as High-Velocity Atmospheric Plasma spraying (HV-APS) which provides non-equilibrium cooling conditions. Since there are eight different intermetallic compounds, as well as martensite transformation, Ni-Al coatings is quite interesting to study. The work purpose is to study the features of the martensitic structure in HV-APS coatings, and also to establish the effect of heating temperature on its decomposition. Materials and methods. Ni-Al coatings were surfaced onto a low-carbon steel substrate using the HV-APS method. Studies of the fine structure of the coatings were carried out using transmission electron microscopy (TEM). In addition, the influence heating temperature on structural transformations of the coatings was analyzed. Results and discussion. Two types of particles are formed in HV-APS coatings: with a dendritic and granular structure. The most part of HV-APS coatings consists of particles with a two-phase grain structure (NiхAl1-х and γ'-Ni3Al grains). Only NiхAl1-x grains undergo martensitic transformation at cooling. Martensite in large grains (sizes greater than 500 nm) has a lamellar structure, while small grains are completely transformed into one martensite plate. In addition, the coatings contain grains in which martensite plates (NiхAl1-х) and β-phases alternated. It is shown the behavior of martensitic plates at colliding with each other, as well as with the γ′-Ni3Al grain. Heating up to 400 °C contribute the begins of martensite decomposition in individual grains with the release of a secondary phase; after heating up to 600 °C all martensite dissolves.

Gallium: a decisive "Trojan Horse" against microorganisms.

Controlling multidrug-resistant microorganisms (MRM) has a long history with the extensive and inappropriate use of antibiotics. At the cost of these drugs being scarce, new possibilities have to be explored to inhibit the growth of microorganisms. Thus, metallic compounds have shown to be promising as a viable alternative to contain pathogens resistant to conventional antimicrobials. Gallium (Ga3+) can be highlighted, which is an antimicrobial agent capable of disrupting the essential activities of microorganisms, such as metabolism, cellular respiration and DNA synthesis. It was observed that this occurs due to the similar properties between Ga3+ and iron (Fe3+), which is a fundamental ion for the correct functioning of bacterial activities. The mimetic effect performed by Ga3+ prevents iron transporters from distinguishing both ions and results in the substitution of Fe3+ for Ga3+ and in adverse metabolic disturbances in rapidly growing cells. This review focuses on analyzing the development of research involving Ga3+, elucidating the intracellular incorporation of the "Trojan Horse", summarizing the mechanism of interaction between gallium and iron and comparing the most recent and broad-spectrum studies using gallium-based compounds with antimicrobial scope.

Ultrasonic-induced amorphization and strengthening mechanisms of ultrasonic vibrations assisted friction stir Al/Ti welds

Integration of aluminum (Al) and titanium (Ti) alloys offers an effective approach to sustainable and high-quality development of the automotive and aviation industries. However, challenges arise when welding Al alloys to Ti alloys due to the formation of detrimental intermetallic compounds at the interface. With the implementation of ultrasonic vibrations, the temperature and strain rate were both increased during Al/Ti friction stir welding (FSW), leading to the formation of an amorphous interlayer, instead of intermetallic compound (IMC), at the interface. The interfacial microcracks were eliminated in the ultrasonic vibrations assisted friction stir welding (UVFSW). There were Ti particles separated from the Ti substrate and dispersed in the Al alloy, thereby resulting in a more gradual and moderate evolution of the interfacial microstructure. Due to the improved interfacial microstructure with ultrasonic vibrations, the lap shear strength was almost twice that of the conventional FSW welds within same welding conditions. Meanwhile, ultrasonic vibrations also improved the fabrication efficiency with a higher optimal traversing speed. The failure mode shifted from interface separation of FSW welds to a shear dimple fracture of the UVFSW welds, demonstrating the better plasticity and reliability of the UVFSW Al/Ti dissimilar joints.

The effects of Ni and Al elements on microstructure and mechanical properties of low carbon CoCrMo alloy coatings

Low-carbon cobalt-based alloy coatings with high ductility and low thermal fatigue crack propagation rates were prepared using laser cladding (LC) technology. The microstructure of the coatings was characterized using SEM, EBSD, and TEM, while the mechanical properties were tested and analyzed. The CoCrMo alloy primarily consists of γ-Co and a minor amount of ε-Co. The addition of Ni increased the stacking fault energy (SFE), resulting in the retention of γ-Co in the alloy. However, the increase of Al content reduced the SFE, leading to the precipitation of Al3Ni intermetallic compound along with a eutectic region with Al3Ni, Cr23C6, and ε-Co. More ε-Co phase appeared after tensile deformation due to the stress-induced transformation induced plasticity (TRIP) effect. Ni addition increased the content of face-centered cubic (fcc) γ-Co, enhancing the coating's ductility by approximately 85 % compared to CoCrMo. With higher Al content, the ε-Co phase increased, and the dispersion of Al3Ni improved the coatings' strength. The jagged structure of the eutectic region increased the resistance to thermal fatigue crack propagation, causing the crack propagated along the grain boundary. Optimal mechanical properties were achieved with the addition of 13 wt% Ni and 7 wt% Al, which achieved a 53 % increase in ductility and a 40 % reduction in the thermal fatigue crack propagation rate compared to CoCrMo.

The promoting effect of Fe on the immobilization of heavy metals in MSWI FA–lead–zinc tailings-based backfill materials under field application: Dynamic simulation leaching and immobilization mechanisms

Currently, research on solid waste-based backfill materials containing municipal solid waste incineration fly ash (MSWI FA) was primarily concentrated at the laboratory stage, with insufficient studies on their leaching safety and heavy metal immobilization mechanisms under field application. This study demonstrated that MLBM (Binder weight ratio: MSWI FA: steel slag (SS): blast furnace slag (BFS): flue gas desulfurized gypsum (FGDG): coal fly ash (CFA) = 10 %:33.6 %:33.6 %:12.8 %:20 %; binder-to-lead–zinc tailings (LZT) ratio was 1:8; mass concentration was 60 %) exhibited excellent leaching safety in actual backfilling. The study found that MLBM posed no risk of heavy metal and anion leaching under various leaching standards. Furthermore, MLBM showed no risk of harmful element leaching within a simulated percolation period of 100 years. The release mechanisms of Pb, As, Zn, and Cr in MLBM were diffusion, diffusion, flushing, and dissolution, respectively. The immobilization efficiency of Pb, Zn, Cr, As, Cl−, and SO42− positively correlated with the pH value (pH>7.5). The immobilization mechanism included: 1) Formation of insoluble heavy metal compounds. In the MLBM system (The pH ranged from 7.89 to 8.87), Fe(III) (Fe(OH)3(aq) and Fe(OH)4−) contributed to the immobilization of Pb2+ and SO42− and oxidized As(III) (H2AsO3−) and Cr(III) (Cr(OH)3(aq)), forming As(V) (HAsO42−) and Cr(VI) (CrO42−), respectively. 2) Adsorption. The negatively charged surface of C–(A)–S–H gel could immobilize Zn2+ and Pb2+ through adsorption, and the ionic forms of Pb(II) and Zn(II) were PbOH+ and ZnOH+, respectively. This study provided theoretical support for the leaching safety and immobilization mechanisms of solid waste-based backfill materials containing MSWI FA in field applications.

Reasonable design of PBA-derived interfacial modified ternary compounds and hollow structure materials in high-performance asymmetric supercapacitors

Prussian blue analogues (PBA), common metal-organic frameworks (MOFs), are typically binary metal compounds. In this study, chromium was incorporated during the preparation of nickel‑cobalt PBA, resulting in the adjustment of the micro-morphology of PBA and the synthesis of small-sized PBA (sPBA) electrode materials with diameters ranging from 20 to 30 nm. These materials underwent various interfacial modifications to yield ternary metal phosphide (sPBA-P) and hollow nanostructures (sPBA-C). Additionally, by integrating graphene oxide (GO) as the growth substrate, successful preparation of GO@sPBA-P and GO@sPBA-C electrode materials was achieved. Significantly, these materials showcase outstanding electrochemical properties and interesting interfacial reactions when employed as cathode and anode components. Through a comprehensive series of characterization analyses, the electrochemical properties and reaction mechanisms of these materials were thoroughly investigated. Ultimately, an asymmetric supercapacitor (ASC) was assembled using the synthesized GO@sPBA-P and GO@sPBA-C to explore the material's potential in energy materials applications.

The growth kinetics of intermetallic compounds by the fast diffusion path at the interface of Co and molten Zn

This study investigates the growth and microstructure formation of intermetallic compounds at the solid/liquid interface of a Co/Zn diffusion couple prepared using an isothermal bonding method and annealed isothermally at 703 K, 723 K, and 743 K for up to 48 h. The experimental observations and analysis revealed the formation of three Zn-rich intermetallic compounds: γ (Co5Zn21), γ1 (CoZn7), and γ2 (CoZn13). The γ2 phase, having the highest Zn content, formed the thickest layer, while the γ and γ1 phases exhibited slower growth. The total thickness of these layers increased proportionally to the annealing time, following a power function. The growth of intermetallic compounds was predominantly controlled by interdiffusion, with the γ2 phase forming island-like structures that merged over time, creating fast diffusion paths of liquid Zn. The annealing temperature had a minimal impact on the growth rate, with slightly faster growth observed at lower temperatures due to finer needle-like interfaces within the molten Zn, which created more efficient diffusion paths. These findings underscore the importance of understanding the kinetics and mechanisms of intermetallic compound formation for optimizing material properties and processing conditions in industrial applications.

Fabrication of a novel microflower BiOCl composite incorporated with rosemary powder for enhanced oxygen vacancies and visible-light photocatalytic efficiency

Incorporating metallic or nonmetallic compounds is a promising method for enhancing the oxygen vacancies (OVs), charge transport, and visible light absorption of a bismuth oxychloride (BiOCl) semiconductor. This research aims to improve the properties of BiOCl by incorporating rosemary powder (RPC). BiOCl photocatalysts with enhanced OVs were synthesized through the addition of 1–4 wt% of RPC using a one-pot solvothermal process. The addition of 3 % RPC resulted in the formation of very small particles on the BiOCl lamellar structures, which were aligned with the (002) plane of carbon quantum dots (CQDs). The uniformly distributed CQDs transformed the BiOCl microstructure from a two-dimensional lamellar structure to a three-dimensional floral structure, leading to an increased surface area and pore volume. The incorporation of RPC enhanced the visible light absorption capacity of BiOCl. The carbon atoms in RPC readily attach to oxygen atoms in the Bi-O bond, disrupting the Bi-O lattice bond and forming OVs. The addition of RPC contributed to a higher number of OVs, which impacted both the energy difference between the valence and conduction bands and their locations. This resulted in better charge transfer and enhanced active species formation. The 3 %-RPC-BOC photocatalyst had the highest efficiency, achieving a 98 % degradation of rhodamine B (RhB) and a 45 % removal of organic carbon within 48 min under visible light. This composite also had excellent stability and reusability, as its crystal structure remained unaltered even after conducting 7 cycles. The primary active species of 3 %-RPC-BOC system is the superoxide radical (·O2-), while the hydroxyl radical (·OH) and hole (h+) operate as minor active species. Additionally, the 3 %-RPC-BOC achieved a high tetracycline (TC) removal rate of 82.1 %, which is 2.21 times higher than that of pure BiOCl.

Electrochemical stability of biodegradable Zn-Cu alloys through machine-learning accelerated high-throughput discovery.

Zn-Cu alloys have attracted great attention as biodegradable alloys owing to their excellent mechanical properties and biocompatibility, with corrosion characteristics being crucial for their suitability for biomedical applications. However, the unresolved identification of intermetallic compounds in Zn-Cu alloys affecting corrosion and the complexity of the application environment hamper the understanding of their electrochemical behavior. Utilizing high-throughput first-principles calculations and machine-learning accelerated evolutionary algorithms for screening the most stable compounds in Zn-Cu systems, a dataset encompassing the formation energy of 2033 compounds is generated. It reveals that most of the experimentally reported Zn-Cu compounds can be replicated, especially the structure of R32 CuZn5 is first discovered which possesses the lowest formation energy of -0.050 eV per atom. Furthermore, the simulated X-ray diffraction pattern matches perfectly with the experimental ones. By formulating 342 potential electrochemical reactions based on the binary compounds, the Pourbaix diagrams for Zn-Cu alloys are constructed to clarify the fundamental competition between different phases and ions. The calculated equilibrium potential of CuZn5 is higher than that of Zn through the forward reaction Zn + CuZn5 ⇌ CuZn5 + Zn2+ + 2e-, resulting in microcell formation owing to the stronger charge density localization in Zn compared to CuZn5. The presence of chlorine accelerates the corrosion of Zn through the reaction Zn + CuZn5 + 6Cl- + 6H2O ⇌ Cu + 6ZnOHCl + 6H+ + 12e-, where the formation of ZnOHCl disrupts the ZnO passive film and expands the corrosion pH range from 9.2 to 8.8. Our findings reveal an accurate quantitative corrosion mechanism for Zn-Cu alloys, providing an effective pathway to investigate the corrosion resistance of biodegradable alloys.

Surrogate model-based assessment of particle damage behaviour of Al[sbnd]Zn[sbnd]Mg alloy

Recent research has found some intermetallic compound particles with even stronger hydrogen trapping capacity (e.g., Al7Cu2Fe) than the age-hardening precipitates that are reported to be the origin of hydrogen embrittlement in aluminium. Such intermetallic compound particles can reduce hydrogen concentration at the interface between the precipitates and aluminium by absorbing hydrogen in their interiors, thus preventing the hydrogen embrittlement of aluminium. However, this cannot be achieved if the particles, which have absorbed large amounts of hydrogen, are damaged due to hydrogen embrittlement. In this study, the hydrogen embrittlement of aluminium was observed in situ by X-ray CT, and the damage behaviour was analysed of all the particles that were located in the gauge section of a single tensile specimen. After exhaustive quantification of the size, shape, and spatial distribution of the particles, coarsening processes identified highly correlated design variables. Subsequently, particle damage behaviour was analysed utilizing a surrogate model using a support vector machine. The damage to Al7Cu2Fe particles could be described only by design variables representing size and shape, while those representing spatial distribution were removed through the coarsening processes. No change was observed in the damage behaviour of Al7Cu2Fe particles with increasing hydrogen concentrations, and it was concluded that the dispersion of Al7Cu2Fe particles is effective in preventing hydrogen embrittlement of aluminium. The contribution of damaged particles to the formation of fracture surfaces and the damage behaviour of Mg2Si particles, where damage is accelerated by hydrogen, were also analysed.