Multilayer Alloy Research Articles

High-cycle and low-cycle fatigue characteristics of multilayered dissimilar titanium alloys

Multilayered structures of dissimilar titanium alloys can achieve excellent fracture ductility and strength, while their fatigue characteristics especially dislocation networks and twin formation are rarely reported. Heterogeneous microstructures are observed in the multilayered TC4/TB8 alloys, including fine acicular α grains, continuous α layer at prior β grain boundaries (αGB) and β matrix on the TB8 layer, together with equiaxed α grains on the TC4 layer. High-cycle fatigue (HCF) and low-cycle fatigue (LCF) tests show that the initial fatigue damage appears at the αGB/β matrix interfaces on the TB8 layer instead of the boned TC4/TB8 interfaces. Since the stress concentration induced by dislocation pile-up is prone to micro-void formation and crack propagation at the αGB/β interfaces. For LCF, the αGB/β interfaces can not only act as impenetrable barriers and sources of lattice dislocations, but also allow the dislocations cross boundaries during cyclic tension and compression because of the high boundary energy. The formation characteristic of deformation twins that is beneficial for the plastic deformation of α grains in TC4 layer during cyclic strain is investigated. Furthermore, the hexagonal dislocation networks are also found within the equiaxed α grains of TC4 layer after LCF, and the role between interface barrier and slip direction in the formation mechanism is analyzed.

Investigation on the Microstructure and Mechanical Properties of Multi-layer and Multi-pass Al Alloy Deposition Based on Cold Metal Transfer Technology

Investigation on the Microstructure and Mechanical Properties of Multi-layer and Multi-pass Al Alloy Deposition Based on Cold Metal Transfer Technology

Tribological investigation of ceramic incorporated novel compositionally graded multilayer tungsten alloys

In this study, novel compositionally graded tungsten alloys incorporating ceramics were prepared using mechanical alloying and pressure-assisted vacuum hot press (VHP) sintering. Three distinct tungsten compositions (W1, W2, and W3) were developed with varying alloying elements and reinforcements, were stacked layer-wise, and then sintered using VHP. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were employed to analyze the morphology and microstructural features of synthesized alloys. The effect of alloying elements and reinforcements on mechanical properties and wear behavior was examined. The results showed improvement in mechanical characteristics and enhanced wear resistance of the compositionally graded tungsten alloys. The hardness was increased due to the formation of carbide phases during milling and sintering. The W1 side exhibited a hardness of 8.4 GPa, while the W3 side reached a hardness of 13.3 GPa. Additionally, the wear behavior of both sides (W1 and W3) was also investigated under different applied loads. At a load of 10 N, the W1 surface exhibited a minimum specific wear rate of 3 × 10−6 mm3/Nm, attributed to the presence of MWCNTs and WC phase. However, the W3 surface reinforced with TiC and cBN showed a minimum specific wear rate of 9 × 10−7 mm3/Nm at a higher load of 20 N. This indicates that the W3 side possessed superior hardness and wear resistance ability as compared to the W1 side of compositionally graded tungsten alloys. The novel compositionally graded approach is useful for developing tungsten alloys with tailored mechanical properties for wear resistance applications.

Additively manufactured low-gradient interfacial heterostructured medium-entropy alloy multilayers with superior strength and ductility synergy

Metallic additive manufacturing (AM) offers near net-shape fabrication but often results in insufficient strength and/or ductility due to voids or cracks, coarse initial crystalline microstructure, insufficient volume fraction of precipitates and yet post-AM strengthening/toughening methods non-destructive to shape are generally lacking. Here, we report a laser-directed energy deposited (L-DED) medium entropy alloy (MEA) with a heterostructure (HS) comprising alternate layers of solid-solution and intermetallic-dispersed MEA that possess ultimate tensile strength of 1132.8 MPa and elongation of 50.6 %, corresponding to strength-ductility synergy higher than other medium- or high-entropy alloys reported. The multilayers were produced from a dual source of CoCrNi MEA powder and a powder mixture of the same MEA, Al and Ti with stoichiometry (CoCrNi)86Al7Ti7, and the remarkable strength-ductility synergy is achieved only after post-L-DED heat treatment, which causes Al and Ti to diffuse across the layers to form a low-gradient HS. The significant back stress due to the HS contributes to the high strength, while the high ductility results from a high strain-hardening rate suppressing necking. This study demonstrates the concept of using AM not just as a near net-shape fabrication method but also a unique tool to produce low-gradient HSs with superb mechanical properties, via the use of multiple powder sources combined with suitable shape-preserving post-fabrication heat treatment.

Development of Composition Modulated Multilayer (NiTi) Alloy Coatings for Improved Corrosion Protection of Mild Steel

Development of Composition Modulated Multilayer (NiTi) Alloy Coatings for Improved Corrosion Protection of Mild Steel

Electrodeposition of Nickel-Tungsten Alloy with Functional Concentration Periodically Graded Material Structure for Low Stress and High Hardness

A nickel-tungsten alloy film was deposited using an electrodeposition process. The tungsten concentration in the nickel-tungsten alloy was controlled by the applied current density. The surface morphology, micro-structure, internal stress, and hardness were characterized as a single-layer structure. Hardness increased as the tungsten content increased, but micro-cracks occurred on the surface. A multi-layered structure was selected to increase the hardness without micro-cracks. The multi-layered nickel-tungsten alloy film was deposited to form two types: functional periodic materials and functional graded materials. These multi-layered structures were deposited by changing the applied current density periodically and gradually, respectively, during the deposition process. The mechanical properties, such as internal stress and hardness of the nickel-tungsten alloy, were characterized as a function of the tungsten concentration of the nickel-tungsten alloy film. As the number of periods increased, the internal stress decreased, and micro-cracks were removed from the surface. However, the gradually varied nickel-tungsten alloy had higher internal stress than the periodically varied alloy. Similar hardness was observed because the concentration of nickel-tungsten film at the top of the multi-layered structure was the same. Overall, we demonstrated enhanced mechanical properties, including low internal stress and high hardness, of concentration periodically graded nickel-tungsten alloy.

The effect of heat treatment on the microstructure and mechanical properties of multilayer AA6061 alloy fabricated by additive friction stir deposition

Multilayer AA6061 aluminum alloy components were successfully fabricated by the additive friction stir deposition (AFSD). The effect of heat treatment on the microstructure and mechanical behavior of the aluminum alloy components was studied. Due to dynamic recrystallization, AFSD AA6061 sample presented a 93.2% average reduction in grain size as compared to base material (BM) (∼ 39.13 µm). Abnormal grain growth was observed in the AFSD-HT sample, and the average grain size of AFSD-HT sample was 592 µm. There was an occurrence of texture formation in the AFSD and AFSD-HT samples, mainly due to severe shear deformation during AFSD process. The maximum texture density of AFSD-HT sample was increased to 17.84. In the BM sample, apart from the β" strengthening phases, hard-brittle intermetallic compounds of Al5FeSi aggregated along the boundaries of the coarser grains. Due to the high temperature generated during the process of AFSD, the β" strengthening phases dissolved into the matrix, and significantly reduced the strength and hardness. After heat treatment, the AFSD AA6016 alloy recovered 18% of its strength at a loss of 2.8% ductility. High density β" strengthening phases precipitated, resulting in increased strength and hardness.

The effect of heat treatment on the microstructure and electrochemical corrosion behavior of multilayer AA6061 alloy fabricated by additive friction stir deposition

Multilayer AA6061 aluminum alloy components were successfully fabricated by additive friction stir deposition (AFSD). The effect of heat treatment on the microstructure and electrochemical corrosion behavior of the AA6061-T6 aluminum alloy components was studied. The average grain size in AFSD samples was 2.67 μm, where 89.7 % of grains were smaller than 5 μm. Abnormal grain growth was observed in the heat-treated AFSD (AFSD-HT) sample, and the average grain size of AFSD-HT sample was 592 μm. In the base material (BM) sample, apart from the β″ strengthening phases, hard-brittle Al5FeSi intermetallic compounds (IMCs) aggregated along the boundaries of the coarser grains. Due to the high temperature generated during the process of AFSD, β″ phases dissolved into the matrix. After heat treatment, a larger amount of fine needle-like β″ phases were re-precipitated in the AFSD-HT sample. Al5FeSi IMCs accelerated the corrosion of the Al matrix. Fine β″ phases significantly inhibited the corrosion expansion to Al matrix and improved the corrosion resistance of AA6061 alloys.

Effect of Sn doping on low-temperature growth of Ge epilayers on half-metallic Co2FeSi

In this study, we demonstrate the low-temperature growth of a Ge layer via Sn doping in a ferromagnet/Ge/Co-based Heusler alloy multilayer on a Si(111) substrate having a vertically stacked structure. The continuous doping of 5% Sn into the Ge interlayer enables the epitaxial growth of the Ge layer on the Co-based Heusler alloy, even at ∼110 °C, and reduces the surface roughness. Elemental mapping shows that low-temperature growth via Sn doping suppresses interdiffusion at the Ge/Co-based Heusler alloy interface. The magnetic properties of the all-epitaxial CoFe/Ge/Co-based Heusler alloy structure are improved. For vertical spin-valve devices with Sn doping, the room-temperature spin signal is enhanced. These results indicate that the chemically abrupt Ge/Co-based Heusler alloy interface enhances the magnitude of the room-temperature spin signal owing to Sn-induced low-temperature growth.

Unveiling mechanisms of self-healing in CoCrFeMnNi/HfNbTaTiZr dual-phase high-entropy alloys: A molecular dynamics simulation study

This study investigates the mechanical properties and self-healing behavior of FCC CoCrFeMnNi/BCC HfNbTaTiZr dual-phase high-entropy alloy (DP-HEA) multilayers using molecular dynamics simulations. The relaxed DP-HEA multilayers have low hexagonal close-packed (HCP) percentages and decreasing "Other" fractions with increasing thickness. DP-HEA multilayers exhibit ductile behavior under uniaxial tensile loading, with stress increasing linearly until the yield strain and then gradually decreasing. Dislocation motion, twinning in the FCC phase, and BCC to HCP local structural transformation contribute to this behavior. Single crystal FCC CoCrFeMnNi and BCC HfNbTaTiZr alloys show different stress-strain responses, while DP-HEAs exhibit no significant stress drop beyond the ultimate strain. Self-healing is observed in DP-HEAs with 5 and 10 nm thickness, with a transformation from HCP to BCC structures. The DP-HEA with 15 nm thickness shows less pronounced self-healing. The interlayer distance between BCC/FCC interfaces influences the self-healing ability of the BCC phase. These findings enhance our understanding of the mechanical behavior and self-healing mechanisms in DP-HEA multilayers, facilitating the design of advanced materials with improved properties.

Friction spot welding multilayer thin Al alloy: Welding mode optimization, microstructure and mechanical properties

In this work, multilayer thin 2024 Al alloy sheets are joined by friction spot welding (FSpW). The effects of welding mode on the microstructure and mechanical properties of the joints are mainly studied. Results show that numerous tiny cracks are observed in the bonding ligament in the joint by single side FSpW, while these cracks can be eliminated by double side FSpW. In the double side FSpW joint, the grains are coarse in the joint center. The grain size increases from the top to the bottom of the joint by single side FSpW. The double side FSpW joints have obviously higher failure loads that the single side FSpW joints. The highest failure strength of 395.6 MPa is obtained at 1200 rpm by double side FSpW.

Layer-By-Layer Assembly of Atomically Precise Alloy Nanoclusters Photosystems for Solar Water Oxidation.

Atomically precise metal nanoclusters (NCs) have garnered tremendous attention as light-harvesting antennas in heterogeneous photocatalysis due to unique atomic stacking mode, quantum confinement effect, and enriched active sites. However, metal NCs as photosensitizers suffer from extremely short carrier lifetime, poor photostability, and difficulty in carrier migration, which hinder the wide-spread utilization of metal NCs in solar energy conversion. To solve these problems, herein, Ag-doped glutathione (GSH)-capped gold NCs, i.e., alloy Au1- x Agx @GSH NCs and non-conjugated insulating polymer of poly(diallyl-dimethylammonium chloride) (PDDA) are utilized as the building blocks for layer-by-layer assembly of spatially multilayered alloy NCs/metal oxide (MO) photosystems. The alternately deposited ultrathin PDDA layer in-between Au1- x Agx @GSH NCs on the MO substrate functions as an efficient charge flow mediator to relay the directional photoelectron transfer over Au1- x Agx @GSH NCs, giving rise to the cascade charge transfer chain. This peculiar carrier migration mode endowed by exquisite interface configuration design significantly boosts the unidirectional electron migration from the Au1- x Agx @GSH NCs to the MO substrate, substantially improving the visible-light-driven photoelectrochemical water oxidation performances of MO/(PDDA-Au1- x Agx )n multilayer heterostructured photoanodes. The work will inspire the rational construction of alloy metal NCs-based photosystems for modulating spatially controllable charge transfer pathway for solar energy conversion.

Effect of square pulse current densities on anticorrosive behavior of Ni–Zn multilayer deposited coatings on mild steel

This paper reports the production of Ni–Zn multilayer alloy coating to improve the anticorrosive behavior of the mild steel material. The deposition technique follows the square wave current pulse technique. Initially, the effect of current densities on the anticorrosive behavior of the Ni–Zn was investigated. Later, the current densities were optimized in different combinations to get a multilayer of Ni–Zn with different degrees of layering. The Ni–Zn multilayer coatings were developed on the surface of mild steel with different numbers of layers by square pulsing current density of 1 Adm−2 and 3 Adm−2. The deposited Ni–Zn alloy coating was studied for its electrochemical behavior toward corrosion. Results revealed that the anticorrosive behavior of the multilayer Ni–Zn alloy coating was found to be many folds higher than that of monolayer Ni–Zn alloy coating. The comparison study of corrosion data revealed that (Ni–Zn)1/3/300 multilayer coatings are less prone to undergo corrosion among all developed monolayer and multilayer coatings. The corrosion rate of (Ni–Zn)1/3/300 was found to be less and in the range of 0.37 mm year−1 among all developed coatings.

Designing composition ratio of magnetic alloy multilayer for transverse thermoelectric conversion by Bayesian optimization

We demonstrated the effectiveness of the machine learning method combined with first-principles calculations for the enhancement of the anomalous Nernst effect (ANE) of multilayers. The composition ratio of CoNi homogeneous alloy superlattices was optimized by Bayesian optimization so as to maximize the transverse thermoelectric conductivity (αxy). The nonintuitive optimal composition with a large αxy of ∼10 A K−1 m−1 was identified through the two-step Bayesian optimization using rough and fine candidate pools. The Berry curvature and band dispersion analyses revealed that αxy is enhanced by the appearance of the flat band near the Fermi level due to the multilayer formation. The magnitude of the energy derivative of the anomalous Hall conductivity increases owing to the large Berry curvature near the flat band along the R-M high symmetry line, which emerges only in the optimized superlattice, leading to the αxy enhancement. The effective method verified here will broaden the choices of ANE materials to more complex systems and, therefore, lead to the development of transverse thermoelectric conversion technologies.

Structural Properties of Zn-Fe Alloy Coatings and Their Corrosion Resistance

Single-layer and multilayer alloy deposits were coated onto a mild steel substrate by a single-bath electroplating process. The developed coating consists of Zn and Fe alloys having different compositions with different layers. The anticorrosion behavior of single-layer and multilayer deposits was evaluated by the potentiodynamic polarization method. The surface morphology of the deposits was studied with a scanning electron microscope. The crystal structure of the deposits was analyzed with the X-ray diffraction technique. The Fe content in the deposit was analyzed by a colorimeter and verified with energy-dispersive X-ray spectroscopy. The micro-hardness tester with a Vickers indenter was used to evaluate the microhardness of the developed single-layer and multilayer coatings. It was found that the microhardness increased with applied current densities. The Zn-Fe multilayer coatings with 300 layers deposited with square and triangular pulses at the applied current density of 2.0/3.0 A dm−2 were five and four times more corrosion-resistant, respectively, than the single-layer coating of the same thickness. The development of Zn-Fe coatings that are resistant to corrosion is particularly important for the automotive industry and steel-based vehicle parts.

The enhancement of mechanical properties and uniform degradation of electrodeposited Fe-Zn alloys by multilayered design for biodegradable stent applications.

Pure Fe is a potential biodegradable stent material due to its better biocompatibility and mechanical properties, but its degradation rate needs to be improved. Alloying with Zn to form Fe-Zn alloy is anticipated to meet the degradation rate requirements while retaining the iron's inherent properties. Therefore, Fe-Zn alloys with monolayered and multilayered structures were prepared by electrodeposition. The alloys' composition, microstructure, mechanical properties, in vitro degradation and biocompatibility were assessed. Results showed that the Zn content ranged from 2.1 wt% to 11.6 wt%. After annealing at 450°C, all the alloys consisted of α(Fe) solid solution and Zn-rich B2 ordered coherent phase, except for the alloy with 11.6 wt% Zn content, in which a Fe3Zn10 phase appeared. The layered structure consisted of alternating columnar-grain and nano-grain layers, which compensated for the intrinsic brittleness of electrodeposited metals and improved the galvanic effect of the alloy, thus increasing the strength and plasticity and changing the corrosion from localized to uniform while augmenting the corrosion rate. The yield strength of the multilayered alloy exceeded 350 MPa, its elongation was more than 20%, and its corrosion rate obtained by immersion test in Hank's solution reached 0.367 mm·y-1. Fe-Zn alloys with lower Zn content had good cytocompatibility with the human umbilical vein endothelial cells and good blood compatibility. The above results verified that the multilayered Fe-Zn alloy prepared by electrodeposition presented enhanced mechanical properties, higher degradation rate, uniform degradation mechanism and good biocompatibility. It should be qualified for the application of biodegradable stents. STATEMENT OF SIGNIFICANCE: A potential biodegradable Fe-Zn alloy, which is difficult to be obtained by the metallurgical method, was prepared by electrodeposition to solve the low degradation rate of iron-based biomaterials. A multilayered microstructure design composed of alternating columnar-grain and nano-grain layers was achieved by changing the electrical parameters. The layered design compensated for the intrinsic poor plasticity of electrodeposited metals. It increased the galvanic effect of the alloy, thus augmenting the corrosion rate and changing the corrosion mode of the alloy from localized to uniform corrosion. The yield strength of multilayered alloy exceeded 350 MPa; its elongation was more than 20%. Moreover, the layered alloy had good cytocompatibility and blood compatibility. It indicates that the alloy is qualified for biodegradable stent application.

The Fabrication and SERS Performance of Multi-layer Hollow Au-Ag Alloy Nano Urchins Structure-based SERS Fiber Probe

The Fabrication and SERS Performance of Multi-layer Hollow Au-Ag Alloy Nano Urchins Structure-based SERS Fiber Probe

Numerical and experimental investigation of probeless friction stir spot welding of a multilayer aluminium alloy compound

This paper presents the experimental and numerical results of the influence of dwell time (30, 60, 90 s), down force (2450, 4900, 7350 N), and rotational speed (1000, 1500, 2000 RPM) on microstructure, microhardness, and material flow during solid-state welding. Probeless friction stir spot welding (P-FSSW) with a flat tool shoulder was assisted to form a metal compound of AA2024, AA6082, and AA5754 aluminium plates with different thicknesses in lap configuration. The analysis of the experimental data and numerical results showed that down force had a significant influence on the material flow and the quality of the welds. High friction energy, and subsequent intensive material flow, promoted the vortexes formation, which improve metals mixing and grain refinements.

Vacancies-mediated atomic diffusion controlled by the interfacial structure of FCC/BCC HEA multilayers

The radiation-induced segregation is one of the major concerns for nuclear materials, as it can damage the service performance of the material. Eutectic high entropy alloy (HEA) multilayer is considered a potential nuclear material for improving the irradiation tolerance of materials, due to its outstanding irradiation tolerance and mechanical properties. Abundant heterogeneous interfaces in eutectic HEA multilayer can interact with irradiation-induced vacancies, thus resulting in changes in the behavior of atomic diffusion and segregation. In the current work, to explore the effects of the heterogeneous interfacial structure on atomic diffusion and segregation, we have investigated the evolution of the elemental distribution in FCC/BCC HEA multilayers with coherent and semicoherent interfaces under vacancy flow in detail. It is found that the segregation and atomic diffusion behaviors of eutectic HEA multilayer are sensitive to the heterogeneous interfacial structure. The semicoherent interface promotes the interface diffusion and interface segregation due to the vacancy annihilation at interface and the intrinsic excess volume of interface. Whereas, the coherent interface is benifcial to the intragranular diffusion because it is transparent for the diffusion of vacancy.

Live-current electrodeposition of Nickel on Zinc from modified Watt’s bath

ABSTRACT The zinc-nickel alloy coating has a better combination of corrosion and wear resistance compared to galvanised steel. Electrodeposition of multilayer zinc-nickel alloy coating on steel is an important industrial process. However, in the case of multilayer deposition, the plating of nickel over the zinc layer has an inherent problem owing to the corrosion of zinc in the conventional acidic nickel electrolytes. Conventionally a copper strike layer is introduced over zinc followed by nickel electroplating. The present work aims at understanding the effect of both Ni2+ ion concentration and live currents on the feasibility and quality of Ni deposition on Zn from a modified Watt’s bath such that nickel can be directly deposited on zinc without a copper strike layer. The coating appearance, thickness and roughness are found to be strongly dependent on nickel-iron concentration and the extent of live current which prevent Zn corrosion by offering cathodic protection while simultaneously depositing nickel on zinc.