Alloy Layer Research Articles

Low contact resistivity and excellent thermal stability of p‐type YbMg0.8Zn1.2Sb2/Fe‐Sb junction for thermoelectric applications

1-2-2 Zintl phase compound is a promising thermoelectric material and holds potential for thermoelectric applications. Currently, there are many reports on Zintl-phase thermoelectric materials with high zT values. However, studies on the contact materials for the Zintl phase compounds have seldom been reported. Herein, an ohmic contact is realized in the YbMg0.8Zn1.2Sb2/Fe junction with a contact resistivity of less than 1 μΩ cm2. The microstructural analysis shows that the interface reaction layer is composed of a Fe-Sb alloy layer and a Sb-poor Zintl layer. After 400 h of annealing at 773 K, the contact resistivity increased to ∼5.69 μΩ cm2 due to the increased thickness of the Sb-poor layer and the decreased Sb content in the Sb-poor layer. To suppress the diffusion of the Sb element, the Fe-Sb layer with the nominal composition of Fe90Sb10 is chosen as the contact material. Our results show that the junction of YbMg0.8Zn1.2Sb2/Fe-Sb exhibits an extremely low contact resistivity, an excellent thermal stability, and good mechanical properties.

Effect of rotation rate on microstructure and mechanical properties of CMT cladding layer of AZ91 magnesium alloy fabricated by friction stir processing

Cladding layers of AZ91 magnesium alloy obtained by cold metal transfer (CMT) technique were subjected to friction stir processing (FSP) with different rotation rates. The experimental results showed that the FSP could significantly refine the crystal grains of the cladding layer, and cause the coarse second phases to be crushed and dissolved into the α-Mg matrix at the same time. As the rotation rate increased, the peak temperature of the stirring zone gradually increased, leading to an increase in the average grain size of the stirring zone. There was no obvious difference in the distribution of the second phase, all of which were dispersed into the α-Mg matrix in the form of granules. Compared with the cladding layer before FSP, the microhardness and tensile properties of the processed cladding layer under each parameter were both significantly improved due to the combined effects of fine-grain strengthening and second phase dispersion strengthening. In addition, the average microhardness, tensile strength and elongation of the stirring zone all increased first, and then decreased with the increase of the rotation rate.

Inhibition effect on microbiologically influenced corrosion of Ti-6Al-4V-5Cu alloy against marine bacterium Pseudomonas aeruginosa

With rapid development of marine infrastructures, materials with better biocorrosion resistance and antibiofouling performance will be highly demanded. Ti6Al4V alloy is susceptible to the above. The inhibition to the microbiologically influenced corrosion of Ti6Al4V-5Cu alloy against Pseudomonas aeruginosa was investigated using antibacterial test, electrochemical techniques, surface analysis, and weight loss test conducted for 2.5 months. At a sputtering depth of 0 nm, the passive film of Ti6Al4V-5Cu alloy was mainly composed of ideal oxide TiO2. With increasing sputtering thickness to 6 nm, Ti2O3 and TiO were detected with a relative fraction of 14.6% and 14.8%, respectively, in the oxide layer of Ti6Al4V-5Cu alloy. In contrast, the outermost layer of Ti6Al4V alloy was predominantly composed of TiO2 but Ti2O3 (22.8%), Al2O3 and V2O5 were also detected. With increasing sputtering depth to 6 nm, fitting revealed the presence of Ti2O3 and TiO with relative fractions of 25.3% and 35.8%, respectively. Yet, a spot of TiO (8%) was also observed at 12 nm in the oxide layer of Ti6Al4V alloy. Although the addition of Cu into Ti6Al4V alloy generated the self-healing property of passive film in the presence of P. aeruginosa, it also reduced resistance to corrosion in general condition.

Effect of Silicon on the Oxidation Kinetics and Microstructure of the Surface Layer of TaCr2 Alloys Obtained by Vacuum Hot Pressing

Effect of Silicon on the Oxidation Kinetics and Microstructure of the Surface Layer of TaCr2 Alloys Obtained by Vacuum Hot Pressing

Development of advanced cold crucible melting of titanium alloys

Cold crucible is used to melt reactive metal scrap at elevated temperatures for high quality castings or to produce spherical powders for additive manufacturing. The most advanced crucibles have a small exit nozzle to pour the molten alloy through the bottom opening protected by graphite or ceramic material. The nozzle operates at high temperature and typically lasts several minutes, possibly adding contamination to the outflowing liquid metal. This paper presents new efforts to improve the technique with the aim to achieve a stable commercial process by introducing melting of scrap metal in the presence of liquid flux of different compositions to purify the liquid metal and to enhance thermal effectiveness. The crucial modification in avoiding contamination is a new type of the non-consumable nozzle made of copper segments and the second coil to supply a high frequency electromagnetic field in the vicinity of the nozzle. The nozzle entrance is protected by a thin solidified layer of the same alloy as the main melt. The AC electromagnetic field adds heating at the outflow, modifies the velocity field, gives a possibility to extract particles, and precludes entrainment of slag into the final casting or into the produced powder. The electromagnetic force permits to control the outflow rate and to increase the superheat of the metal at the outlet. The presence of flux permits shielding of the liquid metal from direct contact with the water-cooled side segments of the crucible. The paper demonstrates the effectiveness of numerical modelling to predict and investigate a variety of options in advancement of the cold crucible technique. Figs 8, Refs 13.

Visualization of Band Shifting and Interlayer Coupling in WxMo1–xS2 Alloys Using Near-Field Broadband Absorption Microscopy

Beyond-diffraction-limit optical absorption spectroscopy provides in-depth information on the graded band structures of composition-spread and stacked two-dimensional materials, in which direct/indirect bandgap, interlayer coupling, and defects significantly modify their optoelectronic functionalities such as photoluminescence efficiency. We here visualize the spatially varying band structure of monolayer and bilayer transition metal dichalcogenide alloys by using near-field broadband absorption microscopy. The near-field spectral and spatial information manifests the excitonic band shift that results from the interplay of composition spreading and interlayer coupling. These results enable us to identify, notably, the top layer of the bilayer alloy as pure WS2. We also use the aberration-free near-field transmission images to demarcate the exact boundaries of alloyed and pure transition metal dichalcogenides. This technology can offer valuable insights on various layered structures in the era of "stacking science" in the quest of quantum optoelectronic devices.

One-Pot Preparation of Lithium Compensation Layer, Lithiophilic Layer, and Artificial Solid Electrolyte Interphase for Lean-Lithium Metal Anode.

Lithium metal is an ideal anode for high-energy-density batteries. However, the low Coulomb efficiency and the generation of dendrites pose a significant limitation to its practical application, while the excess lithium in the battery also generates serious safety concerns. Herein, a layer-by-layer optimized multilayer structure integrating an artificial solid electrolyte interphase (LiF) layer, a lithiophilic (LixAu alloy) layer, and a lithium compensation layer is reported for a lean-lithium metal battery, where each layer acts synergistically to stabilize the lithium deposition behaviors and enhances the cycling performance of the battery. The optimized anode could effectively induce homogeneous reversible lithium deposition under the synergistic effect of multilayer films and keep the integrity of the morphological structure unbroken during the deposition. The presence of the lithium compensation layer allows the half-cell to have a high initial CE of 158.9%, and the action of the LiF layer and lithiophilic layer maintains an average CE of 98.8% over 160 cycles, which further demonstrates the stability of the structure. As a result, when combined with LiFePO4 cathode, an initial capacity of 148 mAh g-1 and a retention rate of 97.5% over 130 cycles were achieved.

Study of surface layers of VT41 titanium alloy after mechanical treatment

The work studies residual stresses in the surface layer, roughness of flat surfaces of titanium alloy VT41 sample, obtained by milling with end mills, as well as conditions for relieving these stresses by means of incomplete annealing. The milling was carried out on a universal vertical milling machine, varying the conditions of the machining allowance in one pass and the cutters.

ОЦЕНОЧНЫЙ РАСЧЕТ ДЕФОРМАЦИЙ И НАПРЯЖЕНИЙ ПРИ ДУГОВОЙ НАПЛАВКЕ СЛОЯ КОРРОЗИОННОСТОЙКОГО СПЛАВА НА СТАЛЬНУЮ ПОВЕРХНОСТЬ

The study objective is to estimate the deformations and stresses that occur when a layer of corrosion-resistant alloy is deposited on a steel surface.
 The problem to which the paper is devoted is to analyze deformations and stresses in the surfaced layer.
 The research method is computer simulation of forming the state of the surfaced layer.
 The novelty of the work is to develop a method for estimating deformations during sequential surfacing of layer beads.
 Study results: the methodology for estimating the stress state and deformations in the surfaced layer is based on solving the equation of compatibility of displacements resulting from multiple heating and cooling of metal during sequential surfacing of beads. 
 Conclusions: it is shown that with multi-bead surfacing, there is an accumulation of plastic deformation in the layers of contact of the surfaced beads, which reaches values that are equal to relative elongation; it is possible to apply the described technique in engineering practice when developing surfacing technology.

A multifunctional nano filler for solid polymer electrolyte toward stable cycling for lithium-metal anodes in lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are considered as very promising energy storage systems due to their higher theoretical performance and lower active material cost. However, the notorious shuttle effect and lithium dendrite growth have severely restricted the industrial production of Li–S batteries. In this study, we used polyethylene oxide (PEO) as the matrix and added multifunctional nanofillers (nano In2O3) to effectively inhibit the shuttle effect caused by the dissolution of lithium polysulphides (LiPSs) in Li–S batteries. As a multifunctional filler, nano-In2O3 not only improves the ionic conductivity of the PEO electrolyte, but also forms a Li–In alloy layer in situ at the polymer/anode interface, which can cause the rapid diffusion of lithium ions and prevent the side reactions between lithium metal anode and the electrolyte. Achieving the effect of stabilizing the lithium metal anode and suppressing the shuttle effect. Multiple problems in the system are solved by introducing a single component with multiple functions. The symmetrical lithium battery based on the PEO/LiTFSI/In2O3 solid polymer electrolyte (PEO/LiTFSI/In2O3 SPE) has higher cycle stability (over 1200 h) because it is more stable to the lithium metal anode. The Li–S full battery also exhibits excellent electrochemical performance. After 500 cycles at 1C, its capacity can be maintained at 570 mAh g−1, the capacity decay rate is 0.038%. The coulombic efficiency (CE) during the cycle is also close 100%.

Study on the mechanical properties gradient in surface oxygen diffusion hardened layer of Ti6Al4V alloy

This paper studies the mechanical properties gradient in surface oxygen diffusion hardened (SODH) layer of Ti6Al4V alloy by four-point bending test, nano-indentation test and Vickers hardness measurement test. The relationships of hardness-oxygen content and hardness-yield stress were also investigated. Tests results show that the outmost ≈25 μm deep surface layer has the highest oxygen content, hardness and yield strength under compression monotonic loading but the lowest cracking strength before yielding under tension loading. However, from ≈50 μm deep position to substrate, the yield strengths under tensile and compressive loading are almost the same. Test result also shows that, with further decrease of oxygen content deeper down in the SODH layer, the hardness and yield strength decrease correspondingly. It is also found that there are linear relationships between oxygen content and Vickers hardness or nano-hardness. The above relationships can be used to estimate the oxygen concentration distribution in the SODH layer by the simple test method of hardness measurement. Since the yield stress also has a linear relationship with hardness, a valid estimate of the yield stress distribution in SODH layer can be obtained as well. The high hardness and compressive yield strength but low cracking tensile strength of the outmost ≈25 μm depth SODH layer can be employed to explain why surface oxygen diffusion treatment can improve greatly the wear resistance of titanium alloy but reduce its tensile mechanical properties and fatigue resistance.

Wet metallization of 3D printed microarchitectures: Application to the manufacturing of bioinspired microswimmers

Untethered microswimmers have been recently proposed as possible candidates for a wealth of biomedical and environmental applications. In view of their translation from laboratory experimentation to clinical practice, it is fundamental to identify low-cost, scalable and flexible manufacturing approaches. The production method explored in the present paper, which responds to all these requirements, consists of a smart combination of two-photon lithography (2PL) and wet metallization. Fully functional bioinspired artificial bacterial flagella (ABFs) are successfully 3D printed following a user-defined model and made magnetically active by depositing a layer of CoNiP alloy on their surface via electroless deposition. In contrast with existing ABFs metallization approaches based on metal evaporation, electroless deposition does not suffer from the shadowing effect, and it can be employed to easily plate hard-magnetic alloys. The specific challenges of the application of electroless plating to the metallization of 2PL printed polymeric templates are identified, discussed and addressed. The manuscript also explores the possibility to impart multiple functionalities to the 3D printed microstructures by applying multiple metallic layers on their surface. Besides the applicative example of ABFs, the metallization methodology presented can be potentially used for the metallization of a great variety of 2PL printed microarchitectures for many possible applications.

Impact damage to fibre metal laminates under compression loading

The effect of in-plane compression loading on the low energy impact response of fibre metal laminates (FML) is investigated. A GLARE®-like FML consisting of bonded layers of aluminium alloy and glass-epoxy composite was impacted at different incident energy levels (up to ∼20 J) while under different axial compression strain levels (up to 8000 μe). Experimental testing and finite element (FE) analysis reveal that compression preloading increases (up to 50%) the maximum impact force experienced by the FML due to shortening of the impact contact time. The out-of-plane deformation of the FML, the amount of plasticity damage to the aluminium layers, and the shape and size of delamination damage to the glass-epoxy layer are dependent on the compression strain level. The FE model predicted the impact response and impact damage to the FML. The FE model is a validated numerical tool to analyse the low energy impact response of FMLs used in compression load-bearing structures.

Optimisation of the bore reaming process in hybrid stacks made of carbon fibre and metal alloys

The present work aims to improve the existing technology of reaming bores in hybrid stacks containing a composite material interlayered with titanium and aluminium alloys. The study was conducted using statistical approaches at the stages of experimental design and data processing in the Statistica 6 and Microsoft Excel 2010 software. The bore roughness was measured using a Taylor Hobson Form Talysurf i200 contact profilometer. The height of the tool build-up edge was investigated using a Bruker ContourGT-K1 optical profilometer. Bore diameters were determined using a Carl Zeiss Contura G2 coordinate measuring machine. An experimental study was carried out using an Atlas Copco PFD-1500 automatic feed drilling unit and a 14 mm MAPAL reamer with a replaceable head. A methodology for a comprehensive experimental study of boring and reaming processes in the “OT4 titanium alloy - VT6 titanium alloy - polymeric composite materials - VT6 titanium alloy - 1933 aluminium alloy” hybrid stack was developed and implemented. It was found that the most significant factors affecting the parameters of bore accuracy, in particular, the deviation from the true bore longitudinal section profile, include the cutting speed in the first and the second degree, as well as the feed. The optimum cutting modes are a cutting speed of 7.24 m/min, a feed of 0.27 mm/rev and a machining allowance of 0.5 mm. As a result, the time of reaming one bore is reduced by 4.6 times. The optimum cooling method, ensuring the increased accuracy and reduced roughness of the bore in the aluminium alloy layer, is cooling by carbon dioxide at a temperature of -56.5°C. As a result of experimental works, basic laws governing the boring and reaming processes in multicomponent hybrid stacks composed by carbon-fibre-reinforced plastics with titanium and aluminium alloys were investigated.

Large-scale sodiophilic/buffered alloy architecture enables deeply cyclable Na metal anodes

The application of Na metal anodes is hindered by the formation of dendrites, which evolves from the initial heterogeneous nucleation. The construction of sodiophilic pure metal layers on substrates can partly improve Na deposition behavior, but huge volume change during the repetitive alloy/dealloy process renders their rapid failure, especially under the high depth of discharge. Inspired by the assets of alloy anodes compared with monometallic anodes in Li/Na ion batteries, a Cu6Sn5 alloy layer is constructed on commercial Cu foils with a huge size of 850 mm × 650 mm via a facile electroless Sn plating approach. The sodiophilic Sn phase can alloy with Na and contribute to an ultralow nucleation overpotential as well as dendrite-free morphology. Meanwhile, the inactive Cu phase acts as buffer media to mitigate the internal stress and volume change induced by the alloy reaction, which prevents the alloy layer from peeling. Based on these synergetic effects, the Cu6Sn5 alloy coated Cu current collector gives rise to a highly prolonged Coulombic efficiency (99.84%) for 2000 cycles and 600 h lifetime under an ultrahigh depth of discharge (80%), which is superior to those of single Sn metal-coated Cu current collector. Furthermore, the full cells coupled with FeS2 cathode can stably operate for 1500 cycles with a decent capacity retention of ∼ 95%.

Highly reversible Mg metal anodes enabled by interfacial liquid metal engineering for high-energy Mg-S batteries

Metallic Mg is a promising anode material for rechargeable magnesium-ion batteries (MIBs) due to its low electrochemical potential and high theoretical capacity. However, low Mg2+ conductivity on the interface of Mg electrode caused by liquid electrolyte passivation hinders its development. In addition, whether Mg dendrites can be formed in Mg metal anodes is controversial. Herein, we find that Mg dendrites can be formed in Mg metal anodes. The diameter of most Mg dendrites is below 100 nm, which is much smaller than Li and Na dendrites. The nanoscale Mg dendrites can easily pierce through the separators with large pore size and cause the internal short circuit of batteries. A simple strategy is proposed to address the issues of Mg metal anodes by painting a liquid metal Ga layer on Mg foil. Metallic Ga can spontaneously alloy with metallic Mg to form a stable, Mg2+-conductive, corrosive-resistant, and magnesiophilic Ga5Mg2 alloy layer. Under the regulation of the Ga5Mg2 alloy layer, a highly reversible, stable, and dendrite-free Mg metal anode is obtained. Enhanced electrochemical performance is achieved both in symmetric cells and Mg-S full cells. This study paves the way for high-energy Mg-metal batteries.

High entropic coatings FeCrNiTiZrAl and their properties

In our proposed empirical model, the anisotropy of the surface energy and the thickness of the surface layer of the high-entropy FeCrNiTiZrAl alloy are calculated. The thickness of the surface layer of this alloy is about 2 nm, which is an order of magnitude greater than the thickness of the surface layer of complex crystals, but is of the same order of magnitude as that of metallic glasses. The hardness and other properties of the high-entropy alloy are the same as for metallic glasses, but are 2-3 times higher than the hardness of stainless steels. The surface energy of the high-entropy FeCrNiTiZrAl alloy is about 2 J/m2, which corresponds to the surface energy of magnesium oxide and other crystals with a high melting point. However, unlike these crystals, the friction coefficients of a high-entropy alloy (~ 0.06) are much lower than that of ordinary steels (~0.8). We have theoretically shown that the friction coefficient is proportionally dependent on the surface energy and inversely proportional to the Gibbs energy, which significantly decreases for a high-entropy alloy, leading to low friction. The high hardness and low coefficient of friction of the high-entropy alloy facilitates the deposition of coatings from them on structural metal products, which contributes to their widespread use.

Gradient microstructure evolution in laser shock peened Ti6Al4V titanium alloy

The microstructures at different depths of Ti6Al4V alloy induced by laser shock peening (LSP) are comprehensively characterized using TEM, EBSD and XRD. The results show that LSP can introduce a gradient microstructure in the surface layer of Ti6Al4V alloy. The evolution mechanism of this gradient microstructure is elucidated. To explore the intrinsic relationship between gradient microstructure and mechanical properties, the corresponding microhardness values are estimated based on the microstructure at different depths. Besides, the synergistic strengthening mechanism of the gradient microstructure is revealed.

Determining alloyed layer thickness in electric discharge alloying by inverse estimation of energy distribution

Electric discharge alloying (EDA) is an important surface modification process, however, accurate determination of alloyed layer thickness is essential for effective utilization of this process in the industry. The spark energy distribution among the tool and workpiece controls alloyed layer thickness. In this work, a novel method is developed for accurate and quick determination of alloyed layer thickness through inverse estimation of energy distribution factor. A nonlinear transient finite element method based direct numerical model is developed for the analysis of EDA. The inverse estimation of the energy distribution factor is carried out by reducing the difference between actual and direct model computed data. For this purpose, an integrated finite element method–artificial neural network based method is developed. Physical experiments at the shop floor were also performed, which suggested that the inversely obtained energy distribution factor is sufficiently accurate in estimating the alloyed layer thickness at changed operating conditions.

WC-High Entropy Alloy Reinforced Long Life Self-Grinding Silage Knife Prepared by Laser Cladding.

The working environment of agricultural knives is bad, which makes the knives wear out easily. A wear resistant layer of AlCoCrFeNi high entropy alloy (HEA) reinforced by tungsten carbide (WC) was prepared by laser cladding on one side of the cutting edge of a 65 Mn silage knife. Both the effects of WC addition on the microstructure and mechanical properties of AlCoCrFeNi (WC)x (x = 0, 0.1, 0.2 and 0.3 in mass percentage) alloys were investigated. All experimental alloys displayed a crystalline structure of simple body centered cubic (BCC). The hardness of the cladding layer increases with the increase of WC content, and the hardness value enhances from 740 HV0.2 to 1060 HV0.2. A self-grinding edge was formed during working for the cladded knives. The cutting quality can be improved and the service life of agricultural knives can be increased meanwhile. The weight loss rate of untreated knives was about 2.64 times that of the cladded knives after a 76 h field experiment.