Alloy Layer Research Articles

Study on laser cladding system of the high-entropy alloy layer on the AZ91D magnesium

A new type of composite layer material system, Al4Ni/Al2CrCuFeNi2Ti high-entropy alloy, was designed. The Al4Ni transition layer was prepared on the surface of an AZ91D magnesium alloy by laser cladding, which solves the problem of excessive melting point difference between the magnesium alloy and the high-entropy alloy. The Al4Ni/Al2CrCuFeNi2Ti high-entropy alloy composite layer with good surface formation was successfully prepared on the AZ91D magnesium matrix. Optical microscope, scanning electron microscope, and x-ray diffraction were used to characterize the microstructure and properties of the composite layer. It showed that the high-entropy alloy layer was mainly composed of simple BCC and FCC solid solution phases. The Al2CrCuFeNi2Ti high-entropy alloy layer, the Al4Ni layer, and the AZ91D magnesium matrix have excellent metallurgical bonds. The hardness of the high-entropy alloy layer was about 12 times that of the AZ91D magnesium alloy. The corrosion resistance of the high-entropy alloy layer in 3.5 wt. % NaCl was also improved.

Ultra-stable Zn metal batteries with dendrite-free Cu-Sn alloy induced high-quality composite Zn mesh

Aqueous zinc ion battery with high security and lost cost has been a promising storage energy device, which is hampered by the dendrite formation on Zn anode. Utilizing three-dimension (3D) substrates is a valid method to suppress dendrites through reducing local current density. Yet, they are also confronted with the issue of uneven deposition. Herein, a low-nucleation-barrier Cu-Sn alloy layer on a stainless-steel mesh (Cu-Sn@SSM) is constructed firstly by a facile co-electrodeposition strategy to eliminate the dendrites formation. The Cu-Sn alloy can easily compound with Zn and changes into Cu-Zn alloy and Sn metal, thus realizing the homogenization of ion distribution and the densification of Zn deposition. As a result, the Cu-Sn@SSM scaffold delivers remarkable Coulombic efficiency (99.4 % for more than 2000 cycles) with an appreciably low nucleation potential of 1 mV at a high current density of 10 mA cm−2. Such high-quality Zn mesh (Zn@Cu-Sn@SSM) exhibits improved uniformity of Zn plating and effective inhibition of side reactions. A long lifespan of more than 1050 h at 10 mA cm−2 with a capacity of 3 mAh cm−2 can be achieved in Zn@Cu-Sn@SSM symmetric cell. Notably, when pairing with NVO cathode, the full battery renders a capacity of 162 mAh/g after 1000 cycles at 2 A/g (vs evident capacity decay and only 400 cycles for the counterpart with Zn@SSM).

Reaction mechanism of Ca-reduction diffusion process used for sustainable recycling Nd-Fe-B sludge

The reduction diffusion (RD) process for Nd-Fe-B sludge has been reported as a green and efficient method for synthesizing recycled Nd2Fe14B magnetic powders. In this work, recycled Nd-Fe-B powders with low impurity content and uniform particle size distribution were successfully prepared. M3 T increased to 146.25 emu/g, which was about 17% and 32% higher than the purged and original sludge, respectively. Then, the recycled Nd-Fe-B sintered magnets with properties of Br = 12.14 kG, Hcj = 12.00 kOe, and (BH)m = 35.05 MGOe were successfully prepared by doping with 37.70 wt% Nd4Fe14B powders. Based on experimental studies of calcium thermal reduction of Nd-Fe-B sludge and thermo-kinetic analysis, the reaction mechanism of the RD method for sludge waste recovery was clarified. In the RD process, the oxides in the sludge were selectively reduced by Ca at 600–950 °C and the reduced Nd diffused to the surface of the Fe core, forming the Nd-Fe-B alloy, where the formation process included the nucleation stage, the alloy layer high-speed growth stage, and the completion stage. And the relationship between the alloy layer thickness and time during the high-speed growth period of 1–3 h was more in line with linear law (d = 5.41 t–4.31). The RD reaction conformed to the unreacted shrinking core model, and its reaction rate control step consisted of a one-way diffusion process for the diffusion of Nd into the Fe core.

Microstructures and mechanical properties of A356-SiCp/A356 cladding composite materials prepared by vacuum Solid–Liquid casting

A356-SiCp/A356 cladding composite materials were prepared by vacuum solid–liquid casting. The interfacial bonding, microstructure, and mechanical properties of this cladding composite material were investigated. The microstructures indicated that there was a good metallurgical combination interface between A356 and SiCp/A356 of the cladding composite material. The tensile tests showed that the bonding strength of the interface was lower than that of the two materials, but fracture occurred on the A356 side as the macrointerface perpendicular to load, while the tensile strength of A356 was higher than that of the cladding composite material. This fracture phenomenon could be explained by the remelt mechanism and grain coarsing mechanism. As a result of the topmost layer of the A356 alloy in contact with the SiCp/A356 composite slurry being remelted when the SiCp/A356 composite slurry was poured, an inseparable metallurgical combination interface was formed, and α-Al grains and eutectic Si on the A356 side near the interface were coarser than those on the interface. The results of this research can provide a reference for manufacturing automotive brake discs with cladding composite materials.

Site-specific preparation of plan-view samples with large field of view for atomic resolution STEM and TEM studies of rapidly solidified multi-phase Al Cu thin films

The present work describes application of a method for site-specific plan-view sample preparation for atomic column resolution scanning transmission and transmission electron microscopy (STEM and TEM) from free-standing thin films of multi-phase Al-alloys after laser irradiation induced rapid solidification (RS). The electron-transparent multilayer thin film samples (amorphous Si3N4 substrate plus metal alloy layer) had a total initial thickness of ≈ 130–200 nm. At such large total sample thickness frequently multiple grains of the same or different phases overlap along the electron beam path in the RS microstructures of the alloys. Consequently, accurate atomic resolution images in TEM and STEM mode, and composition sensitive analytical data of the metastable microstructural features presenting in the RS microstructures cannot be obtained with confidence. Using low-energy concentrated Ar ion beam milling, locally thinned regions with thickness of 20–30 nm with large fields of view ≥ (30 μm)2 suitable for high-resolution TEM/STEM studies have been created with micron-scale site-specificity. As example application, atomic scale resolution TEM/STEM imaging has been performed of the banded grain regions of the RS microstructure established in multi-phase AlCu alloy thin films. The sample preparation strategy described here appears to be readily applicable to freestanding thin film specimens in general.

The growth and corrosion mechanism of Zn-based coating on AZ31 magnesium alloys by novel hot-dip process

A Zn-based coating with excellent corrosion resistance was prepared on the surface of AZ31 magnesium alloy by novel hot-dip process. The microstructure, growth process and corrosion mechanism of coatings were investigated. The results show that good metallurgical bonding and integrated multi-layer phase structure were observed in coatings with sufficient immersion time. This multi-layer phase structure is divided roughly into an alloy layer consisting of Zn + Mg2Zn11 + MgZn2 phases and a diffusion layer consisting of MgZn + Mg7Zn3 phase, which is mainly attributed to the diffusion reaction of Zn and Mg atoms and the subsequent solidification. Furthermore, the corrosion resistance of coated AZ31 is dramatically improved, the low frequency value of the coated AZ31 up to 3541 Ω cm2, more than 90 times higher than bare AZ31 which is 38.1 Ω cm2, the icorr of 4 s coating is 1.948 × 10−5 A cm−2, reduced to 6.6% of bare AZ31 which is 2.895 × 10−4 A cm−2. The outstanding corrosion performance is mainly due to an effective barrier to Mg matrix by the dense multi-layer structure and the compact corrosion products.

Strain compensated type II superlattices grown by molecular beam epitaxy

We investigate a strain compensation method for the growth of complex interband cascade laser structures. For thick InAs/AlSb superlattice clad layers, the sublayer thicknesses were adjusted so that the tensile strain energy in the InAs sublayer was equal to the compressive strain energy in the AlSb sublayer. For the four-constituent active region, as the compressive strain in the Ga0.65In0.35Sb alloy layer was large, a tensile strain was incorporated in the chirped InAs/AlSb superlattice region for strain compensation to the Ga0.65In0.35Sb alloy. A laser structure of thickness 6 μm was grown on the GaSb substrate by molecular beam epitaxy. The wafer exhibited good surface morphology and high crystalline quality.

Fast ion diffusion alloy layer facilitating 3D mesh substrate for dendrite-free zinc-ion hybrid capacitors

Although aqueous zinc ion hybrid capacitors have advantageous integration of batteries and supercapacitors, they still suffer from the inherent problems of dendrite growth and interfacial side reactions on Zn anodes. Herein, a universal fast zinc-ion diffusion layer on a three-dimensional (3D) mesh structure model is demonstrated to effectively improve Zn plating/stripping reversibility. The fast ion diffusion alloy layer accelerates the Zn2+ migration in an orderly manner to homogenize Zn2+ flux and overcomes the defects of the commercial mesh substrate, effectively avoiding dendrite growth and side reactions. Consequently, the proof-of-concept silver-zinc alloy modified stainless steel mesh delivers superb reversibility with the high coulombic efficiency over 99.4% at 4 mA cm−2 after 1600 cycles and excellent reliability of over 830 h at 1 mA cm−2, Its feasibility is also evidenced in commercial zinc ion hybrid capacitors with activated carbon as the cathode. This work enriches the fundamental comprehension of fast zinc-ion diffusion layer combined with a 3D substrate on the Zn deposition and opens a universal approach to design advanced host for Zn electrodes in zinc ion hybrid capacitors.

Enhanced low-frequency microwave absorption performance of FeNi alloy coated carbon foam assisted by SiO2 layer

The hierarchical structures of carbonized melamine foam modified by FeNi alloy and silicon layer (CMF/FeNi-SiO2) have been fabricated by a magnetron sputtering method. The as-prepared CMF/FeNi-SiO2 composites exhibited a three-dimensional porous structure, with the framework uniformly covered by a FeNi layer with several hundred nanometers and an ultrathin SiO2 layer, which demonstrated soft magnetic properties at room temperature. Moreover, the microwave absorption performance of the foam was investigated in the frequency range from 2 to 18 GHz. The results showed that the microwave absorption performance of CMF/FeNi-SiO2 composite was significantly enhanced in the low-frequency range compared with CMF/FeNi. The minimum reflection loss of CMF/FeNi-SiO2 with an absorption thickness of 4.1 mm was about −53 dB at 3.38 GHz and reached an effective absorption bandwidth of 0.93 GHz (from 2.93 GHz to 3.86 GHz). The frequency bandwidth of 8 GHz (2.35 ~ 6.35 GHz, 8.4 ~ 12.4 GHz) with absorption loss ≤ −10 dB and the frequency bandwidth of 2.05 GHz (2.62 ~ 4.67 GHz) with absorption loss ≤ -20 dB demonstrated the CMF/FeNi-SiO2 a high-efficient absorber in the low-frequency band (2–6 GHz), which stemmed from improved impedance matching and attenuation capacities.

Anti-corrosion performance of Si-surface-alloying NdFeB magnets obtained with magnetron sputtering and thermal diffusion

Si alloying in the surface layer of NdFeB magnets was realized by thermal diffusion combined with magnetron sputtering. The surface composition, phase structure and morphology of NdFeB(S–Si) specimens were characterized by an X-ray diffractometer, an X-ray photoelectron spectrometer and a field emission scanning electron microscope, respectively. The corrosion resistance of bare NdFeB(S–Si) was analyzed by static full immersion corrosion test and electrochemical experiments. Effects of sputtering and thermal diffusion on the microstructure and corrosion resistance of the surface layer were studied. Results show that surface alloying layer can effectively improve the corrosion resistance of bare NdFeB with the optimized static total immersion corrosion test time in NdFeB(1S–Si)-800 of 36 h, which is much longer than that of the pristine NdFeB (less than 0.5 h). The Ecorr of NdFeB(1S–Si)-800 positively shifts from −1.05 to −0.92 V, indicating that the corrosion tendency is obviously lower. The Jcorr is 1.45 × 10−6 A/cm2 which is 2 orders of magnitude lower than that of the pristine NdFeB (5.25× 10−4 A/cm2). The intergranular composite oxides existing in Nd-rich phase contribute to the enhancement of corrosion resistance of Si-surface-alloying NdFeB.

Precision-improving manufacturing produces ordered ultra-fine grained surface layer of tungsten heavy alloy through ultrasonic elliptical vibration cutting

High-precision and ultra-fine grained surface of tungsten heavy alloy exhibits superior service performance that is useful for many applications and shows promises for use as key parts in nuclear protection and precision instruments. The present study concentrated on a kind of precision-improving ultrasonic elliptic vibration cutting approaches, which fabricated nanometer-level surface roughness, inhibited subsurface damages evolution, and formed continuous ultra-fine grained layer microstructure. The surface morphologies have been characterized by ultra-depth three dimensional microscope and white light interferometer. Excellent machined surface quality was achieved under ultrasonic elliptic vibration cutting condition, and an ideal surface roughness of Sa = 70.7 nm was obtained. Microstructural alteration studied using EBSD technique and TEM observation confirmed the generation of ultra-fine grained structure. Surface grain size has been reduced from 50 ∼ 100 μm to 50 ∼ 300 nm without cracks and other micro-damages. Research demonstrated that surface energy accumulation and dislocations clustering induced by high-strain rate diamond tool impact provided the primary driving force of ductile-mode removal and grain recrystallization. A dislocation density-based simulation model was carried out to complement the static experimental investigations. The present work on surface formation and microstructural evolution identified that ultrasonic elliptical vibration machining has potential to deliver improved tungsten-based alloys service performance.

Improvement of surface characteristics of mold steel using laser cladding and shock peening

In the automobile industry, improving the properties of the mold improves productivity and reduces the defect rate of the product. In this study, a laser heat source was used to improve the properties of the mold. To improve the surface strength of the mold steel, laser cladding was applied to form a surface alloy layer. In addition, an experiment was performed to improve the tensile residual stress of the cladding layer by applying laser shock peening. A continuous wave high-power fiber laser was used for laser cladding, and a high-peak Nd:YAG pulsed laser system was used for laser peening. As a result, an alloy layer harder by more than 1.5 times than the base material was formed on the surface of the mold steel through laser cladding, and the tensile residual stress of the laser cladding layer with peening applied was improved by about 50%.

Numerical and experimental investigation on distribution of residual stress and the influence of heat treatment in multi-pass dissimilar welded rotor joint of alloy 617/10Cr steel

In the present study, numerical and experimental investigation of stress distribution pattern has been performed for thick walled nuclear rotor pipe joint of Alloy 617 and 10Cr steel. Hot wire Tungsten Inert Gas (HW-TIG) welding process has been adopted for multipass narrow groove welding since it yields better mechanical properties at low heat input than manual TIG welding and decreases the accumulation of residual stress significantly. The residual stress generated at the surface of the welded joint was evaluated experimentally using the Blind hole drilling technique (BHD), and consequently, the distribution of stresses along the thickness of the welded joint was masured using the Deep hole drilling (DHD) method. According to the findings, shrinkage at the HAZ area of the weld influences the stresses generated at the cylinder outer surface. The distribution of residual stresses in the weld region is driven mostly by the bending effect produced during the welding process. The influence of post weld heat treatment (PWHT) on residual stress distribution has also been investigated using both experimental and numerical approaches. Numerical investigations have been performed using ABAQUS finite element method. A 2D finite element model has been developed to simulate the welding process and the subsequent heat treatment, using coupled thermo-mechanical analysis. The residual stress results obtained from the numerical approach were validated with the experimentally obtained results and a good correlation has been found. The lumped pass model along with an equal density heat source has been implemented to minimize the computation complexity without affecting the accuracy of the simulated results. The obtained findings revealed that apart from weld centerline, hoop tensile residual stresses were higher around the buttered layer of Alloy 617 and 10Cr steel in an as-welded state. It has been found that nearly 80% of the stresses generated along the weld section have been released after PWHT.

Surface conversion derived core-shell nanostructures of Co particles@RuCo alloy for superior hydrogen evolution in alkali and seawater

Hydrogen evolution reaction (HER) in alkali involves higher energy barriers and slow reaction kinetics due to involving water dissociation process. Catalysts with proper surface properties are highly needed to optimize the surface binding energy with reaction intermediates and enhance intrinsic catalytic activity. Herein, we present an effective strategy to construct a self-standing catalyst with core-shell structure, which is composited of metallic Co nanoparticles coated by RuCo alloy layer with optimized surface properties. The Ru attracts electrons from Co and optimizes the surface electronic structure. Theoretical calculations demonstrate that the water dissociation barrier on the Co surface is decreased from 0.65 eV to 0.58 eV after alloying with Ru. Experimental results reveal that the synthesized Co@RuCo-3 features highly efficient catalytic activity together with good stability at large current densities for HER in alkali, as well as in alkaline seawater and pure seawater.

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.