Alloy Layer Research Articles

Investigation on experiments and numerical modeling of the residual stress distribution in deformed surface layer of Al6061 alloy after ultrasonic peening treatment

AbstractUltrasonic peening treatment is a modern technique that enhances the surface properties of the metallic components by imposing static and dynamic loadings. The efficiency of this technique dramatically is dependent on the controlling parameters of ultrasonic peening treatment. In this study, an experimental and numerical investigation on ultrasonic peening treatment was carried out. The numerically predicted residual stress profile was verified using x‐ray diffraction measurement. Moreover, a parametric study was performed to investigate the effect of needle diameter, impact number, device moving velocity and static force on residual stress distribution. Based on the results, increasing in needle diameter, impact number and static force had positive effects on residual stress profile. In contrast, higher device moving velocity caused to emerge undesirable effects.

Characterization of the Interfacial Structures of Core/Shell CdSe/ZnS QDs.

Core/shell quantum dots (QDs) have been extensively studied, yet their optical properties widely vary among studies. Such variation may arise from the variation in interfacial structures induced by the subtle difference in each synthetic procedure. Here, we studied the interfacial structures of CdSe/ZnS QDs using the time-of-flight medium energy ion-scattering spectroscopy (TOF-MEIS), which offers the radial elemental distributions as well as the overall elemental compositions of QDs. The TOF-MEIS spectra provided strong evidence for the existence of an alloyed layer at the interface between CdSe and ZnS in typical CdSe/ZnS QDs. On the basis of the emission and absorption spectra of QDs sampled during the synthesis, we conclude that such interfacial alloying is caused by the dissolution of CdSe seeds during the synthesis steps. Such a dissolution mechanism is further corroborated by the observation that the ligand environment of solvent (X or L type) leads to different shapes of interfaces.

Experimental Analysis of Circular Milling for Material Identification in Aerospace Industry

In the airplane design, thousand holes should be manufactured by machining leading this process in the first place for process optimization. Recently, the stack materials used in this application are sheet layers of Titanium alloy, Aluminum alloy and CFRP, which normally are machined under different cutting conditions. There are two main solutions when drilling stacks: using the more conservative ones or changing the parameters for each layer. In orbital drilling the forces are lower, with better quality but with longer machining time, compared to drilling, allowing the measurement and control of the process. Smart machining techniques can be applied for recognising and adapting the cutting parameters in real time, depending on a database for decision-making. In this paper, a technique is proposed to identify the cutting material based on the cutting and feed components of the machining force in a circular milling process. Experiments consist of machining separately Titanium and Aluminium alloy workpieces in a similar range of cutting speed and feed, measuring forces and the position of the cutting tool (X,Y, SP) using the machine-tool data. The results show that it is possible to identify the materials using the calculated tangential and radial force components in the tool referential frame because the values of specific cutting and feed force are significantly different for each material. An specific force map is used as a signature to distinguish the materials in real time machining which can be used for orbital drilling in the next step of the research.

Economic Efficiency of High-Entropy Alloy Corrosion-Resistant Coatings Designed for Geothermal Turbine Blades: A Case Study

The aim of this paper is to establish the cost-effectiveness of high-entropy alloy coatings, using the electrospark deposition technique, designed for a geothermal turbine blade’s leading edge. The deposition of materials with high resistance to corrosion and erosion aims to increase the blade’s service life, reduce maintenance costs and improve production efficiency. According to our previous research on the CoCrFeNiMox high-entropy alloy system, the results showed a high corrosion resistance when in bulk or as a coating, and when tested in geothermal steam and in a saline solution. Based on the results, the high-entropy alloy was subjected to further analyses. The paper focused on two aspects of the research. The first direction was to explore the possibility of obtaining an effective, protective high-entropy alloy layer by the electrospark deposition method. To this end, various tests were performed to demonstrate that the new material possesses superior properties and is suitable for the geothermal environment’s demands. The second direction was to calculate the economic efficiency of coating the areas intensely subjected to wear, based on reports published by the geothermal power plants’ representatives. The final costs were compared with the commercially available equipment parts, and also with the general maintenance costs. From the calculation of the cost efficiency for the CoCrFeNiMo0.85 high-entropy alloy, it resulted that the deposition method and the properties of the material are suitable for the operating conditions, representing an efficient and easy to apply solution to reduce maintenance costs in the geothermal industry.

Mechanism for superior fatigue performance of warm laser shock peened IN718 superalloy after high-temperature ageing

The high cycle fatigue properties of IN718 alloy treated by warm laser shock processing (WLSP) were studied after high-temperature ageing at both room temperature and 600 ℃. The strengthening and toughening mechanism of WLSP on the hardened surface layer of IN718 alloy was elucidated to reveal the highly stable strengthening effects at high temperature. It was found that the thermally assisted surface hardening techniques had more obvious advantages in maintaining fatigue resistance and prolonging fatigue life of the alloy with the hardened surface layer during long-term service at elevated temperature, comparing with the conventional laser shock peening (LSP). After WLSP treatment, complex structures of γ″ phase/high-density dislocation with stacking faults (SFs) and nano-sized twins in γ″ phases surrounded by the more stable and higher density of geometrically necessary dislocations (GNDs), formed in the hardened surface layer. Therefore, a remarkable strengthening effect in the hardened surface layer was achieved due to the production of more stable hetero-deformation induced (HDI) stress. Meanwhile, the substructure evolution, compressive residual stress reduction and γ″ phase growth in the hardened layer of WLSP alloy were also inhibited during high-temperature ageing, owing to the existence of the special structure, contributing stability of microstructure and strengthening effect under conditions of high-temperature ageing and subsequent cyclic loading at high temperature. Thus, both the fatigue crack initiation resistance and initiation time of WLSP alloy can be improved in the surface of specimen. This is the main reason why after high-temperature ageing the fatigue resistance of WLSP sample can be kept stably and the median fatigue strength can be improved at both room temperature and 600 ℃.

Failure Analysis of a Chromium Plating Layer on a Piston Rod Surface and the Study of Ni-Based Composite Coating with Nb Addition by Laser Cladding

The failure of a chromium plating layer on the surface of a piston rod was analyzed, and an Ni-based alloy mixed with a niobium (Nb) composite coating was investigated by means of stereomicroscopy, metallographic microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Vickers hardness testing, and wear testing. The results show that penetrating cracks were present in the chromium layer. Subsequently, the corrosion intensified, resulting in the bubbling, cracking, and peeling of the chromium layer. The cladding layer presented a structure morphology of planar crystalline at the bottom, dendritic at the middle, and equiaxial crystalline at the top. The solidification parameters, which were derived from simulation results, confirmed that the ratios between temperature gradient (G) and solidification speed (S) decreased, and the values of the cooling speeds increased from the bottom to the top of the cladding layer. With an increase in Nb content, the structure became gradually refined and uniformly dense. The cladding layer of the Ni-based alloy mixed with Nb was mainly composed of γ-Ni, Cr23C6, Cr7C3, NbC, and Ni3Nb. NbC could be formed in situ and presented itself in four forms: particles, dendrites, polyhedrals, and networks. The microhardness of the coating with 15% added Nb was enhanced to 400 HV0.2, and the wear resistance thereof was 11.14 times higher than the substrate. After the 15% Nb coating had aged for 16 h, the diffraction peak intensities of Cr23C6 and Cr7C3 significantly increased, and the volume fraction of granular NbC increased from 1.67% to 2.54%. The microhardness was enhanced to 580 HV0.2, and the wear resistance thereof was better than that of the chromium plating layer.

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.