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Acrylate polymer is widely used to manufacture display films as an adhesive. Improper disposal of acrylate polymer-containing display film waste (a kind of E-waste) may cause serious environmental problems. As an effort to develop a display film waste treatment strategy, this study applied a solvent-based method to recover acrylate polymer from display film waste. The solubility of acrylate polymer (e.g. poly(tert -butyl acrylate)) in 18 different organic solvents was calculated using Hansen solubility parameters. As a result, 2-butanol and methyl acetate were chosen as organic solvents for the acrylate polymer recovery from the display film waste. Effects of various recovery parameters (e.g. temperature, time, and stirring speed) on the recovery of acrylate polymer in five different solvent systems consisting of 2-butanol and methyl acetate (2-butanol, methyl acetate, 1:1 mixture, 1:2 mixture, and 2:1 mixture) were explored. 2-Butanol was found to be a better solvent than any others because it is more hydrophobic than methyl acetate. The recovery condition at which the highest acrylate polymer recovery yield in 2-butanol was obtained was T = 30 °C, t = 1 h, and stirring speed of 250 r/min, reaching 8.28 wt%. This study would help to develop an E-waste recycling method that can be recovering value-added products from E-waste. [ABSTRACT FROM AUTHOR]

In this study, a series of FeCoNiAlSix (x = 0, 0.2, 0.4, and 0.6) high-entropy alloys (HEAs) were prepared by mechanical alloying and spark plasma sintering. The effects of Si alloying on the structural, thermal expansion, and magnetic properties of HEAs were investigated. The X-ray diffraction and microscopic results reveal that the crystal structure changes from FCC + BCC to single BCC phase with increasing Si content. By increasing Si content, the coefficient of thermal expansion decreases, especially at high temperatures, indicating that Si has a greater effect on improving the dimensional stability. In addition, the developed HEAs exhibit good saturation magnetization ~ 86.23 emu/g, low coercivity ~ 18.4 Oe, and high electrical resistivity ~ 84 µΩ.cm, indicating the present HEA can be used in soft magnetic applications. Furthermore, the hardness of HEAs increased from 510 ± 10 to 730 ± 10 HV with an increasing Si content due to formation of stable BCC phase. The present study demonstrates that alloying of Si facilitates a balance between desirable physical and mechanical properties. [ABSTRACT FROM AUTHOR]

The study investigates that a high-entropy alloy based on AlCoCrFeNi is mechanically alloyed (MA) for 40 h with 1 wt% Y2O3 dispersed and then consolidated through vacuum hot pressing (VHP). In VHP, three temperatures are used for consolidation: 800 °C, 900 °C, and 1000 °C. Microanalysis of the powder aggregate formed by MA revealed the presence of mostly face-centered cubic (FCC) and body-centered cubic (BCC) phases, along with a metastable AlFe4O12Y3 garnet phase. The enthalpy of mixing Y and Al induced the development of the garnet phase. In addition, after the consolidation of the powder sample at different temperatures, microstructural investigations indicated that the FCC and BCC phases generated during MA were stable owing to sluggish diffusion. By contrast, the garnet phase generated during the MA dissociated into an intermetallic phase based on Yttrium. The slower heating rates associated with VHP (in comparison to the rapid heating rates associated with spark plasma sintering) may be responsible for the dissociation of the garnet phase. The sample sintered at 1000 °C exhibited a bimodal grain distribution, with grain sizes ranging from 100 to 800 nm, as determined by transmission electron microscopy. In addition, this sample had the highest measured hardness of 1353 ± 20 Hv. [ABSTRACT FROM AUTHOR]

This research article presents a comprehensive study on the prediction of thermal conductivity (TC) as a primary outcome for an artificial neural network (ANN) model in the context of nanoenhanced phase change materials (NEPCMs). To improve predictive accuracy and to reduce variation within the NEPCM dataset, a targeted dataset was employed, consisting exclusively of NEPCMs synthesized using paraffin wax (PW) and metal oxide nanoparticles. Unlike existing empirical models that predict TC of NEPCM without simultaneously considering multiple factors influencing it, this study integrates multiple factors, providing a more accurate prediction of NEPCM thermal conductivity. Additionally, the study explores the impact of synthesis parameters on the thermal performance of NEPCMs, focusing on the examination of factors such as the melting temperature of pure phase change material (PCM), nanoparticle size, and NEPCM composition. The thermal characterizations demonstrate outstanding thermophysical properties in NEPCMs, particularly in terms of thermal conductivity, phase change enthalpy, and thermal stability compared to their respective base PCM. An ANN TC prediction model demonstrates exceptional correlation (>99%) with reported NEPCMs, providing a reliable tool for TC forecasting in similar NEPCM categories. The backpropagation ANN model predicts NEPCM TC with a mean squared error (MSE) of 0.031124 within eight epochs. The dataset used exhibits high fit values, with R -values of 0.99825, 0.99208, and 0.9824 for training, validation, and testing, respectively. These values closely match experimentally determined TC, with less than 4% error. [ABSTRACT FROM AUTHOR]

In this study, dry sliding wear of AlSi0.75TiMnFeCux (x = 0, 0.25, 0.5) high-entropy alloy (HEA) produced through mechanical alloying (MA) and spark plasma sintering (SPS) was studied. The microstructure and phase evolution were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The wear behaviour of HEAs was assessed by reciprocating wear monitor under a dry air atmosphere. The findings demonstrated that AlSi0.75TiMnFeCux HEAs were multiphase body-centred cubic (BCC/B2) solid solution structured with complex µ-, L21, and Laves. It was discovered that the microhardness and wear behaviour of AlSi0.75TiMnFeCux were comparable to AlSi0.75TiMnFe HEA after the addition of Cu up to 0.25 molar ratio. The maximum hardness of the AlCu0-0.5FeMnTiSi0.75 HEAs reached around 1021–1035 HV. The tribology results show that an oxidative wear in AlSi0.75TiMnFe while the mixed adhesive-abrasive wear mechanism was prominent in the AlSi0.75TiMnFeCu0.25-0.5 HEAs. [ABSTRACT FROM AUTHOR]

In this study, the effects of Cu addition on AlFeMnTiSi0.75Cux (x = 0, 0.25, 0.5, 0.75, 1.00; in molar ratios) high entropy alloys (HEAs) prepared via mechanical alloying and spark plasma sintering were investigated. The structure, phase, morphology and composition of HEA powders were analysed and the results revealed that the AlFeMnTiSi0.75Cux HEAs exhibited a multiphase structure. Additionally, after sintering at 900 °C, the formation of BCC, µ and L21 phases in the densified HEAs was enhanced. The investigation of the hardness, nanoindentation and compressive properties revealed that the microstructural and mechanical properties of AlFeMnTiSi0.75Cux HEAs were improved at the optimal Cu fraction (0.25 molar ratio). The nanoindentation results revealed that the AlFeMnTiSi0.75Cux HEAs exhibited the highest hardness and elastic modulus (HIT = 19.2 GPa, EIT = 336 GPa). These results improve the current understanding of multiphase HEAs and may pave way for the development of advanced HEAs with superior mechanical properties. [ABSTRACT FROM AUTHOR]

A preliminary study has been performed to understand the effect of pressureless sintering on the surface morphology of the AlFeCoNi alloy by the addition of the Si element. This study aims to determine the possibility of achieving the densification of high entropy alloy using the conventional sintering technique. The results indicate that the HEAs have a single-phase BCC structure even with the addition of Si. The thermodynamic simulation (CALPHAD) was used to predict the phase formation. The variation of crystallite sizes and lattice strains caused by sintering temperatures was also discussed. In addition, densification mechanisms occurring with the different sintering temperatures have been discussed. The formation of porosity was observed, however, the density of HEAs improved with increasing sintering temperature. Ultimately, it was suggested that the present HEAs required higher sintering temperatures and a longer time to achieve high density. [ABSTRACT FROM AUTHOR]

In this study, TiC-reinforced CoCrFeMnNi high-entropy alloy (HEA) composites were prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The phase composition, microstructure, mechanical and thermal expansion behaviour of composite HEAs were investigated. The results reveal that the addition of TiC has no effect on the crystal structure, however, the microstructure and mechanical properties show a strong dependency on the TiC content. Compared to the original HEA, the composite HEA shows decreased grain size, resulting in TiC nanoparticles (NPs) retarding grain growth by pinning the grain boundaries. With increasing TiC content from 0 to 4 wt-%, significant increases in the hardness from 410 to 480 HV and compressive yield strength from 680 to 1100 MPa, which is mainly due to the grain boundary and dispersion strengthening effects. Moreover, the thermal expansion curves show linear increments up to 800°C and decrease with increasing TiC content. [ABSTRACT FROM AUTHOR]

High entropy alloys (HEAs) composed of multi‐metal elements in a single crystal structure are attractive for electrocatalysis. However, identifying the complementary functions of each element in HEAs is a prerequisite. Thus, VxCuCoNiFeMn (x = 0, 0.5, and 1.0) HEAs are investigated to identify the active role of vanadium in improving the electrocatalytic activity for the hydrogen evolution reaction (HER). Structural studies show the successful incorporation of V in the HEA. V1.0CuCoNiFeMn (V1.0‐HEA) shows an overpotential of 250 mV versus the reversible hydrogen electrode (at −50 mA cm−2, 1 m KOH), which is ≈170 mV lower than that of control‐HEA (422 mV). Improves electrical conductivity and the electrochemical surface area of the V1.0‐HEA accelerated HER activity. Furthermore, density functional theory calculations reveal reduced water dissociation and hydrogen adsorption energies of V1.0‐HEA, resulting in the boosted HER kinetics. The effect of V incorporation on the barrier height and active sites at the surface of V1.0‐HEA is schematically explained. This study can be facilitated for the development of highly active HEAs for large‐scale electrochemical water splitting. [ABSTRACT FROM AUTHOR]

An equiatomic CoCrFeMnNi high entropy alloy (HEA) was prepared by the gas atomization process. In addition, high-energy milling was carried out to study the effects of milling parameters on the morphology and crystallographic properties of HEA powders. Phase identification and morphology of milled powders were observed by X-ray diffraction and scanning electron microscopy, respectively. Both the atomized and milled powders exhibited a single-phase face-centered cubic solid solution. The resultant crystallite size (CS) and lattice strain (LS) of milled HEAs were estimated using the Williamson Hall method and predicted using an artificial neural network (ANN) approach. With increasing the milling time from 0 to 240 min, the CS decreased from 39.7 to 6.56 nm and the LS increased from 0.25%–1.48%, respectively. Furthermore, the developed ANN modeling provides an excellent method for the prediction of the CS and LS with excellent accuracies of 96.25% and 93.43%, respectively. [ABSTRACT FROM AUTHOR]

Polyester fiber is a high-molecular-weight compound made from fossil fuels and is used in various synthetic fiber manufacturing processes. In this study, we performed non-catalytic and catalytic pyrolysis experiments using cobalt oxide as a catalyst to recover energy from polyester fiber. The experiment was carried out between 500–900 °C in the presence of N2. Amount of oil formation was the highest at 600 °C in non-catalytic pyrolysis and oil formation of catalytic pyrolysis was the highest at 500 °C. In both non-catalytic pyrolysis and catalytic pyrolysis, gas content was increased and char was decreased with increasing temperature. A marked difference was observed when the catalyst was used; the formation of char was suppressed and oil and gas yields increased. In the catalytic pyrolysis oil, benzoic acid compounds accounted for the largest proportion (16.15 wt%) at 900 °C, but polycyclic aromatic hydrocarbons and phenols were not observed. Benzoic acid is an important precursor material used to synthesize other organic substances, such as phenol and caprolactam. The non-condensable gas content increased from 11.55 wt% to 22.39 wt%, with increasing temperature. In particular, H2 gas yield was 4.44 wt% at 900 °C. Therefore, by using catalytic pyrolysis, high value-added chemicals such as benzoic acid compounds and H2 gas can be recovered at high yield at 900 °C from the polyester fiber. Consequently, unlike the existing treatment methods, the environmental impact of plastics can be reduced by catalytic pyrolysis. [ABSTRACT FROM AUTHOR]

Nanostructured Ti–Fe alloys were fabricated by cryomilling and spark plasma sintering (SPS). Cryomilling was performed for 8 h in a liquid N2 atmosphere, and densification of the alloyed mixture was performed at different SPS temperatures (800, 1000, and 1200 °C). The phase and structure of the Ti–Fe alloyed powder were studied by X-ray diffraction analysis. The morphologies of the cryomilled powders and SPS-treated compacts were investigated by scanning and transmission electron microscopic analyses. The results showed that alloying did not occur completely in the powder mixture after cryomilling and pure Ti and Fe phases were found. However, SPS treatment of cryomilled Ti–Fe powder resulted in a different phase evolution with temperature. Intermetallic compounds were formed in small amounts in the Fe-rich region; however, β-Ti phases were mostly present. The absorption energies of these alloys showed small changes from 460, 452, and 430 MJ/m3 when the SPS temperatures were 800, 1000, and 1200 °C, respectively. The compressive strength values of these Ti–Fe alloys improved with increasing SPS temperature owing to the diffusion of Fe in the Ti matrix, which promoted the dispersion hardening of these alloys. [ABSTRACT FROM AUTHOR]

An Al-Ni alloy system with excellent energy density and mechanical performance is regarded as a novel high-energy–density material to enhance the energy emission of explosives or propellants. In this study, we explored the influence of a process control agent (PCA) varying from 0, 0.1, 0.25, 0.5, to 1.0 (wt.%) on the cryomilling of Al and Ni powder mixtures. The structural and morphological evolution of cryomilled Al-Ni powder was determined by X-ray diffraction, scanning electron microscopy, particle size distribution analysis, and transmission electron microscopy. Differential thermal analysis was used to study the exothermic reaction temperature, and activation energy calculations were performed using Kissinger plots. The results indicated that the addition of PCA changed the Al-Ni aggregate shape from oval to granular. The lamellar size also became finer after adding PCA up to 0.25 wt.% but the lamellar shape changed to granular at 1 wt.% PCA. These nanoscale lamellae serve as nuclei to produce Al-Ni reaction compounds, which gradually decrease the activation energy. The optimal concentration of PCA was determined to be 0.25 wt.% as this concentration decreased the activation energy of the Al-Ni alloy because of the fine, homogeneous, and alternate Al-Ni lamellae in the alloy when cryomilled. [ABSTRACT FROM AUTHOR]

Summary: The ongoing population explosion has led to the rapid consumption of different energy sources. The continuous demand for energy and its associated services for socio‐economic development is concerning due to the reduction of natural energy sources. Therefore, research to explore clean and sustainable energy sources to fulfill this energy demand has continuously been conducted over the past decades. Hydrogen is widely accepted as a possible energy carrier owing to its advantages, such as ease of availability, renewability, and environmentally friendly nature. Hydrogen storage in the liquid or gaseous form poses safety and transportation challenges. In this context, metal hydrides are a vital solution. This review article discusses unique collections of HEA‐based metal hydrides for the first time in conjunction with conventional metal hydrides. This article can potentially guide the materials research community in understanding the current challenges associated with designing novel hydrogen storage alloys from a clean energy perspective and their applications. The review suggests improving the thermodynamics and hydrogen reaction kinetics to enhance hydrogen storage capacity. Finally, the global developing trends are reviewed and critical challenges and promising opportunities are identified. Highlights: Essential aspects of various alloys and their hydrides are analyzed.This review supports the utilization of hydrogen as clean energy fuel and its possible storage measures.The review provides an imperative connection of the metal hydrides, including emerging high‐entropy alloy hydrides, with renewable and sustainable energy.Metal hydrides are an economic option for hydrogen‐based energy applications.This review focuses on present issues and the prospective application of hydrogen storage. [ABSTRACT FROM AUTHOR]

In this study, equimolar AlCuSiFe-x (x = Cr, Mn, Zn, Sn) HEAs were fabricated by mechanical alloying (MA) and spark plasma sintering methods (SPS). The MA was performed for 45 h followed by densification of powder compacts at 650 °C. The results revealed the formation of dual face-centered cubic (FCC) and body-centered cubic (BCC) structures in AlCuSiFe-x (x = Zn, Sn) while a single BCC solid solution was noticed in AlCuSiFe-x (x = Cr, Mn). After SPS treatment, AlCuSiFeSn alloy contained FCC with CuxSny while AlCuSiFe–Zn changed to FCC + BCC structure. Similarly, AlCuSiFeCr and AlCuSiFeMn showed the formation of BCC + FCC with additional σ- and µ-phases in the HEA matrix. The calculated thermodynamic parameters of HEAs also supported the formation of different solid-solution phases in each of the above HEAs. It was found that HEAs with the additive elements Sn and Zn tend to have major FCC phases, while those with Cr and Mn give rise to major BCC with brittle σ- and µ-phase, which further improves their mechanical strength. [ABSTRACT FROM AUTHOR]

In this study, the alloying and phase separation behaviors of AlCoCrFeNi-based high-entropy alloys (HEAs) were investigated. The valence electron concentration (VEC) of the AlCoCrFeNi HEA was modified by adding specific elements (Mg, Ti, Mn, Cu, and Zn) to produce biphasic HEAs. These HEAs were prepared by mechanical alloying for 30 hours, followed by the consolidation of the powders at 1000 °C. The results demonstrated the formation of a body-centered cubic (ordered BCC/B2) phase in AlCoCrFeNi–Mg and AlCoCrFeNi–Ti, while a dual-phase face-centered cubic (FCC) phase and minor BCC phases were observed in AlCoCrFeNi–Cu and AlCoCrFeNi–Zn. AlCoCrFeNi and AlCoCrFeNi–Mn exhibited the precipitation of a σ phase in the BCC matrix and a minor FCC phase. The AlCoCrFeNi–Mn HEA exhibited the highest compressive strength among itself, AlCoCrFeNi–Cu, and AlCoCrFeNi–Zn HEAs, owing to the precipitation of a harder σ phase and a higher ordered BCC/B2 fraction. In addition, the AlCoCrFeNi–Cu and AlCoCrFeNi–Zn HEAs exhibited the maximum fracture strain and absorption energies. We propose that a controlled VEC approach by the addition of suitable elements can be used to tailor the microstructure and phase stability of AlCoCrFeNi HEAs. [ABSTRACT FROM AUTHOR]

In addition to the word-level weight pruning, which excludes the 0-value weights from the neural network inference computation, it is recently demonstrated that the bit-level weight pruning, which excludes the 0-bits in the weight value representation regardless of whether the weight values are zero or not, is very effective to further accelerate the neural network computation without accuracy loss. This work overcomes the inherent limitation of the bit-level weight pruning, that is, the maximal computation speedup is bounded by the total number of nonzero bits of the weights and the bound is invariably considered “uncontrollable” (i.e., constant) for the neural network to be pruned. Precisely, this work, based on the signed-digit encoding 1) proposes a transformation technique which converts the two’s complement representation of every weight into a set of signed-digit representations of the minimal number of essential (i.e., nonzero) bits; 2) formulates the problem of selecting signed-digit representations of weights that maximize the parallelism of bit-level multiplication on the weights into a objective shortest path problem to achieve a maximal digit-index by digit-index (i.e., columnwise) compression for the weights and solves it efficiently using an approximation algorithm; 3) proposes a supporting novel acceleration architecture (DWP) with no additional inclusion of nontrivial hardware; and 4) proposes a variant of DWP to support bit-level parallel multiplication with the capability of predicting a tight worst-case latency of the parallel processing. Through experiments on several representative models using the ImageNet dataset, it is shown that our proposed approach is able to reduce the number of essential bits by 69% on AlexNet, 74% on VGG-16, and 68% on ResNet-152, by which our accelerator is able to reduce the inference computation time by up to $3.57\times $ over the conventional bit-level weight pruning. [ABSTRACT FROM AUTHOR]

High entropy alloys (HEA), multicomponent (5 or more) alloys with an equiatomic or a near-equiatomic composition, provide a unique platform with which to engineer surface composition and active sites for the development of efficient electrocatalysts. Herein, we endeavor to introduce a high entropy alloy (HEA) of CuCoNiFeMn as an active model system for a bifunctional electrocatalyst at neutral-pH, synthesized by a room-temperature high-energy-milling process. The formation of a single-phased face-centered-cubic (fcc) HEA with homogenous distribution of each element was confirmed. In neutral electrolyte (PBS, pH 7.4), as-synthesized HEA shows promising performance, i.e., long-term durability for over 20 h, an overpotential of −320 mV vs. the reversible hydrogen electrode (RHE) for the hydrogen evolution reaction, and 680 mV vs. RHE for the oxygen evolution reaction at high current densities, which are lower than for other controlled electrocatalysts as well as being comparable with reported nanostructured electrocatalysts. Besides, HEA shows much smaller electrical and charge transfer resistance values than its controlled un-alloyed counterpart. Our preliminary results could open a new insights to developing nanostructured HEAs that could be used as efficient electrocatalysts in a neutral water splitting system, thus increasing hydrogen production viability. [ABSTRACT FROM AUTHOR]

A new algorithm for extracting common kernels and convolutions to maximally eliminate the redundant operations among the convolutions in binary- and ternary-weight convolutional neural networks is presented. Precisely, we propose (1) a new algorithm of common kernel extraction to overcome the local and limited exploration of common kernel candidates by the existing method, and subsequently apply (2) a new concept of common convolution extraction to maximally eliminate the redundancy in the convolution operations. In addition, our algorithm is able to (3) tune in minimizing the number of resulting kernels for convolutions, thereby saving the total memory access latency for kernels. Experimental results on ternary-weight VGG-16 demonstrate that our convolution optimization algorithm is very effective, reducing the total number of operations for all convolutions by 2 5. 8 ∼ 2 6. 3 % , thereby reducing the total number of execution cycles on hardware platform by 22.4% while using 2. 7 ∼ 3. 8 % fewer kernels over that of the convolution utilizing the common kernels extracted by the state-of-the-art algorithm. [ABSTRACT FROM AUTHOR]

Novel AlCuFeMnTi–X high-entropy alloy (HEA) powder mixture with individual X = Mg, Si, Zn was mechanically alloyed for 45 h and consolidated at 700°C by spark plasma sintering (SPS). The effect of the addition of Mg, Si and Zn was studied on the microstructural evolution, density and microhardness of the developed HEAs. The results demonstrated that milled HEAs were body-centered cubic (BCC) structured (BCC1 and BCC2). The BCC2 fraction was highest in AlCuFeMnTi–Zn followed by AlCuFeMnTi–Si. However, minor Ti, Si and intermetallic compounds (IMC) were observed in AlCuFeMnTi–Mg with BCC1 major phase. After SPS, the alloying improved, and BCC2-rich HEAs were observed for all compositions. An attractive hardness value was obtained in AlCuFeMnTi–Mg due to the dispersed Cu2Mg precipitates in the BCC2/BCC1 matrix followed by AlCuFeMnTi–Si and AlCuFeMnTi–Zn HEA, respectively. [ABSTRACT FROM AUTHOR]

In this work, we have studied the displacement reaction of Al and SiO2 powder blends by mechanical alloying (MA) for 20 h and low-temperature sintering. The microstructural evolution of powder and compacted specimens were studied by X-ray diffraction and scanning electron microscopy. The extent of the milling on the displacement reaction was studied by differential thermal analysis (DTA). The results show that the reaction between Al–SiO2 couple does not initiate after milling up to 20 h but occurs after thermal treatment of powders. DTA results indicate a lowering in the reaction temperature of Al–SiO2 couple after milling. Following the DTA results, we densified the Al–SiO2 powder compacts at 700°C to produce an in-situ Al–Si/Al2O3 composite. The physical, mechanical, and tribological performance of the composite at different milling times are also reported here. [ABSTRACT FROM AUTHOR]

In this work, we studied the brazing characteristics of Al2O3 and 3D printed Ti–6Al–4V alloys using a novel equiatomic AlZnCuFeSi high entropy alloy filler (HEAF). The HEAF was prepared by mechanical alloying of the constituent powder and spark plasma sintering (SPS) approach. The filler microstructure, wettability and melting point were investigated. The mechanical and joint strength properties were also evaluated. The results showed that the developed AlZnCuFeSi HEAF consists of a dual phase (Cu–Zn, face-centered cubic (FCC)) and Al–Fe–Si rich (base centered cubic, BCC) phases. The phase structure of the (Cu–Al + Ti–Fe–Si)/solid solution promises a robust joint between Al2O3 and Ti–6Al–4V. In addition, the joint interfacial reaction was found to be modulated by the brazing temperature and time because of the altered activity of Ti and Zn. The optimum shear strength reached 84 MPa when the joint was brazed at 1050 °C for 60 s. The results can be promising for the integration of completely different materials using the entropy driven fillers developed in this study. [ABSTRACT FROM AUTHOR]

In this study, we synthesized a new Al16.6Cu16.6Fe16.6Mn16.6Mg16.6Ti16.6 lightweight high entropy alloy (LWHEA) by high energy ball milling and spark plasma sintering (SPS). The effect of milling time (15, 30, 45, and 60 h) and SPS conditions (600 and 700 °C) on microstructure, hardness, and density of LWHEAs were studied. The results showed that milled LWHEA is base centered cubic (BCC) structured, consisting of dual BCC1/BCC2 matrix with dispersed minor Cu2Mg precipitates and Ti. After SPS of milled samples, the BCC2 phase fraction was increased gradually. The distribution of Ti was uniform up to 45 h milled sample SPSed at 600 °C. However, porosity was built up beyond 45 h milling and higher SPS temperature (700 °C). The presence of finer secondary phases in the HEA matrix contributes to the dispersion hardening. The optimum microhardness and density of LWHEA AlCuFeMnMgTi were around 770 HV and 4.34 g cm− 3 which is superior to other conventional alloys such as Al or Ti-based alloys. [ABSTRACT FROM AUTHOR]

The controlled phase transformation approach is a new generation of microstructure engineering for enhancing ductility in ultrafine-grained materials. The present study aims to extend this concept to dual-phase steel for enhanced tensile ductility at high strength. In this study, cold-rolled steel was subjected to annealing at different processing conditions to develop the core–shell microstructure constituting martensite core and ferrite as shell in the matrix. Controlled austenite decomposition was adopted in designing a core–shell-type structure. The evolved microstructure was characterized using a scanning electron microscope and electron backscatter diffraction technique. The results showed that the uniaxial tensile deformation of dual-phase structured steels had a remarkable strength–ductility trade-off. The ductility was increased anomalously at high martensite fractions. Further, the mechanism of damage activity leading to void nucleation and microcrack formation was studied in post-tensile fractured specimens to establish a correlation with tensile deformation characteristics. The possibility and outcomes of this approach are also reported here. [ABSTRACT FROM AUTHOR]

Research on harvesting alternative energy sources is of interest to meet human demands for energy while reducing environmental pollution caused by the extensive use of fossil fuels. Thermoelectric materials are a promising technology for converting heat into electricity. Among thermoelectric materials, the binary bismuth telluride system (Bi-Te) is widely used. To produce high-quality Bi-Te systems with low materials consumption, spark plasma sintering (SPS) is commonly applied. Because SPS is a fast low-temperature process, controlling the ratio and crystallization of Bi-Te is critical for effective energy conversion. Here, we investigated the quality of Bi-Te systems formed by SPS compaction of raw powders with an in-depth examination of the oxidation effects on their thermoelectric performance. With increasing measurement temperature (300→420 K), the mechanically mixed sample and a commercial Bi2Te3 alloy (sintered at 533 K) showed differences in Seebeck coefficients (0.245→0.267 and 0.223→0.246 mVK−1, respectively). The alloy sample showed a decreased figure of merit (0.863→0.331) while that of the mechanically mixed sample (0.543→1.671) increased with temperature. This was related to the degree of oxygen impurity in each Bi-Te process based on XPS analysis. This study proposes that the integration of oxygen species to Bi-Te can be considered to maximize the thermoelectric efficiency at the specified temperature. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to investigate the influence of current density on the morphology and solderability of Pb-free Sn-Cu solder coatings prepared from alkaline stannate baths. Design/methodology/approach: Sn-Cu solder coatings were produced from a plating solution containing sodium stannate, copper stannate, sodium hydroxide and sorbitol additive on copper substrates. The pulse plating experiments were conducted in galvanostatic mode. The plating current density was varied from 5 to 25 mA/cm2, and the morphology of the coatings was studied. The solderability of the coatings was assessed by spread ratio measurement after reflowing the solder coatings at 250°C. Findings: The composition control of eutectic solders is always a challenge in plating. The findings show that Sn-Cu coatings prepared by pulse plating are composed of tetragonal ß-Sn structure and Cu6Sn5 compounds irrespective of bath composition and conditions. The final coatings were very dense and smooth with nodular morphology. It was shown that a eutectic composition can be achieved if we apply a current density of ∼15-20 mA/cm2. The solderability studies suggest that solder coatings plated at and beyond 15 mA/cm2 are more suitable for solder finish applications. Originality/value: The work presents key issues in pulse electroplating of Sn-Cu solder coatings from an alkaline bath. Possible strategies to control the eutectic Sn-Cu composition by plating process are recommended. [ABSTRACT FROM AUTHOR]

In this work, we have attempted to develop the Ag-Cu-Ti filler for bonding ZrO2 to Ti-6Al-4V. The CeO2 nanoparticles were reinforced in the eutectic Ag-Cu-Ti filler via mechanical mixing and melting route. Furthermore, the brazeability, microstructure, and mechanical behavior, as well as brazing performance of the ZrO2/Ti-6Al-4V joints, were assessed. The wettability of the Ag-Cu-Ti matrix was increased from 89 to 98% on Ti-6Al-4V and from 83 to 89% on the ZrO2 substrate after the addition of 0.05% CeO2. Also, there was a depression in the melting point of the composite fillers up to 3°C. The microstructure consists of Cu- and Ag-rich phases and Cu-Ti intermetallic compounds (IMCs). The joint shear strength was improved with the addition of CeO2 up to 0.05 wt.% in the matrix. It was inferred that, for an excellent brazing performance of the ZrO2/Ti-6Al-4V joint, the optimum amount of CeO2 should be 0.05 wt.% in the Ag-Cu-Ti matrix. [ABSTRACT FROM AUTHOR]

A Cu-coated C nanofiber (Cu-CNF) composite is added to a Sn-3.5Ag alloy to fabricate a solder nanocomposite using mechanical stirring and a melting technique. The microstructural features of the samples, i.e., the β-Sn grain size and the distribution and thickness of the Ag3Sn intermetallic compound (IMC), are statistically measured. The wettability of the developed solders is tested on a Cu substrate by contact-angle and spreading-factor measurements. The experimental results indicate that the presence of up to 0.05 wt pct Cu-CNFs in the solder matrix reduces the β-Sn secondary dendritic arm spacing significantly. Additionally, the spread ratio and spread factor are improved to 93 and 96 pct, respectively, owing to the adsorption of surface-active CNFs in the solder matrix. Furthermore, the addition of 0.05 wt pct Cu-CNFs to the Sn-Ag (SA) alloy increases the microhardness, tensile strength, elongation percentage (El pct), and toughness by 40, 35, 11, and 33 pct, respectively. [ABSTRACT FROM AUTHOR]

Lead-free Sn–58Bi–xCeO2 (x in wt% = 0, 0.3, 0.6 and 0.9) composite solder was prepared via mechanical blending and melting route. The ceria nanoparticles (CeO2) were prepared from chemical precipitation method. Further, the variation in microstructure and phase composition, melting point, wetting and mechanical properties were studied through scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, differential scanning calorimetry, spreading ratio, contact angle and tensile testing, respectively. It was shown that Sn–58Bi–xCeO2 composite solders show 16.66 and 32.05% increase in spread ratio and wetting angle, respectively, due to the enhanced melt fluidity up to x = 0.6. The fraction of hard Bi-phase was also refined simultaneously. The tensile results showed a slight decrease in ultimate tensile strength and enhancement in ductility up to x = 0.3 and 0.6 except at x = 0.9. High temperature aging also demonstrated a reduced intermetallic compounds thickness when fraction of ceria nanoparticles in the matrix was up to x = 0.6. It is suggested that for optimum set of soldering properties, the concentration of the nanoparticles should be at 0.6 wt% in the monolithic Sn–58Bi alloy. [ABSTRACT FROM AUTHOR]

The microstructural, mechanical, and tribological behaviors of electroplated Ni on Cu conducting substrates have been investigated in this study. The microstructural studies were performed by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The results showed that initially (111) with (220), (200) Ni texture components were predominant in the coating, and increasing the current density from 0.1 to 0.5 A/cm2 led to the development of a strong (111) texture. The presence of ultrafine grains coupled with a (111) Ni texture improved the coating microhardness and wear properties significantly. It was shown that with an increase in current density, wear resistance of the coatings improved significantly and the electrical resistivity increased due to the highly populated grain boundaries. [ABSTRACT FROM AUTHOR]

Abstract: In this article, the authors present the synthesis of Sn-1.0Ag-0.5Cu (SAC105) alloy embedded with zirconium oxide nanoparticles using simple mechanical blending and casting route. The cast samples were characterized in terms of microstructural evolution, wetting, microhardness, and drop test reliability. The characterizations were performed by using a tabletop X-ray diffraction, field emission scanning electron microscope, and the compositions were identified by energy dispersive spectroscopy. The results showed that addition of ZrO2 nanoparticles significantly refines the grain size, Ag3Sn, and Cu6Sn5 intermetallic compounds thickness by 46, 14, and 26% respectively as compared to the single component SAC105 alloy. The results were also compared with those of standard Sn-3.0Ag-0.5Cu (SAC305) alloy. Although the spreading and microhardness of SAC105 is found to be slightly poor or comparable to SAC305 yet drop test reliability can be improved significantly after addition of ZrO2 nanoparticles appreciably. This kind of refinement results in a cheap alternative to SAC305 with comparable mechanical strength and high solder joint reliability.Graphical Abstract: [ABSTRACT FROM AUTHOR]

The Al-Ni system is known as a high energy density materials (HEDM) because of its highly exothermic nature during intermetallic compound (IMC) formation. In this study, elemental Al and Ni powder were milled to explore the effect of cryomilling atmosphere on the microstructure and exothermic behavior. Scanning electron microscope (SEM) observations show continuous structural refinement up to 8 h of cryomilling. No IMC phase was detected in the X-ray diffraction (XRD) spectrum. Differential thermal analyzer (DTA) results show two exothermic peaks for 8 h cryomilled powder as compared to that of powder milled for 1 h. The ignition temperature of prepared powder mixture also decreased due to gradual structural refinement. The activation energy was also calculated and correlated with the DTA and SEM results. The cryomilled Al-Ni powder is composed of fine Al-Ni metastable junctions which improve the reactivity at a lower exothermic reaction temperature. [ABSTRACT FROM AUTHOR]

The solvothermal decomposition of iron complexes using the heat-up process enables monodisperse Fe3O4 nanoparticle synthesis. Here, we demonstrate that the high reduction potential capability of alkaline metal reagents in the reductive environment allows for pure magnetite phase formation at 200 °C, which is lower than that of typical synthetic method and offers highly crystalline superparamagnetic and ferrimagnetic nanostructures with the ability to control uniformity including spherical and cubic morphology with narrow size distributions. Our method involved reduction of the acetylacetonate and acetate anions to aldehyde and alcohol as an oxygen resource for iron oxide nucleation in an inert condition. For confirming the developed pure surface phase of alkaline metal reagent-assisted magnetite nanoparticle, the magnetic field-dependent shifting of blocking temperature was investigated. The degree of the exchange interaction between core spins and disordered surface spins is attributed to the ratio of core spins and disordered surface spins. The decrease in disordered surface spins deviation due to an enhanced pure phase of magnetite nanoparticles exhibited the negligible shift of the blocking temperature under differently applied external field, and it demonstrated that alkaline metal reagent-induced reductive conditions enable less formation of both disordered surface spins and biphasic nanostructures. [ABSTRACT FROM AUTHOR]

Cu-based compounds can be a good candidate for a low cost solar cell material. In particular, CuO (x : 1-2) has a good visible light absorbing bandgap at 1-2 eV. As for using nanostructures in solar cell applications, metal nanoparticle-induced localized plasmon resonance is a promising way to increase light absorbance, which can help improve the efficiency of solar cells. We fabricated ZnO nanorod/Au nanoparticles/CuO nanostructures to study their solar cell performance. ZnO nanorods and CuO layer were synthesized by the electrodeposition method. Size-controlled Au nanoparticles were deposited using E-beam evaporator for localized surface plasmon resonance (LSPR) effect. By inserting Au plasmon nanoparticles and annealing Au NPs in solar cells, we could tune the maximum incident photon-to-current efficiency wavelength. However, the potential well formed by Au NP at the ZnO/CuO junction leads to charge-trapping, based on the constructed electronic band analysis. LSPR-induced hot carrier generation is proposed to promote carrier transport further in the presence of Au NPs. [ABSTRACT FROM AUTHOR]

We report a modified TiO/ p-Si electronic structure that uses ultraviolet exposure for the incorporation of H. This structure was characterized using various photoelectron spectroscopic techniques. The ultraviolet (UV) exposure of the TiO surface allowed the Fermi energy level to be tuned by the insertion of H radicals, which induced changes in the heterojunction TiO/ p-Si diode properties. The UV exposure of the TiO surface was performed in air. On UVexposure, a photochemical reaction involving the incorporation of UV-induced H radicals led to the creation of a surface Ti-O-OH group and caused interstitial H doping (Ti-H-O) in the bulk, which modified the electronic structures in different ways, depending on the location of the H. On the basis of the band alignment determined using a combined spectroscopic analysis, it is suggested that the UV-induced H incorporation into the TiO could be utilized for the systematic tuning of the heterojunction property for solar cells, photocatalytic applications, and capacitors. [ABSTRACT FROM AUTHOR]

The processing of bulk metals through the application of severe plastic deformation (SPD) provides the potential for achieving exceptional grain refinement leading to ultrafine-grained (UFG) materials. These materials generally exhibit high strength but very limited ductility at room temperature. The recent development in the nanoindentation technique provides significant feasibility in evaluating the micro-mechanical behavior of UFG materials. Accordingly, this review examines the available experimental results showing the enhancement in strength and ductility through nanoindentation analysis in various materials after different SPD techniques. A comprehensive tabulation is also presented listing the available data for the strain rate sensitivity, m, in a variety of UFG metals processed by SPD. [ABSTRACT FROM AUTHOR]

This research describes the micro-mechanical behavior of an Al-Mg alloy system synthesized from two separate commercial Al-1050 and ZK60 alloys through the application of high-pressure torsion (HPT) for five turns at room temperature. The essential mechanical characteristics of the alloys are observed at the corresponding phases in a multi-layered structure at the disk center but the edge contains a metal matrix nanocomposite (MMNC) exhibiting an apparent plastic instability and decreasing strain rate sensitivity under strain rates of 10−4−10−3 s−1. The results demonstrate a significant opportunity for using HPT processing to prepare new alloy systems involving a wide range of MMNCs. [ABSTRACT FROM AUTHOR]

Disks of commercial Al-1050 and ZK60A alloys were stacked together and then processed by conventional high-pressure torsion (HPT) through 1 and 5 turns at room temperature to investigate the synthesis of an Al–Mg alloy system. Measurements of microhardness and observations of the microstructures and local compositions after processing through 5 turns revealed the formation of an ultrafine multi-layered structure in the central region of the disk but with an intermetallic β-Al3Mg2 phase in the form of nano-layers in the nanostructured Al matrix near the edge of the disk. The activation energy for diffusion bonding of the Al and Mg phases was estimated and it is shown that this value is low and consistent with surface diffusion due to the very high density of vacancy-type defects introduced by HPT processing. The results demonstrate a significant potential for making use of HPT processing in the preparation of new alloy systems. [ABSTRACT FROM PUBLISHER]

Aluminum alloys with nanocrystalline (NC) and ultrafine grain (UFG) size are of interest because of their strengths that are typically 30 pct greater than conventionally processed alloys of the same composition. In this study, UFG AA 5083 plate was prepared by quasi-isostatic (QI) forging of cryomilled powder, and the microstructure and mechanical behavior was investigated and compared with the behavior of coarse-grained AA 5083. Forging parameters were adjusted in an effort to strengthen the UFG material while retaining some tensile ductility. Different forging parameters were employed on three plates, with approximate dimensions of 254 mm diameter and 19 mm thickness. The overarching goal of the current effort was to increase strength through minimized grain growth during processing while maintaining ductility by breaking up prior particle boundaries (PPBs) with high forging pressures. Mechanical tests revealed that strength increased inversely with grain size, whereas ductility for some of the experimental materials was preserved at the level of the conventional alloy. The application of the Hall-Petch relationship to the materials was studied and is discussed in detail with consideration given to strengthening mechanisms other than grain size, including dispersion (Orowan), solid solution, and dislocation strengthening. [ABSTRACT FROM AUTHOR]

High-purity aluminum was processed by high-pressure torsion (HPT) under conventional monotonic (m-HPT) and cyclic (c-HPT) conditions where strain reversals are introduced in c-HPT during processing. Measurements show higher values of the Vickers microhardness in the center regions of all disks but these values are higher when processing by c-HPT by comparison with m-HPT for the same total number of turns. Slightly smaller grain sizes are observed in the c-HPT samples. It is shown that all of the microhardness values correlate with the estimated values of the equivalent strain and the results are consistent with earlier data reported under c-HPT conditions when it is recognized that the variation of hardness with equivalent strain is dependent upon the level of recovery within the material. [ABSTRACT FROM AUTHOR]

Al–Mg alloy powder was cryomilled to achieve a nanocrystalline (NC) structure having an average grain size of 50 nm with high thermal stability, and then consolidated by quasi-isostatic forging. The consolidation resulted in a bulk material with ultrafine grains of about 250 nm, and the material exhibited enhanced strength compared to conventionally processed Al–Mg alloy. The hardness of as-cryomilled powder, the forged ultrafine-grained (UFG) material, and the conventional coarse-grained (CG) alloy were measured by nanoindentation using various loading rates, and the results were compared with strain rate sensitivity (SRS) from uniaxial compression tests. Negative SRS was observed in the cryomilled NC powder and the forged UFG material, while the conventional alloy was relatively insensitive to strain rate. The dependence on loading rate was stronger in the NC powders than in the UFG material. [ABSTRACT FROM AUTHOR]

In the field of electronics packaging, Pb-bearing solder alloys are mostly used as robust interconnecting materials. The authors review the developments in Sn-Bi solders, the effects of nanoparticles incorporated into the Sn-Bi solder matrix on the morphology, shear strength, and wettability. [Extracted from the article]

The tensile properties and deformation response of an ultrafine-grained (UFG) Al–Mg alloy with bimodal grain structure were investigated using a micro-straining unit and a strain mapping technique. Atomized Al 5083 powder was ball-milled in liquid N2 to obtain a nanocrystalline (NC) structure, then blended with 50 wt.% unmilled coarse-grained (CG) powder, and consolidated to produce a bimodal grain structure. The blended powder was hot vacuum degassed to remove residual contaminants, consolidated by cold isostatic pressing (CIP), and then quasi-isostatic (QI) forged twice. The resultant material consisted of a UFG matrix and CG regions. The dynamic response during tensile deformation was observed using a light microscope, and the surface displacements were mapped and visualized using a digital image correlation (DIC) technique. The DIC results showed inhomogeneous strain between the UFG and CG regions after yielding, and the strain was localized primarily in the CG regions. Strain hardening in the CG regions accompanied the localization and was confirmed by variations in Vickers hardness. [ABSTRACT FROM AUTHOR]

Among laser additive manufacturing, selective laser melting (SLM) is one of the most popular methods to produce 3D printing products. The SLM process creates a product by selectively dissolving a layer of powder. However, due to the layerwise printing of metal powders, the initial microstructure is fully acicular α′-martensitic, and mechanical properties of the resultant product are often compromised. In this study, Ti-6Al-4V alloy was prepared using SLM method. The effect of heat treatment was carried out on as-built SLM Ti-6Al-4V alloy from 650–1000 °C to study respective changes in the morphology of α/α′-martensite and mechanical properties. The phase transition temperature was also analyzed through differential thermal analysis (DTA), and the microstructural studies were undertaken by optical microscopy (OM) and scanning electron microscopy (SEM). The mechanical properties were assessed by microhardness and compressive tests before and after heat treatment. The results showed that heat treated samples resulted in a reduction in interior defects and pores and turned the morphology of the α′-martensite into a lamellar (α + β) structure. The strength was significantly reduced after heat treatment, but the elongation was improved due to the reduction in columnar α′-martensite phase. An optimum set of strength and elongation was found at 900 °C. [ABSTRACT FROM AUTHOR]

The development of lightweight HEAs with high strength and low cost is an urgent requirement. In this study, equimolar AlCuSiFeX (X = Cr, Mn, Zn, Sn) lightweight HEAs were fabricated by advanced powder metallurgy. The mechanical alloying was performed for 45 h, and the powder compacts were densified at 650 °C. The final results revealed that AlCuSiFeSn lightweight HEA was composed of a single face-centered cubic (FCC) and Cu81Sn22, whereas AlCuSiFeZn showed a dual FCC and body-centered cubic (BCC) structures. Similarly, AlCuSiFeMn alloy contained a BCC + FCC phase with a µ-phase, whereas a σ-phase was present in AlCuSiFeCr in addition to FCC + BCC phases. We also calculated various thermodynamic parameters to predict the solid-solution phase stability of each of the above lightweight HEAs. It was found that lightweight HEAs with additive elements Sn and Zn tend to predominant FCC phases, whereas those with Cr and Mn result in major BCC with hard µ and σ phases, which further improve their mechanical strength. A maximum fracture strain of 23% was obtained for AlCuSiFeSn followed by 19% for AlCuSiFeZn HEA. The compressive fracture mechanisms of these lightweight HEAs are also discussed and reported here. [ABSTRACT FROM AUTHOR]

Brazing fillers for joining applications are essential for manufacturing and designing advanced materials. Several types of brazing fillers have been developed in recent decades to join similar or different engineering materials. Important parts of automotive and aircraft components, including steel, are often joined by brazing. In addition, ceramic components in microwave devices and circuits have been joined with a high level of integration in microelectronic devices. Similarly, in the medical field, metallic implants have been brazed to ceramic dental crowns. These advances have made human life more convenient. However, in brazing, there are certain issues with intermetallic compound (IMC) formation and residual stresses in joints at high temperatures. Nanoparticle-reinforced fillers have been proposed to control IMCs, but there are other dispersion and particle segregation issues at the joints. In this study, various types of brazing fillers, joint fabrication processes, and brazing technologies developed in recent decades are reviewed. Furthermore, new developments in brazing materials and their specific applications are presented. Finally, the emerging areas in brazing, including the recent entropy-modified brazing fillers for various structural and technological fields, are discussed. [ABSTRACT FROM AUTHOR]

This study investigated the effect of sandblasting particle size on the surface topography and compressive stresses of conventional zirconia (3 mol% yttria-stabilized tetragonal zirconia polycrystal; 3Y-TZP) and two highly translucent zirconia (4 or 5 mol% partially stabilized zirconia; 4Y-PSZ or 5Y-PSZ). Plate-shaped zirconia specimens (14.0 × 14.0 × 1.0 mm3, n = 60 for each grade) were sandblasted using different Al2O3 sizes (25, 50, 90, 110, and 125 μm) under 0.2 MPa for 10 s/cm2 at a 10 mm distance and a 90° angle. The surface topography was characterized using a 3-D confocal laser microscopy and inspected with a scanning electron microscope. To assess residual stresses, the tetragonal peak shift at 147 cm−1 was traced using micro-Raman spectroscopy. Al2O3 sandblasting altered surface topographies (p < 0.05), although highly translucent zirconia showed more pronounced changes compared to conventional zirconia. 5Y-PSZ abraded with 110 μm sand showed the highest Sa value (0.76 ± 0.12 μm). Larger particle induced more compressive stresses for 3Y-TZP (p < 0.05), while only 25 μm sand induced residual stresses for 5Y-PSZ. Al2O3 sandblasting with 110 μm sand for 3Y-TZP, 90 μm sand for 4Y-PSZ, and 25 μm sand for 5Y-PSZ were considered as the recommended blasting conditions. [ABSTRACT FROM AUTHOR]

Metallic and alloyed coatings are used widely in several decorative and technology-based applications. In this work, we selected Sn coatings plated on Cu substrates for joining applications. We employed two different plating baths for the fabrication of Sn and Ni coatings: acidic stannous sulfate for Sn and Watts bath for Ni layer. The plating current densities were varied from 100–500 mA/cm2. Further, the wear and friction behavior of the coatings were studied using a ball-on-disc apparatus under dry sliding conditions. The impact of current density was studied on the morphology, wear, and coefficient of friction (COF) of the resultant coatings. The wear experiments were done at various loads from 2–10 N. The sliding distance was fixed to 7 m. The wear loss was quantified in terms of the volume of the track geometry (width and depth of the tracks). The results indicate that current density has an important role in tailoring the composition and morphology of coatings, which affects the wear properties. At higher loads (8–10 N), Sn coatings on Ni/Cu had higher volume loss with a stable COF due to a mixed adhesive and oxidative type of wear mechanism. [ABSTRACT FROM AUTHOR]

We demonstrate that nonpolar m-plane surfaces can be generated on uniform GaN nanosheet arrays grown vertically from the (0001)-GaN bulk material. InGaN/GaN multiple quantum wells (MQWs) grown on the facets of these nanosheets are demonstrated by cross-sectional transmission electron microscopy. Owing to the high aspect ratio of the GaN nanosheet structure, the MQWs predominantly grow on nonpolar GaN planes. The results suggest that GaN nanosheets provide a conduction path for device fabrication and also a growth template to reduce the piezoelectric field inside the active region of InGaN-based light emitting diodes. [ABSTRACT FROM AUTHOR]

We reviewed the research and developments in the field of fatigue failure, focusing on very-high cycle fatigue (VHCF) of metals, alloys, and steels. We also discussed ultrasonic fatigue testing, historical relevance, major testing principles, and equipment. The VHCF behavior of Al, Mg, Ni, Ti, and various types of steels were analyzed. Furthermore, we highlighted the major defects, crack initiation sites, fatigue models, and simulation studies to understand the crack development in VHCF regimes. Finally, we reviewed the details regarding various issues and challenges in the field of VHCF for engineering metals and identified future directions in this area. [ABSTRACT FROM AUTHOR]