Parent Alloy Research Articles

Revealing Multistep Phase Separation in Metal Alloy Nanoparticles with In Situ Transmission Electron Microscopy.

Phase separation plays a crucial role in many natural and industrial processes, such as the formation of clouds and minerals and the distillation of crude oil. In metals and alloys, phase separation is an important approach often utilized to improve their mechanical strength for use in construction, automobile, and aerospace manufacturing. Despite its importance in many processes, the atomic details of phase separation are largely unknown. In particular, it is unclear how a different crystal phase emerges from the parent alloy. Here, using real-time in situ transmission electron microscopy, we describe the stages of the phase separation in face-centered cubic (fcc) AuRu alloy nanoparticles, resulting in a Ru phase with a hexagonal close-packed (hcp) crystal structure. Our observation reveals that the hcp Ru phase forms in two steps: the spinodal decomposition of the alloy produces metastable fcc Ru clusters, and as they grow larger, these clusters transform into hcp Ru domains. Our calculations indicate that the primary reason for the fcc-to-hcp transformation is the size-dependent competition between the interfacial and bulk energies of Ru domains. These insights into elusive, transient steps in the phase separation of alloys can aid in engineering nanomaterials with unconventional phases.

Atomic Origin of Minor Alloying Element Effect on Glass Forming Ability of Metallic Glass

Abstract The glass-forming ability (GFA) of metallic glasses is a key scientific challenge in their development and application, with compositional dependence playing a crucial role. Experimental studies have demonstrated that the addition of specific minor elements can greatly enhance the GFA of parent alloys, yet the underlying mechanism remains unclear. In this study, we use the ZrCuAl system as a model to explore how the addition of minor Al influences the crystallization rate by modulating the properties of the crystal-liquid interface, thereby affecting the GFA. The results reveal that the minor addition of Al significantly reduces the crystal growth rate, a phenomenon not governed by particle density fluctuations at the interface. The impact of minor element additions extends beyond a modest increase in crystal-unfavorable motifs in the bulk supercooled liquid. More importantly, it leads to a significant enrichment of these motifs at the crystal-supercooled liquid interface, forming a dense topological network of crystal-unfavorable structures that effectively prevent the growth of the crystalline interface and enhance GFA. Our results provide valuable insights for the design and development of high-performance metallic glasses.

Rapid Synthesis of Nanoporous Zn Powder by Selective Etching of Al from Micrometer-Sized Zn-Al Powder Particles Produced by Gas Atomization and Its Application in Hydrogen Generation.

The scalable synthesis of non-precious nanoporous metals, such as nanoporous zinc (NP-Zn), nanoporous iron (NP-Fe), and nanoporous aluminum (NP-Al), is crucial for large-scale production of hydrogen through the reaction between non-precious metals and water. The fabrication of bulk NP-Zn by selective removal of Al from sub-centimeter-sized arc-melted Zn-Al parent alloys through free corrosion dealloying usually takes a few days. Here, we demonstrate that this free corrosion dealloying process can be reduced from a few days to 4 min simply using micrometer-sized Zn-Al powder particles with nominal composition Zn40Al60 atomic % produced by gas atomization as the parent alloy. Reducing the size of the parent alloy significantly enhances the dealloying rate. Furthermore, Al and Zn are phase-separated in Zn-Al powder particles due to the gas atomization process, making removing the sacrificial Al phase easy. We used various techniques, including X-ray diffraction, Xe+ plasma focused ion beam/scanning electron microscopy (FIB/SEM), energy-dispersive spectroscopy (EDS), and inductively coupled plasma optical emission spectroscopy (ICP-OES) to thoroughly characterize these materials before and after free corrosion dealloying. The fabricated NP-Zn powder exhibits a hierarchical ligament/pore morphology, with tiny structures with a size of ≈10 nm coming from Zn nanoparticle aggregation during dealloying and large structures in the range of ≈50-200 nm coming from the removal of the sacrificial Al phase. We demonstrate that this NP-Zn can spontaneously react with water at near-neutral pH to produce hydrogen and zinc oxide solid byproducts with a hydrogen generation yield of ≈52% within 60 min.

Dealloying-induced Mn-enhancing nanoporous Fe-based spinel oxides as stable electrocatalysts for oxygen reduction reaction and rechargeable zinc-air battery

The dealloying-induced method is an effective strategy for the construction of low-cost, highly stable nanoporous catalysts. Herein, spinel oxides with nanoporous architecture are successfully constructed by dealloying of Al85Fe15-xMnx (x = 0, 1 and 3 at.%) parent alloy with different Mn dosages. These D-Al85Fe15-xMnx samples exhibit nanoporous and graphene-like edge architecture formed by the vertical staggered arrangement of nanosheets. The dealloyed samples possess high specific surface areas of 43.08–96.56 m2 g−1. As oxygen reduction reaction (ORR) catalysts in alkaline solution, the catalytic performance of the as-fabricated D-Al85Fe15-xMnx is positively related to the Mn doping proportion. The half-wave potential (E1/2) and Tafel slope are in the range of 0.688–0.712 V vs. RHE and 88.0–93.9 mV dec-1, respectively. The D-Al85Fe12Mn3 catalyst with the optimal catalytic performance shows excellent durability, and E1/2 has no significant variety after 2000 cycles accelerating degradation test (ADT). The zinc-air battery (ZAB) utilizing D-Al85Fe12Mn3 as the cathode catalyst exhibits a power density of 85.2 mW cm−2 and a high specific discharge capacity of 782 mAh g-1. The ZAB also has superb cyclic charge/discharge durability, which can work stably for more than 250 h at a constant current density of 5 mA cm−2. The reason for enhanced ORR performance after adding Mn is proposed, which is associated to the fact that Mn can increase the occupancy of B3+ in Oh interstices. This work highlights a simple strategy for constructing nanoporous spinel-based catalysts by dealloying-induced method as a promising candidate for ORR and ZAB cathode catalyst applications.

The effects of Cobalt doping on the structural, electronic, magnetic, and thermodynamic characteristics of the L10-FeNi alloy: First-principle calculations

This study conducts a computational analysis employing density functional theory (DFT) to investigate the effects of Cobalt doping as substitutional defects on the structural, electronic, magnetic, and thermodynamic characteristics of the L 10− FeNi alloy. The aim of this study was to explore their potential applications as alternatives to rare-earth permanent magnets. Two types of substitutional Co-doping (ONi/OFe) in the Ni/Fe-site of the parent alloy have been investigated. The computed formation energy indicates that the incorporation of cobalt defects increases the structural stability of tetragonally distorted L10FeNi via Co-doping. The results we obtained demonstrate that the FeNi:Co (ONi) in the L10-structure has a large enhancement in magnetic moments and saturation magnetization (Ms), whereas for the FeNi:Co (OFe), has a small reduction in Ms. Furthermore, reducing the concentration of cobalt in L10 FeNi:Co alloys is advantageous in diminishing the volumetric thermal expansion coefficient, consequently lowering the Debye temperature and weakening atom interactions. Therefore, Co-substituted FeNi alloys hold promise as potential candidates for rare-earth-free permanent magnets.

Electrodeposition of Ag-Au Alloys and Design of Nanoporous Gold with Controlled Porosity

Due to its unique physicochemical, mechanical, and optical properties, Nanoporous gold (NPG) is of interest for various applications.[1-3] Its monolithic structure with the nanoscale size of ligaments and rich surface electrochemistry make the NPG materials unique for use in electrocatalysts, energy storage, sensors and plasmonics. The length scale of NPG porosity (ligaments & open pores) and its effect on the properties is essential for such a broad range of applications. The porosity size can be controlled by parent alloy composition, dealloying (chemical, electrochemical) method, and the temperature of dealloying and annealing. Using the electrochemical surface processes to change and fine-tune the size, uniformity and hierarchy of the ligament network has been attracting attention as a possible tool for manipulating and designing new and improved NPG functionalities. [4, 5]We will present an all-electrochemical approach to creating NPG thin films with different sizes of porosity from AgxAu1-x alloys. The alloys of various compositions were electrodeposited at the constant potential from a thiosulfate-based solution by controlling the potential and concentration of Ag+ and Au+ ions.[6] The electrodeposited alloys' structural (SEM, AFM) and composition (XPS) characterisation was followed by the selective dissolution of Ag under electrochemical control. Pb monolayer underpotential deposition (UPD) was used to measure the surface area of as-created NPG structures. [7] The surface stress-driven surface alloying [8] taking place during this UPD process was exploited as an electrochemical tool to modify the NPG structure. Combining electrochemical and structural characterisation, we followed the evolution of porosity by controlling the range of the UPD potentials, scan rate and the number of cycles applied. References Biener, J., et al., Nanoporous Plasmonic Metamaterials. Advanced Materials, 2008. 20(6): p. 1211-1217. Qiu, H.J., et al., Correlation of the structure and applications of dealloyed nanoporous metals in catalysis and energy conversion/storage. Nanoscale, 2015. 7(2): p. 386-400. Weissmüller, J. and K. Sieradzki, Dealloyed nanoporous materials with interface-controlled behavior. MRS Bulletin, 2018. 43(1): p. 14-19. Sharma, A., et al., Electrochemical annealing of nanoporous gold by application of cyclic potential sweeps. Nanotechnology, 2015. 26(8): p. 085602. Dorofeeva, T.S., et al., Electrochemically Triggered Pore Expansion in Nanoporous Gold Thin Films. J. Phys. Chem. C, 2016. 120(7): p. 4080-4086. McCurry, D.A., et al., All electrochemical fabrication of a platinized nanoporous Au thin-film catalyst. ACS Appl Mater Interfaces, 2011. 3(11): p. 4459-68. Liu, Y., S. Bliznakov, and N. Dimitrov, Comprehensive Study of the Application of a Pb Underpotential Deposition-Assisted Method for Surface Area Measurement of Metallic Nanoporous Materials. J Phys Chem C, 2009. 113: p. 12362–12372. Nutariya, J., et al., Surface alloying/dealloying in Pb/Au (111) system. ECS Transactions, 2010. 28(25): p. 15-25. Vasiljevic, N. and A. Szczepanska, Surface Alloying During Pb Underpotential Deposition on Au(111). Journal of The Electrochemical Society, 2022. 169(11): p. 112509 (1-8)

Half‐Heusler Alloy CoMnZ (Z = Sb/Sn): Electrode Material for Lithium‐Ion Batteries

ABSTRACTHeusler alloys (HAs) are a well‐known family of compounds generating promising interest due to their robust structure, ease of tailoring their unique properties, and potential applications. The investigations in the direction of the electrochemical performance of these materials as electrodes for rechargeable lithium‐ion batteries (LIBs) have been established theoretically and experimentally. Alloying of alkali metal ions into half‐HAs unit cells can be another route to improve LIBs performance. This work presents our investigations on thermodynamically stable half‐HAs CoMnZ (Z: Sb/Sn) as electrode materials for rechargeable LIBs using the first‐principle calculations based on the density functional theory. The negative formation energies validate the thermodynamic stability of the alloys considered in this study. With increasing Li doping, a structural change from cubic to tetragonal and orthorhombic phase is observed in the host structure, and upon full lithiation (LiMnZ), a cubic structure is attained. The band structure calculations of the host structure and its lithiated phase indicate a metallic nature in these alloys. The calculations are also performed to investigate the structural stability of parent alloys and corresponding lithiated phases. We calculated a storage capacity of around 14.5 Ah/kg for 0.125 atomic fraction of Li atoms, which is increased by nearly 10 times upon full lithiation. A maximum open circuit voltage of around 9.8 V is calculated for Li0.125Co0.875MnSb and CoLi0.125Mn0.875Sb. Thus, all these remarkable results suggest that these intermetallic compounds have a strong potential as the cathode material for LIBs with a robust life and a large capacity.

Mechanical and microstructural profiling of additively manufactured cobalt–nickel functional gradient structure

In this study, a functional gradient material (FGM) structure composed of a nickel alloy (IN718), and a cobalt alloy (CoCrMo) was additively manufactured using a co-axial powder-fed laser-directed energy deposition (L-DED) system. The high manufacturing flexibility of L-DED enabled the seamless deposition of IN718-CoCrMo FGM structure through interfacial bonding driven by thermal gradient and cool-down mechanisms. Microscopic analysis confirmed the absence of cracks or delamination in the CoCrMo-IN718 interfacial bonding region. The SEM-EBSD microstructural analysis and micro-hardness testing were performed on the as-printed CoCrMo-IN718 FGM primarily to correlate the hardness properties-microstructural grain phase morphology between the parent alloys and their interfacial bonding region. It was observed that the average hardness of the CoCrMo-IN718 interface zone (322.83 HV1) fell between IN718 (268.67 HV1) and CoCrMo (359.75 HV1) regions. The EBSD analysis reports indicated that along the build direction of CoCrMo-IN718 FGM, the preferential grain orientation aligned in [100] with grain structure transitioning from equiaxed → columnar → elongated columnar dendrites → equiaxed grain, predominantly comprised of face-centered cubic (FCC)-gamma (γ) phase crystal structures. Relatively, coarser grain structures were observed in the interface bonding region, attributed to the analogous crystallography space groups, and prolonged localized thermal gradients.

Computational Investigation on the Structural, Electronic and Magnetic Properties of Si-Doped L10 FeNi Alloy for Clean Energy

For the first time, this study conducts a computational analysis by employing density functional theory (DFT) to investigate the effects of silicon doping as substitutional defects on the structural, electronic, and magnetic characteristics of the L10-FeNi alloy. The aim of this study was to explore the potential applications of Si-doped FeNi compounds as alternatives to rare-earth permanent magnets. For this, we have performed full potential calculations of L10-FeNi with substitutional Si-doping within a generalized gradient approximation. Two types of substitutional Si-doping (ONi/OFe) in the Ni/Fe site of the parent alloy have been investigated. The computed formation energy (Ef) indicates that the incorporation of silicon defects increases the structural stability of tetragonally distorted L10-FeNi. Moreover, our findings demonstrate that the FeNi:Si(ONi) in the L10-structure has a stable saturation magnetization (Ms), whereas the FeNi:Si (OFe) has a small reduction in Ms. Therefore, Si-substituted FeNi alloys can be tuned to become a good candidate for permanents magnets.

Nitrogenation of Nd(Fe,Mo)12 powders for sintered magnets

The intermetallic Rare Earth-Fe12 (REFe12) compounds are considered as the strongest candidates for alternative high-performance permanent magnet material, thanks to the combination of high magnetocrystalline anisotropy, high Curie temperature and moderate saturation magnetization. However, the NdFe12 based compounds suffer from a weak uniaxial magnetocristalline anisotropy at room temperature. The insertion of light elements, like nitrogen, induces a strong uniaxial anisotropy and an increase of the Curie temperature as well. Nevertheless, the nitrogenation of these compounds have proved to be tricky, as the reaction kinetics is very slow at moderate temperatures, whereas the decomposition of the 1–12 phase occurs at higher temperatures. In the present study the aim is to develop nitrogenated powders suitable for the manufacture of Nd(Fe,Mo)12N-based sintered magnets, starting from Nd(Fe,Mo)12 precursors prepared by strip-casting. The nitrogenation of Nd(Fe,Mo)12 powders was undertaken to analyze the mechanisms of reaction and to determine the experimental conditions allowing to avoid both the formation of α-Fe and the nitrogenation of the Nd-rich intergranular phase. Structural and magnetic investigations are performed on the parent alloys and the nitrogenated powders, allowing to identify the mechanism of the solid-gas reaction and to determine, for the first time to our knowledge, the nitrogen thermodynamic equilibrium pressure between the 1–12 phase and its nitride.

Elucidating the Transition of 3D Morphological Evolution of Binary Alloys in Molten Salts with Metal Ion Additives.

Molten salts serve as effective high-temperature heat transfer fluids and thermal storage media used in a wide range of energy generation and storage facilities, including concentrated solar power plants, molten salt reactors and high-temperature batteries. However, at the salt-metal interfaces, a complex interplay of charge-transfer reactions involving various metal ions, generated either as fission products or through corrosion of structural materials, takes place. Simultaneously, there is a mass transport of ions or atoms within the molten salt and the parent alloys. The precise physical and chemical mechanisms leading to the diverse morphological changes in these materials remain unclear. To address this knowledge gap, this work employed a combination of synchrotron X-ray nanotomography and electron microscopy to study the morphological and chemical evolution of Ni-20Cr in molten KCl-MgCl2, while considering the influence of metal ions (Ni2+, Ce3+, and Eu3+) and variations in salt composition. Our research suggests that the interplay between interfacial diffusivity and reactivity determines the morphological evolution. The summary of the associated mass transport and reaction processes presented in this work is a step forward toward achieving a fundamental comprehension of the interactions between molten salts and alloys. Overall, the findings offer valuable insights for predicting the diverse chemical and structural alterations experienced by alloys in molten salt environments, thus aiding in the development of protective strategies for future applications involving molten salts.

Cost-Effective Microfabricated Silver-Based Paper Cathodes for High-Discharge-Rate Aluminum-Air Batteries

We report a cost-effective microfabricated silver-based air-cathode for high-discharge-rate aluminum-air batteries which are suitable for micro-drone applications. A challenge for batteries for aerial drones is that both high gravimetric energy density and power density are required for extended operation. While air batteries can address the energy density issue, achieving high power density necessitates high loadings of expensive catalytic materials such as platinum (Pt), which can constitute over 99% of the cost in commercial air batteries. [1] Building upon prior research that studied the power performance of an aluminum-air battery (AAB) system with a silver-based cathode, this study further explores the influence of silver (Ag) sputtering conditions and Ag loadings on AAB power performance. [2]The power performance of AAB is significantly influenced by both air flux through the air cathode and electrochemically active catalyst surface area ratio (ECSA). The ECSA is the ratio of the electrochemically active catalyst surface area to its cathode area. Sputtered Ag cathodes with catalyst loadings ranging from 0.03 mg-Ag/cm2 to 0.3 mg-Ag/cm2 consistently show high porosity, indicating good air flux for the microfabricated cathode. Increasing the loading of the sputtered Ag catalyst further can lead to particle agglomeration. To improve power performance and ECSA, a silver-copper (AgCu) co-sputtering technique has been developed, significantly increasing the surface area and power performance.Figure 1 shows cathodes with Ag loadings ranging from 0.038 mg-Ag/cm2 to 0.267 mg-Ag/cm2 under two silver sputtering conditions: 400W+5mTorr and 100W+10mTorr. Within the examined range, the latter sputtering condition shows superior power performance compared to the former. For Ag loadings exceeding 0.1 mg-Ag/cm2, both conditions show decreasing power performance as Ag loading increases, and the 100W+10mTorr curve shows a maximum power at 0.088 mg-Ag/cm2. Figure 2 shows SEM images of 0.038 mg-Ag/cm2, 0.088 mg-Ag/cm2, and 0.19 mg-Ag/cm2 films, using the 100W+10mTorr sputtering condition. Ag particle size increases with higher Ag loading, which can result from particle agglomeration. Figure 3 shows the catalyst layer porosity and the ECSA calculated from the SEM images. All samples show porosity over 90%, indicating good air flux for the microfabricated Ag cathode. The trend of ECSA for different Ag loading correlates well with the power performance, suggesting that the power performance of the microfabricated Ag cathode primarily depends on the ECSA.Further enhancement of the ECSA through AgCu co-deposition is investigated, involving two parent alloy compositions (at%): Ag28Cu72 and Ag16Cu84. Following the co-sputtering, the parent alloy undergoes selective etching of Cu using hydrochloric acid (HCl). Figure 4 compares power performance between Ag28Cu72 and Ag16Cu84. Both curves exhibit an upward trend as the silver loading increases from 0.09 mg-Ag/cm2 to 0.4 mg-Ag/cm2, with Ag28Cu72 samples showing superior power performance. Figure 5 shows an SEM image of Ag28Cu72 parent alloy with 0.32 mg-Ag/cm2 loading after Cu etching, demonstrating that the ECSA increased to 47.52 while maintaining a high porosity of 90.2%. The peak power of Ag28Cu72 0.32 mg-Ag/cm2 sample is increased to 200 mW/cm2. By comparison, a 4mg-Pt/cm2 commercial cathode shows a peak power of 280 mW/cm2.Figure 6 compares the discharge performance of the 0.088 mg-Ag/cm2 cathode with a commercial 4 mg-Pt/cm2 cathode. Both cells can discharge under 1.1 Amp with a power density exceeding 500 W/kgbattery, a threshold sufficient to lift a quadrotor drone. [3] Battery weight encompasses anode, cathode, electrolyte and battery packaging. The 0.088 mg-Ag/cm2 cathode shows a discharge power plateau above 600 W/kgbattery (86% of the 4 mg-Pt/cm2) and an energy density of 228 Wh/kgbattery when discharge power density exceeding 500 W/kgbattery (95% of the 4 mg-Pt/cm2). Remarkably, the material cost of the 0.088 mg-Ag/cm2 cathode is 5000 times less than the 4 mg-Pt/cm2 cathode.

Development of High Strength and Super Electrical Conductive Cu-3Ti-2Si-1.5Ni-xNb Alloys

The study explored the mechanical and electrical behavior of niobium-doped Cu-3Ti-2Si-1.5Ni alloys by Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS), micro-Vickers hardness, and electrical conductivity tests. The stir-casted alloys underwent solution treatment at 900 °C/5 h and cooled in air. Results showed that niobium additions led to significant improvements in the properties of the parent alloy. The ultimate tensile strength, yield strength, hardness, and electrical conductivity reached maximum values of 528 MPa, 437 MPa, 358 HV, and 58.5 %IACS, respectively, at 1.1 wt% Nb addition. The enhancements were attributed to increased precipitation of second phases and refined grain structure. However, the percentage elongation decreased with niobium addition. These findings demonstrate that Cu-3Ti-2Si-1.5Ni alloys with niobium nanopowder exhibit a promising balance of mechanical and electrical performances, making them suitable for advanced engineering applications.

Broadening the Realm of Nanoporous Gold Catalysts: Preparation and Properties When Emanating from AuCu as Parent Alloy

AbstractNanoporous gold (npAu) attracted increasing attention over the last 20 years as a highly active and selective oxidation catalyst in particular at low temperatures. Previous research mainly focused on npAu that was fabricated by corrosive dealloying of AuAg parent alloys. Yet, the use of other binary alloys, such as AuCu, promises interesting variations of the catalytic properties, when considering that residual amounts of the less noble metal were shown to be co‐catalytically involved. Aiming at providing a platform for systematic studies in this direction for Cu, we not only dealt with strategies for a reliable and reproducible preparation of npAu(Cu) catalysts from AuCu, but also with their potential for CO oxidation in comparison to npAu(Ag). We were able to develop an approach based on thermally quenched Au0.3Cu0.7 alloys, providing distinct synthetic advantages as a starting material for the catalyst fabrication versus the thermodynamically more stable AuCu3 intermetallic compound. Using PCD (potentiostatically controlled dealloying), well‐defined pore structures with ligament diameters of ∼40 nm and variable residual Cu concentrations in the range between ∼0.6 at % and ∼1.2 at % could be straightforwardly obtained. After activating such catalysts at 150 °C, they reproducibly showed catalytic activity for aerobic CO oxidation in a broad temperature window between 40 °C and 250 °C. As opposed to npAu(Ag), the activity increased with decreasing residual Cu content, outperforming the former at temperatures above ∼60 °C not only with respect to CO2 formation rates but also with respect to thermal stability. Based on X‐ray photoelectron spectroscopic and transmission electron microscopic results, it was possible to conclude that Cu segregates to the surface and, with rising Cu bulk content, increasingly occurs in form of Cu2+ species at the surface. While the latter are expected to be catalytically inactive, Cu and Cu+ species are likely candidates for the activation of oxygen being not possible on pure Au.

Thermodynamic and elastic properties of laves phase AB2-based alloys and their hydrides: A density functional theory (DFT) study

A first-principles method based on the density functional theory (DFT) was employed in conjunction with quasi-harmonic Debye model to investigate the structural, elastic, and thermodynamic properties of a series of AB2-based Laves phases alloys and their hydrides. Simulation results revealed that the studied materials possess the Laves phase structure with lattice parameters comparable to experimental findings. For the first time, to the best of our knowledge, mixing entropy determined using Debye model was used to classify alloys into (Low- Medium-High Entropy Alloys) LEA, MEA and HEA categories rather than the commonly used ideal solution model, which is often inaccurate and ignores the impact of temperature. Lattice analyses of the alloy materials indicated that cell volume increases with the addition of elements, while the enthalpy of hydride formation indicates that hydrogen absorption in these alloys is exothermic and that the 3.00 H/F.U configuration is energetically stable. The alloys and their hydrides are metallic with no band gap at the Fermi level. The thermodynamic properties were studied using the quasi-harmonic Debye model and it was found that Bulk modulus decreases with increasing volume, and the hydrides possess lower bulk modulus compared to their metallic counterparts. Moreover, Debye temperature decreases with the gradual addition of elements, indicating weaker chemical bonds in ternary and other alloys. All hydrides have lower Debye temperature than their parent alloy materials. Finally, The alloys are classified into low-, medium-, and high-entropy alloys based on mixing entropy calculated using the Debye model. TiMn2 is classified as a low-entropy alloy, ZrMn2, Ti0.5Zr0.5Mn2, and Ti0.5Zr0.5MnFe as medium-entropy alloys, and Ti0.5Zr0.5(MnCr)2, Ti0.5Zr0.5Mn2/3Fe2/3Cr2/3, and Ti0.5Zr0.5Mn0.5Fe0.5Cr0.5Ni0.5 as high-entropy alloys.

On reinforcing the friction stir weld joints of AA5086-H116 using the plasma spray coatings

The fatigue properties of friction stir weld joints of AA5086-H116 alloy, reinforced with Al2O3 particles using the plasma spray coating method, were investigated after single and double weld passes. A relatively uniform distribution of reinforced particles was achieved with superior properties, even higher than that of the parent alloy. The reinforced joints had enhanced hardness as well as joint efficiency, the double pass being superior to the single pass, but at the cost of reduced total elongation. Furthermore, the reinforced double-pass joints exhibited a remarkable ∼ 55%, ∼ 14%, and ∼ 89% increase in fatigue strength compared to the as-weld, the base material, and single-pass joints, respectively. The fractographic examination mainly revealed a defect-free crack initiation mechanism with a few cases of the ones induced by defects. The superior fatigue performance was mainly attributed to the uniform spatial and size distribution of fine Al2O3 particles within the weld nugget zone, thanks to the novel weld reinforcement method used in this study, which provides a promising avenue for improving the fatigue properties of weld joints.

Influence of tool geometry on mechanical and microstructural characteristics of friction stir welded cast alloys

Abstract Cast alloys find suitable applicability in aerospace sector owing to low porosity, high specific strength, corrosion resistance, fluidity and good machinability. The investigation focuses on friction stir welding (FSW) of cast A356 and A2014 alloys with varied range of process parameters, namely tool pin shape (cylinder, threaded cylinder, square, and conical), tool rotation speed (1800–2100 rpm) and welding speed (10–25 mm × min−1). Experimentation on stirwelding was performed based on selected tool pin shape between varied tool rotation and welding speed. The output responses, namely Ultimate tensile strength (UTS) and micro hardness, have been evaluated to study the effect of each tool. The microstructural characteristics of the weld samples were analyzed using optical microscope and scanning electron microscope (SEM) technique. The microstructural observation unveiled that complete fusion prevails between the parent alloys devoid of micro porosities and segregations. The re-crystallization effect resulted in the finer grains. The cylinder-shaped tool with a thread and square shaped tool rendered better strength and hardness properties of 136.6 MPa and 109.4 HV, respectively.

Influence of preparation processes with or without long-time homogenization heat treatment on performance of Nd–Fe–B HDDR products

We investigated the influence of hydrogenation-disproportionation-desorption-recombination (HDDR) preparation processes, with or without long-time homogenization heat treatment, on the microstructure and hard magnetic properties of Nd12.7B6.5Co2.1Cr0.1Al0.5Nb0.3Ga0.5Fe77.3 powders/bonded magnets. Hard magnetic properties such as remanence (Br = 1.01 T), coercivity (Hcj = 949.39 kA/m), and maximum magnetic energy product (BH)max = 181.54 kJ/m3 were achieved for HDDR bonded magnets with homogenization heat treatment. In contrast, magnets prepared without homogenization heat treatment exhibited Br = 0.65 T, Hcj = 854.69 kA/m, and (BH)max = 66.98 kJ/m3. The notable decrease in remanence for magnets prepared without homogenization treatment is attributed to the presence of α–Fe in the parent alloy, which inhibits the hydrogenation-disproportionation process and consequently affects the orientation of the crystallographic texture. Furthermore, we fabricated bonded quadrupole magnetic rings using HDDR powder prepared with homogenization heat treatment. The study also explored the relationship between disproportionation temperature and surface magnetic field intensity for these quadrupole magnetic rings.

Effect of pulse gas tungsten arc welding on the metallurgical characteristics & microstructural evolution in AZ31B magnesium alloy welds

This work assessed the effects of frequency & the pulse duration ratios on the weldability & structure-property relationships for the magnesium alloy AZ31B. In addition, AC/DC pulse welding with different pulse duration ratios was explored, to assess controlled repair welding on magnesium alloy castings. Complete penetration welds can be produced with conventional GTA welding using a heat input of ∼500 J/mm without the need for an active flux. However, the weld metal has a coarse grain structure and micro cracks, suggesting the need for an even better control of heat input for achieving defect free welds. Pulse GTA welding with at lower frequencies give relatively deeper penetration joints at different pulse duration ratios (1:1, 1:2 and 1:4). However, the full penetration welds are possible only with pulse duration ratio of 1:1. All the welds produced under pulsed GTA welding conditions were defect free. The grain sizes of the weld metals were much finer than for conventional GTA welding conditions and have a higher hardness compared to conventional GTA weld & also the parent alloy. Use of AC/DC mix for pulse welding, with the peak current being AC and the base current as DC, yields shallow penetration welds with no defects. The resultant weld metal microstructures are of finer grain size, and with finely distributed β-phase particles. This welding technique can be exploited for repair welding of magnesium alloy castings that have near-surface defects.

Lightweight porous high entropy alloy based on triple-phase eutectic structure matrix

Porous metal materials often show great potential and practical application as structural materials and functional materials in energy, environment and other fields because of their unique structure and properties. This study utilized the potential difference between different phases to immerse the Co18Cr18Fe18Ni26Al10Nb10 triple-phase eutectic high entropy alloy (HEA) into aqua regia, selectively corroding the two phases, and preparing a porous material with a uniform structure. X-ray diffraction (XRD) and the energy dispersive spectroscope (EDS) indicate that the porous material is mainly composed of Laves phase, enriched with Nb element. Compression specimens were prepared into a composite material with porous material wrapping the parent alloy by dealloying method. When the immersion time is up to 3 h, the porous materials still lead to a promising property with a yield strength of 1553.45 MPa and specific strength of 232.55 KN·m/Kg with density of 6.7 g/cm3. This work provides a design strategy to obtain a HEA with lower density and higher specific strength by porous structure.