Free Alloy Research Articles

Improved properties of wire arc directed energy deposited thin-walled Al-6Mg-0.3Sc component via laser shock peening

ABSTRACT Heat treatment free aluminum alloys have been developed for wire arc directed energy deposition (DED) large thin-walled components, but their further performance enhancement methods remain unexplored. In this study, laser shock peening (LSP) treatment was performed on wire arc DED Al-6Mg-0.3Sc components. The results show that LSP creates a gradient microstructure with submicro-grains near the surface. The effects of LSP on defects were quantified by quasi-in-situ CT, demonstrating a reduction in porosity by over 68% together with decreased size. Simultaneously, tensile strength increases by 39.5% to 295.8 ± 6.4 MPa with only a marginal loss of elongation, as compared to the as-deposited (AD) state. This was due to the accumulation of dislocations and continuous dynamic recrystallization lead to grain refinement, as well as the appearance of a triple heterogeneous microstructure. Therefore, this study offers a novel solution for manufacturing of high-performance heat treatment free large thin-walled components.

Comparison of the Young’s modulus of the lead free solder alloy Sn-Ag3.8-Cu0.7 determined by hot tensile tests, ultrasonic measurements and [formula omitted]-Sn single crystal calculations

Sn-based solders are known for their tendency to form coarse grained microstructures. In combination with the high elastic anisotropy of β-Sn, the overall elastic properties and their interpretation require a careful discussion of the structure–property-relationship as elastic constants are often important input parameters for creep or fatigue models. This study therefore investigates the influence of microstructure and testing method on the Young’s modulus E for the widespread lead free solder alloy Sn-Ag3.8-Cu0.7 (SAC387) using bulk specimens. Due to its already high homologous temperature at room temperature (Thom≈ 0.6 = T/Tm for Tm being the melting temperature), hot tensile tests generally bear the risk of superimposed creep deformation. Mechanical testing becomes even more challenging, since yield strengths are usually low for these alloys. Consequently, in addition to the hot tensile tests executed for the engineering strain rate ϵ̇e=1⋅10−3 s−1, two supplemental methods are used to determine the Young’s modulus comprising of the dynamic resonance frequency measurement and the calculation of the Young’s modulus based on single crystal compliance data of the majority phase β-Sn.Young’s moduli yielded from dynamic resonance frequency measurement and calculations based on single crystal compliance data showed comparable results of (E35 °C≈ 55 GPa, E80 °C≈ 51 GPa and E125 °C≈ 48 GPa). Hot tensile tests showed similar data with the largest deviation at 80 °C, where E80 °C≈ 53 GPa was determined. These absolute values and their temperature dependence can be attributed to the microstructure of the cast specimens which show a general preferred orientation of β-Sn grains close to <110> after analysis via electron backscattered diffraction (EBSD). A comparison with literature data revealed significant differences in the Young’s moduli which are likely to be attributed to differences in the preferred orientation of β-Sn grains.

Design and development of thermo-electromagnetic system for spinodal decompositions of FeCrCo alloys

Permanent magnets are essential components of electromechanical devices. Majority of magnets are used in permanent magnet motors that have extensive application in relation to energy efficiency and sustainability like electric vehicles. This research is aimed for efficient manufacturing of FeCrCo permanent magnets. Electromagnets could be utilized for the generation of continuous magnetic field to use in number of manufacturing processes. A two-pole electromagnet, comprising of two solenoids each having 2200 turns of copper wire, was developed. The system was designed to produce magnetic field up to 10 kilo Gauss for spinodal decomposition of FeCrCo alloy samples under thermomagnetic treatment process. Being rare earth free alloys, FeCrCo magnet is gaining research focus as an alternative magnetic alloy for advanced applications. The electromagnetic system design was refined and confirmed by using the Finite Element Method. The experimental values, of magnetic field generated by the two-pole electromagnet setup, were well close to the simulation results. The magnetizing setup was utilized to treat the FeCrCo magnetic alloy samples simultaneously at high temperature (700 °C) and magnetic field (7 kilo Gauss). This thermo-magnetic setup helped to improve the metallurgical structures of FeCrCo to grow and develop more efficiently. Treated samples of FeCrCo alloy demonstrated enhanced magnetic properties due to effective spinodal decomposition. The improvement in magnetic properties was attributed to the elimination of retained alpha phase and formation of more alpha-1 phase.

Unveiling synergistic strength and plasticity enhancement of Mg–Zn–Mn alloy via closed forging extrusion

A cost-effective, high-performance Mg-2.0Zn-1.5Mn alloy was fabricated using closed forging extrusion (CFE). The results reveal that CFE can promote a dynamic recrystallization (DRX) ratio and enhance the residual dislocation density in deformed grains and subgrains. Grain refinement is achieved through multiple DRX mechanisms, particle-stimulated nucleation, and pinning effects. In addition, the basal texture and precipitation behavior are significantly influenced by pre-forging in CFE. Finally, grain refinement and substantial residual dislocations result in a good combination of strength and plasticity, with the ultimate tensile strength of 400 MPa and elongation of 22.1%, respectively. A novel strategy for regulating the bimodal grain structure is proposed to guide the optimization of the mechanical performance of rare-earth free Mg alloys.

Noble metal free high entropy alloys with amorphous based heterostructures for the oxygen evolution reaction

Designing cost-effective catalysts with high activity and stability for the oxygen evolution reaction (OER) is important to scale-up the water electrolysis process for hydrogen production.

The millisecond fabrication of medium-entropy alloy as a high-performance bifunctional electrocatalyst for ultralong-term rechargeable zinc–air batteries

Zinc air battery (ZAB) has widely recognized advantages such as high theoretical energy density, environmental friendliness, and safety. However, its cathodic reactions involve sluggish four-electron process oxygen reduction and oxygen evolution reactions (ORR and OER). Therefore, developing a cheap, efficient and durable dual functional oxygen electrocatalyst has important scientific significance and practical value for the development of ZAB. Herein, we applied noble metal free medium-entropy alloy (CoFeNi) nanoparticles which were in embedded nitrogen doped carbon framework (N-PCF) as a highly active and ultra-stable bifunctional electrocatalyst. The CoFeNi@N-PCF was prepared by high temperature thermal shock approach from ion-exchanged ZIF percussor to ensure the uniform dispersion of medium-entropy alloy, hierarchical porosity and strong metal-support interaction. Due to the medium-entropy induced synergistic effects, the as-prepared bifunctional electrocatalyst has a large ORR onset potential (Eonset) of 0.92 V and half-wave potential (E1/2) of 0.85 V (vs. RHE) in 0.1 M KOH. And the overpotential of OER in 1.0 M KOH is only 320 mV at 10 mA cm−2. When used in ZAB, the as-assembled rechargeable ZAB with the self-supported air electrode provides an extremely high-power density of 203 mW cm−2, a superior specific capacity of 812 mAh g−1, and amazing cycled steadily for 600 h. The assembled flexible ZAB with CoFeNi@N-PCF exhibits an excellent stability (over 45 h) and the excellent bending ability under different angles. This work can provide some new insights into the design and preparation of advanced bifunctional oxygen electrocatalysts for next-generation metal-air batteries.

Reaction with hot air of high entropy alloys strengthened by monocarbides formed from heavy metals: assessment of the oxidation kinetics from the analysis of the chemically changed subsurfaces

As in classical superalloys based on nickel or cobalt, MC carbides can be easily obtained in cast high entropy alloys (HEA) for enhancing their mechanical properties at high temperatures. These carbides may have also some influence on the hot oxidation properties. They can be also not neutral for the oxidation behavior. To explore their possible influence in this field, an equimolar CoNiFeMnCr reference alloy and two versions containing TaC or HfC carbides were prepared by casting and exposed to air at 1000°C. Their oxidation behaviors were studied by characterizing the obtained corrosion products and the modifications induced in the subsurfaces of the samples. Results show that TaC and HfC are moderately involved in the oxidation phenomena but they obviously influence the Cr and Mn diffusion toward the oxidation front. This seemingly aggravates more the already poor oxidation high temperature resistance of the base alloy. However the harmful effect of the TaC seems to be much lower than the one of the HfC, and the TaC–strengthened CoNiFeMnCr alloy is only a little less resistant against oxidation than the carbide–free reference equimolar alloy.

Grafted magnet C-Mn0.5Bi0.5 with a cohesive C-sp2 spin layer and its impacts on the exchange-coupled magnetic properties

The Mn0.5Bi0.5 is a model rare-earth-free alloy of profound properties for uses as small magnets, tools and many other devices. In a view to upgrade its features, here we report that a grafted C-Mn0.5Bi0.5 exhibits superior magnetic properties in small core-shells. It is safer from erosion in air atmosphere. When milling Mn0.5Bi0.5 (a fine powder) with carbon, up to 4 wt%, in hexane (or a similar lubricant) in an autoclave, a grafted C-sp2 layer (S2) forms on refined metallic surfaces (S1) in a C-Mn0.5Bi0.5 core-shell. A compressed lattice, 9.135 g/cm3 crystal density (up to 2.1% larger from a minima shown at a critical 1.5 wt% C dose), results in the S2 (1–2 nm thickness) tightly interlocks the core-shells in this structure. The XRD patterns, lattice images, and XPS/Raman bands corroborate the features are varied at 0–4 wt% C doses. At a critical 1–2 wt% C dose (a percolation threshold), a maximum energy density (BH)max = 10.30 MGOe (15.35 MGOe at 350 K) is tailored, with a coercivity as much as Hc → 12.505 kOe (16.015 kOe at 350 K), at room temperature. A 0.03 μB/C magnetic moment shares a net value, a maximum 66.2 emu/g obtained at 1.7 wt% C. The carbon controls (BH)max and Hc to arise slowly at positive thermal coefficients. The microscopic models insight a way the sp2-C spins integrate collective spin dynamics in the small core-shells in the forms of small clusters. The results are useful for developing material science and technology of this type type rare-earth free ferromagnetic alloys.

Investigation of the Structural and Mechanical Properties of ((82-X) Sn –XCu -18 In) % Alloy with X= 1,2,3,4and 5

Materials Science is concerned with the development or synthesis of new materials . For this reason our interest is focused on the fabrication of new materials , such as lead free solder alloys . Sn-In alloys offer very low melting points and bond well with copper .This study aims to investigate The Structural and mechanical properties of (82-x)Sn -18In alloys with added copper .The Samples were prepared by melting technology From high purity (99 %) elements tin ,indium and copper .XRD showed the formation of a single phase hexagonal structure with a small copper plane, and the addition of copper decreased the particle size of the (82-x)Sn -18 In. The creep test results showed that Cu-containing solder alloys exhibited significant improvements in creep resistance. However, the average activation energy decreases with copper addition from 0.322 to 0.247 eV.

The influence of porosity and precipitates on the corrosion behavior of A356 aluminum alloy

In this article, the pore and precipitation phases of A356 aluminum alloy were regulated by adding element Cu, and the corrosion kinetic behavior was investigated by electrochemical experiments and salt spray test (SST), while the corrosion mechanism of A356 aluminum alloy was studied by scanning electron microscopy (SEM), 3D laser confocal microscopy (LSCM) and atomic force microscopy (SKPFM). The results of both electrochemical and salt spray experiments showed that the corrosion rate increased with increasing Cu content, and the average corrosion rate increased from 0.040 mm y-1 to 0.329 mm y-1 when the Cu content increased from 0 wt% to 7 wt%, and the Cu free alloy exhibited a greater charge transfer resistance. This is mainly due to the addition of Cu on the one hand to increase the number of precipitation phase, Al2Cu become the main precipitation phase, SKPFM test results show that the precipitation phase relative to the Al matrix potential difference in order: Al2Cu (350 ∼ 380 mV), Si (250 ∼ 275 mV), Mg2Si (80 ∼ 110 mV), the increase in potential difference between the two phases to promote the corrosion of occurrence. On the other hand, CT results showed that the average diameter of pores increased from 89.95 µm to 281.00 µm, and the volume fraction increased from 0.05 % to 0.18 %, and the larger and more porous pores help promote corrosion. Therefore, how to control the porosity and precipitation phase is an important factor in regulating the corrosion behavior of A356 aluminum alloy.

Prospects of Using Fe-Ga Alloys for Magnetostrictive Applications at High Frequencies

Fe-Ga is a promising magnetostrictive rare-earth free alloy with an attractive combination of useful properties. In this review, we consider this material through the lens of its potential use in magnetostrictive applications at elevated frequencies. The properties of the Fe-Ga alloy are compared with other popular magnetostrictive alloys. The two different approaches to reducing eddy current losses for such applications in the context of the Fe-Ga alloy, in particular, the fabrication of thin sheets and Fe-Ga/epoxy composites, are discussed. For the first time, the results of more than a decade of research aimed at developing each of these approaches are analyzed and summarized. The features of each approach, as well as the advantages and disadvantages, are outlined. In general, it has been shown that the Fe-Ga alloy is the most promising magnetostrictive material for use at elevated frequencies (up to 100 kHz) compared to analogs. However, for a wide practical application of the alloy, it is still necessary to solve several problems, which are described in this review.

Effects of carbon doping on annealing behavior of a CoCrFeNiMn high-entropy alloy

A 1 at% carbon non-equiatomic doped Co19Cr5Fe38Ni19Mn19 high-entropy alloy was synthesized by vacuum arc-melting in a high-purity argon atmosphere, followed by homogenization, cold rolling, and annealing under various conditions. The evolutions of microstructure and mechanical properties during annealing were systematically studied and compared with the carbon free alloy. Results showed that nano-sized fibrous deformation grains were formed in the 90% cold rolled alloys, resulting in high strength but low plasticity. Recovery sub-structures and recrystallized grains gradually formed with increasing annealing temperature, leading to a significant decrease in defect density, thereby softening the materials and increasing their plasticity. The early stage of recovery was mainly related to the migration of vacancy and interstitial carbon atoms, while dislocation climb became the main recovery mechanism in the late recovery stage. The carbon-doped alloy exhibited a higher recovery activation energy compared with the carbon free alloy. Therefore, 1 at% interstitial carbon effectively increased the recovery and recrystallization resistance of the Co19Cr5Fe38Ni19Mn19 alloy.

Laser In Situ Synthesis and Computational Thermal Analysis of Ti-Al-xCr Alloys: Microhardness, Electrochemical Behavior and Tribological Properties

This work aims to evaluate the effect of chromium (Cr) as a dopant on microstructural evolution, microhardness, electrochemical behavior and tribological properties of ternary Ti-Al-xCr alloys synthesized via laser in situ alloying technology produced from their elemental powders. Computational thermal analyses of 3D printed Ti-48Al and Ti-Al-4Cr alloys were modeled and simulated by means of COMSOL Multiphysics. This was compared to the laser processing parameters to understand the thermal behavior of the alloys during manufacturing. The ternary Ti-Al-xCr alloys were synthesized at a scan speed of 10.58 mm/s and laser power of 450 W. The effects of Cr powder feed rate on Ti-Al matrix were studied at a gas carrier of 1 and 2 L/min, respectively. The microstructural evolution of Ti-Al-xCr alloys was examined using scanning electron microscopy equipped with energy-dispersive spectroscopy. The corrosion and oxidation behavior of the in situ alloyed Ti-Al-xCr were studied using potentiodynamic and thermal gravimetric techniques, respectively. Normalizing heat treatment on microhardness was performed at the temperature of 1350 °C. The findings showed that there was significant decrease in microhardness properties after HT. The computational model demonstrated minimal thermal distribution change proving that minimal or crack free alloys were developed. The results also showed that Cr addition to Ti-Al matrix resulted in improved tribological properties and oxidation behavior of the alloy.

Effect of prior [formula omitted] phase on precipitation kinetics of O-phase in advanced Ti2AlNb alloy

To study the influence of prior α2 phase on O-phase formation kinetics in β matrix, different isothermal heat treatments were performed at 876 and 780 °C using an advanced Ti2AlNb alloy with varying fraction of α2 phase. The kinetics of phase transformations was followed by electric resistivity measurements coupled to multi-scale microstructure characterization using scanning and transmission electron microscopy, energy dispersive X-ray spectrometry (EDS) and quantitative X-ray diffraction. It is revealed that the effect of α2 phase on the formation of O-phase depends on transformation temperature: while at 876 °C prior α2 precipitates lead to significantly slower formation of O-phase, as compared to α2 free alloy, the kinetics of O-phase formation is faster at 780 °C in the presence of α2 phase. Using EDS data as well as accurate measurements of lattice parameter of β phase, the diffusion character of O-phase formation in β matrix with and without prior α2 is shown for 876 °C while at 780 °C the diffusionless character of the O-phase formation is revealed for the beginning of the transformation followed by the partitioning of the alloying elements for prolonged treatment durations.

Influence of Si on the microstructure and C redistribution in martensitic steels

In martensitic steels the distribution of C is fundamental for the technological material properties. However, the effect of Si on C segregation is not known in detail. In this study, the impact of Si on the microstructure of martensitic steels is investigated using scanning electron microscopy and the martensite/austenite orientation relationships are determined using electron backscatter diffraction and transmission Kikuchi diffraction. Transmission electron microscopy and selected area diffraction pattern analysis were used to analyse the intragranular substructure of the martensitic phase. Further, the effect of Si on the redistribution of C is investigated by atom probe tomography in combination with transmission Kikuchi diffraction measurements in order to obtain the local C distribution and correlate it with the crystallography. It was found that the Si addition forms a sigmoidal distribution at the phase boundary and functions as a barrier for C segregation, hence reduces C partitioning into the austenite, while a Si free alloy shows clear C partitioning. Further it was observed that stable C cluster formation occurs along fine twin boundaries in the martensite, inhibiting carbide formation and partitioning of the C into the austenite.

Mechanical properties and durability of cobalt free steel alloy as a developed radioactive waste capsule

In this work, Cobalt-free alloys are prepared as a capsule in which radioactive waste is placed for disposal, and this is a preventive measure to rid the environment of radioactive waste and bury it deep in the earth in a capsule. So, the buildup factor was measured for 1-5-10-40 MFP. The mechanical properties (hardness and toughness) of the processed samples were studied. The hardness was calculated by the Vickers hardness test additionally; the tolerance process was carried out using concentrated chloride acid for 30 days and NaCl 3.5% for 30 days for the studied samples. In this work the resulted developed alloys are resistant to stainless steel 316 L and therefore the alloys are a suitable material in the nuclear field as a container for burying and disposing of waste.

The bulk modulus of β-type Titanium Alloys for Hip and Bone Replacement

Although aluminum (Al) and vanadium (V) have been shown to be cytotoxic, titanium and its Ti-6AI4V alloy have been utilised extensively as implant materials for many years. This is due to new titanium alloys consisting of non-cytotoxic substances like molybdenum (Mo), tantalum (Ta), niobium (Nb), zirconium (Zr), or tin (Sn) have advanced when treated as a cubic β-phase alloy, which has led to the investigation of Al and V free titanium alloys. When configured as a cubic β-phase alloy, they exhibit abnormal corrosion resistance as well as decreased elasticity moduli that are comparable to the substance of the bone they are repairing.&#x0D; This work uses synchrotron x-ray diffraction to calculate the unit cell volume of beta-phase gum metal&#x0D; (Ti–23Nb–0.7 Ta–2Zr–1.2O-TNTZ-O system) at pressures 50, 45, 24, and 40 GPa respectively. The Murnaghan, Viet and Birch-Murnaghan equation of state has been applied using the bulk modulus measurement it was about 88.7GP . Additionally, applying the same technique, the bulk moduli of Ti-7.5Mo-1O, Ti-7.2Mo, and Ti2448 have been determined to be 116.1, 50.2, and 116.2 GPa, respectively. The Ti-7.2Mo system has a below-average bulk modulus when compared to all other alloys. For biomedical applications like hip and human bone replacement, which will be the subject of the study, it would be most appropriate to change the (Ti-xMo-xNb-xTa) alloy and investigate its mechanical properties.

Effect of trace Zn addition on microstructure and corrosion behavior of AA2024 under different aging treatments

The effect of trace Zn (0.67 wt%) addition on the microstructure and corrosion behavior of AA2024 under different aging treatments was investigated. The results reveal that, with trace Zn addition, the corrosion depth decreases at the natural aging condition, but increases at the artificial aging treatment (both the peak aging condition and over aging condition). The corrosion morphology of the Zn-containing alloy under different aging treatments is also different from that of the Zn-free alloy. Compared with the Zn-free alloy, the dealloying process of the S phase in the Zn-containing alloy is slower, which are not conducive to the formation of pitting corrosion. Transmission electron microscope shows that trace Zn addition can promote the nucleation of the intragranular Guinier-Preston-Bagaryatski zones which transform into S phases in the subsequent aging process. Compared with the Zn-free alloy, the S phases of the Zn-containing alloy are coarser at the over aging condition. Moreover, details of how the corrosion morphology of Zn-containing alloys changed and the relationship between the microstructure and the corrosion behavior were discussed. • Trace Zn inhibits the dealloying of Intermetallic S particles. • The local corrosion depth at the natural aging condition is small and the local corrosion depth at the artificial aging condition is large in the AA2024 with trace Zn compared with the Zn free alloy. • Zn segregated at the S-Al interface has been characterized. • Trace Zn promotes the growth and coarsening of grain boundary S phase particles in the AA2024 under artificial aging treatments. • Zn promotes the coarsening of S phase at the grain boundary and the aggregation of Zn at the S-Al interface works together on the local corrosion morphology of the alloy.

Cobalt free refractory high entropy alloys for total joint arthroplasty: In-vitro wear, corrosion and cytocompatibility evaluation

CoCrMo alloys are extensively used for bearing surfaces in total joint arthroplasty (TJA); however, Co poisoning remains a concern. Therefore, we propose a Co free refractory metal based high entropy alloys (RHEAs) for use in TJA. In this work, TiMoNbTaW based RHEA was prepared by arc melting. The alloy was further modified by Cr addition for improvement in wear, corrosion and cytocompatibility. X-ray diffraction revealed single bcc crystal structure where lattice constant decreased upon Cr addition. The improved hardness, yield strength and a ten-fold enhancement in wear resistance with Cr addition is ascribed to its severely distorted bcc lattice. In-vitro corrosion in Hank’s salt solution (HBSS) suggests superior thermodynamic stability and passivation of both RHEAs. Enhanced pitting resistance was seen upon Cr addition. Further, electrochemical impedance spectroscopy (EIS) analysis of the surface film showed an increase in film resistance by an order of magnitude attributed to the presence of Cr2O3 on the TiMoNbTaWCr surface as confirmed by X-Ray photoelectron spectroscopy (XPS) analysis after anodic passivation. Meanwhile, the live/dead imaging and MTT assay indicated good cell viability and proliferation of RHEAs. However, an enhanced cell adhesion and growth on TiMoNbTaWCr RHEA proves its potential applicability as a bearing surface in TJA.

Exceptional reversed yield strength asymmetry in a rare-earth free Mg alloy containing quasicrystal precipitates

This work reports an exceptional reversed yield strength asymmetry at room temperature for a rare-earth free magnesium alloy containing a mass of fine dispersed quasicrystal (I-phase) precipitates. Although exhibiting traditional basal texture, it owns an exceptional CYS/TYS as high as ∼1.17. Electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) examinations indicate pyramidal <c + a> and prismatic <c> dislocations plus tensile twinning being activated after immediate yielding in compression while basal and non-basal <a> dislocations in tension. I-phase particles transferred the concentrated stress by self-twinning to provide the driving force for tensile twin initiating in neighboring grains, thereby significantly increasing the critical resolved shear stress of tensile twinning to possibly the level of pyramidal <c + a> slip, finally leading to the dominance of pyramidal <c + a> slip plus tensile twinning in texture grains. This results in a higher contribution on yield strength by ∼55 MPa in compression than in tension, which reasonably agrees with the experimental yield strength difference (∼38 MPa). It can be concluded that I-phase particles influence deformation modes in tension and in compression, finally result in reversed yield strength asymmetry.