Granular Alloys Research Articles

Структура та властивості багатошарового металу, наплавленого електродними порошковими дротами з осердям із порошків феросплавів та гранульованих твердосплавних матеріалів

Comparative studies of the possibility of using granulated hard alloy powders as a charge of flux-cored wires for electric arc surfacing have been carried out. In the studies, granulated powder of the PG-R6M5 brand with a fraction of 50...300 μm was used. As a standard, a flux-cored wire was used, in the core of which there was a composition of powders of different ferroalloys of the same fraction. The content of the charge components in the core of the standard wire was selected and calculated so as to obtain a similar chemical composition to the wire containing granulated hard alloy powder. The test samples were obtained by layer-by-layer electric arc surfacing under the flux layer with flux-cored wires on low-carbon steel plates. To obtain identical dependences, the flux-cored wires had the same diameter and filling factor and differed only in the content of the core. The test samples were deposited under the same conditions with strict adherence to the deposition regimes, which were monitored using a high-speed analog-to-digital converter. It was determined that the use of granulated hard alloy powder as a charge of flux-cored wire has a positive effect on the melting characteristics of the wire and the stability of the welding process in general in comparison with the standard reference wire, the charge of which contains ferroalloys. This effect can be explained by the greater chemical purity of the granulated powder and the uniformity of the physicochemical properties of its particles in comparison with the powders of various ferroalloys. The determined features of the melting of the wire with a charge with granulated hard alloy powder have a positive effect on the quality of the formation of the multilayer deposited metal and its structure, leading to an increase in its homogeneity, some grinding of the grain and a decrease in the number and size of microdefects, which should positively affect the operational properties of the deposited metal. Keywords: electric arc surfacing, multilayer deposited metal, tool steels, granular hard alloy powder, ferroalloy, metal structure.

Influence of the external magnetic field on structural characteristics of granular Co-Cu thin film alloys

We present the results of experimental studies of the influence of an external magnetic field on the structural characteristics (surface roughness and structural entropy) of nanogranular thin-film system based on Co and Cu. The samples CoxCu100-x in a wide range of compositions (17 at. % ≤ x ≤ 69 at. %) with the thickness of d = 35 nm were obtained by electron-beam co-evaporation using two independent electron guns. After obtaining, the films were annealed in a vacuum at a temperature of 800 K for 30 min. The studies of magnetoresistive properties have shown that the maximum giant magnetoresistance (GMR) amplitude (1.7 % in the transverse and 1.6 % in the longitudinal measurement geometries) in a magnetic field of H = 4.5 kOe at room temperature was observed in the Co21Cu79 film alloy. Transmission electron microscopy showed that this sample contains hcp-Co granules with a size of L = 5 ÷ 12 nm in a matrix of metastable fcc-Cu(Co) solid solution. The influence of the external magnetic field on the structural characteristics and surface morphology of the Co21Cu79 thin-film alloy was investigated using atomic force microscopy (AFM). It was found that a first impact of application of external magnetic field with H = 0.5 kOe causes a decrease in the values of the arithmetic mean Ra, and quadratic mean Rq, of the film roughness and structural entropy S. A decreases in Ra by 8.5 %, Rq by 6.5 %, and structural entropy S by 6.5 % were observed. After application of a larger magnetic field with H = 1.0 kOe and during the subsequent relaxation of the structure within 15 h after the field is turned off, the values of the structural parameters of the film surface did not change significantly.

Microsegregation of Alloying Elements on deformation Structural defects in Granular Nickel Alloy

Samples cut from a disk blank of Russian granulated nickel-based superalloy VZH178P were tested for tensile strength at room temperature and long-term creep at temperature of 750 °C. Transmission electron microscopy showed that, in both cases, stacking faults and microtwins formed during plastic deformation of the alloy. During long-term creep at 750 °C, the alloying elements Cr, Co, Mo, and W segregate on the stacking faults, leading first to the formation of Suzuki atmospheres and then to the nucleation and growth of TCP particles with stoichiometry (Co,Cr)3(Mo,W).

Accelerated Separation of Uranium from Lanthanides (La, Ce, Sm) in LiCl-KCl Eutectic by Porous Aluminum Electrodes

In order to optimize the application of Al electrodes in pyrochemical reprocessing of spent nuclear fuel, the feasibility of porous Al electrodes to separate actinides-lanthanides (An-Ln) in LiCl-KCl eutectic melt was explored. The separation efficiencies and rates of U and lanthanides (La, Ce, Sm) on Al electrodes with regular and irregular and without pores were compared. U was selectively recovered in the form of U-Al alloys by controlling the potential (−1.2 V) on both Al rod and porous Al electrodes. X-ray diffraction (XRD) and scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS) showed that the obtained granular alloys were mainly Al3U and Al4U, and inductive coupled plasma optical emission spectrometry (ICP-OES) indicated that there was almost no Ln in the electrolysis products. Positively, the required separation time was greatly shortened, and the separation rate was effectively improved when porous Al electrodes were used. In addition, the Al honeycomb electrode with regular pores has better kinetic performance compared with Al foam electrodes with irregular pores. The results indicate that the specially designed porous Al electrodes may have a good application prospect for the separation of An-Ln in the pyrochemical reprocessing of spent nuclear fuel.

Characterization of Electrodeposited Cobalt/Copper (Co/Cu) Granular Multilayered Thin Films onto the Anodic Aluminum Oxide (AAO) Substrates

Herein, we report on the characterization of a series of cobalt/copper granular thin films alloys electrodeposited onto the previously pre-treated aluminum substrates, at different deposition time. And a systematic study of their structural and magneto-optical properties were investigated. The proper deposition potentials of Co, and Cu were obtained from the cyclic voltammetry method. It was observed that the easy axis direction of magnetization was parallel to the film plane for all films. The X-ray diffraction (XRD) results revealed that all films had a mixture of hexagonal close-packed (hcp) and face centered cubic (fcc) phases. The Scanning electron microscope images (SEM) and atomic force microscopy (AFM) showed some parallelepiped and ellipsoid shaped rods with an averaged dimension about of 600 nm length, 600 nm width and 200 nm thickness for a sample electrodeposited at room temperature. These rods are irregularly arranged. Their irregular arrangement could explain the large d-spacing in the sample at this temperature. The magnetic analysis of the granular thin films alloys showed the saturation magnetization increased and the coercivity decreased as the deposition time increased. These results showed that the changes in magnetic and structural properties of granular cobalt/copper alloys deposits were substantially depending on the variation of deposition time. Therefore, the change of the deposition time was seen to control the properties of the alloys deposits and hence their properties could be modified for desired purpose.

Constructing CNT@NiCo Texture Anchoring Pt Nanoparticle Catalyst for Highly Efficient Methanol Electrocatalytic Oxidation**

AbstractIn this paper, CNT@NiCo‐s (Carbon nanotube@NiCo‐sheet) and CNT@NiCo‐g (Carbon nanotube@NiCo‐granular) composite carriers were prepared by two special methods. After that, the Pt nanoparticles were loaded on the surface of these composite supports by the sodium borohydride (NaBH4) reduction method to obtain Pt/CNT@NiCo‐s and Pt/CNT@NiCo‐g. Cyclic voltammeter and chronoamperometry were used to determine the methanol oxidation activity and durability of these catalysts. The results show that the doping of the granular NiCo alloy carrier effectively improves the activity and anti‐toxicity of the Pt/CNT catalyst for the methanol electrocatalytic oxidation reaction (MOR). It confirmed that the advantages of Pt/CNT@NiCo‐g catalyst were attributed to a large specific surface area, abundant defects, and abundant oxides and hydroxides, which jointly promoted the electrocatalytic oxidation of methanol.

Material Grain Size Determines Relaxation-Time Distributions in Slow-Dynamics Experiments

By measuring the elastic slow dynamics behavior of various consolidated granular materials and metallic alloys, we show that the evolution of the wave velocity as a function of time can be reproduced by using a continuous relaxation-time spectrum, whose main features can be extracted from the experiments. Here we propose to adopt a Weibull distribution of the relaxation times, that we find to display a maximum, which is related to the material grain size and independent of the conditioning amplitude. These results show that the role of the grain-size distribution is fundamental to quantify slow dynamics effects, as well as to clarify its mesoscopic physical origin. Moreover, they can pave the way for the implementation of advanced characterization methods or nondestructive testing techniques capable of retrieving information on the different spatial scales or defects in the materials under investigation.

Investigation of the features of crystallization of granules of high-strength aluminum alloys of the Al-Zn-Mg-Cu system at ultra-high cooling rates

The article presents the results of studies of the process of obtaining granular materials from high-strength aluminum alloys of the Al - Zn - Mg - Cu system by centrifugation of the melt with ultra-high cooling rates of granules. The concept of a «steam jacket» is introduced, namely, a steam layer that occurs between the granule body and the cooling liquid, which prevents the intensity of heat removal and is an obstacle to increasing the crystallization rate due to the lower thermal conductivity of water vapor. It is established that the formation of a vapor layer always occurs due to the heating of the cooling liquid in contact with the melt drop to boiling temperatures and the transition of the cooler from the liquid phase to steam. The technology of increasing the rate of crystallization of granules due to the constant removal of the vapor layer is proposed. The removal (knocking down) of the vapor shell that occurs around the drop occurs due to the high speed of the drop movement in the cooling medium. Fundamentally important in the industrial implementation of this technology is not so much the design of the device for obtaining pellets by centrifugation of the melt, namely, the high required rotation speed of the spraying crucible of the device under consideration. The results of experimental data are presented to determine the necessary rotation speed of the perforated cup, which ensures the creation of a sufficient initial velocity of the drop movement, leading to a constant churning of the «steam jacket». It is determined that an increase in the rates of heat removal from the crystallized granules and, as a result, an increase in the crystallization rate leads to an increase in the strength characteristics of granular aluminum alloys of the Al-Zn-Mg-Cu system. In particular, in the production of pressed semi-finished products from alloys of the Al-Zn-Mg-Cu system, such as B95, B96c. the increase in the strength characteristics of the material of the press products is up to 15 % compared to the same granular materials obtained by traditional methods with industrial crystallization rates of melt droplets. It is established that this method, based on the removal of the vapor layer around the formed granule, is the only possible one for further increasing the cooling rate and, as a result, the crystallization rate. Reducing the size of granules to the size of powders leads to serious technological problems in the further consolidation of granules and, in fact, is a dead end branch of the further development of granulation methods.

Модель Ізінга для опису магнітних властивостей елементів системи керування авіаційним двигуном

The creation of competitive engines is impossible without the development and implementation of new materials and design and technological solutions. At present, in the engines, nickel alloys obtained by directional crystallization are widely used, including monocrystalline, granular alloys. The use of various composite materials, permanent joints from dissimilar materials is constantly expanding, extensive research is being carried out to create a structure from monolithic ceramics and intermetallic compounds. The successful introduction of unconventional materials is impossible without a thorough study of their structural strength, magnetic properties, features of deformation, and destruction, taking into account the specifics of these materials when developing the design and manufacturing technology of a part or engine unit. The article discusses a software package for the optimal design of control system elements for aircraft gas turbine engines using a description of their magnetic properties. Due to the modular structure of the optimization program, various optimization procedures and calculation programs can be used. It was determined that, for the Ising model, the formation of domains with a given spread of spins at a temperature T and a vector of magnetic induction B is calculated array element using a random number generator. The number of tests L depends on the size of the sample. In the Ising model, all parts of the N*N system are contenders for testing. So, Step corresponds to the number of Monte Carlo steps. Since the parts are selected once on average, it is possible to select one particle several times or not to select it at all. Therefore, the Step value should be significantly greater than one. For a convenient implementation of a certain model, its application with a graphical magnetization interface with a different number of iterations has been considered. When executing the command file, the following should be performed: building a geometric model, building a finite element mesh, applying loads, calculating the stress-strain state (SSS), displaying the results.

Interface behaviour of brazing seam of contact-reaction brazing an AZ31 magnesium with amorphous filler metal

In order to achieve brazing of magnesium alloy without brazing flux, a new AlSiCu amorphous alloy was designed as an intermediate layer. The contact reaction brazing method was used to brazing AZ31 magnesium alloy with AlSiCu amorphous alloy as an intermediate layer. The SEM and OM methods were used to analyze the structure of the brazing seam, and it was found that there were block, granular, and dendritic alloy phases in the brazing seam. The composition of the alloy phases in the brazing seam was measured by EDS analysis, and the intermetallic compounds of Mg Al were found. Unfixed micro-holes were found in the brazing seam held at 450 °C for 15 min, and these micro-holes disappeared and a complete interface connection was formed in the brazing seam when the holding time increased to 20 min. With the increase of brazing time, the brazing seam became wider and the dendrite in the brazing seam began to spread towards the base metal and gradually decreased after holding for 25 min. After holding for 30 min, the dendrite disappeared and the second phase appeared as granular and short rod distribution, and the number decreased significantly. The joint strength increases significantly with the increase of holding time, and the tensile shear strength of the lap joint is 110 MPa. The average hardness of the brazing seam is 94.2 HV, the hardness values of the matrix phase and the second phase are different greatly. The probe was used to analyze the microstructure and morphology of the shear fracture, and it was found that cleavage patterns and dimples existed on the fracture surface at the same time. • The contact reaction brazing method is used to achieve the brazing connection of the AZ31 magnesium alloy. • The AlSiCu amorphous alloy is used as the intermediate layer, and the tissue performance of the joint is improved. • By means of diffusion and differentiation, the shape of the MgAl compound in brazing seam is changed.

Computational and fractographic study of the stable growth of low cycle fatigue cracks in the disk of an aircraft engine turbine under complex loading cycles

The results of a comprehensive computational and experimental study of the kinetics of low-cycle fatigue cracks (LCF) in a turbine disk made of EP741NP granular nickel alloy of an aircraft gas turbine engine under complex loading cycles (CLC) are presented. The configuration of crack fronts was reconstructed using light microscopy. Steps of the blocks of fatigue striations characterizing the crack increment under CLC at the stage of steady crack growth are measured using scanning electron microscopy during microfractographic analysis. The period of LCF crack steady growth is estimated and the reproducibility of the regularities of steady growth is demonstrated which testifies the capability of reliable prediction for LCF crack steady growth. The finite element modeling of the reconstructed crack fronts has been carried out. The values?? of the range of stress intensity factor at each crack front in the area of measuring the pitch of the striation blocks were calculated for the subcycles of complex loading cycles. Using the previously developed physically grounded mathematical model and calculation methodology, forecasting of stable growth of the LCF crack was carried out. The results of forecasting match the data of micro-fractographic analysis unlike the results of LCF crack growth prediction based on Paris law which differ significantly from experimental data.

Influence of the magnetic field on the structural characteristics of granular CoxAg100-x thin film alloys

ABSTRACT We investigated structural-phase state, magnetic and magnetoresistive properties in as-deposited CoxAg100-x thin film alloys with a thickness of 35 nm as a function of composition (20 ≤ x ≤ 80 at.%). The aim of this work was to obtain a granular thin film alloy CoxAg100-x with the maximum amplitude of the giant magnetoresistance (GMR) and study of the magnetic field effect on structural characteristics of its surface. Studies of the effect of the magnetic field on the structural characteristics of the surface of the granular thin film alloy Co39Ag61, that characterized by the highest amplitude of GMR at room temperature, were performed. The GMR value for this sample was 14.7 % in transverse and 13.6 % in longitudinal measurement geometries under the magnetic field Bmax = 1.5 T. The application of the magnetic field led to a decrease in arithmetic mean Ra and the root mean square Rq values of the surface roughness, as well as the structural entropy of the system. At the first application of the magnetic field, the greatest decrease in the roughness of Ra by 19 % and Rq by 16 %, respectively, was observed. These changes persisted with increasing field strength up to B = 0.1 T. During the relaxation process (18 hours after the field was switched off), the structural characteristics of the sample were permanent.

Methods of effective media as optimal methods for modeling the physical properties of nanostructures

This paper considers various methods of effective media as a tool for studying both optical and magneto-optical properties of various nanostructures, primarily magnetic nanostructures. Formulas for finding diagonal and non-diagonal components of the permittivity tensor for all basic approximations of the effective medium were obtained explicitly. These formulas are valid for both nanocomposites and granular alloys. The possibility of predicting various optical and magneto-optical properties of such structures is discussed using the example of the transverse Kerr effect as a promising non-contact method for studying nanostructures for a ferromagnetic nanocomposite (CoFeZr) x (MgF 2 ) 100-x . A possible application of the obtained formulas is discussed. Various methods of effective media make it possible to study nanostructures in a wide range of values of the concentration of the metal (magnetic) component Х . The paper notes and discusses the contribution of various mechanisms that affect the physical properties of such structures, especially in the IR region of the spectrum, where the quasi-classical dimensional effect is most pronounced. The form factor of nanocomposite particles and the average particle size are such contributions that can be taken into account. The contribution of the quasi-classical dimensional effect to the diagonal and non-diagonal components of the structure's permittivity tensor is analyzed within the framework of the Drude-Lorentz model. The problem being solved in this work is relevant, since interesting and important effects are observed in magnetic nanostructures, such as the Kerr effect, anomalous absorption, giant magnetoresistance, tunnel magnetoresistance, and many others. These effects play an important role in modern electronic devices, which makes this work particularly relevant.

Magneto-optical properties of two-layer film systems based on Fe and Cr

The results of the investigation of two-layer Fe/Cr systems using the magneto-optical Kerr effect (MOKE) are presented in this paper. The samples were obtained by thermal evaporation in a vacuum with a thickness of individual layers from 2 nm to 50 nm. It was found that the presence of the Cr layer significantly affects the values of the coercivity and the Kerr angle. At a substrate temperature of 450 K, the value of the coercivity is almost half that of the same sample obtained at room temperature of the substrate. In addition, the influence of the order of deposition of layers, as well as the effect of a thin gold protective layer on the parameters measured by the Kerr method, is shown. These studies have shown that the MOKE can be used as an additional method for studying the composition of multilayer systems, granular alloys and spin-valve systems, using specific software methods.

Controlled growth of PtCo nanoparticles on Ni bowl-like pore arrays as an electrocatalyst for methanol oxidation

PtCo alloy nanoparticles with different Pt–Co atomic ratios supported on a Ni bowl-like pore arrays were controlled synthesized using a two-step electro-deposition strategy with the help of a monodispersed colloidal sphere template. Morphology characterization indicated that shaggy granular PtCo alloy was uniformly grown on the Ni ordered bowl-like pore arrays. Electrochemical measurements in alkaline solution demonstrated that the PtCo/Ni array with the atomic ratio of Pt:Co = 6:1 showed an optimal catalytic activity for methanol oxidation compared to the other PtCo/Ni array, the bowl-like PtCo array and Pt/Ni layered array. The present work provides new opportunities for the rational design of layered composite catalysts with enhanced catalytic performance for application in fuel cells.

Mn-Induced Thermal Stability of L10 Phase in Fept Magnetic Nanoscale Ribbons.

Magnetic nanoscale materials exhibiting the L10 tetragonal phase such as FePt or ternary alloys derived from FePt show most promising magnetic properties as a novel class of rare earth free permanent magnets with high operating temperature. A granular alloy derived from binary FePt with low Pt content and the addition of Mn with the nominal composition Fe57Mn8Pt35 has been synthesized in the shape of melt-spun ribbons and subsequently annealed at 600 °C and 700 °C for promoting the formation of single phase, L10 tetragonal, hard magnetic phase. Proton-induced X-ray emission spectroscopy PIXE has been utilized for checking the compositional effect of Mn addition. Structural properties were analyzed using X-ray diffraction and diffractograms were analyzed using full profile Rietveld-type analysis with MAUD (Materials Analysis Using Diffraction) software. By using temperature-dependent synchrotron X-ray diffraction, the disorder–order phase transformation and the stability of the hard magnetic L10 phase were monitored over a large temperature range (50–800 °C). A large interval of structural stability of the L10 phase was observed and this stability was interpreted in terms of higher ordering of the L10 phase promoted by the Mn addition. It was moreover found that both crystal growth and unit cell expansion are inhibited, up to the highest temperature investigated (800 °C), proving thus that the Mn addition stabilizes the formed L10 structure further. Magnetic hysteresis loops confirmed structural data, revealing a strong coercive field for a sample wherein single phase, hard, magnetic tetragonal L10 exists. These findings open good perspectives for use as nanocomposite, rare earth free magnets, working in extreme operation conditions.

Correlation between the structural state and magnetoresistive properties of granular CoxAg100-x alloy thin films

Extensive investigations into structural, magnetotransport and magnetic properties of granular thin films with a thickness of 20 nm based on Co and Ag in a wide range of component concentrations were carried out: 17 ≤ x ≤ 89 where x is at.% of Co. The samples were obtained by the method of electron beam co-evaporation using two independent electron guns at room temperature. The correlation between the structural-phase state and magnetotransport and magnetic properties was established by TEM method. The threshold of structural percolation in granular films was observed for x ≈ 60%. At lower concentration x < 64%, the films had a phase composition of Ag (fcc) + Co (hcp) and were characterized by an isotropic giant magnetoresistance (GMR). The maximum GMR values of 7.2% and 7.5% in transverse and longitudinal geometry, respectively, were observed at x = 55 at.%. For higher concentrations (x > 70%) the films demonstrated anisotropic magnetoresistance (AMR), which was assumed to be associated with the appearance of ferromagnetic interactions between the cobalt granules.

Fixed joints of dispersion-hardened composite materials based on aluminium, made by friction stir welding

ABSTRACT Structural features and mechanical properties of welded compounds of composite materials on an aluminium basis, with dispersal hardening of particles of aluminium oxide and silicon carbide, obtained by welding friction with mixing, were investigated. It has been shown that the use of friction welding with mixing provides a fairly high level of mechanical properties of compounds of studied composite materials. At the same time, there are no significant phase-structural changes in the seam metal and the accompanying areas of the compound compared to the main material. The mechanical properties and structure of the joints of granular aluminium alloy 01419 and the foundry composite based on the System Al–Zn–Mg have been studied. Welding it is shown that the STP does not initiate significant structural changes in these materials.

A detailed study of magnetic properties and room temperature memory effect in wet chemically prepared [formula omitted][formula omitted] nanostructured alloy

We present the magnetic properties of nanostructured Ni0.2Cu0.8 granular alloy prepared by a chemical reduction process. Zero-field-cooled and field cooled magnetization studies show branching due to the presence of superparamagnetism. The large particle size distribution in our sample is reflected in a broad blocking temperature distribution which on the higher side extends to 390 K. Magnetic field dependence of magnetization shows a superparamagnetic component accompanied with a ferromagnetic part at low temperature with prominent hysteresis loops exhibited at temperatures 2–50 K. The average magnetic moment of nickel (0.5μB) is smaller than its expected ferromagnetic saturation value (0.6μB) indicating that not all Ni atoms contribute to ferromagnetism. The magnetization data are analyzed in terms of an existing core–shell nanoparticle model. The study demonstrates that the overall behavior of the system is that of an assembly of non-interacting superparamagnetic (SPM) particles exhibiting the magnetic memory effect in relaxation dynamics, which has been observed using different experimental protocols, and persists even up to room temperature.

A method for determination of the boundaries of the stage of steady fatigue crack growth and parameters of Paris equation

A method and procedures for determining the boundaries of the second stage of the kinetic crack resistance diagram or fracture toughness kinetic diagram, sample formation within the aforementioned boundaries and determination of the parameters С and n of the Paris equation from the sample are presented. The necessity of developing the method is attributed to the lack of rules and procedures for accurate determination of the boundaries of the second stage in the current standards and regulatory document (RD). The proposed method provides a given accuracy of determination of the number of cycles corresponding to the length of the fatigue crack at the upper boundary of the second stage obtained by numerical integration of the Paris equation with the found values of the parameters С and re. The developed method is based on the application of two criteria R2 and %. Statistical criterion R2 characterizes a degree of deviation of the experimental data from the linear fragment of the kinetic fracture toughness diagram. Parametric criterion у specifies the level of accuracy of the parameters С and re of the Paris equation. This level is set through a comparative evaluation of the experimental and calculated crack length I and the number of cycles N, obtained by integration of the Paris equation within the specified lower and upper limits of the interval of the stable growth of fatigue crack. Application of the method is shown by the example of the experimental data obtained when testing samples of VT9 titanium alloy, deformable nickel alloy EI437BU and granular nickel alloy EP741NP (granules up to 140 pm) at room and elevated temperatures. Application of the method indicates that the experimental and calculated curves "I - N" obtained by numerical integration of the Paris equation differ by less than the specified value of the criterion X ^ 3%, in contrast to the results obtained in accordance to the recommendations of the regulatory documents.