Metallurgical Alloy Research Articles

The effect of high current pulsed electron beam irradiation on microstructure and properties Cu-Fe powder metallurgical alloys

In this paper, Cu-Fe powder metallurgical alloys were firstly fabricated, and a innovative surface modification technique, high current pulsed electron beam (HCPEB), was then irradiated these Cu-Fe alloys with 5 and 10 pulses. The morphologies, microstructure and mechanical properties of the specimens both before and after HCPEB irradiation were studied. The morphologies revealed that the surface of 5-pulsed sample was melted completely, and a large amount of craters were formed. Those craters were eliminated and fused by the subsequent 10-pulsed HCPEB processing. Besides, the distribution of Fe element was fairly homogenous on the irradiated surface. Additionally, the modified microstructures consisted of refined Cu sub-grains, tiny Fe particles, Cu (Fe) solid solution and abundant defects, which played an important role in the improvement of microhardness. The HCPEB irradiated Cu-Fe samples possessed better wear resistance which was ascribed to the reduction of roughness, enhancement of hardness, and formation of lubricating film.

Intimate Ohmic contact to two-dimensional WSe2 via thermal alloying

The most important interface in semiconductor devices is the interface between the semiconductor and the first layer of the metal contact. However, the van der Waals (vdWs) gap in two-dimensional (2D) materials hindered the formation of an intimate contact between the 2D material and the metal electrode, limiting the device performances. We demonstrated a gapless Ohmic contact to 2D WSe2 by forming a Pt−W−Se alloy, which significantly improved the device performances (contact resistance, current on/off ratio, output current density, field-effect mobility, and hysteresis) of the 2D WSe2 field-effect transistor. The contact resistance to 2D WSe2 was reduced by more than seven orders of magnitude after thermal alloying. The disappearance of the vdW gap confirmed by scanning transmission electron microscopy enhanced the hole conduction and quenched the electron conduction. Our strategy of metallurgical alloying is effective to form a low-resistance stable Ohmic contact to WSe2, which paves the way for utilization of the full potential of 2D materials.

How to Design Hydrogen Storage Materials? Fundamentals, Synthesis, and Storage Tanks

AbstractAs the world shifts toward renewable energy, the need for an effective energy carrier is pressing. Hydrogen has often been touted as a universal clean energy vector and the fuel of the future. Unfortunately, mass adoption of the hydrogen economy is slow due to a lack of incentives and technical difficulties in storing hydrogen. Better materials capable of reversible hydrogen uptake/release with hydrogen capacity surpassing 5 mass% at the ambient must emerge. So far, finding such materials has been elusive; alloys capable of ambient hydrogen uptake/release have a low storage capacity while high capacity hydrides have a very high hydrogen release temperature. From metal alloys to complex hydrides, a better understanding of the behavior of hydrogen in hydrides is essential to fine‐tune their properties toward application. Herein, the latest approaches to design hydrogen storage materials based on known hydrides are reviewed with the aim to facilitate the emergence of alternative thinking toward the design of better hydrogen storage materials. Synthetic methods and conceptual approaches to achieve particular hydrogen thermodynamics and kinetics are discussed. These include metallurgical alloying, mechanochemical modification, chemical destabilization, the nanosizing approach, and theoretical modeling and machine learning techniques to guide experimental work.

USING MELT HIGH-TEMPERATURE TREATMENT FOR PROCESSING FOUNDRY WASTES OF HEAT-RESISTANT ALLOY

At present time, metallurgical wastes are used in metallurgical alloys production more and more. The volume accumulation and increase of return age effect on charge pollution by undesirable elements and nonmetallic inclusions. As a result, structure and properties of the casting inevitably get worse. This circumstance must influence on polytherm’s character of physical properties of the melt, necessary temperature and time parameters of the heat-resistant alloy’s melting accordingly. We have researched the temperature dependences of electrical resistance and kinematic viscosity of liquid heat-resistant composites based оn Ni – Nb – Cr – Mo systems. The critical temperatures were determined for the EP902 alloy. Heating up to these temperatures leads to irreversible changes in direction of the melt improving. Interaction was found between the amount of foundry waste and features of temperature dependences of the melt physico-chemical properties. An increase in the amount of foundry waste using in remelting results in the critical temperatures increasing. Influence of the melt conditions on crystallization process and on the structure of hard metal has been studied. The process of alloy EР902 solidification was researched by differential thermal analysis method. It has shown that the crystallization process starts with extraction of solid solution on the base of γ-phases and ends with forming of the eutectic based on the Ni3Nb intermetallic compound. Heating of the melt over the critical temperature leads to an increase of supercooling and does not effect on the eutectic temperature. The processing mode of the high temperature melt treatment was proposed based on the research results of physico-chemical properties of the liquid metal and process of the melt crystallization. It allows obtaining the highest quality of casting of heat-resistant EР902 alloy, which contains significant amount of foundry waste in the charge. The mechanical tests were implemented for experimental samples melted out by the optimal mode of high-temperature melt treatment (HTTM). Application of HTTM for the melts, contained 50 % of foundry waste in charge, allows obtaining the level of strength and plastic properties exceeding the technical requirements, stabilizing and combining it from melt to melt.

Metallurgical processing of titanium aluminides on industrial scale

Plenty of papers with regard to the processing of TiAl alloys via investment casting, forging, rolling, extrusion pressing as well as mechanical machining have been published, whereas the manufacturing of gamma-TiAl based alloys and corresponding semi-finished products has not been entirely described so far. The aim of this paper is to review and evaluate the present technologies of TiAl alloy production on an industrial scale. Metallurgical alloying techniques such as vacuum arc remelting (VAR), plasma arc melting (PAM) and electron beam melting (EBM) are being shortly described and evaluated with regard to their advantages and disadvantages from both technical and economical point of view. Particular focus is set on some specifics in metallurgical processing of TiAl alloys compared to Ti and Ti alloys. Outstanding requests on the accuracy of chemical composition, microstructural homogeneity, acceptable local deviations of alloying elements, small sizes of the products, and, additionally, the very limited wrought processing capability of TiAl alloys require a set of adjusted metallurgical technologies for the manufacturing of semi-finished products. With this regard, the production of small sized semi-finished parts via skull melting technologies and subsequent centrifugal casting in permanent moulds have been successfully developed and industrialized. Both, VAR skull melting (VAR SM) for ingot conversion and induction skull melting (ISM) for the conversion of valuable revert materials result in technically indistinguishable products due to the application of a consistent centrifugal casting technology. Both procedures offer the highest flexibility on product shapes and dimensions for minimizing the specific materials usage, which has a direct positive influence on final component costs. Resulting materials properties of the semi-finished products meet entirely the different (customer related) specification requirements. There are basically no technical limitations with regard to TiAl alloy compositions as it is the case for TiAl alloy manufacturing via other technologies.

SHS TECHNOLOGY OF COMPOSITION FERROALLOYS PART I. METALLURGICAL SHS PROCESS. SYNTHESIS OF FERROVANADIUM AND FERROCHROMIUM NITRIDES

The article presents research findings in the development of a specialized SHS technology for composite ferrous alloys for steel melting and blast furnace iron-making. To resolve the principle goal of creating metallurgical production lines it was developed a new approach to practical implementation of the SHS method – a metallurgical SHS process. The metallurgical version of SHS is based on using different metallurgical alloys as the main raw stock; those include dust-type wastes of ferrite alloys production. In this case, the process of synthesis by combustion is implemented via exothermic exchange reactions. Here, composite materials form; they are based on inorganic compositions bound with iron and/or an alloy based on iron. It has been shown that depending on the aggregate state of source reagents, metallurgical SHS processes can be gasless, gasabsorbing or gas-yielding. Combustion modes for these processes largely differ. To arrange for metallurgical SHS process in weakly exothermic systems, one can use different versions of the thermal bonding principle. The authors have investigated self-propagating high-temperature synthesis of nitrided ferrovanadium and ferrochrome. It has been shown that the phase composition of the source alloy has strong impact on the consistent behaviors of the combustion flow and the combustion mechanism of ferrovanadium (if combustion is taking place in nitrogen atmosphere). In the course of nitriding σ-(Fe – V), process activation takes place; the activation is related to the transformation of the intermetallide into α-solid solution when the phase transition temperature is reached (~1200 °C). The composition structure of ferrovanadium nitride products is formed by the confluence of solid-liquid droplet-particles that consist of molten Fe and solid vanadium nitride. A 3-phase mechanism of ferrochrome interaction with nitrogen facilitates the achievement of a high degree of nitriding. It was shown that the combustion rates of ferrochrome (and chrome) during nitriding in coflow filtration mode increase as the nitrogen flow rate is increased. Here, the degree of ferrochrome nitriding during forced filtration (4.7 – 7.5 % N) is much less than that during non-forced filtration (8.8 – 14.2 % N).

SHS Technology for Composite Ferroalloys. 1. Metallurgical SHS: Nitrides of Ferrovanadium and Ferrochromium

The development of specialized self-propagating high-temperature synthesis (SHS) for complex ferroalloys used in steel smelting and in blast-furnace technology is discussed. To that end, a new approach to the SHS process has been conceived: the metallurgical SHS process, in which the basic raw material consists of various metallurgical alloys including dusty waste from ferroalloy production. In that case, synthesis involves exchange exothermal reactions. The product is a composite based on the initial inorganic compounds; the binder is iron or an iron alloy. Depending on the state of the initial reagents, the metallurgical SHS processes may be gas-free, gas-absorbing, or gas-liberating. For each case, the combustion conditions will be very different. Thermal matching may be used in organizing the metallurgical SHS process in systems that are not strongly exothermal. The self-propagating high-temperature synthesis of nitrided ferrovanadium and ferrochrome is investigated. It is shown that the phase composition of the initial alloy strongly affects the combustion of ferrovanadium in nitrogen. In the nitriding of σ ferrovanadium, transformation of the intermetallide to an α solid solution is activated on reaching the phase-transition temperature (~1200°C). The composite structure of the nitriding products of ferrovanadium is formed under the influence of solid–liquid droplets consisting of molten iron and solid vanadium nitride. Solid-phase reaction of ferrochrome with nitrogen facilitates high degrees of nitriding. The combustion rate of ferrochrome on nitriding during coflow filtration, as in chromium, increases with increase in the nitrogen flow rate. The degree of nitriding of the ferrochrome in forced filtration (4.7–7.5% N) is much less than that in natural filtration (8.8–14.2% N).

Microstructure and properties of Cu-Cr powder metallurgical alloy induced by high-current pulsed electron beam

The purpose of paper is to investigate the microstructure and properties of Cu-Cr alloys induced by high-current pulsed electron beam (HCPEB) irradiation. Microstructure of the alloying layer was studied by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM). The microhardness and friction property were also tested. The microstructure reveals that craters were formed which were fused and eliminated to form flat surface with increase of the pulse number. Additionally, the inter-diffusion of Cu and Cr elements caused component homogenization of the surface melted layer. Besides, the fine grains/particles and Cu (Cr) solid solution were formed. Those factors accounted for a significant increase in microhardness. The lowest COF and wear rate were attributed to the ultrafine Cr particles in the hard Cu matrix.

Surface modification of Cu-W powder metallurgical alloy induced by high-current pulsed electron beam

The purpose of this paper is to investigate the microstructure and properties of Cu-W alloys induced by high-current pulsed electron beam (HCPEB) irradiation. The microstructural observation shows that craters were formed after 5 pulses of HCPEB irradiation. With the increasing numbers of pulses, these craters were further fused and eliminated, which results in an excellent surface finishing. In addition, the composition of melted layer was homogenized because of the inter-diffusion between Cu and W atoms. During the process of HCPEB irradiation, several modifications were formed, including Cu (W) solid solution, ultrafine grains, amorphous phase, and long-period superlattice phase, which significantly increased the microhardness of the surface. The results of sliding wear tests indicate that the HCPEB irradiated samples exhibited better properties as compared to that of the initial one, which was attributed to the ultrafine W particles embedded in the Cu matrix.

Characteristics of Cold and Hot Pressed Iron Aluminum Powder Metallurgical Alloys

Iron powders having average particle sizes of ~40 µm are mechanically mixed thoroughly with aluminum powders ranging from 1 to 10 in wt. %, with an average particle size of ~10 µm. Two different powder metallurgy (PM) techniques, cold and hot pressing, are used to study the effect of the additive element powder on the mechanical properties, wear properties, and the microstructure of the iron based alloys. The hot pressing technique was performed at a temperature reaching up to 500 °C at 445.6 MPa. The cold pressing technique was performed at 909 MPa at room temperature. By increasing the Al content to 10 wt. % in the base Fe-based matrix, the Brinell hardness number was decreased from 780 to 690 and the radial strength from 380 to 228 MPa with reductions of 11.5% and 40%, respectively. Improvement of the wear resistance with the increase addition of the Al powder to the Fe matrix up to five times was achieved, compared to the alloy without Al addition for different wear parameters: wear time and sliding speed.

Aqueous Electrochemical Activity of the Mg Surface: The Role of Group 14 and 15 Microalloying Elements

Comparatively little is known about the aqueous electrochemical characteristics of magnesium (Mg) alloyed with group 14 and 15 elements. A combined analysis of theoretical and experimental studies was used to evaluate the role of such alloying elements in Mg surface reactions. The surface work function and surface hydroxylation reaction enthalpies were calculated, and the surface Pourbaix diagrams were constructed using first principles calculations. Group 14 and 15 elements exhibit the ability to restrict the water splitting and surface hydroxylation reaction upon Mg, thus providing an insight into their ability to suppress cathodic activation of Mg. Experimental studies using polarization, immersion testing, electrochemical impedance spectroscopy (EIS) and Raman spectroscopy verify a decreased electrochemical activity of Mg-0.3 Ge and Mg-0.3 Sb alloys, compared to that of pure Mg. The approaches presented here provide a means by which a metallurgical alloying can be used as a valuable mechanism for controlling Mg surface activity with beneficial implications for various applications of Mg.

Fractal analysis of fracture of powder metallurgical hard alloy

By example of determination of the fractal dimension on a photo of the profile of Palmqvist microcrack obtained as a result of indentation of a Vickers indenter to the surface of a section of metal-ceramic solid alloy (MSA) based on titanium carbonitride, the relationship of microstructure parameters to the characteristic features of the destruction caused by the development of microcrack is studied. An attempt to find the numerical values of the fractal dimension of microcracks is made. As a solid alloy based on titanium carbonitride, alloys of KNT3, KNT7, and KNT12 grades are selected, where the number indicates volumetric content of the binder phase of Ni–Mo in the alloy, respectively.

Surface microstructure and properties of Cu-C powder metallurgical alloy induced by high-current pulsed electron beam

This paper investigates the microstructure and properties of Cu-6C powder metallurgy (PM) alloys irradiated by high-current pulse electron beam (HCPEB). After 20-pulsed HCPEB irradiation, the surface was melted completely and the remelted layer was formed in 2–3 μm thickness, which consisting of ultrafine Cu grains. Within the near irradiated surface, high-density dislocations and vacancy clusters were observed which provide a large amount of paths for carbon atoms to diffuse into Cu matrix, and it leads to the formation of the supersaturated solid solution, causing Cu lattice parameter expansion. In addition, the extreme rapid cycle generated the ultrafine carbon particles at the surface of Cu-6C metallic matrix. The results of microhardness measurements and sliding wear resistance testing indicated that the irradiated sample exhibited better properties than the initial one. The ultrafine carbon particles played an important role in the antifriction properties, which was attributed to the formation of carbonic tribolayer on the hard surface.

In situ TiC–Fe–Al2O3–TiAl/Ti3Al composite coating processing using centrifugal assisted combustion synthesis

The composite coating of a titanium carbide aluminide–alumina-iron composite was synthesized by centrifugal-assisted self-propagating high-temperature synthesis (SHS). The in situ TiC–Al2O3–Fe with intermetallic phases of titanium aluminide (TiAl/Ti3Al) possesses excellent metallurgical properties. This composite was produced from compacted titanium (Ti) and carbon (C) powders in the form of pellets embedded in a tube, which were exposed to very high temperature generated by the thermite Fe2O3 and Al reaction. The process took place in a graphite–steel tube mounted in a centrifugal accelerator machine purposely developed for this function. Functionally graded coating was produced under the centrifugal acceleration field and the product of the thermite reaction (Al2O3 and Fe) infiltrated the TiC pellet and to create a strong, titanium aluminide intermetallic layer. The centrifugal force significantly enhanced both metallurgical alloying and mechanical interlocking between different sample layers during product formation. The purpose of the research addresses the applications of local reinforcement of the ceramic-lined tubes.

Ultrasonic-Assisted Thermocompression Bonding Method of Solder Anisotropic Conductive Film Joints for Reliable Camera Module Packaging

In this paper, to improve the reliability of anisotropic conductive film (ACF) joints in the camera module packaging without any mechanical damages, ultrasonic-assisted thermocompression (TC) bonding was investigated using solder ACFs. This technology uses small lateral-direction ultrasonic vibration during the TC ACF bonding to break solder oxide layers for sufficient solder wetting on the electrodes at ACF joints. Bonded solder ACF joints were investigated in terms of solder ACF joint morphology, resistance, adhesion strengths, and reliabilities. In addition, the stability of camera module components after bonding process was also observed. Ultrasonic-assisted TC bonded solder ACF joints showed excellent solder wetting compared with conventional TC bonded solder ACF joints due to broken solder oxide layers by applied ultrasonic vibration. The Au contents diffused from electroless nickel immersion gold-finished Cu pads to solders was about 12 atomic% in the ultrasonic-assisted TC bonding. The Au contents were three times higher than that of the solders in the conventional TC bonding. In the ultrasonic-assisted TC bonding, ultrasonic amplitude was optimized. At the optimized amplitude, solders were well wetted and showed no mechanical damages of camera module components. Adhesion strength of ultrasonic-assisted TC bonded solder ACF joints was almost the same as that of TC bonded ACF joints due to fully cured resins in these samples. During the unbiased autoclave test (121 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , 2 atm, 100%RH), ultrasonic-assisted TC bonded ACF joints showed no open-circuit failure compared with conventional TC bonded Ni ACF joints due to metallurgical alloy joints between solder balls and electrodes by sufficient solder wetting. These results prove that ultrasonic-assisted TC bonding using solder ACFs can be applied for highly reliable ACF assembly in the camera module packaging without any mechanical damages.

On the state of boride precipitates in grain refined TiAl-based alloys with high Nb content

Abstract The work is aimed at the refinement of primary microstructure appearing in the refractory lightweight structural TiAl-based intermetallics during their solidification from the melt. The green alloy with Ti–46Al–8Nb (at.%) nominal composition is selected for applied study in microstructure engineering. For grain refining, the metallurgical alloying of the material was performed with microcrystalline titanium diboride TiB2 additive, along with subsequent Directional Solidification (DS) in the vertical multizone electro-furnace by power-down technique in pure argon environment. As a result the uniform equiaxed microstructure of Ti–44Al–7Nb–2B (at.%) ingots was produced with low dimensional scattering and characteristic grain diameter of 110–130 μm. DS samples were examined by SEM microanalysis along with EBSD and Auger spectrometry of boride particles in the alloy matrix. It was stated that initial diboride TiB2 additive was completely dissolved and has been afterwards re-precipitated in the course of DS into orthorhombic (Ti,Nb)B monoboride single-crystalline micro-particles of B27 structure, acting as randomly distributed point seeds for inoculated solid grains nucleation. The nature, exact composition and nucleation potency of newly formed borides are discussed along with the nucleation mechanism in relation to the literature data. The addition of trace amount (below 0.1 at.%) of beryllium solute is proposed for the enhancement of β-grain refinement at solidification stage.

Effect of Heat Treatment on the Microstructure and Property of TiAl Alloys Prepared by Gas Atomization Powders

Powder metallurgical TiAl alloy was fabricated by gas atomization powders, and the effect of heat treatment temperature on the microstructure evolution and room tensile properties of PM TiAl alloy was investigated. The uniform fine duplex microstructure was formed in PM TiAl based alloy after being heat treated at 1250/2h followed by furnace cooling (FC)+ 900/6h (FC). When the first step heat treatment temperature was improved to 1360/1h, the near lamellar microstructure was achieved. The ductility of the alloy after heat treatment improved markedly to 1.2% and 0.6%, but the tensile strength decreased to 570MPa and 600MPa compared to 655MPa of as-HIP TiAl alloy. Post heat treatment at the higher temperature in the alpha plus gamma field would regenerate thermally induced porosity (TIP).

A novel fabrication method for TiC–Al2O3–Fe functional material under centrifugal acceleration

Compacted powders of titanium (Ti) and carbon (C) in form of pellets were exposed to a massive amount of heat generated from the thermite reaction of Fe2O3 and Al in a graphite–steel tube mounted in a developed centrifugal accelerator machine. The centrifugal force facilitated the formation of multi-component products during the process. Titanium carbide (TiC) product is joined to an Al2O3–Fe layer, which are the products of the thermite reaction. The existence of centrifugal acceleration had a significant effect on both metallurgical alloying and mechanical interlocking between different layers of the sample to form a functional material. A mathematical model developed for this experiment to describe the speed rate of iron infiltration inside the TiC product as well as viscosity rate variation was presented. The composition, microstructure and mechanical properties confirmed the model.

Mechanochemical synthesis of a TiFe nanocrystalline intermetallic compound and its mechanical alloying with third component

The method of solid-phase mechanochemical synthesis is used to obtain nanostructured ternary alloys based on a TiFe intermetallic compound with manganese, copper and zirconium as alloying components. The phase and structural transformations in the process of the synthesis are determined by x-ray diffraction analysis. The interaction between the resulting compounds and hydrogen is studied, isotherms of absorption and desorption of hydrogen are plotted, and the hydration products are subjected to x-ray phase analysis. It is shown that the use of mechanical activation and the presence of a third component permits activation under less rigid conditions as compared to TiFe obtained by metallurgical alloying.

Electrodeposition of Crystalline GaAs on Liquid Gallium Electrodes in Aqueous Electrolytes

Crystalline GaAs (c-GaAs) has been prepared directly through electroreduction of As(2)O(3) dissolved in an alkaline aqueous solution at a liquid gallium (Ga(l)) electrode at modest temperatures (T ≥ 80 °C). Ga(l) pool electrodes yielded consistent electrochemical behavior, affording repetitive measurements that illustrated the interdependences of applied potential, concentration of dissolved As(2)O(3), and electrodeposition temperature on the quality of the resultant c-GaAs(s). Raman spectra indicated the composition of the resultant film was strongly dependent on both the electrodeposition temperature and dissolved concentration of As(2)O(3) but not to the applied bias. For electrodepositions performed either at room temperature or with high (≥0.01 M) concentrations of dissolved As(2)O(3), Raman spectra of the electrodeposited films were consistent with amorphous As(s). X-ray diffractograms of As(s) films collected after thermal annealing indicated metallurgical alloying occurred only at temperatures in excess of 200 °C. Optical images and Raman spectra separately showed the composition of the as-electrodeposited film in dilute (≤0.001 M) solutions of dissolved As(2)O(3)(aq) was pure c-GaAs(s) at much lower temperatures than 200 °C. Diffractograms and transmission electron microscopy performed on as-prepared films confirmed the identity of c-GaAs(s). The collective results thus provide the first clear demonstration of an electrochemical liquid-liquid-solid (ec-LLS) process involving a liquid metal that serves simultaneously as an electrode, a solvent/medium for crystal growth, and a coreactant for the synthesis of a polycrystalline semiconductor. The presented data serve as impetus for the further development of the ec-LLS process as a controllable, simple, and direct route for technologically important optoelectronic materials such as c-GaAs(s).