Elemental Metal Powders Research Articles

Exploring Mg-Sn Alloys as Electrocatalysts for CO2 Electroreduction

Tin is one of the most selective electrocatalysts for CO2 reduction (CO2RR), mostly thanks to its poor activity towards the hydrogen evolution reaction (HER). Still, Sn electrodes are limited by their very high overpotential. We decided to investigate the electrochemical CO2RR catalytic activity of tin-magnesium alloys that can be easily obtained by thermal annealing from the elemental metallic powders. We found that the alloys exhibit a slightly improved activity in activity and selectivity towards CO2RR with formate as dominant product according to electrochemical and chemical analysis. Post-mortem characterization confirmed that this effect is not due to the alloys performance, but to Sn re-structuration. Most of the Mg is leached from the alloy into the electrolyte during CO2RR, leaving a highly porous Sn structure. These changes in morphology and surface area as triggered by Mg leaching, appear to be at the origin of the enhanced electrocatalytic performance.

Characterization of thermal fatigue properties of lead-free Sn–Cu–Al–Mg solder alloy produced by powder metallurgy method

In the present study, lead-free Sn–Cu–Al–Mg-based solder alloys for electronics packaging were produced. Effects of thermal shock and thermal stress on the crack formation in the Sn-based solder alloys were investigated. Lead-free quaternary Sn–Cu–Al–Mg-based solder alloys were produced by using mechanical alloying and powder metallurgy route. Soldering involves using a molten filler metal to wet the surfaces of a joint. Wave soldering is a method for mass assembly of printed circuit boards involving through holes, surface. Lead-free solder alloys must show high wettability, suitable mechanical properties, electrical conductivity, high electrochemical corrosion resistance, and low cost. Mechanical alloying and powder metallurgy method were used in order to prevent formation of intermetallics and formation of voids. Mechanical alloying–powder metallurgy method could reduce the micro/macro-segregation and provide homogeneous microstructure. Initially, elemental metal powders were mechanically alloyed in a ball mill by using zirconia balls in order to produce alloy powders. Then, the alloy powders were compacted at 300 MPa and then the green specimens were sintered at 180 °C for 60 min. Nondestructive ultrasonic tests and eddy current tests were used for characterization of the solder alloy specimens. Elastic modulus of the Sn alloys was determined by ultrasonic measurements. Electrical conductivity of the specimens was determined by using eddy current tests. Microstructure was studied by scanning electron microscope. Effects of thermal shock and thermal stress on the crack formation in the alloys were investigated by heat treatment cycles in a chamber furnace. Heating cycles for thermal stress consist of heating to 150 °C and slow cooling. Heating cycles for the thermal shock consist of heating and quenching. In addition, electrochemical corrosion behaviour of the Sn solder alloys was investigated in NaCl solution.

Continuous synthesis of high-entropy alloy nanoparticles by in-flight alloying of elemental metals

High-entropy alloy (HEA) nanoparticles (NPs) exhibit unusual combinations of functional properties. However, their scalable synthesis remains a significant challenge requiring extreme fabrication conditions. Metal salts are often employed as precursors because of their low decomposition temperatures, yet contain potential impurities. Here, we propose an ultrafast (< 100 ms), one-step method that enables the continuous synthesis of HEA NPs directly from elemental metal powders via in-flight alloying. A high-temperature plasma jet ( > 5000 K) is employed for rapid heating/cooling (103 − 105 K s−1), and demonstrates the synthesis of CrFeCoNiMo HEA NPs ( ~ 50 nm) at a high rate approaching 35 g h−1 with a conversion efficiency of 42%. Our thermofluid simulation reveals that the properties of HEA NPs can be tailored by the plasma gas which affects the thermal history of NPs. The HEA NPs demonstrate an excellent light absorption of > 96% over a wide spectrum, representing great potential for photothermal conversion of solar energy at large scales. Our work shows that the thermal plasma process developed could provide a promising route towards industrial scale production of HEA NPs.

Високоентропійний NiFeCrWMo сплав, отриманий в процесі механічного легування

In this work, the evolution of the structure and phase composition of the multicomponent Ni-Fe-Cr-W-Mo system during mechanical alloying (MA) of an equiatomic mixture of elemental metal powders in a planetary mill is investigated. The formation of the phase composition and structure of the powdered equiatomic high-entropy NiFeCrWMo alloy at different stages of mechanical alloying was determined by scanning electron microscopy, X-ray diffraction and X-ray spectral analysis. It was found that during 10 hours of МА, a single-phase high-entropy alloy with the structure of a BCC solid solution in the nanostructural state with a crystallite size of 22 nm and a lattice strain (microstress) of 0.61 % was formed. It was shown that the metal components were completely dissolved in the solid state during mechanical alloying, in contrast to their limited solubility under equilibrium conditions. Moreover, despite the different features of the formation of solid solutions in high-entropy alloys and traditional materials, the order of dissolution of element atoms in the lattice of a solid solution follows general principles and occurs depending on the melting point in the following sequence: Ni→Fe→Cr→Mo→W. The average particle size of the produced powdered NiFeCrWMo high-entropy alloy is 3.8 μm, and their shape is predominantly spherical or close to spherical. The microstructure of the particles of the powdered NiFeCrWMo high-entropy alloy at the early stage (1.5 hours) of mechanical alloying is a layered structure formed in the process of grinding, deformation, and cold welding of particles of elemental metal powders. After 10 hours of МА, the microstructure of the alloy particles becomes homogeneous and contains a small amount of WC inclusions as a result of milling due to wear of grinding bodies in the MА process. The obtained NiFeCrWMo high-entropy alloy can be used in the future as a component/binder for other composite materials, for example, hard alloys based on WC to replace Co. Keywords: high-entropy alloy, mechanical alloying, structure, phase composition, solid solution, nanostructure

Two-step hydrogen reduction of oxides for making FeCoNiCu high entropy alloy: Part I – Process and mechanical properties

Iron-based 3d-transition group high-entropy alloys (HEAs), with remarkable wear resistance, high hardness, and excellent mechanical properties, are usually produced by a multiple-step high-energy-consumption smelting process. This study offers a novel process for fabricating FeCoNiCu HEAs by two-step hydrogen reduction using a mixture of Fe2O3, CoO, NiO, and CuO, after which a nearly full dense crack-free HEA was successfully produced. The alloy has a face-centered cubic (FCC) structure and an oxygen level as low as 0.10 wt%. After the first hydrogen reduction at 500 °C for 2 h, the oxygen level decreased from 23.30 wt% to 2.05 wt% and the powder obtained consisted of the elemental metal powder with some minor alloying. A second hydrogen reduction occurred during sintering at temperatures above 800 °C, in which near-full densification (> 99% relative density) was achieved at temperatures as low as 900 °C. All the compositions were homogeneously distributed in the alloy when the temperature was >900 °C, and a Cu-enriched FCC-structured secondary phase with two types of shapes was precipitated in the alloy. The final alloy showed excellent mechanical properties at room temperature, with a hardness of ∼150 HV, compression strength up to 2.2 GPa, compression strain of >12%, tensile strength of 475 MPa, and tensile elongation of 7.9%.

Processing and Characterization of β Titanium Alloy Composite Using Power Metallurgy Approach.

The β titanium alloy matrix composite was made from a mixture of elemental metal powders, including boron carbide. During the high-temperature sintering process, in situ synthesis took place as a result of the TiB and TiC reinforcing phases formed. The identification of these phases was confirmed by X-ray diffraction and microstructural analyses. The presence of unreacted B4C particles and the surrounding reaction layers allowed for the evaluation of diffusion kinetics of alloying elements using SEM and EDS analyses. The direction of diffusion of the alloying elements in the multicomponent titanium alloy and their influence on the in situ synthesis reaction taking place were determined. In addition, the relationship between the microstructural components, strengthening phases, and hardness was also determined. It was shown that in situ reinforcement of titanium alloy produced from a mixture of elemental powders with complex chemical composition is possible under the proposed conditions. Thus, it has been demonstrated that sufficiently high temperature and adequate holding time allows one to understand the kinetics of the synthesis of the strengthening phases, which have been shown to be controlled by the concentrations of alloying elements.

Effects of weight on bit and rotational speed on the friction and wear properties of Fe based diamond bit matrix

All-hydraulic drill has been widely employed in core drilling recently, which results in larger Weight on Bit (WOB) and higher rotational speed to diamond bit. Thus, new requirements of diamond bit abrasiveness are needed to satisfy the severe challenges. To investigate the effects of WOB and rotational speed on the friction and wear properties of diamond bit matrix, an experimental scheme with 2 factors and 4 levels was designed to carry on the friction and wear test, and two kinds of Fe based diamond bit matrix formula systems, i.e. elemental metal powders and pre-alloyed powders were considered. The samples were manufactured by hot-pressing. Test results indicate that the abrasion loss of the Fe based samples increase with the raise of WOB and rotational speed, while the WOB has a bigger significance. The wear mechanism of the bit matrix is dominated by adhesive wear under smaller WOB and lower rotational speed, while abrasive were will become more and more important with the increase of WOB. Besides, samples from the pre-alloyed powders formula system have better performance than the ones from elemental system, the abrasion can be reduced by up to 15.52%, when under the same test conditions.

Heat Treatment of NiTi Alloys Fabricated Using Laser Powder Bed Fusion (LPBF) from Elementally Blended Powders.

The use of elemental metallic powders and in situ alloying in additive manufacturing (AM) is of industrial relevance as it offers the required flexibility to tailor the batch powder composition. This solution has been applied to the AM manufacturing of nickel-titanium (NiTi) shape memory alloy components. In this work, we show that laser powder bed fusion (LPBF) can be used to create a Ni55.7Ti44.3 alloyed component, but that the chemical composition of the build has a large heterogeneity. To solve this problem three different annealing heat treatments were designed, and the resulting porosity, microstructural homogeneity, and phase formation was investigated. The heat treatments were found to improve the alloy’s chemical and phase homogeneity, but the brittle NiTi2 phase was found to be stabilized by the 0.54 wt.% of oxygen present in all fabricated samples. As a consequence, a Ni2Ti4O phase was formed and was confirmed by transmission electron microscopy (TEM) observation. This study showed that pore formation in in situ alloyed NiTi can be controlled via heat treatment. Moreover, we have shown that the two-step heat treatment is a promising method to homogenise the chemical and phase composition of in situ alloyed NiTi powder fabricated by LPBF.

Thermal Stability of Medium- and High-Entropy Alloys of 3d-Transition Metals

A family of high-entropy alloys (HEA) composed of 3d-transitional metals is attracting great interest due to the mechanical, magnetic, and electrical properties that are valuable in the development of advanced structural and functional materials. In this work, we studied X-CoCrFeNi HEAs, where X = Al, Ti, or Cu, produced by mechanical alloying by means of high-energy ball milling. Powder mixture composed of elemental metal powders transforms in a homogeneous alloy (super-saturated solid solution) due to the intense diffusion which takes place during friction and shear deformation of the metal particles during the mechanical alloying. The thermal stability of the HEA phases was experimentally studied in the range 873-1273 K using high-temperature X-ray diffraction and compared with the results of thermodynamic calculations (Calphad).

Fabricating TiNiCu Ternary Shape Memory Alloy by Directed Energy Deposition via Elemental Metal Powders

In this paper, a TiNiCu shape memory alloy single-wall structure was fabricated by the directed energy deposition technique with a mixture of elemental Ti, Ni, and Cu powders following the atomic percentage of Ti50Ni45Cu5 to fully utilize the material flexibility of the additive manufacturing process to develop ternary shape memory alloys. The chemical composition, phase, and material properties at multiple locations along the build direction were studied, using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Vickers hardness testing, tensile testing, and differential scanning calorimetry. The location-dependent compositions of martensitic TiNi and austenitic TiNi phases, mechanical properties, and functional properties were investigated in detail. Variations were found in atomic compositions of Ti, Ni, and Cu elements along the build direction due to the complex interaction between elemental powders and laser processing. Good correlations were present among the chemical composition, phase constituent, hardness, and feature of phase transformation temperatures at various locations. The ultimate tensile strength of the as-deposited TiNiCu alloy is comparable with the previously reported additively manufactured TiNi binary alloys. By adding Cu, a much lower thermal hysteresis was achieved, which shows good feasibility of fabricating ternary TiNiCu shape memory alloys, using elemental powders in the directed energy deposition to adjust the thermal hysteresis.

Influence of pre-alloying on Fe-Cu based metal matrix composite

A pre-alloyed powder (i.e., Fe70Cu30), and elemental metal powders (i.e. Fe and Cu) were selected to study the mechanical properties and microstructures of two groups of Fe-Cu based metal matrix composite (MMC) samples. One group had different Fe/Cu ratios, and the other group had a fixed Fe/Cu ratio with different molten state contents (MSCs). Bending strength, Rockwell hardness and relative density of the samples were tested first, and then SEM and EDS were employed to analyze fracture surfaces of the samples after three-point bending test. Test and observation results show that both Fe/Cu ratio and MSC are significant to the mechanical properties and microstructure characteristics of the Fe-Cu based MMC samples. The mechanical properties increase with the decrease of Fe/Cu ratio at first, but sharply drop when Cu becomes the main ingredient, with the best performance of 1200 MPa and 98 HRB at Fe/Cu ratio of 7:3. The effects of Fe/Cu ratio also indicate that the strengths of bonding interfaces are different, and in descending order are Fe-Fe, Fe-Cu and Cu-Cu respectively. Simultaneously, mechanical properties increase with the rise of MSC in general with the optimal interval of Fe/Cu ratio for impregnated diamond bits being between 8:2 and 3:7. Micro fracture morphologies of the Fe-Cu based MMC samples also indicate that their fracture mechanism can be divided into brittle, plastic and transcrystalline fractures with MSC being the determinant.

Study on the densification behaviour of copper with aluminum &amp; nickel powders through spark plasma sintering

Powder metallurgy is a powder-based manufacturing process of producing new materials with desired properties. Spark plasma sintering (SPS) is one of the effective densification processes in powder metallurgy to produce the powder compacts at a reasonable cost by simultaneous application of pressure and heat. The principal aim of this research work was to create a high-density copper-based shape memory alloy using a ball milling with spark plasma sintering and to analyze the density and hardness of the powder compacts. Three elemental metal powders, namely copper (84 %), aluminum (12 %), and nickel (4 %), were taken in producing the powder compacts. The microstructure of the compacted specimen was analyzed using scanning electron microscopy. The density and hardness of the powder compacts were determined using appropriate tests, and the results were compared with the conventional sintering process. The outcomes indicate that the density and hardness of the powder compacts were improved in the spark plasma sintering.

Preparation of Fe–Si–Al intermetallic alloy and their composite coating for EM absorbing application in 6–18 GHz

An energy efficient and scalable process has been developed for the preparation of intermetallic Fe–Si–Al alloy particles. The preparation process involves initial homogenization & mechanical activation of elemental metal powders followed by vacuum annealing at elevated temperature ~ 650 °C. The physical properties of the as synthesized powders were investigated by means of X-ray Diffraction (XRD), Energy Dispersive Xray Flourence (EDXRF),Vibration Sample Magnetometer (VSM), Scanning Electron Microscope (SEM) and Particle Size Analyser. Composite coatings have been prepared by dispersing 30–60 wt% of Fe–Si–Al alloy in polyurethane (PU) resin. The effect of loading of Fe–Si–Al alloy on dielectric and electromagnetic (EM) properties of composites are studied in 6–18 GHz. A suitable formulation (50 wt% Fe–Si–Al) has been identified, wherein, proper combination of dielectric and magnetic loss of coating composite showed optimal microwave (MW) absorption in 6–18 GHz. The identified composite coating of thickness ~ 1.6 mm showed maximum Return Loss (RL) value ~ − 43 dB at 11.9 GHz and the loss values can exceed more than 10 dB within 6.5 to 16 GHz while varying thickness of coating from 1.2 to 2.2 mm. In the present study, microwave absorption properties of coatings are mainly credited to dielectric and magnetic loss values of the composites. The Fe-Si-Al filled resin composite with optimal loading of alloy particles can be a promising candidate for microwave absorbing coating applications.

Microstructure and mechanical properties of high-nitrogen 16Cr-2Ni-Mn-Mo-xN stainless steel obtained by powder metallurgy techniques

16Cr-2Ni-Mn-Mo-xN (wt%) stainless steel powders were synthesized by mechanical alloying from elemental metal and chromium nitride (Cr2N) powders. Compaction of resulting powders was carried out using spark plasma sintering technology. The X-Ray diffraction and Scanning Electron Microscopy analysis showed that chemical homogeneity improves with increasing alloying time and decreasing nitrides powder content. Analysis of sintering samples showed the formation of α and γ-phase solid solution with nitrogen-containing samples containing undissolved nitrogen inclusions. The results of high-temperature tensile tests showed an increase of tensile stress for the sample containing 50% Cr2N. Furthermore, the microhardness was increased with an increase in the amount of Cr2N.

Effects of planetary ball milling on AlCoCrFeNi high entropy alloys prepared by Spark Plasma Sintering: Experiments and molecular dynamics study

The elaboration of High Entropy Alloys (HEA) was investigated by means of powder metallurgy. We studied the combination of mechanical activation and reactive sintering in the case of AlCoCrFeNi. Elemental metallic powders were first processed by planetary ball milling over a long duration (28 h). The ratio K between the rotating speed of the sun wheel and the relative rotating speed of the grinding vials was set at 0.2 and 1 corresponding to “medium” energy milling. Given the particular hardness of chromium as compared to other elements, the effect of Cr powder size was investigated and optimized. In addition to experimental characterizations of milled powders, Molecular Dynamics simulations were carried out in order to assess the formation of solid solutions. The activated powders were then consolidated by Spark Plasma Sintering at 1000 °C and 1100 °C. A nanostructured lamellar microstructure exhibiting the coexistence of the FCC and BCC phases was synthesized by this solid-state route. The sintered materials exhibited hardness of up to 670 HV. Our final results (i.e., after optimization of the milling and sintering parameters) suggest that mechanical activation combined with reactive sintering is an efficient route to elaborate dense HEA materials.

Microstructure and Mechanical Behavior of AISI 430 FSS Welds Produced with Different Elemental Metal Powder Addition

In this study the effect of the Titanium and aluminum powder addition on microstructure and mechanical properties of AISI 430 ferritic stainless steel welds produced by gas tungsten arc welding was investigated. It’s observed that the addition of aluminium (Al) or titanium (Ti) reducing the grains size, increase the equiaxed grains fraction and improve the mechanical properties with varying degrees. While the addition of mixture (Al+Ti) leads to better improving in mechanical properties and reducing of grains size up to 85 %. The details of tensile tests, optical microscopic observations, microhardness, tensile test and Scanning electron microscopy (SEM) fractography, are discussed.

Microstructure and Mechanical Properties of Nanocrystalline Al-Zn-Mg-Cu Alloy Prepared by Mechanical Alloying and Spark Plasma Sintering.

In this study, Al, Zn, Mg and Cu elemental metal powders were chosen as the raw powders. The nanocrystalline Al-7Zn-2.5Mg-2.5Cu bulk alloy was prepared by mechanical alloying and spark plasma sintering. The effect of milling time on the morphology and crystal structure was investigated, as well as the microstructure and mechanical properties of the sintered samples. The results show that Zn, Mg and Cu alloy elements gradually dissolved in α-Al with the extension of ball milling time. The morphology of the ball-milled Al powder exhibited flaking, crushing and welding. When the ball milling time was 30 h, the powder particle size was 2–5 μm. The α-Al grain size was 23.2 nm. The lattice distortion was 0.156% causing by the solid solution of the metal atoms. The grain size of ball-milled powder grew during the spark plasma sintering process. The grain size of α-Al increased from 23.2 nm in the powder to 53.5 nm in the sintered sample during the sintering process after 30 h of ball milling. At the same time, the bulk alloy precipitated micron-sized Al2Cu and nano-sized MgZn2 in the α-Al crystal. With the extension of ball milling time, the compression strength, yield strength and Vickers hardness of spark plasma sintering (SPS) samples increased, while the engineering strain decreased. The compression strength, engineering strain and Vickers hardness of sintered samples prepared by 30 h milled powder were ~908 MPa, ~8.1% and ~235 HV, respectively. The high strength of the nanocrystalline Al-7Zn-2.5Mg-2.5Cu bulk alloy was attributed to fine-grained strengthening, dislocation strengthening and Orowan strengthening due to the precipitated second phase particles.

Texture Gradient in a Rectangular Extruded Al60Mg40 Metal Matrix Composite

By applying cold extrusion, an elemental metal powder composite Al60Mg40 was prepared. The texture gradient was measured over the cross-section of the extrusion profile using synchrotron radiation while the bulk texture was obtained by neutron diffraction. The aluminum phase shows a typical texture component of plane-strain deformation in the middle part of the sample and a uniaxial deformation texture at the surface. In the central region of the extruded bar, the (0002) Mg pole figure shows a split along the extrusion direction (±ED), which also has been observed in rare-earth containing magnesium alloys. These two poles twist towards the transverse direction on moving towards the surface of the extruded bar; one pole moves to +TD and the other one to −TD. The angle of twist increases towards the TD surface.

Effects of Composition and Post Heat Treatment on Shape Memory Characteristics and Mechanical Properties for Laser Direct Deposited Nitinol

Nitinol structures were synthesized in a fully dense form using a laser direct deposition method. The pure elemental metal powders of nickel and titanium were used and powder ratios were controlled to arrive at the prescribed final chemical compositions of Nitinol. The transformation temperatures of synthesized Nitinol samples with different chemical composition and post heat treatment conditions were systematically analyzed and compared with those of conventional Nitinol. Compared to Nitinol parts produced by other techniques, the laser engineered net shaping (LENS) created the least amount of secondary phase, indicating the possibility of high corrosion resistance. Two step post processing of solution heat treatment and aging heat treatment was carried out to improve the homogeneity of the microstructure and to investigate its effects on phase transformation temperatures. The resultant phase transformation temperatures could be controlled by the heat treatment parameters. Compression test results showed mechanical properties of synthesized Nitinol samples are largely affected by its post heat treatment history while the effect of initial chemical composition was negligible.

Method for the determination of parameters in the sintering process of mixtures of the elemental powders Fe-Cr and Fe-Cr-Ni

The achievement of varied metal alloys through the sintering of mixtures of elemental metallic powders can provide great flexibility of production of these alloys. The possibilities of controlling the composition and the resulting properties of the alloy are of great importance for metallurgy. Otherwise the alloys involving chromium offer many difficulties for their attainment through the process of powder metallurgy (PM). In the formation of alloys with chromium (Cr), an oxide layer that prevents the ideal contact between the particles is formed. Hence the need for researches that study sintering processes and that can solve this difficulty. With this objective, this paper presents a method to determine parameters and describe the sintering process of mixtures of the elemental metallic powders Fe-Cr and Fe-Cr-Ni, assessing the elements’ diffusing capacity and the possible alternative composition of an alloy. The method used Scanning Electron Microscopy (SEM) associated with Energy Dispersive Spectrometry (EDS), X-ray diffraction (XRD) and Vickers microindentation hardness analysis (HV). For the microstructural characterization, we used optical microscopy (OM) and SEM. And EDS mapping was applied for the analysis of the elements’ dispersion.•The method makes it possible to define the ideal sintering time to obtain a good diffusion of the mixtures of the metallic powders Fe-Cr.•With the method, it is possible to verify the dispersion of the powders and whether the microstructure generated is similar to the ones of prealloyed powders.•With the applied procedures, the conditions for the formation of Fe-Cr alloys can be obtained by mixing dissociated and diffusion-bonded elemental metallic powders.