Inert Gas Atoms Research Articles

Characterization of CrMnNi Steel Powders Obtained via Gas Atomization

To obtain a successful product during additive manufacturing, the powder as a raw material must have the high quality. The purpose of this work is to investigate CrMnNi steel powders obtained by inert gas atomization with nickel content: 3, 6, and 9 wt% and to identify dependencies between the powder size and morphology, solidification structure, and change in chemical composition and thermophysical properties. Particle size distribution is measured by a laser scattering analyzer: d50 value are 82.02, 69.32, and 75.54 μm for powders with 3, 6, and 9 wt%, respectively. Surface tension (ST) measurements are made by maximum bubble pressure method: for steels with 3, 6, and 9 wt% at temperature 1500 °C, ST is 1.01, 1.07, and 1.15 mN m−1, respectively. It is found that the change in particle size affects the chemical composition, the content of the ferromagnetic phase and secondary dendritic arm‐spacing. Changes in the content of elements such as S, O, N, and Mn are determined, depending on the diameter of the particles. The influence of changes in content of S, O, and N on the thermophysical properties such as ST is investigated.

Extremely low coercivity of powder Co-rich amorphous alloy obtained by gas atomisation

A novel Co-base soft magnetic powder with ultra-low coercivity was produced by inert gas atomisation. The as-atomised powder is fully amorphous owing to its high glass forming ability and the proper selection of atomisation conditions; it exhibits a very low coercivity (0.130 Oe) mainly due to the low magnetostriction coefficient of Co-based alloys. After production, the powder was annealed at different temperatures between 300 and 600 ºC for 30 minutes. Crystallisation started at around 575 ºC, which is the temperature of the first exothermic peak detected by differential scanning calorimetry. Annealing the powder at temperatures below 550 ºC develops only structural relaxation of the amorphous structure. The smallest coercivity (0.056 Oe) was found in the sample annealed at 400 ºC. On the other hand, an increment of the coercivity of four orders of magnitude occurred after full crystallisation at 600 ºC (394.320 Oe). From the analysis of the curves of anisotropy field distribution, it can be concluded that this Co-base alloy shows lower average anisotropy field, a more gaussian shape and a wider distribution than Fe-base alloys. This is explained by a lower magnetoelastic anisotropy and a more homogeneous distribution of the magnetic anisotropy. The powder exhibits a spherical shape that makes it very suitable as ferromagnetic phase to manufacture powder cores with extremely low hysteresis loss for medium-high frequency applications.

Phase transformation and strengthening of the gas-atomized FeCoCrNiMo0.5Al1.3 high-entropy alloy powder during annealing

Phase evolution and strengthening of the FeNiCoCrMo0.5Al1.3 powder alloy produced via inert gas atomization and annealed in the temperature interval of 300–800 °C have been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and microhardness testing. It was found that annealing at 300–600 °C leads to an increase of the element segregations between the several solid solutions with a rise of the lattice misfit (ε) to 1.5 % and microhardness growth to 1070 HV. It was assumed that elastic stress caused by the element partitioning is the main strengthening mechanism: microhardness rises linearly with misfit rise with dHV/dε = 43400 MPa. Sigma arises after the maximum elastic deformation (in 1.5 %) was reached. Formation of the dispersed coherent sigma phase in the annealing interval 600–800 °C results in the microhardness rise. Oxidation that began at 800 °C in 27 h is accompanied with FCC formation due to a depletion of the B2 in Al caused by Al2O3 formation. Estimation of the activation energy of the initial stage of the solid solution decomposition gives a very low value in 0.65eV, apparently caused by the high concentration of quenched vacancies. The activation energy of sigma formation approximately coincides with the activation energy of self-diffusion in BCC metals (about 2.60 eV).

In situ synthesis of titanium alloy powders reinforced with nanoparticles for powder bed fusion: A step towards safer and more sustainable manufacturing

Additive manufacturing technologies for metallic materials based on powder bed fusion, either with electron (PBF-EB/M) or laser beam (PBF-LB/M) have enormous industrial potential. It is known that the reinforcement of nanoparticles in the metallic matrix improves the mechanical properties. This study presents a novel method for manufacturing reinforced powder particles for PBF technology. The method involves dispersing and dissolving reinforcing nanoparticles in the metallic matrix, resulting in a composite material. The method was applied to a Ti‐6Al‐4V matrix with SiC nanoparticles as reinforcement to develop a new Titanium Matrix Composite (TMC). A route for atomizing the composite material has been developed to scale up the process on an industrial level. The atomized material has been designed to be used as feedstock with PBF-EB/M and PBF-LB/M. The feedstock is a composite powder obtained by the Electrode Inert Gas Atomization (EIGA) process after mixing and dispersing SiC nanoparticles in the Ti‐6Al‐4V matrix and consolidating the mixture into an ingot bar using Hot Isostatic Pressing (HIP). The powder bed fusion process parameters have been studied to obtain specimens with a density greater than 99.9%, and close to 100% after HIP process. The conditions for some heat treatments, such as HIP and stress relief, have been determined. The conditions of machining processes, such as milling and turning, have been studied. The material’s properties, such as chemical composition, microstructure, mechanical strength, and fatigue behavior have been evaluated. Compared to Ti‐6Al‐4V according to the ASTM F2924 standard, both the ultimate tensile strength and yield strength have been improved by 28%, and the elongation at break by between 30% and 60%. Regarding fatigue behavior, an increase of around 30–50% (high-low cycles) has been observed.

Microstructure and Mechanical Properties of Al-Li Alloys with Different Li Contents Prepared by Selective Laser Melting.

Research on the development of new lightweight Al-Li alloys using a selective laser melting process has great potential for industrial applications. This paper reports on the development of novel aluminum-lithium alloys using selective laser melting technology. Al-Cu-Li-Mg-Ag-Sc-Zr pre-alloyed powders with lithium contents of 1 wt.%, 2 wt.% and 3 wt.%, respectively, were prepared by inert gas atomization. After SLM process optimization, the microstructure and mechanical properties of the as-printed specimens were investigated. The densifications of the three newly developed alloys were 99.51%, 98.96% and 92.01%, respectively. They all had good formability, with the lithium loss rate at about 15%. The as-printed alloy with 1% Li content presented good comprehensive properties, with a yield strength of 413 ± 16 MPa, an ultimate tensile strength of 461 ± 12 MPa, and an elongation of 14 ± 1%. The three alloys exhibited a layered molten pool stacking morphology and had a typical heterostructure. The columnar crystals and equiaxed fine grains were alternately arranged, and most of the precipitated phases were enriched at the grain boundaries. The change in Li content mainly affected the precipitation of the Cu-containing phase. When the Li content was 1 wt.%, the following occured: θ phase, T1 phase and TB phase. When Li increased to 2 wt.%, T1 and T2 phases precipitated together. When Li reaches 3 wt.%, δ' phase precipitated with T2 phase. This study provides useful guidance for the future SLM forming of new crack-free and high-strength Al-Li alloys.

Sintering property of micro/nano core-shell molybdenum powder synthesized by mechanochemical process

In this study, a micro/nano core-shell molybdenum powder was synthesized by mechanochemical process to improve its microstructural uniformity and density by pressureless sintering the core-shell powder. The micro-sized spherical Mo powder, prepared through an electrode induction melting inert gas atomization process, was mixed with MoO3 powder and ball-milled using a three-dimensional shaker mixer. A mechanochemical process involving hydrogen reduction was employed to prepare the core-shell Mo powder. The prepared powders were sintered through the compacting and pressureless sintering. The density was measured using a densitometer to analyze the properties of sintered specimens. Phase analysis was performed using X-ray diffraction. In addition, microstructure analysis was conducted using scanning electron microscopy and electron backscatter diffraction. Comparing the sintered core-shell powder to the sintered conventional mixing powder under the same conditions, we observed that the former exhibited a uniform microstructure and higher density. Furthermore, we experimentally demonstrated the dependence of sintering properties on mixing ratio.

Synthesis of micro- and nano-sized zinc sulfide crystallites by the method of self-propagating high-temperature synthesis

The paper presents the results that demonstrate how ZnS crystallites of different sizes can be obtained by the method of self-propagating high-temperature synthesis (SHS). The SHS is possible due to an exothermic reactions occurring in mixtures of Zn and S powders, due to a large amount of heat released (enthalpy of formation being 202 kJ/mol). Pressed powders of Zn and S are placed in a stoichiometric ratio into a reactor filled with Ar or N under a pressure of P>0.5 MPa. After initiated by ignition, the chemical reaction propagates through the mixture to produce a sample in the form of an ingot. ZnS crystallites with a characteristic size of ~ 30 μm are obtained in the traditional solid-state reaction of the SHS. Аfter the passage of the combustion wave, the reaction of the components continues in parallel with crystallization processes, which causes the formation of an active medium where self-organization processes occur. Sometimes, abnormally large ("giant") crystallites with length ~ 1 mm, thickness 0.1-0.2 mm, and regularly-shaped spatial structures are observed. The size of synthesized zinc sulfide crystallites can be changed with a dispersant, NH4Cl. When 5 wt.% of the dispersant is introduced, the monolithic sample is polycrystalline ZnS with a characteristic grain size of ~ 40 μm, and when 7 wt.% is introduced, the grain size decreases to 20 μm. As the concentration of the dispersant is increased to 10 wt. %, the synthesized material becomes loose, the characteristic grain size decreasing to 5-10 μm. At concentrations greater than 10 wt. %, powder-like ZnS is formed. The SHS method makes it possible to obtain meso- and nano-sized ZnS, with grain sizes of order 50 – 100 nm and 2 – 50 nm, respectively, in two ways. The first one consists in the condensation of the substance’s vapor in a rarefied inert atmosphere. When, during the SPS, the pressure of the inert gas changes in the interval from 40 to 400 Pa, a part of the reactants in the form of steam escapes from the ampoule into the reactor bulk. When the steam particles collide with the inert gas atoms, they quickly lose their kinetic energy to form particles with sizes of 2 to 100 nm. To form particles of the required size, it is necessary to adjust the pressure of the inert gas in the reactor. The second method for obtaining nanoparticles by the SBC is based on the use of an inert diluent, which prevents the growth of the forming particles. The main requirement for the diluent material is its inertness to both the reagents in the charge and the synthesized material. The effect of changing the pressure of the inert gas on the size of the obtained nanoparticles manifests itself both directly and indirectly—through the size of the condensation zone. As the gas pressure increases, its density increases, heat removal increases, the rate of crystallization center formation in the gas phase decreases, but the rate of crystal growth increases. As a result, so does the size of the resulting particles. The shape of nanoparticles obtained by this method depends on their size. Nanoparticles of size <20 nm have a shape close to spherical, which is a result changing the relative fraction of the surface energy in the total energy of a nanoparticle as its size decreases. Larger-size particles are faceted.

Influence of Electron Collisions on Electromagnetic Modes of Plasma Produced by Multi-Photon Ionization of an Inert Gas

Collective electromagnetic modes in weakly ionized plasma formed by multiphoton ionization of inert gas atoms, in which the Ramsauer–Townsend effect takes place, are studied. It is shown that at a relatively low energy of photoelectrons of the order of 1 eV, typical for multiphoton ionization, amplification of electromagnetic waves is possible. Amplification is possible both in the case of rare collisions of photoelectrons with neutral atoms and for collision frequencies higher than electron plasma frequency. At photoelectron energies somewhat higher than 1 eV, aperiodic instability can develop with growth rate whose value is comparable to electron plasma frequency. Detailed analytical and numerical analysis of the effect of collisions of photoelectrons with neutral atoms on the dispersion law of electromagnetic wave and the growth rates of instabilities is presented.

Scattering of Positive Muons by Atoms of Inert Gases

Scattering of Positive Muons by Atoms of Inert Gases

Scattering of Positive Muons by Atoms of Inert Gases

In the present work, the cross sections of elastic and inelastic scattering of positive muons by He and Ar atoms at low and medium kinetic energies are calculated by the methods of many-body theory with the use of the ATOM-M software package. For comparison, the results of elastic and inelastic positron scattering at the same energies are also given. The dependence of the phases and scattering cross sections on the charge of the particle and its mass, as well as on the charge of the nucleus of the scattering atom, is discussed.

Potentials of Ultrasonically Atomized Cored Wires for Powder Metallurgy and Additive Manufacturing

Abstract Powder production for additive manufacturing is currently mainly done by inert gas atomization. A new process is the production of low-oxygen and highly spherical metal powders by ultrasonic atomization from a wire or rod feedstock. As a crucible-free process and because of an electric arc as an energy source, even materials with a high liquidus temperature up to 1800 °C can be processed. A limitation of this technique can be found in the continuous processing of high-strength materials, like martensitic hardenable tool steels, from a stiff wired feedstock because of the limited feed ability. This paper investigates the possibility of processing high-strength steel powder using cored wire as the starting material for the ultrasonic atomization process to circumvent the feeding problem of high-strength materials. Thereby, two carbon martensitic hardenable hot work tool steels with a carbon content of 0.12 wt. % and 0.4 wt. % are considered as reference materials. After the atomization process with varying parameters, powders are characterized concerning their morphology, chemical composition, phases formed, and related powder properties. In addition to flowability, the bulk density are also determined. Based on these results, a conclusion will finally be given on the suitability of ultrasonically atomized powders for additive manufacturing and fast sintering techniques.

Hydrogen Embrittlement of Inconel 718 Manufactured by Laser Powder Bed Fusion Using Sustainable Feedstock: Effect of Heat Treatment and Microstructural Anisotropy

This study investigated the in-situ gaseous (under 150 bar) hydrogen embrittlement behaviour of additively manufactured (AM) Inconel 718 produced from sustainable feedstock. Here, sustainable feedstock refers to the Inconel 718 powder produced by vacuum induction melting inert gas atomisation of failed printed parts or waste from CNC machining. All Inconel 718 samples, namely AM-as-processed, AM-heat-treated and conventional samples showed severe hydrogen embrittlement. Additionally, it was found that despite its higher yield strength (1462 ± 8 MPa) and the presence of δ phase, heat-treated AM Inconel 718 demonstrates 64% lower degree of hydrogen embrittlement compared to the wrought counterpart (Y.S. 1069 ± 4 MPa). This was linked to the anisotropic microstructure induced by the AM process, which was found to cause directional embrittlement unlike the wrought samples showing isotropic embrittlement. In conclusion, this study shows that AM Inconel 718 produced from recycled feedstock shows better hydrogen embrittlement resistance compared to the wrought sample. Furthermore, the unique anisotropic properties, seen in this study for Inconel 718 manufactured by laser powder bed fusion, could be considered further in component design to help minimise the degree of hydrogen embrittlement.

Non-Metallic Alloying Constituents to Develop a Wear-Resistant CrFeNi-BSiC High-Entropy Alloy for Surface Protective Coatings by Thermal Spraying and High-Speed Laser Metal Deposition

Compositional alterations to high-entropy alloys (HEAs) allow further evolution of these materials by adjusting their property profiles. This way, they can be used for coating technologies and surface-protection applications. In the present work, minor quantities of the non-metallic alloying constituents, BSiC, were added to the CrFeNi base system. The alloy development was carried out in an electric arc furnace in comparison with the nickel-based alloy Ni-600. With regard to the BSiC-free variant, the wear resistance can be significantly increased. The powder was manufactured by inert gas atomization and characterized, followed by processing via high-velocity oxy-fuel spraying (HVOF) and high velocity laser metal deposition (HS-LMD). Depending on the manufacturing conditions, the proportion and shape of the precipitates within the microstructure differ. Compared to both the reference system and the as-cast condition, the coating systems demonstrated comparable or improved resistance to wear. The evaluation of the process–structure–property relationships confirmed the great potential of developing load-adapted HEA systems using non-metallic alloy constituents in the field of surface engineering.

Mechanisms of non-adiabatic charge-exchange transitions in slow collisions of W ions with He, Ar and Kr atoms

The study of slow collisions of heavy particles is a challenging task from both experimental and theoretical points of view. A powerful tool for the theoretical description of these collisions is the adiabatic theory of transitions in slow collisions developed by Solov’ev (1989), which is applied here to study low-energy charge exchange between tungsten ions and inert-gas atoms at 0.01–1 keV/u. It is found that the main mechanism of charge-exchange transitions in collisions of W+ ions with Ar and Kr atoms at energies below 1 keV/u is the rotational coupling associated with internuclear axis rotation in close collisions, while charge exchange between W8+ ions and He atoms is mainly due to the radial Landau–Zener type transitions. For all cases, potential curves as a function of the internuclear distance are calculated together with the charge-exchange cross sections. The cross sections obtained are compared with experimental data, showing good agreement and explaining the mechanisms of the transitions.

Absorption of Radiation with a Frequency Close to the Transparency Boundary of an Inhomogeneous Plasma Formed by Multiphoton Ionization of Inert Gas Atoms

Absorption of Radiation with a Frequency Close to the Transparency Boundary of an Inhomogeneous Plasma Formed by Multiphoton Ionization of Inert Gas Atoms

In-situ spherical TiB2/Cu composite powder: A new method of liquid phase reaction coupled with gas atomization

The spherical TiB2/Cu composite powder was fabricated by a new method of liquid-phase in-situ reaction coupled with inert gas atomization. The powder morphology, characteristic indexes, microstructure and nanoindentation hardness were investigated. The effects of spheroidization time and solidification rate of atomized molten droplets on powder sphericity and the relationship between in-situ reaction control and TiB2 distribution were discussed. Results indicate that the powder has a good sphericity and d50 is 32.86 μm, in addition to 75% fine powder yield (<45 μm). The in-situ formed TiB2 particles (TiB2p) were uniformly distributed in grain boundaries and intragrain. The rapid solidification of molten droplets and the inhibition of copper grain growth by TiB2p refined the Cu matrix grain size (4.34 μm). The nanoindentation hardness of composite powder is 3.17 GPa, which is 1.9 times higher than that of spherical Cu powder, and the reasons for the increased hardness of powder are also discussed.

Unveiling the interaction of nanopatterned void superlattices with irradiation cascades

Nanopatterned microstructures in materials can have a profound impact on materials’ physical and chemical properties. While voids are typically considered as detrimental defects in irradiated materials, the patterning of nanoscale voids causes the formation of void superlattices and provides a highly efficient mechanism for gas storage. Despite the important applications of nanopatterned defect superlattices, how they degrade under irradiation remains unclear. Here we provide direct observation of the evolution of void superlattices under irradiation and elucidate the interaction of void superlattices with irradiation cascades. We reveal that the instability of void superlattices under irradiation is caused by heterogenous void shrinkage and demonstrate the imperative role of mixed 1D/3D diffusion of self-interstitial atoms and injected inert gas atoms on void shrinkage and void superlattice instability. Understanding the degradation mechanisms of nanopatterned microstructures is essential to designing damage-tolerant materials and broadening their applications in extreme environments.

Influence of Powder Plasticity on Bonding Strength of Cold-Sprayed Copper Coating

When cold spraying is performed at a velocity equivalent to or greater than a specific material-dependent critical velocity, powders suffer intensive plastic deformation and localized heating of interacting surfaces. The thermomechanical reaction of the sprayed powder upon impacting the substrate material triggers thermally dependent metallurgical bonding and/or mechanical interlocking mechanisms. In this study, three Cu feedstocks, fabricated through electrolysis (EP), gas-assisted water atomization (WA), and inert gas atomization (GA), were characterized and annealed before cold spraying. The electron back-scattered diffraction technique was used to analyze the grain structure and plastic microstrain within the powders and coatings. The plastic microstrains that originally existed in the Cu powders were released after 30 min of annealing at 500 °C. The influence of plastic deformation behavior (associated with the grain structure and plastic microstrain of powder feedstocks) on the bonding strength of the cold-sprayed Cu coatings on AA6061 aluminum alloy substrates was examined. The results indicate that EP powder with an asymmetric dendrite morphology was not conducive to the intensive plastic deformation that may cause recrystallized twin grains to form after cold spraying. Furthermore, the homogeneous microstructure of the spherical Cu feedstocks, which may be induced by strain release as recrystallized twin grains and low-angle boundary grain growth through annealing, caused the cold-sprayed Cu coating to have high ductility and low hardness. The findings reveal the low strain hardening and residual stress in the cold-sprayed coating—characteristics regarded as providing key advantages for the bonding strength of the coating.

Particle size dependent microstructure evolution of inert gas atomized nickel base superalloy powders

Powder of an experimental Nickel base superalloy produced through Inert Gas Atomization technique is characterized for its physical properties, chemical composition, morphology, micro-segregation and orientation distribution of grains. The atomized powders exhibits near spherical morphology with average particle size of 61 µm. Micro-chemical analysis reveal, elements like Ti, Mo, Ta and Hf partition at inter-dendritic regions, irrespective of particle size.The extent of micro-segregation however is found to be intimately related to the cooling rate and particle size. The EBSD analysis reveals random texture in the particles with the number of grains per particle decrease with decreasing particle size. The nucleation event is found to be initiated on particle surfaces as evidenced from the dominant presence of the Low Angle Grain Boundaries (LAGBs) near the particle surfaces. The selective growth of favourably oriented nuclei are observed towards the core of the particle and characterized by presence of High Angle Grain Boundaries (HAGBs) in the particle interior. A mechanistic understanding correlating evolution of grain size distribution and micro-segregation with droplet solidification process, has been elucidated through the present study.

Diagnosis of inhomogeneous one-dimensional discrete chains by photon scattering

Among the ways to reduce radiation doses (increasing the distance from the source to the person, reducing the time spent in radiation fields, reducing the radiation dose rate of the source) an important role is played by shielding the source of ionizing radiation.Currently, the use of screens is limited by the small selection of materials and the inconvenience of their use, which complicates their operation, installation and replacement, or disassembly.The propagation of a plane wave in a one-dimensional force chain with Hertzian contacts is analyzed in a linear approximation for cases with the presence of incorporated single and double impurities (defects). The algorithm of analytical solution of control equations and finding of reflection and transmission coefficients of incident radiation is determined. In terms of phase shifts, the frequency criterion of multi-modes of generation of transparent modes for inhomogeneous chains (with double impurities) similar to the Ramsauer-Townsend effect in the scattering of electrons by inert gas atoms is established. The obtained theoretical results are consistent with the data obtained from alternative sources. Possibilities of application of terahertz spectroscopy of radiation transmission for structural diagnostics and detection of in homogeneities, impurities and defects in discrete micro-mechanical (granular) systems are discussed. In particular, preliminary experimental data on scattering of terahertz radiation on samples of granular materials with different degrees of packing, from low to densely packed, which clearly indicate the dependence of the transmittance on the degree of packing and the formation of the corresponding band structure of spectra. The obtained results are also discussed in terms of applications to the creation of the element base of photonic circuitry in the sub millimeter range using decorated with impurities and structured low-dimensional discrete power circuits.