Interstitial Solution Research Articles

Evaluation of microstructural changes in fresh cement paste using AC impedance spectroscopy vs. oscillation rheology and 1H NMR relaxometry

AC impedance spectroscopy (ACIS) is a promising technique for monitoring the microstructure evolution of fresh cement paste in real-time. This paper compared the change of bulk electric resistivity (ρbulk) obtained from ACIS with the developments of storage modulus (G′) and the mean transverse relaxation times (T2) of fresh Portland cement pastes within 5 h. It was found that the three different phases (Phase I, II, and III) on the microstructural build-up process of fresh paste can be accurately distinguished by analyzing ρbulk, as well as G′ and T2. The use of ρbulk fails to characterize the microstructural changes in Phase I due to the great sensitivity on the electrical conductivity of the interstitial solution. However, it can successfully reflect the developing features of microstructure in Phases II and III, and reliably evaluate the impacts of water to cement ratio, superplasticizer, and supplementary cementitious materials on the microstructural development.

Homogeneous dispersion of graphene and interface metallurgical bonding in Sn–Ag–Cu alloy induced by ball milling

The addition of graphene is expected to improve the properties of solder and graphene reinforced Sn–Ag–Cu (GNSs/SAC) is considered to be able to adapt to harsh service environment. However, it is difficult to realize homogeneous dispersion of reinforcement and the metallurgical bonding between graphene and Sn–Ag–Cu alloys. In this study, composite solders with various dispersion of graphene have been prepared by different ball milling method. The microstructure characterization shows that incoherent interface and amorphous interface have been produced between graphene and Sn. The results of Energy Dispersive Spectrometer (EDS) and X-ray diffraction (XRD) indicate that the interstitial solid solution of carbon atoms in β-Sn is the cause of metallurgical bonding. The relative amount of the two types of interfaces and the dispersion of graphene were evaluated. The incoherent interface of composites tends to form at lower milling speed, and its thermal expansion response indicates that the interface has more effective load transfer, while the amorphous interface is opposite. Besides, the {101} fiber texture was also confirmed to be formed during ball milling and sintering. Finally, the nano indentation test verified the metallurgical bond, and the mechanical properties of the GNSs/SAC composites are determined by the interface type and graphene dispersion.

Inversion of Nitrogen Redistribution in Austenitic Steel by Severe Plastic Deformation

Using the Mössbauer spectroscopy and transmission electron microscopy (TEM) methods, the temperature boundary of a strain-induced transformation with the inversion of the direction of nitrogen redistribution is determined in the structure of the FeMn22Cr18N0.83 austenitic steel. Deformation by high pressure torsion in Bridgman anvils below the temperature limit (298 K) leads to an increase in the amount of nitrogen in the interstitial solid solution and deformation above the limit (373 K) leads to a decrease in this value. An increase in the deformation temperature leads to the complete dissolution of the products of cellular decomposition and the formation of submicrocrystalline austenite with secondary nanocrystalline nitrides. Changes in the direction of nitrogen redistribution are explained by the competition between the mechanisms of relaxation of the structure along the paths of dispersion, dissolution of nitrides by dislocation, and decomposition of a solid solution supersaturated with nitrogen.

Potassium-rich granite melt inclusions in zircon from gabbro-hosted felsic stringers, Mid-Atlantic Ridge at 13°34′N: E-MORB connection

We present new data on crystallized micro-inclusions in zircon from clinopyroxene-bearing felsic stringers within gabbronorite of gabbro-peridotite oceanic core complex at Mid-Atlantic Ridge, 13°34′ N. A relatively large (about 49 × 22 μm) crystallized inclusion exposed in situ in thin section consists of the muscovite + biotite + plagioclase + K-feldspar + quartz assemblage. Smaller inclusions (≤20 μm) found in zircon separates consist of silicate minerals, interstitial water solution, and gas bubbles. At temperature close to 800 °C and estimated pressure about 1.5 kbar the inclusions completely homogenize into a K2O-rich (3.9 ± 0.1 wt%), H2O-bearing (about 4 wt%) granite (SiO2 70 ± 2 wt%) melt. Calculations employed DOMINO software show that complete closed-system crystallization of the analyzed melt exactly reproduces mineral assemblage of the large crystallized inclusion (+H2O) at about 1.5 kbar below 600 °C. Granitoid mineralogy of felsic stringers hosting zircon does not correspond to that of the crystallized melt inclusions, with a significantly lower K2O in the former. The K2O loss might result from interaction of the melt with pyroxenes of the host gabbro. This implies that considering felsic granitoid veins, often present in the oceanic lower crustal sections, as simply “frozen melt” is not always justified. Compositional variations of basalt lava glasses from the 13°25′–14° portion of the Mid-Atlantic Ridge show continuous geochemical trends from D-MORB to E-MORB with K2O enrichment up to 0.9 wt%, suggesting mixing from two sources. The most K2O-enriched E-MORB composition (K2O = 0.9 wt%, H2O = 0.7 wt%, K2O/TiO2 = 0.42, (La/Sm)N = 2.45) was assumed as a source of the granitoid inclusions. Computer simulation of equilibrium crystallization of this E-MORB composition returned a granite residual melt closely matching the average composition of the zircon-hosted melt inclusions at 820 °C, 1.5 kbar and melt fraction 5.2 vol%. The result suggests a direct link between the E-MORB magma occurring in the studied area, and the origin of the K-rich granite melt in zircon-hosted inclusions.

Thermodynamic modelling of hydrogen-multicomponent alloy systems: Calculating pressure-composition-temperature diagrams

The applicability of an alloy as a hydrogen storage media mostly relies on its pressure-composition-temperature (PCT) diagram. Since the PCT diagram is composition-dependent, the vast compositional field of high entropy alloys, complex concentrated alloys or multicomponent alloys can be explored to design alloys with optimized properties for each application. In this work, we present a thermodynamic model to calculate PCT diagrams of body-centered (BCC) multicomponent alloys. The entropy of the phases is described using the ideal configurational entropy for interstitial solid solutions with site blocking effect. As a first approximation, it is assumed that the hydrogen partial molar enthalpy of a phase is constant, so the enthalpy of hydrogen mixing varies linearly with the hydrogen concentration. Moreover, the hydrogen partial enthalpy of a phase for a multicomponent alloy was approximated by a simple ideal mixture law of this quantity for the alloy's components with the same structure. Experimental data and DFT calculations were used for parametrization of the enthalpy terms of eight elements (Ti, V, Cr, Ni, Zr, Nb, Hf, and Ta), which are the components of the alloys tested in this work. Experimental PCTs of six BCC multicomponent alloys of four different systems were compared against the calculated ones and the agreement was remarkable. The model and parameters presented here can be regarded as a basis for developing powerful alloy design tools for different hydrogen storage applications.

Утворення твердих розчинів та фаз втілення зa умов іонного бомбардування металів у жевріючому розряді

Regularities of interaction of iron, steels, nickel, copper, titanium with light elements and inert gases in the plasma of the glow discharge studied by methods based on the use of radioactive indicators 55Fe, 44Ti, 14C, 13N, 85Kr, 41Ar (layer-by-layer radiometric analysis of residual integrated activity, macro- and microautoradiography, activation autoradiography), as well as metallography, X-ray analysis and spectral analysis. Processing was carried out according to the diode circuit with parameters of 1 - 55 hours, 0.2 - 2 kV, ~ 500 K. Neutral (argon, krypton) and saturating (nitrogen, ammonia, methane) media were used for processing in the discharge, and further processing of metals previously saturated with nitrogen or carbon was carried out in a neutral medium. It is established that in the process of introduction into metals (Fe, Ti) under the action of a glow discharge burning in a saturating medium, atoms soluble under equilibrium conditions of elements (N, C), there are interstitial solutions and phases that differ from those formed in isothermal annealing, only the presence of supersaturated solid solutions and some violation of the stoichiometry of carbides and nitrides, as well as a steeper decrease in the concentration of the alloying impurity with increasing distance from the surface. The shape of the concentration profiles outside the layer of the interstitial phase is described by an exponential dependence on the square of the penetration depth. As for the penetration into copper of nitrogen, carbon, argon or krypton atoms, insoluble under equilibrium conditions, in ion bombardment in appropriate media from the treated surface to the end of the diffusion zone there is only a solid solution with a concentration that decreases by the exponent. It turned out that further treatment of nickel, iron and steel saturated with light elements by argon and krypton ion bombardment leads to redistribution of alloying impurities, separation of interstitial phases mainly at grain boundaries, surface or at some distance from the surface, which contributes to some disturbance of concentration profile. When processing pre-saturated copper interstitial phases do not occur, but the type of profile changes dramatically, but from the maximum to the end of the diffusion zone is described by the exponent. It is shown that the use of saturating and neutral media, as well as their sequential application for processing in the glow discharge makes it possible to create predetermined doping profiles and enter the required amount of doping impurity. Keywords: glow discharge, radioactive isotopes, light elements, inert gases, diffusion, formation of phases and solid solutions.

In Situ Recombination of Elements in Spent Lithium-Ion Batteries to Recover High-Value γ-LiAlO2 and LiAl5O8.

Recovering valuable materials from spent lithium-ion batteries is an important task because of the asymmetry in resource distribution, supply, and demand around the world. A lithium-ion battery is a combination system of various elements and their oxides. Current recovering technologies focus on the separation of valuable metal elements. They can inescapably bring secondary contamination and cost to the environment due to the addition of leachants and precipitants. To recover valuable materials, in situ recombination of elements in spent lithium-ion batteries can be a more economical and environment-friendly solution. Herein, we developed a technology based on in situ aluminothermic reduction and interstitial solid solution transformation to recover high-value γ-LiAlO2 and LiAl5O8 under vacuum and high-temperature (1723 K) conditions. It was found that the process of Li2O filling into the lattice of O-Al-O structure is an energy-reducing process, while LiAl5O8 was an existing high-energy transition-state matter. Since there was no wastewater generated, the process brought a new environment-friendly method for recovering valuable metals from spent lithium-ion batteries. This study also provides new comprehension regarding the design for high-value products' recovery from multi-element mixed wastes on an atomic scale.

Thermo-kinetic modelling of the giant Snoek effect in carbon-supersaturated iron

Snoek relaxation in interstitial bcc solid solutions is the origin of the Snoek peak in frequency-dependent and temperature-dependent internal friction measurements. When applied to low-carbon steels, the internal friction profiles show a linear dependence of the peak height with carbon content. However, recent Monte Carlo simulations of frequency-dependent internal friction exhibited a non-linear giant peak height at high carbon contents. To investigate this effect in temperature-dependent internal friction, we developed a thermo-kinetic mean-field theory of the Snoek relaxation phenomenon. By taking into account the collective behaviour of the interstitial atoms, our theory predicts (i) a non-linear dependence of the peak height with composition when approaching the order–disorder transition of the alloy; (ii) a shift in the temperature of the peak; (iii) a composition-dependent activation enthalpy of the relaxation time. The theory is exemplified by the case of carbon-supersaturated iron.

Extreme hardening of titanium with colossal interstitial contents of nitrogen and oxygen

Homogenous thin foils of titanium with nitrogen and oxygen in interstitial solid solution were characterized with X-ray diffraction, light optical microscopy and electron backscatter diffraction. Samples covering the broad solubility ranges of O and N were synthesized. The mechanical properties were assessed using nanoindentation and related to the interstitial content, h.c.p. lattice expansion and grain orientation. Effects of surface pile-up and sink-in during nanoindentation were adequately accounted for, yielding hardness and indentation modulus values for nearly the full range of concentrations, finding consistency with theoretical expressions and very limited literature values. The hardening/strengthening achieved by colossal interstitial alloying of O and N correlates with the change in c/a ratio of the h.c.p. Ti lattice as caused by interstitial occupancy.

Dual phase equal-atomic NbTaTiZr high-entropy alloy with ultra-fine grain and excellent mechanical properties fabricated by spark plasma sintering

Super-high strength NbTaTiZr high-entropy alloys (NbTaTiZr HEAs) have been successfully fabricated by the mechanical alloying (MA) with spark plasma sintering (SPS) technology, which is 2-fold compared with that of NbTaTiZr HEAs prepared by vacuum arc melting (VAM). After the SPS process, the bulk NbTaTiZr alloy samples are provided with dual-phase body-centered cubic (BCC) structure and nanoscale grain size about 500 nm that is obviously smaller than that of NbTaTiZr HEA fabricated by VAM. When the sintering temperature is 800 °C, the compressive fracture strength is the highest reaching at 2511 ± 78 MPa. When the sintering temperature is 1000 °C, the fracture strain is the highest reaching at 12.8%, and compressive fracture strength and yield strength also reach at 2274 ± 91 MPa and 2172 ± 47 MPa, respectively. The excellent mechanical properties of bulk NbTaTiZr alloy samples are attributed to the merits of MA and SPS, and the collaboration effect of ultra-fine grains strengthening, solid solution strengthening and interstitial solid solution strengthening.

Phase behavior of binary hard-sphere mixtures: Free volume theory including reservoir hard-core interactions.

Comprehensive calculations were performed to predict the phase behavior of large spherical colloids mixed with small spherical colloids that act as a depletant. To this end, the free volume theory (FVT) of Lekkerkerker et al. [Europhys. Lett. 20, 559 (1992)] is used as a basis and is extended to explicitly include the hard-sphere character of colloidal depletants into the expression for the free volume fraction. Taking the excluded volume of the depletants into account in both the system and the reservoir provides a relation between the depletant concentration in the reservoir and that in the system that accurately matches with computer simulation results of Dijkstra et al. [Phys. Rev. E 59, 5744 (1999)]. Moreover, the phase diagrams for highly asymmetric mixtures with size ratios q ≲ 0.2 obtained by using this new approach corroborate simulation results significantly better than earlier FVT applications to binary hard-sphere mixtures. The phase diagram of a binary hard-sphere mixture with a size ratio of q = 0.4, where a binary interstitial solid solution is formed at high densities, is investigated using a numerical free volume approach. At this size ratio, the obtained phase diagram is qualitatively different from previous FVT approaches for hard-sphere and penetrable depletants but again compares well with simulation predictions.

Improving mechanical properties and tribological performance of Al0.2Co1.5CrFeNi1.5Ti0.5 high entropy alloys via doping Si

Phase evolution, microstructures, mechanical properties and tribological performance of the Si doped Al0.2Co1.5CrFeNi1.5Ti0.5 high entropy alloys (HEAs) were investigated and compared with conventional wear-resistant alloy Stelite-6. The addition of the Si promoted the formation of the silicide (Ti5Si3 and TiSi) in FCC-structured HEAs. The interstitial solid solution strengthening of the Si and the second phase strengthening of the silicide increased the hardness of the HEAs, but reduced compressive strength and fracture toughness. Si doped HEAs showed excellent tribological performance as the friction coefficient decreased monotonously with increasing temperature and Si content. The wear resistance was proportional to compressive strength and fracture toughness. At 800 °C, the wear resistance of the HEAs was about 17 times higher than that of Stelite-6, which was attributed to the good mechanical properties and nano oxide glaze layer on the worn surface.

Sinterability and Luminescence Property of the MgO-YAG:Ce Phosphor Ceramic with Sintering Aids

MgO-YAG:Ce phosphor ceramics with the addition of Y2O3, SiO2, TiO2 and ZrO2 as sintering aids were developed from commercial powders by hot-pressing. In this work, the effects of Y2O3, SiO2, TiO2, ZrO2 on the phase composition, microstructure, sinterability and luminescence intensity of MgO-YAG:Ce phosphor ceramic were investigated. By comparison, the relative density of MgO-YAG:Ce phosphor ceramic with 2 wt.% SiO2 was satisfying, reaching 98.4%, and the luminescence intensity reached the maximum. Because SiO2 and MgO react to form interstitial solid solution Mg2SiO4, which leads to the increase of the grain boundary energy of the MgO matrix, thereby increasing the sintering performance of MgO-YAG:Ce phosphor ceramics. And SiO2 does not react with YAG, maintaining the excellent luminescence properties of YAG itself.

Low-temperature photoluminescence of C60 single crystals intercaled with nitrogen molecules in the wide range of temperatures

The optical properties of C60 single crystals, intercalated with nitrogen molecules, were studied by the spectral-luminescence method at a temperature T = 30 K and excitation by the He–Ne laser (Eexc = 1.96 eV). Intercalation was carried out at a pressure of 30 atm in a temperature range of 200–550 °C. It was found that at sorption temperatures up to 400 °C, the bands of the low-temperature luminescence spectrum of the C60–N2 solutions are broadened without significant energy shift. As a rule, this situation is typical for the case of an increased contribution of the luminescence of “deep X-traps.” The concentration of such exciton emission centers is determined by the degree of occupation of the octahedral cavities of the fullerite fcc lattice by intercalated molecules. This indicates the formation of an equilibrium C60–N2 interstitial solution as a result of physisorption. At sorption temperatures above 400 °C, a significant shift of the luminescence spectrum towards low energies with a considerable inhomogeneous broadening of spectral bands was found for the first time. The shift and significant nonuniform broadening of the luminescence bands are explained by the emergence of a chemical interaction (chemisorption) of nitrogen with fullerene molecules, with the formation of a new nitrogen-containing substance in this case.

Evaluation of tensile properties of thermally aged 316LN stainless steel with varying nitrogen content using ABI technique

Abstract Type 316LN stainless steel (SS) with varying nitrogen content (0.07, 0.14 and 0.22 wt%) was thermally aged at 873 K and 923 K for 20,000 h. The microstructures of thermally aged steels revealed secondary phases such as M23C6 carbides and Fe–Cr–Mo intermetallics at all the nitrogen contents and Cr2N nitrides additionally at 0.14 and 0.22 wt% N. The amount of precipitates increased with increase in nitrogen content and aging temperature. The effect of thermal aging on the tensile properties of 316LN SS was evaluated using automated ball indentation (ABI) technique at 298 K. The flow curves of the steels aged at 873 K were lower than those obtained under unaged condition. Whereas due to ageing at 923 K, the flow stress response gradually increased above the unaged condition with increasing nitrogen content. The ultimate tensile strength varied similarly at 873 K aging condition for all nitrogen levels and was observed to recuperate upon aging at 923 K, except for 0.07 wt% N. Yield strength was not strongly affected by thermal ageing, except the considerable increase in 316LN SS with 0.22 wt% N aged at 923 K. The addition of nitrogen generally imparted interstitial solid solution strengthening to 316LN SS. The higher the nitrogen content and ageing temperature, the higher is the precipitation strengthening due to ageing, which was reflected in the tensile behavior. Transmission electron microscopy examination of ABI deformed zone revealed dislocation-precipitate interactions, precipitate-shear band interaction and pile-up of dislocations at precipitates, influencing the tensile properties.

Ultra-fine grain TixVNbMoTa refractory high-entropy alloys with superior mechanical properties fabricated by powder metallurgy

TixVNbMoTa refractory high-entropy alloys (RHEAs) were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) based on classic VNbMoTaW RHEA. The effect of Ti content on the microstructures and mechanical properties of the TixVNbMoTa RHEAs were systematically investigated. The results showed that the milling powders with more Ti content were agglomerated severely in the early stage of the MA process, leading to the extension of mechanical alloying time. The mechanically alloyed powders in all groups exhibited single body-centered-cubic (BCC) phase after the MA process. The sintered alloys were consisted of ultra-fine matrix and precipitation phase. The grain sizes of the matrix and precipitation phases, as well as the volume fraction of the precipitation phases were increased with the increase of Ti content. The MA and SPS processes and the replacement of Ti not only greatly reduce the densities, but also significantly improved the ductility, strength and specific strength of the alloys. The yield strengths were decreased first and then increased with the increase of Ti content in the TixVNbMoTa RHEAs, which is mainly attributed to the weakened effect of grain boundary strengthening, and the enhanced effect of the substitution solid solution strengthening and the interstitial solid solution strengthening. The rapidly increased sizes and volume fractions of the precipitated phases in Ti1.5 and Ti2 destroyed the continuity of matrix and the coordination of deformation, resulting in the decrease of ductility.

Quantifying the effect of oxygen on micro-mechanical properties of a near-alpha titanium alloy

Titanium alloys are widely used in the aerospace industry, yet oxygen ingress can severely degrade the mechanical properties of titanium alloy components. Atom probe tomography (APT), electron probe microanalysis (EPMA) and nanoindentation were used to characterise the oxygen-rich layer on an in-service jet engine compressor disc, manufactured from the titanium alloy TIMETAL 834. Oxygen ingress was quantified and related to changes in mechanical properties through nanoindentation studies. The relationship between oxygen concentration, microstructure, crystal orientation and hardness has been explored through correlative hardness mapping, EPMA and electron backscatter diffraction (EBSD). It has been found that the hardening effects of microstructure and crystallography are only significant at very low-oxygen concentrations, whereas interstitial solid solution hardening dominates by order of magnitude for higher oxygen concentrations. The role of microstructure on oxygen ingress has been studied and oxygen ingress along a potential α/β interface was directly observed on the nanoscale using APT.

A new insight into the working mechanism of PCE emphasizing the interaction between PCE and Ca2+ in fresh cement paste

Linear polymer, polyacrylic acid (PAA), acrylic acid – 2-acrylamido-2-methylpropane sulfonic acid (AA-co-AMPS) copolymers, and comb-like PCE polymers were used to study their dispersing efficiency in fresh cement pastes with emphasing their interactions with Ca2+ in solution. Fluidity tests show that PAA exhibits an effective fluidizing effect in MgO and CaCO3 systems, while it behaves inversely in cement paste despite its significant adsorption amount because of the deleterious bridging effect caused by Ca2+ ions in the interstitial solution. Dynamic light scattering measurements reveal that the incorporation of side chains into the PAA backbone inhibits the ion-bridging effect, and the PCE with longer side chain and higher side chain density exhibits stronger tolerance to this effect. Interestingly, the AA-co-AMPS copolymers present strong resistance against the ion-crosslinking effect. This suggests that the highly hydrophilic repeating units may act similarly to the side chains in PCEs concerning providing steric hindrance.

Electrodeposition and properties of Со-Re alloys

The present paper considers the electrodeposition of CoRe alloys from a citrate and a citrate-pyrophosphate electrolyte. It has been shown that coatings containing up to 67 at.% Re are deposited from a citrate electrolyte with a current efficiency of 20–40%, and that the use of a citrate-pyrophosphate electrolyte allows the current efficiency for the alloy to be increased, but the coating contains a smaller amount of rhenium – 13.5 аt.%. The corrosion tests carried out in solutions of 3.5% NaCl and 1 M KOH show that the optimal deposition current density in a citrate electrolyte is 30–40 mА·сm−2, at which the most fine-crystalline coatings is formed, which has a corrosion resistance of 3.0 and 1.6 kΩ·сm2 for corrosive solutions. The coating deposited from a citrate-pyrophosphate electrolyte is an interstitial solid solution of rhenium in cobalt, which allows a high corrosive resistance to be achieved, with the high cobalt content giving soft magnetic properties to alloys. The CoRe alloys show electrocatalytic activity in the hydrogen evolution reaction and allow one to reduce by an order of magnitude the exchange current density and by 220 mV the hydrogen overpotential relative to cobalt.

Влияние фазовых превращений в процессе электронно-лучевой 3D-печати и последующей термической обработки на закономерности пластической деформации и разрушение образцов высокоазотистой Cr-Mn-стали

We investigated the phase composition, plastic deformation and fracture micromechanisms of Fe-(25-26)Cr-(5-12)Mn-0.15C-0.55N (wt. %) high-nitrogen chromium-manganese steel. Obtained by the method of electron-beam 3D-printing (additive manufacturing) and subjected to a heat treatment (at a temperature of 1150°C following by quenching). To establish the effect of the electron-beam 3D-printing process on the phase composition, microstructure and mechanical properties of high-nitrogen steel, a comparison was made with the data for Fe-21Cr-22Mn-0.15C-0.53N austenitic steel (wt. %) obtained by traditional methods (casting and heat treatment) and used as a raw material for additive manufacturing. It was experimentally established that in the specimens obtained by additive manufacturing method, depletion of the steel composition by manganese in the electron-beam 3D-printing and post-built heat treatment contributes to the formation of a macroscopically and microscopically inhomogeneous two-phase structure. In the steel specimens, macroscopic regions of irregular shape with large ferrite grains or a two-phase austenite-ferrite structure (microscopic inhomogeneity) were observed. Despite the change in the concentration of the basic elements (chromium and manganese) in additive manufacturing, a high concentration of interstitial atoms (nitrogen and carbon) remains in steel. This contributes to the macroscopically heterogeneous distribution of interstitial atoms in the specimens - the formation of a supersaturated interstitial solid solution in the austenitic regions due to the low solubility of nitrogen and carbon in the ferrite regions. This inhomogeneous heterophase (ferrite-austenite) structure has high strength properties, good ductility and work hardening, which are close to those of the specimens of the initial high-nitrogen austenitic steel used as the raw material for additive manufacturing.