Fe4N Phase Research Articles

The beneficial effect of Fe addition in PbTe-Ni diffusion bonded thermoelectric contact interfaces – A comprehensive phase evolution study

The development of reliable interconnects in thermoelectric (TE) modules is essential for the durability and serviceability of these solid-state devices. PbTe-based devices are used in mid-temperature range applications, with Ni being the most preferred interconnect. Ni reacts with PbTe to form a binary intermetallic, Ni3Te2 (β2). The sustained growth of this phase at higher service temperatures is adversarial to the long-term reliability of interconnects. This paper reports and discusses the beneficiary role of minor Fe-addition in the Ni contact alloy to arrest such unwarranted chemical interaction while ensuring proper bonding. PbTe and Ni-Fe (Fe = 1 at.%, 5 at.%) discs are diffusion bonded at 700 °C for various holding times. The current investigation leads to three noteworthy observations: 1) the formation of Fe-enriched Ni-Fe phase islands at the interface at microscale (1 - 10 µm), (2) Fe-segregation at the local interfaces (∼ 10 nm), and (3) the growth of a Ni-rich metastable Ni3-xTe phase, not present in Ni-Te binary phase diagram. Detailed examinations of these phenomena and crystallographic relations (β2 and Ni3-xTe) are conducted through advanced analytical TEM/STEM techniques. Furthermore, the PbTe-Ni reaction formulation is modified to accommodate such a Fe-enrichment phenomenon and is validated through free energy calculations.

Microstructure and properties of plasma cladding Ni-based alloy coated on 40Cr Surface

Three Ni-based alloys (Ni60, Ni65, Ni60W) were selected to be coated on the surface of 40Cr and 20 steel. The microstructure, phase composition and elemental distribution of the coatings were characterised respectively to discuss the effects of different substrates, cladding materials, and processes. The corrosion and thermal fatigue behaviour of the coatings were investigated. The results show that the coatings prepared by plasma cladding have a dense microstructure with few defects and a white bright band of a certain thickness was formed between the coating and the substrate. The white bright band between the coating prepared by flame spraying and the substrate was not obvious. The main phase compositions of the coatings are Cr23C6, Cr7C3, Ni2.9Cr0.7Fe0.36 and FeNi3 phases, with the W2C phase also present in the Ni60W coating. The heat-affected zone (HAZ) of the coating is influenced by the coating preparing processes, substrate material and process state of substrates: the size of the HAZ of the plasma cladded coating is smaller than that of the flame sprayed coating, the HAZ of the 40Cr substrate is smaller than that of the 20 steel, and the HAZ of the tempered 40Cr substrate is smaller than that of the annealed 40Cr substrate. The Ni-based alloy coating can effectively improve the surface hardness of the substrate. The Ni65 alloy powder is the most effective (HV0.5992), followed by the Ni60W alloy powder (HV0.5798) and finally the Ni60 alloy powder (HV0.5712). The Ni65 alloy coating has the relatively best thermal fatigue properties, followed by the Ni60W alloy coating and the Ni60 alloy coating is the relatively worst. At the same time, the corrosion resistance of different Ni-based alloy coatings is consistent with the thermal fatigue properties of the coatings.

Surface nanocrystallization of pure iron achieved by anodization-reduction treatment and its effect on lower-temperature nitriding behaviors

In this work, a novel method named anodization-reduction composite treatment was designed to achieve surface nanocrystallization on pure iron materials. Subsequently, this method was employed as pretreatment for gas nitriding of pure iron and its effect was studied systematically. The experimental data illustrated that a 1.3 μm thick Fe2O3 layer with nanoporous structure was successfully fabricated by anodization treatment in solutions containing 0.1 M NH4F and 1 M H2O. After hydrogen reduction at 400 °C, the nanoporous Fe2O3 layer was transformed to pure layer with nanoparticles stacked structure. Additionally, each particle is composed of several pure iron grains with size of 2–10 nm. After lower-temperature gas nitriding at 400 °C, a dense compound layer composed of Fe3N and Fe4N phases with thickness of 3 μm was formed on surface of anodization-reduced sample. The anodization-reduced nitrided sample show the higher hardness, lower friction coefficient and improved wear resistance than those of original nitrided sample. The acceleration of nitriding process may be attributed to the increased adsorption area of nitrogen atoms, rapid diffusion effect in nanocrystalline and more nucleation sites for nitrides. This paper provides a novel surface nanocrystallization method for iron to reduce its nitriding temperature or duration.

Comparison of carbon and nitrogen accumulation rate between bog and fen phases in a pristine peatland with the fen-bog transition.

Long-term carbon and nitrogen dynamics in peatlands are affected by both vegetation production and decomposition processes. Here, we examined the carbon accumulation rate (CAR), nitrogen accumulation rate (NAR) and δ13 C, δ15 N of plant residuals in a peat core dated back to ~8500 cal year BP in a temperate peatland in Northeast China. Impacted by the tephra during 1160 and 789 cal year BP and climate change, the peatland changed from a fen dominated by vascular plants to a bog dominated by Sphagnum mosses. We used the Clymo model to quantify peat addition rate and decay constant for acrotelm and catotelm layers during both bog and fen phases. Our studied peatland was dominated by Sphagnum fuscum during the bog phase (789 to -59 cal year BP) and lower accumulation rates in the acrotelm layer was found during this phase, suggesting the dominant role of volcanic eruption in the CAR of the peat core. Both mean CAR and NAR were higher during the bog phase than during the fen phase in our study, consistent with the results of the only one similar study in the literature. Because the input rate of organic matter was considered to be lower during the bog phase, the decomposition process must have been much lower during the bog phase than during the fen phase and potentially controlled CAR and NAR. During the fen phase, CAR was also lower under higher temperature and summer insolation, conditions beneficial for decomposition. δ15 N of Sphagnum hinted that nitrogen fixation had a positive effect on nitrogen accumulation, particular in recent decades. Our study suggested that decomposition is more important for carbon and nitrogen sequestration than production in peatlands in most conditions and if future climate changes or human disturbance increase decomposition rate, carbon sequestration in peatlands will be jeopardized.

A Study on the Corrosion Resistance of a Coating Prepared by Electrical Explosion of 321 Metal Wire

Corrosion is known as a breakdown effect that causes the deterioration of substances in enriched petroleum/gas conditions. This reaction occurs in all materials, which is highlighted in alloys. In the present study, the morphological properties, as well as the corrosion resistance behavior of the AISI1045 steel substrate coated with 321 austenitic stainless steel metal particulate fillers, were investigated. The electro-explosive spraying technique was employed to achieve a homogenous coating on the substrate surface. According to the results, the grain size of the 321 austenitic stainless steel coating layer was shrunk and reduced to 1–3 μm after the coating procedure. The coated layer also showed a homogenous and uniform thickness with an average value of 137 μm. Also, the average adhesion strength of 49.21 MPa was obtained between the sprayed coating and the substrate. The analytical analysis found the presence of Fe-Cr and Fe-Ni phases in the coating layer. The hardness of the original metal wire is 186 HV, and the microhardness of the coating after spraying is 232 HV. After subjecting the specimen to the corrosion examination, a 0.1961 mm/a corrosion rate was obtained for up to 120 h. Moreover, the corrosion products of CaCO3, Fe3O4, and MgFe2O4 were determined by XRD analysis. Furthermore, the observed results were further confirmed by the data obtained from EPMA and EDS evaluations. Hence, this study implies the beneficial role of electro-explosive sprayed alloy 321 austenitic stainless steel in creating a protective layer against corrosion on 45 steel substrate in an enriched oil/water environment.

Hybrid molecular dynamic Monte Carlo simulation and experimental production of a multi-component Cu–Fe–Ni–Mo–W alloy

High-entropy alloys are a class of materials intensely studied in the last years due to their innovative properties. Their unconventional compositions and chemical structures hold promise for achieving unprecedented combinations of mechanical properties. The Cu–Fe–Ni–Mo–W multicomponent alloy was studied using a combination of simulation and experimental production to test the possibility of formation of a simple solid solution. Therefore, Molecular Dynamics and hybrid Molecular Dynamic/Monte Carlo simulations from 10K up to the melting point of the alloy were analyzed together with the experimental production by arc furnace and powder milling. The Molecular Dynamics simulations starting with a bcc type-structure show the formation of a single-phase bcc solid solution type-structure, whereas using Monte Carlo one, generally produced a two-phase mixture. Moreover, the lowest potential energy was obtained when starting from a fcc type-structure and using Monte Carlo simulation giving rise to the formation of a bcc Fe–Mo–W phase and a Cu–Ni fcc type-structure. Dendritic and interdendritic phases were observed in the sample produced by arc furnace while the milled powder evidence an separation of two phases Cu–Fe–Ni phase and W–Mo type-structures. Samples produced by both methods show the formation of bcc and a fcc type-structures. Therefore, the Monte Carlo simulation seems to be closer with the experimental results, which points to a two-phase mixture formation for the Cu–Fe–Ni–Mo–W multicomponent system.

The Fe addition as an effective treatment for improving the radiation resistance of fcc NixFe1-x single-crystal alloys

In this work, five different compositions of fcc Ni and NixFe1-x single crystal alloys namely Ni, Ni0.88Fe0.12, Ni0.77Fe0.23, Ni0.62Fe0.38, Ni0.38Fe0.62 were irradiated by 1.5 MeV 58Ni ions at room temperature in a wide fluence range (4 × 1013 to 4 × 1015 ions/cm2). The role of Fe addition on the radiation resistance of the NixFe1-x single crystals was studied by transmission electron microscopy (TEM), ion channeling technique (RBS/C) and nanoindentation techniques. The Multi-Step Damage Accumulation analysis revealed the cross-sections for damage formation significantly decreases for Ni0.38Fe0.62 and Ni0.62Fe0.38 as compared to that in pure Ni single crystal, which is consistent with RBS/C and TEM results. The results of nanoindentation show that Ni0.62Fe0.38 alloy possesses the highest hardness (2.96 GPa) among the other compositions in a pristine state. To interpret this result, hybrid Monte Carlo/ Molecular dynamics simulations were used to check the presence of the ordered crystal phase structure for NixFe1-x binary alloys. The simulation results have shown that depending on the iron content, we deal with different amounts of FeNi3 (L12) phase. This result revealed that in Ni0.62Fe0.38 alloy, nanoprecipitate FeNi3 (L12) phase (around 20%) is formed inside the disordered matrix, which could be one of the main reasons for the high hardness of this alloy before irradiation.Additionally, we have found adding iron reduced the number and size of the defects (as a result of ion irradiation) in NixFe1-x because the Fe element is more stable than Ni, which results from the electron configuration of both elements in the excited state. Therefore, the more iron in the material, the fewer defects are created.

Synergistic effect of residual elements on oxidation rates and oxide/metal interface characteristics in a low-carbon steel oxidized at 1180°C for 3 hours

ABSTRACT Residual elements (Cu, Ni and Sn) of various contents have been added to a low-carbon steel to simulate the scenario of increased use of scrap during steel production. The samples were oxidized in air to represent reheating before hot rolling, using thermogravimetry analysis (TGA). Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were employed to investigate the microstructure and the enrichments at the oxide/metal interface. Results showed the residual elements had an impact on the roughness of the scale/metal interface, internal Fe oxides formation, the amount of Ni&Cu enriched Fe phase and Cu&Sn enriched liquid phase at the interface, and the depth and spacing of the liquid phase penetrations along the grain boundaries. Thermodynamic simulation predicted the effect of residual elements on liquid phases formation at the interface, with good agreement between prediction and experimental results. The influence of residual elements on the oxidation rate was discussed.

Homogeneity, Hardness Distribution, and Metallurgical Behavior of SS-304 Cladding Surface with Si, Ni, and TiO2

ABSTRACT In the present study, an attempt was made to develop surface cladding on SS-304 steel by utilising a mixture of EWAC (70% nickel-based powder as an early warning and caution), 20% Si, and 10% TiO2 (Titanium dioxide) powder via microwave energy. The microwave cladding process on the SS-304 (stainless steel-304) was carried out in the in-house developed set-up on the microwave. The microwave cladding process was carried out at 900 W with a 2.45 GHz frequency for 120 s. The microstructure image of the developed surface showed the presence of TiO2 particles. A uniform cladding layer with fewer dark pixels has been observed. Higher homogeneity of the cladding layer and cladding surface reduces the dimensional deviation of the developed cladding surface. The XRD of the cladding surface shows the presence of FeNi3, NiSi2, Ni3C, NiC, Ni2Si, FeNi, and TiO2 phases. Uniform hardness distribution for the cladding layer and cladding surface was observed, while hardness distribution in SS-304 after solidification a severe variability. The hardness of SS-304 was improved by about 42.42% after the microwave cladding of Ni, 20% Si, and 10% TiO2. The main reason for the increase in hardness is the formation of different hard phases such as Ni3C, NiC, and TiO2 phases.

Influence of Fe on the Hydrogen Storage Properties of LaCeNi Alloys.

LaNi5 intermetallic compounds with a hexagonal CaCu5 type structure can react reversibly with hydrogen. The element substitutions in LaNi5 can significantly change the hydrogenation properties, allowing to tune them to a large extent. It could be very advantageous to partially replace Ni or La with other elements to reduce the cost of this alloy as well as the equilibrium pressure of absorption and desorption. The hydrogen storage properties of ball-milled AB5 alloys containing the elements La, Ce (A-rare elements) and Ni, Fe (B-transition metals) were studied in this paper. Although the substitution of Ni (atomic radius 1.49 Å) with Fe atom (atomic radius 1.56 Å) increased the unit cell volume from 86.4149 to 87.947 5 Å3 of the LaNi5 phase, its hydrogen storage capacity was still close to the value 1.4 wt %. The enthalpy (ΔH) of hydride formation for hydrogen absorption and desorption of the experimental alloys was in the range of 29-32.6 kJ/mol. A very favorable effect of Fe on the sorption properties was found in the significant reduction of the equilibrium pressure of absorption and desorption. These studied experimental Fe-containing alloys were able to store hydrogen at 300 K and with pressure under 0.1 MPa. The fastest sorption kinetics of hydrogen was found in alloys with FeNi phase particles located on the surface of the powder. However, if the FeNi phase was segregated at the grain boundaries, it acted as a barrier limiting the growth of the hydride phase. This led to a decrease of the hydride sorption kinetics.

Metallic cladding through microwave energy of the mixture of Ni and 15% SiC powder on AISI 304: A green approach in surface engineering

In the present study, an attempt was made to develop surface cladding on AISI 304 steel by utilizing a mixture of Ni and 15% SiC powder via microwave energy. The microwave cladding process on the AISI 304 was carried out in the in-house developed set-up on the microwave. The microwave cladding process was carried out on 900 W with a 2.45 GHz frequency for 120 seconds irradiation time. SEM images showed a uniform cladding layer and cladding surface with SiC wt.% of 15 and irradiation time of 120 seconds. The energy dispersive X-ray (EDX) pattern of AISI 304 cladding surface coating with Ni and 15% SiC. EDX pattern showed the element weight percent of Ni, Fe, Cr, Si, O, and C is 58%, 22%, 4.98%, 5.97%, 1.45%, and 7.6%, respectively. EDX pattern for the cladding layer showed the element's weight percent of Fe, Ni, Si, C, O, and Cr is 46.34%, 27.3%, 11.12%, 7.9%, 4.2%, and 3.14%, respectively. XRD of the cladding surface shows the presence of Fe, FeNi3, NiSi2, Cr2C, Ni3C, Fe2SiO4, and SiC phases. The average hardness of the cladding surface and cladding layer was found to be about 324 HV and 306 HV, respectively. The hardness of the cladding surface was improved by about 46.60%. Fatigue strength of AISI 304 without and with the microwave cladding of the mixture of 15% SiC and Ni powder was found to be 210 MPa and 245 MPa, respectively, at the cyclic load of 1 × 107 cycles. Though, a micrograph of AISI 304 with the microwave cladding of the mixture of 15% SiC and Ni powder shows the fatigue wear, wear debris, and plastic flow of SiC particles after the wear testing.

Heterostructure of NiFe@NiCr-LDH for Active and Durable Oxygen Evolution Reactions in Alkaline Media.

Developing cost-effective, efficient, and durable catalysts for oxygen evolution reactions (OER) is the key for promoting large-scale H2 production through electrochemical water splitting. Herein, we report a facile method for fabricating an NiFe@NiCr-LDH catalyst toward alkaline OER. The electronic microscopy technique revealed that it has a well-defined heterostructure at the interface between the NiFe and NiCr phases. In 1.0 M KOH, the as-prepared NiFe@NiCr-LDH catalyst shows excellent catalytic performance, evidenced by an overpotential of 266 mV at the current density of 10 mA cm-2 and a small Tafel slope of 63 mV dec-1; both are comparable with the RuO2 benchmark catalyst. It also exhibits robust durability in long-term operation, manifested by a 10% current decay in 20 h, which is superior to that of the RuO2 catalyst. Such excellent performance is attributed to the interfacial electron transfer that occurs at the interfaces of the heterostructure, and the Fe(III) species facilitate the formation of Ni(III) species as active sites in NiFe@NiCr-LDH. This study offers a feasible strategy for preparing a transition metal-based LDH catalyst for OER toward H2 production and other electrochemical energy technologies.

The Microstructure and Properties of Ni-Si-La2O3 Coatings Deposited on 304 Stainless Steel by Microwave Cladding

In this investigation, microwave radiation was used alongside a combination of Ni powder, Si powder, and La2O3 (Lanthanum oxide) powder to create surface cladding on SS-304 steel. To complete the microwave cladding process, 900 W at 2.45 GHz was used for 120 s. "Response surface methodology (RSM)" was utilized to attain the optimal combination of microwave cladding process parameters. The surface hardness of the cladding samples was taken as a response. The optimal combination of microwave cladding process parameters was found to be Si (wt.%) of 19.28, a skin depth of 4.57 µm, irradiation time of 118 s, and La2O3 (wt.%) of 11 to achieve a surface hardness of 287.25 HV. Experimental surface hardness at the corresponding microwave-cladding-process parameters was found to be 279 HV. The hardness of SS-304 was improved by about 32.85% at the optimum combination of microwave cladding process parameters. The SEM and optical microscopic images showed the presence of Si, Ni, and La2O3 particles. SEM images of the "cladding layer and surface" showed the "uniform cladding layer" with "fewer dark pixels" (yielding higher homogeneity). Higher homogeneity reduced the dimensional deviation in the developed cladding surface. XRD of the cladded surface showed the presence of FeNi, Ni2Si, FeNi3, NiSi2, Ni3C, NiC, and La2O3 phases. The "wear rate and coefficient of friction" of the developed cladded surface with 69.72% Ni, 19.28% Si, and 11% La2O3 particles were found to be 0.00367 mm3/m and 0.312, respectively. "Few dark spots" were observed on the "corroded surface". These "dark spots" displayed "some corrosion (corrosion weight loss 0.49 mg)" in a "3.5 wt.% NaCl environment".

Atomic Migration and Ordering of Binary Ferromagnetic Intermetallic L10Phases and Influences of Alloying Elements and Electric Fields

The ordered body‐centered tetragonal intermetallic phase of FeNi is a promising candidate for high‐performance permanent magnets without rare‐earth elements. However, on earth FeNi is found naturally only in the disordered face‐centered‐cubic A1 phase. Herein, the atomic migration and ordering processes in binary intermetallic phases are investigated within the framework of density‐functional theory. The main objectives are 1) to develop a thorough understanding of the thermally activated diffusion processes at the atomic scale and 2) to make a critical assessment in how far electric field and current effects can be effective means for an enhanced hardening‐by‐ordering of disordered, soft‐ferromagnetic alloys. The scope is extended from FeNi to the hard‐ferromagnetic phases of FePt, FePd, MnAl, and MnGa as well as ternary Fe(Pt,Ni) alloys. These materials cover a wide range of thermal‐ordering time scales and related experimental feasibility.

Microstructure and mechanical properties of FeCoCrNiAl0.1N high entropy alloy nitride coatings synthesized by cathodic arc ion plating using alloy target

To promote the industrial application of high entropy alloy nitride (HEAN) coatings, the cathodic arc ion plating deposition process was explored to deposit FeCoCrNiAl0.1 N using casting HEA alloy targets. We investigated the impacts of nitrogen pressure and bias voltage on the microstructure, mechanical characteristics, and friction behaviors. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to analyze the microstructures. It was found that compositions for all coatings were uniformly and the coatings mainly consisted of FCC-HEA, CrN, AlN, and FeN phases. The nano hardness and plastic deformation resistance, characterized by nano-indentation, both increased with the nitrogen pressure and certain bias voltage (<150 V). Coating deposited with 2.0 Pa and 150 V presented the maximum hardness of 32.9 GPa and the highest H3/E2 value of 0.1 GPa. The hardening mechanism was focused. Coatings deposited with low nitrogen pressure presented better crack resistance under scratch load. The friction behaviors were presented based on the combined studies of friction curves, wear track profiles, and morphologies. FeCoCrNiAl0.1 N coatings revealed excellent wear resistance with relatively lower COF (ranging from 0.43 to 0.51).

Simulation of thermal decomposition of γ′-Fe4N using molecular dynamics method

α″-Fe16N2 is a promising environmentally friendly rare-earth-free permanent magnet material with ultra-high saturation magnetization. Recent research has demonstrated experimentally through a thermally quenching treatment using γ′ phase Fe4N as a precursor to synthesize α″-Fe16N2 in bulk format. In this research using Molecular Dynamics (MD) simulation, we investigated the γ′-Fe4N phase thermal decomposition process and the potential phase transition from face center cubic (fcc)-phase to body center tetragonal (bct)-phase. As nitrogen concentration is higher in γ′-Fe4N (5.9 wt. %) than that in α′-Fe8N or α″-Fe16N2 (3 wt. %), Nitrogen bond formation through atom diffusion is studied with a “Nitrogen-rich” grain boundary (GB) model to find out whether lower-Nitrogen content bct Fe–N solid solution can be formed. Modified Embedded Atom Method (MEAM) interatomic potential of Fe–N system is applied. Post-processing including Nitrogen bond mapping/tracking is also performed for the thermostat-controlled heating and quenching simulation process. We also applied virtual XRD computation to characterize the material crystallographic texture before and after the thermal treatment.

Mechanical properties of Al-Si matrix composites synergistically reinforced by high-entropy alloy and SiC nanoparticles

To improve the mechanical strength and ductility of Al-20Si matrix composites, a novel strategy was proposed by constructing nanoparticle-rich zones (NPR) in where SiC nanoparticles were embedded into fine-grain high-entropy alloy particles (SiC@HEA). Due to the specific arrangement of SiC in HEA reinforcement, the mechanical properties of as-fabricated Al composites with hierarchical microstructure were improved significantly. The influences of hierarchical structure and interface between the NPR zones and Al matrix on tensile strength and ductility were systematically studied. The results show that the designed composite exhibits NPR zones and nanoparticle-free (NPF) zones, leading to a typical bimodal structure. The NPR zones have a higher density of geometrically necessary dislocations (GND) than NPF zones, and hence it can act as “hard” regions by enhanced dislocation strengthening and grain refinement. The large Al grains in NPF zones actet as “soft” regions to promote plastic deformation. The SiC@HEA/Al interface featured a dual-layer, including the inner layer (∼200 nm) of Ni2Si, FeNi, Ni3Si2, and FeSi phases, and the outer layer (∼300 nm) of Ni5Si2, Ni2Si, and FeNi phases. A good combination of tensile strength (251 MPa) and elongation (9%) was realized in SiC@HEA/Al composite. This study provides a new route to fabricate composites with enhanced both strength and ductility.

Solvent Influence on the Magnetization and Phase of Fe-Ni Alloy Nanoparticles Generated by Laser Ablation in Liquids.

The synthesis of bimetallic iron-nickel nanoparticles with control over the synthesized phases, particle size, surface chemistry, and oxidation level remains a challenge that limits the application of these nanoparticles. Pulsed laser ablation in liquid allows the properties tuning of the generated nanoparticles by changing the ablation solvent. Organic solvents such as acetone can minimize nanoparticle oxidation. Yet, economical laboratory and technical grade solvents that allow cost-effective production of FeNi nanoparticles contain water impurities, which are a potential source of oxidation. Here, we investigated the influence of water impurities in acetone on the properties of FeNi nanoparticles generated by pulsed laser ablation in liquids. To remove water impurities and produce "dried acetone", cost-effective and reusable molecular sieves (3 Å) are employed. The results show that the Fe50Ni50 nanoparticles' properties are influenced by the water content of the solvent. The metastable HCP FeNi phase is found in NPs prepared in acetone, while only the FCC phase is observed in NPs formed in water. Mössbauer spectroscopy revealed that the FeNi nanoparticles oxidation in dried acetone is reduced by 8% compared to acetone. The high-field magnetization of Fe50Ni50 nanoparticles in water is the highest, 68 Am2/kg, followed by the nanoparticles obtained after ablation in acetone without water impurities, 59 Am2/kg, and acetone, 52 Am2/kg. The core-shell structures formed in these three liquids are also distinctive, demonstrating that a core-shell structure with an outer oxide layer is formed in water, while carbon external layers are obtained in acetone without water impurity. The results confirm that the size, structure, phase, and oxidation of FeNi nanoparticles produced by pulsed laser ablation in liquids can be modified by changing the solvent or just reducing the water impurities in the organic solvent.

Deposition characterization of high-manganese (13Mn) steel built via directed energy deposition and its wear behavior

High-manganese steel (HMS) has high work-hardening and impact toughness as well as excellent wear resistance. In this study, directed energy deposition (DED) was employed to deposit HMS onto the surface of Inconel 718. The deposition characteristics were analyzed according to laser power and powder feed rate. From the results, the lowest amount of pores and lack of fusion were observed when the laser power was 1050 W and the powder feed rate was 4 g/min. In the first layer of the deposited HMS, the Laves phase was formed due to fusion with Inconel 718, while the hardness rapidly decreased to 250 HV because of the low hardness of the Fe–Ni phase. A wear test was conducted according to different loads and RPMs using the ball-on-disc method, with the results indicating that a higher load led to a lower wear rate. When the wear load was high, the surface hardness increased after the wear test, and surface severe plastic deformation (SSPD) thickened. Such phenomena occurred because the grains near the surface underwent refinement and the dislocation density increased as the load increased. An oxide layer was generated on the surface at 300 RPM, but no oxide layer was formed at 100 RPM. As an oxide layer was not formed, the wear rate was the highest at 100 RPM due to direct contact between the ball and matrix. This study demonstrates the industrial applicability of surface coating using HMS as a powder for maximizing wear resistance.

Investigation of powder bed laser fusion additive manufacturing of 93W, 5.6Ni, 1.4Fe tungsten heavy alloys

Tungsten exhibits a variety of interesting properties with significant potential for advanced applications but is currently limited by the difficulty of forming complex shapes for end-use parts. Additive manufacturing using powder bed laser fusion techniques may offer an alternative method of forming tungsten parts with greater design flexibility. To investigate this potential, two 93W, 5.6Ni, 1.4Fe tungsten heavy alloy (WHA) powders were densified using a Renishaw AM 400 laser melting system to >99.8% theoretical density and the resulting microstructures assessed. High densification was possible utilizing long exposure times to maximize melting at low laser powers, low to moderate laser powers to avoid overheating the FeNi phase, and small point distances, hatch distances, and layer heights to maximize remelting. SEM investigation of the resulting microstructure revealed two distinct phases: nearly pure W and ∼ 90% W-rich W-Ni-Fe. This was believed to be the result of complete melting of the NiFe powder and either dissolution of tungsten within the liquid NiFe matrix or partial melting of the tungsten powder. High cooling rates in the additive manufacturing process resulted in a tungsten-rich W-Ni-Fe matrix phase compared to traditional liquid phase sintered WHA alloys. Microhardness testing was conducted to begin assessment of resulting mechanical properties, with extremely high hardness values being measured when compared with expected literature values. Fine microstructure and high W content in the matrix phase contribute to these high hardness values, but further investigation is needed.