Ni Powders Research Articles

In-situ preparation of Ni@ZrO2 nanocapsules powder by DC arc plasma for internal electrode of MLCC

Zirconium oxide-coated Ni nanocapsules (Ni@ZrO2 NCs) were in-situ fabricated by DC arc plasma in a nitrogen atmosphere. The co-evaporation of a target mixture consisting of coarse ZrO2 and Ni powders resulted in the formation of Ni@ZrO2 core-shell nanocomposites (NCs). The high energy states of excited ions (Ni3+, Zr4+, O2−, N2+, etc.) within the arc plasma region were recorded in real time by online optical emission spectroscopy (OES), which becomes visible evidences of the energy conditions for the fabrication of Ni@ZrO2 NCs. These nanocapsules underwent preferential formation of zirconium oxide species based on the oxygen potential rule, followed by the nucleation and subsequent growth processes. The Ni@ZrO2 NCs exhibited improved oxidation resistance, with an onset temperature for sintering approximately 40 °C higher than that of pristine Ni nanoparticles (NPs). Additionally, these NCs displayed an appropriate shrinkage rate, with a volume change of about 7.1% at 1200 °C. The symbiotic relationship between the ZrO2 shell and the Ni core within each nanoparticle suggests enhanced interfacial stability, rendering these NCs a promising material for the advancement of multi-layer ceramic capacitors (MLCCs).

Simultaneous extraction and separation of Ni(OH)2, Ni powder and Ni plate from waste nickel-cobalt scrap in one spot: Control sequence of electrical reduction

Extracting valuable metals from waste lithium-ion batteries is beneficial to the long-term growth of social economy and environmental maintenance from lithium-ion batteries, yet it faces serious challenges. The study aims to propose a harmless and efficient electrolysis method for selectively preparing nickel products from lithium-ion batteries leachate by controlling the competitive reductive order for Ni2+ and H2O. Compared with current pyrometallurgy, hydrometallurgy, and bio-metallurgy methods, electrolysis method allows selective preparation of different nickel products. No additional chemicals are introduced, or no membrane limitation. Achieving zero pollution emissions while saving costs. The results of serial experiments show that the level of nickel reduction can be controlled to produce different types of nickel products. The current efficiency reached a maximum value of 84.7±4.5%. 125 A/m2, 0.05 M Ni2+, 1.5 h, 60 A/m2, 0.1 M Ni2+, 2 h, 125 A/m2, 0.25 M Ni2+, 2 h are the optimal conditions for forming Ni(OH)2, black powder Ni and silvery flake Ni, respectively. In electrolysis process, selective nickel products, H2 and O2 can be prepared. H2 can be used as clean energy and increases economic benefits. This study provides a clean and high-efficiency method for selectively preparing nickel products from lithium-ion batteries leachate.

A Novel Processing Route in the Mechano-Synthesis of Austenitic 58Fe25Ni17Cr Oxide Dispersion Strengthened Cast Alloy through Y<sub>2</sub>O<sub>3</sub> Pre-Linking

A powder metallurgical process has been applied to synthesize the FeNiCr+Y2O3 oxide dispersion strengthened (ODS) alloys. The composition of the reinforcing Y2O3 added into matrix was varied from zero to 2.0 percent weight. Raw powders were carefully weighed with a four-digit balance. Y2O3 powder was pre-linked into Fe powder as the dominant element in the matrix by manually ground for half an hour. Ni and Cr powders were then mixed evenly for the next a half hour to obtain FeNiCr+Y2O3 precursor. Avoiding agglomeration and grain coarsening, the precursor was uniformly homogenized by milling for 20 hours. The precursors were then compressed at an isostatic pressure of 100 kN to 12 grams of pellets each. To prevent sample erosion during smelting with an electric arc furnace (EAF), crystal growing mechanism by conventional sintering was performed at 900 °C for 2 hours. This strengthens the bonds between precursors in forming ODS alloys. The samples were then melt-casted in the arc by 4 times flips. As a result, the neutron diffraction analysis and SEM-EDS strongly reveal the austenitic crystal structure and Y2O3 oxide successfully dispersed in the cast-alloy respectively. The microstructures with Y2O3 oxide spread uniformly overall the cast-alloy surfaces.

Thermodynamic analysis of production parameters and microstructural evolution in shape memory Ni(50-x)Ti(50)Fe(x) (x = 5, 10) alloy synthesized by combustion synthesis

This study represents an initial effort to produce NiTiFe shape memory alloys via the self-propagating high-temperature synthesis (SHS) process. The synthesis successfully yielded Ni45Ti50Fe5 and Ni40Ti50Fe10 alloys from elemental Ni, Ti, and Fe powders at three distinct preheating temperatures (240, 330, 420 °C). To support empirical findings, thermodynamic analysis using Factsage Thermodynamic Software was employed to correlate reaction propagation behavior with chemical composition. The calculation showed that the addition of 5 at.% Fe to the B2 phase did not hinder reaction self-propagation. This conclusion was supported with the ∆Hf/Cp ratio and transient liquid ratio, computed using the sub-lattice model, which closely resembled that of NiTi. Whereas 10 at.% Fe that synthesized at preheating temperature of 240 °C exhibits struggle, thus an increase in triggering time causes an effect on crystallite size and a decrease in porosity. Empirical results confirmed these findings, albeit influenced by ignition times. An increase in the liquid ratio due to the adiabatic temperature rise can also result in a reduction of NiTi content when the Fe ratio is increased, consequently diminishing the driving force for the reaction. In the sample containing – 5% Fe, the main phase is B2, and the R martensitic phase is also present. Ms is determined to be – 38.7 °C. SEM analyses revealed the presence of Ti2Ni and Ti2Ni3 phases in the upper and lower regions, while the distribution in the middle section is more homogeneous. No martensitic transformation was observed in 10% Fe. Additionally, nanocrystalline regions were detected within the samples by transmission electron microscopy, contributing to a nuanced understanding of their structural properties.Graphic abstract

Deposition of NiAl/Al3Ni2(CrB2) Coatings from Ni, Al and CrB2 Powders Using Mechanical Synthesis in Planetary Ball Mill.

Interest in composite thick coatings with an intermetallic matrix stimulates the development of new deposition techniques like the co-milling of pre-alloyed NiAl powder with platelet-shaped substrates. Obtained coatings were up to several micrometers thick as cold-welding of intermetallic particles was effective only at the start of this process, while later, chipping prevailed over added material. The present experiment covered the co-milling in the planetary ball mill of Ni and Al elemental powders (1:1 molar ratio) with AISI 304 steel platelets for 32 h at 300 rpm. Next, this process was repeated with an admixture of 15 wt.% of CrB2 powder. In both cases, their milling succeeded in producing up to a 200 μm coating after 4 h. The use of light, scanning and transmission electron microscopy (LM/SEM/TEM) helped to establish that the coatings had gradient microstructures with more refined crystallites of NiAl, Al3Ni2 and CrB2 closer to the surface. With the addition of a ceramic phase, the coatings presented higher hardness and lower friction during dry wear tests both at RT and at 500 °C.

Химико-металлургический синтез субмикронных порошков W + Ni со структурой “ядро (W) – оболочка (Ni)”

The conditions for obtaining composite W + Ni powders with the core (W) –shell (Ni) structure and alloys based on them were studied in the work. W + Ni powders (5, 10, 20 wt.%) were obtained by the chemical-metallurgical method. The influence of nickel content, its precursor (nickel chloride or nitrate) and temperature treatment regime on the phase composition of the powders was studied. During the work, it was found that the nickel concentration does not affect the phase composition of the powder, however, 5 wt. % Ni is not enough to cladding all tungsten particles. A powder containing the least amount of impurities was obtained from nickel chloride after reduction annealing at 400 – 600 °C and from nickel nitrate after annealing at 550 °C. After annealing at 750 and 950 °C, the formation of the Ni4W intermetallic compound was observed, which may be due to the presence of oxygen and oxides on the surface of tungsten particles. An alloy based on 0.9 W + 0.1 Ni powder obtained from nickel chloride and annealed at 600 °C was produced by Spark Plasma Sintering at a temperature of 1050 °C and a pressure of 50 MPa. The phase composition of the central region of the obtained alloys did not change during the sintering process, however, the formation of the η1-phase Ni3W3C was observed on the surface, which is a product of the interaction of the initial powder with the graphite mold. The obtained alloys had a homogeneous microstructure; no traces of abnormal grain growth or formation of large γ-phase particles were observed. The Vickers hardness Hv10 of tungsten alloys sintered without isothermal holding was 5.6 ± 0.3 GPa, and the alloys sintered with 20-minute isothermal holding at 1050 °C — Hv10 = 4.9 ± 0.3 GPa.

Environmentally responsible synthesis of high-performance P2-Na2/3[Ni1/3Mn2/3]O2 sodium-ion battery cathodes

An environmentally responsible synthesis of Na2/3[Ni1/3Mn2/3]O2 (NNMO) enabled by direct conversion of metallic Ni powder, releasing only O2 and H2O as byproducts. The resulting NNMO exhibits excellent cycling performance as a Na-ion battery cathode.

Soft magnetic properties of Fe-Ni powder cores in the high frequency range

Fe-Ni cores are excellent candidates for switching regulator inductors, transformers, reactors and in-line noise filters. Herein the influence of the phenol binder content on the microstructure and magnetic properties of Fe-50 wt% Ni powder cores in the high frequency range is investigated. Regardless of the binder content, all cores form a disordered A1 phase. The saturation magnetization (4πMs) and initial permeability increase as the binder content decreases. The core with a binder content of 0.5 wt% shows a relatively high 4πMs of 1.38 T and the highest permeability value of 70.9. Moreover, the total core loss (Pcv) with frequency ranges from 5 kHz to 1 MHz under a magnetic flux density of 10 mT depending on the binder content. A binder content of 3.0 wt% significantly reduces Pcv in the high frequency range above 100 kHz. At a frequency of 500 kHz, the Pcv values are 154.9, 128.7, and 133.8 kW/m3 for the cores with binder contents of 0.3, 0.5, and 1.0 wt%, respectively, but the value drastically decreases to 60.5 kW/m3 for a binder content of 3.0 wt%. Thus, the binder, which acts as an insulator layer between particles, affects the eddy current and consequently, Pcv. These results demonstrate that Fe-Ni powder cores exhibit excellent soft magnetic properties at various frequencies and suggest that a binder content of 3.0 wt% may realize optimal properties for future high frequency applications.

Influence of starting WC particle size and sintering conditions on structure and properties of WC-Ni-Co coarse grain ceramics

Sintering temperature is the key factor affecting the structure and performance of tungsten carbide (WC) ceramics. Thus, the effect of sintering temperature on the microstructure and mechanical properties of WC-Ni-Co coarse grain ceramics, obtained from the mixture containing: 60wt.% of ultra-coarse WC, 30 wt.% of fine WC, 7 wt.% of Co and 3wt.% of Ni powders, was analysed. The mechanical properties of WC ceramics did not change much when the sintering temperature was varied between 1410 and 1430 ?C and the comprehensive performances of the ceramics were the best in this temperature range. In order to confirm that the coarse grain WC-Ni-Co ceramics can be applicable for harsh environments, it was compared with the standard WC-Co ceramics of the same grain size, and the reasons and mechanisms for the differences in microstructure and properties between the two ceramics were tested and analysed. The study shows that the average grain size of two ceramics does not differ much, and there are no decarburisation, graphite-phase and other impurity phases inside the ceramics. In addition, the difference in the mechanical properties is also small. However, the addition of Ni effectively improves the corrosion resistance of the WC-Co ceramics. Therefore, WC-Ni-Co can replace WC-Co ceramics as shield cutting tool material with the same grain size.

High entropy alloy cladding on mild steel substrate using microwave energy at 2.45 GHz: An insight from multi-physics simulation study to experimental investigations

Microwave hybrid heating (MHH) has emerged as a novel technology for cladding high-entropy alloy (HEA) powders on metallic substrates. The existence of a multi-material system (Al, Co, Cr, Ni, and Ti powder) in HEA provides difficulties in microwave cladding. These problems are addressed in the current study by employing silicon carbide as a susceptor material for MHH to microwave-clad AlCoCrNiTi HEA on a mild steel substrate. A multi-physics model of the microwave cladding setup was constructed to investigate the cladding properties. The model was verified using experimental data, and simulation was used to examine the electric field, resistive losses, energy distributions, and temperature-time profile. The simulation results indicated that the electric field intensity, resistive losses, and energy distribution were at their maximum near the susceptor and the cladded surface. As a result, the HEA-cladded surface reached a temperature of 1030 °C at the central plane. This is comparable to the experimental temperature of 1041 °C in 41 min, which shows an error of <10 %. From the microstructural investigation, the HEA powder exhibited a flaky microstructure and a uniform distribution of all the constituents, resulting in a solid metallurgical link between the HEA powder and substrate. The surface hardness of mild steel components was enhanced intensely by three times with the inclusion of AlCoCrNiTi HEA cladding.

Effects of bonding temperature on mechanical properties and interfacial morphology of YG8/40Cr joints fabricated using SPS diffusion bonding

The diffusion bonding of YG8 cemented carbide and 40Cr steel was performed using spark plasma sintering with Ni powder as the interlayer. The influence of bonding temperatures ranging from 700 to 1100 °C on the bonding interface morphology, mechanical properties, and failure mechanism of the joints was studied. By calculating the diffusion coefficients of Ni and Fe and observing the changes in the interface morphology, the pores at the Ni/40Cr interfaces were identified as Kirkendall voids formed because of the unbalanced diffusion of Ni and Fe. The diffusion activation energy of Ni in Fe was 87.37 kJ/mol, and that of Fe in Ni was 58.08 kJ/mol. The use of a pulsed current significantly reduced the diffusion activation energy, making diffusion easier. The bending strength of the joints increased sharply in the range from 700 to 900 °C, subsequently increased slowly, and tended to stabilise in the range from 900 to 1100 °C. The highest bending strength of 1080 MPa was achieved for the joint bonded at 1100 °C, which was attributed to the improved bonding of the YG8/Ni and Ni/40Cr interfaces and the resulting effects of the interlayer plastic constraint. The thickness of the CoNi diffusion zone at the YG8/Ni interface appeared to form a decisive factor in determining the failure locations of the joints. As the bonding temperature increased, the improved diffusion of Co and Ni enhanced the metallurgical bonding of the YG8/Ni interface, and the fracture position shifted from the polished surface of the YG8 base material (700 °C) to the Ni interlayer (1100 °C).

Microstructure and tribology of cold spray additively manufactured multimodal Ni-WC metal matrix composites

Cold spray produces thick and dense deposits that can be applied in additive manufacturing or as a repair to recover damaged components. One potential materials system is WC-reinforced Ni composites, which are known for a combination of high hardness and toughness. WC particle size and distribution are some of the most important variables that impact the mechanical properties and wear resistance. In this study, thick multimodal Ni-24 vol%WC composite coatings were additively manufactured using the cold spray technique. Spherical Ni powder and two types of WC particles, i.e., cast and agglomerated, were used as feedstock materials. The microstructure, porosity, WC distribution, and microhardness of coatings were investigated in comparison with cold-sprayed Ni and Ni-agglomerated WC coatings with similar WC fill ratios. Dry sliding wear of multimodal Ni-WC coatings was studied with a sliding speed of 3 mm/s under normal loads of 5 and 12 N and was then compared to Ni and composite coatings made with only agglomerated WC. Multimodal Ni-WC coatings with an altered distribution of WC particles offered an improvement in friction and wear as compared to Ni-agglomerated WC coatings. Characterization of worn surfaces revealed the formation of tribofilms following compaction of wear debris. A more stable tribofilm that developed to a higher coverage was identified for coatings with multimodal WC particles at both tested loads. However, the protective role of tribofilms was reduced at a higher load, caused by subsurface crack propagation. Subsurface microstructure of worn surfaces that are induced by sliding wear was studied, and a correlation between the mechanical properties and microstructure and wear mechanism of coatings was made. Overall, our findings highlight the potential of cold spray additive manufacturing in producing multimodal Ni-WC composite coatings with enhanced wear resistance.

Mechanical and electrochemical properties of porous NiTi intermetallics synthesized via rapid thermal explosion

In this paper, porous NiTi intermetallic was synthesized via a modified thermal explosion (TE) method, utilizing Ni (74 μm, 38 μm, 5 μm, 100–200 nm) and Al element powders as raw material. The exothermic behavior and phase transition of porous NiTi intermetallic compounds were studied. The results showed that with the refinement of Ni particle size, the heat release decreased, and the Ti-74 μm sample was the product of two eutectic reactions. Their mechanical properties were verified by the Vickers hardness tester and universal testing machine, and the corrosion behavior of porous NiTi intermetallic compounds in phosphate-buffered saline (PBS) solution was studied by electrochemical tests. Among them, Ti-5 μm exhibits the most homogeneous microstructure and favorable mechanical properties, which has a porosity of 31.7 % and a compressive strength of 321.71 MPa. However, corrosion resistance is sacrificed due to the high open porosity. This study holds great promise for precise control microstructural characteristics and optimization of mechanical and electrochemical properties of porous NiTi intermetallics.

TRIBO-CORROSION INVESTIGATION ON MATERIAL 316LX MANUFACTURING RESULT OF 3D PRINTING MATERIAL ADDITIVES IN 5% H2SO4 SOLUTION

Tribocorrosion is a type of material degradation caused by simultaneous wear and corrosion of metal surfaces caused by laminar or turbulent flow. Additive manufacturing technology plays an important role in its application to precision components and complex assemblies. This study developed a 316LX material with Fe, Ni, Cr, and other powder alloys that was processed into an ultra-protective wire as a 3D printing filler. This simulation of tribocorrosion conditions was performed on a triboester machine. This simulation is expected to provide important insights and understanding into the behavior and properties of the 316LX 3D printing material, especially when exposed to abrasion and corrosion conditions in a sulfuric acid solution environment. Corrosion Rate Testing of 316LX Material Additives Using Potentiodynamic Methods in a Modified Rotating 5% Sulfuric Acid Fluid. In addition to corrosion rate, the Vickers hardness, metallography, and shrinkage of the 316LX green part material were also tested at 1000oC after sintering.

Soft magnetic composite of Ni3Fe/ZnFe2O4 type obtained by mechanical alloying/milling and spark plasma sintering

Soft magnetic composite powder of Ni3Fe/ZnFe2O4 type has been obtained by mechanical milling of nanocrystalline Permalloy (Ni3Fe) particles with ZnFe2O4 particles. The nanocrystalline Ni3Fe particles were synthesised by mechanical alloying of elemental Ni and Fe powder. During the milling time, some of the ZnFe2O4 particles are embedded on the surface, and others are encapsulated in the volume of the Permalloy particles, creating a „raisin-bread” like structure. Also, at the surface of the Ni3Fe particles, a quasi-continuous layer of zinc ferrite is formed. The as formed composite particles have a structure of pseudo core-shell type, with a “raisin-bread” core. Upon mechanical milling, the phases are preserved according to X-ray diffraction (XRD) investigations, although the system magnetisation presents a slight decrease. The densification of the composite powder has been carried out using spark plasma sintering (SPS) technique at a sintering temperature range of 500–700 °C without holding time. The density and the electrical resistivity of the samples increase upon increasing the sintering temperature. Higher magnetisation is obtained for the sample sintered at 700 °C and accompanied by a lower coercive field. Upon sintering, a reaction at interface, between the Ni-based alloy and zinc ferrite occurs, leading to the formation of a new phase. The testing of the toroidal-shaped magnetic composite in the alternative current regime shows that the best results are obtained on the sample sintered at 700 °C. The losses decomposition was performed and showed that the dynamic losses become predominant after 1 kHz. The samples have been investigated by X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), vibrating sample magnetometer (VSM) for powder samples and by DC and AC magnetic investigation by hysteresisgraph method and electrical resistivity investigations for the sintered compacts.

Combining direct ink writing with reactive melt infiltration to create architectured thermoelectric legs

We present a new additive-reactive synthesis method where inks – cast into molds or 3D-additively extruded into architectured shapes – are reacted into intermetallic thermoelectric compounds. The new method, as demonstrated for equiatomic TiNiSn, combines: (i) extrusion printing (or casting) of inks containing Ni and Ti powders, (ii) debinding and reactive sintering to form a porous NiTi network, (iii) network infiltration with liquid Sn and subsequent reaction to synthesize the TiNiSn phase. Thin plates, created through this method, show high phase purity and low residual porosity. A thermoelectric figure of merit zT = 0.47 ± 0.05 is achieved at 800 K, within the broad range of values (zT = 0.3–1.0) reported for TiNiSn createdviatraditional powder hot-pressing methods. Layered TiNiSn microlattices – after 3D ink-extrusion printing and infiltration – exhibit high relative densities and minimal undesirable secondary phase content, with a Seebeck coefficient on par with the ink-cast TiNiSn plates, demonstrating that thermoelectric legs with far-ranging architectural freedom can be created additively with this novel reactive manufacturing method. Numerous other thermoelectric (and other) compounds, currently limited to basic geometries due to brittleness, are amenable to this new method based on a sequence of reactive sintering/infiltration of cast or ink-extruded precursors.

Lightweight TiC based cermet fabricated by a pre-solid phase sintering-assisted pressureless infiltration process

This paper introduces a novel process, known as pre-solid phase sintering-assisted pressureless infiltration (PSPS-PI), aimed at addressing issues related to the segregation of hard particles and excessive porosity in the manufacturing of lightweight cermet based on TiC. The PSPS-PI process involves compressing a green TiC powder compact with a minor Ni powder addition, followed by vacuum-based solid-phase sintering to create a fully consolidated TiC preform. This study explores the influence of TiC particle size and Ni content on the microstructure and properties of TiC–Cu composites, conducting a comparison with direct pressureless infiltration (D-PI). The results indicate that the high-melting-point Ni element promotes the formation of sintering necks between TiC and Ni, aiding in the consolidation of TiC particles. The stable skeleton ensures that TiC particles remain in their initial positions during subsequent pressureless infiltration, effectively preventing TiC powder segregation. TiC and Ni create a dissolutive wetting system during pressureless infiltration. The formation of the Ni2SnTi intermetallic compound significantly enhances the wettability with Cu alloy, leading to a reduction in porosity and the occurrence of crack defects within the composite. As particle size decreases, the preform's porosity decreases, resulting in a reduced proportion of soft metal binder and lower residual stress. Consequently, finer TiC powder leads to improved cermet hardness and a reduction in the number of micro-crack defects. In general, PSPS-PI allows for the attainment of low porosity, a uniform microstructure, enhanced hardness, and outstanding wear resistance in the lightweight cermet based on TiC with the appropriate TiC particle size (D50 = 10.2 μm), achieving a remarkable hardness of 642.9 (Hv30) and excellent toughness.

Microstructure and properties of Ni-Ti based gradient laser cladding layer of Ti6Al4V alloy by laser powder bed fusion

An economical gradient layer was successfully prepared on Ti6Al4V alloy produced by laser powder bed fusion (L-PBF) using only composition design, gravity segregation, and laser cladding of micrometer-sized Ni powder, nanoscale SiC and Y2O3 powders. The microstructure of the layer was systematically studied to analyze the reasons for its improved wear and corrosion resistance. The results indicated that the cladding layer comprised top, middle, lower, and bottom layers. The main phases in top layer were Ti2Ni and β-Ti. Whereas the middle layer is composed of two regions, one with a similar structure to the top layer, and the other is the nickel-enriched area denoted as NEAm where the main phases were Ti2Ni, TiNi, and amorphous. The main phase of the lower layer was TiNi. Owing to the close distance between the bottom layer and the substrate, there was a significant increase of Ti in the bottom layer, and so the bottom layer and the top layer contained the same main phases. The soft phase of TiNi in lower layer would prevent the propagation of cracks that may occur in the top layer. The solidification and formation process of the gradient structure of the cladding layer was analyzed with Scheil model, and the simulation results were consistent with the experimental results. A nanocomposite system consisting of Ti3Si, α-Ti, and β-Ti was found for the first time in this study. The relationship between Ti3Si and α-Ti was coherent, and the relationship between α-Ti and β-Ti satisfied the Burgers orientation relationship. The mechanism of the nanocomposite system generation was that Si was enriched at the grain boundaries after the formation of Ti2Ni, where Ti and Si combined to form Ti3Si, and then Ti3Si was used as nucleating particles to form β-Ti/α-Ti. The α-Ti and β-Ti in the fusion line area at the bottom layer also satisfied the Burgers coherent relationship, indicating excellent bonding strength between cladding layer and substrate. A large number of solute atoms in the solid solution, pinning of second-phase particles, and the amorphous were the fundamental reasons for the substantial improvement in hardness and wear resistance. A small amount of Ni in the top layer increased the polarization of the cathodic reaction, keeping the corrosion current low. In addition, numerous dispersed fine phases in the top layer increased the resistance of charge transfer at the phase interfaces, which was the fundamental reason for the improved corrosion resistance.

The deterministic effect of laser energy density on the microstructures of novel duplex stainless steel fabricated via in-situ alloying in laser powder bed fusion

Distinctive microstructures and distributions of novel duplex (ferrite δ + austenite γ) stainless steel can be fabricated using in-situ alloying of Fe–Cr–Mn alloy and pure Ni powders by tuning laser energy density in powder bed fusion. At low-level energy density (∼60 J/mm3), ferrite solidification dominates and results in bimodal ferrite of columnar and equiaxed grains. At medium energy density (∼100 J/mm3), fine acicular Widmanstätten austenite satisfying the Nishiyama-Wassermann orientation relationship was produced within the coarse grains of δ, which is the predominant phase although ferrite and austenite solidification occur. At high-level energy density (∼194 J/mm3), ferrite and austenite solidification occur and the resultant microstructure consists of nearly equivalent fine equiaxed-grained δ and γ. The key difference in the microstructure was attributed to the different melt pool overlapping and types, which can be characterized by the size and local ratio of Cr equivalent (Creq) and Ni equivalent (Nieq) values (Creq/Nieq). The melt pool characteristics fundamentally determine the local solidification and transformation mode at different energy densities. The testing results have shown that the novel duplex stainless steel possesses excellent mechanical properties compared to conventionally-manufactured counterparts.

The Preparation and Properties of Ni2Al3 Intermetallic Compound Coating

In this work, a Ni2Al3 intermetallic compound coating was prepared on 45 # steel by combining methods of low-pressure cold spray and heat treatment. Firstly, powders mixed with Ni powders, Al powders, and Al2O3 powders as a mass ratio of 20:6:4 were sprayed on surface of 45 # steel by low-pressure cold spraying technology to prepare a Ni-Al pre-coating. Subsequently, the pre-coating was annealed at 570 °C in an argon atmosphere for 12 h to obtain the Ni2Al3 intermetallic compound coating. The composite coating was characterized using TEM, SEM, and XRD. High temperature oxidation performance of the composite coating was analyzed by isothermal oxidation tests conducted at 600 °C in air atmosphere for 96 h. The results show that the composite coating is composed of Ni2Al3 phase. Under a high-temperature oxidation environment, a protective oxide film composed by Al2O3 and NiO was formed on the coating surface, which resulting in a superior high-temperature oxidation resistance compared to 15CrMo heat-resistant steel. The mechanism of the Ni2Al3 coating resistance to high-temperature oxidation is that an oxide film mainly composed of Al2O3 and NiO formed on the surface during the high-temperature oxidation process; this oxide film can effectively resist oxidation and protect the substrate material from oxidation at a high temperature of 600 °C.