Water-atomized Iron Powder Research Articles

Impact of laser scanning strategies on microstructure in laser powder bed fusion (LPBF) of nanoparticle-infused pre-alloyed water-atomized iron powder

This study investigates how two scan strategies impact the microstructural and tensile properties of nanoparticle-infused pre-alloyed water-atomized low-alloy iron powder (Fe-1.50Cu-1.75Ni-0.50Mo) during Laser Powder Bed Fusion (LPBF) under uniform volumetric energy density laser conditions. The two strategies were the rotation method (ROT), in which the laser scan vector was rotated by 67° for each layer (10°, 77°, 144°, 211°, …), and the zig-zag method (ZZ), in which the vector was rotated by 90° for each layer (45°, −45°, …). As a result, the relative density of the ROT specimens was measured to be 95.61 ± 1.01 %, while that of ZZ specimens was 99.76 ± 0.17 %. Furthermore, the surface roughness of ROT specimens was higher than that of ZZ specimens (24.05 μm vs. 10.30 μm). It was found that the scan strategy influences not only the bulk characteristics but also the microstructural changes of the specimens, due to variations in intrinsic heat treatment (IHT). In the ZZ specimens, the regular laser scanning direction resulted in a uniform microstructure across different heights. However, in the ROT specimens, the laser scanning direction varied from layer to layer, with fluctuating heat dissipation influencing the melt pool structure, recrystallized grain distribution, sub-grain cellular structure, and precipitation behavior to obtain lower density and higher surface roughness than those of ZZ samples. Therefore, the samples printed using the ZZ method are found to be advantageous for printing pre-alloyed WA iron powders with uniform microstructure and reliable tensile properties.

Effect of Iron Powder Type on Friction and Wear Properties of Copper-Based Friction Powder Metallurgy Material

The sintered copper-based friction materials for high-speed train brake pads have a complex composition that should possess good physical, mechanical, and tribological properties in practical applications. For this article, four kinds of friction materials were prepared by powder metallurgy technology and the effects of iron powders on the microstructural and tribological properties of copper-based friction materials were characterized using a scanning electron microscope (SEM) and x-ray diffraction (XRD). The results showed that iron powder as an enhancing component could effectively change the friction and wear properties of the experimental materials. The copper-based friction materials containing hydroxy iron (1–5 μm) have a relatively higher coefficient of friction: The friction coefficient was significantly improved by 16.8% compared with reduced iron under a rotation speed of 4000 r/min. The friction coefficient of friction material containing water-atomized iron powder is relatively reliable with 3000–7000 r/min speed range. In a high-speed environment, the friction surface of material containing reduced iron or hydroxy iron (1–5 μm) mainly has cracks and brittle fractures, and the material containing hydroxy iron (10 μm) or water-atomized iron has an obvious layered structure and shows fatigue wear.

Carbon-coated iron nanopowder as a sintering aid for water-atomized iron powder

The paper examines the influence of carbon coating on iron nanopowder used as a sintering aid for water-atomized iron powder. Iron nanopowder without such a coating was used as a reference sintering aid to isolate the influence of the carbon coating. Both nanopowder variants were characterised using XPS and HRTEM. The results showed a core–shell structure for both variants. The iron nanopowder is covered by a 3–4 nm thick iron oxide layer, while the carbon-coated iron nanopowder is encapsulated with several nanometric carbon layers. Thermogravimetry conducted in a pure hydrogen environment shows a multipeak behaviour for the carbon-coated iron nanopowder, while a single peak behaviour is observed for the iron nanopowder. Two types of micro/nanobimodal powders were obtained by mixing the nanopowder with water-atomized iron powder. Improved linear shrinkage was observed during sintering when the carbon-coated iron nanopowder was added. This can be explained by the reduction in surface diffusion in the nanopowder caused by the carbon coating, which allows the nanopowder to sinter at higher temperatures and improves densification. Carbon and oxygen analysis, density measurements, optical microscopy and JMatPro calculations were also performed.

A new strategy for metal additive manufacturing using an economical water-atomized iron powder for laser powder bed fusion

We develop a pre-alloyed water-atomized (WA) iron powder for laser powder bed fusion (LPBF)-based 3D printers; such a powder has never been used for 3D printing. The powder features low levels of nano-sized Cu-Ni-Mo; these alloying elements are placed into the concavities of the iron powder. When these powders were used for LPBF printing, the processing window for the volumetric energy density ranged from 93 to 130 J/mm3. However, careful control of laser power (150 – 225 W) and scan speed (500 – 900 mm/s) was essential. In terms of production, a maximum relative density of 99.67% was achieved upon application of an energy density of 108 J/mm3 (175 W, 700 mm/s). An average hardness of 217.1 ± 4.7 HV was obtained, exhibiting stable standard deviations and confirming excellent mechanical homogeneity. Energy-dispersive X-ray spectroscopy mapping revealed excellent chemical homogeneity; this translated to good mechanical homogeneity because of the uniform mixing of the nano-sized alloying elements. The printed tensile bars were stable and of a relatively high aspect ratio. Tensile strength measurements revealed that samples prepared using the partially pre-alloyed iron powder were better than those fabricated from simple raw WA iron powder; the former samples exhibited an ultimate tensile strength (UTS) of 460.91 MPa with elongation of 6.98% and the latter a UTS of 197.15 MPa with elongation of 0.45%. Therefore, the pre-alloyed WA iron powder developed in this study can successfully be used in LPBF and presents a more cost-effective alternative to traditional gas atomized iron powders.

Electron Beam Powder Bed Fusion of Water Atomized Iron and Powder Blends.

In the present state of the art, highly spherical alloy powders are employed as feedstock in powder bed fusion processes. These powders are characterized by high flowability and apparent density. Their elaborate fabrication process is reflected in high powder price, adding a significant fraction to the cost of additively manufactured parts. Thus, the use of non-spherical powders, such as water atomized material, can lower costs significantly. Here, the electron beam powder bed fusion (PBF-EB) of standard water atomized iron powder used for press-and-sinter is studied. Despite raking problems, using the coating mechanism in standard configuration samples with densities exceeding 99% were fabricated. In a further step, the addition of alloying elements by powder blending is explored. Important powder properties of feedstock blended from irregular and spherical powders are characterized. The PBF-EB processing of two alloys is presented. The first represents a low carbon steel. Samples were characterized by metallographic cross-section, energy dispersive X-ray (EDX) mapping, and mechanical testing. The second alloy system is a FeCrAl. After PBF-EB processing of the powder mixture, chemical homogeneity was achieved. Besides the low cost, this approach of using water atomized powder mixed with master alloy offers the advantage of high flexibility for potential application.

Analysis of preheating temperature field characteristics in selective laser sintering

Selective laser sintering technology has broad application prospects in the manufacture of small batch parts with complex structure. In the sintering process, the preheating efficiency and temperature of powder layer determine the processing quality. A method of preheating powder by lamp radiation and tropical heat conduction is proposed in this paper. The thermal radiation model is established, and the angle coefficient is introduced to describe the proportion of radiation energy on the surface of powder layer. Based on the geometric characteristics of the powder cylinder, the heat conduction process is simplified to one-dimensional heat conduction along the radial direction, and the heat conduction model is established. The coupled temperature field under two actions is obtained by combining the heat radiation model with the heat conduction model. The uniformity coefficient [Formula: see text]/[Formula: see text] of the temperature field is defined to represent the uniformity of the preheating temperature field of the powder layer. By comparing the uniformity coefficient [Formula: see text], a more uniform temperature field can be obtained when the height coefficient is 1.8 under combined action. The validity of the model is verified by a comparative experiment with processed water atomized iron powder. Constructing uniform temperature field can effectively reduce the deformation of parts and improve the forming quality.

A New Strategy Addressing the Increasing Demand for Metal Additive Manufacturing Using an Economical Water-Atomized Iron Powder for Laser Powder Bed Fusion

A New Strategy Addressing the Increasing Demand for Metal Additive Manufacturing Using an Economical Water-Atomized Iron Powder for Laser Powder Bed Fusion

Capsule-free hot isostatic pressing of sintered steel to full density using water atomised iron and Cr-alloyed powder consolidated by cold isostatic pressing

ABSTRACT Powder metallurgy (PM) steel with enhanced density is essential for meeting the demands on high strength and high-performance applications. In this study, cold isostatic pressing (CIP) is applied for consolidating water-atomised iron and Cr-alloyed steel powder to reach about 95% densification before sintering. Additionally, the effect of the lubricant and graphite addition on the compressibility of the different base powder types was evaluated. The maximum green densities of ≈7.55 g cm−3 for iron powder and ≈7.45 g cm−3 for Cr-alloyed powder were reached after CIP at 800 MPa. The sintering at 1250°C with added graphite allowed to achieve increased densification to ≈7.60 g cm−3 for the iron and ≈7.50 g cm−3 for Cr-alloyed grades, respectively. These levels were sufficient for surface pore closure, which allowed the application of the capsule-free hot isostatic pressing (HIP) after sintering to reach full density. This approach paves the way for manufacturing large-sized PM components.

Sintering of bimodal micrometre/nanometre iron powder compacts - A master sintering curve approach

Though press and sinter powder metallurgy (PM) steel offers cost-effective solutions for structural applications, there is a constant drive for improvement in their density. Addition of nanopowder to the conventional micrometre-sized metal powder is explored to improve the sinter density. In this study, the effect of nanopowder addition in varying amounts has been studied. Carbonyl iron powder (<5 μm) and water atomized iron powder (<45 μm) were used as the base powder to which varying amounts of iron nanopowder (<100 nm) was added. Dilatometric sintering studies under pure hydrogen atmosphere were carried out to analyze the densification behavior. The results revealed that the bimodal powder mixture containing 25% nanopowder exhibited the highest green density for both carbonyl and ASC 300 compacts. Master sinter curve for compacts was developed based on the dilatometer data. The apparent activation energy for sintering decreased with an increase in nanopowder content. This is reflected in the values of work of sintering.

Powder Technology of Metal Materials ~ Iron Powder ~

Iron powder is one of the “long-seller” material because it has been used since B. C. 300. Iron powder is mainly used for powder metallurgy in recent years. On the other hands, it is also used for the functional applications by using chemical reaction, such as body warmer, deoxidant and agricultural application. There are the several methods to produce iron powder, and reduced and water atomized iron powders are mainly used for the powder metallurgy due to their good compactibilities. In this paper, the details of production process of iron powders containing alloyed steel powders in JFE steel, which produces both reduced and water atomized iron powders, are described. In addition, the powder characteristics of these two kinds of iron powders are also described. The expansion of functional applications such as additive manufacturing process or magnetic cores is expected in the future, thus additional improvement of iron powders quality will be required.

Sintering behaviour of compacted water-atomised iron powder: effect of initial state and processing conditions

ABSTRACT Conventional ferrous powder metallurgy relies on uniaxial die-pressing of powder before sintering. The operation causes particle rearrangement and deformation and the initial state of the compact ultimately determines the sintering behaviour. In this study, sintering was investigated for water-atomised iron powder compacted at three different pressure levels, with and without admixed graphite. Electron back-scatter diffraction of the powder and compacts showed a large increase in low-angle grain boundaries after compaction. The sintering of the compacts was investigated by means of dilatometry in hydrogen. The initial compaction strongly influences sintering shrinkage, particularly in the low-temperature, high-diffusivity ferrite region which can account for up to 80% of the recorded shrinkage. Only a small fraction of the total shrinkage originates from the austenite phase, even at high sintering temperatures. However, the ratio of sintering shrinkage in ferrite and austenite changes with compaction pressure, carbon content and heating rate.

Electromagnetic Characteristics and Corrosion Resistance of New Magnetosoft Materials Based on Capsulated Iron Powders

A new method of depositing an insulating multifunctional oxide coating on metal particles was developed. Such coatings increase corrosion resistance and insulate metal particles from each other. On base of capsulated by oxide coating water-atomized iron powder ASC100.29, new composite soft magnetic materials were synthesized, which are able of replacing electrical steel in devices. Structural, electromagnetic properties and corrosion characteristics of the obtained composites were studied. It was found that the synthesized composite materials have low electromagnetic losses, high values of magnetic induction(up to 2.1 T) and good corrosion resistance. The results demonstrate that the use of such materials in power supplies, chokes, transformers, stators and rotors of electric machines and other products ensures their stable operation under various conditions.

Magnetic Comparison Between Experimental Flake Powder and Spherical Powder for Inductor Cores at High Frequency

This article is the first work to carefully investigate the characteristics of iron loss per weight and relative permeability between the flake and spherical powders with a sinusoidal excitation up to a high frequency of 3.5 MHz in experiments using three separate measurement systems. The composition of the considered powder samples contains 0.001 wt% C, 0.012 wt% Si, 0.09 wt% Mn, 0.0004 wt% P, 0.008 wt% S, and 0.06 wt% O. The flake particle has the preferred orientation that the easy axes are normal to the platelet face, and the water atomized iron powder was processed with ball milling with the lubrication. Key objectives of the utilization of the three independent measurement systems with different specialized equipment and probes are to cross-check and overcome unexpected measurement errors of the related devices in use for validating measured results thoroughly. Experimental results demonstrate the much better performances on the iron loss per weight and relative permeability of the flake powder than that of the spherical powder at high frequencies. Physics-based explanations for the measured results are also presented. Furthermore, two estimation functions based on a six-parameter Steinmetz equation for the measured iron loss of the powders are developed by using MATLAB.

Reduction of surface oxide layers on water-atomized iron and steel powder in hydrogen: Effect of alloying elements and initial powder state

The reduction of surface oxide layers covering commercial water-atomized iron and steel powder grades have been investigated using model thermogravimetric reduction cycles in hydrogen. The influences of powder composition and initial condition on the oxide reduction were studied for three powder grades and compared to Fe2O3. Isothermal and dynamic measurements were conducted to assess the reduction progress and kinetic analyses were then used to calculate the apparent activation energies of reduction. Chromium-alloyed powder showed significantly lower activation energies compared to iron powder and Fe2O3, likely originating from the presence of Cr oxide in the oxide layer. The reduction was also found to be strongly affected by the initial state of the oxide layer which reflects the powder production. Surface analysis by X-ray photoelectron spectroscopy (XPS) showed a progressive increase in Cr with gradual reduction of the oxide layer, indicating its presence and possible involvement in the oxide reduction.

Effect of Nanopowder Addition on the Sintering of Water-Atomized Iron Powder

A promising method of improving the densification of powder metallurgical steel components is to blend nanopowder with the otherwise typically used micrometre-sized powder. The higher surface-to-volume ratio of nanopowder is hypothesized to accelerate the sintering process and increase the inter-particle contact area between the powder particles. This is supposed to enhance the material transport and improve the densification. In the present investigation, water-atomized iron powder (− 45 μm) was mixed separately with pure iron and low-carbon steel nanopowder, each at a ratio of 95 to 5 pct. These powder mixes were compacted at different pressures (400, 600 and 800 MPa) and then sintered at 1350 °C in a pure hydrogen atmosphere. The sintering behavior of the powder blend compacts was compared to that of the compact with micrometre-sized powder only. Densification commenced at much lower temperatures in the presence of nanopowder. To understand this, sintering at intermittent temperatures such as 500 °C and 700 °C was conducted. The fracture surface revealed that the nanopowder was sintered at between 500 °C and 700 °C, which in turn contributed to the densification of the powder mix at the lower temperature range. Based on the sintering experiments, an attempt was made to calculate the activation energy and identify the associated sinter mechanism using two different approaches. It was shown that the first approach yielded values in agreement with the grain-boundary diffusion mechanism. As the nanopowder content increased, there was an increase in linear shrinkage during sintering.

Oxide reduction and oxygen removal in water-atomized iron powder: a kinetic study

Reduction of oxides during sintering is a prerequisite for the manufacturing of powder metallurgy steels. Inadequate control of the sintering atmosphere may impede sinter neck formation and cause entrapment and growth of oxides in sinter necks, ultimately deteriorating the mechanical properties of sintered components. In this study, the oxide reduction and oxygen removal in water-atomized iron powder was investigated by means of thermogravimetric analysis in pure hydrogen. Two principal mass loss events were recorded, corresponding to the removal of the surface oxide layer at around 400 °C and reduction of internal and stable oxides in the range 600–1350 °C. The apparent activation energies of these mass loss processes were determined by means of kinetic analyses, giving values around 100 kJ mol−1 and 200–400 kJ mol−1, respectively. The validity of the results was asserted using hematite reference samples which displayed good correlation with the reduction of the surface oxide layer, thereby showing that the powder surfaces are covered by an Fe2O3 oxide. The high-temperature mass loss, with no analogy in the reference samples, is believed to originate from a combination of oxygen removal from internal oxides and stable oxide particulates on the surface. Analysis of the oxide reduction in iron powder compacts show a slightly lower activation energy for the oxide layer reduction, indicating an influence of the compaction step on the initial state of the powder and oxide layer. At the same time, the high-temperature mass loss event was shifted to higher temperatures, which is believed to be caused by the increasingly restricted mass transport of reduction products along the pores in the sintered compact.

The Magnetic Properties of a Magnetically Soft Composite Material for Use in the Low-Frequency Range

The key magnetic characteristics of a magnetic composite material developed on the basis of ASC 100.29 iron powder and other magnetic composites based on different iron powders are measured and contrasted to the parameters of 3412 electrical steel (type E320). At field strengths up to H = 5–6 kA/m, the magnetic induction in the developed composite material is inferior to that in the electrical steel, whereas the developed composite surpasses the steel at stronger fields. At a field strength H = 25 kA/m, the magnetic induction in the composite material is Bm = 1.95–2.0 T, while for the steel it is Bm = 1.84 T, both materials having the same density of 7.7 g/cm3. We also measure relative magnetization losses in composite materials fabricated using air- and water-atomized iron powders, and the latter, which are purer, are found to exhibit some advantages. Owing to low hysteresis losses, the prepared composite material can be used in electrical machines that operate at higher specific powers and especially in those operating at high rotation velocities—applications in which electrical steels exhibit high losses.

Laser directed energy deposition of water-atomized iron powder: Process optimization and microstructure of single-tracks

Although iron, as a basic metal, has been used commonly in industry, the use of an advanced technique such as additive manufacturing (AM) may offer more opportunities. For example, AM of iron-based powders for functional prototypes would likely be beneficial in the automotive industry, since this industry has commonly used iron alloys for prototypes and functional parts produced by conventional technologies. This paper presents Laser Directed Energy Deposition through Powder Feeding (LDED-PF), a class of AM, of irregular-shape inexpensive water-atomized iron powder. A setup with a lateral powder-fed nozzle was deployed to deposit single-tracks using different processing parameters. The experimental design and optimization model were implemented based on the response surface methodology when the regression model was tested by the variance analysis. The desirability function was used to identify the optimal processing window to obtain the single-tracks with a minimized dilution and a maximized bead height and high powder efficiency. The results showed that the geometrical characteristics of the single-tracks have a high dependency on the key LDED-PF processing parameters. In addition, the microstructure and phase composition of the single-tracks were investigated by SEM and EDS, revealing that the deposits were generally composed of the ferrite phase.

Tailoring green and sintered density of pure iron parts using binder jetting additive manufacturing

Binder jetting additive manufacturing (BJAM) is a comparatively low-cost process that enables manufacturing of complex and customizable metal parts. This process is applied to low-cost water-atomized iron powder with the goal of understanding the effects of printing parameters and sintering schedule on maximizing the green and sintered densities of manufactured samples, respectively. The powder is characterized by using scanning electron microscopy (SEM) and particle size analysis (Camsizer X2). In the AM process, the effects of powder compaction, layer thickness, and liquid binder level on green part density are investigated. Post-process heat treatment is applied to selected samples, and suitable debinding parameters are studied by using thermo-gravimetric analysis (TGA). Sintering at various temperatures and durations results in densities of up to 91.3%. Image processing of x-ray computed tomography (μCT) scans of the samples reveals that porosity distribution is affected by powder spreading, and gradients in pore distribution in the sample are largely reduced after sintering. The resulting shrinkage ranges between 6.7 ± 3.0% and 25.3 ± 2.8%, while surface roughness ranges between 11.6 ± 5.0 μm and 32.1 ± 3.4 μm. The results indicate that the sintering temperature and time might be tailored to achieve target densities anywhere in the range of 64% and 91%, with possibly higher densities by increasing sintering time.

Low cost irregular feed stock for laser powder bed fusion

Spherical powders are almost exclusively deployed for metal laser powder bed fusion (LPBF) additive manufacturing (AM). In this work, low-cost irregular powder feedstock is studied for its potential in three key areas to meet minimum AM process requirements, namely: (1) hopper flow, (2) layer spreading, and (3) de-powdering. Irregular water-atomized Iron powder was used as the study population, while spherical plasma-atomized Inconel 625 powder was used as the control. Powder flow characteristics were obtained using a FT4 Powder Rheometer (Freeman Technology). Layer spreading was evaluated indirectly via powder bed density measurements. Measurements were quantified by using printed artifacts for captive powder and evaluated using isopropanol infiltration and three-dimensional computed tomography (CT) imaging (Zeiss Xradia 520 Versa). Powder clearing from fine channels was quantified through vision-based measurements of printed artifacts (Dino-Lite DinoCapture 2.0). The results from this work demonstrated that: (1) A larger opening and steeper hopper angle are necessary to maintain a mass flow regime with the irregular powder. (2) Powder bed density is similarly consistent across the bed indicating adequate spreadability. (3) Water-atomized Iron powder has better de-powdering characteristics in the smallest cleared 0.6 mm diameter features, likely due to its 15% lower bed density.