Fe Alloy Powders Research Articles

Effects of Hot Extrusion Temperature Conditions on the Hardness and Electrical Conductivity of Rapidly Solidified Al-Fe Alloys.

Rapidly solidified Al-Fe alloys produced by hot extrusion are a promising replacement for copper-based electrical conductors because of their light weight. However, the effects of the extrusion temperature conditions on the mechanical and electrical properties of extruded materials are unknown. The present work investigated the effects of billet preheating temperature, in situ temperature during extrusion, and additional heat treatment after extrusion on hardness and electrical conductivity. An air-jet atomized Al-2.3%Fe alloy powder was pre-sintered into cylindrical billets and then hot-extruded. The hardness of the extrudates decreased as the in situ temperature during extrusion increased above 650 K. The billet preheating temperature affected the in situ temperature during extrusion. Additional annealing after extrusion decreased the hardness. The cause of the decrease in hardness was coarsening of the grain of the aluminum matrix. The electrical conductivity increased with higher billet preheating temperatures before extrusion or additional annealing after extrusion; however, an in situ temperature rise for a few seconds during extrusion did not affect the conductivity. The increase in electrical conductivity was considered to be caused by a decrease in the amount of solute iron, which requires holding the material at a high temperature for longer than several minutes.

Effect of grain boundary reconstruction and regenerated main phase shell on magnetic properties in high-abundance (NdLaCeY)-Fe-B magnets

The (NdLaCeY)-Fe-B magnets with 45–50 wt% high-abundance rare earth substitution were systematically investigated by co-mixing high boron content matrix phase and Pr–Fe alloy powders (0, 1, 3, 5, 7, and 9 wt%) during the preparation process. The coercivity of magnets increased successively with the addition of Pr70Fe30 (wt.%) and reached 9.32 kOe at the addition amount of 9 wt% from the initial 7.33 kOe without addition, while the remanence had a very small decrease of only 0.13 kGs. The analyses showed that the B-rich phase in the high-boron powders reacted with Pr70Fe30 to form the main phase shell, forming a core-shell structure with a Pr-rich shell and a Y-rich core. Meanwhile, the grain boundary was significantly widened with the introduction of Pr70Fe30. Then, just the improved anisotropy of the main phase grain surface, accompanied with the enhanced magnetic de-coupling effect between the main phase grains, resulted in a great coercivity increment. Notably, on the remanence, the beneficial effect of increased main-phase proportion by regenerated grain shell had a competitive relationship with the deteriorating effect of the magnetic dilution by the non-magnetic material introduction, thus under the combined effects, the remanence firstly increased and then decreased with the addition of Pr–Fe.

Preparation and properties of multiphase solid-solution strengthened high-performance W–Cu alloys through alloying with Mo, Fe and Ni

In this study, high performance W–Mo–Cu–Ni–Fe alloy samples with additions of Mo (0–6 wt%), Ni and Fe (total content: 2.5 wt% and 5 wt%) were obtained through liquid-phase sintering at lower temperature, with the raw material of ultrafine W–Mo–Cu–Ni–Fe composite powder. Ultrafine W–Mo–Cu–Ni–Fe alloy powder with strong sintering activity and uniform composition was obtained by two-stage reduction means composed of carbothermic pre-reduction and hydrogen deep deoxidation steps. Significantly, the bonding ability of W/Cu phase interface and the wettability of two phases are greatly improved due to the presences of Ni and Fe. Moreover, the addition of appropriate Mo content was advantageous to the formation of W–Mo solid solution. All alloy samples achieved higher densification degrees to guarantee that the sintered blocks possess outstanding overall performances. Especially, by adjusting Ni/Fe ratio, the highest tension strength and elongation of were achieved by W-2wt.%Mo-1.75 wt%Ni-0.75 wt%Fe-27.5 wt%Cu sintered block, which were 567 MPa and 10.37%, respectively. Moreover, owing to the presences of W–Mo and Cu–Ni–Fe solid solutions, this alloy also had the highest microhardness and bending strength of 446 HV and 1473 MPa, respectively. As increasing Mo content from 0 wt% to 6 wt%, the compression strength of sintered blocks was improved, and failure strains of all the sintered blocks are close to 100%, respectively. However, even though the Cu matrix network structure is more evenly distributed as a result of the existences of added Ni and Fe, the electronic movement ability of the sintered blocks was reduced, leading to a significant decrease in conductivity.

Structural and magnetic properties of Ni substituted FeCo alloy obtained through polyol process

Fe alloy powders with optimum magnetic properties are in demand for the fabrication of soft magnetic composites that find applications in power electronics and more electric vehicles. Fe-Co-Ni alloys with particles exhibiting spherical morphology and body-centered cubic structure are synthesized using a facile instant reduction polyol process. Curie temperatures from 840 to 760 °C are obtained with Ni substitution in the range of 7–14 at.%. The effective magnetic anisotropy realized using a modified law of approach to saturation and the Curie temperature studies suggests an additional amorphous phase that affects the magnetic behavior. The multidomain Fe-Co-Ni alloy particles have the potential for high-temperature applications as their effective magnetic anisotropies of 20–25 kJ/m3 are lower than Fe and FeCo powders.

Microstructural evolution of Al–15Fe alloy produced by mechanical milling and centrifugal atomization

In this study, the Al-15 wt % Fe powders were prepared using two methods: (1) milling of the initial alloy in a ball or a planetary mill; (2) centrifugal atomization. The effect of milling time and distribution of temperature field during atomization on the morphology and microstructure of the Al-15 wt % Fe alloy powders were investigated. After milling, the powders have an agglomerate structure with a size of Al13Fe4 about 4.1–5.4 μm. Using centrifugal atomization at a blades rotation speed of 2800 rpm resulted in a microstructure consisting of α-Al-matrix, stable Al13Fe4 (10–15 μm) and random oriented short fibres of metastable Al6Fe (2.3 ± 2.2 μm). Randomly oriented fibres are formed due to deformation processes that act on the particles during cooling and crystallization. The formation of the metastable Al6Fe is associated with a high cooling rate of nearly 106–108 °C/min. The influence of the particle shape on the temperature field was simulated. The stable Al13Fe4 occurs in the centre of the powders according to the low solidification velocity. The crystallization of a uniform structure is possible for particles of regular shape. The matrix of the atomized powder has a cellular microstructure, which introduces an additional reinforcing effect to the Al-15 wt % Fe alloy.

Effect of Fe doping on microwave absorption performance of magnetic powder NdNi5

Soft magnetic alloy powder NdNi5-xFex (x = 0.0, 0.1, 0.3, 0.4) was prepared by vacuum arc melting, homogenization annealing and ball milling methods. The reflection loss of NdNi5-xFex powders were discussed based on the structural morphology, measured hysteresis loops and electromagnetic parameters. The lattice distortion and the saturation magnetization of NdNi5-xFex powders increase and the formant of the electromagnetic parameter moves toward the low frequency. The absorption peak of reflection loss also moves toward low frequency. In addition, the Nd–Ni–Fe alloy powder can achieve the best absorption bandwidth, and the minimum reflection loss value of 1.29 GHz and − 29.29 dB, respectively, with the addition of Fe content is 0.1. Add Fe content appropriately, and adjusting the thickness can effectively improve the absorbing performance of the material in c-band, so the powder has a good application prospect in c-band.

Study of microstructure evolution and properties of Cu-Fe microcomposites produced by a pre-alloyed powder method

In this work, Cu-based microcomposites were fabricated by powder metallurgy of gas-atomized Cu-15wt% Fe alloy powder, followed by drawing to various strains. The microstructure evolution and the resultant mechanical and electrical properties were investigated by scanning electron microscopy, electron backscatter diffraction, and tensile testing, among other techniques. The results indicated that during drawing, the Fe phase evolved into nanoscale filaments along the longitudinal direction. With increasing drawing strain, both the Cu grains and the Fe filaments were refined gradually, giving rise to a mean thickness of approximately 25nm for the Fe filaments at a total strain of 4.0. The iron oxides particles formed due to contamination of oxygen maintained unchanged during drawing process. In addition, it was found that an intermediate aging during the drawing can significantly enhance the electrical conductivity of the microcomposites without sacrificing their strength. The present process involving an initial powder with a homogenous distribution of Cu and fine Fe phases makes it possible to obtain microcomposites with an ideal combination of electrical and mechanical properties at lower drawing strain, compared to those produced by conventional casting methods.

High-Temperature Decomposition of Fe- and Cr-Doped NiO Produced by a Novel Flame Spray Technique

A novel thick film technology has been developed for the manufacture of electric heating elements from partially oxidised Ni–Cr–Fe alloy powder. The sprayed films were a mixture of metallic alloys and Ni-based oxides. Electron microscopy and analysis were used to monitor the transformations in the films during subsequent heat treatment. In particular, it was found that homogeneous grains of Cr- and Fe-doped Ni-based oxides transformed into NiO grains containing numerous Ni-, Cr- and Fe-rich spinel particles with a typical size of 40 nm.

Microstructure and high-temperature wear properties of in situ TiC composite coatings by plasma transferred arc surface alloying on gray cast iron

In this work, an in situ synthesized TiC-reinforced metal matrix composite (MMC) coating of approximately 350–400 µm thickness was fabricated on a gray cast iron (GCI) substrate by plasma transferred arc (PTA) surface alloying of Ti–Fe alloy powder. Microhardness tests showed that the surface hardness increased approximately four-fold after the alloying treatment. The microstructure of the MMC coating was mainly composed of residual austenite, acicular martensite, and eutectic ledeburite. Scanning electron microscopy (SEM) and X-ray diffraction analyzes revealed that the in situ TiC particles, which were formed by direct reaction of Ti with carbon originally contained in the GCI, was uniformly distributed at the boundary of residual austenite in the alloying zone. Pin-on-disc high-temperature wear tests were performed on samples both with and without the MMC coating at room temperature and at elevated temperatures (473 K and 623 K), and the wear behavior and mechanism were investigated. The results showed that, after the PTA alloying treatment, the wear resistance of the samples improved significantly. On the basis of our analysis of the composite coatings by optical microscopy, SEM with energy-dispersive X-ray spectroscopy, and microhardness measurements, we attributed this improvement of wear resistance to the transformation of the microstructure and to the presence of TiC particles.

A comparative analysis of solubility, segregation, and phase formation in atomized and cryomilled Al–Fe alloy powders

Bulk nanostructured and ultrafine-grained binary Al–Fe alloys have been studied in the past for their remarkable strength, hardness, and thermal stability. These properties have been attributed to a combination of solid solution strengthening, precipitate strengthening, and grain boundary strengthening. However, to date, no systematic investigation has been performed to address the factors that govern the evolution of the various metastable and equilibrium precipitates that form as a result of thermal exposure. In this study, Al–2at.%Fe and Al–5at.%Fe powders were synthesized via helium gas atomization and argon gas atomization, respectively. Cooling rates upwards of 106 K s−1 were achieved resulting in an intermetallic-free starting structure, and a map of the structure as a function of cooling rate was established. Electron backscatter diffraction analysis revealed the presence of a larger number of low-angle grain boundaries relative to high-angle grain boundaries, which influenced nucleation and precipitation of the metastable Al6Fe phase. Cryomilling of the atomized powder was subsequently performed, which led to grain refinement into the nanometer regime, dispersion of the Fe-containing phases, and forcing of 2at.%Fe into solution within the Al matrix compared to negligible Fe in solution in the as-atomized state. Finally, differential scanning calorimetry was utilized to elucidate the metastable Al6Fe precipitation temperature (~300 °C) and subsequent phase transformation to the equilibrium Al13Fe4 phase (~400 °C). An activation energy analysis utilizing the Kissinger method revealed three important factors, in order of importance, for ease of Al6Fe precipitation: segregated regions containing iron, availability of nucleation sites, and the number of diffusion pathways.

Effects of Dy71.5Fe28.5 intergranular addition on the microstructure and the corrosion resistance of Nd–Fe–B sintered magnets

To satisfy high-temperature applications, heavy rare-earth (RE) Dy is commonly introduced into the Nd–Fe–B sintered magnets to improve the coercivity. In addition to forming (Nd, Dy)2Fe14B, Dy also exists in the intergranular RE-rich phase. Hence, understanding the effect of Dy on the electrochemical characteristics of the RE-rich phase and corrosion resistance of the magnet is of importance. In this work, eutectic alloy Dy71.5Fe28.5 powders were added into the (Pr0.2Nd0.8)12.3FebalB6.1 magnet through binary-alloy approach to investigate the corrosion resistance of the magnet in electrochemical and hot/humid environments. The results demonstrate that Dy is enriched in the intergranular phase, improving its electrode potential and stability due to the higher electrode potential of Dy than Nd or Pr. As a consequence, the electrode potential difference between the 2:14:1 phase and the RE-rich phase is reduced, improving the corrosion resistance. Furthermore, formation of (Pr, Nd, Dy)2Fe14B shell with stronger local anisotropy surrounding the 2:14:1 phase grains improves the coercivity with a slight remanence loss. Therefore, intergranular adding Dy–Fe alloy powders can obtain both high magnetic properties and good corrosion resistance simultaneously.

Nanocrystalline Ni-30wt%Fe Supersaturated Solid Solution Synthesized by Mechanical Alloying

Ni-30wt%Fe elemental power mixture was mechanically milled under argon atmosphere for variuos times up to 25h.The evolution of Ni-Fe alloying during milling and the microstructure of the as-milled powders were characterized by XRD, EPMA (electron probe microanalysis), SEM and TEM, respectively. The results show that nanocrystalline Ni (Fe) supersaturated solid solution alloy powders with 30wt. % Fe in composition can be synthesized by mechanical milling of the elemental powder mixture. Both the content of Fe dissolved and the microstrain developed in the as-synthesized Ni (Fe) solid solution phase increase, while the crystallite size decreases, steadily with increasing milling time. In particular, the Ni-30wt%Fe alloy powders obtained by 25h milling consist of a single Ni (Fe) supersaturated solid solution phase with average crystallite size of about 15nm and accumulated microstrain as high as 1.12%. DSC tests show that the nanocrystalline Ni-30wt%Fe alloy powders have a lower melting temperature than the elemental powder mixture, attributed to the unique Ni (Fe) solid solution phase structure, the nanocrystallization, and the high strain energy.

FABRICATION OF IN SITUFe-Ti-B COMPOSITE COATING BY LASER CLADDING

Laser cladding was applied to deposit in situ Fe - Ti - B composite coatings on mild carbon steel with precursor of ferrotitanium, ferroboron and pure Fe alloy powders. The composite coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron probe microanalysis (EPMA). Wear resistance of the laser-cladded Fe - Ti - B coatings was evaluated under dry sliding condition at room temperature using block-on-ring wear tester. Results indicate that in situ reinforcements of TiB 2 and Fe 2 B can be synthesized in the Fe - Ti - B coatings. The amount of TiB 2 increases with the increase of content of ferrotitanium and ferroboron in the precursor. Reinforcements are formed through the liquid-precipitation route following the solidification path of the Fe - Ti - B system. Hardness and wear properties of the coatings improved significantly in comparison to the as-received substrate due to the presence of hard reinforcements.

Corrosion resistance of Al–Cu–Fe alloy powder coated with silica using an ultrasound-assisted sol–gel method

Al–Cu–Fe alloy powder, a high-effective lubrication oil additive, was coated by conventional sol–gel method employing tetraethoxysilane (TEOS) as the precursor for purpose of improving its corrosion resistance. The best condition was obtained according to an orthogonal experiment (L9(34)). Then, the sol–gel method was modified by employing ultrasound to study the effects of both the ultrasonic power and irradiation time on the coating process. Finally, the coated powder had an high corrosion resistance in the acid media of pH 1. The obtained samples were characterised by FTIR, XRD, SEM and EDS.

A study of densification and on factors affecting the density of Ni x –Fe100 − x nanopowders prepared by mechanical alloying and sintered by spark plasma

Mechanical alloying through high-energy ball milling was used in the production of Ni–Fe alloy powders from elemental Ni and Fe powders of average particle size 80 and 25 μm, respectively. High-energy planetary ball milling at room temperature was performed for various time durations ranging between 2 and 100 h. SPS apparatus was used for sintering of powder particles. Density of all specimens was reported and a maximum densification of 99 % was achieved in 50 wt.% Ni–Fe milled for 16 h prior to spark plasma sintering at 1,223 K.

Microstructure and Properties of Fe-Based Composite Coating by Plasma Jet Surface Metallurgy

The Fe-based composite coatings were formed by plasma jet surface metallurgy using Fe, C, W, Cr and Al alloy powders on the low carbon steel. The morphology, microstructure, interface structure and the distribution of the in situ particles in the coatings were observed with optical microscope, scanning electron microscope and x-ray diffraction analysis. The results show that metallurgical bonding is obtained between coating and substrate, and the microstructure of coatings is mainly composed of γ-Fe, (Fe,Cr,W,Nb)7C3 and AlFe particles which are synthesized in stiu, are dispersivly distributed in the coatings. The micro-hardness gradually increased from bottom to the top of the coating, the maximum is 986 Hv0.1, about 4 times larger than that of the steel substrate.

2Mg–Fe alloys processed by hot-extrusion: Influence of processing temperature and the presence of MgO and MgH 2 on hydrogenation sorption properties

2Mg–Fe alloy powder produced by high-energy ball milling was processed by hot extrusion at temperatures of 200 °C and 300 °C to produce bulk samples. The alloys were hydrogenated for 24 h under hydrogen pressures of 24 bar (to produce the Mg 2FeH 6 phase) and 15 bar (to produce a mixture of MgH 2 + Mg 2FeH 6 phases), respectively. After the hydrogenation treatments, the complex hydride Mg 2FeH 6 was identified in both conditions, while the MgH 2 and MgO phases were observed only after extrusion at 200 °C. Desorption temperatures varied with the extrusion conditions; extrusion at 300 °C resulted in a desorption onset temperature about 68 °C lower than that of samples extruded at 200 °C, and about 200 °C lower than that of commercial MgH 2. Extrusion at the lower temperature did not change the number of stored defects (point defects, dislocations, voids, stacking faults, vacancies and others) produced in the milling process and increased the preferential sites for hydride nucleation, increasing the hydrogen storage capacity. The presence of MgO produced the beneficial effect of grain boundary pinning, but delayed the onset temperature of desorption. The combined presence of MgH 2 and Fe after hydrogenation at 15 bar seems to play a catalytic role that considerably hastened the Mg–H reactions and increased the desorption kinetics. However, the desorption kinetics in both conditions was still low.

Characterization of High-Temperature Abrasive Wear of Cold-Sprayed FeAl Intermetallic Compound Coating

FeAl intermetallic compound coating was prepared by cold spraying using a mechanically alloyed Fe(Al) alloy powder followed by post-spray annealing at 950 °C. The high-temperature abrasive wear test was carried out for the FeAl coating at a temperature range from room temperature to 800 °C. The high-temperature abrasive wear of a heat-resistant stainless steel 2520 was performed for comparison. It was observed that the abrasive wear weight loss of FeAl coating was proportional to wear cycles in terms of sample revolutions at the tested temperatures. It was found that with the increase of the test temperature higher than 400 °C, the wear rate of cold-sprayed FeAl coating decreased with the increase of test temperature, while the wear rate of the heat-resistant steel increased significantly. The results indicate that the high-temperature abrasive wear resistance of the cold-sprayed FeAl intermetallic coating increased with the increase of the wear temperature in a temperature range from 400 to 800 °C. The wear resistance of cold-sprayed FeAl coating was higher than that of heat-resistant 2520 stainless steel under 800 °C by a factor of 3.

Microstructure and mechanical properties of bulk nanocrystalline Al–Fe alloy processed by mechanical alloying and spark plasma sintering

Nanocrystalline Al–5 at.% Fe alloy powders produced by mechanical alloying were consolidated by spark plasma sintering. The sintered sample showed high strength >1000 MPa with a large plastic strain of 15% at room temperature and 500 MPa at 350 °C. Microstructure characterizations by transmission electron microscopy and atom probe tomography revealed that the sintered samples are composed of α-Al and Al 6Fe nanocrystalline regions with 90 nm in diameter and a minor fraction of Al 13Fe 4 phase and coarsened 0.5–1 μm α-Al grains. This bimodally grained feature is attributed to the relatively large plastic strain for the strength level of 1000 MPa at room temperature.

Correlation of Microstructure with Hardness, Wear Resistance, and Corrosion Resistance of Powder-Injection-Molded Specimens of Fe-Alloy Powders

In this study, the powder injection molding (PIM) process was applied to Fe-alloy powders. Microstructure, hardness, wear resistance, and corrosion resistance of the PIM specimens were analyzed and compared with those of a conventional stainless steel, SS316L. When Fe-alloy powders were injection molded and then sintered at 1200 °C or 1250 °C, completely densified specimens with almost no pores were obtained. They contained 63 to 80 vol pct of hard (Cr,Fe)2B dispersed in the austenite or martensite matrix. Since these (Cr,Fe)2B borides were very hard, thermally stable, and corrosion resistant, hardness, high-temperature hardness, wear resistance, and corrosion resistance of the PIM specimens of Fe-alloy powders were 2 to 5 times as high as those of the stainless steel. Such property improvement suggested new applicability of the PIM products of Fe-alloy powders to structures and parts requiring excellent mechanical properties.