Fe-based Alloy Powders Research Articles

Size-dependent structure and magnetocaloric properties of Fe-based glass-forming alloy powders

We investigated the influence of particle size on the microstructure and magnetocaloric effect of Fe-based alloy powders (11 μm to 100 μm in diameter). The degree of structure order varies with the powder size. The 11 μm to 18 μm powders show the largest peak magnetic entropy change (MEC). Increasing the degree of structure order tends to decrease the maximum MEC. Nevertheless, enhancement of refrigerant capacity and MEC (above 70 K) is achieved when the crystalline phase content is ∼50% (above 75 μm) in the 75 μm to 100 μm powders. Exponent n of the field dependence of MEC increases with the decrease in powder size above 22.5 K. The size dependence of the structure and properties is associated with the fact that a larger particle has a slower cooling rate and takes a longer time to form medium-to-long range ordered structures.

Unusual high Bs for Fe-based amorphous powders produced by a gas-atomization technique

Fe-based alloy powders with a high Fe content of about 81 at.% were produced by a gas-atomization technique. Powders of Fe81Si1.9B5.7P11.4 (at.%) alloy showed a good glass forming ability and exhibited unusual high saturation magnetic flux density of 1.57 T. The core-loss property at a frequency of 100 kHz for the compacted core made of the Fe81Si1.9B5.7P11.4 powder is evaluated to be less than 500 kW/m3 under a maximum induction of 100 mT. Moreover, good DC-superposition characteristic of the core was also confirmed. These results suggest that the present Fe-based alloy powder is promising for low-loss magnetic-core materials and expected to contribute in miniaturization of electric parts in the near future.

Fabrication of high hardness and corrosion resistance coatings from Fe-based alloy powders

ABSTRACTGas atomized Fe50Cr24Mo21Si2B3 powders were used to form Fe-based alloy coatings by the air plasma spray method. The coatings exhibited high amorphous nature and extremely low porosity of 0.41% in about 200 µm thickness. The Fe-based coating exhibits an average hardness about 1255 Hv. The Fe-based coatings could be potentially applied as functional surface protective coatings.

Effect of a small addition of Ti on the Fe-based coating by laser cladding

Abstract In this study, the coatings were fabricated on a low carbon steel substrate by laser cladding using the Fe-based powders mixed with different Ti content. The effects of the Ti and its content on the microstructure, phase compositions and microhardness of the clad layers are studied systematically. The results show that, the addition of Ti into Fe-based alloy powder changes the morphology and microstructure of the coatings obviously. The equiaxed grains or dendritics appear instead of dendrite structures, and the microstructure becomes refined and uniform. In addition, with the increase of Ti content, the dilution rate of the coatings goes up and the size of crystal phase in the deposits becomes larger, which makes the hardness of high-doped layers decrease sharply. Meanwhile, the reasons for these differences are analyzed in detail. At last, by comparison, the Fe-based mixed with 1 wt.% Ti coating has the most desired performance. It has high hardness which is not sensitive to the scanning speed under the condition that the ratio of the powder feed rate to the scanning rate is constant. And the hardness distribution through the clad layers is much stable.

Fabrication of FeSiBPNb amorphous powder cores with high DC-bias and excellent soft magnetic properties

Fe-based amorphous magnetic alloy powders with a composition of (Fe0.76Si0.09B0.1P0.05)99Nb1 were first prepared by water atomization, and then amorphous magnetic powder cores were produced from a mixture of the amorphous alloy powders with diameters of below 75μm and different volume of insulation and bonding materials by mold compacting with a compact pressure of 2200MPa at room temperature. The amorphous magnetic cores exhibit superior DC-bias properties and excellent soft magnetic properties after appropriate heating treatment. The DC-bias properties of the present amorphous magnetic cores just decrease 15% as the external field increases to 100Oe. Meanwhile, it also exhibits a high permeability of 56 at 1MHz and a low core loss of 451W/kg at Bm=0.1T and f=100kHz. The present Fe-based amorphous magnetic powder cores with superior DC-bias properties are a potential candidate for a variety of industrial applications.

Fe계 벌크 비정질 합금을 이용한 레이저 용접층의 파손 거동

In this study, Fe-based bulk amorphous alloy powder manufactured using gas atomization fabrication was used for laser welding. the fracture behavior of welding layer were analyzed. Tensile test results show that the destruction occurred immediately after the elastic deformation, After plastic deformation of the substrate, the destruction occurred. The actual maximum tensile strength of the welding layer and the substrate are 959.9MPa and 220.4MPa. welding layer were each 485.5±21 and 197.4±21 to the substrate and the actual microhardness, The welding layer has very high hardness. The welding layer showed a very weak fine acicular structure. The base material was shown in the micro structure appear a coarse grain. SEM observations of the fracture after the tensile test. Fracture morphology of the base metal and the welding layer showed ductile fracture and brittle fracture,

Refinement of Fe-based alloy doped Ti cladding layer

The aim of this paper is to achieve the refinement of cladding coatings by using re-melting process. In this study, Fe-based alloy powder and Fe-based alloy mixed with Ti powder were used as cladding materials, and the cross-section morphologies and characteristics of different coatings were compared and analyzed. Subsequently, high-speed re-melting experiment has been done on a selected layer and the refinement of the coatings had been achieved. With the increase of re-melting scanning speed, the area and crystalline size of refined zone decrease obviously. Meanwhile, a three-dimensional (3D) finite element model (FEM) has been built to provide a thermal field analysis for laser re-melting. Finally, the refinement of the entire overlapping coating has been achieved.

A New High Precise Powder Feeder for Fabricating Functionally Gradient Metal Component

In this paper, a new high precise powder feeder designed for fabricating functionally gradient metal component was presented. The mechanism, control principle and computer control program of the powder feeder were introduced and the powder feeding precise test experiments were carried out with Ni-based alloy powders, Fe-based alloy powders and ceramic powders in the particle average diameter of 15-350 Microns. Experimental results showed that the powders mixtures obtained from the high precise powder feeder are continuous and stable. The precision of delivering powders mixture can be weighed within 2% error scope comparing to the desired mixture quality and the flexible proportion of different powders mixture can be easy changed in the computer control program by synchronously controlling the powder feeder motor’s rotation speed.

Effect of strengthening particles on the dry sliding wear behavior of Al2O3–M7C3/Fe metal matrix composite coatings produced by laser cladding

In the present work, Al2O3–M7C3 particle reinforced iron matrix composite coatings were fabricated on a steel substrate by laser cladding with different mixtures of Fe-based alloy powder and Al/Fe2O3 thermite reactants. The microstructure of the composite coating was investigated by X-ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. The hardness and dry sliding wear properties of the composite coatings were also investigated by Vickers microhardness and block-on-ring dry sliding wear test. The results show that Al2O3 ceramic and M7C3 carbide are in situ synthesized by laser cladding. With the increase of thermite reactants, the amount of Al2O3 ceramic and M7C3 carbide in the composite coatings increases gradually. The microstructure is characterized by a cellular dendritic structure at the bottom, a typical cellular microstructure in the middle and an equiaxed crystal at the top of the composite coatings. The increased thermite reactants significantly enhance the microhardness and the wear resistance of the composite coatings, which should be ascribed to the grain refinement strengthening, precipitation hardening and solid solution strengthening.

Influence of plasma on the densification mechanism of SPS under multi-field effect

The densification mechanism of an Fe-based alloy powder containing tiny oxide particles under the synergic multi-field effect of spark plasma sintering (SPS) was investigated. Metallographic microscopy and scanning electron microscopy were used to observe the morphology of samples sintered at different temperatures, and the temperature distribution in an individual spherical powder particle during sintering was calculated in consideration of the influence of plasma, which was qualified and quantified through the analysis of the U-I curve. The plasma was observed to play a substantial role in activating and heating the samples at the very early stage of sintering, whereas the joule-heat effect played a dominant role during sintering. Moreover, the plasma also facilitated the diffusion and migration of materials for neck formation.

Effect of defocus manner on laser cladding of Fe-based alloy powder

This investigation was focused on the influences of defocus manner and composite powders on laser cladding. Combining with the transmission characteristic of parallel Gaussian laser beam through a focusing lens, the energy distribution of the cross section of the laser beam in positive and negative defocused zone was analyzed and also verified by laser dotting ablation. Comparing with positive defocus, the negative defocus is an effective way for high quality laser cladding providing more advantages. Therefore, the negative defocus method is selected to solve the problem of high dilution rate and pores in the overlapping coating. The study showed that by adjusting the process parameters, a coating with low dilution and free of pores can be achieved easily in the negative defocus. Finally, the microstructure and microhardness of Fe-based alloy mixed with 5wt.% Cr3C2 coating were analyzed.

Microstructure formation and fracturing characteristics of grey cast iron repaired using laser.

The repairing technology based on laser rapid fusion is becoming an important tool for fixing grey cast iron equipment efficiently. A laser repairing protocol was developed using Fe-based alloy powders as material. The microstructure and fracturing feature of the repaired zone (RZ) were analyzed. The results showed that regionally organized RZ with good density and reliable metallurgical bond can be achieved by laser repairing. At the bottom of RZ, dendrites existed in similar direction and extended to the secondary RZ, making the grains grow extensively with inheritance with isometric grains closer to the surface substrate. The strength of the grey cast iron base material was maintained by laser repairing. The base material and RZ were combined with robust strength and fracture resistance. The prevention and deflection of cracking process were analyzed using a cracking process model and showed that the overall crack toughness of the materials increased.

Microstructure and properties of laser cladding FeCrBSi composite powder coatings with higher Cr content

FeCrBSi alloy powder with higher Cr content was used for laser cladding by employing a 3kW solid-state laser. Ni- and Fe-based alloy powders, which were more resistant to cracking, were added into FeCrBSi alloy powder with higher Cr content to increase the ductile phases, lower thermal expansion coefficient, and reduce the crack sensitivity of the cladding layer. FeCrBSi alloy powder with higher Cr content combined Ni- and Fe-based alloy powder were cladded on the substrates, which yield two different phases. The hard phases of the cladding layer were mainly composed of carbide phase M23C6, and the ductile phases which played a lubrication function in the cladding layer were mainly composed of austenite γ-Fe and γ-Ni. The ductile phases increased by adding Ni- and Fe-based alloy powder into FeCrBSi alloy powder with higher Cr content, and the hard phases became sparser relatively. Smooth cladding layers, which were free of macroscopic pores, cracks and void between the adjacent tracks, were achieved. Therefore, the toughness of the cladding layer was improved, and the crack tendency was reduced. Three kinds of composite powder were obtained. The composition and morphology of the cladding layer were analyzed, and the microhardness between the hard phases and the ductile phases was compared. The average microhardnesses of the three cladding layers varied from HV0.2 760 to HV0.2 950.

Laser Processing of Fe-Based Bulk Amorphous Alloy Coatings on Titanium

Laser Engineered Net Shaping (LENS™), a solid freeform fabrication technique, was employed for the processing of Fe-based bulk amorphous alloy (Fe BAA) powder on titanium. One and two layers of the Fe BAA were deposited with the same processing parameters. SEM and XRD analyses of the Fe BAA coatings revealed the retention of the feedstock powder’s amorphous nature. The mixing of the feedstock powder in the titanium substrate was very small. A crystalline-amorphous composite microstructure evolved from the laser processing in all types of coatings. The coatings were further laser remelted. The amorphous character was found to increase and the crystallites were found to grow during remelting. The Fe BAA coatings showed higher hardness and smaller wear volume compared to the Ti substrate. A further increase in these properties was observed after laser remelting treatment. During the wear testing in NaCl solution, Ti substrate showed intergranular corrosion, whereas the Fe BAA coatings showed signs of low and localized fretting corrosion in a saline environment. Our results demonstrate that using LENS™, amorphous coatings can be deposited on metallic substrates.

Production of in situ TiB2+TiC/Fe composite coating from precursor containing B4C-TiO2-Al powders by laser cladding

Steel matrix composites reinforced with TiB2+TiC reinforcement were produced by laser melting mixture of B4C, TiO2, Al and Fe-based self-melting alloy powders. The results show that TiB2+TiC ceramic particles were synthesized from the reaction of B4C, TiO2 and Al alloys during laser cladding process. The reinforcement particles were evenly distributed in the coating. TiB2 grew in rectangle shape, but TiC presented irregular cubic shape. The wear resistance of the coating was higher than that of the substrate of 1045 steel; meanwhile, the friction coefficient of the coating was considerably lower than that of 1045 steel.

Microstructural Evolution of Fe-Based Metallic Glass/2024-Al Powder during High Energy Ball Milling Process

Nanostructured Al alloy powder was prepared by ball milling of a mixture of Fe-based metallic glass (FMG) powder and 2024-Al alloy powder. Microstructural evolution and mechanical properties of the milled composite powder were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and micro-hardness test. It is revealed that after 24h milling, the grain size of the Al alloy powder reduced to about 30nm, and the FMG particles were uniformly distributed throughout the Al matrix. The mechanical test indicated that the micro-hardness of the powder was significantly improved.

Fabrication and Microstructures of WC-Based Composites by Plasma Jet Metallurgy

The WC-Fe bulk composites were prepared by means of the plasma jet metallurgy using WO3, C and Fe-based alloy powder as raw materials. Phases of the composites were mainly WC, W2C, M6C, M7C3 and (Fe, Ni).The WC grains formed in situ had rectangular or triangular shapes with size of 30-70μm. The growth morphology of Fe3W3C was faceted polygon and herringbone. The formation of the unique composite microstructure was attributed to the incomplete peritectic reaction between W2C and Fe3W3C.

Effects of (Cr,Fe)2B borides on hardness in powder-injection-molded product fabricated with Fe-based alloy powders

In the present study, a powder injection molding (PIM) product containing (Cr,Fe)2B borides was fabricated with Fe-based alloy powders, and its microstructure and hardness were investigated in relation with volume fraction of (Cr,Fe)2B. In the Fe-based alloys designed by the thermodynamic calculation, the volume fractions of (Cr,Fe)2B increased with increasing (XCr+XB) value, and were well matched with those obtained from the thermodynamic calculation. The hardness of the Fe-based alloys linearly increased with increasing volume fraction of (Cr,Fe)2B. When Fe-based alloy powders were injection-molded and sintered at 1165°C, a densified microstructure with almost no pores was obtained. In the sintered microstructure, 56vol% of (Cr,Fe)2B borides, together with a few pores (porosity; 0.5%), were relatively homogeneously distributed in the tempered martensite matrix, which resulted in the very high hardness over 600 VHN. Such a high hardness suggested that the present Fe-based alloy powders could be readily adopted for fabricating PIM products or for replacing conventional stainless steel PIM products.

Annealing temperature effect on microstructure, magnetic and microwave properties of Fe-based amorphous alloy powders

Fe74Ni3Si13Cr6W4 amorphous alloy powders were annealed at different temperature (T) for 1.5h to fabricate the corresponding amorphous and nanocrystalline powders. The influences of T on the crystalline structure, morphology, magnetic and microwave electromagnetic properties of the resultant samples were investigated via X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and vector network analyzer. The results show that the powder samples obtained at T of 650°C or more are composed of lots of ultra-fine α-Fe(Si) grains embedded in an amorphous matrix. When T increases from 350 to 750°C, the saturated magnetization and coercivity of the as-annealed powder samples both increase monotonously whereas the relative real permittivity shows a minimal value and the relative real permeability shows a maximal value at T of 650°C. Thus the powder samples annealed at 650°C show optimal reflection loss under −10dB in the whole C-band. These results here suggest that the annealing heat treatment of Fe-based amorphous alloy is an effective approach to fabricate high performance microwave absorber with reasonable permittivity and large permeability simultaneously via adjusting T.

Microstructure and Hardness of TiC Particle-reinforced Fe Self-fluxing Alloy Powders Based Hybrid Composite Prepared by High Energy Ball Milling

The Fe-based self-fluxing alloy powders and TiC particles were ball-milled and subsequently compacted and sintered at various temperatures, resulting in the TiC particle-reinforced Fe self-fluxing alloy hybrid composite, and the microstructure and micro-hardness were investigated. The initial Fe-based self-fluxing alloy powders and TiC particles showed the spherical shape with a mean size of approximately 80 <TEX>${\mu}m$</TEX> and the irregular shape of less than 5 <TEX>${\mu}m$</TEX>, respectively. After ball-milling at 800 rpm for 5 h, the powder mixture of Fe-based self-fluxing alloy powders and TiC particles formed into the agglomerated powders with the size of approximately 10 <TEX>${\mu}m$</TEX> that was composed of the nanosized TiC particles and nano-sized alloy particles. The TiC particle-reinforced Fe-based self-fluxing alloy hybrid composite sintered at 1173 K revealed a much denser microstructure and higher micro-hardness than that sintered at 1073 K and 1273 K.