Fe2B Phase Research Articles

Microstructure and Wear Resistance of FeCrBSi Plasma-Sprayed Coating Remelted by Gas Tungsten Arc Welding Process

Herein, an FeCrBSi coating was fabricated via plasma spray on AISI1045 steel, and subsequently, a gas tungsten arc welding (GTA) process was employed to remelt the coating. The microstructure, microhardness, fracture toughness and surface roughness of the coating before and after remelting were investigated, as well as the wear resistance was tested by a UMT-3-type sliding wear apparatus. The results showed that, upon remelting, most defects in the as-sprayed coating were effectively eliminated, the surface roughness decreased by 43%, and the coating–substrate interface bonding changed from mechanical to metallurgical. The phase composition of the as-sprayed coating was primarily α-Fe and a small amount of hard Fe3B phase, while the remelted coating consisted of α-Fe and (Fe,Cr)23C6 and a small quantity of CrB. In addition, remelting the coating was found to induce a 287.6% increase in the fracture toughness, a 33.4% increase in the average microhardness, and a 47.5% decrease in the wear volume, while the failure mechanism changed from abrasive wear to fatigue wear upon remelting. Therefore, GTA remelting of plasma-sprayed coating was found to be a feasible method to obtain a coating with good wear resistance.

Structural, magnetic and mechanical properties of Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 nanocrystalline hard magnet

Microstructural, magnetic and mechanical properties of Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 nanocrystalline hard magnets produced by rapid solidification technique and subsequent thermo-magnetic annealing have been investigated in this study. X-ray diffraction analysis revealed that the as-cast Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 magnet has 60% Nd2Fe14B, 16% α-Fe, 9% Fe3B and 15% amorphous phases, whereby, Nd2Fe14B being the majority phase. Thermomagnetic annealing induces a complete crystallization of Nd2Fe14B, α-Fe, Fe3B and amorphous phases and establishes ideal volume fractions between phases leading to improvement in magnetic properties. Scanning and transmission electron microscopy show nano-scaled hard Nd2Fe14B grains surrounded with soft α-Fe and Fe3B grains. The Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 magnet annealed at 993 K for 15 min shows values of coercivity iHc, remanence Br and maximum energy product (BH)max up to 861 kA/m, 0.68 T and 81.9 kJ/m3, respectively. Compressional stress strain measurements elucidated that mechanical properties of alloys are affected by the morphology of phases as well as crystal structure. As-cast Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 magnet demonstrates the hardness (Hv) of 960 ± 20 and compressive stress (σf) of 1270 ± 10 MPa, which tend to decrease by thermo-magnetic annealing process.

Enhancement of hardness, modulus and fracture toughness of the tetragonal (Fe,Cr)2B and orthorhombic (Cr,Fe)2B phases with addition of Cr

This study analyzes the influence of Cr content on hardness H, elastic modulus E and fracture toughness KIC of the M2B boride by means of nanoindentation experiments. Additionally, properties of the Fe3(C,B) phase are determined. Samples of the M2B phase are casted and microstructurally characterized by means of scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. At a Cr content higher than 14.7 atom% the M2B phase transforms from tetragonal into orthorhombic structure. The tetragonal M2B type possesses an optimum of H (21 ± 1 GPa), E (373 ± 6) GPa and KIC (3.5 ± 0.7 MPam) at 4–5 atom% Cr. The hardness, modulus and toughness of the orthorhombic M2B phase increase with Cr content and reach values of H = 27 ± 0.7 GPa, E = 473 ± 9 of and KIC = 3.26 ± 0.8 MPam at maximal investigated Cr content of 55 atom%. The hardness of the M2B phases decreases around 2.3–3.2 GPa as a function of indentation depth, which is known as the indentation size effect. Hardness and fracture toughness of M2B phase outperform conventionally used M7C3 carbides and are similar to MC-carbides. Findings can be used in novel alloying approaches in order to optimize the performance and reduce cost of tool steels.

Effect of the Boron Content on the Amorphization Process and Magnetic Properties of the Mechanically Alloyed Fe92−xNb8Bx Powders

The effect of the B content on the microstructural, structural, and magnetic properties of partially amorphous Fe92−xNb8Bx (x = 5, 10, 15, and 20) alloys has been investigated by means of scanning electron microscopy, X-ray diffraction, high and low-temperature extraction-type magnetometers. The XRD results reveal the formation of a nanocomposite structure where nanocrystalline bcc α-Fe and Fe2B phases are embedded into an amorphous matrix. The FeB boride is observed for higher boron contents (x = 15 and 20), and the crystallite sizes are in the range of 7–24 nm. As the B content increases, the amorphous phase-relative proportion and coercivity increase, whereas the saturation magnetization decreases. An important magnetic hardening occurs by lowering the temperature from 400 to 5 K for x = 20% B. The variation of the Curie temperature can be attributed to the heterogeneity of the amorphous matrix.

Annealing Effects on Microstructure and Magnetic Properties of (NdPr)9.5(FeNbCoCu)79.5(BC)11 Nanocomposite Magnets

Annealing effects on microstructure and magnetic properties of (NdPr)9.5(FeNbCo)79.5(BC)11 ribbons were investigated. It was observed that Nd2Fe14B and Fe3B phases were directly formed at low spinning speed. Then, the alloys transformed to an amorphous state at a speed of 20 m/s. Annealed at 700 ∘C for 10 min, the amorphous alloys as-quenched at 20 m/s crystallized into a nanocomposite composed of Nd2Fe14B and $\alpha $ -Fe phases. The formation of Fe3B phases was inhibited. The magnetic properties firstly increased and then decreased with the increasing of annealing time. The optimum magnetic properties were achieved in the alloys annealed at 700 ∘C for 10 min. The corresponding coercivity, remanence, and the maximum energy product was 427.5 kA/m, 0.94 T, and 101.2 kJ/m3, respectively. In addition, fine and uniform grains were formed. The average grain size was 10 nm.

Effects of temperature and atmosphere on microstructure and tribological properties of plasma sprayed FeCrBSi coatings

FeCrBSi coatings were deposited using an atmospheric plasma spray (APS) technique. The coated specimens were heat-treated at temperatures varying from 300 to 700 °C for 1 hour in air or nitrogen atmospheres. Effects of heat treatment on microstructures, phase compositions, hardness and tribological performance of the coatings were investigated. It was discovered that depending on the temperature and atmosphere, the heat treatment led to intersplat oxidation and caused recrystallization of the coatings. The as-sprayed FeCrBSi coating was mainly consisted of α (Fe, Cr) solid solution phases, while Cr7C3 and Fe3B phases gradually precipitated especially at high temperature, resulting in significantly enhanced hardness. In comparison to the as-sprayed coatings, the coatings heat-treated in nitrogen atmosphere showed lower friction coefficients. With increasing the treatment temperature, the wear resistance exhibited decrease first and then increase. Worn surface analyses suggested that the wear failure was governed by abrasion wear and intersplat debonding of the coatings. Thus, hardness increment and intersplat oxidation became competing factors influencing the wear resistance. When compared to the coatings heat-treated in air, the coatings heat-treated in nitrogen exhibited a significantly higher wear resistance due to the prevention of intersplat oxidation.

The effect of temperature and time on microstructure and friction performance of RE-borosulphurizing composite coatings

In this study, 45 carbon steel was RE(rare earth)-borosulphurized at 850 °C, 900 °C, and 950 °C for four different periods of time: 3, 5, 7 and 9 h. The microstructure examination and thickness measure of the diffusion layers were carried out by metallographic microscope and Scanning Electron Microscope (SEM). X-ray diffraction (XRD) was used to characterize the phase composition of the coatings. A ring-on-block wear tester was employed to measure the coatings friction coefficients. The results revealed a saw-tooth shaped and compact morphology of the RE-borosulphurizing layers (RBSL). The coatings thickness was found to increase with the increase of temperature and time. The maximum and the minimum values of the coating thickness were determined to be 98 μm and 32 μm, respectively. The minimum value of the FeB phase thickness was about 7.23 μm. The lowest friction coefficient value was 0.212 which occurred at 850 °C with a 10 N applied load and the maximum friction coefficient value was 0.571 which occurred at 850 °C with a 100 N applied load. The activation energy of RBSL was determined to be 138.6 kJ mol−1 using Arrhenius approach, which is lower than those of other boronizing processes.

Effect of the Laser Scan Rate on the Microstructure, Magnetic Properties, and Microhardness of Selective Laser-Melted FeSiB

FeSiB alloys have been fabricated by selective laser melting (SLM) using a laser scan rate of 0.1–1.5 m/s, laser power of 90 W, scan line spacing of 40 μ m, and layer thickness of 50 μ m. X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, profilometer, microdurometer, and vibrating sample magnetometer have been used to investigate the structural, microstructural, roughness, microhardness, and magnetic property changes during the laser melting process. The produced samples exhibit a nanocomposite structure consisting of nanocrystalline α-Fe0.95Si0.05 and Fe2B phases embedded into an amorphous e-FeSi-type matrix. The selective laser-melted samples show high density, low surface roughness, higher microhardness values (1654–2273 Hv), and soft magnetic properties (Ms = 188.6–199 emu/g and Hc = 43.8–73 Oe).

Improvement in Endurance of Conveyor Hauling Chain Components Made of Structural Steels by Electrolytic Boriding

Results are given for a study of electrolytic boriding of components made of different grades of steel (steels 20, 40Kh, and 50), and boriding technology, results of metallographic and x-ray structural analyses, and a study of the quantitative change in FeB and Fe2B phases through the depth of a diffusion layer is provided. Comparative results of research show the operating properties after various forms of chemical heat treatment and heat treatment.

A Kinetic Model for the Boriding Kinetics of AISI D2 Steel During the Diffusion Annealing Process

In this work, a diffusion model was proposed to estimate the boron activation energies for FeB and Fe2B layers during the pack-boriding of AISI D2 steel at temperatures of 1223, 1253 and 1273 K for a treatment time varying between 2 and 10 h. This model considers the effect of boride incubation times during the formation of the FeB and Fe2B phases. To study the influence of diffusion annealing process on the boriding kinetics of AISI D2 steel, the mass balance equations were modified in order to follow the evolution of boride layers as a function of annealing time for the specified boriding parameters. Finally, the kinetic model was validated by a comparison of the experimental thicknesses of boride layers with the predicted ones at a temperature of 1243 K for 2, 4 and 6 h. A simple equation was then obtained for estimating the total time necessary to get a single boride layer (Fe2B) that depends on the boriding parameters and on the thickness of each boride layer prior to the diffusion annealing process.

A new preparation method of Fe2B: Generating rodlike/scale-like Fe2B by dealloying Fe78Si9B13 atomized particle

Chemical dealloying is currently studied to produce nanoporous structure suited for use in battery, catalysis, sensors and other electrochemical applications. Moreover, experimental values on mechanical properties or stability of the Fe2B are limited since it is very difficult to extract Fe2B from bulk casting irons or to investigate an effective method to prepare Fe2B sample. Here, we have prepared rodlike/scale-like Fe2B by dealloying Fe78Si9B13 atomized particle during which the Fe and FeSi phases are etched away, leaving Fe2B phase. The morphology of Fe2B can be controlled from rod-like to scale-like, amplifying the applied fields of iron borides on the surface of parts and components. The magnetic property (saturation magnetization, remanence and coercivity) evolution of Fe78Si9B13 during chemical dealloying is also investigated.

Glass formation and soft magnetic properties of novel Fe-rich Fe-B-Ti-Zr bulk metallic glasses

Composition design is an important issue concerning the development of bulk metallic glasses (BMGs), especially applicable Fe-based bulk metallic glasses (BMGs). In this work, new quaternary Fe77B18TixZr5-x (x = 1–4) BMGs were developed by promoting metastable transformation in solidification process. Their glass formation, thermal and soft magnetic properties have been investigated. Thermal analysis proves that the combined additions of Ti and Zr in the alloys have significant advantage in improving the glass forming ability (GFA). However, the alloy with best GFA does not show the optimal thermal performance, and such inconformity in MGs was usually neglected previously. We further explain the origin of the improvement in GFA and the inconformity between GFA and thermal properties by investigating the phase evolution of the crystalline alloys. Proper combined additions of Ti and Zr can promote the precipitation of metastable Fe23B6 phase, which is advantageous to GFA as the diverse crystallization pathways reflect different crystallization resistances in solidification. Owing to the high Fe content, the amorphous ribbons exhibit high saturation induction of over 1.3 T.

Kinetics and mechanical properties of borided GCr15 bearing steel

The kinetics and mechanical properties of borided GCr15 bearing steel was investigated. The boriding treatment was carried out in a solid medium at 1123, 1173, 1223, and 1323 K for 2, 4, 6, and 8 h. The microstructures and mechanical properties of the boride layer were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, and Vickers hardness tester, and the growth kinetics characteristics were also studied based on experimental data. The results indicate that the boride layer has a smooth and compact morphology, and the presence of FeB and Fe2B on the steel substrate is confirmed by X-ray diffraction analysis. The thickness and hardness of the boride layer increase with treatment time and temperature, where the thickness ranges from 33.4 to 318.5 μm. The increased hardness is mainly because of the increase in the highly hard FeB phase content. The content of Fe2B phase, which has a low hardness, decreases with an increase of layer thickness. The hardness of the boride layer HV0.1 ranges within 1630-1950, and it is increased by 5 to 6 times compared with the matrix. The hardness test results of the boride layer cross section indicate that there is a wide transition of hardness gradient between the boride layer and the matrix. The kinetic equation based on the experimental data and Arrhenius equation was investigated, the active energy of B element in the GCr15 bearing steel is 188.595 kJ·mol-1, and the derived kinetic equation is verified by experiments. The results indicate that the maximum error between the theoretical derivation and experimental derivation is 4.93%. Therefore, the derived kinetic equation can effectively predict the thickness of the boride layer on GCr15 bearing steel.

Non-isothermal crystallization kinetics and soft magnetic properties of the Fe67Nb5B28 metallic glasses

Differential scanning calorimetry (DSC) was used to investigate the thermal behavior and non-isothermal crystallization kinetics of the Fe67Nb5B28 metallic glasses prepared by melt-spinning method. DSC traces exhibit that the crystallization takes place through a single exothermic reaction, and it processes a good thermal stability in thermodynamics. The activation energies for nucleation and grain growth processes were calculated to be 536 ± 22 and 559 ± 20 kJ mol−1 by Kissinger equation, respectively, and 551 ± 24 and 574 ± 20 kJ mol−1 by Ozawa equation, respectively. It means that the grain growth process is more difficult than the nucleation process. The variation of local Avrami exponent n(x) with crystallized fraction x demonstrates that the crystallization mechanism varies at different stages. The n(x) is larger than 2.5 at the initial stage of 0 < x < 0.3, implying a mechanism of diffusion-controlled three-dimensional growth with increasing nucleation rate. The n(x) decreases from 2.5 to 1.5 in the range of 0.3 < x < 0.65, suggesting that the crystallization belongs to three-dimensional nucleation and grain growth with decreasing nucleation rate. And n(x) lies between 1.0 and 1.5 in the range of 0.65 < x < 0.95, indicating that the crystallization corresponds to the growth of particles with an appreciable initial volume. Low-temperature annealing corresponds to the precipitation of α-Fe, Fe2B, and Fe23B6 phases, and further annealing leads to the formation of α-Fe, Fe2B, and FeNbB phases. The magnetic properties in relation to microstructure change of the Fe67Nb5B28 metallic glasses are discussed.

Interfacial morphology and corrosion-wear behavior of cast Fe-3.5 wt.% B steel in liquid zinc

The corrosion-wear behavior of Fe-3.5wt.%B steel in liquid zinc was investigated via the block-against-ring technique. Owing to the protective ability of the Fe2B phase, this steel exhibited better corrosion-wear resistance than a 316L stainless steel. SEM, XRD, and EDS of the corrosion-wear interface indicated that the corrosion-wear process of Fe-3.5wt.%B steel consists of the following steps: corrosion of the matrix, fragmentation and removal of FeZn13, and failure of the Fe2B. The intensified mechanical effect of wear resulted in significant deterioration (via fracture and removal of FeZn13, and spallation Fe2B) of corrosion-wear interface, which exacerbated corrosion, and facilitated the corrosion-wear process.

Effect of Hf addition on the glass forming ability, thermal and magnetic properties in the (Fe86B13Cu1)100 − xHfx alloys

In this study, the effect of Hf addition on the glass formation ability (GFA), micro structural, thermal and magnetic properties were investigated in the Fe-B-Cu alloy with high saturation magnetization (Ms). It is found that the addition of Hf is beneficial for improving GFA of (Fe86B13Cu1)100−xHfx Alloys. The melt-spun ribbons at x=0.75 and x=1.0 show an entirely amorphous structure by x-ray diffraction and have two obvious separated exothermic peaks on DSC curves, Hf element plays a positive role on postponing the first crystallization and improved the thermal stability of the amorphous Fe-B-Cu-Hf alloys. As x=0.75, the melt-spun ribbon has a higher apparent activation energy of Fe3B phase than of the ribbon at x=1.0, and the first crystallization is easier than the second crystallization. Therefore it was easy to obtain an α-Fe/amorphous dual phases structure alloy ribbons with few or without Fe3B phase by a suitable annealing process near peak temperature of the first crystallization. After annealing, the saturation magnetization (Ms) was tested by vibrating sample magnetometer, and the value of x=0.75 changes slightly first, then increase obviously and reach the maximum 220emu/g at 750K higher Tp2. This alloy shows a good glass forming ability and a high saturation magnetization.

Effect of Boride Incubation Time During the Formation of Fe2B Phase

Our present study focuses on the numerical simulation of the boronized layer growth kinetics on the iron substrate of the XC38 steel, the boronizing treatment is performed in a liquid medium composed of borax and silicon carbide. We mainly calculated the incubation time of the boronized layer formation. Aimed at estimating the boronizing treatment kinetics of XC38 steel, we initially used experimental data. The study was conducted to determine the law of borided layers growth and estimate the boron diffusion coefficient in the Fe2B layer. The diffusion coefficient obtained from this experiment is: D Fe 2 B = 1 . 388 × 10 − 4 exp − 207 . 8 × 10 3 j RT m 2 s − 1 In order to calculate the incubation time of the Fe2B layer, we adapted the mathematical model, which is based on the second law of Fick. This model takes into account the thermodynamic properties of the Fe-B phase diagram. The comparison of the results obtained by the simulation with those obtained experimentally verifies the validity of the theoretical study and a good agreement was obtained as well.

Metallic Glass Formation Upon Rapid Solidification of Fe60Cr8Nb8B24 (at%) Alloy through LASER Cladding and Remelting

Fe60Cr8Nb8B24 (at%) amorphous powder and ingot were submitted to LASER cladding and remelting process, respectively. Fe-based coatings were produced using different LASER processing parameters and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vickers microhardness. All coatings obtained by LASER cladding (LC) and layers obtained by LASER surface remelting (LSR) with shorter and median interaction times (scanning speeds of 16.7 and 66.7mm/s), irrespective of overlap value, presented peaks of the crystalline phases α-Fe, Fe2B and the FeNbB intermetallic. In addition, layers obtained by LSR with shorter interaction time (150mm/s), in general, presented only peaks of the α-Fe and Fe2B phases, except that produced with overlap value of 20%, more amorphous. SEM results showed that, regardless of LASER process, the coatings presented cracks, some pores and FeNbB intermetallic phase. All coatings obtained by LC and that obtained with shorter interaction time, by LSR, showed a Vickers microhardness, 1086 to 1329HV and 2161 to 2294HV, respectively, significantly higher than the substrates, AISI steel: 170HV and Fe-Cr-Nb-B: 1921HV.

Hardness and modulus of Fe2B, Fe3(C,B), and Fe23(C,B)6 borides and carboborides in the Fe-C-B system

This work provides a comparative and comprehensive study of the indentation hardness and indentation modulus of iron-rich borides and carboborides of types Fe2B, Fe3(C,B), and Fe23(C,B)6. In addition, the hardness and elastic modulus of Cr-rich M7C are investigated for comparative purposes. We investigated the impact of increasing B content and indentation size effect (ISE). The phases of interest were stabilized in cast Fe-C-B alloys that varied with respect to the B/(B+C) ratio and heat treatment. The resulting microstructures were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and wavelength X-ray spectroscopy (WDS). Dynamic in-situ nanoindentation experiments based on the method of continuous stiffness measurement (CSM) were coupled to SEM and EBSD investigations to determine the mechanical properties of the individual borides and carboborides as a function of the indentation depth. The results were compared to values obtained for the Cr-rich M7C3 carbide. It was found that the hardness of the B-rich Fe3(C,B) phase is considerably higher than pure Fe3C and increases with increasing B content. The ISE was present in all investigated phases, and the hardness decreased as a function of indentation depth. The hardness at infinite indentation depth H0 was estimated according to the model of Nix and Gao. The Fe2B phase was found to be the hardest phase (H0=19.04GPa), followed by M7C3 (H0=16.43GPa), Fe3(C,B) (H0=11.18 to 12.24GPa), and Fe23(C,B)6 (H0=10.39GPa).

Study on the erosion characteristics of boride coatings by finite element analysis

In this paper, tensile stress distribution in the surface of high-parameter steam turbine blade anti-erosion boride coatings under single particle impact was investigated using a nonlinear finite element software ABAQUS/explicit based on the actual erosion environment in power units. The results showed that the single Fe2B phase coating hardly had stable anti-erosion capability when the coating thickness was less than 20μm under the continuous impacts. For the bilayer boride coating composed of top phase FeB and bottom phase Fe2B, the whole coating began to show the stable anti-erosion performance with top FeB phase coating thickness of 120μm from the standpoint of maximum surface tensile stress reduction. Anti-erosion performance of single Fe2B phase boride coating was 23.15% higher than the bilayer boride coating. Besides, the optimum parameters configurations for boride coatings were studied.