Fe2B Layers Research Articles

Investigating Growth of Iron Borides with the Formation of Monolithic Fe2B Layer on AISI 304 Stainless Steel via Cathodic Reduction and Thermal Diffusion-Based Boriding

Investigating Growth of Iron Borides with the Formation of Monolithic Fe2B Layer on AISI 304 Stainless Steel via Cathodic Reduction and Thermal Diffusion-Based Boriding

Simulation of the incubation time for the formation of (FeB/Fe2B) bilayer on pure iron

Abstract In this work, a mathematical model was used in order to study the growth kinetics of (Fe2B/FeB) bilayer during bori-ding process basing on the second Fick’s law and mass balance equation. The run of the numerical simulation allowed calculating the incubation time (τ) of each boronized layer (Fe2B or FeB), and estimating the effect of this parameter on the growth of the boronized layer. The boride incubation time for forming the FeB or Fe2B layer on the pure iron substrate was incorporated into the present mathematical model. To simulate the value of the growth rate constant and the incubation time for the bilayer configuration, the experimental data available in the literature concerning the boronizing of pure iron were considered. Based on the experimental and simulation results, it was shown that the incubation time decreases with increasing temperature in the FeB and Fe2B phases. It was concluded from this study that the thickness of each boride layer depended on its growth rate constant and on another parameter kτ which was the rate constant of incubation time.The obtained results confirmed the validity of the present mathematical model and gave a good estimate of the incubation time during the formation of each boride layer as well as formulated the variation of this parameter with a mathematical equation. Furthermore, the comparison of experimental data with the simulated results of boronized layer thickness allowed to validate the present model.

Simulation of boronizing kinetics of ASTM A36 steel with the alternative kinetic model and the integral method

Abstract In this study, two different mathematical models have been proposed for estimating the diffusivities of boron in the Fe2B layer on ASTM A36 steel in the range of 1173 to 1273 K with exposure times of 2 to 8 h. The boride incubation period required for the formation of such a layer was constant regardless of the boriding conditions. In both approaches, the boron diffusivity in the iron phase was considered in an unsaturated matrix. The first approach was derived from the mass balance equation at the (Fe2B/substrate) interface while the second approach employed the integral diffusion model. The calculated values of boron activation energies for ASTM A36 steel were found to be very comparable for the two approaches (161.65 and 160.96 and kJ mol-1). Afterwards, these values of activation energy were confronted with the results from the literature. Experimental validation of these two approaches has been done by comparing the experimental value of Fe2B layer thickness measured at 1123 K for 2.5 h with the simulated values. Finally, the predicted values of Fe2B layer thickness were in line with the experimental measurement.

Kinetic Analysis of Pack-Borided Gray Cast Iron

Abstract In this work, a gray cast iron containing copper of grade EN-GJL-250 was pack-borided within the temperature range of 800°C–1,000°C with treatment times of 2–6 h. According to the X-ray diffraction analysis, the Fe2B phase has been identified over the surface of this material and the boride layer has an average thickness between 20.8 ± 2.9 and 149.1 ± 10.2 µm. The morphological aspect of the Fe2B layer was investigated with a scanning electron microscope. The regression model based on the ANOVA analysis has been established to investigate the growth kinetics of boride layers on EN-GJL-250 gray cast iron. The boron activation energies in the EN-GJL-250 cast iron were estimated as 148.03 and 147.96 kJ mol−1 by the parabolic growth law and the mean diffusion coefficient method, respectively. Furthermore, the experimental Fe2B layers’ thicknesses were in accord with the predicted values given by the regression model and the MDC method.

Influence of the Boriding Process on the Properties and the Structure of the Steel S265 and the Steel X6CrNiTi18-10

In the performed experiment, changes in the microstructure of steels S265 and X6CrNiTi18-10 due to their chemical-thermal treatment by boriding were studied. The boriding process was performed in a Durborid boriding powder at 900 0C. During this process, surface layers of Fe-B borides were formed in both analyzed sorts of steels. The layers differed in their morphology and composition due to the different degree of alloying of the matrix of analyzed steels by additive elements. The formed Fe-B layers showed high adhesive and cohesive resistance in both materials. Due to changes in the micro-structure of S265 steel, especially due to significant coarsening of the original grain of its matrix, its resistance to tribological abrasion after the boriding process decreased. The opposite effect was ob-served for X6CrNiTi18-10 steels. As a result of boriding, both analyzed materials changed their corro-sion resistance.

Growth kinetics of the FeB/Fe2B boride layer on the surface of 4Cr5MoSiV1 steel: experiments and modelling

The boriding of 4Cr5MoSiV1 steel was performed in the temperature range of 860°C–980 °C to examine the influence of boriding conditions on the boride layers. The experimental results show the formation of FeB and Fe2B layers with the predominant saw-tooth morphology. The boride layer depth increases with increase the boriding temperature and time. Thick and compact boride layers could be obtained at temperatures higher than 900 °C. The growth kinetics of boride layers is characterized by a parabolic curve. FeB and Fe2B exhibit a hardness of 1600HV0.1 and 1300HV0.1, respectively, which is 4 and 3 times that of the substrate. A diffusion model, based on the boron concentration profiles of the surface layers and the parabolic growth law, was established to predict the growth kinetics of the boride layers including both the FeB and the Fe2B layer. A satisfactory agreement between the model and experimental results was obtained. The work thus provides an approach to investigate and to predict the boride layer growth of 4Cr5MoSiV1 steel in the boriding process.

Effect of the Boron Powder on Surface AISI W2 Steel: Experiments and Modelling

The effect of boron powder on surface AISI W2 steel and growth kinetic of the boride layer is studied. Boron powder mixture was used in the powder pack boriding; this process was carried out in the temperature range from 1173 to 1273 K with exposure times ranging from 2 to 8 h. The presence of boride was confirmed by optical microscopy, X‐ray diffraction, and the distribution of alloy elements in boride layers with energy‐dispersive spectrometry using scanning electron microscopy. A mathematical model of the growth kinetics of the single layer was proposed and boron diffusion coefficient was determined by mass balance equation. The morphology of Fe2B layer was smooth and boron activation energy in W2 steel was estimated as 187.696 kJ·mol−1. The kinetic model was validated with two experimental conditions, a contour diagram describing the evolution of Fe2B layer as a function of time and temperature parameters for industrial application.

Importance of trimethyl borate temperature used during gas boriding for microstructure, nanomechanical properties and residual stresses distribution on the cross-section of the produced layer

The aim of this work was to indicate the possibility of applying organic compounds as a boron source for gas boriding. In the present work the trimethyl borate was used as an organic boron source for gas boriding process. The process was carried out at 950 °C for 2 h in gaseous atmosphere composed of N2–H2–B(CH3O)3. The temperature of trimethyl borate influenced on its concentration in gas atmosphere. As a result, depending on B(CH3O)3 temperature of 20 °C or 50 °C, it was possible to arranging the two types of process: boriding and borocarburizing, respectively. In the case of gas boriding the single-phase Fe2B layer was produced. The high temperature of B(CH3O)3 caused release of free atoms of carbon, therefore there existed favorable conditions for carburizing. The produced borocarburized layer consisted of two zones: an outer Fe2B borided layer and an inner carburized zone. The thickness of boride layer was higher after boriding process than simultaneous borocarburizing process, 10.8 μm and 7.8 μm, respectively. Whereas, the depth of zone of carbon diffusion was equal ca. 400 μm. For nanomechanical properties, as well as, the residual stress distribution the nanoindentation tester Anton Paar NHT3 equipped with the Berkovich diamond tip under a maximum load of 10 mN was used. In both layers, the highest hardness HIT (7.8–17.9 GPa) and highest Young's modulus (222–368 GPa) were measured in Fe2B layer. However, the presence of thick zone of carbon diffusion was the reason for gradually decrease in hardness in the cross section of borocarburized layer. Moreover, the presence of carburized zone advantageous influenced on residual stresses distribution across the layer. The gradually changes of residual stresses from compressive to tensile were observed in the case of simultaneous gas borocarburized layer. Such a situation was more advantage than those obtained for gas borided layer.

Mean Diffusion Coefficient Method in Studying Armco Iron Boriding Kinetics

Activation energy of boron diffusion during pack boriding of armco iron with a constant incubation time for boride formation is estimated using a mean diffusion coefficient model. Experimental verification is accomplished for the model by boriding armco iron at 1253 K for 5 h. Good correspondence is obtained between experimental and calculated Fe2B layer thicknesses.

Duplex surface treatment on microalloy steels by dehydrated paste pack boriding and pack carburizing

In this work, a novel duplex surface treatment is carried out on API X60 microalloy steels by boronizing and carburizing. Firstly, the dehydrated paste pack boriding (DPPB) on microalloy steels was carried out at a temperature of 1273 K for 8 h of exposure time. Then, the pack carburizing (PC) was conducted on borided steels at 1173 K temperature for four different exposure times. The layers formed by DPBP and DPBP+PC, were caracterized by X-ray difrraction, scanning electron microscopy, and energy dispersive spectroscopy. The results show that DPBP+PC promotes the formation of coatings outermost cementite layer with a range of depth (15.30–45.34 µm) over the boride layer. Hardness and Young's modulus of DPPB+PC were measured using the nanoindenter with a Berkovich diamond tip under load of 100mN. The higher average indentation hardness (HIT=1.53±0.25 GPa) and Young's modulus (EIT=212.70±2.4 GPa) were characteristic of carburized layer as well as Fe2B layer was characterized by HIT=20.56±0.80 GPa, and EIT=300.9±15.57 GPa, these parameters have an important influence on wear resistance to improve the performance in practical applications.

Modeling of the Kinetics of Boron Diffusion in Dehydrated Paste Pack-Borided AISI M2 Steel Based on Two Mathematical Approaches

Abstract In this work, two mathematical approaches were used in order to determine the values of activation energies in the iron monoboride (FeB) and diiron boride (Fe2B) layers on AISI M2 steel. The required experimental data about the boriding kinetics of AISI M2 steel were taken from the literature to estimate the values of boron diffusion coefficients in the FeB and Fe2B layers in the range of 1,173 K to 1,273 K produced by the dehydrated paste pack-boriding. The first approach was based on the integral method, whereas the second approach employed the Dybkov model. The estimated values of activation energies for boron diffusion in the FeB and Fe2B layers were in the range of 232.77–246.86 kJ mol−1 and 218.58–231.29 kJ mol−1, respectively. Finally, the experimental thicknesses of FeB and (FeB + Fe2B) layers obtained for 1, 3, 5, and 7 h at 1,173, 1,223, and 1,273 K were compared with the predicted thicknesses by using these two approaches. A good concordance was achieved between the experimental data and the simulated results.

Recycling of the Powder-pack Boriding Mixture: Microstructural Characterization of Fe2B Layers on ASTM A36 Steel

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Wear resistance of diffusion annealed borided AISI 1018 steel

Boriding improves the mechanical and chemical properties of steels. However, the discontinuity of mechanical properties at the FeB-Fe2B interphase can induce shear failure. As a solution, post-boriding treatments to dissolve the FeB layer are applied.In this study, new results on the wear behavior of AISI 1018 steel exposed to powder-pack boriding process (PPBP) and to the diffusion annealing process (DAP), which were evaluated through ball-on-flat linear reciprocating wear tests under different sliding distances are presented. Vickers microhardness characterization was also performed. After DAP a change from tensile to compressive residual stresses at the surface of the material was found, as well as a two-fold increase in wear and fracture resistance. Failure mechanisms on the surface of the wear tracks, for both treatment conditions, were mainly grooving and adhered material as observed by scanning electron microscopy.

Spin-orbit torque generated from perpendicularly magnetized Co/Ni multilayers

We report the existence of a spin-orbit torque generated from charge to spin conversion in perpendicularly magnetized ferromagnetic material through spin-torque ferromagnetic resonance (ST-FMR) measurement. We fabricated a trilayer structure consisting of a Cu spacer layer sandwiched between an in-plane magnetized FeB layer and perpendicularly magnetized Co/Ni multilayers. From the ferromagnetic resonance under DC bias current application, we observed a significant linewidth modulation in the FeB layer attributed to the charge to spin conversion generated from Co/Ni multilayers. In-plane angular dependence and the magnetization polarity dependence of the linewidth modulation reveal that two types of charge to spin conversion with different symmetry coexist in the single Co/Ni multilayers.

Simulation of Boriding Kinetics of AISI D2 Steel using Two Different Approaches

Diffusion of boron in FeB and Fe2B layers under solid boriding of steel AISI D2 (the Russian counterpart is Kh12MF) is simulated. Two approaches are used to assess the diffusion coefficients in solid-phase boriding, i.e., the concept of the mean value of diffusion coefficient in the FeB – Fe2B system and consideration of the growth kinetics of each of the two boride layers with the use of a system of conventional differential equations describing the partial chemical reactions by a parabolic law (the Dybkov method). The activation energies of boron diffusion in the FeB and Fe2B layers of steel AISI D2 are computed. The condition of extreme boriding is used to verify the two approaches experimentally. Comparative analysis of the computed and published data shows their good agreement.

Structure and properties of a boronized crankshaft coating

In this study, the boronizing method was applied to a crankshaft of a diesel engine, and exposed to bending and torsional stress and pressure, and the material characterization was examined. The boronizing method was applied to the crankshaft at 950 °C for 4 hours. Optical microscope, microhardness, SEM, EDAX, XRD, wear, TGA and corrosion analyses were performed to determine the material characterization. According to the results obtained, the optical and SEM images showed the presence of FeB and Fe2B layers, and EDAX and XRD analyses showed the presence of boron and its compounds. A 6.7-fold increase in hardness was observed in the microhardness analysis and 4-fold wear resistance was observed in the wear analysis. Resistance of 85 % was observed in the corrosion analysis and oxidation delay of 300 °C were observed in the TGA test. After wear analysis, SEM and XRD analyses were performed and the surfaces were examined.

Growth kinetics of Fe2B layers formed on the AISI 4150 steel by different approaches

In the present work, the AISI 4150 steel has been pack-borided in the temperature range of 1123-1273 K for a treatmenttime of 2 to 8 h. The mixture of powders containing 20% B4C, 10% KBF4 and 70% SiC has been used for producing a singleboride layer (Fe2B) at the surface of AISI 4150 steel. The presence of Fe2B phase has been confirmed by XRD analysis.The SEM observations have been done to investigate the morphology of boride layers and measure their thicknesses.The cohesion of boride layers has been evaluated by using the Daimler-Benz Rockwell-C indentation technique.The borided sample at 1173 K for 8 h has shown a best cohesion of boride layer to the substrate in comparison to the sampletreated at 1173 K during 2 h. Kinetically, different approaches have been used to estimate the boron diffusion coefficients inthe Fe2B layers and to predict the value of Fe2B layer thickness obtained at 1253 K for a treatment time of 2.5 h. Theestimated values of activation energies for boron diffusion in AISI 4150 steel have been in the range of 193.45 to 199.74 kJmol-1. These values of activation energies have been depended on the diffusion models used. In addition, a good agreementhas been observed between the experimental value of Fe2B layer thickness obtained at 1253 K for 2.5 h with the predictedvalues from these different diffusion models.

Application of integral method for investigating the boriding kinetics of AISI 316 steel

The present work is dealing with the modelling of boriding kinetics of AISI 316 steel in the temperature range 1123–1273 K. A diffusion model based on the integral method was used in order to investigate the kinetics of formation of FeB and Fe2B layers and that of diffusion zone formed on AISI 316 steel by considering the presence of boride incubation times. By using a particular solution of the resulting differential algebraic system, the diffusion coefficients in FeB, Fe2B and diffusion zone (DZ) were estimated as well as the corresponding values of activation energies. Finally, this present diffusion model has been experimentally validated for two additional boriding conditions (1243 K for 3 and 5 h of treatment). A good concordance was observed between the experimental and the simulated results in terms of layers’ thicknesses.

Evaluating the mechanical behavior of electrochemically borided low-carbon steel

In this study, mechanical properties of borided low carbon steels were investigated with different testing methods namely tensile, Erichsen cupping and three-point bending tests along with fracture toughness and hardness measurements. For boriding, a new electrochemical based boriding called as CRTD-Bor (Cathodic Reduction and Thermal Diffusion based boriding) was chosen. The main advantages of CRTD-Bor are its high boride growth rate and its environmentally friendly nature. Cross-sectional scanning electron microscope inspections along with thin film X-ray diffraction analyses confirmed the fast boride layer formations (i.e. about 40 μm thick Fe2B layer in 5 min). On the other hand, some mechanical degradations were observed on the borided substrates such as decrease in yield and ultimate strength values. However, the improvement of flexural stress were detected which reached to 2.5 times higher after 30 min of boriding. The fracture toughness values were found as 0.44 MPa·m1/2, 1.34 MPa·m1/2 and 3.7 MPa·m1/2 for sole FeB, the interphase of FeB/Fe2B and Fe2B regions, respectively. Furthermore, the surface hardness of borided steels was measured around 1400 HV which exhibited excellent adhesion to the substrate as long as the boride layer composed of single Fe2B.

Modeling of the Growth Kinetics of Boride Layers in Powder-Pack Borided ASTM A36 Steel Based on Two Different Approaches

An indispensable tool to choose the suitable process parameters for obtaining boride layer of an adequate thickness is the modeling of the boriding kinetics. In this work, two mathematical approaches were used in order to determine the value of activation energy in the Fe2B layers on ASTM A36 steel during the iron powder-pack boriding in the temperature range of 1123–1273 K for treatment times between 2 and 8 h. The first approach was based on the mass balance equation at the interface (Fe2B/substrate) and the solution of Fick’s second law under steady state (without time dependent). The second approach was based on the same mathematical principles as the first approach for one-dimensional analysis under non-steady-state condition. The measurements of the thickness (Fe2B), for different temperatures of boriding, were used for calculations. As a result, the boron activation energy for the ASTM A36 steel was estimated as 161 kJ·mol−1. This value of energy was compared between both models and with other literature data. The Fe2B layers grown on ASTM A36 steel were characterized by use of the following experimental techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray Spectroscopy (EDS). Finally, the experimental value of Fe2B layer’s thickness obtained at 1123 K with an exposure time of 2.5 h was compared with the predicted thicknesses by using these two approaches. A good concordance was achieved between the experimental data and the simulated results.