Fe2B Layers Research Articles

Kinetic Investigation and Wear Properties of Fe2B Layers on AISI 12L14 Steel

In the current study, the powder-pack boriding was applied to the AISI 12L14 steel in the temperature range 1123 K to 1273 K for an exposure time between 2 and 8 hours. The produced boride layer was composed of Fe2B with a sawtooth morphology. A diffusion model based on the integral method was applied to investigate the growth kinetics of Fe2B layers. As a main result, the boron diffusion coefficients in Fe2B were estimated by considering the principle of mass balance at the (Fe2B/substrate) interface with an inclusion of boride incubation times. The value of activation energy for boron diffusion in AISI 12L14 steel was estimated as 165 kJ mol−1 and compared with other values of activation energy found in the literature. An experimental validation of the present model was made by using four different boriding conditions. Furthermore, the Rockwell-C adhesion test was employed to assess the cohesion of boride layers to the base metal. The scratch and pin-on-disc tests were also carried out to analyze the effect of boriding on wear behavior of AISI 12L14 steel.

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.

Growth of the Fe2B layer on SAE 1020 steel employed a boron source of H3BO3 during the powder-pack boriding method

In this study, an alternative powder-pack boriding mixture containing H3BO3 as boron source was prepared and used for boriding of SAE 1020 steel. The boriding treatment was carried out in the temperature range of 850–950 °C for a treatment time ranging from 4 to 12 h. The generated boride layers were characterized by different experimental techniques such as optical microscope, SEM, XRD analysis and the Daimler-Benz Rockwell C indentation test. The powder-pack boriding mixture was analyzed by TGA and DTA methods and the possible chemical reactions that may be occurred during boriding were investigated. Furthermore, the growth kinetics of the boride layer forming on SAE 1020 steel substrates was investigated. A regression model based on a full factorial design was used to estimate the boride layers' thicknesses as a function of the boriding parameters. A single phase boride layer with saw-tooth morphology was formed on the steel samples. The value of boron activation energy for SAE 1020 steel was estimated as 183.15 kJ/mol. The comparisons were made between the empirical values of the boride layers' thicknesses with estimated ones. The contour diagrams were plotted for estimating the thickness of boride layer as a function of the temperature and time.

Fracture Toughness of Thick Boride Layers Estimated by the Cross-Sectioned Scratch Test

New results about the fracture toughness (Kc) of thick boride layers estimated by the cross-sectioned scratch test are presented in this study. The FeB-Fe2B layers developed at the surface of borided AISI 1018 and AISI 1045 steels and the Fe2B layer formed on the borided AISI 1045 steel exposed to a diffusion annealing process (DAP) were used for this purpose. The cross-sectioned scratch tests were performed with a Vickers diamond stylus drawn across the thick boride layer under a constant load to produce a half-cone-shaped fracture near to the top surface of the borided steels. The height of the half-cone-shaped fracture as a function of the cross-sectioned scratch loads was used to determine the fracture toughness of the FeB and Fe2B layers. The results showed a fracture resistance of $$\sim2.8\,{\text{MPa}}\sqrt m$$ for the FeB layer formed at the surface of borided AISI 1045 steel. Likewise, the effect of the DAP on the surface of the borided AISI 1045 steel promoted the formation of an exclusively Fe2B layer, with an increase in the fracture toughness of the whole boride layer around $$5\,{\text{MPa}}\sqrt m$$ . Finally, the principle of the technique can be used to minimize the influence of the anisotropic properties on the fracture toughness along the depth of boride layers.

Analysis of the growth kinetics of Fe2B layers by the integral method

In this study, an alternative approach based on the integral method was proposed to estimate the values of boron diffusion coefficients in the Fe2B layers grown at the surface of Armco iron. The set of differential algebraic equations (DAE) system was obtained to estimate the value of activation energy for boron diffusion when pack-boriding of Armco iron in the range of 1123 to 1273 K taking into account the boride incubation time. The present model has been validated by making a comparison between the experimental value of Fe2B layer thickness obtained at 1253 K for 5 h and the predicted results by using two different approaches. A good agreement was observed between these two set of data.

A fuzzy neural network approach for modeling the growth kinetics of FeB and Fe2B layers during the boronizing process

In this paper, we develop a boronizing process simulation model based on fuzzy neural network (FNN) approach for estimating the thickness of the FeB and Fe2B layers. The model represents a synthesis of two artificial intelligence techniques; the fuzzy logic and the neural network. Characteristics of the fuzzy neural network approach for the modelling of boronizing process are presented in this study. In order to validate the results of our calculation model, we have used the learning base of experimental data of the powder-pack boronizing of Fe-15Cr alloy in the temperature range from 800 to 1050 °C and for a treatment time ranging from 0.5 to 12 h. The obtained results show that it is possible to estimate the influence of different process parameters. Comparing the results obtained by the artificial neural network to experimental data, the average error generated from the fuzzy neural network was 3% for the FeB layer and 3.5% for the Fe2B layer. The results obtained from the fuzzy neural network approach are in agreement with the experimental data. Finally, the utilization of fuzzy neural network approach is well adapted for the boronizing kinetics of Fe-15Cr alloy.

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.

Nanomechanical characterization and fracture toughness of FeB and Fe2B iron borides produced by gas boriding of Armco iron

FeB and Fe2B hard ceramic phases were produced in Armco iron using gas-boriding in N2–H2–BCl3 atmosphere. This process was carried out at 920°C (1193K) for 3h and caused acceleration in the diffusion of boron into the surface of a base material in comparison with other acceptable methods of diffusion boriding. FeB and Fe2B layers were characterized by a strong zonation, obtaining the average thickness of 32μm and 125μm, respectively. Young's moduli and hardness of iron borides were measured using the nanoindenter with a Berkovich diamond tip under load of 50mN. The higher average indentation hardness (HIT=20.95±0.93GPa) and Young's modulus (EIT=308.86±26.44GPa) were characteristic of FeB phase. Fe2B boride was characterized by HIT=17.42±0.80GPa, and EIT=252.96±15.57GPa. The fracture toughness of iron borides was measured by microindentation technique using a Vickers diamond indenter under load of 100gf (about 0.981N). The average fracture toughness (Kc), measured in FeB zone, was equal to 1.79±0.70MPa·m1/2. Fe2B phase was characterized by higher fracture toughness, obtaining Kc=2.42±0.66MPa·m1/2. However, at FeB/Fe2B interface the increase in brittleness was detected. Such a situation was caused by the differences in coefficients of thermal expansion of both iron borides and their mechanical properties. It could provide the preliminary cracks at this interface after cooling. During indentation, the value of shear stress probably exceeded the value of normal compressive stress. It could cause the failure at this interface, facilitating cracks' propagation.

Kinetics of boron diffusion and characterization of Fe2B layers on AISI 9840 steel

In this work, the AISI 9840 steel was subjected to the powder-pack boriding in the temperature range of 1123–1273 K for various times ranging from 2 to 8 h. A kinetic model based on the principle of mass conservation at the growing interface was used to estimate the boron diffusion coefficients through the Fe2B layers. The pack-borided samples were experimentally characterized by different techniques such as: Scaning electron microscopy, XRD analysis, Microhardness Vickers testing. The Daimler-Benz Rockwell-C indentation technique was used to assess the adhesion quality of boride coatings on AISI 9840 steel. Finally, the scratch and pin-on-disc tests for wear resistance were respectively performed using an LG Motion Ltd and a CSM tribometer under dry sliding conditions. The boron activation energy for the AISI 9840 steel was estimated as 193.08 kJ /mol by applying the present model. To confirm and extend the validity of the diffusion model, the experimental values of Fe2B layers thicknesses obtained for other boriding conditions were compared with the predicted values.

Characterization and Study Hard Layer on Steels Grade Machinery

The paper also presents the growth kinetics of the hard layers on the surface grade machinery steels type AISI 9840 with a boron dehydrated paste. The thermochemical treatment was performed at three different temperatures: 1173, 1223, and 1273 K, with 2, 4, 6, and 8 h treatment time for each temperature. The presence of the hard layers FeB and Fe2B formed on the surface AISI 9840 was confirmed by cross sectional observation by scanning electron microscopy (SEM), XRD analysis and the distribution of alloy elements from hard layers was confirmed by energy dispersive spectroscopy (EDS). Using the law of parabolic growth the mobility of boron was included potential influence of boron, treatment time, temperature and time incubation in hard layers. Finally, nanoindentation technique test the modulus and hardness are obtained of the FeB and Fe2B hard layers.

Pack-boriding of AISI P20 steel: estimation of boron diffusion coefficients in the Fe<SUB align="right">2B layers and tribological behaviour

In the present study, the AISI P20 steel was pack-borided in the temperature range of 1,123-1,223 K for treatments times between 2 and 8 h. A new kinetic model based on the integral method was used to estimate the boron diffusion coefficients in the Fe2B layers. As a result, the activation energy for boron diffusion in the AISI P20 steel was estimated as 194.3 kJ mol−1. This value of energy was compared with the literature results. Furthermore, to validate experimentally the present model, two additional boriding conditions were used. The morphology of cross-sections of borided samples was examined by scanning electron microscopy. The formation of a single boride layer was confirmed by x-ray diffraction analysis. The Daimler-Benz Rockwell-C indentation technique was used to evaluate the cohesion of boride layers on the surface of AISI P20 steel. Finally, the scratch and pin-on-disc tests for wear resistance were carried out by means of a LG Motion Ltd and a CSM tribometer respectively under dry sliding conditions.

Evolution of boride layers during a diffusion annealing process

New results about the evolution of the FeB-Fe2B layers during a diffusion annealing process (DAP) are presented in this work. First, the growth of the boride layers over the surface of an AISI 1045 steel was developed by means of the powder-pack boriding process (PPBP) at temperatures of 1173–1273K with different exposure times for each temperature. The boron diffusion coefficients in the FeB and Fe2B were estimated according to the mass balance equations on the growth interphases, and expressed as a function of the boriding temperatures by the Arrhenius equation. Moreover, the DAP was conducted on borided samples obtained at 1273K with 4–8h of exposure using a SiC atmosphere, and considering the theoretical values of annealing times proposed by the extended model. The evolution of the boride layer microstructure was represented by the interphase velocities of the FeB/Fe2B and Fe2B/substrate, and the relationships between the growth of the Fe2B at the expense of the FeB layer for the applied range of annealing times.

Kinetics and Tribological Characterization of Pack-Borided AISI 1025 Steel

AbstractIn this present study, the AISI 1025 steel was pack-borided in the temperature range of 1,123–1,273 K for different treatment times ranging from 2 to 8 h. A diffusion model was suggested to estimate the boron diffusion coefficients in the Fe2B layers. As a result, the boron activation energy for the AISI 1025 steel was estimated as 174.36 kJ/mol. This value of energy was compared with the literature data. To extend the validity of the present model, other additional boriding conditions were considered. The boride layers formed on the AISI 1025 steel were characterized by the following experimental techniques: scanning electron microscopy, X-ray diffraction analysis and the Daimler–Benz Rockwell-C indentation technique. Finally, the scratch and pin-on-disc tests for wear resistance were achieved using an LG Motion Ltd and a CSM tribometer, respectively, under dry sliding conditions.

Thermochemical Boriding of Fe–5% Cr Alloy

Boriding of the Fe–5% Cr alloy in amorphous boron powder with KBF 4 as an activator at 850–950°C and reaction times of 3600–28800 sec results in the formation of two boride layers at the interface between the reagents. The outer layer bordering boron consists of the FeB phase, while the inner one adjacent to the alloy base consists of the Fe 2 B phase. The average chromium content of the FeB layer is 4.2 wt.% (2.7 at.%) and of the Fe 2 B layer is 4.5 wt.% (3.5 at.%). The formation of boride layers is sequential, rather than simultaneous. The Fe 2 B layer forms and grows first. The FeB layer does not show up until Fe 2 B reaches a necessary minimum thickness exceeding 100 μm, for example, at 850°C. The characteristic feature of both layers is a profound texture. Their diffusional growth kinetics is close to parabolic, x 2 = 2k 1 t. The temperature dependence for the growth rate constant of the Fe 2 B layer in the time range 3600–14400 sec, when the FeB layer still has not formed between boron and Fe 2 B, is described by an Arrhenius relation, k 1 = 7.00 ∙ 10 −6 exp(−135.0 kJ × × mol −1 /RT). The microhardness is 15.6 GPa for the FeB layer, 13.0 GPa for the Fe 2 B layer, and 0.87 GPa for the alloy base. The dry abrasive wear resistance of borided Fe–5% Cr alloy samples found from weight loss measurements is more than one order of magnitude greater than that of their base. Surface boride coatings may be employed in manufacturing products, parts, and materials for functional applications to enhance their service characteristics.

Influence of discharge time on properties of plasma electrolytic borocarburized layers on Q235 low-carbon steel

The plasma electrolytic borocarburizing (PEB/C) process on Q235 low-carbon steel was carried out at 330 V in 30% borax solution with glycerine additive at 5 min, 15 min and 30 min. The influence of plasma discharge time on microstructure, phase constituent, hardness, corrosion behaviors and tribological properties of PEB/C hardening layers were evaluated. Plasma discharge behaviors were investigated by the optical emission spectroscopy (OES) method. The surface loose layer of the PEB/C samples mainly consists of Fe2B, Fe2O3, Fe3C, and FeB phases, but the Fe2B phase is a dominant phase in boride layer. It is found that a Fe2B layer about 20 μm thick for 30 min or 8 μm for 15 min PEB/C treatment was formed on the Q235 low-carbon steel. The PEB/C treatment could significantly improve the hardness, corrosion and wear resistance of Q235 low-carbon steel, which was related to the formation of Fe2B phase. By increasing the borocarburizing time, the corrosion potential shifted toward the noble direction, the corrosion current gradually decreased to 1.049 × 10−6 A cm−2. The wear rate of PEB/C steel reduced with increasing the discharge time, and the PEB/C sample for 30 min against Si3N4 ball had the lowest wear rate of 5.43 × 10−7 mm3/N·m, which was only 1/673 of the bare Q235 steel substrate.

Growth kinetics of boride coatings formed at the surface AISI M2 during dehydrated paste pack boriding

The growth kinetics of the boride coatings (FeB and Fe2B) at the surface of AISI M2 high speed steels were studied in this work. Boriding thermochemical treatment was carried out by dehydrated paste pack at three different temperatures 1173, 1223, and 1273K and four exposure times 1, 3, 5, and 7h, respectively. The presence of FeB and Fe2B phases was identified by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction method. In order to obtain the boron diffusion coefficients at the FeB/Fe2B boride coatings, a mathematical model based on the mass balance at the growing interfaces was proposed under certain assumptions. Likewise the parabolic growth constants and the boride incubation time were established as a function of the parameters η(T) and ε(T). The activation energy values estimated for the FeB and Fe2B layers were 233.42 and 211.89kJmol−1 respectively. A good agreement was obtained between the simulated values of boride layer thicknesses and the experimental results. Finally, empirical relationships of boride coating thickness as a function of boriding temperature and time are presented.

Boriding kinetics and mechanical behaviour of AISI O1 steel

In this work, American Iron and Steel Institute (AISI) O1 steel was pack borided in the temperature range of 1123–1273 K for treatment times between 2 and 8 hours. A kinetic model was proposed for estimating the boron diffusion coefficients through the Fe2B layers. As a result, the boron activation energy for the AISI O1 steel was estimated as 197·2 kJ mol− 1. This value of energy was compared to the literature data. In addtion, to extend the validity of the present model, two additional boriding conditions were done. The Fe2B layers grown on AISI O1 steel were characterised by use of the following experimental techniques: scanning electron microscopy, X-ray diffraction analysis and Daimler-Benz Rockwell-C indentation technique. Finally, the scratch and pin on disc tests for wear resistance were respectively performed using an LG Motion Ltd and a CSM tribometer under dry sliding conditions.

Mechanical Behavior of Iron Boride Formed in the Surface of an AISI W2

The present study reports the growth of layers formed in the surface of the boride steel AISI W2; by the application of the dehydrated paste-pack boriding process and using three different temperatures at 1173, 1223 and 1273 K, with 2, 4, 6 and 8 h of exposure. The substrate and the boride Fe2B were analysed quantitatively and qualitatively. The growth of the boride layer Fe2B was examined using optical microscopy (OM), scanning electron microscopy (SEM-EDS) and X-ray diffraction (XRD). The properties were mechanically evaluated, using a Vickers indenter with loads of 0.5 and 1 N, with a constant distance of 15 μm and 30 μm. To determine the fracture toughness (Kc) and the adherence of the boride layer Fe2B, the Rockwell C test method (VDI 3198) was used. The morphology present in the boride Fe2B layer showed a smooth flat, whit ranged thickness from 13.96 ± 1.61 μm to 79.86 ± 4.13 μm. The presence of boride Fe2B layers of steel substrate was confirmed by XRD and the distribution of alloying elements by Energy Disperses for Spectroscopy (EDS). The hardness of the boride layers Fe2B ranged from 157 9± 17 to 1875 ± 25 HV. The fracture toughness of boride Fe2B layer observed ranged from 4.15 to 4.75 MPam1/2. The boride layer has a scale delamination H3 to H6. The boride layers formed in the surface have the function to increase the service life of W2 steels used in the industry.

Diffusion model and characterisation of Fe<SUB align="right">2B layers on AISI 1018 steel

An approach was suggested to study the kinetics of formation of Fe2B layers grown at the surface of AISI 1018 steel by the pack-boriding process. The kinetic model considered the principle of mass conservation at the (Fe2B/substrate) interface to evaluate the boron diffusion coefficient of Fe2B in the temperature range of 1,123-1,273 K. Validation of the model was made by comparing the experimental Fe2B layer thickness with the predicted value for the borided sample at 1,253 K during 5 h. In addition, the generated boride layers were analysed by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction analysis. Finally, a contour diagram describing the evolution of Fe2B layer thickness as a function of treatment time and temperature was also proposed. Finally, the boron activation energy for AISI 1018 steel was estimated as 159.3 kJ mol−1 basing on our experimental results.

A Simple Kinetic Model for the Growth of Fe2B Layers on AISI 1026 Steel During the Powder-pack Boriding

AbstractThis work focused on the determination of boron diffusion coefficient through the Fe