Growth Kinetics Of Boride Layers Research Articles

Impact of the DC intensity and electrode distance on pulsed-DC powder-pack boride layer growth kinetics

In this study, novel findings were obtained regarding the influence of current intensity and electrode distance on the growth of the FeB-Fe2B layer during pulsed-DC powder pack boriding (PDCPB). Boride layer formation was carried out on AISI 1018 and AISI 4140 steels at 900 °C for 2700 s, considering current intensities ranging from 2.5 to 7.5 A and electrode distances of 10, 15, and 20 mm for each current intensity. The growth of the FeB-Fe2B layer was enhanced as the current intensity/electrode distance increased. This was related to the contribution of electromigration, the amount of powder mixture (used during the PDCPB) between electrodes, and Joule heating. Analysis of variance was performed on borided steels to assess the impact of the current intensity/electrode distance on the boride layer growth. The results revealed weight coefficients of approximately 50% for current intensity, around 40% for electrode distance, and a combined contribution of both variables of no more than 3.5%. Finally, multiple regression analyses were conducted to estimate boride layer thickness expressions as a function of the independent variables. The model results demonstrated a 5% error when compared to the experimental boride layer thickness.

A KINETIC STUDY OF THERMOCHEMICALLY BORIDED AISI 316L STAINLESS STEEL

Biomaterials are used in different parts of human body as replacement implants in medical applications. An implant material should have high biocompatibility, corrosion and wear resistance, and suitable mechanical properties in terms of safety and long-service period. There are only a few biocompatible implant materials: AISI316L stainless steel is one of the materials used in this type of applications. They have relatively poor wear resistance. Boriding being a thermochemical diffusion treatment is one of the processes to improve their wear resistance. Borides are formed by introducing boron atoms by diffusion onto a substrate surface and they are non-oxide ceramics and could be very brittle. The growth kinetics of boride layer is analyzed by measuring depth of layers as a function of boriding time within a temperature range. In this study, the effects of Ekabor-2 bath on formation mechanism and properties of boride layer in thermochemical diffusion boriding of AISI316L stainless steel were investigated. Different temperatures and durations were applied in boriding operations and hardness, optical microscopy, XRD, EPMA and SEM studies were performed to detect the properties of boride layers. It was found that thickness of boride layer increased with increasing temperature and time; the basic phase in the boride layer formed was Fe2B and FeB phase also formed. It was also found that surface hardness values of borided materials increased depending on temperature and time of boriding process; surface hardness values of borided materials are approximately 10 times higher than surface hardness values of non-borided AISI316L stainless steel and formation activation energy of boride layer is 149.3 kjmol-1.

Research on Properties and Growth Kinetics of Boride Layer of Fe-Based Powder Metallurgy Material Boriding Strengthened with Rare Earth

The Fe-based powder metallurgy material was directly sintered and boriding with CeO2 respectively by a pack powder boriding method to obtain a specimen with a boride layer. Boriding treatment was performed at 1123–1323 K for 3–10 h. The morphology and the thickness of the boride layer were observed with a ultra-depth-of-field microscope and a scanning electron microscope (SEM). The phase composition of the boride layer was analyzed by X-ray diffractometer. The quality of the bonding strength between the boride layer and the substrate was evaluated by the Rockwell-C adhesion test. The results showed that boriding with 2 wt% CeO2 will inhibit the boriding treatment at low temperature and promote it at high temperature. Boriding with 4 wt% CeO2 will inhibits the boriding process at both low and high temperature, and the inhibition becomes stronger as the temperature increases, the inhibiting effect at 1323 K is 9 times that at 1123 K. The quality of the bonding strength of the boride layer with CeO2 is better than that specimen without CeO2 and the quality of the bonding strength with 2 wt% CeO2 is approved by the HF3 grade according to the specifications.

Effect of Carbon Content and Boronizing Parameters on Growth Kinetics of Boride Layers Obtained on Carbon Steels.

Boronizing is a thermochemical treatment performed to produce hard and wear-resistant surface layers. In order to control the process and obtain boride layers with the desired properties, it is very important to know how the boronizing parameters and the chemical composition of the treated steel affect the boronizing. The aim of the present study is to investigate the influence of carbon content in carbon steels, boronizing temperature, and boronizing duration on the growth kinetics of boride layers. For this purpose, three carbon steels (C1y5, C45, and C70W2) were boronized in solid medium. The experimental results show that there is a linear relationship between the carbon content and the activation energy values, and between the carbon content and the frequency factors. In addition, a statistical analysis was performed to determine the contribution of each factor. The ANOVA showed that boronizing temperature has the highest effect on the boride layer thickness, followed by the boronizing duration, while the carbon content of the steel has the least effect on the boride layer thickness. Based on a regression model, an empirical equation was derived to estimate the thickness of the boride layer on carbon steels as a function of carbon content, boronizing temperature, and duration.

Pulsed-DC powder-pack boriding: Growth kinetics of boride layers on an AISI 316 L stainless steel and Inconel 718 superalloy

An alternative method called pulsed-DC powder-pack boriding process (PDCPB) is presented in this study. The main components of the PDCPB consisted of a metal box containing the specimen embedded in a powder mixture, and placed between two electrodes, which were connected to a DC power supply, and a programmable electronic control device producing the polarity changes during the process. A set of boriding conditions were carried out on the surfaces of AISI 316 L stainless steel and Inconel 718 superalloy using a constant current input of 5 A with polarity inversion cycles of 10 s. After the PDCPB, the boride layers were characterized by optical microscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy.The growth kinetics of the boride layers was established using a diffusion model that considered the mass balance equations at the growth interfaces, in which the boron diffusion coefficients in the layers were expressed as a function of the boriding temperatures to estimate the boron activation energies in the borided materials. The change of polarity in the electrodes allowed a uniform flux of boron during the process, obtaining similar layer thicknesses on the surfaces of the material exposed to the pulsed-DC field. Finally, the results showed that the growth rate of the layers was increased by the effect of the pulsed-DC field, whilst the boron activation energies, in the borided materials, decreased drastically compared to those obtained for the conventional powder-pack boriding process.

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.

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.

Investigation of the Diffusion Rate of Boron Atom in AISI D3 Steel

The present study reports on the kinetics of borided AISI D3 steel. Boriding thermochemical treatment was carried out in a solid medium consisting of B4C, SiC and KBF4 powders mixture at 1123, 1173 and 1223 K for 2, 4 and 6 h, respectively. The boride layer was characterized by optical microscopy, X-ray diffraction technique and micro-Vickers hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed the existence of FeB, Fe2B, CrB and Cr2B compounds. The thickness of the boride layer increased with an increase of the boriding time and the temperature. The hardness of the boride compounds formed on the surface of the steels ranged from 1652 to 1984 HV0.05, whereas Vickers hardness values of the untreated the steels was 608 HV0.05. The boron activation energy (Q) was estimated as equal to 174.261 kJ/mol for the borided AISI D3 steel. The growth kinetics of boride layers forming on the borided AISI D3 steel was also analyzed.

Characterization and growth kinetics of boride layers on Ti-5Mo-5V-8Cr-3Al alloy by pack boriding with CeO2

Pack boriding with CeO2 experiments were performed on the β-type Ti-5Mo-5V-8Cr-3Al alloy (TB2 alloy) using boriding powder at the temperature of 950–1100 °C for 5–30 h. The boride layers characteristics were investigated by means of X-ray diffraction, scanning electron microscope, electron probe microanalysis, high resolution transmission electron microscope, and microhardness and wear tests. The results showed that two layers, including the outer TiB2 layer and the inner TiB layer, can be found in the boride layers. The TB2 alloy pack-borided with CeO2 at 1100 °C and 30 h have microhardness of 28 GPa and coefficient of friction of 0.282. The growth kinetics of TiB and TiB2 layers obey the diffusion model of d = kt0.5. The activation energies of boron in TiB and TiB2 layers during the pack boriding with CeO2 are 91.539 kJ/mol and 146.825 kJ/mol, respectively.

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.

Modeling of the Growth Kinetics of Boride Layers during the Diffusion Annealing Process

In the current work, a diffusion model was suggested to estimate the boron activation energies for FeB and Fe2B layers on the gas-borided Armco iron at temperatures of 1073, 1173, and 1273 K for a treatment time varying between 1.33 and 4 h. This model takes into account the effect of boride incubation times during the formation of the FeB and Fe2B phases. The mass balance equations were reformulated to describe the evolution of boride layers after applying the diffusion annealing process. In addition, the time needed to completely dissolve the FeB phase in the boride layer was also predicted. This predicted time was influenced by the boriding parameters during the diffusion annealing process.

Surface evolution and growth kinetics of Ti6Al4V alloy in pack boriding

The surface of Ti6Al4V alloy was modified using the pack boriding at temperatures of 950–1100 °C with an interval of 50 °C for 5, 10, 20 and 30 h in a powder mixture. The surface and boride layers were examined by scanning electron microscopy, X-ray diffraction, electron probe microanalysis, micro-hardness tester and universal wear and friction tester. Growth kinetics of boride layers on the surface of Ti6Al4V alloy were modelled with two diffusion models of d2 = Dt and d = kt0.5 based on the experimental boride layer thicknesses, boriding times and temperatures. The total thickness of boride layer was determined by TiB layer at T < 1050 °C and by TiB2 layer at T ≥ 1050 °C. The diffusion model of d = kt0.5 turned out more accurate in predicting the thicknesses of boride layers. The diffusion activation energy for B in TiB2 layer was calculated as 231.177 kJ mol−1. The borided Ti6Al4V alloy at 1100 °C for 10 h showed the largest surface hardness and smallest coefficient of friction due to its quite smooth and compact surface.

Microstructure, Growth Kinetics and Some Mechanical Properties of Boride Layers Produced on Pure Titanium by Molten-Salt Boriding

To modify the surface properties of pure titanium, boride layers had been fabricated by the boron molten-salt diffusion on pure titanium surfaces in the temperature range of 900-1100 °C for 5- to 30-h treatments. The results demonstrated that the boride layers were mainly composed of TiB whiskers and TiB2 layers without the rutile titanium oxide TiO2. Two diffusion models were introduced to model the growth kinetics of boride layers. The parabolic growth constants and the boron diffusion coefficients were obtained. The boron activation energies for TiB2 and TiB were 225.617 and 165.266 kJ mol−1, respectively. The surface microhardness of the borided titanium decreased with the increase in distance from the surface. The results of wear tests indicated that the wear properties had been improved significantly compared to the pure titanium under dry sliding conditions.

Kinetics of the Formation of Boride Layers on EN-GJL-250 Gray Cast Iron

In the present work, the EN-GJL-250 gray cast iron was pack-borided in a powder mixture consisting of 5 % B4C, 5 % NaBF4, and 90 % SiC. The boriding treatment was carried out in the temperature range 900°C–1000°C during 2, 4, and 6 h. The morphology of the generated boride layers was observed by an optical microscope and a scanning electron microscope. The phases in the borided layer were identified by X-ray diffraction (XRD) analysis, and Vickers microhardness testing was used to determine the microhardness profiles along the boride layers. The growth kinetics of boride layers was studied and the mass gain was estimated for the given boriding conditions. The regression model was also used to predict the total boride-layer thickness. As a result, the boron activation energy for EN-GJL-250 gray cast iron was estimated as 134.21 kJ mol−1 and compared with the literature data.

Characterization of boride coatings on a ductile cast iron

In this work, the EN-GJS-400-15 cast iron was pack-borided in a powder mixture composed of 5% B4C, 5% NaBF4 and 90% SiC at the three temperatures: 900, 950 and 1000°C for 2, 4 and 6 h, respectively. The pack-borided EN-GJS-400-15 cast iron was characterized by the following experimental techniques: optical microscopy, XRD analysis and Microhardness Vickers tester. The growth kinetics of boride layers was also investigated. As a consequence, the boron activation energy was found to be 212.28 kJ mol–1 for the EN-GJS-400-15 cast iron. Based on a regression model, a useful equation was derived to estimate the boride layer thickness as a function of the boriding parameters (time and temperature). A good agreement was then obtained between the predicted values of boride layers thicknesses and those measured experimentally. In addition, an iso-thickness diagram was proposed to be used as a simple tool to select the boride layers thicknesses according to the potential applications of EN-GJS-400-15 cast iron in industry.

Boriding of High Chromium Steels

Two boride layers having different kinds of microstructure are formed on the surface of industrial high chromium steel (13 and 25% Cr) samples during their interaction with boron powder at 850–950ºC and reaction times 3600–43200 s (1–12 h). In the case of 13% Cr steel, the outer layer bordering boron consists of the FeB phase, whereas the inner layer adjacent to the solid substrate consists of the Fe2B phase. Each layer is a homogeneous phase. It is a microstructure of the first kind. With 25% Cr steel, each of boride layers is two-phase. The outer layer comprises the FeB and CrB phases, while the inner layer the Fe2B and Cr2B phases. It is a microstructure of the second kind. Both boride layers on both steels are characterized by a profound texture. Growth kinetics of boride layers obeys a parabolic relation. Boride layers with the microstructure of the second kind exhibit a much higher dry abrasive wear resistance than those with the microstructure of the first kind. Keywords: 13 and 25% Cr steels, boride layers, chemical composition, growth kinetics, microstructure, phase identity, wear resistance.

Effect of rare earth addition on diffusion kinetics of borided TC21-DT titanium alloy

In this study, the properties and growth kinetics of boride layers, generated on the surface of TC21-DT alloy using appropriate amount of powders of boron carbide (B4C) and rare earth oxide (CeO2) were investigated. By conducting a series of experiments at different temperatures of 1123, 1223 and 1273 K for periods up to 10 h, the effects of rare earth (RE) addition on the growth kinetics of boride layers were studied. The characteristics of the boride layers were examined by scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction and micro-Vickers hardness tester. The results showed that the boron diffusion in boride layers was obviously accelerated by RE addition and the activation energy for RE addition-boriding in TC21-DT alloy was greatly decreased to 58.13kJ/mol, which was approximately 40% lower than that of conventional one, without RE addition.

Growth kinetics of boride layers formed on GGG 40.3 ductile iron

Abstract In this study, kinetics of boride layers formed on the surface of ferritic GGG 40.3 ductile iron were investigated by conducting a series of experiments in Ekabor I powder at 850, 900 and 950 °C treatment temperature for 1, 2 and 4 h by using Ekabor I powder. Also, box boronizing was carried out at 950 °C for 4 h with Ekabor II powder to investigate effect of powder size. At the same time, it has been investigated whether or not iron boride layers were obtained using different powder mixtures instead of commercial powder (SiC + KBF4 + B4C). Also, the 85 wt.-% B4C + 15 wt.-% Na2CO3 powder mixture has been used. The study was aimed to inhibit the release of fluorine gas and to perform environmentally friendly working. After the experiments, it turned out that the depth of boride layers depending on treatment temperature and time ranged from 38 to 198 μm. The presence of borides were confirmed by X-ray diffraction, optical microscopy and scanning electron microscopy. A saw tooth shape morphology of boride layers has been detected in optical microscopy and scanning electron microscopy.

Growth kinetics of boride layers formed on 99.0% purity nickel

The present study reports on the kinetics of borided Nickel 201 alloy. The thermochemical treatment of boronizing was carried out in a solid medium consisting of B4C and KBF4 powders mixture at 1123, 1173 and 1223 K for 2, 4 and 6 h, respectively. The boride layer was characterized by optical microscopy, X-ray diffraction technique and micro-Vickers hardness tester. X-ray diffraction analysis revealed the existence of NiB, Ni2B, Ni3B and Ni4B3 compounds at the surface of borided Nickel 201 alloy. The thickness of the boride layer increased with an increase in the boriding time and the temperature. The hardness of the nickel borides formed on the surface of the nickel substrate ranged from 1642 to 1854 HV0.05, whereas the Vickers hardness value of the untreated nickel was 185 HV 0.05. The growth kinetics of boride layers forming on the borided Nickel 201 alloy was also analysed. The boron activation energy (Q) was estimated as equal to 203.87 kJ mol-1 for the borided Nickel 201 alloy.

Modelling of paste boriding process

In this work, a new model was suggested to simulate the paste boriding process. This model was based on the numerical solving of the diffusion equations in both boride layer and substrate by taking into account the displacement of (Fe2B/substrate) interface. This diffusion problem with moving boundary was solved via a front tracking method. The numerical resolution was achieved by the finite difference method using an implicit scheme. The suggested model was able to predict the boride layer growth kinetics and the boron concentration profiles. The present model was validated by comparing the simulation results with the experimental data available in the literature. The obtained results were also compared to the models previously reported.