Boride Layer Research Articles

Використання боридних і силіцидних покриттів у ДВЗ: технологічний аспект

The main regularities of the process of forming on refractory metals the single-phase, multi-phase, multi-layer composite coatings with high heat resistance and durability are examined in the article. A study of boride coating on refractory metals was conducted, which showed that a single-phase coating is formed on metals that possesses good adhesion to the base. Based on the results of X-ray phase and micro-X-ray spectral methods of analysis, the formation of a monoboride phase on molybdenum and tungsten and a boride phase on niobium and tantalum was revealed. A study of the effect of temperature on the process of diffusion silicification of refractory metals was carried out, which showed that in the range of 950–1100 0С, a single-phase coating is formed, which consists of disilicides of МеSi2 metals. A further increase in the temperature of the saturation process was found to lead to a sharp increase in the thickness of the silicide layer. It was proved that an effective diffusion barrier is the boride phases of refractory metals, which ensure the stability of the diffusion part of the multicomponent coating. The boride phases were determined to be more stable than silicide phases in relation to the metal base. Due to the formation of silicoboride phases at the border of boride and silicide layers, high stability of the borosilicide coating is ensured. The presence of penetrating impurities in the metal matrix leads to poor protection of the oxide film of the diffusion coating and, as a result, to low durability. A mechanism for the transfer of penetrating impurities from the depth of the metal to the boundary of the powder medium is proposed. The obtained borosilicate-saturated metal technological parameters allow forming a diffusion coating with a fine-grained structure on refractory metals. To ensure high protective characteristics, the formation of the layered part of the coating should be further researched.

Monolayer molybdenum diborides containing flat and buckled boride layers as anode materials for lithium-ion batteries.

The materials community is interested in discovering new two-dimensional (2D) crystals because of the potential for fascinating features. In this work, by employing a systematic first-principles DFT analysis and MD simulations, we investigated the potential applications of monolayer Mo borides containing flat and buckled boride rings named P6/mmm and R3̄m MoB2 as anode materials of lithium-ion batteries. Our preliminary investigations show that the MoB2 monolayers possess significant structural, thermodynamic, mechanical, and dynamical stability. Due to their distinctive crystal structures, the Mo borides exhibit unique electronic properties, as expected. Additionally, we discovered that the highly negative Li adsorption energy achieved can aid in stabilizing the Li's adsorption on the surface of MoB2 rather than clustering, which ensured its suitability for LIB anode applications. The low computed Li-ion and Li-vacancy migration energy barrier provides robust charge/discharge performance even at a fully lithiated state, signifying their extraordinary possibility of being a suitable anode material for Li batteries. Both the monolayers can hold a maximum of two layers of Li ions on both sides to give a huge specific capacity of 912 mA h g-1, much higher than graphene and MoS2-based anodes. The computed in-plane stiffness constants demonstrate that the monolayer pristine and lithiated MoB2 satisfies Born's criteria, implying its mechanical flexibility. Additionally, its strong mechanical and thermal properties at the pristine and the lithiated state indicate that the 2D MoB2 can withstand massive volume expansion at a high temperature of 500 K during the lithiation/de-lithiation reaction and is remarkably beneficial for manufacturing flexible anodes. Based on the above findings, these two newly designed classes of monolayers of MoB2 are anticipated to open a new avenue for the upcoming generation of lithium-ion batteries.

Investigation of corrosion properties of box boring din 20MnCr5 steel bars

In this study, boriding process was carried out on Ø11 mm diameter DIN 20MnCr5 quality steel bars, used in chain elements such as links and rings, and fasteners such as bolts, at 950oC boronizing temperature, boriding times of 2.5 and 7.5 hours. In this study, the formation and growth of the boride layer and the metallographic structure, the coating thickness and corrosion properties of the boronized steels were investigated depending on the boriding conditions. In the box boriding process, Ekabor-II powder mixture, with its commercial name, was used as boriding powder. According to the optical microstructure results made as a result of box boriding, the coating thickness was 371.5 μm in the Ø11 mm diameter boronized DIN 20MnCr5 steel bar for 7.5 hours boriding times while it was 195.6 ?m in that steel bar for 2.5 hours boriding times. Corrosion experiments were carried out in solutions prepared by adding 3.5% NaCl to distilled water. According to the results of the immersion test, the lowest corrosion rate in mdd was measured as 112 mg/(dm2 × day) in the Ø11 mm diameter, 7.5 hour boronized sample, and the highest corrosion rate in mdd was 1456.75 mg/(dm2 × day) in the untreated Ø11mm diameter sample. In the potentiodynamic polarization test, parallel results were obtained for immersion corrosion. Corrosion rate values (icor) were measured at the highest value of 209 × 10−6 A/cm2 in the untreated Ø11 diameter sample, while the lowest icor value was 0.0039 × 10−6 A/cm2 in the Ø11 mm diameter sample borided for 7.5 hours.

ELECTRON-ION-PLASMA SYNTHESIS OF MULTILAYER CR-B FILMS

The paper analyzes the Cr-B film structure formed via argon plasma-assisted deposition on pretreated 12Cr18Ni10Ti stainless steel using the COMPLEX electron-ion-plasma setup (IHCE SB RAS, Russia, Tomsk). The analysis shows that after simultaneous deposition of chromium and boron, the Cr-B film represents a multilayer structure consisting of alternating amorphous boron and nanocrystalline chromium boride layers. At a total film thickness of 1 μm, the thickness of its amorphous and nanocrystalline layers measures 2.0-7.0 and 2.0-2.5 nm, respectively. The steel layer adjacent to the film contains Fe<sub>2</sub>B nanoparticles. Their presence in the steel is due to its preliminary electron beam irradiation and boriding. The micro-hardness of the Cr-B film is 29.0 GPa (standard deviation 4.1 GPa), and its Young's modulus is 200 GPa.

Boriding Treatment of Low Alloy Steels: Effect of Holding Time and Temperature

Boriding is a thermochemical treatment that can be applied to improve the mechanical and chemical properties of steels by surface modification while stilling adequate substrate properties. This kind of treatment is widely used to protect the degradation of the mechanical parts’ surface against wear. The boride atoms introduced into the steel can produce a hard metallic compound formed by diffusion and precipitation. The present study has been conducted in order to obtain an iron borides layer on two types of steel substrates 16NC6 and 20MC5 by using a powder consisting of B4C, NaBF4 and, SiC. The solid boriding treatment was carried out in an electric furnace heated to 950°C for three holding times of 2h, 4h and, 6h. The present research work focuses an the effect studying of holding time as a parameter on the thickness, structure, morphology, and hardness of layers obtained on low carbon steels by the case boriding. As confirmed by structure and microstructure characterization, the hard boride layers produced form two phases of FeB and Fe2B.

Growth Kinetics, Microstructure Evolution, and Some Mechanical Properties of Boride Layers Produced on X165CrV12 Tool Steel

The powder-pack boriding technique with an open retort was used to form borided layers on X165CrV12 tool steel. The process was carried out at 1123, 1173, and 1223 K for 3, 6, and 9 h. As a result of boriding the high-chromium substrate, the produced layers consisted of three zones: an outer FeB layer, an inner Fe2B layer, and a transition zone, below which the substrate material was present. Depending on the applied parameters of boriding, the total thickness of the borided layers ranged from 12.45 to 78.76 µm. The increased temperature, as well as longer duration, was accompanied by an increase in the thickness of the FeB zone and the total layer thickness. The integral diffusion model was utilized to kinetically describe the time evolution of the thickness of the FeB and (FeB + Fe2B) layers grown on the surface of powder-pack borided X165CrV12 steel. The activation energy of boron for the FeB phase was lower than that for the Fe2B phase. This suggested that the FeB phase could be formed before the Fe2B phase appeared in the microstructure. The high chromium concentration in X165CrV12 steel led to the formation of chromium borides in the borided layer, which increased the hardness (21.88 ± 1.35 GPa for FeB zone, 17.45 ± 1.20 GPa for Fe2B zone) and Young's modulus (386.27 ± 27.04 GPa for FeB zone, 339.75 ± 17.44 GPa for Fe2B zone). The presence of the transition zone resulted from the accumulation of chromium and carbon atoms at the interface between the tips of Fe2B needles and the substrate material. The presence of hard iron and chromium borides provided significant improvement in the wear resistance of X165CrV12 steel. The powder-pack borided steel was characterized by a four times lower mass wear intensity factor and nine times lower ratio of mass loss to the length or wear path compared to the non-borided material.

Indentation fracture toughness of boronized unalloyed and alloyed ductile iron

This study was carried out to investigate the fracture toughness of boride layers in ductile irons using a Vickers indentation method and to demonstrate the method's reliability. For this purpose, alloyed (Cu, Ni, and Mo) and unalloyed ductile cast irons were borided for 2, 4, 6, and 8 h at 900 and 950 °C temperatures. The morphology of the boride layer was studied using an optical microscope. The hardness profiles and thicknesses of the boride layers were measured. Boron compounds were discovered using the X-ray diffraction method. The fracture toughness of the boride layer was tested using the Vickers indentation method under a 300g load. In unalloyed cast iron, the surface hardnesses obtained by boriding were 5, 45-6, 69 times higher than that of the unboronized iron hardness. In general, alloyed iron produces thicker boride layers under the same boriding parameters. Depending on the boriding time, the fracture toughness increased at 900 °C and decreased at 950 °C in both types of cast iron.

The Diffusion Coatings for Industrial Tool Application

The diffusion boriding process allows to increase the abrasion and corrosion resistance of the majority of steel grades. The aim of this study was to determine the influence of the chemical composition of the substrate of various steel grades on the microstructure of boride coatings produced using two diffusion methods: pack cementation boriding using EKABOR-2 and paste-pack boriding using EKABOR-PASTE on the substrate of tool and structural steels:. The boriding processes were carried out at 1000oC in an argon atmosphere for 4h. Scanning microstructure investigations of the obtained coatings indicate that a high content of alloying elements increasing the FeB (Cr, Mo, W) phase, results in the formation of an external, continuous layer of FeB borides. It was found that with increasing alloying element and carbon concentration, the total thickness of the boride coatings decreases. In particular, a chromium content below about 1%, with a carbon content below about 0.4%, significantly limits or prevents the formation of the FeB phase. Increasing the content of alloying elements and carbon, results in a change in the morphology of the iron borides.

The effect of alloying elements in Ti-5Mo-5V-8Cr-3Al alloy on growth kinetics of TiB whiskers in boride layer

As one of the important ways to improve surface properties of Ti alloys, the boride layer prepared by the pack boriding is closely related to the growth and morphology of TiB whiskers in the boride layer, whereas the growth and morphology of TiB whiskers are significantly affected by alloying elements in the alloys. This work systematically explored the effect of alloying elements in β-type Ti-5Mo-5V-8Cr-3Al Ti alloy on growth kinetics of TiB whiskers and thickness of the boride layer using experiment and first-principles investigations. After boriding, an outer TiB2 layer and an inner TiB whisker + Ti layer are formed on Ti surface. TiB/β-Ti interface herein is non-coherent with the orientation relationships of (011)TiB//(1¯1¯ 0)β-Ti and [1¯ 00]TiB//[1¯ 11]β-Ti. Alloying elements segregated at the interface can increase diffusion energy barrier and slow down diffusion rate of active [B] atoms, and further reduce growth rate of TiB whiskers. Finally, a theoretical model for the boride layer growth on Ti surface was proposed.

Adhesion behaviour of borided AISI 4140 steel

ABSTRACT In this study, the adhesion behaviour of the borided AISI 4140 steel was estimated. A di-iron boride layer (Fe2B = ∼22 µm) was obtained on the surface of the AISI 4140 steel preheated at 773 K for 30 min to prevent thermal shock; afterwards, the samples were exposed to 1173 K for 30 min. The scratch tests were developed over the surface of the Fe2B/substrate system using a Rockwell-C diamond indenter with a normal force increasing from 0.5–80 N. The friction coefficient behaviour and the residual depth values were measured considering the scratch length that was monitored during the test, according to the ASTM C1624 standard procedure. Critical loads were determined through the combination of the normal force and visual inspection over the worn surface with cracks (cohesive failure) or detachment (adhesive failure) and are explained according to the mechanical properties of the Fe2B/substrate system.

Effect of carbon and nitrogen diffusion zone on growth mechanism of boride layer produced on Q235 Steel

The purpose of this study was to indicate the effect of the presence of the carbon and nitrogen diffusion zone below the boride layers of Q235 low-carbon steel. The boride layers were produced by cathodic plasma electrolysis treatment (PET). Based on the results, the boride layer thickness on the treated samples at 260 V and 300 V varied from 10 μm to 22 μm. The XRD and GDOES analysis demonstrate that the boride layer on the treated samples mainly consists of single Fe 2 B phase, and the top loose layer mainly contain Fe 2 O 3 , Fe 3 C, Fe 4 N, and BN phases. The boride layers exhibited excellent scratch resistance compared to the bare Q235 steel. In addition, the plasma electron temperature was around 3000–4500 K, and the frequency spectra of acoustic signals were related to the voltage-time and current-time curves. At the high temperature and strong electric field, the decomposition reaction of electrolyte and the growth mechanism of the boride layers were discussed. Schematic of reactions in vapor gaseous envelope around the Q235 steel cathode during the plasma electrolysis process. • The boride layers on Q235 steel were produced by cathodic plasma electrolysis treatment. • The boride layers exhibited excellent scratch and adhesion resistance. • The OES and air acoustic spectra were measured. • Decomposition reactions of electrolyte and growth mechanism of boride layer were discussed.

Comparison and Analysis of Diffusion Models: Growth Kinetics of Diiron Boride Layers on ASTM A283 Steel

Hard-coated surfacing of a few micrometers is widely applied to increase the efficiency of tools, e.g., for cutting, forming, and casting applications. Therefore, the base thermodiffusion surface treatment is a practical solution to these issues by hardening surface layers with interstitial elements such as carbon, nitrogen, and boron. In particular, within this study, the growth kinetics of an iron boride layer on ASTM 283 steel were investigated with two diffusion models of the powder-pack boriding technique in the temperature range of 1123-1273 K with different treatment periods. The first model, called the steady-state diffusion model, used the modified version of the mass balance equations at the Fe2B/substrate growth interface, the parabolic growth law, and the solution of Fick's second law without time dependence. At the same time, the second diffusion model was based on Goodman's method, also called the integral heat balance method. Afterward, the diffusion coefficient of boron in the Fe2B phase was calculated by fitting the experimental data to the models. Nevertheless, the estimated value for the activation energy of ASTM A238 steel in both diffusion models was coincident (168.2 kJ∙mol-1). A mathematical analysis was implemented by means of a power series (Taylor series) to explain this similarity. The SEM examinations showed a solid tendency to saw-tooth morphology at the growth interface with the formation of the Fe2B layer, whose presence was verified by XRD analysis. The tribological characterizations, including the tests of Rockwell-C indentation, pin-on-disc, and Vickers hardness test method, were used to analyze the antiwear features of the Fe2B layers. Finally, this value of energy was compared to the literature for its experimental validation.

INVESTIGATION OF CORROSION AND ADHESION BEHAVIORS OF BORONIZED ASP® 2012 STEEL

Tool steels are extensively used in sheet metal forming dies in order to prolong the life of dies and reduce the cost of production. Powder metallurgy tool steels are also alternatively preferred because of their low-risk metallurgical behavior owing to their compositions by which bulk steel would be difficult to produce, such as high amount of carbides or high alloying elements. Such advantage is desired if the steel has a narrow range of fine grain sizes and is less metallurgically affected by the heat treatment process due to having large surface area of fine grains. In this study, ASP® 2012 powder metallurgy steel containing high amounts of Si, Cr, Mo and W was selected for boronizing by the boron-giving thermochemical process. The boride layers on the surface of ASP® 2012 tool steel were metallographically characterized by various characterization techniques including adhesion strength test, SEM and XRD. The effects of corrosion kinetics and chemical composition of steel on the amount and types of boride layers formed on P/M steel of ASP® 2012 after powder-pack boriding were investigated. The results indicate that, according to the Rockwell-C indentation test, the best adhesion in the boride layer was obtained in samples borided at 850°C for 4 h, while the worst adhesion was obtained in ASP® 2012 steel boronized at 950°C for 4 h. Corrosion rates of boronized ASP® 2012 steel were decreased compared to nonboronized ASP® 2012 steel.

Microstrutural, mechanical characterizations and corrosion behaviour of borides layers on Inconel 718 superalloy

The exposure of mechanical components to bad weather and conditions, such as corrosive environments, is recurrent, making the use of nickel alloys in various market segments favorable due to their high corrosion resistance as compared to other types of materials. However, the need to increase the shelf-life and performance of these materials turns surface treatments into an important alternative to optimize surface properties, which makes it possible to use alloys in new applications. In this scenario, the boriding process is a valuable treatment option, since it allows for the improvement of surface properties in ferrous and non-ferrous materials. In the present study, the boriding thermochemical treatment was performed on the Inconel 718 alloy, under different temperature and time conditions. The roughness, microstructure and mechanical properties of the alloy were evaluated by confocal microscopy, scanning electron microscopy, X-ray diffraction and instrumented indentation, respectively. The results showed that, as the temperature or time parameters increase, there is increased layer thickness and hardness, as well as evidence of formation of CrB, FeB and Ni3B + Ni2B + Ni4B3 in the layer. The assessment of the behavior of the treated samples subjected to corrosion testing was performed by using the potentiodynamic polarization technique, revealing less corrosion potential and no passivation in the boride layers.

Effects of Nb on borosiliciding of CoCrFeNiNbx high-entropy alloy

The effect of Nb addition (2, 5, 10 at. %) on the borosiliciding behavior of CoCrFeNiNbx high-entropy alloy was studied. Vacuum arc melted CoCrFeNiNbx alloys consisted of FCC and Laves-C14 phases. The increase of Nb in the alloys resulted in a decrease of the amount of FCC phase and an increase of the amount of Laves phase. A multiphase boride layer (BL) and a silicon-rich layer (SL) were evident with the formation of Ni2Si, FeB, Fe2B, Co2B, Cr5B3, Nb5Si3 and NbB2 phases after the thermochemical treatment. The Nb5Si3 and NbB2 phase formation was caused by the Nb addition into the CoCrFeNi alloy. The thickness of the SL + BL dramatically decreased, and the thickness of the transition zone/diffusion zone (DZ) decreased with increasing Nb content. The Nb content in the alloys hinders the inward diffusion of Si/B atoms and decreases the Si/B penetration depth. The total layer thicknesses were 45 μm, 27 μm and 12 μm for the alloys containing 2, 5 and 10 at. % Nb, respectively. The surface hardness values of alloys increased after surface treatment.

Tribocorrosion and corrosion behavior of double borided layers formed on Ti-6Al-4V alloy: An approach for applications to bio-implants

TiB2 and TiB double layers were formed on surface of Ti-6Al-4V by a diffusional process at 850 ͦC for 4–16 h. EIS and XPS analyses revealed that formation of a passive film on the coated samples in a PBS solution increased corrosion resistance of Ti-6Al-4V. Tribocorrosion rate of the borided samples decreased up to 40 times compared with Ti-6Al-4V under a reciprocating condition and normal loads of 0.5–15 N against an alumina ball. The presence of B2O3/H3BO3 tribofilm on the borided samples led to a lower coefficient of friction and a more stable fluctuation of OCP.

Structural and electronic evidence of boron atomic chains

The structure and chemical state of a boron chain, isoelectronic to polycumulene, were obtained with a combination of positron diffraction, photoelectron spectroscopy, and first-principles calculations. In the present work, an array of boron chains was found in a copper boride layer on a metal crystal substrate. The band structure of this material was determined to be electronically doped and hybridized by neighboring copper atoms. These boron atom chains exhibit a unique electrophilic character that is specific to the element. The properties of boron chains in the copper boride layer and the substrate effect are systematically investigated together.

Microstructure of a chrome-boriding of induction hardened DIN Ck 45 steel

Abstract In this study, boriding of DIN Ck 45 steel, which is hard chrome plated after induction hardening, is used as a linear shaft in 3D printers. The boriding treatment, which was carried out by the pack-boriding method, was carried out in an atmosphere-controlled furnace at 1273 K for 2 h. The thickness, morphology, hardness, and chemical composition of the boride layer formed on the sample surface as a result of the boriding process using Ekabor 2 boriding agent were examined and compared with the un-borided sample. The microstructure images were obtained with a digital camera integrated into an optical microscope, and these images were analyzed in detail with the help of an image analysis program. After the optical microscope examinations were completed, point EDX analyzes were performed on the image obtained with the help of SEM. As a result of EDX analysis, it was determined that the layer formed on the material surface was only chromium boride formed by the interaction of chromium and boron element. Finally, the hardness measurements of the borided sample were carried out with the help of Vickers indenter and then differences were compared with the un-borided sample.

Microstructural characterization and dry sliding wear behavior of boride layers grown on Invar-36 superalloy

Invar-36 is extensively used in fields where high corrosion resistance and dimensional stability are required. However, its hardness limits its use in tribological applications, such as in the manufacture of bulky composite tooling for the aerospace and automotive industries. In this paper, powder-pack-boriding is proposed for the production of the boride layer on Invar-36 superalloy at 975 °C for 5 and 7 h using the nano-sized boriding powder mixture of 90 wt% B4C and 10 wt% NaBF4 as a boron source. The grown boride layers were characterized using scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD), 2D- and 3D-profilometry, microhardness measurements and ball-on-plate type wear tests. Microstructural characterization revealed a complex and homogenous boride layer mainly consisting of NiB, FeB and Fe2NiB phases with 176.9–189.1 μm thickness. The surface hardness of Invar-36 increased from 150.7 to 1109.5 HV0.05 after the boriding process. The improvement in surface hardness of the grown boride layer enhanced the wear resistance of the Invar-36 superalloy by 28.6–105 times.

Characteristics of boronized Ti6Al4V alloy using boric acid based boronizing mixture

Boronizing processes of Ti alloys are generally performed in atmosphere-controlled furnaces. In this study, it is aimed to carry out boronizing process under atmospheric conditions by using an alternative boronizing mixture containing boric acid and to better the surface characteristics of Ti6Al4V alloy by boronizing. The efficiency of the boronizing mixture was evaluated by performing boronizing at different process temperatures (900-1100 °C) and durations (12 and 20 h). Microstructural (OM, SEM) and chemical (XRD, EDS, XPS) analyzes were performed to characterize the boride layers formed on the surfaces of the boronized samples. As a consequence of these analyzes, it was found out that a two-phase boride layer (TiB2 + TiB) was obtained in the samples. In addition, in vitro tests were done for specifying the bioactivity of boronized samples. In order to determine the effect of boronizing on the corrosion resistance of Ti6Al4V alloy, corrosion tests were performed by the Tafel extrapolation method. The adhesion behavior of the boride layers was determined by the Daimler-Benz Rockwell C indentation test. As a result, boronizing studies have been performed successfully without atmospheric-controlled conditions and it has been defined that surface characteristics of the Ti6Al4V alloy have bettered through the boride layers formed on the alloy surface.