Iron Boride Coatings Research Articles

Microstructure, mechanical and electrochemical behavior of magnetron-sputtered carbothermic reduced iron-boride ceramic coatings

In this study, magnetron sputtered carbothermic reduced iron boride (FeB) coatings were developed on grey cast iron (GCI) substrates at different substrate temperatures. The impact of substrate temperature on structural, mechanical, and corrosion behavior was examined for two FeB deposition scenarios: FeB coatings deposited at room temperature (RT) and at 500 °C substrate temperature. The evolution of phases and microstructure was studied using XRD and FESEM, respectively. The mechanical properties, creep, deformation behavior, and adhesion strength (scratch test) of the deposited coatings were investigated using nanoindentation at ambient temperature. The highest hardness and Young’s modulus of 16 GPa and 231 GPa respectively, were achieved at 500 °C due to microstructural enhancement. Potentiodynamic polarization and electrochemical impedance spectroscopy were used to evaluate the corrosion behavior of the coatings. The results show that substrate temperature strongly influences the surface morphology of the coatings, which in turn governs the mechanical and corrosion behavior of the FeB coating. The FeB-coated GCI at 500 °C substrate temperature showed higher resistance to scratching, better mechanical properties, and improved corrosion resistance which is attributed to the enhanced adhesive strength, refined microstructure, and formation of protective oxide layers of FeB on the surface of the coatings.

Increasing corrosion resistance of AISI 1010 steel by boride coatings

AbstractBoriding is the process of coating the metal surface with a ceramic metal boride layer by the diffusion method. Iron borides, one of the metal borides, are called ceramics because they are covalently bonded compounds. Iron boride coatings contain strong Fe–B and B–B covalent bonds. In this study, the effect of boronizing on the corrosion resistance of AISI 1010 steel was investigated. Baybora‐1 which has recently been patented was used as boronizing agent. AISI 1010 steel was borided at 950°C for 2, 4, and 6 h using the solid method. The microstructure, hardness, and corrosion rate of the samples were investigated. The change in the corrosion rate of the samples was determined by the corrosion test specified in the ASTM G31‐72 standard. The results showed that the hardness of the iron boride layer formed on the surface as a result of the boronizing process was greater than that of the matrix. As a result of the boriding process, the hardness of the iron boride layer on the steel surface reached approximately eight times the hardness of the substrate matrix. The thickness of the iron boride layer on the steel sample surface was measured at 950°C for 2 and 6 h, respectively, as 45 ± 12 and 155 ± 13 µm. It was concluded that the boriding process increased the corrosion resistance of steel.

Adhesive wear behavior of gas tungsten arc welded FeB-FeMo-C coatings

Abstract In this article, a gas tungsten arc welding is used as a high energy density beam to form a surface over 0.15% carbon steel with FeB, FeMo, and graphite powders. The microstructure, microhardness, and dry-sliding wear behavior of the composite coating were investigated using optical micrography, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectrometry. Microstructural investigations reveal that FeB-reinforced coating exhibited a homogeneous microstructure that consists of dendrites and eutectic. A lot of types of carbide and borides were formed. MoB4, Fe2MoC, B8C, Mo2BC, MoB, Fe3Mo, Fe3B, B25C, Fe7C3, FeB, Mo2B5, and MoC were seen in coated surfaces. Graphite iron boride coatings obtained by the gas tungsten arc welding process improved the wear resistance of carbon steel.

Advanced iron boride coatings to enhance corrosion resistance of steels in geothermal power generation

ABSTRACT Iron boride coatings obtained by the CVD-based thermal diffusion process are proposed and evaluated for the first time for high-temperature corrosion and scaling conditions in geothermal power generation. The testing results in different corrosion environments are presented. The influence of structure and surface composition on the materials’ performance is demonstrated. The dual-layer boride-based coatings successfully withstand the actions of high temperature/high pressure water and steam with a presence of H2S, CO + CO2, chlorides and hydrocarbons in simulating conditions and strong acidic environments. They demonstrated minimal scaling and corrosion when the materials were immersed into the modelling mixes of chloride salt solutions with SiO2 or SiO2+Fe2O3 at elevated temperatures and into the brine solution at boiling. These advanced ceramic coatings and technology should promote significant extension of the steels’ service life in harsh geothermal-related corrosion environments.

Influence of Iron Boride Coating on Flow‐Accelerated Corrosion of Carbon Steel

Flow‐accelerated corrosion (FAC) often occurs in piping systems made of carbon steels and other steels and alloys in power generation and mineral processing, when the products are subjected by extremely high‐velocity corrosive fluid flows. Under these extreme conditions, dissolution and subsequent degradation and thinning of the metallic surfaces occur due to corrosion–erosion resulting in a quick rupture of the piping products. Herein, iron boride‐based coatings obtained through the proprietary thermal diffusion process are selectively applied onto the inner surface of carbon steel A106B piping sections to protect the steel against FAC. The coated and uncoated steel piping sections are tested using the high‐turbulence corrosion loop device with flow rates up to 120 gal min−1 (≈450 L min−1) in boric acid‐based solutions. Changes of wall thickness of the piping sections and their structures are examined and evaluated. The pipe sections with iron boride coatings demonstrate significantly lower degradation in the studied FAC conditions compared with the bare carbon steel. Promising behavior of the coating can be explained by its well‐consolidated double‐layer structure composed of iron borides with high hardness, chemical inertness, and strong diffusion‐induced bonding between the protective layers and the steel substrate.

Erosion studies of the iron boride coatings for protection of tubing components in oil production, mineral processing and engineering applications

Heavy oil production, oil sand and mineral processing require protection of steel components against sand erosion and erosion-corrosion. Boronized coatings on carbon steels obtained through thermal diffusion process were evaluated in the dry sand and slurry erosion conditions at low impingement angles commonly occurred in industrial applications. The specially designed system allowed testing either multiple sets of samples or full-size tubular sections with diameters of 180–220 mm. The boronized coatings consisted of dual iron boride layers FeB and Fe2B with a total thickness of ~200 μm demonstrated significantly higher erosion resistance over carbon steel commonly used in industry. High performance of the boride coatings is defined by their high hardness, dual protective layer with a well-consolidated structure and diffusion related bonding with steels. Erosion wear mechanism is discussed based on examination of coating's structure and composition and analysis of testing conditions. The components and tubing with inner or inner and outer protective iron boride coatings can be successfully employed in downhole oil production conditions, mineral processing and various engineering applications.

Mechanism of Texture Formation in Iron Boride Coatings on Low-Carbon Steel

In this paper, the boriding of low-carbon steel was studied. We found that FeB phase forms on the surface of low-carbon steel at the initial stage, and then Fe2B nucleates on the FeB, with a crystallographic relation between the two phases. In the third stage, Fe2B further grows on the FeB phase, and FeB starts to diminish. A model is proposed to explain the formation of the textured FeB and Fe2B phases. It is found that the strong anisotropy of the FeB lattice structure and the lattice matching between FeB and Fe2B are the reasons for the preferred crystallographic development in the boride coating.

Boride-based coatings for protection of cast iron against wear

The components made of cast irons require protection against wear in severe service conditions. Surface engineering can be used to prevent mechanical failures of cast iron components due to excessive friction-related wear. The iron boride-based coatings can be applied on the entire working surfaces of large-size complex shape cast iron components through the thermal diffusion process. Tribological properties of these coatings obtained have been studied using the pin-on-disc test configuration in simulating application conditions. The obtained iron boride coatings demonstrated significantly lower wear losses compared to bare cast iron, stable behaviour of coefficient of friction during time and no structural degradation and spalling. The superior wear resistance of boride-based coatings on cast iron is dealt with the combination of their high hardness, specific ‘sawtooth’ double-layer morphology obtained through the thermal diffusion process, diffusion-related bonding to the substrate, self-lubricating thin ‘tribo-film’ formed during friction and high thermal and chemical stability.

Iron boride-based thermal diffusion coatings for tribo-corrosion oil production applications

Engineering components and tubing systems for the down-hole applications in the oil production should withstand severe friction, sliding abrasion and corrosion actions. To resolve wear and corrosion issues, the hard iron boride-based coatings on steels obtained through the thermal diffusion process can be applied on the entire working surfaces of large size and complex shape products. The behavior of these coatings obtained at Endurance Technologies Inc. has been studied in the friction–abrasion, friction–corrosion and friction–abrasion–corrosion conditions simulating oil production service conditions. Tribological studies have been conducted using the “rod-on-flat” reciprocating sliding method in the conditions simulating actual application conditions. The synergistic actions of harsh conditions results in a higher rate of materials destruction. The obtained iron boride coatings demonstrated significantly lower wear losses with no delamination and spalling than untreated steels and Ni- and Cr-based coatings. The encouraging tribo-corrosion test results for boride coatings are explained by their high hardness and chemical inertness, specific structure obtained through the thermal diffusion process with reduced micro-crack propagation and the thin “tribofilm” formed during a friction mode. Successful application of the products with the boride protective coatings is reported.

Experimental investigation on erosion resistance of iron boride coatings for steam turbines at high temperatures

In this paper, high temperature erosion tests are performed on four typical anti-erosion coatings for high-parameter steam turbine blades using pneumatic accelerated erosion method to simulate the actual erosion environment in power units. With the employment of scanning electron microscope, energy-dispersive X-ray spectroscopy, glancing-angle X-ray diffraction, and Vickers indentation testing techniques, detailed microscopic analysis of samples is conducted to reveal the underlying causes affecting the anti-erosion performance of coatings. Results show that, under the solid particle erosion at high temperature, boride coatings with more compact structure and higher hardness have stronger anti-erosion ability, whose erosion rate is only 30–50% that of HVOF Cr3C2 coatings under the same erosion condition. Boride coatings composed of duplex phase (FeB and Fe2B) have lower anti-erosion damage capability than that of boride coatings composed of single Fe2B phase. Under high-speed large incidence angle impingement, the surface layer of FeB cracks easily and rapidly propagates to the subsurface layer Fe2B phase under the sustained impingement from particles, resulting in the flaking off and failure of coatings. Single Fe2B phase boride coatings have smaller hardness gradient in the depth direction and higher fracture toughness than boride coatings composed of duplex phase, so that exhibit more stable excellent erosion resistance under different erosion parameters. Therefore, single Fe2B phase boride coatings should be used as the preferred wear resistant coating for turbine blades solid particle erosion problem.

Effect of substrate roughness, time and temperature on the processing of iron boride coatings: experimental and statistical approaches

The effect of substrate roughness, time and temperature on the formation of iron boride coatings onto AISI-1018 steel substrates by paste-boriding thermochemical (PBT) process has been studied. Three parameters were considered: substrate roughness (0.015, 0.2, 0.8 and 1.2 µm), time (1, 2, 4, 6 and 8h) and temperature (700, 800, 900 and 1,000°C). Coatings were characterised by SEM and XRD; Fe2B and FeB phases were identified. The ANOVA showed that temperature is the parameter with the highest contribution on the iron boride thickness (66.96%), followed by time (15.48%) and substrate roughness (7%). In addition, the interaction of the substrate roughness with temperature and time contributed with 5.7 % to the formation of the iron boride coating. Based on a regression model, an empirical equation and contour levels representing the layer thickness were proposed to estimate the iron boride coatings thickness. The growth kinetic showed that the maximum layer thickness and the minimum activation energy Q = 119.7 kJ/mol are characteristic of a PBT process with substrate roughness of 0.8 µm. Diffusion coefficients and activation energies of each PBT process with different substrate roughness are also given.

Self-Affine Patterns of Boride Layers

In this study, the evaluation of interfaces on iron boride Fe2B growth obtained by paste boriding process was carried out. Fractal geometry is used like a powerful tool for the roughness analysis present during iron boride growth. Experiments were performed in AISI 1045 steel at temperatures of 1193K for exposure times of 2, 4 and 6 h, and 1223K for treatment times of 2, 4, 5 and 6 h, varying the boron paste thicknesses in the range of 1 – 5 mm for each temperature and time. The fronts of the interfaces in iron boride coatings were characterized and digitized with mean of an optic microscope and Scion Image software. Self-affine methods were applied to the interface growths for validate the fractality of the system. It was established that the interface width, ω , scales to ω (L) ∼ L H , where H represents the roughness exponent of the boride layers.

Wear/Friction Behaviour of FeB and FeB/h-BN Coatings Sprayed by Atmospheric Plasma Spraying

Abstract The crushed and rounded ferroboron (FeB) powders of Fe-18.8B-0.2C-0.5Si-0.8Al (wt.%) were deposited onto an aluminum substrate by atmospheric DC plasma spraying to improve its tribological properties. Hexagonal boron nitride (h-BN) powders which have excellent lubricating properties similar to graphite were incorporated into the boride powders as a solid lubricant by a sintering process to obtain protective coatings with a low friction coefficient. As-sprayed coatings are composed of mainly FeB, iron matrix supersaturated with boron owing to the rapid solidification of molten droplets flattened on a substrate. The friction and wear behaviour of each coating were evaluated using a ring-on-disk type wear tester in paraffin based oil with an air atmosphere. It was found that sintering of iron boride powder with h-BN powder (5 wt.%) is an acceptable method for producing a protective composite coating against friction and wear. The evaluation of friction and wear results shows that iron boride coatings exhibit high seizure load and good anti-wear performance.

Evaluation of the corrosion resistance of iron boride coatings obtained by paste boriding process

An evaluation of corrosion resistance of boride coatings in AISI 304 steel was carried out. Formation of iron boride layers (FeB and Fe2B) at the material surface was obtained by paste boriding process. Boron paste thicknesses of 4 and 5 mm were applied to the steel surface. A thermochemical treatment, for each boron potential, was carried out at temperatures of 1173, 1223 and 1273 K; with exposure times of 4 and 6 h. Corrosion resistance of the borided samples was evaluated by the electrochemical techniques of open circuit and polarization resistance with a 0.1 M solution of NaCl. Dependence between the polarization resistance and the experimental parameters is observed. The results show that the corrosion resistance is maximized with a treatment time of 4 h and a boron paste thickness of 4 mm.

Wear behaviour of iron boride coatings produced by VPS technique on carbon steels

The vacuum plasma spray (VPS) technique is a useful tool for designing the characteristics of the coatings and, thus, the tribological properties of coated components. In the present paper, the wear properties of iron boride coatings produced by means of VPS technique on AISI 1040 steel samples were evaluated as a function of their microstructural characteristics. One coating type was obtained by using Fe 2B pure powder, the other with differentiated FeB + α-Fe blends, with the FeB content increasing and α-Fe content decreasing from the matrix to the surface. Wear tests were performed by means of a tribometer in block-on-ring configuration, without lubricant and in air, by using 40- and 60-N coupling loads and 0.8- and 1.6-m s −1 sliding velocities. On Fe 2B coated samples, wear is essentially oxidative until the failure of the coating, the fragments of which cause a third body abrasion. On the FeB + α-Fe coated samples the wear mechanism is mainly oxidative and the coating totally wears out without spalling as a consequence of its graded structure, which succeeds in both improving the adhesion of the coating to the substrate and reducing the residual stress at the coating–substrate interface.

Properties of iron boride films prepared by magnetron sputtering

Iron boride coatings have been deposited on glass and steel substrates by sputtering of a FeB target. Whatever the deposition conditions are, no crystallised compound is detected by X-ray diffraction. In order to obtain further information on the chemical environment of sputtered atoms, X-ray photoemission spectroscopy and conversion electron Mössbauer spectrometry have been performed. The atomic ratio Fe/B in the films has been estimated from XPS results. It is ranging between 1.3 and 1.4, explaining the amorphous structure of the deposited films. The Mössbauer analyses show that the sputtered atoms are homogeneously distributed in the films. The crystallisation of the deposited films has been realised by vacuum annealing at 600 °C. Then, FeB and Fe 2B diffraction peaks are detected after this thermal treatment. Mechanical properties and electrical resistivity of sputtered iron boride films have been investigated in connection with the argon flow rate injected in the deposition reactor. The films are hard (approx. 20 GPa) and their electrical resistivity is low (approx. 200 μ Ω cm). Moreover, their deposition rate is higher than that of others borides synthesised in the same reactor with similar deposition conditions.

Effects of alloying elements on the growth of iron boride coatings

Etude de l'influence des elements d'alliages sur la composition, l'ordre cristallographique, l'epaisseur et la morphologie a l'interface des couches de borure de fer croissant sur les alliages Fe-C-Cr, Fe-C-Ni et Fe-C-Mn en comparaison avec le fer pur