Iron Boride Research Articles

Crystal structures and compressibility of novel iron borides Fe2B7 and FexB50 synthesized at high pressure and high temperature

We present here a detailed description of the crystal structures of novel iron borides, Fe2B7 and FexB50 with various iron content (x=1.01(1), 1.04(1), 1.32(1)), synthesized at high pressures and high temperatures. As revealed by high-pressure single-crystal X-ray diffraction, the structure of Fe2B7 possesses short incompressible B–B bonds, which make it as stiff as diamond in one crystallographic direction. The volume compressibility of Fe2B7 (the bulk modulus K0= 259(1.8) GPa, K0′= 4 (fixed)) is even lower than that of FeB4 and comparable with that of MnB4, known for high bulk moduli among 3d metal borides. FexB50 adopts the structure of the tetragonal δ-B, in which Fe atoms occupy an interstitial position. FexB50 does not show considerable anisotropy in the elastic behavior.

Characterization of natural zeolite clinoptilolite for sorption of contaminants

The nanoparticles technology has received considerable attention for its potential applications in groundwater treatment for the removal of various pollutants as Cadmium. In this work, iron boride nanoparticles were synthesized in pure form and in presence of homo-ionized zeolite clinoptilolite, as support material. These materials were used for removing Cd (II) from aqueous solutions containing 10, 50, 100, 150, 200, 250, 300 and 400 mg/L. The characterization of these materials was made by using X-ray Diffraction, Scanning Electron Microscopy and Mossbauer Spectroscopy. Pure iron boride particles show a broad X-ray diffraction peak centered at 45∘ (2𝜃), inferring the presence of nanocrystals of Fe2B as identified from Mossbauer Spectroscopy. The size of these Fe2B particles was within the range of 50 and 120 nm. The maximum sorption capacities for Cd (II) of iron boride particles and supported iron boride particles in homo-ionized zeolitic material were nearly 100 %. For homo-ionized zeolite and homo-ionized zeolite plus sodium borohydride was ≥ 95 %.

Effect of the method of introducing alloying compositions on the properties of the surface layer in iron–carbon alloy castings during lost-foam casting

The structure, the phase composition, and the properties of the surface layer in steel and cast iron castings are analyzed after alloying by B4C–Ti and B4C–FeTi compositions during lost-foam casting using different methods of their introduction. It is found that, irrespective of the method of introducing an alloying composition, the processes of physicochemical interaction between the alloying-composition components and a poured melt (according to the mechanism of self-propagating high-temperature synthesis) lead to the formation of titanium and iron borides, nitrides, carbides, and carbonitrides.

Effect of laser modification of B–Ni complex layer on wear resistance and microhardness

Abstract The paper presents the results of microstructure observations, microhardness measurements and wear resistance tests of B–Ni complex layers. Boronickelizing is a three-step process of layer production on metallic substrate. Nickel modified boronized layers were called ‘boronickelized’. Nickel plating was applied first and, as a result, nickel coatings with a varying thickness were obtained. Diffusion boronizing was carried out as a second step. Boronickelized layer was formed following the merger of galvanic and diffusion processes. In the third step the galvanic-diffusion boronickelized layer was obtained by remelting it with a CO 2 laser beam. Galvanic-diffusion boronickelized layer had a dual-zone microstructure. The first zone was continuous and nickel-enriched, and characterized by reduced microhardness, whereas the second zone was characterized by needle-shaped microstructure, with microhardness similar to Fe 2 B iron borides. After laser modification steel specimens with the boronickelized layer consisted of remelted zone (MZ), heat affected zone (HAZ), and substrate. It was found that increasing the thickness of nickel coating leads to decreasing the microhardness of the remelted zone. Increasing thickness of nickel coating causes the reduction of wear resistance of boronickelized layer modified by laser beam. The application of a nickel coating thicker than 20 µm causes incomplete remelting of needle-shaped microstructure of boronickelized layer.

The Structural Properties of Fe-Ti-B Based Alloys Produced by Mechanical Alloying

In the present study, the production of Fe-Ti-B based alloys was realized and their structure and properties were investigated. Mechanical alloying proceeds by the continual cold welding and fracturing of the constituent mixture of Ti+4B+5Fe powder when subjected to the large compressive forces of a high speed mill. The powder charge together with 7 mm diameter steel balls were loaded into a tool steel grinding container at approximately 350 RPM for 20 h. The samples were shaped as cylinder of O15×8 mm dimensions by uniaxial pressing at 450 MPa. Then, the green body materials were produced by sintering at 1100 ◦C for 1 4 h in argon atmosphere. The morphology of composite materials was investigated by optical microscopy and scanning electron microscopy and phase analysis was realized by x-ray di raction analysis. The bulk densities of the materials were measured using by Archimedes method. Also, the micro-hardness of the samples was measured by Vickers indentation technique. As a result, Fe, iron boride (FeB, Fe2B) and titanium boride (TiB2) phases were detected in the phase analysis of the Fe-Ti-B based materials. The hardness of the materials was measured between 1107 HV0.05 and 1551 HV0.05, depending on sintering time. The densities of the samples were determined between 4.205 g/cm and 4.219 g/cm.

Study of residual stresses, microstructure, and hardness in FeB and Fe2B ultra-hard layers

Boriding is a thermochemical diffusion-based process of achieving ultra-hard surface on metals. Two distinct crystalline phases, i.e. tetragonal Fe2B and orthorhombic FeB can exist in the surface layer penetrated by boron ions. In our contribution, we have studied the microstructure, the hardness, and the spatial distributions of both phase composition and residual stresses (RS) in samples exhibiting either single-phase Fe2B or duplex Fe2B-cum-FeB character. The indispensable knowledge of the elastic constants used in the stresses calculations from the measured strains by X-ray diffraction were gained from the refined lattice parameters of both iron borides employing density functional theory implemented in CASTEP software by Materials Studio. In the studied case, there is only minor occurrence of preferred orientation in the Fe2B phase and the evaluated RS have compressive character gradually decreasing from its maximum value on the very surface.

Effect of Relative Humidity on the Tribological Properties of Self-Lubricating H3BO3Films Formed on the Surface of Steel Suitable for Biomedical Applications

The effect of environmental humidity on the self-lubricating properties of a thin film of boric acid (H3BO3) was evaluated. H3BO4films were successfully formed on the surface of AISI 316L steel. The study was conducted on AISI 316L steel because of its use in biomedical applications. First, the samples were exposed to boriding to generate a continuous surface layer of iron borides. The samples were then exposed to a short annealing process (SAP) at 1023 K for 5 min and cooled to room temperature while controlling the relative humidity (RH). Five different RH conditions were tested. The purpose of SAP was to promote the formation of a surface film of boric acid from the boron atoms present in the iron boride layers. The presence of the boric acid at the surface of the borided layer was confirmed by Raman spectroscopy and X-ray diffraction (XRD). The self-lubricating capability of the films was demonstrated using the pin-on-disk technique. The influence of RH was reflected by the friction coefficient (FC), as the samples cooled with 20% of RH exhibited FC values of 0.16, whereas the samples cooled at 60% RH showed FC values of 0.02.

Structural, magnetic and thermal characterization of amorphous FINEMET powders prepared by wet mechanical alloying

Abstract Fe73.5Cu1Nb3Si13.5B9 (at.%) amorphous alloy has been prepared from elemental powder mixture by wet mechanical alloying route, using benzene as process control agent (PCA). The powder has been investigated from the structural, thermal and magnetic point of views. After 15 h of wet mechanical milling, the alloy is obtained in nanocrystalline state, further increase of milling time leading to the progressive amorphization of the alloy. Full amorphization of the alloy is reached after 80 h of wet mechanical alloying. A significant decrease of the particle size is observed during alloy formation, the further increase of the milling time leading only to minor changes of the particles size. By DSC investigation, the primary crystallization of amorphous powder was found to take place at around 570 °C leading to the formation of Fe–Si alloy and iron borides. The Curie temperature of the amorphous material is 280 °C. The XRD investigations of the fully crystallized alloy (heated up to 900 °C) reveal the presence of the NbC phase into the alloy microstructure as a result of powder contamination with carbon. The decrease of the saturation magnetization of the powder upon increasing milling time was observed and is discussed in the light of the structural and chemical changes induced by milling process. A post milling annealing at 300 °C leads to the enhancement of the saturation magnetization due to the stress release and the removal of the benzene adsorbed on the powder surface.

Electron-Beam Surfacing Wear-Resistant Coatings, Reinforced Refractory Metal’s Borides

Structural and phase states of wear-resistant coatings obtained by cladding of self-fluxing nickel-based powder mixtures (77 % Ni, 15 % Cr, 2 % B, 3 % Si, 3 % Fe and others) using an electron beam injected in the atmosphere were investigated. The fabricated coatings possessed the complex gradient structure combining hard and ductile components. In the structure of coatings iron borides (Fe2B) surrounded by the ductile matrix represented by Fe, Ni-based γ-solid solution were observed. An increase in the volume fraction of a high strength component in the coating can be reached by additional alloying of the surface by amorphous boron. In this case, microhardness of the coating increases up to 1200 HV.

Electron-Beam Cladding of Boron Carbide on Low-Alloyed Steel at the Air Atmosphere

An investigation of coatings obtained by cladding of boron carbide on a low-alloyed steel substrate by an electron beam injected into the air atmosphere was carried out. It was shown that hardened layers had a heterogeneous structure formed during rapid cooling. It was established that a volume fraction of iron borides in the surface layer had a considerable impact on mechanical properties of the material studied.

Research on the tribological properties of iron borides as diffusion coatings

Friction tests of diffusion boride coatings were performed by rod-plate and rod-sleeve techniques at loads of 147-1960 N. It was shown that the Fe2B layer can demonstrate plastic deformation under the conditions. In the case of M11 (AISI) alloyed steel, diffusion boriding results in the extremely favorable hierarchical self-organization of defensive coatings and high wear resistance. The alloying of iron borides by chromium contributes to an increase in plasticity in these phases and a decrease in the coefficient of friction. The influence of the nature of the substrate and quenching treatment on the surface-relief characteristics before and after tribological tests, as well as on linear wear, has been determined.

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 Precarburization on Growth Kinetics and Mechanical Properties of Borided Low-Carbon Steel

Boriding is a thermochemical process employed widely for increasing the resistance of ferrous materials to wear and corrosion. In this work, the influence of precarburization on microstructure, boride layer thickness, microhardness, growth kinetics, and mechanical properties of untreated and borocarburized AISI 1015 steel is studied. The thickness of boride layer ranges from 205.9 to 215.9 µm for borocarburized specimens to a maximum of 247.7 µm for borided AISI 1015 steel. The carbon content in the case improves the microstructure by the formation of single-phase iron boride mainly on the surface. Boride layer thickness decreases with increase in carbon content of the case. Activation energy for the borided AISI 1015 steel is 119.22 KJ/mol. The activation energies are 174.4 and 194.7 KJ/mol for borocarburized AISI 1015 steel having 0.30% C and 0.45% C, respectively. The activation energy increases with increase in carbon content due to precarburization. Empirical relations have been developed to predict boride layer thickness and are well correlated with experimental values for the process temperature and time. Tensile strength ranges from 421 to 599 N/mm2. Impact strength of borided specimens varies between 386.7 and 493.3 N-m while for borocarburized specimens it ranges between 103.7 N-m and 183.3 N-m. Fracture behavior of borided and borocarburized specimens under tensile and impact tests has been analyzed.

Tribological properties of boride based thermal diffusion coatings

Engineering components, e.g. tubing systems for the down-hole applications in the oil and gas industry (in particular, sucker rod pumps, progressing cavity pumps and some other components of the artificial lifting systems), as well as numerous valves and seats, bearings, gears and plungers, require protection against friction and sliding abrasion service conditions. The hard boride based coatings on steels and alloys obtained through the thermal diffusion process have a high potential for these severe application conditions over many other types of coatings as they can be obtained on the entire working surfaces of large size and complex shape products. Intensive tribological studies of the iron boride based coatings on carbon steel obtained at Endurance Technologies Inc. have been conducted using the Cameron–Plint testing unit (reciprocating sliding of the metallic rod under the load over a flat surface of the coated samples). The friction wear loss, friction coefficient and structural changes of the coatings have been studied in dry and lubricating (water–oil) friction conditions, which simulate actual application conditions. It was demonstrated that the obtained boride coatings have the friction loss significantly smaller than untreated steel (e.g. ∼10–30 times in the dry conditions and at least 5 times in the lubricating conditions) with no peeling and flaking-off. The friction coefficients of the boride coatings are steady over the test duration. The influence of the thickness on the boride coatings performance is demonstrated. The encouraging results are explained by the specific coating structure of the hard coating obtained through the thermal diffusion process and the thin ‘tribofilm’ formed during a friction mode.

Special Features of Preparation of Saturating Mixtures for Diffusion Chromoborating

Chemical and granulometric composition of components of saturating media are investigated using a JEOL JSM-7001F electron microscope with X-MAX energy dispersive analyzer, and microstructure of the main fractions is investigated. Iron and carbon boride powders prepared by the methods of thermochemical treatment and solid phase alloying by grinding in a high-load planetary mill are analyzed.

Effect of Hard Coatings on Surface Gray Iron on Fracture Toughness

The characterization and fracture toughness with hard coatings formed at the surface of gray cast irons class 30 is evaluated in the present study. The formation of hard coatings was obtained out means of the pack boriding process; the treatment was carried out at temperatures of 1173 and 1223 K during 6 hours. The layers were evaluated by the techniques of X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and microindentation across the thickness of the iron boride layer. Three-point bending tests are carried out to examine the fracture toughness of gray cast irons boriding according to the ASTM 399 standard. Consequently, the stress intensity factor was evaluated by means of the finite element method (FEM) using the package ANSYS 11. 0 creating a two-dimensional model with elements of singularity around the tip crack. The results were compared with the experiments and have been found to be in good correlation.

Laser production of B–Ni complex layers

The paper presents the results of modification with nickel and laser treatment of boronized layers produced on C45 steel. The objective of the study was to investigate the microstructure and selected properties of the new layer. The boronized layer modified with nickel was produced by the galvanic-diffusion method. Galvanic coating was produced first; next the galvanic-coated sample was diffusion boronized at 950°C for 4 h. This resulted in a two-zone microstructure consisting of a continuous subsurface zone and underlying needle-like iron borides. In the continuous zone microhardness was in the range of 1100–1200HV0.1 while in the second zone of the needle-like microstructure the microhardness was between 1600HV0.1 and 1400HV0.1. Galvanic-diffusion boronickelized layers were modified by using CO2 laser technology. As a result of the laser beam impact the presence of three zones was observed: remelted (MZ), heat affected (HAZ) and the substrate. Laser heat treatment was carried out by two methods. The first method consisted of remelting the galvanic-diffusion layer. The second method consisted of alloying galvanic coating with boron. Microhardness measurements of the surface layers were made before and after laser modification. An advantageous effect of laser modification on the microhardness of boronickelized layers was found. Microhardness profiles of boronickelized layers after laser modification were characterized by a smooth transition from the remelted zone through the heat affected zone to the substrate. In the remelted zone the microhardness was approximately 1100HV0.1. In this study, also an X-ray phase analysis was carried out. Nickel boride phases Ni3B and Ni4B3 were detected in the nickel modified boronized layer. In addition, the nonequilibrium phase of iron boride Fe3B occurred in the laser-modified layers. Laser modification had a positive effect on the wear resistance of nickel modified boronized layers.

Electronic structures and mechanical properties of iron borides from first principles

The structural properties, mechanical behaviors and electronic structures of FeB4 and FeB2 have been studied systematically by first-principles calculations considering the strong correlation effect. Our results show that FeB4 is incompressible and hard, but the recently reported superhard feature [Phys. Rev. Lett. 111 (2013) 157002] is not supported by the present calculations. Interestingly, we find that FeB2 rivals FeB4 in hardness. By analyzing their crystal geometries, band structures and density of states, we elucidate the underlying origins of the related physical properties.

Size and Crystallinity Dependence of Magnetism in Nanoscale Iron Boride, α-FeB

A nanoscale boride, α-FeB, with grains of variable size and crystallinity was synthesized by precipitation from solution followed by heat treatment (450 °C, 550 °C, 750 °C, 1050 °C). Analysis of transmission electron micrographs, electron diffraction, and magnetic measurements suggests superparamagnetism at room temperature for the smaller, more disordered particles of FeB, while the larger, more crystalline particles of α-FeB, with a particle size of approximately 20 nm, display open magnetic hysteresis loops and blocking. In contrast to the soft ferromagnetism of bulk β-FeB, which was synthesized by conventional solid state reaction at 1500 °C, the sample of α-FeB annealed at 1050 °C is a harder ferromagnet, possibly due to stacking faults that pin the magnetic domains; these stacking faults are apparent in the high resolution transmission electron micrographs. The changes in magnetic behavior are visible from the varying blocking temperatures (63 K, 94 K, 150 K, and >320 K from the smallest to the largest particles) and correlate with the transformations from amorphous to α-FeB and from α-FeB to β-FeB.

Microstructural Characteristics and Tribological Behavior of HVOF-Sprayed Novel Fe-Based Alloy Coatings

Thermally-sprayed Fe-based coatings have shown their potential for use in wear applications due to their good tribological properties. In addition, these kinds of coatings have other advantages, e.g., cost efficiency and positive environmental aspects. In this study, the microstructural details and tribological performances of Fe-based coatings (Fe-Cr-Ni-B-C and Fe-Cr-Ni-B-Mo-C) manufactured by High Velocity Oxygen Fuel (HVOF) thermal spray process are evaluated. Traditional Ni-based (Ni-Cr-Fe-Si-B-C) and hard-metal (WC-CoCr) coatings were chosen as references. Microstructural investigation (field-emission scanning electron microscope FESEM and X-Ray diffractometry XRD) reveals a high density and low oxide content for HVOF Fe-based coatings. Particle melting and rapid solidification resulted in a metastable austenitic phase with precipitates of mixed carbides and borides of chromium and iron which lead to remarkably high nanohardness. Tribological performances were evaluated by means of the ball on-disk dry sliding wear test, the rubber-wheel dry particle abrasion test, and the cavitation erosion wear test. A higher wear resistance validates Fe-based coatings as a future alternative to the more expensive and less environmentally friendly Ni-based alloys.