Fe2B Boride Research Articles

Magnetic and structural characterization of the mechanically alloyed Fe 75Si 15B 10 powders

Nanocrystalline Fe 75Si 15B 10 powders were obtained by mechanical alloying in a high energy planetary ball mill. Morphological, microstructural, structural and magnetic property changes during the milling process were followed by scanning electron microscopy, X-ray diffraction and magnetic measurements. The crystallite size reduction to the nanometer scale (6–13 nm) is accompanied by an increase in atomic level strain. The Fe 2B boride phase is formed after 5 h of milling. The dissolution of B and Si into the Fe lattice leads to the formation of bcc α-Fe(Si,B) solid solution. On prolonged milling time, a mixture of highly disordered α-Fe(Si,B) solid solution and Fe 2B boride is obtained. The coercivity and magnetization values are 55 Oe and 6.7 emu/g, respectively, after 150 h of milling.

Structural characterisation of the mechanically alloyed Fe<SUB align=right>57Co<SUB align=right>21Nb<SUB align=right>7B<SUB align=right>15 powders

X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to investigate the phase identification and the thermal behaviour of the mechanically alloyed Fe57Co21Nb7B15 powders. The diffusion of B into the Nb lattice leads, after 1 h of milling, to the formation of a bcc Nb(B) solid solution with a lattice parameter close to a = 0.3425 nm. The solid state reaction between Fe and B gives rise to the formation of Fe23B6 and Fe2B boride phases after 3 and 6 h of milling, respectively. On further milling (96 h), an amorphous matrix (∼80%), where nanocrystalline bcc α-Fe, bcc Nb(B), Fe2B and Fe3B phases were embedded, is obtained. The broad exothermic reaction in the DSC scans consists of several exothermic peaks and spreads over the entire temperature range 100-700°C. The enthalpy release at temperatures below 300°C can be attributed to recovery and strain relaxation. Crystallisation and grain growth are the dominating processes at high temperatures.

TiB2-reinforced composite coating by gas tungsten arc welding

In situ synthesized TiB2-reinforced Fe-based coating was fabricated by gas tungsten arc welding (GTAW) on AISI-4340 steel substrate using cheaper Fe–Ti, Fe–Cr, Fe–W, Fe–B alloys and B2O3 powders. The effects of processing parameters on the coating were investigated experimentally. Primary dendrites of ferrite (α) phase and complex TiB2, Fe2B borides were detected at the coated surface. The experimental results show that either coated surface or interface microstructures were formed by the distribution of particularly boron and titanium concentration. The difference in hardness of the microstructures is specifically attributed to the type of borides. The type, dimension, and the volume concentration changes of borides were correlated with the parameters as the concentration of additives and the dilution from the base material. The surfaces were subsequently characterized by scanning electron microscopy (SEM), the energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD), and differential thermal analysis (DTA).

Mechanical Properties of Boronizing Steels as Repercussion of Boron Phases

Results of the boride surface layers investigation, obtained by torsion and bending, show better ductility of the monophase Fe2B boride layers than the binary-phase FeB + Fe2B boride layers. This is especially outstanding for samples that are under higher thermal and mechanical load, where the binary-phase layer because of higher local stresses probably has tendency to fall away, respectively to husk.

Correlation of Microstructure with Hardness, Wear Resistance, and Corrosion Resistance of Powder-Injection-Molded Specimens of Fe-Alloy Powders

In this study, the powder injection molding (PIM) process was applied to Fe-alloy powders. Microstructure, hardness, wear resistance, and corrosion resistance of the PIM specimens were analyzed and compared with those of a conventional stainless steel, SS316L. When Fe-alloy powders were injection molded and then sintered at 1200 °C or 1250 °C, completely densified specimens with almost no pores were obtained. They contained 63 to 80 vol pct of hard (Cr,Fe)2B dispersed in the austenite or martensite matrix. Since these (Cr,Fe)2B borides were very hard, thermally stable, and corrosion resistant, hardness, high-temperature hardness, wear resistance, and corrosion resistance of the PIM specimens of Fe-alloy powders were 2 to 5 times as high as those of the stainless steel. Such property improvement suggested new applicability of the PIM products of Fe-alloy powders to structures and parts requiring excellent mechanical properties.

Measurement of Fracture Toughness in AISI 1018 Borided Steels by Vickers Indentation

This study evaluates the fracture toughness of Fe2B boride layers formed by the paste boriding thermochemical process on an AISI 1018 steel surface. The samples were placed in acrylic molds for the impregnation of boron carbide paste with thickness of 4mm over the sample surfaces to produce the diffusion into the steel. The aforementioned treatment considered one temperature, T= 1273 K, and three exposure times t=5, 6 and 8 h. Later, the borided samples were prepared metallographically to determine the mean values of the layer thicknesses and to produce Vickers microindentations at 45 m from the surface, applying four loads (1.9, 2.9, 4.9 and 9.8 N). The microcracks generated at the corners of the Vickers microindentation were considered as experimental parameters, which are introduced into two Palmqvist cracks models to determine their corresponding fracture toughness KC. As a result, the experimental parameters, such as exposure time and applied load are compared with the resulting fracture toughness of the borided phase.

Growth Kinetics of Boride Layers: A Modified Approach

This study evaluates the boron diffusion in the Fe2B phase formed at the surface of AISI 1018 steels during the paste boriding process. The treatment was carried out at temperatures of 1123, 1173, 1223 and 1273 K with 2, 4, 5, 6 and 8 h exposure times for each temperature using a 4 mm layer thickness of boron carbide paste over the material surface. The boron diffusion coefficient Fe2B D was determined by the mass balance equation and the boride incubation time assuming that the boride layers obey the parabolic growth law, while the boron concentration profile along the interphase Fe2B/substrate was unknown. The boron diffusion coefficient was interpreted as a function of the treatment temperature, obtaining the activation energy value for diffusion controlled growth of Fe2B boride phase.

Microstructure, Hardness, and Wear Resistance of Powder-Injection-Molded Products of Fe-Based Metamorphic Powders

Powder injection molding (PIM) process was applied to Fe-based metamorphic alloy powders, and microstructure, hardness, and wear resistance of the PIM products were analyzed and compared with those of conventional PIM stainless steel products. When Fe-based metamorphic powders were injection-molded and then sintered at 1200 oC, completely densified products with almost no pores were obtained. They contained 34 vol.% of (Cr,Fe)2B borides dispersed in the austenitic matrix without amorphous phases. Since these (Cr,Fe)2B borides were very hard and thermally stable, hardness, and wear resistance of the PIM products of Fe-based metamorphic powders were twice as high as those of conventional PIM stainless steel products. Such property improvement suggested new applicability of the PIM products of Fe-based metamorphic powders to structures and parts requiring excellent mechanical properties.

Growth of boride layers on the 13% Cr steel surface in a mixture of amorphous boron and KBF4

Two borides FeB and Fe2B were found to form as separate layers at the interface between a 13% Cr steel and boron at 850–950 °C and reaction times up to 12 h. The average chromium content is 8 at.% in the FeB layer and 9 at.% in the Fe2B layer. Both layers are characterized by a pronounced texture. The strongest reflections are {002} and {020} for the orthorhombic FeB phase and {002} for the tetragonal Fe2B phase. Diffusional growth kinetics of boride layers are close to parabolic and can alternatively be described by a system of two non-linear differential equations, producing a good fit to the experimental data. Annealing of a borided steel sample in the absence of boriding media results in disappearance of the FeB layer. Microhardness values are 17.9 ± 1.5 GPa for the FeB layer, 16.1 ± 0.9 for the Fe2B layer and 5.9 ± 0.3 GPa for the steel base. The abrasive wear resistance of the FeB layer is 25 times greater than that of the steel base. The Fe2B layer yields about a 15-fold increase in wear resistance of steel samples.

Fracture Toughness of Iron Boride Layers Obtained by Paste Boriding Process

The fracture toughness of the Fe2B phase was evaluated in this study. Formation of the Fe2B boride is carried out though paste boriding process applied on AISI 1045 steel surface. The treatment was carried out at temperatures of 1193, 1223 and 1273 K for 6 h using a 5 mm thick boron paste. A Vickers microhardness tester was used to generate microcracks at a load of 200g. The indentations were made across the thickness of the iron boride layer at four different distances from the substrate. The experimental results show that the critical stress intensity factor KIC for the Fe2B phase shows a potential law dependence on crack length; this contradicts the concepts of Linear Elastic Fracture Mechanics, which establish that the fracture toughness value is a constant of the material.

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.

Microstructure and mechanical properties of powder-injection-molded products of Cu-based amorphous powders and Fe-based metamorphic powders

In the present study, a powder-injection molding (PIM) process was applied to Cu-based amorphous alloy powders and Fe-based metamorphic alloy powders, and microstructure, hardness, and wear resistance of the PIM products were analyzed and compared with those of conventional PIM stainless steel products. Injection-molded Cu-based amorphous powders were hardly sintered even at temperatures just below the melting temperature as most of amorphous phases were replaced by crystalline phases. When Fe-based metamorphic powders were injection-molded and then sintered at 1200 °C, completely densified products with almost no pores were obtained. They contained 34 vol.% of (Cr,Fe) 2B borides dispersed in the austenitic matrix without amorphous phases. Since these (Cr,Fe) 2B borides were very hard and thermally stable, hardness, high-temperature hardness, and wear resistance of the PIM products of Fe-based metamorphic powders were twice as high as those of conventional PIM stainless steel products. Such property improvement suggested new applicability of the PIM products of Fe-based metamorphic powders to structures and parts requiring excellent mechanical properties.

Study of microcracks morphology produced by Vickers indentation on AISI 1045 borided steels

In this work, we analyzed the roughness morphology of indentation microcracks produced by the Vickers microindentation in the iron boride Fe 2B. Using the paste boriding process, the boride layers were formed at the surface of AISI 1045 steels. The diffusion processes were carried out with 5 mm of boron paste thickness over the substrate surface at three different temperatures (1193, 1223 and 1273 K) with two different time exposures. The indentations in each Fe 2B layer were made using a constant load of 200 g at four different distances from the surface. The fracture behavior of the Fe 2B borided phase is found to be brittle in nature. The profiles of microcracks formed at the corners of the indentations were obtained using the scanning electronic microscopy and were analyzed within the framework of fractal geometry. We found that all indentation microcracks display a self-affine invariance characterized by the same roughness (Hurst) exponent H = 0.8 ± 0.1. The effect of the self-affine roughness of indentation microcracks on the measured fracture toughness is discussed within the framework of the mechanics of self-affine cracks. It is pointed out that the arrest of indentation microcracks is controlled by the fractal fracture toughness, which for the Fe 2B borided phase is found to be K fc = 0.42 ± 0.02 MPa m 0.75 at all distances from the surface.

Diffusional Growth Kinetics of Boride Layers at the 13% Cr Steel Interface with Amorphous Boron

Two borides FeB and Fe2B were found to form as separate layers at the interface between a 13% Cr steel and boron at 850-950 oC and reaction times up to 12 h. The chromium distribution within the boride layers is rather irregular. Its average content is 8 at. % in the FeB layer and 9 at. % in the Fe2B layer. Both layers are characterized by a pronounced texture. The strongest reflections are {002} and {020} for the orthorhombic FeB phase and {002} for the tetragonal Fe2B phase. Diffusional growth kinetics of boride layers are close to parabolic and can alternatively be described by a system of two non-linear differential equations, producing a good fit to the experimental data.

Dimensional analysis in the growth kinetics of FeB and Fe<SUB align=right>2B layers during the boriding process

Dimensional analysis is presented as a powerful tool in the study of the paste boriding process. In particular, a dimensional method is used to study the growth kinetics of the boride layers FeB and Fe2B. Experiments were performed in AISI 1045 steel and AISI M2 steel, to test the suggested model. Results indicate that the growth of boride layers obeys power laws of the form γ = αχβ, where the α and β constants are a function of the material and the interface of interest.

Characterization of boronized layers on a XC38 steel

Boronizing of an XC38 steel was performed by immersion in molten salts. These were based on a borax containing three reducing agents: boron carbide (B4C), aluminium (Al) and silicon carbide (SiC). This work gives a survey on the nature and quality of the layers which were obtained according to the boronizing bath. The mechanical features (hardness, scratch and wear resistance) of the deposited layers are discussed according to the experimental conditions used for their characterization. Effects of the boronizing bath composition on the obtained layers' quality are also discussed.According to the borax's reducing agents, the boronized layer deposited on the XC38 steel was either single- or double-phase. Al and B4C led to double-phased boronized layers, whereas SiC gave way to a single-phase layer. All the layers were of comparable hardness which was about 2100 HV on the samples for the boride FeB and 1800 HV for the boride Fe2B.The scratch and “pin-on-disk” wear resistance depended on the layers' microstructure. The best values of scratch and wear resistance were obtained for SiC which led to the formation of a single-phase layer. The apparition of scaling occurred at loads superior to 200 N.

Laser surface modification of carburized and borocarburized 15CrNi6 steel

The paper presents the results of laser heat treatment (LHT) of carburized and borocarburized 15CrNi6 low-carbon steel. Laser tracks were arranged by CO 2 laser beam as multiple tracks formed in the shape of a helical line. The microstructure and properties of these diffusion layers were compared with those obtained after through-hardening. The microstructure after carburizing and LHT consists of adjacent characteristic zones: re-melted zone (coarse-grained martensite), carburized layer with heat affected zone (fine acicular martensite), carburized layer without heat treatment and the substrate (ferrite and pearlite). The highest measured microhardness (about 820 HV) was observed in re-melted and heat affected zones. The increase of distance from the surface was accompanied by a gradual decrease of microhardness up to 400 HV beneath the HAZ and up to 250 HV in the core of steel. The carburized layer after LHT exhibited a higher resistance to frictional wear compared to a carburized layer after through-hardening. The microstructure after borocarburizing and LHT consists of the following characteristic zones: iron borides of laser-modified morphology (FeB and Fe 2B), carburized layer with heat affected zone (martensite and alloyed cementite), carburized layer without heat treatment and the substrate (ferrite and pearlite). The highest microhardness was obtained in the iron boride zone. The microhardness of FeB boride extended up to 2200 HV and for the Fe 2B boride up to about 1300–1600 HV. With increased distance from the surface, the microhardness gradually decreases to 800 HV in HAZ, 400–450 HV in the carburized layer without heat treatment and to 250 HV in low-carbon substrate. The iron borides after LHT assume a globular shape, which leads to a lower texture and porosity of the borided layers. The increased resistance to friction wear of the borocarburized layers is certified in comparison with the borided layer after conventional heat treatment (through-hardening).

Use of fuzzy logic for modeling the growth of Fe2B boride layers during boronizing

In this study, the evaluation of the phase Fe2B growth in AISI 1045 steel during paste boronizing was carried out. Fuzzy logic Mamdani and Takagi–Sugeno methods were used as the technical model. The experimental procedure was performed in a solid paste medium, at temperatures range of 1193–1273 K; for 2, 4 and 6 h; and modifying the boron potential (paste thickness) at the metal surface. Membership functions were proposed for fuzzification and defuzzification of the input and output values. The system structure utilized was based on two membership functions for the input (time and paste thickness), and one for the output (layer growth). Comparing the results, given by the fuzzy logic system with experimental data, the medium error generated from the Mamdani method was 2.61%, and from the Takagi–Sugeno was 3.62%. It is concluded that the technique of fuzzy logic is an alternative for modeling the growth of borided phases.

Structure refinements of iron borides Fe2B and FeB

Abstract Crystals of the iron borides FeB and Fe2B were obtained from two different high temperature synthesis routes, viz. in combined copper/gallium flux and under high pressure conditions. Their crystal structures were investigated at room and low temperatures. Structure models from the literature were confirmed. The position of the boron atoms was unambiguously determined. FeB (Pnma, no. 62) contains zig-zag chains of boron atoms in which the boron atoms are coordinated by seven iron atoms in the form of a mono-capped trigonal prism. Fe2B (I4/mcm, no. 140) contains single boron atoms in a square antiprismatic iron atom coordination.

Deformation-induced dissolution of the Fe2B boride in nanocrystalline α-Fe

Structural-phase transformations in the α-Fe+Fe2B composite with a total boron content of 15 at. % during mechanical grinding in a planetary ball mill have been studied using X-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. It has been established that dissolution of the Fe2B boride with the formation of an amorphous phase and segregations of boron atoms at grain boundaries occur after the grain size reaches 3 nm. In this work a comparative analysis of the deformation-induced dissolution of Fe2B and Fe3C in the Fe-B and Fe-C systems has been made and the possible mechanisms of the structural-phase transformations have been discussed.