Fe2B Boride Research Articles

Properties and Growth Kinetics of the Boride Layer of a Boriding-Strengthened Fe-Based Powder Metallurgical Material

The Fe-based powder metallurgical material was directly sintered by the packed powder boriding method to obtain specimens with the boride layer. These materials were treated at 1123, 1223, and 1323 K for 3, 5, 7, and 10 h, the morphology and thickness of the boride layer were examined with SEM. The phase composition of the boride layer, was analyzed with X-ray diffractometer, and the Rockwell-C indentation test was used to estimate the quality of the bonding strength between the boride layer and substrate. The growth kinetics of the layer was fitted to obtain the plot of thickness variation dynamics. The boride layer thickness is 35–183 μm. The biphase (Fe2B+FeB), and single-phase Fe2B boride layers are obtained at 1323 K and at 1123 and 1223 K, respectively. The quality of the bonding strength of the boride layer obtained at 1223 K for 5 h is approved by the HF3 grade according to the specifications. The diffusion activation energy of B atoms in this experiment is 164 kJ/mol. The sintering temperature and boriding time are closely related to the thickness of the boride layer, and the relationship between the boriding time and the thickness of the boride layer is parabolic. The squared thickness and boriding time are linearly related and consistent with the Arrhenius formula. The microhardness of the boride layer is significantly higher than that of the substrate. The number of defects in the layer is growing with time. The characteristic comb-tooth shape of the boride layer is gradually passivated, and the tip is not obvious until the front edge of the layer is relatively flat. This phenomenon is more pronounced at high temperatures.

Structure, phase composition and properties of borowolframed coating on steel 20 after microarc chemical heat treatment

The results of the research devoted to the study of structure, phase composition, micro hardness and wear resistance of the borowolframed coating on steel 20, that was obtained by the method of microarc chemical heat treatment, are presented. With the help of microrentgenospectral analysis, it was found that during microarc borowolframing, both grain-boundary and trans crystallite diffusion of boron, carbon and tungsten occurs, which avoided the formation of brittle carboborid eutectics along the boundaries of plastic grains of the layer base. X-ray phase analysis in the diffusion coating found iron and tungsten borides Fe2B and W2B5, tungsten carbide WC, boron nitride BN and iron intermetallic with tungsten Fe7W6. The micro hardness of the borovolframed layer was 12-13 GPa. The wear rate of the borowolframed samples is reduced by 4.4 times in comparison with steel 20 in the initial structural state.

Laser Surface Alloying of Austenitic 316L Steel with Boron and Some Metallic Elements: Microstructure.

Austenitic 316L steel is known for its good oxidation resistance and corrosion behavior. However, the poor wear protection is its substantial disadvantage. In this study, laser surface alloying with boron and some metallic elements was used in order to form the surface layers of improved wear behavior. The microstructure was studied using OM, SEM, XRD, and EDS techniques. The laser-alloyed layers consisted of the only re-melted zone (MZ). The hard ceramic phases (Fe2B, Cr2B, Ni2B, or Ni3B borides) occurred in a soft austenitic matrix. The relatively high overlapping (86%) resulted in a uniform thickness and homogeneous microstructure of the layers. All the laser-alloyed layers were free from defects, such as microcracks or gas pores, due to the use of relatively high dilution ratios (above 0.37). The heat-affected zone (HAZ) wasn’t visible in the microstructure because of the extended stability of austenite up to room temperature and no possibility to change this structure during fast cooling. The use of the mixtures of boron and selected metallic elements as the alloying materials caused the diminished laser beam power in order to obtain the layers of acceptable quality. The thickness of laser-alloyed layers (308–432 μm) was significantly higher than that produced using diffusion boriding techniques.

Mechanical Properties and Corrosion Resistance of Borosintered Distaloy Steels

Distaloy SA is a sponge iron powder (nominal composition: Fe-1.75Ni-1.5Cu-0.5Mo) widely used in the production of powder metallurgy (P/M) parts in the automotive industry. In this study, Distaloy SA powders were sintered in two different atmospheres, one consisting of pure Ar gas (traditional sintering) and the other consisting of a mixture of 90 wt.% B4C and 10 wt.% NaBF4 powders (borosintering). To investigate the effects of the different sintering atmospheres, the P/M samples were characterized using density measurements, surface roughness tests, scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, microhardness measurements, nanoindentation experiments, wear tests and corrosion tests. On the surface of the borosintered samples, a 160-325 µm thick double-phase FeB + Fe2B boride layer was formed. The hardness (1405-1688 HV) and elastic modulus (122.21-162.42 GPa) of the surface were significantly improved with the borosintering treatment compared to conventional sintering (215-250 HV, 63.28-94.86 GPa). Borosintering also provided low friction coefficient values and an increased wear resistance compared to conventional sintering. A significant increase in corrosion resistance was also observed with the borosintering treatment in three different solutions. The corrosion rates of both sintered and borosintered samples were ranked as NaCl < HCl < H2SO4. The borosintered samples displayed superior corrosion resistance compared to the sintered samples, especially in the acid solutions. The results of this study show that significant cost savings can be achieved by combining the boriding and sintering treatments in a single borosintering process.

Investigation of the Critical Behavior, Magnetocaloric Effect and Hyperfine Structure in the Fe72Nb8B20 Powders.

Microstructure as well as magnetic, thermal and magnetocaloric properties of the mechanically alloyed Fe72Nb8B20 powders have been investigated by means of Mössbauer spectrometry, differential scanning calorimetry (DSC), and magnetic measurements. The Mössbauer spectrometry results showed the formation of nanostructured Fe(B) and Fe(Nb) solid solutions, Fe2B boride, and an amorphous phase. The endothermic and exothermic peaks that are observed in the DSC curves might be related to the Curie temperature, and the crystallization of the amorphous phase, respectively. The critical exponent values around the magnetic phase transition of the amorphous phase (TC = 480 K), are deduced from the modified Arrott plots, Kouvel−Fisher curves and critical isotherm examination. The calculated values (β = 0.457 ± 0.012, γ = 0.863 ± 0.136 and δ = 3.090 ± 0.004) are near to those of the mean field model, revealing a dominating role of magnetic order arising due to long-range ferromagnetic interactions, as the critical exponents are mean-field-like. The maximum entropy change and the refrigerant capacity values are 1.45 J/kg·K and 239 J/kg, respectively, under a magnetic field of 5 T.

The Influence of the Third Element on Nano-Mechanical Properties of Iron Borides FeB and Fe2B Formed in Fe-B-X (X = C, Cr, Mn, V, W, Mn + V) Alloys.

In this study, the influence of alloying elements on the mechanical properties of iron borides FeB and Fe2B formed in Fe-B-X (X = C, Cr, Mn, V, W, Mn + V) alloys were evaluated using instrumented indentation measurement. The microstructural characterization of the alloys was performed by means of X-ray diffraction and scanning electron microscope equipped with an energy dispersive X-ray analyzer. The fraction of the phases present in the alloys was determined either by the lever rule or by image analysis. The hardest and stiffest FeB formed in Fe-B-X (X = C, Cr, Mn) alloys was observed in the Fe-B-Cr alloys, where indentation hardness of HIT = 26.9 ± 1.4 GPa and indentation modulus of EIT = 486 ± 22 GPa were determined. The highest hardness of Fe2B was determined in the presence of tungsten as an alloying element, HIT = 20.8 ± 0.9 GPa. The lowest indentation hardness is measured in manganese alloyed FeB and Fe2B. In both FeB and Fe2B, an indentation size effect was observed, showing a decrease of hardness with increasing indentation depth.

The structure of alloys of boron-rich corner of Fe–В–C phase diagram

The structure and microdurometric characteristics of the Fe–В–С alloys in the range of high concentration of boron (&gt;16.0 wt. % B) and low concentration of carbon (≥ 0.1 wt. % С) were investigated in this work. The methods of quantitative metallographic, X-ray, differential thermal, fluorescent spectral and microdurometric analyses were applied. Carbon was established to dissolve completely in phase constituents of the investigated alloys, forming solid solutions based on iron borides FeB, FeB2, FeB~4 or FeB~19. It was suggested the existence of one eutectic transformation between borides FeB2 and FeB~4 as well as two peritectic transformations between borides FeB and FeB2 or FeB~4 and FeB~19 correspondingly in the studied concentration range. The formation of boride FeB~4 was explained by its stabilization in the presence of carbon in the alloys. After annealing in vacuum at 900 °C for 10 hours with following quenching, the structure became coarser, but no traces of phase decomposition were revealed in the most alloys. Microhardness of the phases observed in the structure of the investigated alloys increased in the following sequence: FeB→FeB2→FeB~4→FeB~19.

Fe-Me-B Diffusion Layers for Surface Modification of Carbon Steels

Multicomponent boron-based diffusion layers are capable to provide a wider variety of surface improvements compared to pure boriding. In this research, we consider a way to increase mechanical properties of carbon steels by using two-component thermal-chemical treatment (TCT) such as boroaluminizing (B+Al), and boronickelizing (B+Ni). Diffusion treatment of steel surface was carried out by pack method in powder mixtures, and pastes, containing the above-mentioned elements and sodium fluoride as an activator. The exposure time was 3 hours, the treatment temperature was 950 °C. Pure boriding was conducted additionally to compare with two-component methods. The metallographic analysis revealed diffusion layers with a tooth-like structure after boriding and B+Ni. Typical composition of boride layer with iron boride FeB as an outer phase and Fe2B as an inner one was obtained after the first method. EDS analysis revealed a small amount of Ni (less than 1%) in boronickelized layer. Although XRD analysis revealed Ni2B, Fe3Ni3B besides iron borides and carboborides after B+Ni. Another structure was obtained after B+Al – namely a layered microstructure with outer softer iron aluminides and iron borides beneath. The thickest layer was obtained after boriding with the thickness of 140-160 μm, where higher value corresponds to low-carbon steel and vice versa. While for boroaluminizing the layer thickness was around 120-140 μm and for boronickelizing - 60-100 μm. Microhardness profiles differ significantly depending on the TCT method. For instance, initial high values followed by a drastic drop of hardness for boriding and boronickelizing. Wave type profiles characterize the microhardness distribution on boroaluminized samples. Wear tests indicated that samples with boride layer were the most wear resistant and the least resistant were the samples after B+Al. Fe-Me-B layers with the tooth-like structure are superior to the ones with the layered structure.

Investigation of Dry Sliding Wear Behavior of Pack Boriding Fe-Based Powder Metallurgy

The powder compact was directly sintered by a pack boriding process to prepare a Fe-based material having a boride layer. The boriding process was carried out at 850 °C, 950 °C and 1050 °C for 3, 5 and 10 h. The morphology of the boride layer was observed by a metallographic microscope, and the thickness of the boride layer was measured. The surface hardness of the boride layer was measured by a Rockwell hardness tester, the phase composition of the boride layer was analyzed by X-ray diffractometer and the friction and wear properties of the sample were tested on the HT-1000 friction and wear tester. The results show that the boride layer was mainly composed of Fe2B single phase, and its thickness was uniform and firmly bonded to the substrate. The thickness and hardness of the layer gradually increased with time and temperature. The binding force between the layer and the substrate would be decreased while the thickness of the layer was too thin or too thick. Boriding at 850 °C and 950 °C resulted with formation of Fe2B phases, while FeB and Fe2B boride phases occurred at 1050 °C. The boride layer has good wear resistance in the friction and wear experiments, the wear mechanism of the boride specimen is mainly the fatigue spalling caused by plastic deformation of microcracks, while the un-bored samples show severe oxidation and plastic deformation.

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.

Phase-structure formation and features of the behavior of iron–high-carbon ferrochrome–nickel boride powder materials under abrasive wear conditions

The study covers the effect of nickel boride (Ni 3 B) additives on phase-structure formation, physical and mechanical properties and resistance of iron – high-carbon ferrochrome powder (35 wt.%) to abrasive wear. It was found that Ni 3 B additives provide the formation of a multiphase, microheterogeneous structure of a matrix-filled material consisting of chromium steel and solid inclusions of complex chromium-iron carbides such as Ме 3 С, Me 7 C 3 and Me 23 C 6 and borides FeB, Fe 2 B that significantly increase the microhardness of solid phases from 8.34 to 11.65 GPa. It was also revealed that the increase in the content of a doping additive from 3.5 to 8.7 wt.% increases base material resistance to abrasion wear from 6.9 to 12.2 km/mm and decreases hardness from 75 to 68 HRA and bending strength from 1560 to 844 MPa. The method of optical profilometry was used to study the topographical features of worn surface morphology to estimate the depth and local development of wear on sample surfaces with standardized roughness parameters calculated based on 2D or 3D profiles. Average roughness parameters for each composition were found to be R a = 0.44÷0.6, R z = 0.49÷1.2 μm, and R p = 0.26÷0.56 μm for materials doped with Ni 3 B, and R a = 1.860 μm, R z = 0.813 μm, R p = 3.356 μm for the base material. It was shown that the promising compositions that combine acceptable physical and mechanical properties and improved abrasive wear resistance are materials based on the Fe–35%FeН800 system containing 5.2–6.9 wt.% of Ni 3 B.

Efficient photocatalytic CO2 reduction mediated by transitional metal borides: metal site-dependent activity and selectivity

Transitional metal borides Ni3B, Co3B and Fe2B can serve as effective and low-cost cocatalysts to boost photocatalytic CO2 reduction performances.

Study of structure and properties of steel 38KhN3МFА after low-temperature liquid borating

The effect of low-temperature liquid borating on the structure and hardness of steel 38KhN3МFА is studied. It is found that in the borating process at temperature 600...660 °C and duration 8...32 hours boride coating with thickness of 6...19 μm with surface hardness of 1900...2000 HV is formed on the steel surface. The optimal borating regimes are determined, in which hardened layer with solid core is formed. The presence of two boride phases FeB and Fe2B in the boride layer is established by metallographic, X-ray and electron microscopic analyzes.

Determination of thermodynamic stability of FeB monoboride

In this paper we investigate the phase composition and phase transformations in the Fe-B system alloys with boron content in the range of 9.0–15.0 wt.%. We use microstructural, X-ray diffraction, differential thermal and durometric analyzes to determine the physical properties of the alloys. The experimental findings show that in the as-cast alloy structure there is Fe5B3 phase in small quantities along with FeB monoboride and Fe2B boride. The Fe5B3 phase is formed as a result of the peritectic reaction L+FeB→Fe5B3 at the temperature of 1680 K. The eutectic transformation L→Fe5B3 +Fe2B occurs in the boron concentration range of 8.8–10.5 wt.%. After annealing of the Fe-B alloys at the temperature of 1473 K and cooling with the rate of 102 K/s we observe the occurring of the Fe5B3 phase. To spot an opportunity of the secondary monoboride formation in the alloys under consideration, we calculate the thermodynamic characteristics of stability of the system.&#x0D; Accounting for the contribution of the first degree approximation of high-temperature expansion of thermodynamic potential of FeB iron monoboride in a Fe-B binary alloy enables us to study its thermodynamic stability. It is shown that stability decrease of FeB at 1423 K allows suggesting that at this temperature the phase transformation occurs and this fact correlates to the differential thermal analysis results.

In Situ Formation of TiB2 in Fe-B System with Titanium Addition and Its Influence on Phase Composition, Sintering Process and Mechanical Properties.

Interaction of iron and boron at elevated temperatures results in the formation of an E (Fe + Fe2B) eutectic phase that plays a great role in enhancing mass transport phenomena during thermal annealing and therefore in the densification of sintered compacts. When cooled down, this phase solidifies as interconnected hard and brittle material consisting of a continuous network of Fe2B borides formed at the grain boundaries. To increase ductile behaviour, a change in precipitates’ stoichiometry was investigated by partially replacing iron borides by titanium borides. The powder of elemental titanium was introduced to blend of iron and boron powders in order to induce TiB2 in situ formation. Titanium addition influence on microstructure, phase composition, density and mechanical properties was investigated. The observations were supported with thermodynamic calculations. The change in phase composition was analysed by means of dilatometry and X-ray diffraction (XRD) coupled with thermodynamic calculations.

Influence of Overheating and Cooling Rate on the Structures and Properties of Alloys of the Fe–B System

It is shown that the overheating of a melt by 150°K over the liquidus curve and a cooling rate of 102−104 °K/sec favor the formation of a homogeneous finely divided eutectics in Fe–B alloys with boron contents of 2.0–4.5 wt.% and inhibit the appearance of primary crystals of iron in hypoeutectic alloys and Fe2B boride in hypereutectic alloys. It is established that, under these conditions, Fe3B iron boride is formed in the eutectics. This improves the mechanical and corrosion properties of these alloys.

Prediction Model for Studying the Growth Kinetics of Fe2B Boride Layers during Boronizing

Prediction Model for Studying the Growth Kinetics of Fe2B Boride Layers during Boronizing

Structure, phase composition, mechanical properties and wear resistance of steel after microarc boriding and vanadation

Boriding is a common method of thermo-chemical treatment of steel products. It increases their hardness and wear resistance, but also increases the surface fragility, has a long duration and high labor intensity. The combined coating with boron and vanadium is used to improve the properties, and it is possible to apply microarc surface alloying to reduce the duration of the diffusion saturation process. This makes it possible to intensify the diffusion of alloying elements by forming a gas discharge zone at the surface of the steel product. The aim of this work was to study the structure, phase composition, mechanical properties and wear resistance of steel after boriding and vanadation. During the experiments, a lubricant containing boron carbide powders B4C and ferrovanadium FeV80 were used, which was applied to the surface of the steel sample. During boriding and vanadation of steel a surface layer with a thickness of 150 – 190 μm is formed. It has a base with microhardness of 7.8 – 8.3 GPa and light grey granular inclusions and eutectic areas with microhardness of 13.5 – 14.0 GPa. Further there is a carbonized layer of eutectoid concentration, passing into the original ferrite-perlite structure. The content of alloying elements in the characteristic points of the surface layer was determined, which confirmed the increased content of carbon, vanadium and boron in the base layer, areas of eutectic and carbide phase. X-ray phase analysis revealed the presence of iron borides FeB and Fe2B, vanadium borides VB2 and V2B3 and vanadium carbide VC0.88 in the surface layer. Mechanical properties of coatings were studied by microindentation of its cross-section with registration and analysis of deformation diagram under loading and subsequent unloading of the indenter. Hardness at indentation in the base layer increased to 7.95 GPa, in dispersed inclusions – to 13.90 GPa. The modulus of elasticity for indentation in the base and inclusions is 238 MPa and 340 MPa, respectively. Creep and proportion of the plastic component in microindentation is naturally reduced with increase in hardness. Fine inclusions of iron borides, vanadium borides and carbides significantly increase the steel wear resistance. It has increased in 4 times during friction against the fixed abrasive particles in comparison with the initial state.

Formation of Surface Layers on Fe70Si15B15 Alloy upon Heating in an Inert Atmosphere with Air Impurities

The composition of surface layers formed during high-temperature interaction between Fe70Si15B15 alloy and air impurities in an inert atmosphere is determined using equilibrium thermodynamic means. It is shown that at T = 1473 K, Fe3O4, FeSiO3, and B2O3 are at the interface between the alloy and the gas. Intermediate layers of internal oxidation contain FeSiO3, B2O3, SiO2, and BN. The iron-based region adjacent to the alloy contains silicides Fe3Si and FeSi; borides Fe2B and FeB; and nitride BN. At a relatively low concentration of air impurities in the inert gas, the destruction of a surface film consisting mainly of SiO2 is detected in the temperature range of 1600–1800 K as an anomaly on the damping decrement polytherm of free torsional vibrations of the crucible with the melt.

Isothermal Section of the B-Cr-Fe System at 873 K

An experimental study of the phase equilibria of the B-Cr-Fe ternary system at 873 K by means of x-ray diffraction and scanning electron microscopy has been carried out. Iron and chromium solid solutions, six chromium borides Cr2B, Cr5B3, CrB, Cr3B4, CrB2 and CrB4, two iron borides Fe2B and FeB, intermetallic σ phase, and β-rhombohedral B were identified in the B-Cr-Fe model alloys after long-term annealing (2160-2300 h). Solubilities of chromium in iron borides and iron in chromium borides were determined. No ternary phase was found in the system. Based on the experimental results, an isothermal section of the B-Cr-Fe system at 873 K was established.