Chromium Borides Research Articles

Nanoindentation of B4C-HfB2 particulate ceramic composite doped with Cr–B compounds

Mechanical behavior of B4C - HfB2 particulate ceramic composite doped with CrB + Cr3B4 chromium boride compounds were studied by nanoindentation. Hardness, Young's modulus, and indentation stress - indentation strain behavior of B4C and HfB2 phases was computed. It was found that hardness and Young's modulus of B4C matrix phase in B4C - HfB2 doped with Cr - B was increased as compared to those hardness and Young's modulus of pure B4C. It was also found that indentation stress was relieved by “pop-in” events in some of the B4C grains, however, the “pop-in” discontinuous events were always observed upon indentation of HfB2 grains, that lead to a decrease in hardness of HfB2 from 40 to 50 GPa before “pop-ins” to 28–32 GPa after “pop-ins”. The obtained results can be further used in calculations of thermal residual stresses in B4C and HfB2 phases of B4C - HfB2 particulate ceramic composite.

Novel Tetragonal Boron Pnictides BX (X = N, P, As, Sb, Bi) with Square B2X2 Motifs from Crystal Chemistry and First Principles

Novel tetragonal (P42/mnm) boron pnictides BX (X = N, P, As, Sb, Bi) with chromium boride (crb) topology exhibiting a square B2X2 motif with resulting edge- and corner-sharing tetrahedra were predicted from crystal chemistry and extensively characterized by density functional theory (DFT) calculations. All new BX phases were found to be cohesive with decreasing cohesive energy along the series. Mechanically stable with positive sets of elastic constants, all crb phases exhibit slightly lower hardness than other BX polymorphs due to increased openness of the crystal structures. All-positive phonon frequencies characterize the crb BX family except for X = Bi, which shows a slight acoustic instability; also, the shape of the phonon spectra changes from band-like for X = N, P, As to flat bands for the heavier elements. The electronic band structures reveal insulating to semiconducting properties for crb BX, depending on the pnictogen nature along the series.

Mechanochemical synthesis, purification, and optimization studies of Cr boride@MgO particles

Chromium boride, an advanced ceramic material, is commonly produced by powder metallurgy methods using elemental boron and chromium powder, borothermic reactions, or boron carbide reduction of Cr2O3. In this study, a mechanochemical method for the production of chromium boride was developed, subsequent purification was performed, and the whole process was optimized. The amounts of Cr2O3, B2O3, and Mg in the initial powder blends were determined by computational thermodynamic methods based on their equilibrium compositions. Firstly, stoichiometric starting-powder blends were milled at different durations (1, 2, 3, 4, 5, and 8 h). The optimum purification route was determined using acid leaching experiments carried out with different acids, at different temperatures, and concentrations. Secondly, powders prepared in excess amounts were synthesized at the optimum duration (5 h) and leaching condition (0.1 M HCl, 25 °C). For the 100 wt % excess B2O3, 25 wt % excess Mg and 0.8 moles of Cr2O3 composition, annealing was conducted at 1100 °C. Characterization studies, X-ray diffractometry (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), transmission electron microscopy (TEM), and atomic absorption spectroscopy (AAS) were conducted on the milled and leached powders. After annealing, CrB, CrB2, Cr3B4 and MgO phases were obtained in the XRD patterns. The particle sizes of the resulting materials were also analyzed, and it was found to be nearly 3.11 μm after annealing. Finally, the TEM analysis revealed that the MgO peak evident in the XRD patterns was MgO shell covering the Cr boride particles having submicron sizes; hence, a pure Cr boride@MgO core-shell structure was obtained.

Surface modification of die steels by liquid boriding

The research investigates the effect of liquid boriding on the microstructure, composition and microhardness of the surface layer on 5KhNM and 3Kh2V8F die steels. Boriding was carried out for 8 hours at 850 and 1000 °С in a melt based on sodium tetraborate and sodium salts. After high-temperature exposure during the boriding process, the samples were quenched in oil and tempered. Next, the samples were subjected to metallographic, X-ray spectral, X-ray diffraction and durometric analyses. As a result of processing, boride diffusion layers were obtained on the surface of 5KhNM and 3Kh2V8F steels up to 100 and 130 μm thick, respectively. It has been established that iron borides Fe2B and FeB are formed on the surface of both steels. In addition, chromium boride CrB is additionally formed on the surface of 5KhNM steel, increasing the maximum microhardness of the layer to 2130 HV. The maximum microhardness of 3Kh2V8F steel reaches 1709 HV due to the formation of borides and carbides in the layer. A study of the surface topography after boriding showed that the roughness parameter Ra of 5KhNM steel increased by 1.87 times, and of 3Kh2V8F steel by 1.78 times compared to the initial state.

Research of Increase of the Wear Resistance of Machine Parts and Tools by Surface Alloying

The work scientifically substantiates the application of an effective technology for increasing the wear resistance of machine parts and tools due to complex diffusion saturation of the surface layer of parts made of iron-carbon alloys in the process of casting on gasified models based on the optimization of the composition of saturating mixtures and the establishment of patterns of structure formation.
 The possibility of strengthening the surface of castings from cast iron SCH20 and steels of various composition (25L, 30L, 35L, 45L, 25HL, 110H13L), obtained by methods of casting in an open mold and on gasified models, has been established. It is shown that the diffusion boride layer on 35L steel, obtained during casting, has an order of magnitude greater thickness (up to 5 mm) compared to the diffusion layers obtained by chemical-thermal treatment methods (up to 0.25 mm). Analytical dependencies have been established that connect the components of the composition of the mixture (chromium boride (CrB2), boron carbide (B4C), graphite, bentonite, sodium fluoride (NaF)), which saturates, with wear resistance and the thickness of the diffusion layer after hardening in the process of obtaining a casting by the method of casting on gasified models.
 A new composition of the saturating medium has been developed for surface strengthening in the production of cast parts from gray iron, carbon and alloy steels by simultaneous saturation with boron and chromium, containing chromium boride, boron carbide, graphite, bentonite, sodium fluoride (50-60 wt. % B4C + 20-25 wt. % CrB2 + 2-3 wt. % + 5-15 wt. % finely dispersed graphite + 5-7 wt. % bentonite). The application of the developed strengthening technology allows to improve operational properties, in particular, the wear resistance of machine parts and tools up to 25 times (compared to previously used methods), as well as to reduce the labor intensity of the strengthening process by up to 3.5 times.
 Tests of dies for pressing wood waste into briquettes made of 45L steel, strengthened with the help of the developed technology, showed that their stability increases more than 4.5 times compared to the previously used ones made of HVH steel strengthened by carbonitriding, and the use of the developed strengthening technology allows reduce the cost of manufacturing this part by 1.5 times.

Dually Sulphophilic Chromium Boride Nanocatalyst Boosting Sulfur Conversion Kinetics Toward High-Performance Lithium-Sulfur Batteries.

The sluggish kinetics of sulfur conversions have long been hindering the implementation of fast and efficient sulfur electrochemistry in lithium-sulfur (Li-S) batteries. In this regard, herein the unique chromium boride (CrB) is developed via a well-confined mild-temperature thermal reaction to serve as an advanced sulfur electrocatalyst. Its interstitial-alloy nature features excellent conductivity, while the nano-lamination architecture affords abundant active sites for host-guest interactions. More importantly, the CrB nanocatalyst demonstrates a dual sulphophilicity with simultaneous Cr─S and B─S bondage for establishing strong interactions with the intermediate polysulfides. As a result, significant stabilization and promotion of sulfur redox behavior can be achieved, enabling an excellent Li-S cell cyclability with a minimum capacity fading rate of 0.0176% per cycle over 2000 cycles and a favorable rate capability up to 7C. Additionally, a high areal capacity of 5.2mAhcm-2 , and decent cycling and rate performances are still attainable under high sulfur loading and low electrolyte dosage. This work offers a facile approach and instructive insights into metal boride sulfur electrocatalyst, holding a good promise for pursuing high-efficiency sulfur electrochemistry and high-performance Li-S batteries.

Investigation on microstructure and mechanical properties of boron-modified 13Cr5Ni2Mo by powder-pack boriding

ABSTRACT The main objective of the present paper is to investigate the effect of pack boriding treatment at 950°C/4 h on surface 13 Cr supermartensitic stainless steel. Scanning electron microscopy and X-ray diffractometry were used to characterise the grown boride layers microstructures. In addition, we performed 3D profilometry, microhardness measurements, nanoindentation tests with a Berkovich diamond tip, Daimler-Benz Rockwell-C adhesion, and ball-on-disk wear tests in order to evaluate the mechanical properties. After boriding, the phases were found to be iron borides (FeB/Fe2B), chromium borides (CrB), nickel borides (Ni2B), and molybdenum borides (Mo2B). The results showed that the use of the powder-pack boriding process on 13Cr SMSS at 950°C/4 h conducted in the presence of dual phases (FeB/Fe2B) improved the mechanical properties compared to untreated material.

Microstructure and Properties of Chromium Boride–Chromium Carbide–Alumina Composite Coatings Prepared by Reactive Plasma Spraying

Microstructure and Properties of Chromium Boride–Chromium Carbide–Alumina Composite Coatings Prepared by Reactive Plasma Spraying

Study on Microstructure of Pack-Borided GH4169 Alloy

The structure of the solid pack-boriding layer of nickel-based alloy is studied in this paper. The nickel-based alloy GH4169 was subjected to pack-boriding treatment at 850 °C and 950 °C, and the structure of the alloy boriding layer was studied. After the boriding treatment, a relatively continuous and uniform boriding layer was formed on the surface, which was mainly composed of nickel borides and chromium borides. The sample formed a layered structure of a boriding layer, diffusion zone, and substrate. After boriding treatment, Cr migrated to the surface to form CrB, Cr5B3, and Cr2B chromium borides, while Ni migrated to the lower part of the boriding layer to form Ni2B and Ni3B nickel borides.

Influence of Laser Beam Power on the Temperature Distribution and Dimensions of the Molten-Pool Formed during Laser Boriding of Nimonic 80A-Alloy

Laser boriding is a surface treatment that involves the simultaneous re-melting and mixing of the alloying material, containing amorphous boron blended with diluted polyvinyl alcohol, with the substrate material (Nimonic 80A-alloy). As a result of high cooling rates, the boride layer is formed from a solidifying molten pool. The thickness of the produced layer depends on the laser treatment parameters, e.g., power of the laser beam, scanning rate, and laser beam radius. These parameters influence the temperature distribution on the cross-section of laser tracks and, thus, directly determine the size of the molten pool, from which the boride layer is formed after crystallization. In the present study, laser borided layers were produced on Nimonic 80A alloy using a CO2 molecular laser. Differences in the laser beam power used resulted in the formation of layers of different thicknesses, which resulted directly from the differences in the temperature distribution in the treated material. The amount of boron in the molten pool directly influenced the obtained hardness of the laser borided layer. It was found that the lower laser beam power had an advantageous effect on the hardness due to the higher percentage of nickel borides and chromium borides in the layer. The reasons for this situation are discussed in detail.

Development and characterization of boride-reinforced CoCrFeNi composites

CoCrFeNi is a face-centered cubic (FCC) high entropy alloy (HEA) that exhibits high ductility both at room temperature and at cryogenic temperatures but has limited strength. The present study is focused on addition of TiB2 to the CoCrFeNi HEA with the goal of developing materials with better combinations of strength and ductility. HEA composites with varying amounts of TiB2 were prepared by arc melting under an argon atmosphere. The resulting alloys were subjected to chemical, microstructural, and mechanical characterization. Interaction of TiB2 with chromium in the HEA matrix during melting resulted in its decomposition, leading to in-situ formation of chromium borides with plate morphology. A eutectic mixture, consisting of a hard phase (chromium boride) and a tough phase (the FCC matrix) was also developed with the amount of the eutectic mixture increasing with increasing amount of TiB2 added to the HEA. Mechanical characterization of the developed composites revealed a very wide range of mechanical properties, including yield strengths ranging from 180 MPa to 1282 MPa, hardness values ranging from 200 to 750 HV, and elongation ranging from 3.4% to more than 60%. Outstanding combinations of mechanical properties could also be obtained, for example the HEA composite developed by addition of 6 wt% TiB2, exhibited very high hardness (400 ± 10 HV) and very high yield strength (918 MPa), along with very good values of elongation before fracture (30%). The results in this study demonstrate that development of ceramic-reinforced HEA composites can help in obtaining alloys with excellent combinations of strength and ductility.

Standstill corrosion of the BNi-2/316L brazing joints in a stirling engine

A stirling engine was stored for about two years. When the engine was started, the cooler in the engine was found leaked, which affects the normal operation of the entire equipment. After dismantling, brazing seems between the cooling tubes and the cylinder were detected leaked by air pressure tests. The leaked sites were further determined at the diffusion zones of the brazing joints by the X-ray tomography and microscopic inspections. The crevice penetrated the diffusion zones, where chromium in the matrix depleted due to the formation of chromium borides. Considering the storage environment and the corrosion characteristics, the cause of the leakage is confirmed at the combined effect of standstill corrosion and crevice corrosion in the Cl- containing water. In addition to the failure cause, the wide brazing clearance and formation of nitrogen borides are considered to be two factors that promoted corrosion. Based on the above analysis, suggestions are proposed to prevent recurrence of corrosion and improve the corrosion resistance of the BNi-2/316L brazing joint.

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.

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.

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.

The importance of plasma paste boriding parameters for thickness, nanomechanical properties, residual stress distribution and fracture toughness of layers produced on Nimonic 80A-alloy

Borided layers of different thickness were produced on Nimonic 80A-alloy using plasma paste boriding method. The process was carried out at the temperature of 750 °C, 800 °C and 850 °C for 3 h and 6 h. All produced layers consisted of a fine-grained mixture of nickel borides and chromium borides. Higher boriding temperature and time resulted in the obtaining of boron-rich CrB phase in the microstructure of the borided layer. Simultaneously, this layer was characterized by higher hardness and Young’s modulus. Compressive residual stresses were generated in all produced layers. However, the most advantage course of the curve is characteristic of the borided layer produced at the highest temperature and time. The increase in layer thickness was accompanied by a decrease in the crack’s length (from 33.8 to 7.7 µm), as well as an increase in the fracture toughness (from 0.4439 to 2.4087 MPa·m1/2).

STRUCTURE AND PROPERTIES OF POWDER GAS-PLASMA COATINGS BASED ON NICKEL

The development of modern technology requires a constant increase in reliability and durability of products. Widely used in the practice of domestic and foreign engineering coatings from electrolytic chromium for several hundred hours are triggered, they are unsatisfactorily working on friction and wear at high temperatures. The subject of the study were powder materials based on nickel PG-SR3 and PG-SR4. The work is devoted to the study of the formation of gas-plasma coatings on parts of the cylinder-piston group of internal combustion engines using self-fluxing powders based on nickel, as well as the structure and properties change after coating sputtering, its reflow, subsequent hardening. The purpose of this work is to study powder materials applied to the working surfaces of piston rings by gas-thermal spraying. The object of the study are processes of formation of the structure and properties of coatings from powder materials. The presence in the deposited layer of a solid solution based on nickel, carbide phase, borides of chromium and nickel, chromium silicides is established. The greatest macro- and microhardness is possessed by fused layers containing the greatest number of strengthening phases. The conducted researches and industrial tests allowed to introduce the coating into production.

Structure and properties of powder gas-plasma coatings based on nickel

Problem. The development of modern technology requires a constant increase in reliability and durability of products. Widely used in the practice of domestic and foreign engineering coatings from electrolytic chromium for several hundred hours are triggered, they are unsatisfactorily working on friction and wear at high temperatures. The subject of the study were powder materials based on nickel PG-SR 3 and PG-SR 4. The work is devoted to the study of the formation of gas-plasma coatings on parts of the cylinder-piston group of internal combustion engines using self-fluxing powders based on nickel, as well as the structure and properties change after coating sputtering, its reflow, subsequent hardening. Goal. The purpose of this work is to study powder materials applied to the working surfaces of piston rings by gas-thermal spraying. The object of the study are processes of formation of the structure and properties of coatings from powder materials. Methodology. Plasma sputtering modes were carried out with the following constant parameters: sample rotation speed - 45 rpm, linear speed of sample movement relative to the plasma jet - 18.4 m/min; the diameter of the charge line in the anode nozzle is 2 mm; the distance from the place of introduction of the powder to the cut of the nozzle is 4 mm; the axis of the plasma jet is perpendicular to the axis of rotation of the sample. Radiographically, a multiphase structure is registered in the initial powder. The most fully presented solid solution lines based on nickel and carbide phase Cr23С6 type. But many lines cannot be clearly identified. A match can be found with the main lines of chromium and nickel borides, chromium silicides. The X-ray pattern of the fused layer quite completely coincides with the X-ray pattern of the powder. Chromium carbide lines and the strongest lines of other phases are preserved on the radiograph of the unmelted layer. Preservation of phase lines in the deposited layer without reflow and the layer after quenching indicates that these phases are formed during primary crystallization. This is confirmed by the metallography of the original powder and the original layer. In the structure of the powder, crystals are visible, as well as a dispersed mixture of phases between them. Electron microscopic studies show that in the area of coarse mixtures, oriented areas are observed, in the area of fine mixtures - non-oriented, less dispersed. Results. The presence in the deposited layer of a solid solution based on nickel, carbide phase, borides of chromium and nickel, chromium silicides is established. The greatest macro- and microhardness is possessed by fused layers containing the greatest number of strengthening phases. Originality. Gas-thermal sputtering of powder materials applied to the working surfaces of piston rings is used, which significantly increases their operational properties in comparison with other methods. Practical value. The conducted researches and industrial tests allowed to introduce the coating into production. Conclusions. As a result of the conducted researches on surfacing and heat treatment of coatings made of PG-SR powders, it was confirmed that the best properties have fused coatings. For coatings made of PG-SR powders, heat treatment is undesirable, as it deteriorates the structure and properties of the coating.

Determination of fracture toughness of boride layers grown on Co1.21Cr1.82Fe1.44Mn1.32Ni1.12Al0.08B0.01 high entropy alloy by nanoindentation

Multiphase boride layers consisting of (CoFe)2B, (Fe0.4Mn0.6)B, Cr2Ni3B6 and (Cr0.4Mn0.6)B were formed on the surface of Co1.21Cr1.82Fe1.44Mn1.32Ni1.12Al0.08B0.01 high entropy alloy by powder-pack boronizing at 900 °C, 950 °C and 1000 °C for 4 h. The nanohardness (H), modulus of elasticity (E) and fracture toughness (KC) of the multiphase boride layers were determined based on the load–displacement (P-h) curves obtained in the nanoindentation tests. Three distinct regions were identified on the cross-sections of the produced layers: an outer layer consisting of MeB-type borides, an inner layer consisting of Me2B-type borides and the transition zone. The microstructural aspects of the layers were investigated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. Detailed analysis of the influence of the chemical composition on hardness, elastic modulus and fracture toughness in the three regions indicated that the most critical factor influencing the mechanical properties was the presence of chromium, iron and cobalt borides in the microstructure. Especially the formation of chromium borides reduced the fracture toughness of the transition zone.

Influence of alloying (Cr, Fe, Ni) on the corrosion resistance of layers formed by electron-beam processing

The paper presents the results of comparative analysis of the properties of coatings based on chromium, nickel and iron borides. The alloy obtained in the process of electron-beam surfacing of the powder mixture “amorphous boron – 10 wt.% chromium” has the best properties. This is explained by the structures, fine chromium borides Cr2B and complex iron borides (Fe, Cr)2B, distributed in the austenitic matrix. The material modified in this way in a nitric acid solution corrodes at a rate of 0.02 mm/year. In sulfuric acid, its corrosion rate is 0.81 mm/year.