Boride Phases Research Articles

Joint Electroreduction of Chromium and Boron Ions and Electrochemical Synthesis of Chromium Borides in Halide–Oxide Melts

The electroreduction of oxygen-containing chromium ions $${\text{CrO}}_{{\text{4}}}^{{{\text{2}}-}}$$ and $${\text{C}}{{{\text{r}}}_{{\text{2}}}}{\text{O}}_{{\text{7}}}^{{{\text{2}}-}}$$ and their joint electroreduction with fluoroborate ion $${\text{BF}}_{{\text{4}}}^{ - }$$ in the equimolar KCl–NaCl melt at 1073 K are studied by cyclic voltammetry. The electroreduction of $${\text{CrO}}_{{\text{4}}}^{{{\text{2}}-}}$$ and $${\text{C}}{{{\text{r}}}_{{\text{2}}}}{\text{O}}_{{\text{7}}}^{{{\text{2}}-}}$$ proceeds via two steps to form chromium oxide Cr2O3 in the first step. In the second step, Cr2O3 also precipitates in the case of the electroreduction of $${\text{CrO}}_{{\text{4}}}^{{{\text{2}}-}}$$ , and a mixture of Cr2O3 and metallic chromium is formed due to the electroreduction of $${\text{C}}{{{\text{r}}}_{{\text{2}}}}{\text{O}}_{{\text{7}}}^{{{\text{2}}-}}$$ . Against the background of the KCl–NaCl melt, fluoroborate ion can interact with the $${\text{C}}{{{\text{r}}}_{{\text{2}}}}{\text{O}}_{{\text{7}}}^{{{\text{2}}-}}$$ ion to form chromium ( $${\text{Cr}}{{{\text{O}}}_{{\text{2}}}}{\text{F}}_{{\text{4}}}^{{{\text{2}}-}}$$ ) and boron ( $${\text{BOF}}_{{\text{2}}}^{-},$$ BOF) oxyfluoride complexes. The possibility that electrochemical synthesis of chromium boride phases occurs in a halide–oxide melt is shown by the joint electroreduction of chromium and boron oxyfluoride complexes.

Dual‐Phase Engineering of Nickel Boride‐Hydroxide Nanoparticles toward High‐Performance Water Oxidation Electrocatalysts

AbstractThe development of earth‐abundant and efficient oxygen evolution reaction (OER) electrocatalysts is necessary for green hydrogen production. The preparation of efficient OER electrocatalysts requires both the adsorption sites and charge transfer on the catalyst surface to be suitably engineered. Herein, the design of an electrocatalyst is reported with significantly enhanced water oxidation performance via dual‐phase engineering, which displays a high number of adsorption sites and facile charge transfer. More importantly, a simple chemical etching process enables the formation of a highly metallic transition boride phase in conjunction with the transition metal hydroxide phase with abundant adsorption sites available for the intermediates formed in the OER. In addition, computational simulations are carried out to demonstrate the water oxidation mechanism and the real active sites in this engineered material. This research provides a new material design strategy for the preparation of high‐performance OER electrocatalysts.

New (FeCoCrNi)-(B,Si) high-entropy metallic glasses, study of the crystallization processes by X-ray diffraction and Mössbauer spectroscopy.

The role of B and Si in the formation of (FeCoCrNi)100-x-yBxSiy high-entropy metallic glasses is studied. It is found that a content of B between 10 and 20 at% and of Si between 5 and 15 at% is able to produce a completely amorphous structure. The microstructural evolution of two of this high-entropy metallic glass compositions, (FeCoCrNi)80B20 and (FeCoCrNi)80B10Si10, have been studied by X-ray diffraction and Transmission Mössbauer Spectroscopy. In both compositions, the first crystallization process corresponds to the formation of metastable, M3B, and stable, M2(B,Si), borides where M stands for metallic atoms. In the Si containing sample a BCC phase also appears. At the second crystallization stage the metastable and the BCC phases disappear and stable M2B or M2(B,Si) phases begin to grow simultaneously with an FCC structure that presents a distribution of possible environs. The fully crystallized structure consists of boride and silicide phases and a paramagnetic FCC phase. The presence of Si promotes the crystallization of a BCC phase and the refinement of the microstructure leading to smaller and more uniform grains.

Dry-sliding wear of the 316L/h-BN composites produced under crack ammonia atmosphere

Wear is one of different problems in mechanical failures of moving components. When a component encounters friction force on its surface, crack initiation tends to occur and wear follows crack propagation. Thus, the moving parts of automobiles should have proper wear resistance for long-time services, in addition to having high strength and hardness for heavy load operation. A self-lubricating material with compromised tribological and mechanical properties is important for some moving components. In this work, self-lubricating composites, metal matrix composites embedded with a solid lubricant, made from 316L stainless steel powder mixed with different hexagonal boron nitride (h-BN) contents of 10%, 15% and 20% by volume. The mixed powders were compacted into green parts (according with MPIF Standard 42) with density of 6.5 g·cm-3. Then, the green parts were sintered at 1100, 1150, 1200, 1250 and 1300°C under cracked ammonia (75% H2+25% N2) atmosphere for 60 min. The experimental results revealed that increases of hardness and strength sintered 316L matrix by reduction of pore amount and size were due to the increase of sintering temperature. However, the increase of h-BN content resulted in increase of pore amount and size. Additions of h-BN content up to 20 vol. % reduced friction coefficient of the sintered composites. At sintering temperatures of equal to and higher than 1200°C, h-BN did not react with 316L stainless steel powders to form intergranular boride phase. The sintered composites produced under the maximum experimental sintering temperature of 1300°C showed low specific wear rate.

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.

Microstructural and tribological properties of induction cladded NiCrBSi /WC composite coatings

In this study, the Ni-based WC reinforced MMC coating was conducted by a novel process called induction cladding (IC). Powder mixtures of NiCrBSi and NiCrBSi-WC were pre-located on an AISI 316 stainless steel chamber and heated at 1200 °C for 20 min with a high frequency induction coil in an Ar atmosphere and cooled in the same environment. The coating layer showed an intense and non-porous metallurgical bond to the stainless steel. As a result of the microstructural and phase analysis of the coating layer, γ‑nickel main phases with Ni3B, Ni3Fe, Ni3Si, Cr23C6, CrB and Cr7C3 were determined in dendritic and cellular regions. In addition, WC and W2C phases were observed in reinforced samples. The average hardness value of the IC clad coating was 2.8 times higher, compared to AISI 316, due to the formation of hard carbide and boride phases in the interdendritic regions. The COF values and wear rate of the cladded samples were decreased compared to the AISI 316. Increasing the amount of WC reinforced powder used in the IC process increased the wear resistance by up to 10 times to be compared with the stainless steel AISI 316.

Dual-phase high-entropy ultra-high temperature ceramics

A series of dual-phase high-entropy ultra-high temperature ceramics (DPHE-UHTCs) are fabricated starting from N binary borides and (5-N) binary carbides powders. > ∼99 % relative densities have been achieved with virtually no native oxides. These DPHE-UHTCs consist of a hexagonal high-entropy boride (HEB) phase and a cubic high-entropy carbide (HEC) phase. A thermodynamic relation that governs the compositions of the HEB and HEC phases in equilibrium is discovered and a thermodynamic model is proposed. These DPHE-UHTCs exhibit tunable grain size, Vickers microhardness, Young’s and shear moduli, and thermal conductivity. The DPHE-UHTCs have higher hardness than the weighted linear average of the two single-phase HEB and HEC, which are already harder than the rule-of-mixture averages of individual binary borides and carbides. This study extends the state of the art by introducing dual-phase high-entropy ceramics (DPHECs), which provide a new platform to tailor various properties via changing the phase fraction and microstructure.

Effect of boron on microstructure evolution and properties of wear-resistant cast Fe–Si–Mn–Cr–B alloy

The purpose of this study was to clarify the effect of boron content on the microstructure evolution, mechanical properties, and three-body abrasive wear property of as-cast Fe–Si–Mn–Cr–B alloys, and to reveal the wear mechanism of Fe–Si–Mn–Cr–B alloys. The results indicated that the microstructure of the Fe–Si–Mn–Cr–B alloy was mainly composed of bainite, retained austenite (RA), M3B2, and M2B (M stands for the metal atom, in this case, it refers to Fe, Cr, and Mn). With the increase of boron content, the volume fraction of the boride phase increased, the morphology of the boride phase was dominated by fishbone, the microhardness of the boride phase and the macrohardness of the alloy increased, and the wear resistance of the alloy was significantly enhanced. Compared with the 0.5wt.% B alloy, the macrohardness of the 2.0wt.% B alloy was increased by 19.5%, the maximum microhardness of the boride phase reached 1440 HV0.2, the Charpy impact toughness was reduced by 45%, and the wear resistance was increased by 268%. The morphology, content and distribution of the boride phase play a key role in improving the hardness and wear resistance of the alloy. The synergy between the high-hardness boride phase and the softer metal matrix phase, which was composed of bainite and RA, gave the alloy excellent wear resistance. The main wear mechanisms of the alloy were abrasive wear and fretting wear.

Effect of In-Situ Synthesized Boride Phases on the Impact Behavior of Iron-Based Composites Reinforced by B4C Particles

The objective of this study is to investigate the impact behavior of iron-based composites reinforced with boron carbide (B4C) particles and in-situ synthesized iron borides (Fe2B/FeB). The composite specimens (Fe/B4C) were fabricated by hot-pressing under a pressure of 250 MPa at 500 °C, and sintered at a temperature of 1000 °C. The effects of the reinforcement ratio on the formation of in-situ borides and impact behavior were investigated by means of different volume fractions of B4C inside the iron matrix: 0% (un-reinforced), 5%, 10%, 20%, and 30%. Drop-weight impact tests were performed by an instrumented Charpy impactor on reinforced and un-reinforced test specimens. The results of the impact tests were supported with microstructural and fractographical analysis. As a result of in-situ reactions between the Fe matrix and B4C particles, Fe2B phases were formed in the iron matrix. The iron borides, formed in the iron matrix during sintering, heavily affected the hardness and the morphology of the fractured surface. Due to the high amount of B4C (over 10%), porosity played a major role in decreasing the contact forces and fracture energy. The results showed that the in-situ synthesized iron boride phases affect the impact properties of the Fe/B4C composites.

Boron addition in a non-equiatomic Fe50Mn30Co10Cr10 alloy manufactured by laser cladding: Microstructure and wear abrasive resistance

A non-equiatomic Fe50Mn30Co10Cr10 alloy was prepared by laser cladding, and the effects of boron addition on the microstructure, hardness and abrasive wear-resistance were investigated. Elemental powders were mixed using an attritor mill for 30 h and then applied by laser cladding on a stainless steel 316L substrate. The effect of boron addition (0.1, 0.66 and 5.40 at%) on the alloy microstructure was assessed using optical and electron microscopy, and the phase composition was studied using X-ray diffraction. The laser claddings were exposed to abrasive wear conditions using the dry sand/rubber wheel test. The microstructure of the laser claddings exhibited columnar dendrites formed by two crystalline structures (fcc and hcp) with the same chemical composition. The hcp structure was the result of the partial martensitic transformation of the fcc structure. Boron addition led to the formation of a eutectic phase along the interdendritic regions with a crystalline structure consistent with M2B-type borides (M = Cr, Fe). Hardness and abrasive wear-resistance of the laser claddings were strongly influenced by boron content. When boron content was increased from 0 at% to 5.40 at% the microhardness of the material was from 291 HV to 445 HV. Similarly, the boron content improved the behaviour against abrasive wear due to the increased volume fraction of borides in the microstructure. The high content of the boride phase in the laser cladding with 5.40 at% B allowed reducing the abrasive wear rate by more than 30% when compared with the alloy without boron content.

Experimental investigations of reciprocating wear behavior of metal matrix (Ti/TiB) composites

In this paper, the reciprocating wear behavior of titanium–titanium boride composites with 20 and 40 (by vol. %) titanium boride (TiB) particles IS investigated in dry sliding conditions against Al2O3 ceramic balls. The trials have been observed at three loading conditions such as 5, 10 and 15 N load. The composites were processed by three powder metallurgical techniques such as spark plasma sintering (SPS), vacuum sintering (VS) and hot isostatic pressing (HIP). The electron probe microanalysis (EPMA) was used to analyze the homogeneity of Ti and boride phases in the composites. The hardness and indentation fracture resistance were evaluated using nano-indentation technique. The load–depth curves of indents for Ti–TiB shows the deviations of the modulus of elasticity within the spark plasma sintering (SPS), vacuum sintering (VS) and hot isostatic pressing (HIP).The wear resistance of the fabricated samples was analyzed using reciprocating wear tester. The SPS composite (Ti–38.5% TiB) showed lower coefficient of friction (0.07), lower wear volume (0.4368 mm3) and wear rate (0.000276 mm3/m) when compared to HIP and VS, which is attributed to the presence of fine titanium boride needles of high hardness, contributing to improving wear resistance. The surface morphology reveals that the composites processed through spark plasma sintering (SPS) and hot isostatic pressing (HIP) are subjected to minor plastic deformation. The outcome of this work is more beneficial to automotive brake pad, precision manufacturing and locomotives to avoid critical wear failures.

A new approach to sintering and boriding of steels “Boro-sintering”: Formation, microstructure and wear behaviors

In this study, sintering and boriding methods are applied as a single step, and it is aimed to gain time and economic advantage. For this purpose, powder mixtures prepared in suitable compositions were subjected to sintering and boro-sintering processes. In the boro-sintering process, the sintering was carried out in the boriding atmosphere and the two processes were carried out together. The processing, microstructure, hardness and dry sliding wear behavior of the samples were studied. The powders were pressed under different pressures, and their effects on the properties of the final component were investigated. The sintering process was carried out for 2 h at 1000 °C, and the boro-sintering process was carried out at 1000 °C for 2, 4 and 6 h. Fe2B and Fe2B + FeB boride phases occurred depending on the boro-sintering process duration. Boride layer thickness varied between 120 and 400 μm according to boro-sintering duration and cold press pressure. Vickers micro-hardness and Ball-on-disc wear tests were performed on the samples. Whereas 205–215 HV hardnesses were obtained in the sintered samples, 1252–1705 HV hardness values were reached by boro-sintering process. Increased cold pressing pressure reduced wear losses. However, the long boro-sintering time increased surface hardness, but reduced wear resistance.

Effect of the Rare Earth Element Yttrium on the Structure and Properties of Boron-Containing High-Entropy Alloy

The effects of rare earth yttrium with 0.1, 0.2 and 0.5 atomic ratios on the microstructure and properties of FeCoNi1.5CuB high-entropy alloy were investigated. The results show that the lattice distortion of the matrix alloy is increased after yttrium addition. There are three characteristic zones: the bulk trivalent boride phase zone, basement zone and yttrium-rich precipitate zone. When the yttrium atom ratio is > 0.2, the nanoscale YB6 particles disperse uniformly in the yttrium-rich zone, which can improve the strength of the alloy. As for the mechanical properties, the FeCoNi1.5CuBY0.2 alloy has the highest strength. The corresponding compressive strength, yield strength and maximum compression ratio have been increased by 19.9%, 75.4% and 37%, respectively, compared with those of FeCoNi1.5CuB alloy. This is attributed to the solid solution, grain refinement and dispersion strengthening in the presence of yttrium addition.

Microstructural and Mechanical Evaluations of Transient Liquid Phase Bonded In X-750/BNi-3/SAF 2205

In this study, dissimilar joining between SAF 2205 duplex stainless steel and Inconel X-750 superalloy produced by TLP process was investigated. This process was done at temperature of 1100 °C for different bonding times of 1, 15, 30, 45 and 60 min. The effect of different bonding times on the microstructure and mechanical properties of the welded samples was studied. Microstructure of the samples was analyzed by optical microscopy and scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy. X-ray diffraction analysis was used to determine the formed phases in the bonding area. Microhardness and shear strength tests were done to evaluate the mechanical properties of the joints. It was found that the joint area contains the γ-Ni solid solution, eutectic compounds with intermetallic phases beside precipitated secondary phases. The γ-Ni solid solution, BN, BCN, CrB, Ni3Si and Ni3B were the main phases in the joining area. Maximum microhardness was found in athermally solidified zone, due to the presence of hard and brittle intermetallic and boride phases. The maximum shear strength (368 MPa) was obtained for the sample with the bonding time of 45 min, due to the completion of isothermal solidification and removal of eutectic compounds.

Slurry Erosion Performance of Ni + B4C Microwave Composite Clads

Abstract A composite clad of Ni-based alloy and B4C was developed on austenitic steel substrate through microwave hybrid heating. The B4C was added with Ni-based alloy powder in various weight proportions (0%, 5%, 10%, and 20%). The clads were investigated for the microstructural details, nanohardness and slurry erosion performance. Silt collected from river Uhl was used as the erodent for the slurry erosion test. Slurry erosion performance of the clads was evaluated at an impact angle of 90 deg and jet velocity of 40 m/s. Microstructural characterization confirms the uniform distribution of hard (boride and carbide) phases in the Ni-based matrix of the microwave composite clads. The presence of hard phases in the Ni-based matrix enhanced the slurry erosion resistance performance.

Microstructural Evaluation during dissimilar transient liquid phase bonding of TiAl/Ni-based superalloy

The paper aims at understanding solidification phenomena and solid state precipitations during dissimilar transient liquid phase bonding of γ-TiAl intermetallic compound to IN718 Ni-based superalloy using a quinary Ni–7Cr–3Fe–4.5Si–3.2B (wt%) filler metal. The mechanisms of intermetallic formation via solidification and solid state reactions are discussed. The joint is featured by the formation of Ni-rich solid solution in an isothermal solidification zone near to IN718, Ni-rich solid solution and isostructural binary phases solid solution designated as Al1-xNi3Six in an isothermal solidification zone near to TiAl, boride/silicide and boro-silicide formation during binary and ternary eutectic-type solidification in an athermal solidification zone, fine nickel silicide precipitation during cooling in the joint centerline, and in-situ precipitation of Cr–Mo–Nb rich borides in a diffusion affected zone. On the other hand, Ni from the filler metal reacted with γ-TiAl base metal, leading to the formation of Ti2Ni, τ2-Al2TiNi and τ4-AlNi2Ti compounds on the reaction layer adjacent to TiAl substrate. The evaluation of different zones of the bond region showed that some brittle phases with high hardness are formed in the bond region. It was identified that the presence of the eutectic gamma solid solution between boride phases within the joint centerline can decrease the detrimental effect of the intermetallic phases on the joint toughness.

Prediction of superconductivity in pressure-induced new silicon boride phases

The crystal structures and properties of boron-silicon (B-Si) compounds under pressure have been systematically explored using particle swarm optimization structure prediction method in combination with first-principles calculations. Three new stoichiometries, ${\mathrm{B}}_{2}\mathrm{Si}$, BSi, and ${\mathrm{BSi}}_{2}$, are predicted to be stable gradually under pressure, where increasing pressure favors the formation of silicon rich B-Si compounds. In the boron-rich compounds, the network of boron atoms changes from ${\mathrm{B}}_{12}$ icosahedron in the ambient phases to the similar buckled graphenelike layers in the high-pressure phases, which crystalize in the same $P\overline{3}m1$ symmetry but with different numbers of boron layers between adjacent silicon layers. Phonon calculations show that these structures might be retained to ambient conditions as metastable phases. Further electron-phonon coupling calculations indicate that the high-pressure phases of boron-rich compounds might superconduct at 1 atm, with the highest ${T}_{c}$ value of 21 K from the Allen-Dynes equation in $P\overline{3}m1$ ${\mathrm{B}}_{2}\mathrm{Si}$, which is much higher than the one observed in boron doped diamond-type silicon. Moreover, further fully anisotropic Migdal-Eliashberg calculations indicate that ${\mathrm{B}}_{2}\mathrm{Si}$ is a two-gap anisotropic superconductor and the estimated ${T}_{c}$ might reach up to 30 K at 1 atm. On the silicon-rich side, ${\mathrm{BSi}}_{2}$ is predicted to be stable in the ${\mathrm{CuAl}}_{2}$-type structure. Our current results significantly enrich the phase diagram of the B-Si system and will stimulate further experimental study.

Influence of Cr and W addition on microstructure and mechanical properties of multi-step sintered Mo2FeB2-based cermets

The influence of Cr and W addition on microstructure and mechanical properties of Mo2FeB2-based cermets, prepared by multi-step sintering, is systematically evaluated by XRD, SEM, EDS, and TEM. After liquid-phase sintering, the final microstructure of Cr-doped Mo2FeB2-based cermets is similar to that of traditional Mo2FeB2-based cermets. The cermet, with 2.5% Cr content, exhibits superior comprehensive mechanical properties, i.e., Rockwell hardness, transverse rupture strength (TRS) and fracture toughness of 87.6 HRA, 2179 MPa and 21.7 MPa m1/2, respectively. In contrast, for W-doped Mo2FeB2-based cermets, a large amount of W-enriched (Mo,Fe,W)3B2 solid solutions precipitated around undissolved Mo2FeB2 particles, resulting in the formation of black core/gray rim structure. Particularly, a transition layer, with several atomic layer thickness, is observed between (Mo,Fe,W)3B2 rim phase and Fe-based binder phase, which corresponds to B-deficient (Mo,Fe,W)3B2−x orthorhombic boride phase. Moreover, the lattice mismatch between (Mo,Fe,W)3B2 and (Mo,Fe,W)3B2−x is found to be 1.9%. When doped with 5 wt% W, Mo2FeB2-based cermet exhibit superior comprehensive mechanical properties with Rockwell hardness of 84.6 HRA, TRS of 2088 MPa and fracture toughness of 24.4 MPa m1/2. The increase of fracture toughness (KIC) can be ascribed to the presence of W-rich transition layer.

Multiple crystal phases of intermetallic tungsten borides and phase-dependent electrocatalytic property for hydrogen evolution.

Four stoichiometric W-B intermetallic phases, including W2B, WB, WB2 and WB3, are synthesized, and their hydrogen-evolution electrocatalytic properties and electronic structures are investigated comparatively. The electrocatalytic activity for the hydrogen evolution reaction is found to first increase from W2B to WB2 and then decrease; and this activity trend can be rationalized based on their different degrees of hybridization between d orbitals of W and sp orbitals of B.

The influence of chromium as a diffusive additive in the boronizing treatment of AISI 4140 steel on the corrosion resistance of the coating evaluated by Electrochemical Impedance Spectroscopy (EIS)

A large variety of protective coating is being used in industrial applications to improve the resistance of the metallic substrates against corrosion. The pack-cementation method for boronizing and borochromizing is effective to produce extremely hard and corrosion resistant thick coatings and, additionally, is a low-cost and simple technique. In the present study, AISI 4140 steel specimens underwent boronizing and afterwards chromizing by the pack-cementation method using B4C as boron source and Fe-Cr as chromium source, respectively. In both treatments the appropriate activators were used. After chromizing the boronized substrate, a mixed boride phase FeCrB was formed, as it was confirmed by X-ray Diffractometry (XRD). The boronized and the borochromized specimens were subjected to Electrochemical Impedance Spectroscopy (EIS). From the analysis of the frequency response of the coating systems (Bode and Nyquist display), the conclusion that the borochromized specimens were significantly more corrosion resistant was extracted. Finally, data of optical and electron microscopy contribute to the validity of the conclusions.