Formation Of Borides Research Articles

Effect of Alloyed Coating Composition on Composite Casting Surface Layer Properties

A method of casting surface alloying during casting using gasified models with the formation of a wear-resistant surface layer is considered. The increase in wear resistance is due to formation of boride and carbide components by means of self-propagating high-temperature synthesis between alloyed coating components that occurs during casting manufacture. Results of comparative tests for materials under abrasive wear are presented. Data are given for material composition, structure, and hardness.

High-temperature deformation behaviour of duplex stainless steel with hard boronised layer

In order to understand the high-temperature deformation behaviour of alloy having hard surface layer, thermo-mechanically treated duplex stainless steel (DSS) is boronised for 0.75–6 h at 1223 K and subsequently deformed under compression mode at the same temperature under strain rate condition of 1 × 10−3, 2 × 10−4 and 6 × 10−5 s−1 until strain of 0.4. The substrate microstructure is almost isotropic with grain size after boronising with layer thickness between 1.61 and 2.74 μm. X-ray diffraction results confirm the formation of boride on DSS surface. The surface hardness of DSS increases from 387 to 1000–2400 HV after boronising. Uniform boronised layer with thickness of 20–40 μm is formed at DSS surface. Compression results show that the flow stress of the deformation increases with the strain rate and boronising time. For the boronised samples, the flow stress range is between 5 and 89 MPa. To determine the actual effect of the boronised layer on the flow stress, the results are also compared with those from un-boronised samples having similar microstructure. The results suggest that at a constant grain size, even with the hardest layer, the effect of hard surface layer on the flow stress almost could be negligible when the deformation rate is slow, but at faster deformation rate, even in the layer with the least hardness, the flow stress shows a significant increase. It is also observed that the hard boride surface disintegration could be avoided at a sufficiently low deformation flow stress that could be attributed to superplasticity.

Titanium Boride and Titanium Silicide Phase Formation by High Power Diode Laser Alloying of B <sub>4</sub>C and SiC Particles with Ti: Microstructure, Hardness and Wear Studies

Titanium Boride and Titanium Silicide Phase Formation by High Power Diode Laser Alloying of B <sub>4</sub>C and SiC Particles with Ti: Microstructure, Hardness and Wear Studies

Optimization of Ni-B coating bath and effect of DMAB concentration on hardness and wear

In this study, reducing agent amount, stabilizer amount, coating bath temperature and stirring speed parameters were examined for optimization of electroless Ni-B coatings, and the effect of reducing agent amount on hardness and wear of the coating was investigated. The pH of the electroless Ni-B coatings made for 1 h was set to 6, nickel chloride (NiCl2.6H2O) as the nickel source, sodium acetate (C2H3NaO2) as the complexing agent, thiourea as the stabilizer (CH4N2S) and DMAB ((CH3)2NBH2) as the reducing agent was used in the coatings. The bath parameters were varied as; the amount of reducing agent (2 g/L, 3 g/L and 4 g/L), coating bath temperature (65°C, 70°C and 75°C), stabilizer amount (0.5 mg/L, 1 mg/L, and 2 mg/L) and stirring speed (250, 300 and 350 rpm). After determining the optimum conditions, the effects of the amount of reducing agent on the coating were examined. Scanning Electron Microscopy (SEM), X-ray diffractometer (XRD), Vickers nano-hardness test and tribometer were used for characterization of coatings. In the optimization studies, it was observed that the coating morphology was in the form of cauliflower and columnar structures were formed in the cross-section images. According to optimization results on the morphologies, the samples which compact and free-crack have been investigated phase structure, hardness and tribology properties. In XRD analysis, coatings produced with different amounts of reducing (DMAB) are amorphous as-deposited, after annealed at 400°C for 2 h, nickel borides (Ni2B and Ni3B) phases are formed and increased the preferential orientation (111) of the nickel crystal plane. The effect of DMAB concentration on coating was examined in as-deposited condition and post annealing. The formation of nickel borides after annealing increases the hardness. The effect of DMAB concentration on the coating after annealed was examined and it was observed that the wear resistance of the dense and homogeneously dispersed sample in the coating matrix was more perfect than other samples. Consequently, hardness (850 HV), coefficient of friction (0.37) and wear rate (2.92 × 10−7 mm3/Nm) of B2 sample which free-crack and compact was obtained. These results indicate a high strengthen B2 sample produced with 3 g/L DMAB concentration and 70°C bath temperature could utilize in a harsh medium.

To question about Fe5B3 boride formation in boron-rich Fe–В alloys

The structure of boron-rich iron alloys in the concentration range of 9.0–15.0 wt. % В, 0.01–0.17 wt. % C, Fe – the balance (with charge impurities of Si, Al, Mn) was investigated in this work. The methods of metallographic, X-ray, stop-quenching, scanning electron microscopic, energy dispersive, and fluorescent spectral analyses were applied. The FeB- and Fe2B-based solid solutions are proved to be the major constituents of the investigated alloys. No evidence is found for the possible formation of the Fe5B3 boride via peritectic reaction L+FeB→Fe5B3 at 1650 K and its further decomposition via eutectoid reaction Fe5B3→FeB+Fe2B at 1410 K. It is shown that the phase under consideration is iron hemiboride alloyed mainly by silicon which peritectically forms from primary crystals of iron monoboride and the rest of liquid at 1650 K. The thermal effect at 1410 K is assumed to be caused by a heat production connected with polymorphic transformation α-FeB→β-FeB in the presence of carbon.

Effect of filler metal on the microstructural evolution and mechanical properties of wide gap brazed K417G superalloy joints

Abstract Ni-based superalloy K417G was brazed using different contents of additive alloy + braze alloy mixed powder filler metal. The effect of filler metal constitutions on the microstructural evolution and mechanical properties of the joint was examined in detail. The interfacial formation mechanisms of K417G alloy brazed joint were analyzed. Results indicated that the γ + γ′ matrix phase first forms at the wide gap brazing region during brazing . B segregation appeared and borides formed fine particles of M3B2. The M3B2 phase and γ/γ′ eutectic phase were derived from the residual liquid phase during the cooling process. The boride size and formation of γ/γ′ eutectic phase with a low melting point were restrained when the proportion of additive alloyincreased; thus, the microstructural homogeneity of the wide-gap brazed region was improved. B atoms uniformly diffused through the K417G alloy and its additive alloy when the proportion of additive alloy was increased to 95 wt.%. The tensile properties of the joint were improved due to the absence of a low-melting-point eutectic phase and a significant reduction in the number of brittle borides.

A Novel Synthesis of Manganese Borides Supported on Multi-Walled Carbon Nanotubes As a Catalyst for the Hydrolysis of Sodium Borohydride

The current world energy crisis is concerned with the depletion of natural resources usedby power industries. Hydrogen energy produced from feedstock materials such as sodium borohydride (NaBH4) arises as a potential solution for energy demand, but it meets a challenge in finding a durable, efficient and economical catalyst.1,2 A catalyst is required to produce a usable amount of hydrogen through the hydrolysis reaction of NaBH4, due to the limitation that the procedure does not occur quickly enough on its own.2 Metal borides have been researched and applied in various industries as an effective catalyst, but the method of production appears to be costly and eco-unfriendly.3,4 In this study, manganese metal organic frame works (Mn-MOFs) and multi-walled carbon nanotubes (MWCNTs) were applied to synthesize supported manganese borides at room temperature in aqueous conditions. The MOFs have been applied in solving environmental pollution issues and enhance the catalytic effect.5 When combined with MWCNT, it further improves the stability, surface area, and reusability of the manganese borides. The reduction of Mn-MOFs leads to the formation of manganese borides on MWCNTs in the presence of NaBH4, which acts as both a reduction agent and a hydrogen feedstock material in this experiment. The physicochemical structures of the obtained composite, MnB@MWCNT was characterized via x-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and inductively coupled plasma (ICP). The catalytic capability of MnB@MWCNT was tested in an aqueous solution of NaBH4 under various conditions. The catalytic ability and reusability of MnB@MWCNT was measured by a water displacement method while the activation energy was found using a plot of the Arrhenius equation which utilized various temperature trials of 283 K, 295 K and 303 K.6 Five consecutive reusability trials were performed separately in which the production of hydrogen fell from 62.12 mL to 18.44 mL by the final trial and the activation energy was ultimately calculated to be 119.86 kJ mol-1. The results of this synthesis support the idea that supported manganese borides supported over multi-walled carbon nanotubes can act as an efficient catalyst in hydrogen evolution reactions, in the presence of hydrogen feedstock materials.

On the performance of weld overlay characteristics of Ni–Cr–Si–B deposition on 304 ASS using synergetic pulse-GMAW process

Ni–Cr–Si–B alloy deposition on 304 ASS is executed by making use of automated processes like PTA, laser cladding, etc., which are supportive in the mass production. However, for repairment and job-specific works, such processes become more expensive and hence cost-effective pulse-GMAW process is proposed. The effect of current on the coating characteristics is investigated. Microstructure reveals a eutectic structure near interface, which changes to a hypereutectic near the top surface. γ-Ni, carbides and borides phases are observed in coating, which increases hardness (529.3 HV1.0) and wear resistance (20 times). The present study reveals an inverse relation of hardness and wear resistance with current due to increased iron content in coating at higher current which suppresses boride formation.

Effect of B on improving wetting and imbibition of sintered porous Ta by Cu melt

The present study focuses on the interaction between copper melts and porous tantalum plates (purity, 99.99 wt% Ta). The samples were prepared by sintering tantalum powder with different grain size and were characterized by 65% porosity. A procedure to perform direct observations of the interaction between the melt and plates was developed. Equipment for high-speed recording of dipping of the samples into the melt was designed. The frame rate was up to 5000 fps. A high-vacuum furnace with a graphite heater was used. Wetting experiments were performed in the temperature range of 1100–1400 °C.As expected, at temperatures near 1150 °C the tantalum cake coated with an oxide layer is not wetted by pure copper and does not imbibe it. Rising temperature slightly improves wetting. Doping the copper melt with 2 at.% B at 1150 and 1275 °C reduced the contact angle to 60° it dropped below 25° at 1400 °C. The reason for the observed phenomenon was that doping with boron results in reactive wetting and formation of tantalum boride. Wetting of the porous samples was compared to wetting of cast tantalum plates.The kinetics of imbibition with Cu(B) melt were recorded. The imbibition dependence changed from power-law to linear one as temperature increased from 1275 to 1400 °C. This behavior is associated with degradation of the tantalum boride layer.

Thermodynamic Estimation of the Solidification of Borides and Carbides from Boron-Containing Iron–Carbon Melts

Abstract—The probability of the formation of solid iron borides and boron and iron carbides from Fe–C–B melts is thermodynamically estimated. The Gibbs energy of a chemical reaction is taken as a criterion for the solidification of these phases. The following standard states are used: for iron, pure liquid iron; for carbides and borides, a pure solid at temperature T; for boron and carbon, a pure liquid supercooled (metastable) element. The results of experimental diagnostics of the structure and composition of experimental castings made of carbon steels with surface alloying with boron-containing components (ferroboron, boron carbide) are presented. The solidification of borides and carbides from the melts under study was shown to occur at high boron and carbon concentrations and low temperatures.

Wide Gap Brazing of Inconel 738LC Nickel-Based Superalloy: Metallurgical and Mechanical Characteristics

This paper addresses the microstructure properties relationship of wide gap brazed Inconel 738LC. Amdry 718 and a Ni-Cr-Fe-Si-B alloy were used as high melting particles (HMPs) and low melting particles (LMPs), respectively. The effect of the amount of LMPs, 30, 40, and 50 pct, on the microstructure and the shear strength of the joint, was investigated. The microstructure in the brazing zone consists of Ni-based solid solution and eutectic-type microconstituents that is nickel-rich and chromium-rich borides. Nickel-rich borides only observed in the presence of the high amount of LMPs, because of the low Cr-B ratio in the filler alloy. At the brazing/base metal interface, high diffusion of melting point depressant (MPD) elements to the base metal led to the formation of small blocky Cr-rich borides in Ni-rich solid solution matrix. The nickel-rich and chromium-rich borides have a hardness value of about 1200 and 830 HV, respectively, which is remarkably higher than the other regions. By increasing the amount of LMPs from 30 to 50 pct, the joint shear strength decreases from 422 to 373 MPa due to the higher volume fraction of the brittle boride phase in the joint. For all brazed joints, the cleavage fracture mode was observed, which can be ascribed to the interlinked network of the brittle eutectic-type microconstituents. The X-ray diffraction pattern confirms that the preferred location for crack propagation is eutectic boride phases.

Mean Diffusion Coefficient Method in Studying Armco Iron Boriding Kinetics

Activation energy of boron diffusion during pack boriding of armco iron with a constant incubation time for boride formation is estimated using a mean diffusion coefficient model. Experimental verification is accomplished for the model by boriding armco iron at 1253 K for 5 h. Good correspondence is obtained between experimental and calculated Fe2B layer thicknesses.

In situ formation of molybdenum borides at hardfacing by arc welding with flux-cored wires containing a reaction mixture of B4C/Mo

This paper reports a study into the formation of the phase composition, structure, and properties of arc welding coatings by the flux-cored electrode materials from the Fe-Mo-B-C system. The welding alloys were applied using the flux-cored arc welding (FCAW) electrodes, which consisted of a shell made from the low-carbon steel filled with a reaction powder mixture that contained boron carbide and molybdenum in a ratio of 1:1. The calculation of the phase composition of alloys that correspond to the surfaced layers by a CALPHAD method using the Thermo-Calc OpenCalphad software shows that under the equilibrium conditions the boride phases of molybdenum and ferrite cannot co-exist. The main phase of such alloys is a FeMo 2 B 2 compound, which forms the eutectics with austenite. Given that the eutectic structures with borides are characterized by high brittleness, the introduction of components was conducted in the form of a reaction mixture in order to obtain the in situ formed boride phases in the form of separate structural components. Analysis of the results of studying the microstructure and phase composition of coatings reveals that they consist of three main structural components: the eutectic (FeMo 2 B 2 +ferrite) and the grains of molybdenum tetraboride MoB 4 . Thus, under the conditions of arc welding using the reaction mixture, an irregular structure is formed, which is favorable in terms of ensuring wear resistance due to the high microhardness of MoB 4 >27 GPa. The hardness of the coatings obtained is at the level of 63–65 HRC, and the wear resistance is higher compared to standard high-chromium alloys (grades Т620 and Т590) by 2‒2.5 times. This makes it possible to recommend the coating of a given system for hardfacing the working surfaces of equipment in the coal, processing, woodworking industries, etc., where abrasive wear is the dominant type of surface wear

Effect of the Microwave Heating on Diffusion Kinetics and Mechanical Properties of Borides in AISI 316L

In this study, the effect of microwave heating on boride formation and diffusion kinetics in 316L stainless steel alloys was investigated. Boriding was carried out in microwave furnace with 2.9 kW power and 2.45 GHz frequency. Four different boriding temperatures (800, 850, 900 and 950 °C) were used. Boriding was performed for 2, 4 and 6 h for each temperature. Boron layer thicknesses of boride layers were determined by optical microscope. SEM images were taken from the cross sections of the borided samples. Boron activation energy was determined as 244.15 kJ/mol in microwave environment. Two times thicker boride layer was obtained by microwave boriding process compared to the conventional heating process. The mechanical properties of the boride layers formed by microwave boriding (Young’s modulus, hardness, yield strength, residual thermal stress) were determined by nanoindentation tests.

Boride formation behaviour and their effect on tensile ductility in cast TiAl-based alloys

Boron has been used to refine the microstructures in TiAl castings, such as low-pressure turbine (LPT) blades, to improve mechanical properties. However, boride precipitates with undesirable morphologies could reduce ductility and even entirely remove the benefits of grain refinement. Boride size and morphology in variant alloys based on Ti45Al2Mn2Nb1B has found to be closely related to alloying element species and solidification conditions, leading to distinctly different boride formation behaviour. It has been shown that Hf promotes the formation of thin curvy boride flakes whilst Ta promotes the formation of thick straight boride ribbons in the studied cooling rate range. The boride crystal structure changes from TiB with the B27 structure for coarse straight boride to TiB with Bf structure for the curvy boride. Curvy borides have the strongest effect in reducing ductility, regardless of alloy composition.

Creep induced precipitation of the (Cr,Mo)5B3-type boride in γ/γ′ eutectic of a Ni-based superalloy

Boron segregation and boride formation at grain boundaries are generally accepted in Ni-based superalloys. However, the addition of boron was found to result in the formation of a high density of nanosized M5B3 (where M is a mixture of Cr, Mo) particles in γ/γ′ eutectics of a Ni-based superalloy during high-temperature creep in this work. M5B3 phase precipitated at γ/γ′ eutectics keeps a well-defined orientation relationship with the eutectics, which is [001]γ/γ′//[001]M5B3, (020)γ/γ′//(130)M5B3. And these nanosized borides could block dislocation slip, result in stress concentration surrounding γ/γ′ eutectics and facilitate crack initiation at γ/γ′ eutectic/matrix interface during the creep at high temperatures.

Structural and Phase Evolution upon Annealing of Fe76Si9−xB10P5Mox (x = 0, 1, 2 and 3) Alloys

Alloying elements play an important role in adjusting the magnetic and thermal properties of Fe-based amorphous alloys. In this work, the effect of Mo addition on the thermal stability, structural evolution, and magnetic properties of Fe76Si9B10P5 metallic glass was studied. The study revealed that the substitution of a small amount of Mo (1 at.%) for Si enhances the glass-forming ability (GFA) but reduces the thermal stability of the alloy, causing a reduction of the supercooled liquid region. Substitution of up to 3 at.% Mo for Si lowers the Curie temperature from 677 to 550 K and the saturation magnetization drops from 160 to 138 Am2/kg. The structural evolution was evaluated by annealing the glassy samples at different temperatures, revealing that the crystallization proceeds in multiple steps, beginning with the formation of different iron borides (FeB, Fe2B, FeB2 and Fe23B6) followed by transformation to a mixture of more stable phases.

Mechanosynthesis of metastable cubic δ-Ta1−xN

The formation of the cubic δ-Ta1−xN phase by high-energy ball-milling from tantalum and boron nitride (h-BN) is explored. Two different molar ratios Ta:BN, 1:1 and 2:1, were used. X-ray diffraction, scanning electron microscopy, surface area analysis by the Brunauer-Emmett-Teller method, and thermogravimetric analysis were used to characterize the products obtained. In both molar ratios and after a few minutes of milling, the mechanosynthesis of δ-Ta1−xN was observed. Increasing the entropy of the system by introducing vacancies and point defects by the high-energy ball-milling process seems to stabilize the cubic δ-Ta1−xN phase, as previous theoretical studies had reported. The phase obtained depends on the molar ratio used: in the molar ratio 1:1 a non-stoichiometric δ-Ta1−xN phase is obtained, while in the molar ratio 2:1 a stoichiometric δ-TaN phase and secondary phases are obtained. The amorphous boron remains dispersed in the material until the mechanical energy is high enough to trigger the formation of tantalum borides.

Effect of Boron Content and Cooling Rate on the Microstructure and Boride Formation of β-Solidifying γ-TiAl TNM Alloy

Boron is a unique and popular grain refiner element in cast titanium aluminide (TiAl) alloys, as it helps to improve mechanical properties if properly alloyed. However, the formation mechanism of different types of borides in cast TiAl alloys is not yet clearly understood. This study seeks to correlate the chemical composition and cooling rate during solidification of cast TiAl alloys, with the type of boride precipitated and the resulting microstructure. Several β-solidifying γ-TiAl alloys of the TNM family were cast, alloying boron to a starting Ti-44.5Al-4Nb-1Mo-0.1B (at.%) alloy. The alloys were manufactured with an induction skull melting furnace and poured into a stepped 2, 4, 8 and 16 mm thickness mold to achieve different cooling rates. On one hand, the results reveal that boron contents below 0.5 at.% and cooling rates during solidification above 10 K/s promote the formation of detrimental ribbon borides. On the other hand, boron contents above 0.5 at.% and cooling rates during solidification below 10 K/s promote the formation of a refined microstructure with blocky borides. Finally, the formation mechanisms of both ribbon and blocky borides are proposed.

Development and application of a complex model of titanium diboride plasmosynthesis

An integrated multifactor mathematical model of plasmosynthesis of titanium diboride was developed. The model includes 3 submodels: “Plasma generation”, “Evaporation of raw materials”, “Boride formation”. The model provides the implementation of multivariate research and engineering calculations of plasma processing technological indicators of various types of titanium-containing raw materials, industrial products and waste. The convergence of the predicted and practical results for various types of raw materials is 10.4-12.9%. In all cases, lower values of practical data are noted in comparison with the calculated ones, which is due to the influence of non-isothermal heat carrier gas.