Types Of Borides Research Articles

BORIDE LAYER GROWTH KINETICS ON X90CrMoV-18 STEEL

Boronizing is a type of thermal diffusion with the primary goal of increasing the surface hardness, wear and corrosion resistance. The wear resistance of boronized parts depends on the type of borides that form on the steel surface and their thickness. This study investigated the properties of boride layers formed on X90CrMoV-18 martensitic stainless steel, using pack boronizing carried out in a temperature range of 850–1000 °C and in durations of (1, 3 and 5) h. Results indicate a difference in the boride layer thickness of 3–80 µm and volume share of boride phases depending on the temperature and time of boriding. From the boriding compound depth, values of the frequency factor and activation energy were determined using the Arrhenius equation. With these values, the parabolic equation for predicting the growth rate of a boride layer was formulated and validated for different times and temperatures of boriding.

Quasi-Two-Dimensional Nanostructures from AlB2-Type Metal Borides: Physicochemical Insights and Emerging Trends

Transition-metal diborides are a class of abundantly available ceramic materials that exhibit a landscape of rich properties such as extraordinary high strength, exceptional hardness, and high-melting points. To date, these materials have been investigated primarily for their bulk scale properties. Many of these transition-metal diborides adopt an AlB2-type structure. In this type of structure, the metal atoms are sandwiched between alternating layers of boron atoms. Examples of these types of borides include, magnesium diboride (MgB2), titanium diboride (TiB2), chromium diboride (CrB2), etc. The AlB2-type structure is appealing for a plethora of reasons, primary among them is the inherent presence of boron atoms arranged in a honeycomb pattern reminiscent of the graphenic arrangement. This provides an opportunity to access two-dimensional (2D) boron. Recent research trends indicate a rising interest in nanoscaling these borides to yield 2D nanostructures. Research groups across the globe are currently pursuing this very objective, and multiple reports have already emerged showing that it is possible to nanoscale these bulk AlB2-type borides into nanosheets. One of the routes that researchers have adopted to this end is the well-recognized, top-down exfoliation. This involves methods such as liquid-phase exfoliation, mechanical exfoliation, and chemically induced selective extraction. This review will chronicle the research evolution of top-down exfoliation of metal borides from a physicochemical context and present the reader with a summary of these methods and the associated findings. We will also briefly discuss the various areas where these nanoscaled metal borides have just started finding applications toward sustainable technologies and present our perspective on where the field is headed. We hope that this review will be a timely addition to the fast-evolving literature on nanoscaling metal borides.

Measurement of Doppler broadening of prompt gamma-rays from various zirconium- and ferro-borons

Peak shape analysis was performed for the energy spectra of Doppler-broadened prompt γ-rays generated by neutron capture reactions with various boride or boron samples. Significant differences were observed between nonmetallic and metallic borides. Minor differences between the peak shapes of prompt γ-rays from zirconium- and ferro-borons were evaluated by a peak fitting method. The identification performance for zirconium- and ferro-borons and other types of borides was measured.

The Importance of Phase Composition for Corrosion Resistance of Borided Layers Produced on Nickel Alloys.

The plasma paste boriding process was used for production of the borided layers on pure nickel and nickel-chromium alloys. The produced layers consisted of nickel borides only (in the case of nickel) or a nickel and chromium borides mixture (in the case Ni–Cr alloys). The objective of this investigation was to indicate the importance of the presence of chromium for corrosion resistance of non-borided alloys, as well as to indicate the influence of phase composition of borided layers on their corrosion resistance. Pure nickel was characterized by higher corrosion resistance, in comparison to the nickel-based alloys. Increased chromium content in nickel alloys resulted in their high susceptibility for pitting corrosion. All borided samples were characterized by higher corrosion resistance than the non-borided samples. However, the phase composition of borided layers influenced their corrosion resistance. Due to the microstructure which consisted of one type of borides (nickel borides), borided nickel had the highest resistance to corrosion, whereas the presence of chromium borides in layers produced on nickel-chromium alloys caused a decrease in corrosion resistance.

Assessing the Influence of Cr and Fe in the Filler Metal on Dissolution and Isothermal Solidification Kinetics During TLPB of Ni-Based Superalloys

The influence of chromium and iron’s absence (BNi-3) and presence (BNi-2) in boron-containing filler metals (FM) on the TLPB behavior of IN718 base metal (BM) was examined. Results indicate that the absence of Cr and Fe in the FM significantly aggravated BM dissolution and gap widening, particularly when similar degrees of brazing beyond the FM liquidus temperature occurred. This led to a higher complete isothermal solidification time, despite a higher rate of isothermal solidification (IS) and initial boron uptake displayed by the IN718/BNi-3 joint. EDS and quantitative image analysis performed within the DAZ concluded that differences observed in the rate of IS were related to the amount and type of borides forming in the DAZ. The lack of Cr in the BNi-3 favored the formation of Cr-poor:B-rich Cr(Mo,Nb)B borides, leading to a higher rate of B uptake by the base metal. Joints made from the Cr containing BNi-2 FM displayed a combination of Cr-rich:B-poor CrB and Cr(Mo,Nb)B borides leading to lower rates of B uptake.

Mechanical properties and cell proliferation response of borided biomedical titanium alloys with different crystalline structures

A comparative study was conducted in order to investigate hardness, fracture toughness, adhesion and cell proliferation properties of boride layers produced on medical grade titanium materials with different crystalline structures. For this purpose, α type Cp-Ti, α + β type Ti-6Al-4V and β type Ti-45Nb were borided by using powder-pack boriding technique. Boride layers on titanium alloys exhibited hardness values up to 40.2 ± 2.7 GPa with low fracture toughness depending on the types of borides formed in boride layers. The adhesion tests showed that thickness, brittleness and morphology of boride layers have strong effect on adhesion of boride layers. However, no intensive failure developed on boride layers which proofs that adhesions of surface layers are sufficient. The influence of surface topography and chemical composition of boride layers on biocompatibility was examined. The proliferation of Saos-2 cells on each sample was quantified after 72 h by MTT assay. It was demonstrated that cell growth on borided Cp-Ti and Ti-6Al-4V alloy are less than their unborided ones (control). In comparison to Cp-Ti and Ti-6Al-4V alloy, Ti-45Nb alloy has increased number of cells proliferated on its both borided and unborided surfaces.

The Role of Base Metal Chromium in Determining the TLPB Behavior of Ni-Based Alloys Using a Boron-Containing Braze

The TLPB behavior of Ni/Ni-Si-B and Ni-Cr-Fe/Ni-Si-B base metal/braze joints was examined to determine the role chromium in the base metal has during joining of Ni-based alloys using a boron-bearing braze metal. The isothermal solidification (IS) rate in these two braze joints at 1075 °C was measured using DSC. Microstructural evolution within the diffusionally affected zone (DAZ) was examined both in terms of the type of borides formed and their volume fraction, using image analysis and phase equilibria predictions. Overall, the results show that when the base metal (BM) contains an appreciable concentration of Cr the IS rate decreases significantly. This was due to the formation of a low volume fraction of CrB within the DAZ, dictated by phase equilibria. Conversely, in the pure Ni base metal (BM) the thermodynamically favored boride was Ni3B, present at high volume fractions, resulting in rapid IS. A direct link between the boride microstructure of the DAZ and the rate of IS was established.

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.

Characterization of eutectic borides formed during solidification of borated stainless steel 304B4

AISI 304B4 stainless steel (SS) containing 1.3 wt.% boron was cracking extensively during fabrication of neutron shields for Prototype Fast Breeder Reactor (PFBR). However, earlier study on 304B4 steel showed good resistance to weld solidification cracking due to eutectic backfilling in the cracks during welding. In order to understand the backfilling mechanism in this steel, microstructural characterization was performed on 304B4 SS in solution-annealed and re-melted and solidified conditions. In solution-annealed condition, microstructure of 304B4 SS consists of austenite matrix with random distribution of blocky Cr2B-type borides. On contrary, as-solidified microstructure reveals the primary austenite dendrites and interdendritic eutectic of (Fe,Cr)2B-type borides of varying morphologies. In addition to (Fe,Cr)2B, spheroidal non-equilibrium Fe23(CB)6-type borides were also found inside the austenite dendrites. The eutectic liquid rich in boron and Fe, which has low solidus temperature, contributes significantly to backfilling of hot cracks formed during welding. This was confirmed through characterization of eutectic borides in the as-solidified structure which shows Fe-rich (Fe,Cr)2B and Fe23(CB)6 types of borides. Finally, reasons behind severe liquation cracking of 304B4 SS observed during fabrication of neutron shield has been explained based on Scheil’s solidification simulations.

Effect of Quenching Temperature on Microstructure and Properties of Al-Bearing High-Boron High-Speed Steel

Microstructure and properties of the alloys could be changed by heat treatment process. In this work, effect of quenching temperature on the microstructure of Al-bearing high-boron high-speed steel (AB-HSS) was investigated by means of optical microscopy, scanning electron microscopy and X-ray diffraction. Hardness and wear resistance of AB-HSS at different quenching temperatures were tested by rockwell hardness tester, microhardness tester and wear tester, respectively. The experimental results indicate that the microstructure of as-cast AB-HSS is mainly composed of pearlite, ferrite, M2B-type boride and M23(C, B)6-type borocarbide. After quenched treatment, the matrix transforms into the martensite and the type of boride has no obvious change. The morphology of boride changes from continuous network and fish-bone to isolate shape and granular distribution. As quenching temperature increases, the hardness of alloy increases. The hardness reaches 65.1 HRC when quenching temperature is 1110 °C. The wear resistance of alloy gradually increases with the increase in quenching temperature. The wear resistance is the best when the quenching temperature reaches 1110 °C.

Thermophysical and mechanical properties of CrB and FeB

ABSTRACT Fuel debris in the Fukushima Daiichi nuclear power plant is thought to contain borides that are generated from B4C control material. In order to successfully devise methods to effectively remove the debris material, characterization of the properties of the fuel debris is essential. This paper presents some of the thermophysical and mechanical properties of two types of borides, FeB and CrB, and compares them with those of Fe2B and ZrB2. These are the representative borides that might have been generated in the Fukushima Daiichi (1F) nuclear power plant accident. We observed that the thermal conductivity values of both CrB and FeB are much lower than that of ZrB2, and are similar to that of Fe2B. Moreover, the Vickers hardness and fracture toughness of FeB and CrB are almost identical to each other, and similar to those of ZrB2 and Fe2B.

Influence of niobium and molybdenum addition on microstructure and wear behavior of laser-borided layers produced on Nimonic 80A-alloy

Abstract Laser alloying was used for production of thick layers on surface of Nimonic 80A-alloy. For laser surface modification, three types of pre-coated pastes were applied: with amorphous boron, with amorphous boron and molybdenum as well as with amorphous boron and niobium. The microstructure, hardness and wear resistance of produced layers were studied in details. The presence of different types of borides in re-melted zone depended on the paste composition and caused an increase in hardness up to about HV 1000. The wear resistance was evaluated by calculation of mass wear intensity factor Imw and relative mass loss of specimen and counter-specimen. The wear behavior of the tested frictional pairs was determined by 3D interference microscopy, scanning electron microscopy equipped with EDS microanalyzer. The significant increase in abrasive wear resistance was observed in comparison to untreated Nimonic 80A-alloy. The lowest mass loss intensity factor was characteristic of laser-alloyed Nimonic 80A-alloy with boron and niobium (Imw=1.234 mg/(cm2·h)). Laser alloyed-layers indicated abrasive wear mechanism with clearly visible grooves. Laser alloying with boron and niobium resulted in the additional oxidative wear mechanism. In this case, EDS patterns revealed presence of oxygen on the worn surface of specimen.

Wear Resistant Duplex Stainless Steels Produced by Spray Forming

In this work, boron-modified duplex stainless steels were prepared by spray forming using design guidelines provided by thermodynamic calculations. Firstly, an investigation of stable phases and phase formation sequence in duplex steels containing high levels of boron was conducted. The calculation indicated that there was an eutectic point at around 1 wt% boron with different primary phase formations upon equilibrium solidification. For hypoeutectic compositions, the primary phase was δ-Ferrite, whereas for hypereutectic a metallic boride (M2B) should form. Additionally, eutectic reactions for both compositions should lead to the formation of borides M2B and M3B2. Secondly, spray forming experiments were conducted based on the thermodynamic calculations. Sample preparation was carried out using a conventional superduplex steel (2507) as starting material. Two different compositions were selected: one hypoeutectic (0.8 wt% B) and one hypereutectic (2.5 wt% B). The microstructural investigation revealed the formation of different types of borides embedded in an austenitic-ferritic matrix. Finally, the wear resistance was evaluated with the dry sand/rubber wheel test and a significant improvement was observed for boron-containing steels in comparison with the same steel without boron. This improvement was attributed to the presence of fine and well-distributed boride particles that protected the austenitic-ferritic matrix from material removal.

Formation of iron borides and iron nitrides in interaction of iron powder with boron nitride powder

ABSTRACTThe paper considers a way of iron nitrides production in monolithic specimens. The relevance for iron nitrides production is conditioned by the promise in using phase Fe16N2 (α’’-phase) as a hard-magnetic material due to the high value of the saturation magnetization (2.3 T at 4.2 K). By means of X-ray diffraction analysis, scanning electron microscopy, and magnetic parameter measurements, the study analyzes the structure and magnetic properties of metal alloy based on iron, obtained as a result of interaction between iron and boron nitride powders after their mixing, pressing, and heat treatment at 1550°C in the atmosphere of nitrogen. The heat treatment results in metal fragments exudation from the ceramic part of the briquette. The microstructure of the fragments is composed of primary deposited iron, eutectic colonies of Fe – iron boride type, and incorporation of iron nitrides. The obtained metal fragments are characterized by high coercivity (0.50 kOe).

Investigation of Hardness of Ternary Borides of the YCrB4, Y2ReB6, Y3ReB7, and YMo3B7 Structural Types

The metal borides: YReB4, YCrB4 (YCrB4 structural type), Y2ReB6, Sc2ReB6 (Y2ReB6), Y3ReB7, Y3MoB7, and Y3WB7 (Y3ReB7), and YMo3B7 (YMo3B7) structural types, and their solid-solutions: YRe1–xCrxB4, Y1–xScxCrB4, Y2–2xSc2xReB6, Y2Re1–xCrxB6, and YMo1–xWxB7 were analyzed using powder X-ray diffraction and energy-dispersive X-ray spectroscopy, and studied for their mechanical properties. These metal borides possess unique crystal structures, not found in any other type of borides: alternating metal and boron layers with boron being arranged in 5-, 6-, and 7-member rings (YCrB4, Y2ReB6), corrugated cages of 5- and 13-member boron rings (Y3ReB7), as well as stacked layers of ribbons of hexagonal boron atoms 6 rings wide (YMo3B7). Although none of these borides in pure form possess high hardness, their solid solutions are superhard (Vickers hardness above 40 GPa): 42.48 ± 2.13 GPa for an alloy with a nominal composition of (YRe0.5Cr0.5):4B, 42.02 ± 2.05 GPa for (Y0.5Sc0.5Cr):4B and 41.33 ± 2.18 GPa for (YScRe):6B...

Kinetic Study of the Growth of Hard Layers on a Low Carbon Steel

ABSTRACTIn the present work the kinetic growth is analyzed for a hard coating applied on a low carbon steel AISI 8620. A thermochemical treatment of bored with dehydrated paste at temperatures of 900, 950 and 1000 °C with a residence time of 2, 4, 6 and 8 h. The morphology and types of borides formed on the surface of the steel were evaluated by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The layer formed has a size of 20 to 113 μm which will be dependent on the process temperature, the treatment time and the alloy elements of the substrate. Hardness of 1493-1852 HV are presented for treatment times and temperatures established in this study. The kinetics of growth were determined and analyzed using a mathematical model of diffusion, evaluating the penetration of the biphasic layer that is determined as a function of the time and temperature of the thermochemical treatment (TCT). The results show the increase in the growth constants (k) with respect to the bored temperatures. The activity energy (Q) of the material AISI 8620 was also obtained.

Precipitation and evolution of boride in diffusion affected zone of TLP joint of Mar-M247 superalloy

Boride precipitation is difficult to avoid in nickel based superalloys during transient liquid phase (TLP) bonding process. In the present work, the Mar-M247 alloy was joined by transient liquid bonding with Ni-Cr-B amorphous filler at 1120 °C. The morphology, distribution and crystal structure of precipitated borides in the diffusion affected zone (DAZ) were investigated. It is found that two types of carboborides and three types of borides are formed in DAZ when the isothermal solidification is completed, which are M23(C,B)6, M6(C,B), M3B2, granular M5B3 and acicular M5B3, respectively. Strip-type M3B2 and chain-type M4B3 borides exist at grain boundaries. Acicular M5B3 borides grow about 10 μm into the DAZ from joint/substrate interface, and the width of this area does not change with prolonging holding time. In order to find the characteristic of borides precipitation in DAZ during the stage of the filler melts, an experiment of accurate controlling TLP bonding was carried out using a differential scanning calorimetry (DSC) apparatus. The phase transformation driving force of boride and boron concentration profiles during initial bonding stage were also calculated to discuss the mechanism of the acicular boride precipitation. Thermodynamic calculation indicates that the boron concentration greater than 0.19 wt% is a necessary condition for the formation of acicular boride at 1065 °C, indicating that acicular M5B3 borides had already precipitated before the beginning of isothermal solidification.

Microstructure evolution of Inconel 625 with 0.4 wt% boron modification during gas tungsten arc deposition

Gas tungsten arc deposits were made on substrate of stainless steel 304 using IN625 wires modified with 0.4 wt% B in shielding argon. The temperature profiles were simulated by the modified Rosenthal 3D equation. The re-melting boundary correlated well with the hardness profile and corresponding microstructure evolution along the as-manufactured sample. The upper section had higher hardness than the lower section. This high hardness was attributed to the existence of continuous eutectics (Laves phase and NbC) in the inter-dendritic regions. These eutectics in the lower section partially re-melted in this multi-pass process to form non-continuous features contributing to a lower hardness. Moreover, fine isolated borides precipitated out from the γ matrix in lower section as a result of the multiple thermal cycles. The eutectic phases were identified to be Laves phase with few NbC. The isolated borides were confirmed as M5B3 type of boride by TEM. Modeling of the segregation behavior of the major alloying elements according to Clyne-Kurz equations was conducted and the results were in good agreement with chemical concentration profiles.

Study of the Structure and High-Temperature Mechanical Properties of a Steel with an Elevated Content of Boron

The structure and mechanical properties of steel with an elevated content of boron are studied after tensile tests at a high temperature. In its initial condition, the structure of the steel contains two types of borides [TiB2 and (Fe, Cr)2B] distributed uniformly in a ferritic matrix. The range of satisfactory process ductility is shown to be 1050 – 1150°C; at 1200°C the metal undergoes brittle fracture due to local fusion of individual regions of the structure.

Potential and limitations of microanalysis SEM techniques to characterize borides in brazed Ni-based superalloys

Brazed Ni-based superalloys containing complex phases of different Boron contents remain difficult to characterize at the micrometer scale. Indeed Boron is a light element difficult to measure precisely. The state-of-the-art microanalysis systems have been tested on a single crystal MC2 based metal brazed with BNi-2 alloy to identify boride precipitates. Effort has been made to evaluate the accuracy in Boron quantitation. Energy-dispersive and wavelength-dispersive X-ray spectroscopy attached to a Scanning Electron Microscope have first been used to determine the elemental composition of Boron-free phases, and then applied to various types of borides. Results have been compared to the ones obtained using a dedicated electron probe microanalysis, considered here as the reference technique. The most accurate method to quantify Boron using EDS is definitely by composition difference. A precision of 5at.% could be achieved with optimized data acquisition and post-processing schemes. Attempts that aimed at directly quantifying Boron with various standards using EDS or coupled EDS/WDS gave less accurate results. Ultimately, Electron Backscatter Diffraction combined with localized EDS analysis has proved invaluable in conclusively identifying micrometer sized boride precipitates; thus further improving the characterization of brazed Ni-based superalloys.