Morphology Of Boride Research Articles

Microstructure evolution and mechanical properties of Fe–Cr–B alloys with varying Mo additions

The continuously net-like morphology of borides accounts for the poor toughness of Fe–Cr–B wear-resistant alloys. To effectively modify the morphology of Fe2B, Mo element has been introduced in Fe–Cr–B alloys, and the microstructure evolution and mechanical properties have been systematically investigated. The results show Fe–Cr–B alloys are mainly composed of martensite, M2B, M23(B, C)6 and lamellar M3B2 after Mo addition. With the increase of Mo addition, the content of M3B2 increases gradually while that of M23(B, C)6 increases firstly and then decreases. Consequently, the net-like structure of M2B can be effectively broken to acquire the isolated bulk-like morphology, which is mainly attributed to the growth inhibition effect of lamellar structure M3B2. In addition, the hardness varies depending on the volume fraction of borides. However, the fracture toughness of Fe–Cr–B alloy can be dramatically improved by 34.3% with Mo addition increasing from 1 to 4%. Grain morphology modification of M2B plays the predominant role in the toughness improvement because the crack propagation path can be blocked. Furthermore, the lamellar M3B2 structure can effectively hinder the cracking propagation so as to improve the alloy's fracture toughness. Mo addition has been proved to be an effective way to modify the grain morphology of M2B hard phase.

Effects of cooling rate on borides morphology and structure in cast β-solidifying γ-TiAl alloy

Borides have been found to play a significant role in determining the mechanical properties of cast TiAl alloys. In order to investigate the influence of cooling rate on the morphology and structure of borides, SEM and HRTEM techniques were utilized to analyze borides in Ti-43Al-4Nb-1Mo-0.5B (at. %) cast plates with varying thicknesses. A higher cooling rate was observed to result in the formation of elongated, curvy borides with high aspect ratios, increased planar faults, and complex structures consisting of a combination of B2 phase and various boride phases. Conversely, a slower cooling rate yielded shorter bar-shaped borides with fewer planar faults. This variation in boride morphology can be attributed to the differing thicknesses of the solute-rich layer, where the eutectic reaction occurs, at the solidification front during fast and slow cooling processes. Bf-TiB with a habit plane of (010) was identified as the dominant phase at all cooling rates. Borides in the [100] and [001] directions demonstrated a faster growth rate compared to those in the [010] direction. Additionally, HRTEM results indicated the presence of TiB2 while Ti3B4 was absent. This can be explained by the limited phase region of Ti3B4 in both the binary Ti-B and ternary Ti-Al-B phase diagrams, which is the smallest among all phases. These findings enhance the understanding of how cooling rate influences the morphology and structure of borides in TiAl alloys, thus providing insights for optimizing alloy design and manufacturing processes.

The Role of Boron Addition on Solidification Behavior and Microstructural Evolution of a High Niobium-Containing TiAl Alloy

This work investigates the role of boron addition in the solidification behavior and microstructural evolution during the heat treatment process of Ti-46Al-8Nb-xB (x = 0.1, 0.7, 1.4, 2.5 at.%). The results show that the solid solution boron element prefers to occupy the interstitial vacancies of the α2 phase in the alloy. However, the solid solubility of the boron element in high Nb-containing TiAl alloys is extremely low. Therefore, it does not have a significant effect on the lattice distortion of α2 and γ phases in the alloy. When the boron content is added up to 0.1%, a B27-type TiB precipitated phase is produced in the alloy. The morphology of borides mostly shows short rod-like structures, and a few show long curved shapes. And the addition of boron refines both the alloy colony size and the lamellar structure. Furthermore, it is also found that boron addition weakens the casting texture of the alloy. After a solid solution and different time aging heat treatment process, the microstructure of different boron content alloys have experienced obvious coarsening phenomenon. However, the morphology of the boride is closely related to boron content and heat treatment.

Effects of boron, Hf and Ta content on boride morphology and microstructure of β-solidified γ-TiAl alloys

Boron is the most commonly used grain refining element in γ-TiAl alloys and the morphology of the borides has a significant influence on the room temperature plasticity of γ-TiAl alloys. In this paper, the effect of boron, Hf and Ta content on boride morphology and microstructure of a γ-TiAl alloy (Ti-43.5Al–4Nb–1Mo-0.5B) were investigated. The boride morphology transitions from flat to curved as boron content increases from 0.5% to 0.8%. With a further increase in boron content, the curved borides change into short rod-like and granular. Boride morphology changes from flat to curved When Hf is added. Conversely, when Ta is added, the length and width of the borides become smaller and dendritic borides with complex morphology appear. The combination of solid solution strengthening (boron, Hf and Ta), precipitation strengthening (borides) and grain refining increases the alloy's hardness. Furthermore, the flat borides are rich in Nb and Ta, whereas the curved borides are rich in Al. The present study shows that the addition of Ta can refine the size of borides, which may have a positive effect on improving the room temperature properties of the γ-TiAl alloy.

Boride evolutionary behavior and mechanism in the TLP repaired IN738 superalloy with crack-like defects

Boride evolution in the transient liquid phase (TLP) repaired cracks for IN738LC alloy had important influence on mechanical properties. The microstructure of the repaired crack contained two typical zones: isothermal solidification zone (ISZ) and diffusion affected zone (DAZ). There were blocky and acicular borides with hexagonal crystal structure in the DAZ, and boride morphology depended on the interfacial distance, Cr/B content, and aging time. i) As the distance from the ISZ/DAZ interface increased, blocky borides gradually decreased and acicular borides began to form. ii) When Cr and B were sufficient, blocky borides firstly formed. When the content decreased to a certain extent, borides would not form. iii) As aging time increased, the amount of blocky borides gradually increased due to the diffusion of B. Meanwhile, acicular borides began to form along (111) plane, which could effectively reduce the interfacial energy.

Effect of Chromium on Microstructure and Oxidation Wear Behavior of High-Boron High-Speed Steel at Elevated Temperatures.

In order to investigate the effect of Cr content on the microstructures and oxidation wear properties of high-boron high-speed steel (HBHSS), so as to explore oxidation wear resistant materials (e.g., hot rollers), a scanning electron microscope, an X-ray diffractometer, an electron probe X-ray microanalysis and an oxidation wear test at elevated temperatures were employed to investigate worn surfaces and worn layers. The results showed that the addition of Cr resulted in the transformation of martensite into ferrite and pearlite, while the size of the grid morphology of borides in HBHSSs was refined. After oxidation wear, oxide scales were formed and the high-temperature oxidation wear resistance of HBHSSs was gradually improved with increased additions of Cr. Meanwhile, an interaction between temperature and load in HBHSSs during oxidation wear occurred, and the temperature had more influence on the oxidation wear properties of HBHSSs. SEM observations indicated that a uniform and compact oxide film of HBHSSs in the worn surface at elevated temperatures was generated on the worn surface, and the addition of Cr also reduced the thickness of oxides and inhibited the spallation of worn layers, which was attributed to improvements in microhardness and oxidation resistance of the matrix in HBHSSs. A synergistic effect of temperature and load in HBHSSs with various Cr additions may dominate the oxidation wear process and the formation and spallation of oxide films.

Microstructures and mechanical properties of Ti–44Al–5Nb–3Cr–1.5Zr–xMo–yB alloys

Abstract

Effects of boron content on the microstructure and mechanical properties of twin-roll strip casting borated steel sheets

High borated steel sheets containing 0.25 wt% to 4.0 wt% boron including hypoeutectic (0.28 wt% B and 2.11 wt% B), eutectic (2.43 wt% B) and hypereutectic (4.01 wt% B) compositions were tried to be fabricated by a novel strip casting technology, and the effects of boron content on sub-rapid solidification behavior and subsequent microstructural evolution together with mechanical properties was studied. It was found that the morphology of borides depended greatly on the boron content. When increasing boron, the morphological change of borides was network-like → grainy → cluster-like → plate-like. Various orientation relationships between different morphological borides and γ-Fe in as-cast steels were also identified. After subsequent hot-rolling and solution-treating, ultra-fine (<10 μm) borides were obtained in hypoeutectic and eutectic steels. Benefiting from that, excellent mechanical properties was achieved, which was much better than that of steels prepared by traditional ingot casting. Particularly, when the boron content approached eutectic composition, of which the effect on the microstructure and mechanical properties was more sensitive. The steels containing 2.11 wt% and 2.43 wt% boron exhibited different morphological borides with a total elongation of 14.1% and 8.0%, respectively. Moreover, a thin hypereutectic borated steel sheet was also prepared, but the borides were very large and the total elongation was very low. The correlation between microstructure and strength was clarified based on the Hall-Petch behavior and intermetallic strengthening effect. Smaller γ-grains and higher volume fraction of borides were responsible for higher strength. The plastic behavior of steels was influenced by strain-hardening rate that was determined by the volume fraction of γ-Fe matrix. A better sustainable strain-hardening capability was beneficial to extend the stage of uniform deformation and enhance the ductility. In addition, the mechanical properties of steels were also decided by the fracture mechanism that was dominated by the size of borides.

Effect of TiB2 addition on microstructure and fluidity of cast TiAl alloy

Effects of TiB2 addition on Microstructure and Fluidity of Ti–48Al–2Cr–2Nb + xTiB2 (x = 0.18, 0.36, 0.54, 0.72, 0.9, 1.8 wt%) alloys fabricated by vacuum non-consumable tungsten arc melting were investigated. Results showed that with adequate TiB2 addition (0.72% TiB2 and more), the as-cast microstructure transformed from coarse columnar grains to fine equiaxed grains, and the grain size was reduced from 800 μm to 200 μm. The morphology of borides transformed from flake to block and needlelike, resulted from the dissolution and re-precipitation of original TiB2 powders. The fluidity of TiAl alloy was improved by the addition of TiB2, and the T4822–0.72TiB2 alloy showed the largest filling length of 266.5 mm, 17.4% higher than that of the matrix alloy. The enhancement of fluidity and the cessation mechanism of melt flow for the TiB2-containing TiAl alloy were analyzed and discussed in light of the microstructure evolution, borides and solidification characterization.

Investigation on Microstructure Evolution and Strengthening Mechanism in Boron-Bearing Advanced High Strength Steel

Investigation on the casting, hot-rolling and heat treatment process of a high boron-bearing advanced high strength steel was conducted. The scanning electron microscopy (SEM), electron-probe micro-analyzer (EPMA), electron backscattered diffraction (EBSD) and X-ray diffraction (XRD) were employed to analyze the evolution of microstructure which includes the phase constitution and boride morphology during hot processing. Through the control of as-casted, heat treated microstructure and using interrupted tensile tests, the strengthening mechanism was revealed. Results showed that, the strain-induced ferrite transformation of austenite and grain size were the decisive factors which control the strength and ductility, while the defects and internal stress etc. were the secondary factors.

Pack-boriding of low alloy steel: microstructure evolution and migration behaviour of alloying elements

ABSTRACTLow alloy steel was pack-borided at different processing temperatures (at 850, 950, and 1050°C) and times (2, 4, and 6 h). The microstructural characterisation of boronized steel showed the presence of three zones, namely boronized region containing finer grains and columnar geometry of (Fe, M)2B (where M = Cr, Mn, Mo, and Ni), transition zone, and non-boronized core. The concentrations of the alloying elements in (Fe, M)2B were increased from the surface to the core of the specimen. The pattern of slope variation of boron concentration–depth profile (obtained using GDOES) was linked with the boride morphology and process temperature. Pack-boriding of steel led to the development of systematic trend in slope variation of overall concentration–depth profiles of the alloying elements. The composition and morphology of boride affected the trend of slope variation for the boride-forming alloying elements. However, for Al and Si, the trend of slope variation was connected to the boride morphology and the composition of the matrix. Chemistry of the matrix was strongly dependent on the migration kinetics of the alloying elements during the boride growth. The migration kinetics of Cr, Mn, Mo, and C were found almost equivalent to the rate of boride growth. However, Ni, Al, and Si were migrated at a slower rate. Si showed the lowest migration kinetics among the alloying elements. The concentrations of the alloying elements having higher migration kinetics remained constant in the matrix during the boride growth.

Microstructure evolution of monocrystalline superalloy with boron addition

The as-cast and heat treated structures of nickel-base monocrystalline superalloy DD90 were observed, using an optical microscope (OM) and a scanning electron microscope (SEM), and the effect of different contents of B on γ/γ′ eutectic structure, carbide and borides morphology and volume fraction were studied. Boron addition had no significant effect on dendrite morphology, the volume fraction of eutectic increased with the increasing of boron level. The morphology of carbides changed from layers, needle, block and the layer-typed to the smaller block. The morpgologies of carbides in as-cast state mainly were blocky, octahedral and Chinese script like. The carbides precipitated as dispersed blocky and octahedral after thermal treatment. With the increasing of boron level, the volume fraction of borides increased and the content of W + Mo + Cr + Re became much high. The morphology of borides mainly were slender rod and grain after thermal treatment.

Performance of GH4169 brazed joint using a new designed nickel-based filler metal via cluster-plus-glue-atom model

A novel Ni-Cr-Si-B filler metal with the cluster formula of [Cr-Ni12]B2Cr + [B-Ni8Cr]BSiCr based on the cluster-plus-glue-atom model was designed for vacuum brazing GH4169 alloy. The effect of brazing temperature and brazing time on microstructure and shear strength of GH4169 alloy joints was investigated. The brazed seam was mainly composed of γ-Ni solid solution. (Nb, Ti)-rich phase and (Cr, Nb, Mo)-rich borides distributed in diffusion zones. The diffusion and aggregation of B, Cr, Nb, and Mo resulted in the variation of phase contrast and morphology of borides. Coarse precipitations in the joint brazed at 1240 °C consisted of borides, Laves phase and δ phase. The shear strength of joints was principally dominated by the brittle precipitations in diffusion zone, and the homogenization of microstructure improved the room-temperature shear strength to 820 MPa with the high-temperature shear strength of 627 MPa for the joint brazed at 1240 °C/20 min. The joint fractured in diffusion zone and brazed seam, and the existence of borides and Laves phase in diffusion zone provide the potential origin for crack growth.

Tailoring of Metal Boride Morphology via Anion for Efficient Water Oxidation

AbstractThe metal‐metalloid materials have received a massive interest as oxygen‐evolving catalysts due to their ability for charge transfer between different elements and modified electronic structures lowering the kinetic energy barriers of the electrochemical processes. Herein, a facile and systematic preparation of metal borides by chemical reduction is reported, with morphologies ranging from nanoparticles to nanosheets which is driven by a careful selection of metal salts solution. The iron doping in cobalt boride nanosheets is found to be an effective approach to further tune the water oxidation activity. The as‐prepared catalyst exhibited superior oxygen evolution performance in 1.0 m KOH as the optimized ternary CoFe boride needs an overpotential of 265 mV to achieve a current density of 10 mA cm−2 at a mass loading of 0.3 mg cm−2.

Effect of isothermal quenching on microstructure and properties of a forged and unforged Fe-B cast alloy

Abstract The effect of isothermal quenching on microstructure and properties of forged and unforged Fe-B cast alloy were investigated in this paper. The prepared samples were analyzed using scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that, after isothermal quenching, the matrix transforms into lower bainite, but the morphology of boride remains nearly unchanged compared with its as-cast condition. Compared with water quenching, the hardness of forged and unforged samples after isothermal quenching is lower than the hardness of that after water quenching. The impact toughness of forged and unforged samples after isothermal quenching is higher than after water quenching. In two-body abrasion test, the wear resistance of forged and unforged samples after isothermal quenching is lower than that of forged and unforged samples after water quenching. In three-body abrasion test, the wear resistance of forged and unforged samples after isothermal quenching shows opposite behavior and is higher than that of forged and unforged samples after water quenching.

Effect of High Configuration Entropy and Rare Earth Addition on Boride Precipitation and Mechanical Properties of Multi-principal-Element Alloys

A series of multi-principal-element (MPE) alloys have been prepared by adding Ni, Mn, Al, Cu and Y into the reference CoCrFe-B alloy. The microstructure and mechanical properties of these MPE alloys have been investigated thoroughly. It is found that the addition of the elements can inhibit boride precipitation in the designed alloys and the solid solution strengthening effect induced by interstitial boron atoms is more significant than that by boride precipitation. The MPE alloys with the fcc phase as the main solid solution phase have a higher boron solubility and hence less boride precipitation, than those with the bcc phase as the main solid solution phase. The addition of yttrium can improve the boron solubility, decrease boride precipitation, control the boride morphology and, importantly, simultaneously improve the compressive strength and ductility of boron-containing MPE alloys.

Microstructure characterization, mechanical properties and toughening mechanism of TiB2-containing conventional cast TiAl-based alloy

Effects of TiB2 addition on microstructure and mechanical properties of Ti–48Al–2Cr–2Nb+(0.72,1.62)wt% TiB2 alloys fabricated by the induction skull melting (ISM) process were investigated. Results showed that the TiB2-induced microstructure was characterized by randomly orientated fully lamellar colonies and both the colony size and lamellae spacing were refined (100μm and ~185nm, respectively) by TiB2 addition. The borides were identified to be TiB2 with plate, needle and block morphologies, determined by different growth stages during solidification. At room temperature and 700°C, the TiB2-containing alloys exhibit non-deteriorated fracture toughness and superior tensile properties than that of the as-cast and heat-treated matrix alloys. Furthermore, the fracture toughness anisotropy was eliminated due to the randomly orientated lamellar microstructure induced by TiB2 addition. The fine TiB2 particles with special morphology (plate and needle) and the easy-to-deform ligament bridges induced by the refined microstructure can account for the notable fracture toughness of the studied TiB2-containing alloys. The main toughening mechanism was analyzed and discussed in light of the microstructure characterization, size and morphology of borides and the deformed ligament bridges.

Effects of M2CO3 (M = Li, Na, K) on electrolytic boronising of titanium in Na2B4O7 melts

The effect of M2CO3 (M = Li, Na, K) on electrolytic boronising of titanium in Na2B4O7–20M2CO3 was investigated. The phase composition of boride was determined by X-ray diffraction. The morphology of boride was determined by scanning electron microscopy, and the composition of boride was measured by X-ray energy dispersive spectroscopy. The results show that the boride layer comprised TiB2 and TiB. TiB2 presented a dense phase, whereas TiB presented whiskers. TiB2 became thicker in the order of Li2CO3, Na2CO3 and K2CO3, in the melts. Simultaneously, TiB whiskers gradually changed from short and thick to long and thin. This change was due to the different polarisation abilities of alkali metal ions in M2CO3 (M = Li, Na, K).

Microstructure and Mechanical Properties of Austempered High Boron Cast Iron with Modification and its Mechanism Discussion

A kind of austempered boron alloyed high silicon cast alloy was developed though modification with Ti and controlling austempering temperature, the impact toughness of which increases to 20.7 J/cm2, which is more than triple that of the previous work. The alloy with modification exhibits obvious grain refining both in matrix and boride, improved the morphology of boride into discontinuous network and small particles. The phenomenon and mechanism are discussed in the article, it proved TiC is possible to act as the nuclei of eutectic boride and Ti can be an effective modifier.

Titanium Boride in High Nb Containing TiAl Alloy: Morphology and Effect on Mechanical Properties

The morphology of titanium boride in as-cast and as-forged Ti-45Al-8.5Nb-(W, B, Y) alloy containing 0.2at. % boron and the effect of borides on tensile and creep properties of the alloy are investigated. The results show that in as-cast alloy the morphology of boride appears mainly convoluted ribbons with some flakes and particles. With the extent of forging increases, the length of the ribbons decreases and their distribution is more uniform. The long ribbon in as-cast alloy is detrimental to tensile properties at both room temperature (RT) and high temperatures. The short ribbon in as-forged alloy is not harmful to RT tensile properties, but is harmful to tensile and creep properties at high temperatures. The harmful effect of the boride is due to the strain incompatibility of boride and matrix, which causes many cavities at boride/matrix boundaries and results in ultimate fracture.