B2 Solid Solution Research Articles

Compositionally complex AlB2-type diborides in dissociated air plasma

Multi-metal compositionally complex (CC) AlB2-type diboride solid solutions (SS) containing IV-V-VI group elements are garnering a steadily growing research interest. The present work explores the composition dependence of oxidation resistance on nominally equiatomic (Hf,Me,Ta,Ti,Zr)B2 SS, Me = Nb or Cr, exposed to a dissociated air plasma (total pressure of about 1 kPa): specimens were exposed for 5 min at some selected set points between 1800 K and 2500 K using a solar furnace. The CC diboride with Nb showed superior resistance to oxidation compared to that with Cr. The experimental results showed good agreement with predictions based on a thermodynamic assessment.

EFFECT OF TiC ADDITION ON MICROSTRUCTURE AND PROPERTIES OF LASER CLADDING AlCoCrFeNi2.1 COATINGS ON H13 STEEL

[Formula: see text][Formula: see text][Formula: see text][Formula: see text]xwt.%TiC ([Formula: see text], 6, 9) coatings were prepared on H13 steel by laser cladding (LC) technology. It was characterized by a friction and wear test machine, optical microscope (OM), X-ray diffractometer (XRD), hardness tester, etc. The effects of different TiC contents on the microstructure and properties of [Formula: see text] coatings were analyzed. The results show that the coating microstructure without TiC addition is dominated by coarse columnar crystals and dendrites. After the addition of TiC, the coated massive crystals and equiaxed crystals become finer. XRD analysis reveals that the phase structure of the coating has FCC, B2 solid solution phase and TiC-reinforced phase. TiC phase can significantly improve the hardness of the coating. The microstructure reveals that fine TiC particles are widely distributed among the dendrites of the FCC matrix. The hardness and friction wear experiments revealed that the average hardness of the coatings with TiC has increased significantly compared to that of the substrate. The hardness of the [Formula: see text] with 9%TiC coating increased by 184.6% compared to that of the substrate. The friction coefficient was the smallest at 0.748. The lowest self-corrosion current was [Formula: see text][Formula: see text][Formula: see text]. The [Formula: see text] with 9%TiC coating had the best corrosion resistance.

Phase evolution, mechanical properties, and corrosion resistance of Ti2NbVAl0.3Zrx lightweight refractory high-entropy alloys

Herein, a series of Ti2NbVAl0.3Zrx (x = 0.25, 0.5, 0.75, 1) light refractory high entropy alloys were designed and prepared based on the concept of B2 ordering and solid solution strengthening. The Zr0.25, Zr0.5, and Zr0.75 alloys exhibited a disordered BCC + ordered B2 duplex structure, while the Zr1 alloy displayed a BCC single-phase structure. The addition of Zr hinders the formation of B2 ordering, transforming the alloy from a BCC + B2 duplex structure to a BCC single-phase structure. The Zr0.75 alloy has a yield strength of 1022 MPa and a tensile strain of ∼9.4 %. Furthermore, electrochemical tests were conducted in 3.5 wt% NaCl solution revealed that the Ti2NbVAl0.3Zrx LRHEAs showed high resistance to pitting corrosion. Incorporating the Zr element enhanced the polarization resistance and reduced the corrosion rate; however, excessive Zr content led to a shift in micro-galvanic corrosion from the nanoscale to the microscale, resulting in pitting corrosion. The passivation film compositions of the four alloys formed at a potential of 0.7 VSCE were analyzed by X-ray photoelectron spectroscopy, and their corrosion resistance in a chlorine-containing environment was examined in depth.

Effect of CaB6 addition on the microstructure and mechanical properties of Ti–24Nb–4Zr-2.5Mn alloys fabricated by spark plasma sintering

Balancing the strength, ductility and Elastic modulus of β-Ti alloys is still a great challenge for medical implantation, extremely limiting its further applications. Herein, we prepared a fine-grain β-type Ti–24Nb–4Zr-2.5Mn alloy with high performance by adding CaB6 deoxidizer via mechanical alloying and spark plasma sintering. The effects of CaB6 addition on the microstructure and mechanical properties were systematically investigated, and the results show that adding a trace amount of CaB6 will form in-situ nano-sized CaTiO3 particles and micro-sized (Ti,Nb)B2 solid solution whiskers, which can significantly refine the grain size and inhibit the grain boundary movement and dislocation motion, thus improving the comprehensive mechanical properties of Ti–24Nb–4Zr-2.5Mn alloys. With a trace addition of 0.1 wt% CaB6, the Ti–24Nb–4Zr-2.5Mn alloy exhibits an excellent combination of high strength of ∼971 MPa, good ductility of ∼17.8% and low elastic modulus of ∼79.1 GPa. This work may provide a new methodology to prepare high-performance biomedical Ti alloys.

Processing and optical behavior of dense (Hf,Zr)B2 solid solutions for solar energy receivers

While individual borides and, more recently, quinary High Entropy Transition Metal Borides have been investigated, the fabrication and characterization of bulk binary to quaternary solid solutions are barely explored. In this work, dense (Hf0.5Zr0.5)B2 is produced by Spark Plasma Sintering (SPS) from powders prepared by Self-propagating High-temperature (SHS). SHS produced a multiphase product, whose secondary phases are fully converted into the desired diborides during the subsequent SPS step. Optical properties of (Hf0.5Zr0.5)B2 are evaluated for the first time with focus on the possible use as novel high-temperature solar thermal absorber, by hemispherical reflectance measurements and calculation of solar absorptance, temperature-dependent spectral selectivity and absorber opto-thermal efficiency at various solar concentration ratios. To optimize the material, a chemically etched surface texture was realized to modify the optical properties. The etched sample showed a higher solar absorptance (0.71) and a lower spectral selectivity than the unetched one, with consequent higher opto-thermal efficiency at all temperatures for solar concentration ratios 1000 ÷ 3000, while at lower concentration ratios and temperatures >1400 ÷ 1600 K, the unetched sample shows the highest efficiency. These results show the promising properties of binary diborides for solar thermal applications.

Synthesis, sintering, mechanical properties, and oxidation behavior of (Zr0.5Me0.5)B2 (Me = Ta, Hf) solid solutions

In this work, (Zr0.5Ta0.5) B2 and (Zr0.5Hf0.5) B2 solid solutions are produced in dense form by coupling the Self-propagating High-temperature (SHS) and Spark Plasma Sintering (SPS) routes. A single boride phase solid solution is formed in both cases by SPS (1850 °C, 20 min) from the multiphasic ceramic powders preliminarily obtained by SHS. The use of small amounts of graphite during SPS is highly beneficial to eliminate oxide contaminants (from 14.5–16.0 wt% to 2.1–2.8 wt%), improve powder consolidation (from 87-90 % to 97.5–98 %), and make the operating conditions milder. Better mechanical properties are exhibited by the binary ceramics with respect to ZrB2 produced by SHS-SPS. The presence of Ta makes the performance of (Zr0.5Ta0.5)B2 superior compared to the Hf-containing system, with hardness, Young's modulus, and fracture toughness equal to 22.1 GPa, 636.9 GPa, and 2.46 MPa m1/2, respectively. On the other hand, (Zr0.5Hf0.5) B2 shows higher oxidation resistance in flowing and stagnant air at elevated temperatures.

Electrical discharge machinable B4C–(Zr, Ti)B2 composites with enhanced mechanical properties

B4C30 vol% (ZrxTi1-x)B2 (x = 0.2, 0.4, 0.6 and 0.8) composites were fabricated via in-situ reaction by spark plasma sintering using B4C, ZrC, TiC and B powders as raw materials at 2000 °C. The effects of the Zr/Ti ratio in the (ZrxTi1-x)B2 phase on the microstructure and mechanical properties of the composites were investigated. The electrical discharge machining performance of the composites was evaluated. The formation of (Zr, Ti)B2 solid solutions was beneficial to fully dense composites with refined grains. The grain size of the (Zr, Ti)B2 phase first gradually decreased from 1.26 µm to 0.89 µm and then increased to 1.23 µm with the decreasing ZrC/TiC molar ratio. The material removal rate was slightly decreased from 6.56 mm3/min to 5.17 mm3/min with the decreasing ZrC/TiC molar ratio. The combined solid-solution and fine-grain strengthening has made the B4C30 vol% (Zr0.2Ti0.8)B2 composite enhanced Vickers hardness, flexural strength, and fracture toughness of 28.31 GPa, 772 MPa, and 6.56 MPa·m1/2, respectively, with a relative density of 99.73%.

Controllable growth of (Hf, Zr)B2 solid solution coating via CVD for ultra-high temperature ablation of C/C composites

In this paper, we have successfully addressed the challenges of cracking and spalling in HfB2 coatings during ablation through the novel synthesis of (Hf, Zr)B2 solid solution coatings using the chemical vapor deposition (CVD) method. The ablation resistance of the coating exhibited an initially improving trend followed by a subsequently deterioration as the Zr content increased. When the Hf/Zr molar ratio in the (Hf, Zr)B2 solid solution coating was 1:1, a thicker Hf-Zr-O amorphous oxide layer was formed during ablation, which acted as a barrier, preventing the inward diffusion of oxygen. As a result, the (Hf0.5Zr0.5)B2 solid solution coating exhibited superior ablation resistance with a mass ablation rate of only −0.216 mg/s and a linear rate of −0.089 µm/s. These findings underscore the enormous potential of boride solid solution UHTC as exceptional candidates for ultra-high temperature ablation resistant applications.

Effect of structure and phase composition on the physical and mechanical properties of hot extruded titanium alloy Ti–3Al–2.5V tubes

This study investigates the impact the hot extrusion process variables on the physical and mechanical properties of Ti–3Al–V alloy The research examines four tube segments extracted from various hot-extruded tubes of Ti–3Al–2.5V alloy, with an outer diameter (OD) of 90 mm and a wall thickness of 20 mm. The manufacturing process involves expanding sleeves with a horizontal hydraulic press to achieve an OD of 195 mm, followed by heating to 850–865 °C prior to extrusion. The tube segments are labeled as 1, 2, 3, and 4, corresponding to their order of production. Our findings demonstrate that an increase in the number of extrusions in the α + β area from tube 1 to tube 4 leads to a reduction in the primary α-phase volume fraction and an increase in the β-transformed structure volume fraction. These changes are attributed to the higher final extrusion temperature resulting from more intense deformation heating during hot tooling (die and mandrel) processes. Additionally, elevating the final extrusion temperature from tube 1 to tube 4 leads to a notable decrease in the residual β-solid solution volume fraction and a reduction in the “sharpness” of the α-phase tangent-oriented texture. The alterations in the structural and phase state of the alloy from tube 1 to tube 4 are found to influence the contact modulus of elasticity and microhardness. These identified relationships can be utilized to optimize the process variables for the extrusion of multiple Ti–3Al–2.5V alloy tubes.

Microstructure and mechanical properties of SiC composite ceramics modified by (TixZr1–x)B2 solid solution

Dense SiC-(TixZr1–x)B2 composite ceramics were prepared via solid-state spark plasma sintering (SPS) by controlling the proportion of ZrB2 (in the range of 5–25 vol%). Through data fitting, a linear functional relationship was established between x and 2θ for the (TixZr1–x)B2 solid solution, which rendered it amenable to characterization analysis. The results show that the 2-D morphology of (TixZr1–x)B2 tended to transform from angular to round as the ZrB2 proportion was increased, which was beneficial in crack deflection and increasing the fracture toughness. Moreover, the growth of SiC grains around the solid solution was inhibited, which improved its mechanical properties. The composite ceramic containing 15 vol% of ZrB2 had the best mechanical properties, with its Vickers hardness, bending strength and fracture toughness reaching 26.12 GPa, 499 MPa, and 6.45 MPa•m1/2, respectively.

High-temperature oxidation resistance of ternary and quaternary Cr-(Mo)-Si-B2-z coatings — Influence of Mo addition

The Si-based alloying of transition metal diborides is a promising strategy to improve their limited oxidation resistance in high-temperature environments. In this study, we investigate the oxidation resistance of ternary and quaternary Cr-(Mo)-Si-B2-z coatings sputter-deposited from alloyed CrB2/TMSi2 targets (TM = Cr or Mo). The as-deposited Cr-(Mo)-Si-B2-z coatings are stabilized in the single-phased hexagonal AlB2-structure, except the high-Si containing Cr0.26Mo0.11Si0.24B0.39 presenting amorphous character. The Mo-containing Cr-Mo-Si-B2-z films exhibit relatively high hardness compared to their ternary Cr-Si-B2-z counterparts, obtaining up to 26 GPa due to the formation of (Cr,Mo)B2 solid solutions. The Si-alloying in ternary and quaternary coatings provides oxidation resistance up to 1200 °C, owing to the formation of highly protective double-layered scales consisting of SiO2 with a Cr2O3 layer on top, inhibiting oxygen inward diffusion. The quaternary Cr0.31Mo0.07Si0.15B0.47 coating is distinguished by superior oxidation resistance with lower porosity and void formation compared to the ternary Cr0.37Si0.16B0.47. Mo proved to be the key element for the higher stability and enhanced oxidation resistance due to the evolution of the MoSi2 phase at ~600 °C. This phase formation controls the Si diffusion and mobility within the microstructure, thus reducing the porosity and governing the Si supply to form SiO2 scale. The quaternary Cr0.31Mo0.07Si0.15B0.47 coating maintained an oxidation resistance up to 30 h at 1200 °C by forming a 2.5 μm dense amorphous Si-based oxide scale with a thin Cr2O3 on top.

Effect of transition metal on the structure and oxidation behavior of ZrB2 (0 0 0 1): Experimental and theoretical calculations

ZrB2 can withstand extreme environments, but the high-temperature oxidation prevented them from being applied as possible thermal protection system materials. The effect of transition metal (Tm = Ta, Hf, Mo, and W) on oxidation resistance of ZrB2 was systematically investigated by the first principles calculations, including ab initio molecular dynamics, and experimental tests. The results showed that the doped atoms, especially Hf atom, increased the adsorption energy of O atoms, which prohibited the O adsorb on the surface of ZrB2. Besides, the energy barrier of O atom migration on the Hf-doped surface and inward migration is 0.60 eV and 6.68 eV, which is higher than the un-doped surface. This showed that Hf performs well in inhibiting the diffusion of O. The reason was that the doped atoms increased the strength of B-Zr and O-Zr bonds, respectively. Finally, to verify the theoretical calculations, ZrB2 and (Zr, Tm) B2 solid solutions were prepared by using pressure-less sintering and the thermal gravimetric tests were carried out. The experimental results showed that the (Zr, Tm) B2 solid solutions have better oxidation resistance than ZrB2, which is consistent with the results from our theoretical calculations. In this work, the modification mechanism of doping atoms on the oxidation resistance of ZrB2 was explained from the point of view of adsorption and diffusion. And it provides guidance for promoting the application of ZrB2 at high temperature.

Study on microstructure, mechanical properties and thermal performance of single-phase (Ti,Zr,Hf)B2 solid solution

Study on microstructure, mechanical properties and thermal performance of single-phase (Ti,Zr,Hf)B2 solid solution

Effect of HfSi2‐induced intergranular liquid phase on densification behavior of ZrB2

AbstractThe densification behavior and mechanical properties of ZrB2‐based composites were investigated. The results demonstrated that the fully dense ZrB2‐based composites could be obtained at lower sintering temperature (1600°C) and pressure (30 MPa) when the content of HfSi2 was above 20 vol.%. The as‐sintered composite was a special core–shell structure, with ZrB2 as the core and (Zr, Hf)B2 solid solution as the shell. The core–shell structure resulted from the diffusion of Hf atom into the boride matrix, which could accelerate the densification. In addition, the intergranular liquid phase induced by the HfSi2 addition filled the micropores of the composites effectively during the sintering. When the content of HfSi2 increased to 20 vol.%, its compressive strength, hardness, and fracture toughness all reached the maximum values, which were 1617 MPa, 15.99 GPa, and 2.44 MPa m1/2, respectively.

Получение, структура и свойства твердых растворов диборидов (Hf1 – хTaх)B2

Porous sinters of solid solutions were obtained from the elements by the SHS method and then crushed in a ball mill to a fraction of d50 < 10 µm. Single-phase (Hf1 – хTах)B2 solid solutions with a wide range of compositions were obtained by a hot pressing. Detailed investigations of structure and properties were carried out. The plotted lattice parameters vs. solid solution stoichiometry diagrams confirmed the Vegard’s law. SEM, TEM, and EDX structural analysis demonstrated the existence of a HfВ2 – TaB2 single-phase solution region. The structure of samples (lamellas) of (Hf0.8Ta0.2)B2 and (Hf0.6Ta0.4)B2 solid solutions was analyzed by TEM. It has been established that with an increase in the content of tantalum, the size of subgrains decreases to 0.2 – 1 µm. This correlates with the CSR size determined by the X-ray diffraction method. Studies of mechanical properties of single-phase solid solutions have shown that (Hf0.8Ta0.2)B2 and (Hf0.6Ta0.4)B2 possessed extremely high hardness of 63–70 GPa and elastic modulus of 550 – 587 GPa. Electrical resistance dependence on temperature was investigated, values of heat capacity, thermal diffusivity and thermal conductivity coefficients were determined in a wide range of (Hf 1 – xTax)B2 solid solution compositions.

Эволюция состава и морфологии порошка сплава Ti – 18 Zr – 15 Nb в процессе гидридно-кальциевого синтеза

Medical β-alloys of the Ti – Zr – Nb system are promising materials for creating bone implants that do not contain metals toxic to the human body. Powder metallurgy makes it possible to create porous structures based on this class of materials, thereby improving the osseointegration of bone tissues. However, the shape and size of the pores in an implant depend on the size and morphology of the initial powder. In light of this, the effect of the temperature and duration of calcium-hydride synthesis on the phase composition and morphology of the Ti – 18 Zr – 15 Nb (at. %) powder is studied in the current research. It has been established that with an increase in the duration and temperature of synthesis, the average size of powder particles increases, and the powder morphology and particle size distribution law change due to the formation of agglomerates. It has also been shown that during the formation of the β-solid solution, the synthesis process occurs in three stages. The first stage is governed by reduction reactions on the contact surface “oxide – liquid calcium”. The third stage is controlled by solid solution heterodiffusion. At the second stage, the synthesis process combines both mechanisms.

Microstructure evolution and compressive property variation of AlxCoCrFeNi high entropy alloys produced by directional solidification

The AlxCoCrFeNi (molar radio, x = 0.3, 0.6, 0.9 and 1.2) high entropy alloys (HEAs) were directionally solidified at the withdrawal rate of 150 μm/s. The effects of Al content on microstructure evolution, element segregation as well as compressive property were investigated. It was found that the increase of Al content resulted in the formation of BCC crystal structure. Meanwhile, the microstructure of AlxCoCrFeNi HEAs transformed from dendrite to equiaxed dendrite. The Al0.3CoCrFeNi HEA formed a single FCC solid solution phase, the Al0.6CoCrFeNi HEA consisted of CoFeCr-enriched FCC solid solution phase + NiAl-enriched BCC solid solution phase, the Al0.9CoCrFeNi and Al1.2CoCrFeNi HEAs were composed of NiAl-enriched B2 solid solution phase + CoFeCr-enriched BCC solid solution phase. Morphology of solid-liquid interface was coarse dendrite or typical dendrite. As the Al content increased, the compressive strain of directionally solidified AlxCoCrFeNi HEAs decreased from 21.26% to 18.05%, and the ultimate compressive strength increased first and then decreased. The improvement of strength results from crystal structure transition and solution strengthening. As the Al contents increased from 0.6 to 0.9, the crystal structure of AlxCoCrFeNi HEAs transformed from CoFeCr-enriched FCC structure + NiAl-enriched BCC structure to CoFeCr-enriched BCCstructure + NiAl-enriched B2 structure. The strain of Al0.3CoCrFeNi HEA was higher than others, and Al0.9CoCrFeNi HEA exhibited the maximum ultimate compressive strength of 2114.57 MPa.

Comparative first-principles study of the (TiZrHfNbTa)B2 high entropy solid solution and its constituent binary diborides

The stability, electronic and phonon structures, optical, mechanical and thermodynamic properties of the random high entropy (TiZrHfNbTa)B2 solid solution (alloy) were studied in comparison with those of TiB2, ZrB2, HfB2, NbB2 and TaB2 using first-principles calculations. The mixing enthalpy of −0.842 kJ/mol of atoms for the high entropy diboride points to that it is stable against decomposition into the constituting binary diborides. All the diborides studied are thermodynamically, mechanically and dynamically stable. The dielectric function, reflectivity and extinction coefficient of the diboride compounds were comprehensively studied. Both (TiZrHfNbTa)B2 and binary diborides are found to be good reflective materials in infrared, visible and ultraviolet regions. The calculated elastic moduli, B/G ratio, Vickers hardness, fracture toughness and Debye temperature of (TiZrHfNbTa)B2 are medium between largest and lowest ones of the constituents, approximately obey the rule of mixture. Calculations of the stress-shear strain relations for (TiZrHfNbTa)B2 point to the possibility of the activation of both basal and prismatic slip systems. The elastic moduli and linear compressibility exhibit the spatial anisotropy inherent to hexagonal structures. The thermodynamic characteristics of the diborides studied are well reproduced in a temperature range up to 800–1000 K.

Study on the toughening mechanism of in-situ synthesis (TixZr1−x)B2 in solid-state sintered SiC composite ceramics

High-dense SiC-(TixZr1−x)B2 composite ceramics were fabricated by in-situ synthesis of (TixZr1−x)B2 solid solution using solid-state spark plasma sintering (SPS). 64 vol% SiC, 20 vol% ZrB2, 15 vol% TiB2, and 1 vol% graphite powders are chosen as raw materials. The composite ceramics has the relative density of 99.97 %, the Vickers hardness of 24.71 GPa, the flexure strength of 435 MPa and the fracture toughness of 8.05 MPa • m1/2. Compared with the single-phase SiC ceramics and SiC-TiB2 composite ceramics, the fracture toughness of SiC-(TixZr1−x)B2 composite ceramics increased by 242.6 % and 53.6 %, respectively. A shell-core structure is found in the SiC-(TixZr1−x)B2 composite ceramics, in which (TixZr1−x)B2 solid solution is the core and fine SiC grain is the shell. The results show that the toughening effect of solid-state sintered SiC-(TixZr1−x)B2 composite ceramics is attributed to the shell-core structure.

Production and characterization of spark plasma sintered (Ti,Nb)B2 solid solutions with graphene nanoplatelets and hexagonal boron nitride

For this study, (Ti,Nb)B2 solid solutions were consolidated by spark plasma sintering. In addition, (Ti,Nb)B2 with graphene nanoplatelets (GNPs) and hexagonal boron nitride (h-BN) were produced to evaluate the potential of the new structural materials. The phase formation, microstructure, mechanical properties, oxidation resistance and room temperature reflectance, and absorbance features of (Ti,Nb)B2 were investigated. X-ray diffraction and Transmission electron microscopy observations showed that a complete solid solution phase was formed when the samples were sintered at 1850 °C for 5 min under 50 MPa. Ti0.75Nb0.25B2 exhibited a relative density of ∼98.6%, a hardness of ∼20.5 GPa, and an indentation fracture toughness of ∼3.4 MPa·m1/2. It was found that the presence of 1 vol% h-BN as an additive enhanced the hardness (∼10%) and fracture toughness (∼30%) of Ti0.75Nb0.25B2 by activating toughening mechanisms. The GNP added Ti0.75Nb0.25B2 proved to have better oxidation resistance and optical absorbance than the other materials used in the study.