Vanadium Diboride (VB2) Synthesized at High Pressure: Elastic, Mechanical, Electronic, and Magnetic Properties and Thermal Stability (original) (raw)
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Compressibility of AlB 2 -type transition metal diborides
Journal of Physics: Condensed Matter, 2002
The pressure behaviour of a series of transition metal borides has been studied both experimentally and by means of ab initio calculations. X-ray diffraction patterns measured up to ∼50 GPa for VB 2 and ZrB 2 show no obvious phase transition. Bulk moduli of 322 and 317 GPa, respectively, were obtained using a Murnaghan equation of state. Hartree-Fock LCCO (linear combination of crystal orbitals) calculations performed for TiB 2 have allowed its compression behaviour to be studied. The bulk modulus obtained (292 GPa) and the proposed important contribution of the interlayer interaction to the elastic behaviour under high pressure are consistent with the experimental results for the other borides.
Elastic and Acoustic Properties of XB 2 (X= V, Nb & Ta) Transition Metal Diborides
The elastic properties, acoustic properties and mechanical properties of the group VB transition metal diborides like VB 2 , NbB 2 and TaB 2 have been studied along unique axis at room temperature. The second-and third order elastic constants (SOEC & TOEC) have been calculated for these diborides using Lennard–Jones potential model. The velocities V L and V S2 increases with the angle from the unique axis and V S1 have maximum at 45° with unique axis of the crystal. The inconsistent behaviour of angle dependent velocities is associated to the action of second order elastic constants. Debye average sound velocities of these compounds are increasing with the angle and has maximum at 55° with unique axis at room temperature. Hence when a sound wave travels at 55° with unique axis of these materials, then the average sound velocity is found to be maximum. The mechanical properties o f V B 2 are better than T a B 2, because VB 2 has low ultrasonic attenuation comparison than T a B 2. The diborides are good electrical conductors; they are attractive for the same types of applications as other hard refractory materials such as in composite and in hard coating. Traditional applications o such materials are based on their interesting combination of mechanical and transport properties.
Physicomechanical properties of diborides of metals of groups IVa, Va, sintered under high pressure
Soviet Powder Metallurgy and Metal Ceramics, 1987
The properties of borides of high melting metals sintered under high pressure have so far not been studied. As regards their carbides, it is known that sintering under high pressure leads to increased microhardness and a change of the microstructure [i]. As a rule, the borides of high melting metals are harder and less brittle than carbides [2], and they are therefore promising material to be used in cutting tools. For evaluating the brittleness of borides of the transition metals of groups IVa, Va, various criteria and methods were used [2-6], in consequence of which the obtained data (Table i) are sometimes mutually contradictory. In the present work we investigated the sinterability of diborides of transition metals of groups IVa, Va under high pressure, and also some physicomechanical properties of the obtained specimens: microhardness, microbrittleness, and brittle microstrength.
Elastic Behaviour of Diborides Under High Pressure
Journal of Scientific Research, 2009
The present study deals with the elastic behaviour of diborides (BeB2, MgB2 and NbB2) under high pressure with the help of equation of state (EOS) using the elastic data reported by Islam et al. It is concluded that EOS, which are based either on quantum statistical model or pseduopotential model, only are capable of explaining high pressure behaviour of the solids under study.  Moreover the value of first order pressure derivative of bulk modulus at infinite pressure (Kinfinity) is greater than 5/3 and thus the diborides under study do not behave as Thomas-Fermi electron gas under high compression. Keywords: Equation of state; High Pressure; Diborides. © 2009 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v1i2.1189Â
Fabrication and Characterization of Quinary High Entropy-Ultra-High Temperature Diborides
Ceramics
Due to their inherent chemical complexity and their refractory nature, the obtainment of highly dense and single-phase high entropy (HE) diborides represents a very hard target to achieve. In this framework, homogeneous (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, and (Hf0.2Zr0.2Nb0.2Mo0.2Ti0.2)B2 ceramics with high relative densities (97.4, 96.5, and 98.2%, respectively) were successfully produced by spark plasma sintering (SPS) using powders prepared by self-propagating high-temperature synthesis (SHS). Although the latter technique did not lead to the complete conversion of initial precursors into the prescribed HE phases, such a goal was fully reached after SPS (1950 °C/20 min/20 MPa). The three HE products showed similar and, in some cases, even better mechanical properties compared to ceramics with the same nominal composition attained using alternative processing methods. Superior Vickers hardness and elastic modulus values were found for the (Hf0.2Nb0.2Ta0.2...
The pack-boronizing of pure vanadium under a controlled atmosphere
Applied Surface Science, 2010
Pack boronizing of pure vanadium was performed at 1100 • C for 4, 8, 12 and 16 h under a controlled atmosphere. Characterization of the boride formed on the surface of pure vanadium was carried out by metallographic techniques, profilometry, SEM-EDS, XRD and microhardness measurements. The metallographic studies revealed that a single boride layer with dense, compact and relatively smooth morphology was formed on the surface of pure vanadium. The interface between boride layer and base metal was wavy in nature. The formation of only the VB 2 phase on pure vanadium was confirmed by surface and crosssectional XRD analysis. The microhardness of the boride layer was approximately 3700 HV for all boriding times. Fracture toughness of the boride layer was evaluated using Vickers indentation, giving the value of 2.1-5.9 and 1.7-3.4 MPa m 1/2 for Palmqvist and median/radial approaches, respectively. Thickness of the boride layer increased almost parabolically from about 23 to 50 m with boriding time. Surface roughness of the coating was relatively increased from approximately 0.58 to 2.25 m by boriding duration.
High‐pressure sintering of ultrafine‐grained high‐entropy diboride ceramics
Journal of the American Ceramic Society, 2020
Herein the ultrafine grained (Hf 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2)B 2 high-entropy diboride ceramics was successfully fabricated by high pressure sintering technology for the first time. The results showed that the grain size, relative density, and Vickers hardness of the as-fabricated samples all increased gradually with increasing sintering temperatures from 1373 K to 1973 K. The relative density and mean grain size of the as-sintered samples at 1973 K were 97.2% and 684 nm, respectively, and simultaneously they exhibited excellent comprehensive mechanical properties, combining a Vickers hardness of 26.2 GPa and a fracture toughness of 5.3 MPa•m 1/2 , which were primary attributed to the fine grain strengthening mechanism and microcrack deflection toughening mechanism.
2001
The electronic structure and ground state properties of AlB 2 type transition metal diborides TMB 2 ͑TMϭSc, Ti, V, Cr, Mn, Fe, Y, Zr, Nb, Mo, Hf, Ta͒ have been calculated using the self consistent tight-binding linear muffin-tin orbital method. The equilibrium volume, bulk moduli (B 0), pressure derivative of bulk moduli (B 0 Ј), cohesive energy (E coh), heat of formation (⌬H), and electronic specific heat coefficient (␥) are calculated for these systems and compared with the available experimental and other theoretical results. The bonding nature of these diborides is analyzed via the density of states ͑DOS͒ histogram as well as the charge density plots, and the chemical stability is analyzed using the band filling principle. The variation in the calculated cohesive properties of these materials is correlated with the band filling effect. The existence of a pseudogap in the total density of states is found to be a common feature for all these compounds. The reason for the creation of the pseudogap is found to be due to the strong covalent interaction between boron p states. We have made spin polarized calculations for CrB 2 , MnB 2 , and FeB 2 and found that finite magnetic moments exist for MnB 2 and CrB 2 whereas FeB 2 is nonmagnetic.
Review of transition-metal diboride thin films
Vacuum, 2021
We review the thin film growth, chemistry, and physical properties of Group 4-6 transition-metal diboride (TMB 2) thin films with AlB 2-type crystal structure (Strukturbericht designation C32). Industrial applications are growing rapidly as TMB 2 begin competing with conventional refractory ceramics like carbides and nitrides, including pseudo-binaries such as Ti 1-x Al x N. The TMB 2 crystal structure comprises graphite-like honeycombed atomic sheets of B interleaved by hexagonal close-packed TM layers. From the C32 crystal structure stems unique properties including high melting point, hardness, and corrosion resistance, yet limited oxidation resistance, combined with high electrical conductivity. We correlate the underlying chemical bonding, orbital overlap, and electronic structure to the mechanical properties, resistivity, and high-temperature properties unique to this class of materials. The review highlights the importance of avoiding contamination elements (like oxygen) and boron segregation on both the target and substrate sides during sputter deposition, for better-defined properties, regardless of the boride system investigated. This is a consequence of the strong tendency for B to segregate to TMB 2 grain boundaries for boron-rich compositions of the growth flux. It is judged that sputter deposition of TMB 2 films is at a tipping point towards a multitude of applications for TMB 2 not solely as bulk materials, but also as protective coatings and electrically conducting high-temperature stable thin films.
Journal of Physics: Condensed Matter, 2007
The elastic properties of selected transition-metal ͑TM͒ nitrides and carbides in B 1 structure are studied using the ab initio density-functional perturbation theory. We find that ͑1͒ the inequality B Ͼ GЈ Ͼ G Ͼ 0 holds for all these materials, where B = ͑C 11 +2C 12 ͒ /3, GЈ = ͑C 11 − C 12 ͒ / 2, and G = C 44 with C ij the elastic constants, and ͑2͒ G has large values when the number of electrons per unit cell Z V = 8 or 9. The fitted curve of G vs. Z V predicts that rocksalt MoN is unstable, and TM carbonitrides ͑e.g., ZrC x N 1−x ͒ and di-TM carbides ͑e.g., Hf x Ta 1−x C͒ have maximum G at Z V Ϸ 8.3.