Complex Boride Research Articles

Cast NiAl/Ni20Al3B6 composites by centrifugal SHS

Cast NiAl/Ni20Al3B6 composites containing 2.3–3.5 wt % B have been prepared by centrifugal SHS for the first time. The composite materials comprised of a solid-solution matrix based on NiAl with inclusions of Ni20Al3B6 and complex boride (Mo, Cr)B. Best results were achieved at centrifugal accelerations 150–200 g in open air. Cast materials based on NiAl and τ-borides seem promising for use in turbine power units.

Complex boride metal-matrix composites by SHS under high gravity

Mo2NiB2 and Mo2FeB2 metal-matrix composites (MMCs) were prepared by metallothermic SHS in a centrifugal machine. Our SEM and XRD data suggest that thus synthesized cast materials represent a ductile Ni or Co matrix doped with uniformly distributed inclusions of Mo2NiB2 or W2CoB2 particles. The metal matrix was found to contain grid-type structural elements formed by nickel aluminides. Addition of alloying agents into a green mixture was found to markedly change the microstructure and morphology of resultant MMCs. The Vickers hardness of synthesized MMCs was found to vary between 950 and 1200 HV.

Site preference and magnetic orderings in the intermetallic boride series M1.5Rh5.5B3 (M = Cr, Mn, Fe, Co, Ni) from first principles DFT calculations

The structural parameters, chemical bonding and magnetic properties of the ternary boride series M1.5Rh5.5B3 (M=Cr, Mn, Fe, Co, Ni) were investigated by first principles DFT calculations. The calculated crystallographic lattice parameters corroborate well with the experimental results of the reported Fe1.3Rh5.7B3 single crystal. In the most stable structural model used, Fe-dumbbells as well as isolated Fe-atoms exist. From spin polarised calculations, ferromagnetism is found for the members with M=Fe, Co, while ferrimagnetism is more stable for Mn1.5Rh5.5B3 and Pauli paramagnetism is more stable for M=Cr, Ni. The total magnetic moment per formula unit for the M=Mn, Fe and Co phases is calculated to be 3.32, 5.00 and 3.26 μB, respectively. According to COHP chemical bonding analysis, Rh−B contacts are mainly responsible for the structural stability, while Rh−M interactions influence the magnetic behavior of these complex borides.

Microstructure and mechanical properties of Fe–Al–Ti–B alloys with additions of Mo and W

Four quinary Fe–Al–Mo–Ti–B and Fe–Al–W–Ti–B alloys based on Fe3Al produced by vacuum induction melting were investigated regarding their microstructure and mechanical properties. The microstructures consist of a Fe3Al matrix with complex borides along grain boundaries. Compared to other Fe3Al-based alloys the present alloys show favourably low ductile-to-brittle transition temperatures (BDTT) and a markedly high creep strength at 650°C. The latter is most pronounced for an alloy whose strength, besides strengthening by solid solution hardening through Mo and by the boride precipitates, is further enhanced by stabilising the D03-ordered structure up to higher temperatures.

Drastic Change of Magnetic Interactions and Hysteresis through Site-Preferential Ru/Ir Substitution in Sc2FeRu5–xIrxB2

The quinary members of the complex boride series Sc2FeRu5–xIrxB2 were synthesized by arc melting the elements and characterized by powder and single-crystal X-ray diffraction as well as metallographic and energy-dispersive X-ray analyses. The use of a 4d/5d mixture allows distinguishing these elements with X-ray diffraction methods, thus enabling the study of site preference and its influence on the magnetic properties.The magnetic measurements reveal several changes of magnetic ordering within the series: from antiferromagnetism (Sc2FeRu5B2) to ferromagnetism (Sc2FeRuIr4B2) and finally to metamagnetism (Sc2FeIr5B2). Within the quinary series, the magnetic moments continuously increase with increasing amounts of Ir in one (8j) of two possible Wyckoff sites. The members with x = 2 and 3 represent the first hard magnetic borides of transition metals.

Complex borides based on AlLiB14 as high-temperature thermoelectric compounds

AlLiB14 is examined as a potential high-temperature thermoelectric material. First-principles methods are used to investigate the thermoelectric behavior and it is found to have a band gap of 2.13 eV, and an electronic dispersion with characteristic indicative of having a high Seebeck coefficient. Semiclassical Boltzmann transport theory predicts that AlLiB14 will have a Seebeck coefficient greater than 200 μV K(-1), at temperatures near 1000 K and carrier concentrations around 1 × 10(20) cm(-3). Using a elasticity based expression for the thermal conductivity, the thermoelectric figure of merit is approximated to be 0.45 × 10(-3) T at moderate doping levels.

高耐食マトリックスを有するNi - Cr - Mo - B 系ガスアトマイズ粉末の複硼化物生成挙動 に及ぼすB 量および熱処理の影響

高耐食マトリックスを有するNi - Cr - Mo - B 系ガスアトマイズ粉末の複硼化物生成挙動 に及ぼすB 量および熱処理の影響

Synthesis, crystal structure investigation and magnetism of the complex metal-rich boride series Crx(Rh1−yRuy)7−xB3 (x=0.88–1; y=0–1) with Th7Fe3-type structure

Powder samples and single crystals of the new complex boride series Crx(Rh1−yRuy)7−xB3 (x=0.88–1; y=0–1) have been synthesized by arc-melting the elements under purified argon atmosphere on a water-cooled copper crucible. The products, which have metallic luster, were structurally characterized by single-crystal and powder X-ray diffraction as well as EDX measurements. Within the whole solid solution range the hexagonal Th7Fe3 structure type (space group P63mc, no. 186, Z=2) was identified. Single-crystal structure refinement results indicate the presence of chromium at two sites (6c and 2b) of the available three metal Wyckoff sites, with a pronounced preference for the 6c site. An unexpected Rh/Ru site preference was found in the Ru-rich region only, leading to two different magnetic behaviors in the solid solution: The Rh-rich region shows a temperature-independent (Pauli) paramagnetism whereas an additional temperature-dependent paramagnetic component is found in the Ru-rich region.

The complex metal-rich boride Ti1+xRh2−x+yIr3−yB3 (x=0.68, y=1.06) with a new structure type containing B4 zigzag fragments: Synthesis, crystal chemistry and theoretical calculations

Polycrystalline samples and single crystals of the new complex boride Ti1+xRh2−x+yIr3−yB3 (x=0.68; y=1.06) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere and characterized by X-Ray diffraction as well as EDX measurements. The crystal structure was refined on the basis of single crystal data. The new phase, which represents a new structure type containing trans zigzag B4 fragments as well as isolated boron atoms crystallizes in the orthorhombic space group Pbam (Nr. 55) with the lattice parameters a=8.620(1)Å, b=14.995(2)Å and c=3.234(1)Å. First-principles density functional theory calculations using the Vienna ab-initio simulation package (VASP) were performed on an appropriate structural model (using a supercell approach) and the experimental crystallographic data could be reproduced accurately. Based on this model, the density of states and crystal orbital Hamilton population (for bonding analysis) were calculated, using the linear muffin-tin orbital atomic sphere approximation (LMTO-ASA) method. According to these calculations, this metal-rich compound should be metallic, as expected. Furthermore, very strong boron–boron interactions are observed in the trans zigzag B4 fragment, which induce a clear differentiation of two types of metal–boron contacts with different strength. The observed three-dimensional metal–metal interaction is in good agreement with the predicted metallic behavior.

HIP法で固化成形したNi-Cr-Mo-B系耐食耐摩耗合金の諸特性に及ぼすCr，Mo量の影響

The effects of Cr and Mo contents on the properties of hot isostatic pressed (HIPed) materials with the compositions of Ni-X%Cr-Y%Mo-1.5%B (mass%) ((X,Y)=(10,36),(22,26),(34,16)) were investigated. Raw powders for these P/M materials were produced by gas atomization, followed by sieving less than 500 μm. The consolidation by HIP was carried out at 1423 K for 5 h under 147 MPa. Crystal structures and microstructures of these materials were investigated by X-ray diffraction analysis and scanning electron microscopy, respectively. Mechanical properties of Rockwell hardness and bending strength, corrosion resistance by immersion tests into various acid solutions and wear resistance by Ohgoshi-type abrasion test were also evaluated.Tetragonal M3B2 and M5B3 type complex borides were observed in the consolidated P/M materials. These complex borides with the size of approx. less than 5 μm were finely dispersed in Ni-based matrix. They showed Rockwell hardness from 40 to 50 HRC, which value increased with increasing Mo/Cr ratio, and bending strength comparable to that of P/M material with the composition of Co-1.6%C-30%Cr-8%W (ST-12). In addition, the present Ni-22%Cr-26%Mo-1.5%B P/M material with the most excellent mechanical properties revealed higher corrosion resistance than Ni-16%Cr-16%Mo-3.5%W-6.5%Fe (C-276) alloy and wear resistance comparable to ST-12.

ChemInform Abstract: Scaffolding, Ladders, Chains, and Rare Ferrimagnetism in Intermetallic Borides: Synthesis, Crystal Chemistry and Magnetism.

AbstractThe new complex boride phases Ti8Fe3Ru18B8 and Ti7Fe4Ru18B8 are synthesized by arc‐melting of the elements.

Rational Design of Complex Borides – One‐Electron‐Step Evolution from Soft to Semi‐Hard Itinerant Ferromagnets in the New Boride Series Ti2FeRu5–nRhnB2(1 ≤n≤ 5)

AbstractThe new Ti2FeRu5–nRhnB2series (n= 1–5) was synthesized by arc melting of stoichiometric amounts of the elements. These phases were characterized by X‐ray diffraction methods as well as EDX measurements. All phases in the series are isostructural and crystallize with the Ti3Co5B2type structure (space groupP4/mbm, no. 127). Magnetic susceptibility measurements reveal that all phases order ferromagnetically below Curie temperatures found between 220 and 390 K. Furthermore, a strong dependence of the coercive field as a function of VEC (valence electron count) is observed in the series: An evolution from soft (in the Rh‐richer and VE‐richer region) to semi‐hard (in the Ru‐richer and VE‐poorer region) magnetic materials is found.

Scaffolding, Ladders, Chains, and Rare Ferrimagnetism in Intermetallic Borides: Synthesis, Crystal Chemistry and Magnetism

Single-phase polycrystalline samples and single crystals of the complex boride phases Ti(8)Fe(3)Ru(18)B(8) and Ti(7)Fe(4)Ru(18)B(8) have been synthesized by arc melting the elements. The phases were characterized by powder and single-crystal X-ray diffraction as well as energy-dispersive X-ray analysis. They are new substitutional variants of the Zn(11)Rh(18)B(8) structure type, space group P4/mbm (no. 127). The particularity of their crystal structure lies in the simultaneous presence of dumbbells which form ladders of magnetically active iron atoms along the [001] direction and two additional mixed iron/titanium chains occupying Wyckoff sites 4h and 2b. The ladder substructure is ca. 3.0 Å from the two chains at the 4h, which creates the sequence chain-ladder-chain, establishing a new structural and magnetic motif, the scaffold. The other chain (at 2b) is separated by at least 6.5 Å from this scaffold. According to magnetization measurements, Ti(8)Fe(3)Ru(18)B(8) and Ti(7)Fe(4)Ru(18)B(8) order ferrimagnetically below 210 and 220 K, respectively, with the latter having much higher magnetic moments than the former. However, the magnetic moment observed for Ti(8)Fe(3)Ru(18)B(8) is unexpectedly smaller than the recently reported Ti(9)Fe(2)Ru(18)B(8) ferromagnet. The variation of the magnetic moments observed in these new phases can be adequately understood by assuming a ferrimagnetic ordering involving the three different iron sites. Furthermore, the recorded hysteresis loops indicate a semihard magnetic behavior for the two phases. The highest H(c) value (28.6 kA/m), measured for Ti(7)Fe(4)Ru(18)B(8), lies just at the border of those of hard magnetic materials.

ChemInform Abstract: Complete Titanium Substitution by Boron in a Tetragonal Prism: Exploring the Complex Boride Series Ti3‐xRu5‐yIryB2+x (0 ≤ x ≤ 1 and 1 < y < 3) by Experiment and Theory.

AbstractSingle crystals of Ti3Ru2.9Ir2.1B2, Ti2.63Ru3.4Ir1.6B2.37, Ti2.27Ru2.5Ir2.5B2.73, and Ti2Ru2.8Ir2.2B3 are prepared by arc melting of the elements (copper crucible, Ar atmosphere).

Phase Evolution in Boride-Based Cermets and Reaction Bonding onto Plain Low Carbon Steel Substrate

Reaction sinter bonding is a process that aims to bond two materials for improvement in properties through reactive sintering technique. The process has been effectively used to sinter hard materials like borides in situ which not only possess excellent oxidation resistance, good corrosion resistance but also resistant to abrasive wear. Sinter bonding is a unique surface modification process achieved through powder metallurgy and is competent with other techniques like boronizing sintering and sinter-brazing since it eliminates the additional operations of heat treatment and assembly and removes the inherent setbacks with these processes. This study focuses on identifying the phase evolution mechanism using characterization tools like x-ray diffractometry and energy dispersive spectroscopy and study of sinter bonding of the boron containing precursors (Mo-Cr-Fe-Ni-FeB-MoB) onto plain carbon steel. A microstructure containing Fe-based matrix dispersed with complex borides develops with temperature in the tape cast sheets. A fivefold increase in hardness between plain carbon steel in wrought condition and sinter bonded steel was observed. The multilayer consisted of a reaction zone adjacent to the interface and was investigated with the composition profile and hardness measurements. A model of sinter bonding between the cermet and the steel has also been proposed.

Synthesis, Crystal Structure, and Ru/Ir Site Preference in the Complex Boride Series Ti2FeRu5–xIrxB2 and Zr2Fe1–δRu5–x+δIrxB2 (x = 1–4, δ < 0.15)

AbstractPolycrystalline samples and single crystals of the complex boride series Ti2FeRu5–xIrxB2 and Zr2Fe1–δRu5–x+δIrxB2 (x = 1–4, δ < 0.15) were synthesized by arc melting the elements and characterized by powder and single‐crystal X‐ray diffraction as well as energy dispersive spectroscopy. All quinary phases could be synthesized in the titanium series, whereas only the first two ruthenium‐rich phases are stable and both are always present in nearly all synthetic targets of the zirconium series. These compounds crystallize in the tetragonal space group P4/mbm (Z = 2) and they represent the first quinary substitutional variants of the Ti3Co5B2‐type structure containing a mixture of 4d/5d transition metals. Their structures consist of layers of ruthenium and iridium atoms, building trigonal, tetragonal, and pentagonal prisms, in which the other elements are located. The trigonal prisms are filled with boron and the pentagonal prisms accommodate either titanium or zirconium. The tetragonal prisms are filled either with iron (in the Ti series) or with an iron‐rich Fe/Ru mixture (in the Zr series). Ruthenium and iridium share two sites in these structures leading to a strong size‐dependent site preference in both series.

Complete Titanium Substitution by Boron in a Tetragonal Prism: Exploring the Complex Boride Series Ti3−xRu5−yIryB2+x (0 ≤ x ≤ 1 and 1 < y < 3) by Experiment and Theory

Polycrystalline samples and single crystals of four members of the new complex boride series Ti(3-x)Ru(5-y)Ir(y)B(2+x) (0 ≤ x ≤ 1 and 1 < y < 3) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The new silvery phases were structurally characterized by powder and single-crystal X-ray diffraction as well as energy- and wavelength-dispersive X-ray spectroscopy analyses. They crystallize with the tetragonal Ti(3)Co(5)B(2) structure type in space group P4/mbm (No. 127). Tetragonal prisms of Ru/Ir atoms are filled with titanium in the boron-poorest phase (Ti(3)Ru(2.9)Ir(2.1)B(2)). Gradual substitution of titanium by boron then results in the successive filling of this site by a Ti/B mixture en route to the complete boron occupation, leading to the boron-richest phase (Ti(2)Ru(2.8)Ir(2.2)B(3)). Furthermore, both ruthenium and iridium share two sites in these structures, but a clear Ru/Ir site preference is found. First-principles density functional theory calculations (Vienna ab initio simulation package) on appropriate structural models (using a supercell approach) have provided more evidence on the stability of the boron-richest and -poorest phases, and the calculated lattice parameters corroborate very well with the experimentally found ones. Linear muffin-tin orbital atomic sphere approximation calculations further supported these findings through crystal orbital Hamilton population bonding analyses, which also show that the Ru/Ir-B and Ru/Ir-Ti heteroatomic interactions are mainly responsible for the structural stability of these compounds. Furthermore, some stable and unstable phases of this complex series could be predicted using the rigid-band model. According to the density of states analyses, all phases should be metallic conductors, as was expected from these metal-rich borides.

ChemInform Abstract: Structure, Bonding, and Magnetic Response in Two Complex Borides: Zr2Fe1‐δRu5+ δB2 and Zr2Fe1‐δ (Ru1‐xRhx) 5+δB2.

AbstractZr2Fe0.87Ru5.13B2 and Zr2Fe0.82(Ru/Rh)5.18B2 are synthesized by arc melting of stoichiometric mixtures of the elements followed by annealing at 1000 °C (14 d).

Effects of Chromium and Molybdenum Contents and Heat Treatment on Behavior of Complex Boride Forming in Ni-Cr-Mo-B Gas Atomized Powder

The effects of Cr and Mo contents and the heat treatment on the properties of gas atomized powders with Ni-Xmass%Cr-Ymass%Mo-1.5mass%B compositions ((X, Y)=(10, 36), (22, 26), (34, 16)) were investigated. Examined powders were produced by gas atomization, followed by sieving under 150 μm. These powders were heat treated at various temperatures to investigate its effect.As a result, tetragonal M3B2 and tetragonal M5B3 type complex borides were observed in examined powders before and after heat treatment. Compositions and crystal structures of complex borides varied depending on Cr and Mo contents in examined powders and compositions of Ni-based matrix phases also varied. Vickers hardness after 1473 K heat treatment increased with increasing the Mo/Cr ratio of examined powder.

Structure, bonding, and magnetic response in two complex borides: Zr 2Fe 1− δRu 5+ δB 2 and Zr 2Fe 1− δ(Ru 1− xRh x) 5+ δB 2

Polycrystalline samples of two complex intermetallic borides Zr 2Fe 1− δ Ru 5+ δ B 2 and Zr 2Fe 1− δ (Ru 1− x Rh x ) 5+ δ B 2 ( δ=ca. 0.10; x=0.20) were synthesized by high-temperature methods and characterized by single-crystal X-ray diffraction, energy dispersive spectroscopy, and magnetization measurements. Both structures are variants of Sc 2Fe(Ru 1− x Rh x ) 5B 2 and crystallize in the space group P4/ mbm (no. 127) with the Ti 3Co 5B 2-type structure. These structures contain single-atom, Fe-rich Fe/Ru or Fe/Ru/Rh chains along the c-axis with an interatomic metal-metal distance of 3.078(1) Å, a feature which makes them viable for possible low-dimensional temperature-dependent magnetic behavior. Magnetization measurements indicated weak ferrimagnetic ordering with ordering temperatures ca. 230 K for both specimens. Tight-binding electronic structure calculations on a model “Zr 2FeRu 5B 2” using LDA yielded a narrow peak at the Fermi level assigned to Fe–Fe antibonding interactions along the c-axis, a result that indicates an electronic instability toward ferromagnetic coupling along these chains. Spin-polarized calculations of various magnetic models were examined to identify possible magnetic ordering within and between the single-atom, Fe-rich chains.