Specific volume and elastic properties of glassy,icosahedral quasicrystalline and crystalline phases in Zr–Ni–Cu–Al–Pd alloy

Elastic properties, phase composition, microstructure and specific volume changes in the Zr₆₅Ni₁₀Cu₅Al_7.5 Pd_12.5 glassy alloy during progressive devitrification have been studied by ultrasonic pulse, X-ray diffractometry, transmission electron microscopy and Archimedean methods, respectively, in terms of structure and properties change. On heating the glassy alloy initially forms an icosahedral phase and then a mixture of tI12 Zr₂Ni^ss and β-Zr^ss crystalline phases after annealing at 993 K for 300 s, and lastly tI12 Zr₂Ni^ss, tI6 Zr₂Pd and hP9 Zr₆Al₂Ni crystalline phases after prolonged annealing at 993 K for 7.2 ks. In an as-solidified state the alloy shows high Poisson’s and K/G ratios of 0.42 and 7, respectively. These parameters are responsible for its good ductility. The structural changes are accompanied by decreases in specific volume, bulk modulus, Lamé parameter and Poisson’s ratio. Small specific volume changes upon primary devitrification suggest a close relation between the glassy and the icosahedral structures. The existence of the icosahedral local order, which exhibits rigidity for three-dimensional shear deformation with mixed mode II mode III, may be responsible for good elasticity of the glassy alloy.     

In situ visualization of Ni–Nb bulk metallic glasses phase transition

We report the results of in situ investigation of the structural evolution and crystallization behavior of Ni-based bulk metallic glass. The X-ray diffraction, transmission electron microscopy, nanobeam diffraction, differential scanning calorimetry, radial distribution function and scanning tunneling microscopy (STM)/spectroscopy techniques were applied to analyze the structure and electronic properties of Ni_63.5Nb_36.5 glasses before and after crystallization. According to our STM measurements, the primary crystallization originally starts with the Ni₃Nb phase formation as a leading eutectic phase. It was shown that surface crystallization differs drastically from bulk crystallization due to the possible surface reconstruction. The mechanism of Ni_63.5Nb_36.5 glass alloy two-dimensional crystallization was suggested, which corresponds to the local metastable (3 × 3) ?  Ni(1 1 1) surface phase formation. The possibility of different surface nanostructures developing by annealment of the originally glassy alloy in an ultrahigh vacuum at a temperature lower than the bulk crystallization temperature was shown. The increase of the mean square surface roughness parameter R_q while transforming from a glassy to a fully crystallized state can be caused by concurrent growth of Ni₃Nb and Ni₆Nb₇ bulk phases. The simple empirical model for the estimation of Ni_63.5Nb_36.5 cluster size was suggested, and the value obtained (about 8 Å) is in good agreement with the corresponding STM measurements (8–10 Å).     

Air-oxidation of a Co-based amorphous ribbon at 400–600 °C

The oxidation behavior of a commercial Co₆₉B₁₂Si₁₂Fe₄Mo₂Ni₁ amorphous ribbon (Co6-AR) was studied over the temperature range of 400–600 °C in dry air. The results showed that virtually no oxidation occurred at 400 °C. On the other hand, the oxidation kinetics of the Co6-AR alloy at 450–600 °C generally followed a multi-stage parabolic-rate law, and the parabolic-rate constants (k_p values) tend to increase with increasing temperature. It was found that the oxidation rates of the glassy alloy are slower than those of pure Co, indicative of a better oxidation resistance. An exclusive scale of CoO was observed after the oxidation of the glassy alloy in the temperature range of interest, and several crystalline phases formed on the substrate beneath the scale, consisting of pure Co (both FCC and HCP structures), Co₃B, Co₂Si, CoFe, and Co₂B (absent at 450 °C), which indicated the occurrence of crystallization.     

Solid state amorphization and crystallization in Zr66.7Pd33.3 metallic glass

We observed quasicrystal-to-amorphous-to-crystal (Q–A–C) transition in Zr_66.7Pd_33.3 metallic glass. The unique disordering–ordering phase transition was induced by 2 MeV electron irradiation at 298 K. Electron irradiation can induce not only the solid-state amorphization but also crystallization of a glassy structure under the same irradiation conditions. The Q–A–C transition can be explained by change in the phase stability of crystal, quasicrystal and amorphous phases by electron irradiation induced atomic displacement.     

Local structure variations in Al89La6Ni5 metallic glass

Reduced density functions (RDFs) from electron diffraction measurement of an Al₈₉La₆Ni₅ metallic glass were obtained and analysed using Reverse Monte Carlo (RMC) refinement accompanied by density functional theory calculations. Three different RDFs were observed from regions in close proximity (within microns) of each other, with the first/second peaks respectively located at 2.76/3.32, 2.90/3.46 and 2.96/3.55 Å (all ±0.02 Å). The first type of RDF was found to be the more prevalent. X-ray dispersive spectroscopy and electron energy loss spectroscopy showed no measurable composition variations on this scale. According to the RMC refinements, the variations in the peaks are due to slight lengthening in the mean Al–Al and larger lengthening of the Al–La first-neighbour contacts, while the mean Al–Ni contact shortens. These local structure variations in a nominally homogeneous Al₈₉La₆Ni₅ metallic glass are likely to be important to the understanding of metallic glass properties.     

Surface modeling and chemical solution deposition of SrO(SrTiO3)n Ruddlesden–Popper phases

Strontium titanate (STO) is a preferred substrate material for functional oxide growth, whose surface properties can be adjusted through the presence of Ruddlesden–Popper (RP) phases. Here, density functional theory (DFT) is used to model the (1 0 0) and (0 0 1) surfaces of SrO(SrTiO₃)_n RP phases. Relaxed surface structures, electronic properties and stability relations have been determined. In contrast to pure STO, the near-surface SrO–OSr stacking fault can be employed to control surface roughness by adjusting SrO and TiO₂ surface rumpling, to stabilize SrO termination in an SrO-rich surrounding or to increase the band gap in the case of TiO₂ termination. RP thin films have been epitaxially grown on (0 0 1) STO substrates by chemical solution deposition. In agreement with DFT results, the fraction of particular RP phases n = 1–3 changes with varying heating rate and molar ratio Sr:Ti. This is discussed in terms of bulk formation energy.     

Formation,ductile deformation behavior and soft-magnetic properties of (Fe,Co,Ni)–B–Si–Nb bulk glassy alloys

Fe-based [(Fe,Co,Ni)_0.75B_0.2Si_0.05]₉₆Nb₄ bulk ferromagnetic glassy alloy rods with the diameters up to 4 mm were synthesized by copper mold casting. The addition of Ni element caused no decrease in glass-forming ability and fracture strength, but increased the compressive deformation ductility of this Fe-based bulk glassy alloy system. The glassy alloy rods exhibit super-high fracture strength over 4000 MPa, high Young's modulus over 200 GPa, elastic strain of 0.02 and plastic strain up to 0.005. The bulk glassy alloys also exhibit good soft-magnetic properties, i.e., high saturation magnetization of 0.8–1.1 T, low coercive force below 3 A/m, and high permeability of 1.6–2.1 × 10⁴ at 1 kHz. The success of synthesizing a super-high strength Fe-based bulk glassy alloy with some compressive plastic strain and good soft-magnetic properties is encouraging for future development of Fe-based bulk glassy alloys as new engineering and functional materials.     

Glass-forming ability and soft magnetic properties of (Co0.6Fe0.3Ni0.1)67B22+xSi6−xNb5 bulk glassy alloys

The glass-forming ability (GFA) and soft-magnetic properties of (Co_0.6Fe_0.3Ni_0.1)₆₇B_22+xSi_6?xNb₅ (x = 0–1.5) bulk glassy alloys was investigated. The DSC curves show that the (Co_0.6Fe_0.3Ni_0.1)₆₇B_22+xSi_6?xNb₅ bulk glassy alloys have a wide supercooled liquid region (ΔT_x) of about 60 K, and high reduced glass transition temperature (T_g/T_l) lies in the range from 0.628 to 0.649. By copper mold casting method, the bulk glassy alloys with diameters up to 4.5 mm can be formed. In addition to high GFA, the Co-based bulk glassy alloys also exhibit good soft-magnetic properties, i.e., saturation magnetization of 0.58–0.61 T, low coercive force of 0.83–1.46 A/m, and high permeability of (1.79–2.2) × 10⁴ at 1 kHz under a field of 1 A/m. These Co-based bulk glassy alloys are promising for future applications as a new structural and functional material.     

Effects of temperature and the incorporation of W on the oxidation of ZrB2 ceramics

The effects of tungsten additions and temperature on the oxidation behavior of nominally pure ZrB₂ and ZrB₂ containing 4, 6 or 8 mol% of W after oxidation at temperatures ranging from 800 to 1600 °C were investigated. For pure ZrB₂, the protective liquid/glassy layer covering the surface as a result of oxidation was evaporated above 1500 °C. For (Zr,W)B₂ specimens, the liquid/glassy layer was present after exposure up to 1600 °C. The higher stability of the liquid/glassy phase in the W-containing compositions was attributed to the presence of tungsten in the liquid/glassy phase, resulting in improved oxidation resistance for ZrB₂ samples containing W.     

Liquid structure as a guide for phase stability in the solid state: Discovery of a stable compound in the Au–Si alloy system

A new crystalline ground state was discovered in the Au–Si system through first-principles electronic structure calculations. The new structure was found using the experimentally and theoretically determined local atomic structure in the liquid as a guide for the solid state. Local atomic structure in the liquid was matched with that for all known crystal structures as compiled in the Pauling File structural database. The best matching crystalline structures were then explicitly calculated using first-principles methods. Most candidate crystal structures were found to be close, but above the enthalpy of a composition weighted average of the face-centered cubic Au and diamond structure Si terminal phases, but one crystal structure was more stable than the terminal phases by about 10 meV atom^–1 at T = 0 K. As first-principles simulations of local structure are feasible for most liquid alloys, the present methodology is applicable to other alloys lying near a eutectic composition.     

Defect structures and ternary lattice site preference of the B2 phase in the Al–Ni–Ru system

The energies for stoichiometric and defected binary and ternary B2 phases in the Al–Ni–Ru ternary system were calculated from first-principles. The dominant compositions-conserving constitutional defect structures for NiAl and RuAl have been determined as (Al, Ni)(Ni, Va) and (Ru, Al, Va)(Al), respectively. It was observed that Ru prefers the Ni-sublattice in NiAl, while Ni has a very strong preference for the Ru-sublattice in RuAl. Furthermore, the results indicate that a miscibility gap is likely to be stable at low temperatures in the NiAl–RuAl pseudobinary system.     

The Y–Cu–Mg system in the 0–66.7 at.% Cu concentration range: The isothermal section at 400 °C

Synthesis and characterization of about fifty alloys were performed in order to construct the isothermal section of the Y–Cu–Mg ternary system at 400 °C in the 0–66.7 at.% Cu concentration range. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS) and X-ray powder diffraction (XRPD) techniques were used to examine microstructures, identify phases and define their compositions and crystal structures. Phase equilibria in the investigated compositional region are characterized by the absence of extended ternary solid solutions and by the presence of at least ten ternary phases. Crystal structures of the previously reported Y₂Cu₂Mg, Y₅Cu₅Mg₈, Y₅Cu₅Mg₁₃, Y₅Cu₅Mg₁₆ and YCuMg₄ phases were confirmed. A ternary phase with homogeneity range around the YCu₄Mg stoichiometry was found, crystallizing in the cF24--MgCu₄Sn structure type; at 400 °C this phase coexists with a ternary solid solution based on the binary Laves phase Cu₂Mg, which dissolves about 5 at.% Y. The equiatomic YCuMg phase was also found to exist: from the analysis of X-ray powder patterns it is suggested to crystallize in the hP9--ZrNiAl structure type (a = 0.74449(4) nm, c = 0.39953(2) nm). Two other stoichiometric ternary phases were detected, of approximate compositions Y₂₅Cu₁₈Mg₅₇ and Y₁₃Cu₉Mg₇₈, whose crystal structures are still unknown. In the Mg-rich region, a ternary phase forms characterized by a large homogeneity region.     

Fabrication and soft-magnetic properties of Fe–B–Nb–Y glassy powder compacts by spark plasma sintering technique

Magnetic properties of (Fe_0.72B_0.24Nb_0.04)_95.5Y_4.5 sample were investigated. The sample was produced from glassy powders made by the gas-atomization and consolidation using the spark plasma sintering (SPS) technique. Maximum relative density of 99.5% was achieved in the spark plasma sintered (SPSed) compact due to the viscous flow enhanced by the applied stress even under the glass transition temperature. X-ray diffraction pattern of the compact indicates that the glassy structure was maintained through the SPS process. However, the results of differential scanning calorimetry (DSC) showed that the glass transition temperature and crystallization temperature of the SPSed glassy compact shift to a higher and lower temperature, respectively, that is, a smaller ΔT_x. Saturation magnetization of the SPSed glassy compact became 10% higher than that of the initial glassy powder. The Curie point was enhanced from 522 K for the glassy powder to 548 K for the SPSed glassy compact. Spin-exchange interaction is expected to be enhanced by a short-range scale atomic rearrangement caused by the high applied stress and temperature during the SPS process.     

Fabrication and characterization of bulk glassy Co40Fe22Ta8B30 alloy with high thermal stability and excellent soft magnetic properties

In this work, Co₄₀Fe₂₂Ta₈B₃₀ alloy as a new bulk metallic glass with a wide supercooled liquid region of 74 K and excellent soft magnetic properties was prepared by the powder metallurgy method. Glassy Co₄₀Fe₂₂Ta₈B₃₀ powders were obtained by ball milling of melt-spun glassy ribbons at a cryogenic temperature and subsequently consolidated by hot pressing into disk-shaped specimens 10 mm in diameter and 2 mm thick. It was found that the new glassy alloy exhibited the largest diameter compared with the other Co-based bulk metallic glasses produced in the well-known Co–Fe–Ta–B alloying system up to now. The influence of the consolidation time on the microstructure and magnetic properties of the bulk samples was investigated by X-ray diffraction, differential scanning calorimetry, vibrating sample magnetometry and Faraday magnetometry. The results indicate that the new alloy exhibits a long incubation time before crystallization upon annealing above the glass transition temperature: noticeably longer than for other known (Co,Fe)-based amorphous alloys. The glassy bulk sample consolidated for 600 s at 923 K had a relative density of 99.2%, a saturation magnetization of 46.6 A m² kg^?1, a Curie temperature of 425 K and a low coercivity of 6 A m^?1. In addition, the new bulk glassy alloy exhibited ultra-high hardness of 13.48 GPa. The mechanisms by which the thermal stability and incubation time prior to crystallization increase are explained in accordance with pair correlation function analysis.     

An in situ bulk Zr58Al9Ni9Cu14Nb10 quasicrystal-glass composite with superior room temperature mechanical properties

An in situ bulk Zr₅₈Al₉Ni₉Cu₁₄Nb₁₀ quasicrystal-glass composite has been fabricated by means of copper mould casting. The microstructure and constituent phases of the alloy composite have been analyzed by using X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy. Icosahedral quasicrystals were found to be the majority phase and the grain size is in half-μm scale. In between the I-phase grains is a glassy phase. Optical microscopy and scanning electron microscopy revealed that the as-cast alloys were pore-free. The microhardness of the composite is about 5.90 ± 0.30 GPa. The room temperature compression stress–true strain curve exhibits a 2% elastic deformation up to failure, and a maximum fracture stress of 1850 MPa at a quasi-static loading rate of 4.4 × 10⁻⁴ s⁻¹. The mechanical property is superior to the early developed quasicrystal alloys, and is comparable to Zr-based bulk metallic glasses and their nanocomposites. The quasicrystal-glass composite exhibits basically a brittle fracture mode at room temperature.     

Thermoelectric properties of ternary and Al-containing quaternary Ru1−xRexSiy chimney–ladder compounds

The thermoelectric properties of ternary and Al-containing quaternary Ru_1?xRe_xSi_y chimney–ladder phases have been studied as a function of the Re concentration with the use of directionally solidified alloys. The Ru_1?xRe_xSi_y chimney–ladder phases exhibit n- and p-type semiconducting behaviors, respectively, at low and high Re concentrations, at which the X(=Si)/M(=Ru + Re) ratios are respectively, larger and smaller than those expected from the VEC (valence electron concentration) = 14 rule. The absolute values of both Seebeck coefficient and electrical resistivity increase as the extent of the deviation from the VEC = 14 rule increases, i.e. as the alloy composition deviates from that corresponding to the p–n transition (x ≈ 0.5), indicating that the carrier concentration can be controlled by changing the extent of compositional deviation from the ideal VEC = 14 composition. The highest values of the dimensionless figure of merit obtained are 0.47 for ternary (x = 0.60) and 0.56 for Al-containing quaternary alloys. The reasons for the systematic compositional deviation from the ideal VEC = 14 compositions observed for a series of chimney–ladder phases are discussed in terms of atomic packing.     

Structural transformations of bioactive glass 45S5 with thermal treatments

We report on the structural transformations of Bioglass^® during thermal treatments. Just after the glassy transition, at 550 °C, a glassy phase separation occurs at 580 °C, with the appearance of one silicate- and one phosphate-rich phase. It is followed by the crystallization of the major phase Na₂CaSi₂O₆, from 610 to 700 °C and of the secondary phase, silico-rhenanite, at 800 °C. The latter evolves from the phosphate-rich glassy phase, which is still present after the first crystallization. In order to control the processing of glass-ceramic products from Bioglass^®, crystallization kinetics were studied via differential scanning calorimetry measurements in the range of 620–700 °C and temperature–time–transformation curves were established.     

Glassy alloy composites for bit-patterned-media

With the aim of developing a novel perpendicular bit-patterned-media, combined process of thermal imprinting of glassy alloy thin film and embedding Co/Pd multilayer was developed. Nano hole array with a hole diameter of 30 nm was successfully formed onto Pd-based glassy alloy thin film by thermal imprinting. Co/Pd multilayer was overlaid on a textured Pd-based glassy alloy thin film. After finishing by sputter etching, prototype bit-patterned-media was prepared. Switching behavior examined under magnetic field of ±10 kOe reveals that the isolated magnetic dots began to switch at 10 kOe. These results suggest that the prototype composite has a strong possibility for the realization of next generation bit-patterned-media with high data density.     

Novel FePBNbCr glassy alloys “SENNTIX” with good soft-magnetic properties for high efficiency commercial inductor cores

According to a recent study, Fe-based glassy alloys are expected good soft-magnetic properties such as high saturation magnetization and lower coercive force. We focused on Fe-based glassy alloys and have succeeded in developing novel glassy Fe_97?x?yP_xB_yNb₂Cr₁ (x = 5–13, y = 7–15) alloys for an inductor material. The glassy alloy series of Fe_97?x?yP_xB_yNb₂Cr₁ (x = 5–13, y = 7–15) have high glass-forming ability with the large critical thickness of 110–150 μm and high B_s of 1.25–1.35 T. The glassy alloy powder with chemical composition Fe₇₇P_10.5B_9.5Nb₂Cr₁ exhibits an excellent spherical particle shape related to the lower melting point and liquid phase point. In addition, Fe–P–B–Nb–Cr powder/resin composite core has much lower core loss of 653–881 kW/m³, which is approximately 1/3 lower than the conventional amorphous Fe–Si–B–Cr powder/resin composite core and 1/4 lower than the conventional crystalline Fe–Si–Cr powder/resin composite core due to the lower coercive force of 2.5–3.1 A/m. Based on above results, the glassy Fe₇₇P_10.5B_9.5Nb₂Cr₁ alloy powder enable to achieve ultra-high efficient and high quality products in a commercial inductor. In fact, the surface mounted inductor using Fe–P–B–Nb–Cr powder/resin exhibits the high efficiency of approximately 2.0% compared with the conventional inductors made of the crystalline Fe–Si–Cr powder/resin composite core.     

Microstructure evolution of nanoprecipitates in half-Heusler TiNiSn alloys

The microstructures of thermoelectric TiNiSn half-Heusler alloys have been studied in detail. For concentration ratios that are slightly rich in Ni, a high density of Heusler-phase nanosized precipitates tended to precipitate within a half-Heusler matrix. The morphology and average size of the Heusler nanoprecipitates were very sensitive to the Ni concentration ratio in the half-Heusler matrix of the alloys. Smaller Heusler nanoprecipitates with coherent ellipsoidal (<5 nm) and disc (<10 nm wide) morphologies tended to precipitate within the matrices of alloys with slightly elevated Ni concentration ratios (Ti:Ni:Sn = 1.0:1.1:1.0). However, much larger coherent discs (<45 nm wide and <5 nm thick), semicoherent platelets (up to 1 μm long and <30 nm thick) and spheres (up to 1 μm wide) were observed in the matrices of the alloys with larger Ni concentration ratios (Ti:Ni:Sn = 1.0:1.2:1.0). Tetragonal structures were observed in the coherent Heusler nanoprecipitates. The formation of such structures was closely associated with the size, morphology and interface coherency of the nanoprecipitates. Moreover, most of the coherent Heusler nanoprecipitates were preferentially oriented parallel to the cubic {0 0 1}_HH orientations. Interfacial defects between the Heusler and half-Heusler phases, as well as lattice point defects, Ni antisites and vacancies, were found to be closely related to the formation of the Heusler nanoprecipitates. A mechanism has been proposed in this study to describe the coarsening of the Heusler nanoprecipitates via the formation of lattice point defects and interfacial defects.