Effect of V content on microstructure and mechanical property of a TiVCuNiAl composite fabricated by spark plasma sintering

Ultrafine-grained (Ti₄₀Cu_22.9Ni_19.4Al_17.7)_x(Ti₈₀V₂₀)_1−x (x = 0.35 and 0.55) composites were fabricated by spark plasma sintering and crystallization of amorphous phase. Outstanding difference in microstructure and mechanical property is found for the two composites. Microstructure observation shows that the two composites all consist of body-centered cubic β-Ti and face-centered cubic (Cu, Ni)–Ti₂ regions but have opposite matrix and reinforcing phases. Meanwhile, mechanical property examination indicates that the composites for x = 0.35 exhibit far higher fracture strength and far larger fracture strain compared with the composites for x = 0.55 fabricated under the same parameter conditions. The different mechanical properties for the two composites can be explained by the different fracture mechanisms resulted from their different microstructures.     

Giant magnetoimpedance in nanocrystalline Fe90.3−xZr7B2.7Cux (0.5 ≤ x ≤ 1.5) as-spun ribbons

The nanocrystalline ribbons Fe_90.3−xZr₇B_2.7Cu_x with low Cu contents can be directly obtained through melt-spinning technique with an appropriate low quenching speed such as 22 m/s. Sizes of bcc-Fe grains precipitated in Fe_90.3−xZr₇B_2.7Cu_x as-spun ribbons were 17 nm for x = 0.75, 15 nm for x = 1 and 12 nm for x = 1.25. The addition of Cu reduces grain size of bcc-Fe in as-spun nanocrystalline Fe_90.3−xZr₇B_2.7Cu_x ribbons. Among the investigated samples (0.5 ≤ x ≤ 1.5), the largest magnetoimpedance can be obtained in the nanocrystalline Fe_80.3Zr₇B_2.7Cu₁ as-spun ribbon with x = 1. The value of magnetoimpedance (Z(H) − Z(0)) / Z(0) under H = 90 Oe for Fe_80.3Zr₇B_2.7Cu₁ as-spun ribbon reaches − 28.2% at a frequency of 1 MHz.     

Deformation behavior of a Ti-based bulk metallic glass composite with excellent cryogenic mechanical properties

Excellent mechanical properties as high as 2760 MPa fracture strength and 18.4% plastic strain are obtained in Ti₄₈Zr₂₀Nb₁₂Cu₅Be₁₅ bulk-metallic-glass (BMG) composite at cryogenic temperature (77 K). The novel cryogenic plasticity of present composite is determined by good cryogenic plasticity of dendrites induced effective interaction between dendrites and shear bands. Improved cryogenic yield strength of dendrites is responsible for the increase of cryogenic yield strength of the present composite. Continuous matrix other than the dendrites is believed to initiate the fracture behavior. This finding demonstrates that in situ dendrite-reinforced BMG composites can be a kind of promising materials for low-temperature applications.     

Preparation and dielectric properties of Sr(Ti0.95Zr0.05)O3 ceramics doped with CaOTiO2SiO2 (CTS)

Sr(Ti_0.95Zr_0.05)O₃ ceramic was sintered using x mol.% CTS (x = 0, 0.5, 1.5, 4, 7) as sintering additive for the first time. Although Sr(Ti_0.95Zr_0.05)O₃ ceramic could not be fully sintered even at 1420 °C, the densification temperature could be decreased to 1280 °C by using CTS, which begin melting when temperature reaches higher than 1150 °C. The microstructures of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Apparent density and the dielectric properties were established at room temperature. The measuring frequency was 1 MHz. The microstructure and dielectric properties greatly changed depending on the amount of CTS additive. The optimum concentration to obtain nicer dielectric properties was 0.5 mol.%.     

Influence of SrTiO3 modification on dielectric properties of Mg(Zr0.05Ti0.95)O3 ceramics at microwave frequency

The microwave dielectric properties and microstructures were investigated in the (1?x)Mg(Zr_0.05Ti_0.95)O₃–xSrTiO₃ (hereafter referred to as (1?x)MZT–xST) system. The compounds were prepared via the conventional solid-state reaction. Compositions in the (1?x)Mg(Zr_0.05Ti_0.95)O₃–xSrTiO₃ system were designed to compensate the negative temperature coefficient of the resonant frequency of Mg(Zr_0.05Ti_0.95)O₃. The values displayed nonmonotonic mixture-like behavior, because the TiO₂ phase was formed in the MZT composite ceramics with increasing x. A close zero τ_f of 0.2 ppm/°C could be achieved at 0.96MZT–0.04ST with ?_r = 20.8 and Q × f = 257,000 GHz.     

Improved electrochemical hydrogen storage capacity of Ti45Zr38Ni17 quasicrystal by addition of ZrH2

Ti₄₅Zr₃₈Ni₁₇ + xZrH₂ (x = 5, 10, 15 and 20 wt%) composite materials are produced by ball milling for 20 min. The results of XRD measurement show that the composite materials contain icosahedral quasicrystal phase (I-phase), FCC phase with a Ti₂Ni type crystal and C14 Laves phase. After adding ZrH₂, the composite materials include not only the individual phases mentioned above, but also the ZrH phase. These composite materials are used as the negative electrode material of the nickel-metal hydride batteries. The electrochemical hydrogen storage characteristics of the material after adding ZrH is investigated. The Ti₄₅Zr₃₈Ni₁₇ + xZrH₂ (x = 5, 10, 15 and 20 wt%) composite material has reached the maximum discharge capacity (83.2 mA h/g) when x equals 10. This maximum discharge capacity is much higher than that of Ti₄₅Zr₃₈Ni₁₇ alloy without ZrH. After adding ZrH_2, the high-rate discharge ability and the cycling stability are enhanced simultaneously. The improvement of the electrochemical properties can be attributed to the synergistic effects of ZrH₂, and the synergistic effects in the composite electrodes are probably attributed to the entry of most of hydrogen atoms from weakly bond strength of the Zr-H to the I-phase structure in electrochemical reaction.     

Effects of Sn content on thermal stability and mechanical properties of the Ti60Zr10Ta15Si15 amorphous alloy for biomedical use

The (Ti₆₀Zr₁₀Ta₁₅Si₁₅)_100−xSn_x (x = 0, 4, 8, 12 at.%) amorphous ribbons were prepared by the single roll melt-spinning method, and the effects of the Sn content on the thermal stability, the elastic modulus and nanohardness of the Ni-free Ti-based alloys were investigated. It is found that Sn additions decrease the glass formation ability of the Ti₆₀Zr₁₀Ta₁₅Si₁₅ alloy. The content of Sn addition has an important impact on the elastic modulus and nanohardness of the alloys. The amorphous alloy with 4% Sn addition exhibits the highest the elastic modulus and nanohardness, which are 111 GPa and 7.0 GPa, respectively. The correlation between the mechanical properties and Sn content was discussed based on the free volume containing in the as-spun ribbons.     

Electronic structure of Cu100−xZrx (x = 40, 50, 60) metallic glasses

The electronic structure of Cu_100−xZr_x (x = 40, 50, 60) metallic glasses was investigated by ultraviolet photoelectron spectroscopy and X-ray photoemission spectroscopy, the valence band spectra of these alloys were analyzed by a large shift of the Cu d-band peaks to higher binding energies upon increasing Cu content. Photoemission experiments and first-principles calculations prove that the values of density of states at Fermi level of Cu_100−xZr_x metallic glasses are mainly dominated by Zr rather than Cu. This work will enlighten further research on understanding the inheritance of metallic glasses and designing new metallic glasses with unique properties.     

The effect of Si addition on the microstructure and magnetic properties of Permalloy prepared by mechanical alloying method

In this paper, we report the preparation of nanostructured (Ni₅₀Fe₅₀)_100?xSi_x and (Ni₈₀Fe₂₀)_100?xSi_x powders prepared by the mechanical alloying method. Elemental maps using scanning electron microscopy as well as X-ray diffraction results showed that iron and silicon dissolved in the nickel lattice homogeneously and formed a face-centered cubic γ-(Ni (Fe–Si)) uniform solid solution after milling for 24 h. By increasing Si content up to 20 at.%, estimated crystallite sizes for Ni₅₀Fe₅₀ and Ni₈₀Fe₂₀ alloys were reduced from ～35 and 46 nm to ～9 and 17 nm, respectively. Up to 5 at.% Si, microstrain decreased due to dynamic and static recovery which were prevailing mechanisms due to high work hardening rate of powders. By increasing the Si content, saturation magnetization decreased and different rates of grain refinement resulted in dissimilar behavior of coercivity for two compositions. The maximum saturation magnetization (～156 emu/g) and minimum coercivity (～10 Oe) were achieved for the Ni₅₀Fe₅₀ and (Ni₅₀Fe₅₀)₈₀Si₂₀ alloys, respectively.     

High dielectric constant observed in (1 − x)Ba(Zr0.07Ti0.93)O3–xBa(Fe0.5Nb0.5)O3 binary solid-solution

Binary solid-solutions of the (1 ? x)Ba(Zr_0.07Ti_0.93)O₃–xBa(Fe_0.5Nb_0.5O₃) system, with 0.1 ≤ x ≤ 0.9,were fabricated via a solid-state processing technique. X-ray diffraction analysis revealed that all samples exhibited a single perovskite phase. The BaFe_0.5Nb_0.5O₃ also promoted densification and grain growth of the system. Dielectric measurements showed that all samples displayed a relaxor like behavior. The x = 0.1 sample presented a dielectric-frequency and temperature with low loss tangent (<0.07 at 10 kHz). For x > 0.2 samples, the dielectric data showed a broad dielectric constant–temperature curve with a giant dielectric characteristic. In addition, a high dielectric constant > 50,000 (at 10 kHz and temperature > 150 °C) was observed for the x = 0.9 sample.     

Phase composition and solid solution strengthening effect in TiZrNbMoV high-entropy alloys

TiZrNbMo_xV_y high-entropy alloys (HEAs) with x = 0–2, y = 1 and y = 0.3, respectively, were designed and prepared by copper mold casting technology. The phase composition and stability of these HEAs were investigated. It is shown that the HEAs with low content of V are composed of only one type of bcc solid solution phase (SSP), and demonstrate excellent phase stability at 1273 K. The high content of V and Mo results in the formation of two types of bcc SSPs and the decrease of phase stability in the HEAs. Based on the previously proposed criteria, the formation ability of solid solution phase for this kind of HEAs was comprehensively evaluated. The compressive mechanical properties of the as-cast and annealed HEAs were measured. It has been found that Mo plays a strong solid solution strengthening effect on this kind of HEAs. Especially, TiZrNbMo_0.3V_0.3 has the yield strength and plastic strain of 1312 MPa and >50%, respectively, and still maintains the excellent plastic deformation ability even after annealed at 1273 K for 72 h. The strengthening effect in this kind of HEAs is considered to be due to the shear modulus mismatch. The solubility limit of HEAs is correspondent to shear modulus mismatch of 29.     

Biomedical TiNbZrTaSi alloys designed by d-electron alloy design theory

We report on the formation of ultrafine-grained (Ti_69.71Nb_23.72Zr_4.83Ta_1.74)_100 − xSi_x (at.%, x = 0, 2 and 5) alloys designed by d-electron alloy design theory and fabricated by spark plasma sintering of nanocomposite powder precursor. The designed and fabricated alloys exhibit a high yield and fracture strength of 1296 MPa and 3263 MPa along with an ultra-large fracture strain of 65% under compression. Meanwhile, they display low elastic modulus of 37–48 GPa. The high-performance titanium alloys without toxic elements show high potential for application as biomaterials.     

Ferroelectric and piezoelectric properties of [(Ba1−3x/2Bix)0.85Ca0.15](Ti0.90Zr0.10)O3 lead-free piezoelectric ceramics

Bismuth-modified barium calcium zirconate titanate ceramics [(Ba_1?3x/2Bi_x)_0.85Ca_0.15](Ti_0.90Zr_0.10)O₃ (BBCTZ) have been prepared by the conventional solid-state reaction method, and effects of Bi content on the electrical properties of BBCTZ ceramics were systematically investigated. BBCTZ ceramics endure a phase transition from the coexistence of rhombohedral and tetragonal phases, a tetragonal phase, to a cubic phase with increasing Bi content. The Curie temperature, the remanent polarization, and the dielectric loss of BBCTZ ceramics gradually decrease with increasing the Bi content. The BBCTZ ceramic with x = 0.0075 exhibits an optimum electrical behavior: d₃₃ ～ 361 pC/N and k_p ～ 40.2%.     

Facile synthesis of cubic fluorite nano-Ce1−xZrxO2 via hydrothermal crystallization method

Nano-Ce_1?xZr_xO₂ (x = 0.15, 0.25, 0.5) were synthesized via co-precipitation using NH₄OH as precipitant and hydrothermal crystallization. The XRD results confirmed that the cubic fluorite nano-Ce_1?xZr_xO₂ can form in NH₄OH solution (pH > 10) at 150 °C for 12 h, and well crystallized 20–50 nm nano-Ce_1?xZr_xO₂ were obtained at 200 °C for 22 h. The crystal growth of Ce_1?xZr_xO₂ was suppressed under higher OH^? concentration and crystallite size decreased with increasing concentration of NH₄OH. Ce3d XP spectra showed that the main valence state of the cerium on Ce_1?xZr_xO₂ surface is +4, and substituting Ce⁴⁺ with Zr⁴⁺ has no obvious influence on Ce³⁺/Ce⁴⁺ ratio.     

Investigation of glass-forming ability,deformation and corrosion behavior of Ni-free Ti-based BMG alloys designed for application as dental implants

We developed new Ti-based bulk metallic glassy (BMG) alloys in Ti–Zr–Pd–Cu–Sn system without Ni element for application as biomaterials. These BMG alloys have a high potential to be applied as metallic biomaterials in various forms, such as melt-spun ribbons and cylindrical rods with a diameter of 4 mm. We also investigated of new Ti-based BMG alloys with higher glass-forming ability (GFA) for medical market as dental implants. These Ti-based BMG alloys do not contain Ni, Al and Be elements which are well known to be harmful for human body. In particular, a rod sample of the Ti_44.1Zr_9.8Pd_9.8Cu_30.38Sn_3.92Nb₂ BMG alloy with a diameter of 3 mm produced by copper mold casting exhibits a compressive strength of 1990 MPa and a Young's modulus of 99 GPa. In addition, the Ti_44.1Zr_9.8Pd_9.8Cu_30.38Sn_3.92Nb₂ BMG shows a large supercooled liquid region of 62 K and a reduced glass-transition temperature, T_rg( = T_g / T_m) of 0.61. The high thermal stability of the supercooled liquid allowed the fabrication of cylindrical rod specimens up to 5 mm in diameter. Thus the studied alloy exhibits high glass-forming ability (GFA) and a large size enough to be used for dental implants. The Ti_44.1Zr_9.8Pd_9.8Cu_30.38Sn_3.92Nb₂ BMG alloy also has a high corrosion resistance and is passivated at the lower passive current density of approximately 10^? 2 A m^? 2, 10^? 3 A m^? 2 and 10^? 2 A m^? 2, in 1 mass% lactic acid, PBS (phosphate-buffered saline without calcium and magnesium salts solution) and HBSS (Hank's balance salt solution without calcium, magnesium and phenol red), respectively, at 310 K, which are lower than those of pure Titanium and Ti–6Al–4V alloy.     

Experimental investigation and thermodynamic calculation of the phase equilibria in the Cu–Mo–Ni ternary system

The phase equilibria at 900 °C, 1000 °C, 1100 °C, 1200 °C and 1300 °C in the Cu–Mo–Ni system were experimentally determined by means of optical microscopy (OM), electron probe microanalyzer (EPMA) and X-ray diffraction (XRD) on the equilibrated alloys. The experimental results firstly found that the fcc-type miscibility gap exists at 900 °C, 1000 °C, 1100 °C and 1200 °C in the Cu–Mo–Ni system, and the solubility of Cu in the MoNi phase at 900 °C, 1000 °C, 1100 °C and 1200 °C are about 0.5 at.%, 1.5 at.%, 1.7 at.% and 4.0 at.%, respectively. The as-cast Cu₂₀Mo₂₀Ni₆₀ (at.%), Cu₂₀Mo₃₀Ni₅₀ (at.%), Cu₁₀Mo₆₀Ni₃₀ (at.%), Cu₇₀Mo₁₀Ni₆₀ (at.%), Cu₂₀Mo₆₀Ni₂₀ (at.%) and Cu₈₀Mo₁₀Ni₁₀ (at.%) alloys appear the separated macroscopic morphologies, which are caused by the liquid phase separation on cooling, while the as-cast Cu₁₀Mo₂₅Ni₆₅ (at.%), Cu₃₂Mo₅Ni₆₃ (at.%) and Cu_30.7Mo_6.3Ni₆₃ (at.%) alloys show the homogenous microscopic morphologies. On the basis of the experimental data investigated by the present and previous works, the phase equilibria in the Cu–Mo–Ni system were thermodynamically assessed by using CALPHAD (Calculation of Phase Diagrams) method, and a consistent set of the thermodynamic parameters leading to reasonable agreement between the calculated results and experimental data was obtained.     

Investigation of magnetic properties of Fe61Co8Zr4−xY2+xNi5Nb5B15 amorphous alloys (x = 0, 1) in the form of ribbons

Amorphous Fe₆₁Co₁₀Zr_4?xY_2+xNb₅B₁₅ (x = 0, 1) samples in the form of a ribbon with a thickness of approximately 30 μm and a width of about 4 mm have been investigated. The ribbons were obtained by a single roller melt-spinning method with the wheel linear velocity equal to 35 m/s. Microstructural studies, using X-ray spectroscopy, confirmed that samples in the as-quenched state were fully amorphous. Measurements carried out using a vibrating sample magnetometer allowed values of coercivity and saturation magnetization to be obtained. On the basis of performed measurements, it can be stated that Fe₆₁Co₈Zr₄Y₂Ni₅Nb₅B₁₅ alloy exhibits superior soft magnetic properties compared with the Fe₆₁Co₈Zr₃Y₃Ni₅Nb₅B₁₅ alloy. The former alloy possesses: a higher value of saturation magnetization, almost double the value of magnetic permeability, approximately half the value of coercivity and substantially smaller core losses than the latter alloy.     

Mössbauer study on amorphous and nanocrystalline (Fe1−xCox)86Hf7B6Cu1 alloys

As-quenched and nanocrystalline HITPERM-type (Fe_1−xCo_x)₈₆Hf₇B₆Cu₁ alloys were investigated by conventional Mössbauer spectroscopy. The spectrum of as-quenched alloy presents a typical broadened and overlapped sextet, which confirms that the as-quenched alloy in fully amorphous state. After nanocrystallization, each spectrum of the alloys studied consists of three components: crystalline phase, interface and residual amorphous matrix except x = 0.8 alloy. Co addition increases the hyperfine field and the maximum value exhibits in the x = 0.2 alloy. The Fe concentration in bcc-FeCo crystals and the fraction of crystalline phase influenced by Co addition are opposite. The forming of boride phases after prolonged annealing decline the soft magnetic properties of the alloy studied.     

Porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2: A novel strategy towards making ultrahigh temperature ceramics thermal insulating

Transition metal diborides based ultrahigh temperature ceramics (UHTCs) are characterized by high melting point, high strength and hardness, and high electrical and thermal conductivity. The high thermal conductivity arises from both electronic and phonon contributions. Thus electronic and phonon contributions must be controlled simultaneously in reducing the thermal conductivity of transition metal diborides. In high entropy (HE) materials, both electrons and phonons are scattered such that the thermal conductivity can significantly be reduced, which opens a new window to design novel insulating materials. Inspired by the high entropy effect, porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ is designed in this work as a new thermal insulting ultrahigh temperature material and is synthesized by an in-situ thermal borocarbon reduction/partial sintering process. The porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ possesses high porosity of 75.67%, pore size of 0.3–1.2 μm, homogeneous microstructure with small grain size of 400–800 nm, which results in low room temperature thermal diffusivity and thermal conductivity of 0.74 mm² s⁻¹ and 0.51 W m⁻¹ K⁻¹, respectively. In addition, it exhibits high compressive strength of 3.93 MPa. The combination of these properties indicates that exploring porous high entropy ceramics such as porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ is a novel strategy in making UHTCs thermal insulating.     

Plastic deformation behaviors of Ni- and Zr-based bulk metallic glasses subjected to nanoindentation

Plastic deformation behaviors of Ni₄₂Ti₂₀Zr_21.5Al₈Cu₅Si_3.5 and Zr₅₁Ti₅Ni₁₀Cu₂₅Al₉ bulk metallic glasses at room temperature were studied by nanoindentation testing and atomic force microscopy under equivalent indentation experimental conditions. The different chemical composition of these two bulk metallic glasses produced variant tendencies for displacement serrated flow to occur during the loading process. The nanoindentation strain rate was calculated as a function of indentation displacement in order to verify the occurrence of displacement serrated flow at different loading rates. Atomic force microscopy revealed decreasing numbers of discrete shear bands around the indentation sites as loading rates increased from 0.025 to 2.5 mNs^− 1. Variations in plastic deformation behaviors between Ni and Zr-based glasses materials can be explained by the different metastable microstructures and thermal stabilities of the two materials. The mechanism governing plastic deformation of these metallic glasses was analyzed in terms of an established model of the shear transformation zone.