Influence of minor Si addition on the glass-forming ability and mechanical properties of Pd40Ni40P20 alloy

The influence of a minor Si addition on the glass-forming ability and mechanical properties of Pd₄₀Ni₄₀P₂₀ alloy was investigated. It is suggested that the minor Si addition can adjust the composition to be closer to eutectic, which favors a large undercooling. Furthermore, Si addition led to an enhancement in the ductility of Pd–Ni–P bulk metallic glasses. Simultaneously it is of great interest that there are nanoscale and microscale wavy steps observed on the fracture surface of Pd₄₀Ni₄₀Si₄P₁₆ metallic glass. It is suggested that a quickly running crack dissipates excess energy in terms of stress wave, leaving such wavy traces on the fracture surface of the deformed Pd-based metallic glass.     

Thermodynamic approach to free volume kinetics during isothermal relaxation in bulk Pd–Cu–Ni–P20 glasses

Isothermal relaxation behavior just under glass transition region was investigated for bulk Pd₄₀Ni₄₀P₂₀ and Pd_42.5Cu₃₀Ni_7.5P₂₀ metallic glasses. The densification of the bulk sample during relaxation was examined directly by density measurement using conventional Archimedean technique. The density of as-quenched Pd₄₀Ni₄₀P₂₀ increased monotonously with time. From the density data of Pd₄₀Ni₄₀P₂₀ glass, the free volume relaxation was examined and the kinetics was well described by a stretched exponential function with Kohlrausch exponent less than unity. These glasses also showed a clear two-step relaxation that may be a feature peculiar to bulk metallic glasses.     

Structural behaviour of Pd40Cu30Ni10P20 metallic glass under high pressure

The structural behaviour of Pd₄₀Cu₃₀Ni₁₀P₂₀ bulk metallic glass as a function of hydrostatic pressure up to 47.4 GPa was investigated by means of in situ high energy synchrotron X-ray diffraction patterns. Monotonic changes are observed in the diffraction data without any indication of a phase transition. In real space all maxima of the atomic pair correlation function including the nearest neighbour distance are decreasing and scale with pressure. The volume as function of hydrostatic pressure is extracted from the diffraction data. For the largest hydrostatic pressure of 47.4 GPa the volume is reduced by 18%. The bulk modulus B₀ = 178 GPa was calculated from the diffraction data. The dependence of volume on pressure of Pd₄₀Cu₃₀Ni₁₀P₂₀ metallic glass can be well described by the Birch–Murnaghan equation of state.     

Pd20Pt20Cu20Ni20P20 high-entropy alloy as a bulk metallic glass in the centimeter

A Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ bulk metallic glass (BMG) with a high-entropy (HE) alloy composition and a maximum diameter of 10 mm was fabricated by fluxed water quenching. The system and composition of the Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ alloy were determined from a prototype ternary Pd₄₀Ni₄₀P₂₀ BMG in accordance with two strategic alloy designs of (1) HE alloy defined by an equi-atomic alloy with five or more elements and (2) exchangeability of the constituent elements with a similar chemical nature in the periodic table. Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ HE-BMG had a supercooled liquid range of 65 K and a reduced glass transition temperature of 0.71. Successful formation of Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ HE-BMG is significant to develop new alloys for HE alloys and BMGs.     

Dynamic response of a Pd40Ni40P20 bulk metallic glass in tension

Tensile behavior of a bulk metallic glass Pd₄₀Ni₄₀P₂₀ was characterized under both quasi-static and dynamic strain rate conditions. No major difference was observed. Multiple shear bands formed in samples tested at the dynamic strain rate. However, shear band interaction appears to have an insignificant effect on the plasticity of the alloy.     

Multicomponent nanoporous metals prepared by dealloying Pd80−xNixP20 metallic glasses

We report the formation of Pd-based multicomponent nanoporous metals by electrochemically dealloying the Pd_80−xNi_xP₂₀ metallic glasses. It was found that both the compositions and the pore sizes of the nanoporous metals can be tailored by the Ni content in the glassy Pd_80−xNi_xP₂₀ precursors. Moreover, the Pd-based nanoporous metal with the optimized composition and the pore size exhibits better electrocatalytic performance towards the oxidation of the formic acid when compared with the commercial Pd/C catalyst.     

Local atomic structure of Pd–Ni–P bulk metallic glass examined by high-resolution electron microscopy and electron diffraction

Structural fluctuation in a Pd₄₀Ni₄₀P₂₀ bulk metallic glass is investigated by transmission electron microscopy and electron diffraction. Local atomic ordered regions with a fcc-(Pd,Ni) type structure was sharply imaged by a high-resolution electron microscopy (HREM) attached with a Cs-corrector. Interference function for the glassy state was obtained from electron-diffraction intensity profiles using energy-filter and imaging-plate techniques. We used a reverse Monte Carlo (RMC) simulation method to develop a realistic structure model. The model consists of a dense-random-packing structure, in which an fcc ordered region with Pd, Ni, and P atoms was embedded. The structure model is consistent with the diffraction and HREM results. In Voronoi polyhedral analysis of the RMC simulated structure, P-centered (Pd,Ni)-P trigonal prisms are found primarily in the matrix structure embedding the fcc-cluster. Around Pd and Ni atoms deformed-fcc type polyhedra were frequently observed. From these local structural features, nanoscale phase separation was revealed to occur during the glass formation.     

Assessment of rheological and thermodynamic properties of the Pd40Ni40P20 bulk metallic glass around glass transition using an indentation creep technique

The thermodynamic and rheological properties of the Pd₄₀Ni₄₀P₂₀ bulk metallic glass are explored by means of an indentation creep technique around the glass transition. We have developed a dedicated instrumented indentation apparatus allowing to assess the mechanical properties at elevated temperatures. The analysis of results is made possible by using the viscoelastic solutions of contact mechanics. We also analyse the thermodynamics of creep around glass transition to estimate the activation free energy changes from the activation free enthalpy changes via the shear modulus – temperature data. The shear viscosity values extracted using this technique allow for the derivation of activation energies (free enthalpy 210 kJ/mol, enthalpy 456 kJ/mol, entropy 410 J/mol/K) for the flow process. All these properties were found to closely match with those obtained using conventional techniques for viscosity measurements. Compared to the latter, the indentation creep technique requires small volumes and samples are easy to prepare. It is therefore expected that such a technique might be employed for the study of glass transition in metallic glasses.     

Pd20Pt20Cu20Ni20P20 高熵金属玻璃的热稳定性和热塑成形性

采用差示扫描量热法、X射线衍射和热力学分析研究了Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀高熵金属玻璃（HEMG）的热稳定性和热力学性能。结果表明,与其他经典贵金属基金属玻璃相比,Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ HEMG具有相当的性能和鲜明的特点。     

Low temperature heat capacity and electrical resistivity of the Ti40Zr25Cu12Ni3Be20 glass forming alloy

Gaining knowledge of electronic structure provides useful information for understanding unique properties of metallic glasses. In this study, low temperature heat capacity and electrical resistivity of the glass forming Ti₄₀Zr₂₅Cu₁₂Ni₃Be₂₀ alloy with glassy, quasicrystalline, or crystalline states below 300 K were investigated. The precipitation of the I-phase was revealed in the initial crystallization process of the Ti₄₀Zr₂₅Cu₁₂Ni₃Be₂₀ BMG. The glassy state has higher state density at Fermi level than its quasicrystalline or crystalline counterparts, which could be interpreted by the electron localization in glassy state as well as a pseudo-Brillouin zone formed nearby Fermi surface in the quasicrystalline state. None of the three states showed superconductivity phenomenon down to 1.9 K. Temperature dependence of resistivity for both the glassy state and the quasicrystalline state exhibited negative temperature coefficient and was less sensitive to temperature than the crystalline state. The electrical resistivity showed a smaller value for the I-phase than that for the glass due to lower structural integrity of I-phase. Electrical resistivity as well as heat capacity measurements indicated that the electronic structure of the quasicrystalline state is quite similar to glassy state but far from crystalline state.     

Elastic constants of amorphous and single-crystal Pd40Cu40P20

We have measured the adiabatic second-order elastic constants of amorphous Pd₄₀Cu₄₀P₂₀ (isotropic, two independent elastic constants) and single-crystal Pd₄₀Cu₄₀P₂₀ (tetragonal, six independent elastic constants) over the range 3.9 < T < 300 K. Below ∼20 K, the elastic constants of single-crystal Pd₄₀Cu₄₀P₂₀ vary as C(T) = C(0)[1 − bT² − dT⁴], which is the same temperature dependence found in metallic elements. In contrast, below ∼20 K the elastic constants of amorphous Pd₄₀Cu₄₀P₂₀ vary as C(T) = C(0¹)[1 − aT]. The bulk modulus of amorphous Pd₄₀Cu₄₀P₂₀ is approximately 2% lower than that of crystalline Pd₄₀Cu₄₀P₂₀, whereas the shear modulus of the glass is 13–36% lower than the four independent shear moduli of the tetragonal crystal. The lower moduli of the glass are best explained by additional atomic displacements, beyond those experienced by the atoms in a crystal, that occur because the atoms in glasses do not occupy centers of symmetry.     

Micromechanisms of serrated flow in a Ni50Pd30P20 bulk metallic glass with a large compression plasticity

Serrated flow is a characteristic feature of plastic deformation of bulk metallic glasses (BMGs) with a large compression strain. However, the underlying mechanisms of the discrete plasticity in the disordered solids have been debated for many years. Here, we report mechanical behavior and microstructural evolution of a Ni₅₀Pd₃₀P₂₀ BMG subjected to uniaxial compression testing. Extensive nanocrystallization within shear bands and in the vicinity of fracture surfaces was observed and various crystal defects, including dislocations, twins and kink bands, were detected in the resultant nanocrystals. These observations suggest a microscopic mechanism of the serrated flow of the BMG, i.e. the stress drop is caused by local strain-softening and the arrest of shear bands is associated with in situ nanocrystallization.     

Pd40Ni40Si5P15 bulk metallic glass properties variation as a function of sample thickness

This work presents a comparative study of different properties variation of Pd₄₀Ni₄₀Si₅P₁₅ bulk metallic glass (BMG), namely: density, hardness, relaxation enthalpy and mechanical properties as a function of the sample thickness. The samples were produced in the form of a long pyramid by conventional Cu-mold casting in an Ar atmosphere. The results illustrate significantly different sensitivity of these properties of the glassy phase to the cooling rate. The difference in crystallization behavior is also discussed.     

Hydrogenation properties of shape memory Ti(Ni,Pd) compounds

The effect of Pd substitution on the crystal structure and hydrogenation properties of TiNi compound has been investigated. Ti(Ni,Pd) are pseudo-binary compounds. The unit-cell volumes of B2 (Austenite) and B19 (Martensite) structures linearly increase with Pd substitution in Ti_1.04Ni_0.96?xPd_x samples. The hydrogenation properties of Pd-substituting Ti(Ni,Pd) compounds are not affected by the crystal structure of the parent compounds. For all samples, hydrogen absorption occurs without showing any clear plateau pressure in Pressure-Composition-Isotherm (PCI) curves. All hydrided samples crystallise in the tetragonal I 4/mmm space group. At 6 MPa of hydrogen pressure and T = 423 K, the hydrogenation capacity of Ti(Ni,Pd) compounds reaches 1.52 hydrogen atoms per formula unit (H/f.u.) for x = 0.1 and then gradually decreases with Pd content down to 0.93 H/f.u. for x = 0.5. Ti_1.04Ni_0.86Pd_0.10 sample yields a discharge capacity of 148 mAh/g at C/5 regime when used as negative electrode in Ni-MH battery. The hydrogenation properties of Pd-substituting Ti(Ni,Pd) compounds are discussed in detail by comparison with previous studies on Zr substituting, (Ti,Zr)Ni compounds.     

Hydrogenation of Zr–Cu–Al–Ni–Pd metallic glasses by electrochemical means

Amorphous materials of Zr–Cu–Ni–Al systems have shown attractive electrochemical hydrogen absorption properties. A comparison between Zr₆₀Cu₁₅Al₁₀Ni₁₀Pd₅ and Zr₆₅Cu_17.5Al_7.5Ni₁₀ reveals that the palladium (Pd) increases the hydrogen absorption capacity. Charging melt-spun Zr₆₀Cu₁₅Al₁₀Ni₁₀Pd₅ ribbons electrochemically to different hydrogen-to-metal (H/M) ratios and following the effusion of hydrogen by thermal desorption analysis (TDA) reveals hydrogen desorption from interstitial sites of high energy levels at temperatures below 630 K. Zirconium hydrides are formed above 630 K. At higher temperatures partial desorption of hydrogen occurs. The thermal stability observed with differential scanning calorimetry (DSC) of the amorphous phase has been significantly deteriorated by hydrogen absorption. After hydrogenation, the crystallization behaviour shows suppression of the characteristic quasicrystalline phase and depends on the hydrogen content. Therefore, at low hydrogen concentrations H/M = 0.3, Cu and/or Cu-rich phases are primarily formed while at high hydrogen concentrations H/M ≥ 0.9 Zr-hydride phase(s) are mainly formed.     

Pd71.5Cu12Si16.5金属玻璃的氢相关性能

钯基金属玻璃在氢相关工业中具有潜在的应用价值。在本工作中,我们通过电弧熔炼、铜辊甩带的方法制备了Pd_71.5Cu₁₂Si_16.5 金属玻璃的宽带样品。通过常规X射线衍射仪和短波长X射线应力分析仪的X射线衍射谱确定了样品的完全非晶态结构。在室温、100kPa压力条件下,对样品进行了多次的吸、放氢循环实验。经过10次以上的循环后,样品没有发生破坏,表现出良好的抗氢脆性能。通过气体直接渗透的方法进一步测试了Pd_71.5Cu₁₂Si_16.5 金属玻璃及其同成分晶态合金的氢渗透性能。在金属玻璃的过冷液相区温度范围内,其氢渗透率明显高于晶态相,这一结果由金属玻璃在该区间内的等温保持引入了更多的自由体积进行解释。     

Thermodynamics,kinetics, and crystallization of Pt57.3Cu14.6Ni5.3P22.8 bulk metallic glass

We report on differential scanning calorimetry (DSC) studies to characterize the thermodynamics, kinetics and crystallization processes of the bulk metallic glass-forming alloy Pt_57.3Cu_14.6Ni_5.3P_22.8. The heat capacity of the alloy is measured for the crystalline, glassy and supercooled liquid phases. The heating rate dependence of the glass transition is used to calculate the kinetic fragility. Crystallization kinetics are determined under isothermal conditions and used to construct a time–temperature-transformation (TTT) diagram. The experimentally determined crystallization kinetics are fit to calculate the activation energy for crystallization. Our results suggest that Pt_57.3Cu_14.6Ni_5.3P_22.8 is neither a thermodynamically nor a kinetically stabilized glass former. Other contributions, including the activation energy for crystallization and the use of a flux are considered in the discussion to explain the good glass formability of this alloy.     

The isothermal and isochronal kinetics of the crystallisation of bulk amorphous Pd40Cu30P20Ni10

The amorphous alloy Pd₄₀Cu₃₀P₂₀Ni₁₀ has been produced by water quenching the molten alloy. The kinetics of crystallisation has been measured by means of isothermal and isochronal differential scanning calorimetry. The associated microstructural changes have been analysed using scanning electron microscopy. Special interest has been devoted to the influence of isothermal pre-annealing on subsequent isochronal crystallisation kinetics. By applying appropriate isothermal pre-annealing temperatures, nucleation of the crystalline phases takes place to different extents. Accordingly, the initial state for the subsequent isochronal crystallisation could be changed gradually with respect to the number of pre-existing nuclei. This leads to a gradual change of the mode of nucleation from site saturation to continuous nucleation during the crystallisation. The corresponding change of the kinetic parameters has been used to determine the activation energies of nucleation and growth separately.     

Effects of Nitrogen on the Glass Formation and Mechanical Properties of a Ti-Based Metallic Glass

Effects of nitrogen addition on glass formation and mechanical properties of the Ti42.5Cu40Zr10Ni5Sn2.5metallic glass were systematically investigated. It was found that a small amount of nitrogen addition facilitated the glass formation by suppressing formation of the competing eutectic structure. Unlike large atomic size elements such as Hf and Pd which usually deteriorate specific strength, nitrogen can also increase the specific strength of the current Ti-based BMGs. The results are not only helpful for understanding glass-forming ability in general, but also useful in developing cost-effective, high-performance Ti-based bulk metallic glasses with enhanced glass-forming ability.     

Syntheses and physical properties of quasi-one-dimensional chloro-bridged Ni–Pd mixed-metal MX-chain compounds,Ni1−xPdx(chxn)2Cl3

A series of single crystals of quasi-one-dimensional chloro-bridged Ni–Pd mixed-metal MX-chain compounds, Ni_1−xPd_x(chxn)₂Cl₃ (chxn=1R,2R-diaminocyclohexane) have been obtained by electrochemical oxidation methods. In order to investigate the competition between the electron correlation in the Ni(III) states and the electron–phonon interaction in the Pd(II)–Pd(IV) mixed-valence states in the Ni–Pd mixed-metal compounds, the infrared spectra, resonance Raman spectra, X-ray photoelectron spectra and Auger spectra have been measured. These results show that the Pd(II)–Pd(IV) mixed-valence states are influenced by Ni(III) and gradually approaching to the Pd(III) states with the increase of the Ni(III) components as observed in Br-bridged complexes, Ni_1−xPd_x(chxn)₂Br₃.