The metallic glass former Pd-Ni-P is well known for its pronounced stability against crystallization. Samples of this alloy vitrify completely at low cooling rates down to 0.1 K/s. The addition of copper to this alloy system reduces further the crystallization kinetics significantly. Investigations on critical cooling rates were performed on Pd-Cu-Ni-P alloy by means of isothermal nucleation experiments. The results indicate a critical cooling rate in the order of 5.10−3 K/s, which is the lowest one presently known for metallic glass-formers. The high stability against crystallization during cooling allows for simultaneous measurements of its thermodynamic properties within the entire temperature range from the regime of the liquid to the glassy state. Heat capacity measurements were carried out by differential heat-flow calorimetry and the coefficient of thermal expansion was determined by applying sessile drop technique. The results can be described within the free-volume model.

We have studied plastic deformation, including “serrated flow,” of bulk metallic glasses under quasi-static uniaxial compression. The deformation response is essentially elastic-perfectly plastic, but the “plastic” deformation actually consists of sections of elastic loading separated by abrupt load drops. The load drops are due to the formation of shear bands, which represent the primary mechanism of plastic deformation

In Zr-Ti-Cu-Ni-Al bulk metallic glasses, fracture occurs after about 1-2% plastic strain, but in Zr-Ta-Cu-Ni-Al metallic glass the plastic strain to failure can be as large as 6-7%. The difference appears to be due a strong tendency for the shear bands in this alloy to branch. The branching presumably reduces the stress concentration on the shear bands, retarding the onset of fracture. No evidence is seen for the formation of crystalline phases in this alloy.

The structure, the soft magnetic properties and the core losses for Fe-Zr-Nb-B(-Cu) nanocrystalline alloys were investigated. It has been already reported that the typical ternary nanocrystalline Fe90Zr7B3 and Fe84Nb7B9 alloys exhibit good soft magnetic properties and a small negative and a small positive magnetostriction (λs), respectively. The soft magnetic properties of the nanocrystalline Fe84–90(Zr, Nb)7B3–9 quaternary alloys with mixed compositions of Fe90Zr7B3 and Fe84Nb7B9 cannot be improved whereas very small magnetostrictions are obtained. The quaternary alloys with 7 at% (Zr + Nb) have structures of an amorphous with α-Fe phases on the free and roll-contacted surfaces at an as-quenched state. The crystalline surface layers deteriorate the soft magnetic properties at a crystallized state. The high saturation magnetic induction of 1.64 T, the high permeability of 60,000 at 1 kHz and the very low core loss of 0.9 W/kg at 1.4 T and 50 Hz are obtained for the Fe85.5(Zr1/3Nb2/3)6B8.5 alloy containing 6 at% of (Zr + Nb) content with nearly zero-λs produced by crystallizing the single amorphous phase without the crystalline surface layers. The thermal stability of the core loss of the quaternary alloy is significantly higher than that of the Fe78Si9B13 amorphous alloy. The crystalline surface layers of the Fe84–90(Zr, Nb)7B3–9 quaternary alloys disappear by 1 at% Cu addition, which results in significant improvement of the soft magnetic properties at a crystallized state.

Effects of boron (B) on crystallization, glass forming ability (GFA) and magnetic properties of amorphous Fe91−xZr5BxNb4 (FZBN) were studied in the B content ranging from 0 to 36 at%. The amorphous FZBN crystallizes to μ-Fe in primary crystallization mode at B≤ 20 at% and to Fe-Zr-B-Nb cubic phase with lattice constant of 1.0704 nm and μFe in eutectic mode in the range from 22 at% to 30 at% B. The change of crystallization mode is accompanied by the sharp enhance of glass transition and crystallization temperatures. The GFA of FZBN alloys changes with B content and reaches the largest near 27.5 at % B. Curie temperature (Tc) and magnetization at room-temperature (MRT) and 78K (M78K) for the amorphous FZBN increase with increasing B content. However, the change laws of the Tc and the magnetizations are somewhat different in the composition ranges of 5 to 20 at% B and 22.5 at% to 30 at% B.

The large values over 300 kA/m at room temperature were found for the coercive field of Nd50Fe40Si10−xAlx (x = 0; 10) amorphous melt-spun ribbons and cast rods. The dependence of the coercive field on the thickness and the preparation method, namely the cooling rate, is ascribed to the existence in the amorphous matrix of very small ferromagnetic clusters, which approach of a single magnetic domain. Coercivity increases substantially up to 600 kA/m by decreasing the temperature down to 200 K, although the measurements are carried out in low fields (up to 800 kA/m). The Mässbauer spectra can be fitted to two Fe sites with magnetic moments ranging from 1.25 to 2.20νB depending on the additional element.

With the aim of developing a bulk glassy Fe-based alloy with good soft magnetic properties by the powder metallurgy technique, we have applied the pulse current sintering technique to a Fe70Al5Ga2P9.65C5.75B4.6Si3 glassy alloy powder with a large supercooled liquid region of 60K before crystallization. The existence of the supercooled liquid region was found to enable us to form a bulk glassy alloy with a very high relative density of 99%. The resulting bulk glassy alloy exhibits good soft magnetic properties, i.e., 1.17T for flux density at a field of 800A/m, 12.0A/m for coercive force and 8000 for maximum permeability which are much superior to those for the bulk amorphous Fe-Si-B alloy prepared by the same sintering method. The much better soft magnetic properties for the multicomponent Fe-based bulk alloy are attributed to the combination of the high relative density and the unique amorphous structure with the features of high packing density and long-range homogeneous atomic configurations. The first success of forming the bulk amorphous alloy with good soft magnetic properties by the powder metallurgy technique is expected to enable us to use as practical soft magnetic materials.

Bulk metallic glasses exhibit extraordinary strength and elastic properties, but the lack of extensive plastic deformation and the catastrophic nature of failure limit the usefulness of the monolithic alloy. This work presents an overview of the results of fracture and fatigue crack growth experiments for a bulk metallic glass matrix composite with a Zr-Ti-Nb reinforcement phase precipitated in situ. The composite exhibits stable crack growth at stress intensities nearly double the fracture toughness of the monolithic glass. This is associated with the formation of a distributed damage zone at the crack tip. While the second phase had a marked effect on the fracture behavior, there was very little change to the fatigue crack growth results. Fractography suggests that the second phase particles are too small to cause crack bridging or significantly change the crack path.

A new Ag-Sm-Fe nanocomposite material was obtained by high-energy ball-milling of elemental μ-Fe powder and melt-spun Ag-Sm flakes. Magnetic Fe nanocrystals were thus embedded in a paramagnetic Ag-based matrix. Synchrotron radiation powder diffraction and temperature dependent Mössbauer spectroscopy were used to study the nanometer scale Fe/Ag(Sm) intermixing mechanism. The evolution of the average grain size and microstrains in the Ag-based matrix vs. the milling time were obtained from the analysis of the X-ray diffraction linewidths. For reference Fe powder samples, a bimodal grain size distribution was evidenced by Mössbauer spectroscopy. The magnetic behaviour of the Fe nanocrystals was analysed with respect to the superparamagnetic relaxation effect and collective excitations. The nanometer scale intermixing of Fe nanocrystals in the Ag-based matrix is completed when the Fe and matrix grains have comparable dimensions.

An in-situ electron diffraction structure analysis of La55Al25Ni20in the supercooled liquid temperature range (ΔTx) revealed a gradual structural change with a local phase separation due to strong atomic correlations especially of La-La and Al-Ni. On the basis of the structural data, structure models corresponding to the structures at temperatures between Tg and Tx were constructed using molecular dynamics (MD) simulation technique. These constructed structure models were then utilized for MD simulations to understand plastic deformation in the supercooled liquid state under a constant strain-rate. A larger elongation was obtained for the structure in the middle of the ΔTx range, but for the structure near Tx the elongation was relatively smaller which was supposed to be due to the local phase separation. These simulation results correspond well to the experimental elongation behaviors in the superplastic deformation that the elongation is enhanced in the middle of ΔTx but suppressed as the temperature is increased towards Tx.

In order to gain insight into the influences of formation of an icosahedral phase in Zr-based metallic glasses on the physical properties, thermal and electrical properties of Zr70Ni10Pd20 metallic glass were investigated. From DSC analyses, activation energies for the phase transition from an amorphous to an icosahedral phase and from the icosahedral to a crystalline (Zr2Ni) phase were estimated to be 3.42 and 3.07 eV, respectively. The effect of the phase transformations on the electrical resistivity was successfully observed; the resistivity clearly exhibits an increase and a decrease corresponding to the transitions from the amorphous to the icosahedral phase and from the icosahedral to the crystalline Zr2Ni phase, respectively. It is concluded that the increase of the resistivity upon the precipitation of the icosahedral phase is due to an increase of the volume fraction of the icosahedral grains, which possess higher resistivity.

The thermophysical properties in the stable and undercooled liquid phase of a series of Zr- based metallic glass forming alloys have been investigated under the condition of reduced gravity on board spacelab. Properties measured included the specific heat capacity and the enthalpy of fusion, the electrical resistivity, the total hemispherical emissivity, and the thermal transport properties. Results for the bulk metallic glass forming alloys indicate a pronounced change in chemical short range order in the liquid phase as function of temperature.

Local atomic structures around Zr and Pt in a quasicrystalline Zr80Pt20 alloy, and amorphous and quasicrystalline Zr70Ni10Pt20 alloys have been determined by the anomalous x-ray scattering (AXS) method. A distinct prepeak observed in an intensity profile of the amorphous Zr70Ni10Pt20 alloy indicates existence of strong chemical short-range order (CSRO) clusters in the amorphous phase. Total coordination numbers around Zr and Pt in a nearest neighbor region in both alloys have been evaluated. The values around Pt are almost equal to 12 in the amorphous and quasicrystalline states suggest formation of icosahedral clusters around Pt. Some of crystalline structures formed from the quasicrystalline phases by annealing consist of icosahedral clusters of Zr and Ni atoms, or polyhedral clusters of Zr and Pt atoms similar with icosahedral clusters. The present result appears to support that the phase transformation from the amorphous to the crystal through the quasicrystal is explained by the icosahedral CSRO clusters in the amorphous and quasicrystalline states.

Diffusion in metallic glasses and in the supercooled liquid state is of considerable interest not only from the technological point of view but also in terms of fundamental science, particularly in connection with the glass transition. Within the framework of the mode coupling theory the glass transition is a kinetic phenomenon characterized by the arrest of viscous flow at a critical temperature Tc well above the calorimetric glass transition temperature Tg. Below Tc the theory predicts cooperative hopping processes. We present results from isotope effect measurements which indeed confirm the highly collective nature of diffusion in metallic glasses and suggest cooperative hopping processes to be closely related to the universal low-frequency excitations as observed in recent molecular dynamic simulations. In accord with the mode coupling scenario these cooperative hopping processes are also observed in the supercooled liquid state of the new bulk metallic glasses well above Tg. The reported kink in the Arrhenius plot for diffusion of various elements is shown to be related to structural changes above Tg, e.g., an increase in free volume as probed by positron annihilation, but not to a change in the diffusion mechanism. Measurements of the activation volume of diffusion indicate that, depending on the structure of the glass, cooperative hopping may take place without assistance of thermally generated defects or via delocalized thermal defects. Moreover, we provide evidence of the existence of an opposite Kirkendall effect in interdiffusion between certain amorphous alloys that combine slow diffusion via thermal defects and fast direct diffusion.

The crystallization behavior of a series of alloys in the Zr-Ti-Cu-Ni-Be system is studied. Upon cooling from the molten state with different rates, alloys with compositions ranging along a tie line from (Zr75Ti25)55(Ni45Cu55)22.5Be22.5 (Vit1) to (Zr85Ti15)55(Ni57Cu43)17.5Be27.5 (Vit4) show a continuous increase in the critical cooling rate to suppress crystallization. In contrast, thermal analysis of the same alloys shows that the undercooled liquid region, the temperature difference between the glass transition temperature and the crystallization temperature, is largest for compositions midway between the two endpoints, revealing that glass forming ability does not correlate with thermal stability. The relationship between the change in glass forming ability and thermal stability is discussed with reference to a chemical decomposition process.

Nanocrystalline Fe85Zr7B6Cu2 and Fe87.2Zr7.4B4.3Cu1.1 (at. %) samples have been obtained by annealing Melt-spun ribbons for 1hr at various temperatures in the range 593K to 953K. Structural characterization by means of X-ray diffraction and thermomagnetic analyses reveal the manifestations of Fe nanocrystals embedded in an amorphous matrix. The coercive field has been measured by a Förster coercimeter at temperatures ranging between 50 K and 300 K, and the room temperature domain structure has been monitored by magneto-optical Kerr effect. Both, the as cast as well as the sample annealed above 813K display soft magnetic properties at room temperature, exhibiting a coercive field below 10 A/m, and wide regular domains. In contrast, the samples annealed at 750 K, corresponding to the beginning of the crystallization process, undergo a magnetic hardening, showing higher coercive fields (up to 150 A/m for Fe87.2Zr7.4B4.3Cu1.1) and a dull domain pattern. When these magnetically harder samples are cooled, their coercivity is reduced. Thus, the magnetic hardening is attributed to the exchange decoupling between crystallites, due to the proximity of the Curie temperature of the amorphous phase.

This paper reviews work on the wear of metallic glasses in general, as well as reporting recent results on the abrasive wear of bulk metallic glasses. The distinctive mechanical properties of metallic glasses make their wear resistance of fundamental interest. Metallic glasses, and the partially or fully crystalline materials derived from them, can have very good resistance to sliding and abrasive wear. Standard wear laws are followed, with behaviour similar to that of conventional hardened alloys. The microhardness and abrasive wear resistance are measured for four bulk metallic glasses (based on La, Mg, Pd or Zr). The hardness and wear resistance correlate well with the Young's modulus of the glass.

The thermal expansion coefficients of glass-forming Zr-based alloys were measured in the melt, the undercooled liquid and the glassy/crystalline state. Due to the high reactivity of the liquid material the experiments were performed containerlessly in an electrostatic levitator. We used an optical method where the samples were imaged with a high-resolution CCD- camera and the volume of the samples was evaluated by digital image processing. The coefficients of thermal expansion in the liquid and in the solid state could be determined from the volume versus temperature curves. The results can be compared with measurements in the electromagnetic levitation facility TEMPUS performed under microgravity conditions in the mission MSL-1 and ground based DMA-measurements. The thermal expansion data can be interpreted in terms of the free volume model.

The constitution of the 66.67 at.% Zr isopleth of the Zr-Cu-Ni-Al quaternary system has been studied, utilizing X-ray diffraction and electron probe microanalysis to establish phase equilibria at 800°C, and differential scanning calorimetry to study the liquidus hypersurface. As would be expected in a four-component system, phase equilibria were found to be complex. However, it was determined that the isoplethal subsection Zr2Cu-Zr2Ni is pseudobinary, and subsequently a large portion of the quaternary isopleth is pseudoternary, comprising equilibria involving the phases Zr2Cu, Zr2Ni and Zr6NiAl2. Moreover, these three phases participate in a pseudoternary eutectic reaction: L → Zr2Cu + Zr2Ni + Zr6NiAl2 at 852°C. Utilizing the thermal analysis data, the composition of the eutectic point was estimated to lie very near that of the well-known bulk metallic glass forming alloy Zr65Cu17.5Ni10Al7.5. The compositional proximity of a “deep” eutectic valley to this quaternary alloy thus provides a thermodynamic rationale for its high glass forming ability.

Glass-forming ability, thermal stability and nucleation behavior of a Pd40Cu30Ni10P20 alloy prepared using a high purity polycrystalline phosphorus are investigated. The critical cooling rate for glass formation for the high purity alloy is the same as that for the previous result, but the improvement of undercooling reaches about 80 K as compared with the fluxed ordinary alloy. In comparison with the non-fluxed alloy, the solidified structure of the present highly purified alloy is significantly different. The non-fluxed sample shows the characteristic “island-like” structure consisted of acicular fcc-Pd2Ni2P solid solution and Cu3Pd intermetallic compound. These acicular phases appear to be caused by the growth of quenched-in nuclei. In the isothermal experiment, nucleus density exhibits time dependence even at 683 K near the nose temperature. It is assumed that the crystallization behavior for the highly purified alloy is closer to homogeneous nucleation from quenched-in nuclei dominant behavior. In order to investigate the nucleation behavior, in-situ TEM observation was carried out. Spherical Pd15P2 particle with a diameter about 15 nm is observed, and this spherical region repeats generation and annihilation during isothermal annealing. The reason for the high glass-forming ability is discussed on the basis of the obtained results.

Continuous amorphous wires with high strength and good ductility have been produced for the Zr55Al10Ni5Cu30and Zr55Ti5Al10Ni10Cu20alloys by a rotating disk casting technique. The rotating disk, which is made of copper, has a semicircular groove on its upside surface. The amorphous wires have a nearly circular cross-section, smooth peripheral surfaces and diameters in the range from 0.5 to 1.5mm. The amorphous alloy wires have good bending ductility. The maximum tensile strength, μf, is 1600 MPa for Zr55Al10Ni5Cu30 amorphous wire and 1900 MPa for Zr55Ti5Al10Ni10Cu20 amorphous wire, respectively. The success of forming amorphous alloy wires in a continuously long form by the present casting method is important for the further extension of application fields of amorphous alloys.