Microstructural change by friction stir processing (FSP) is examined in Zr-Al-Cu-Ni bulk metallic glass. The microstructure in the friction zone (FZ) exhibits an amorphous “band-like” structure, and a small number of nanoscale crystalline particles are observed along the “band-like” structure. The change in hardness with the microstructural change is examined and it is revealed that the hardness in FZ greatly increases although the volume fraction of crystalline phase is very limited. The increasing hardness is possibly explained from the combined effect of low temperature annealing during FSP and nano-size of crystalline particles.

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In this study, three Fe-base amorphous alloys with quite different critical cooling rates were subjected to twin-roll strip casting to see the possibility of fabricating amorphous sheet by the same process. Continuous cooling transformation (CCT) diagrams of the alloys were calculated using the heterogeneous nucleation theory coupled with thermal data obtained during cooling to evaluate their critical cooling rates and glass forming abilities (GFAs). It shows that the GFAs calculated by CCT diagram are in agreement with the experimental results, while the well known empirical thermal parameters do not agree with the experimental results. Optimum twin-roll strip casting conditions have been determined based on the calculated critical cooling rates and the simulated thermal behavior of the sheet during twin-roll strip casting.

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We investigated the microstructure and mechanical properties of the porous Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glassy specimens fabricated by a spark plasma sintering process starting from the low sintering temperature, short holding time and rapid cooling. No crystallization within powder particles as well as at the interfaces between powder particles was identified by scanning and transmission electron microscopic observations. The sintered porous bulk metallic glassy specimens exhibited larger plastic strain and lower Young’s modulus than those of the as-cast alloy specimen. The increase in the plastic strain can be related to the pores in the sintered porous bulk glassy samples which generate multiple shear deformation events.

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In the present study, amorphous Mg₄₉Y₁₅Cu₃₆ and Ti₅₀Cu₂₈Ni₁₅Sn₇ alloy powders were synthesized separately by using a mechanical alloying technique. The dual-phase (Mg₄₉Y₁₅Cu₃₆)_100−x(Ti₅₀Cu₂₈Ni₁₅Sn₇)_x (x=0, 10, 20, 30, 40, and 50 vol%) powders were prepared by mixing the corresponding amorphous powders. The amorphous dual-phase powders were then consolidated into bulk metallic glass (BMG) discs. The amorphization status of as-prepared powders and BMG discs was confirmed by X-ray diffraction and by using a differential scanning calorimeter. The microstructure of the BMG discs showed that the Ti₅₀Cu₂₈Ni₁₅Sn₇ phase is distributed homogeneously within the Mg₄₉Y₁₅Cu₃₆ matrix. The (Mg₄₉Y₁₅Cu₃₆)₅₀(Ti₅₀Cu₂₈Ni₁₅Sn₇)₅₀ BMG disc exhibited a relative density of 97.2% and its Vickers microhardness was 526±20 kg/mm².

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Two-type sintered specimens of Zr₅₅Cu₃₀Al₁₀Ni₅ glassy alloy powder blended with and without 10 vol% ZrO₂ ceramic powder, which had the similar relative density, were fabricated by a spark plasma sintering process in order to clarify the reinforced mechanical effect of ZrO₂ particulates in the metallic glassy matrix composite. The structure, thermal stability and mechanical properties of the two-type sintered specimens were investigated. Two-type sintered specimens as well as original metallic glassy powder exhibited similar thermal stability. No crystallization of the metallic glassy matrix was demonstrated during the spark plasma sintering process. The plastic ductility of the sintered Zr₅₅Cu₃₀Al₁₀Ni₅ glassy matrix composite was enhanced by adding the ZrO₂ particulates into the metallic glassy alloy. The improvement was originated from the structural inhomogeneity caused by the micro particles inclusion.

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Pure Cu (99.96%) and pure Zr (99.8%) sheets were stacked and severely deformed up to equivalent strain of 16 by the accumulative roll bonding (ARB) process conducted at RT. The ARB processed sheets showed nanolamellar structure of Cu and Zr. The DSC curves of the ARB processed multi-layers exhibited characteristic exothermic peaks, which were similar to the previous results reported in a mechanical alloying study. When the ARB processed specimen was annealed at 400°C, at which the first exothermic peak appeared, most of the volume transformed into amorphous phase. The ARB processed and then 400°C annealed specimen showed obvious glass transition. That is, there is a possibility to fabricate bulk metallic glass sheet through severe plastic deformation and thermally activated amorphization.

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Low density Ca-Mg-Al-based bulk metallic glasses containing additionally Cu and Zn, were produced by a copper mold casting method as wedge-shaped samples with thicknesses varying from 0.5 mm to 10 mm. The compositions of the alloys were selected using recently developed specific criteria for glass formation. A structural assessment using the efficient cluster packing model was applied and showed a good ability to represent these glasses. Thermal properties of the new metallic glasses, such as the glass transition, crystallization and melting temperatures, as well as heats of crystallization and melting are reported. The effect of the alloy composition on glass forming ability is discussed.

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It is known that cooling rate from the liquid state is an important factor for producing the bulk metallic glasses. However, almost no other factors such as electric and/or magnetic fields were investigated. The present authors have reported that the glass-forming ability of Mg-Cu-Y and Fe-Co-B-Si-Nb alloys is enhanced with increasing electromagnetic vibration force. The electromagnetic vibrations affect the increase of the cooling rate and the decrease in the number of crystal nuclei directly, but don’t affect the crystal growing rate. However, effects of the electromagnetic vibrations are not fully investigated so far. Thus, this study aims to investigate effect of the purity and superheating on the glass-forming ability of Mg-Cu-Y alloys by the electromagnetic vibration method. It was found that the glass-forming ability of Mg-Cu-Y alloys is sensitive to the purity of an Ar atmosphere under which the mother alloy is prepared. However, the glass-forming ability was enhanced by the electromagnetic vibrations even if the mother alloy was prepared under low purity Ar. The enhancement of the glass-forming ability by the electromagnetic vibrations in the liquid state was decreased with the increase of superheating. These results support the presumption that disappearance or decrement of the clusters by the electromagnetic vibrations applied to the liquid state causes suppression of crystal nucleation.

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There have been many alloy systems for the Mg based bulk metallic glasses (BMGs), with the previous optimum composition being Mg₆₅Cu₂₅Y₁₀. In this study, new optimum alloy designs are made based on the theoretical model involving the electron per atom e⁄a-related criterion and the recent model of optimum composition extension from the binary eutectic-pair criterion. Both models suggest that the optimum Mg based BMGs might possess a composition with a lower amount of Mg element. It follows that a series of Mg based BMGs with 50–65 at% Mg and 10–25 at% rare earth element are prepared. The glass forming ability, thermal characteristics, and mechanical performance are examined and discussed.

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The effects of addition of Al and equivalent atomic ratio of Ag and Al on the glass-forming ability (GFA) of the Cu₅₀Zr₅₀ alloy are investigated. It is found that the alloy with the highest GFA is the Cu₄₆Zr₄₆Al₈ alloy in ternary (Cu₅₀Zr₅₀)_100−xAl_x alloys, and the critical diameter is at least 8 mm. The simultaneous addition of Ag and Al is more effective to increase the glass-forming ability of the binary Cu₅₀Zr₅₀ alloy. The critical diameter of a glassy rod is 12 mm for the Cu₄₂Zr₄₂Al₈Ag₈ alloy. High stabilization of the supercooled liquid is the reason for high GFA of the Cu₄₆Zr₄₆Al₈ and Cu₄₂Zr₄₂Al₈Ag₈ alloys. Both glassy alloys exhibited high fracture strength above 1960 MPa, but no distinct plastic strain is seen. There is no evident difference in the mechanical properties of the as-cast Cu₄₂Zr₄₂Al₈Ag₈ glassy rods with different diameters.

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The isothermal Cu–Ti–Zr phase diagram at 800°C was constructed by means of 36 equilibrated alloys. Electron microprobe analyses were used to determine the phase compositions and phase relationships. Most of the Cu–Zr binary intermetallic phases show a large Ti solubility and extend to the ternary region. CuTi₂ and CuZr₂ form a complete solid solution as a Cu(Ti,Zr)₂ phase. One ternary phase, Cu₂TiZr, formed at the central region. These phase relationships are quite different from the 703°C isotherm mainly determined by X-ray analysis.

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The glass-forming ability of Nb-Ni-Ti-Zr quaternary alloys has been evaluated by combining the Calculation of Phase Diagrams method with the Davies-Uhlmann kinetic approach. Time-temperature-transformation (TTT) curves were obtained for steady state nucleation for the calculations, which give the time required for the formation of detectable amounts of a crystalline phase from a supercooled liquid as a function of temperature. Then, the critical cooling rates for glass formation were calculated from the TTT curves. Among the input parameters for the calculation of the TTT curves, the driving force for crystallization of the crystalline phase was derived using the thermodynamic function of each phase formulated in previous studies. The calculations show that the critical cooling rates for Nb_40−x−yNi₆₀Ti_xZr_y alloys decrease with increasing Zr content up to 20 mol%Zr. In particular, the calculated values for the Nb₁₀Ni₆₀Ti₁₀Zr₂₀ and Nb₅Ni₆₀Ti₁₅Zr₂₀ alloys were around 10⁰ K/s.

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The structural behavior of rapidly quenched Cu-Zr amorphous alloys was analyzed. High energy X-ray diffraction patterns and atomic pair correlation functions exhibit monotonic changes with composition. The experimental results can be well described by a solid solution-like replacement of Cu and Zr atoms in the whole composition range. No indications are observed that would support the existence of phase separation in the supercooled liquid state of the binary Cu-Zr alloys. For Cu₆₀Zr₃₀Ti₁₀ and Cu₆₀Zr₂₀Ti₂₀ bulk metallic glasses the formation of ultrafine nanostructures are proven upon heating. The transformation starts below the glass transition temperature. Phase separation in Cu-Zr-Ti bulk metallic glasses is related to primary crystallization.

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The difference in electron irradiation induced crystallization behavior of melt-spun amorphous phase among Zr_66.7M_33.3 (M=Cu, Ni and Pd) alloys was investigated. An amorphous phase was unstable under electron irradiation and the irradiation induced crystallization of the amorphous phase occurred in the three alloys. The phase selection of electron irradiation induced crystallization in Zr_66.7Pd_33.3 was obviously different from that in Zr_66.7Cu_33.3 and Zr_66.7Ni_33.3, while there was no significant difference between the latter two. The origin of the unique phase selection in Zr_66.7Pd_33.3 alloy was discussed based on the database of electron irradiation induced crystallization in Zr-based alloys.

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Electron irradiation induced crystal-to-amorphous-to-crystal (C-A-C) transition in metallic glasses was investigated in various metallic glasses among binary Zr-based, ternary Fe-Nd-B and Fe-Zr-B alloys. In situ observation of the TEM microstructures and corresponding SAD patterns was performed by ultra high-voltage electron microscope (UHVEM). The origin of amorphization, crystallization and C-A-C transition was discussed based on the temperature-Gibbs free energy diagram.

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The effect of electron irradiation on the phase transformation in binary Fe-Nd and ternary Fe-Nd-B alloys was investigated. Electron irradiation induced nano-crystallization of amorphous-to-crystal (A-C) transition was observed in several Fe-Nd-B metallic glasses. In Nd₂Fe₁₄B compound, solid-state amorphization (SSA) of crystal-to-amorphous (C-A) transition occurred under electron irradiation. With further irradiation, the amorphous phase obtained by SSA transformed to the nano-crystalline phase through irradiation induced crystallization, resulting in crystal-to-amorphous-to-crystal (C-A-C) transition. A-C, C-A and C-A-C transition were also observed in some ternary Fe-Nd-B and binary Fe-Nd alloys. The electron irradiation technique is effective for the formation and control of nano-crystalline structure through A-C transition of amorphous phase and/or C-A-C transition of metallic compounds.

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Electropulsing by means of discharge of a condenser with the decay time (τ) of ms causes the athermal crystallization of metallic glasses when the initial current density (i_d0) is higher than the threshold value (i_d0,c). It is indicated that the major local amorphous structures in Zr₅₀Cu₅₀ are the amorphous structures with the short range order (SRO) similar to crystalline cubic (c) ZrCu which is the equilibrium crystalline phase above 988 K, although the mixture of crystalline Zr₂Cu and Zr₇Cu₁₀ is the equilibrium phase below 988 K. Electropulsing tests on Zr₅₀Cu₅₀, Zr₅₀Cu₄₀Al₁₀ and Zr₅₀Cu₃₅Al₁₀Ni₅ metallic glasses indicate that the amorphous structures with SRO similar to cZrCu are the major local amorphous structures in these metallic glasses, and their volume fractions decrease in the order of Zr₅₀Cu₅₀, Zr₅₀Cu₄₀Al₁₀ and Zr₅₀Cu₃₅Al₁₀Ni₅. The amount of the amorphous structures with SRO similar to cZrCu may govern the thermal stability of these metallic glasses. Further in Zr₅₀Cu₅₀ metallic glasses, the inverse transformation from the electropulsing-induced fine crystallites to the amorphous phase for subsequent electropulsing with increasing i_d0, and the Ostwald-ripening-like phenomenon under electropulsing were observed.

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A thermodynamic calculation scheme based on a CALPHAD method has been studied to evaluate the relative glass forming abilities (GFAs) of multicomponent alloy systems. The concept of the normalized driving force has been developed for estimation of the relative GFAs of different alloy systems. Driving forces of formation of crystalline phases under metastable supercooled liquid state have been calculated for different alloy systems to predict the possible crystalline phases and the maximum driving forces normalized by the respective melting temperatures are correlated with the experimentally obtained GFAs of the alloys. It shows that the estimated relative GFAs of different alloy systems based on the normalized driving forces agree well with the experimental results.

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We present a simple thermodynamic calculation for a strongly partitioning eutectic system, to examine how the critical nucleus energy changes, depending upon assumptions of the chemical diffusion. The calculations show that for strongly partitioning systems, the maximum undercooling may occur at a composition significantly different than the eutectic composition, particularly if the rate of diffusion is slow in the undercooled state. These simple calculations emphasize the role that partitioning and composition may play in determining optimal compositions in metallic glass systems, which typically occur near (but not at) deep eutectic compositions.

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In this paper, a pseudo-ternary (La_0.5Ce_0.5)₆₅Al₁₀Co₂₅ alloy with high glass-forming ability (GFA), identified by the formation of glassy rods up to 12 mm in diameter by copper mold casting, was reported. Furthermore, according to the viewpoint that similar element coexistence can be beneficial to improve the GFA, Cu was chosen as the similar element to substitute for solute Co in (La_0.5Ce_0.5)₆₅Al₁₀(Co_1−xCu_x)₂₅ alloys (0≤x≤1). The influence of this substitution on thermal stability, melting and solidification behaviors of these metallic glasses was evaluated. The optimized (La_0.5Ce_0.5)₆₅Al₁₀(Co_0.6Cu_0.4)₂₅ alloy with high reduced glass transition temperature (0.66) and the large nominal supercooled degree (114 K) can form the fully glassy rods up to at least 25 mm in diameter by tilt-pour casting.

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The Mg₅₈Cu₃₁Y_11−xNd_x (x=0∼11) amorphous alloy rods with 3∼10 mm in diameter were prepared by Cu-mold injection method. The XRD result reveals that these entire Mg₅₈Cu₃₁Y_11−xNd_x alloy rods exhibit a broaden diffraction pattern of amorphous phase. A clear T_g (glass transition temperature) and supercooled region (about 70 K) were revealed for all of those Mg₅₈Cu₃₁Y_11−xNd_x amorphous alloy rods. The single stage crystallization of the Mg₅₈Cu₃₁Y₁₁ alloy was found to change into two stages crystallization when large amount of Nd element was added into this alloy. In parallel, the crystallization temperature (T_x) and supercooled region (ΔT_x) present a decreasing trend with increasing Nd content. The highest γ value of 0.414 occurs at the alloy compositions of Mg₅₈Cu₃₁Y₄Nd₇ and Mg₅₈Cu₃₁Y₆Nd₅ in this alloy system. Therefore, suitable addition of Nd element can obviously increase the glass forming ability for the Mg₅₈Cu₃₁Y_11−xNd_x alloy system.

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Crystal nucleation and time evolution during isothermal annealing in amorphous Zr₂Ni at several temperatures just below a crystallization temperature T_x and in supercooled liquid of metallic glass Zr₂Cu are examined using a technique of differential thermal analysis. Time dependence of the fraction of crystallization at several temperatures is analyzed by the Johnson-Mehl-Avrami equation. The Avrami exponent is 3.0±0.2 for Zr₂Ni and varies from about 3 to 7 for Zr₂Cu with increasing temperature. It is suggested for Zr₂Ni that the crystal growth at temperatures just below T_x is ruled by a short range diffusion process of constituent elements. The time evolution of crystallized fraction was not well scaled by the half of complete time for full crystallization.

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We studied the effects of phosphorus (P) on the Ni nanocrystalline morphology of Ni-P amorphous alloy thin films subjected to focused ion beam (FIB) irradiation. The P contents in the amorphous alloys varied from 14 to 20 at%. The nanocrystals induced by FIB irradiation of Ni-20.2, 15.6, and 14.0 at%P amorphous alloys had a face-centered-crystal (f.c.c.) structure and showed unique crystallographic orientation relationships to the geometry of the focused ion beam, with {111}_f.c.c. parallel to the irradiated plane and ⟨110⟩_f.c.c. parallel to the direction of the projected ion beam, respectively. The Ni nanocrystals formed by FIB irradiation precipitated in the same manner as aggregates, and the average size of the Ni nanocrystals increased as the P content decreased. These results indicate that the P content does not affect the crystallographic orientation relationships but does influence precipitation distribution of the Ni nanocrystals.

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Ni-Zr metallic glasses have been recognized to be unstable in comparison with Cu-Zr metallic glasses. An analysis of Voronoi polyhedra in the RMC simulations based on the diffraction data could characterize the atomic configurations around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prism-like, Archimedian antiprism-like, and similar polyhedra. In contrast, icosahedron-like polyhedra are preferred for Cu. The Ni-Zr glasses have been reported to stabilize by adding Al. Therefore, in this work, the analysis of Voronoi polyhedra around Ni, Zr and Al atoms for Ni₂₅Zr₆₀Al₁₅ ternary metallic glass was carried out in order to clarify the difference between the atomic structures for the binary and ternary metallic glasses. Trigonal prism-like, Archimedian antiprism-like and similar polyhedra, which are dominated in the Ni-Zr metallic glasses, decreased in number by adding Al to the Ni-Zr system. On the contrary, the number of icosahedron-like polyhedra was found to increase. The results apparently indicate that the addition of Al into Ni-Zr binary system promote the formation of icosahedron-like polyhedra in the structure. Therefore, from these results, we can easily recognize that icosahedron-like polyhedra play an important role to stabilize the structure of metallic glasses.

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The local structure in the glassy state is investigated in the Zr₈₀Pt₂₀ and Zr₇₀Cu₃₀ binary and Zr₇₀Al₁₀Ni₂₀ ternary alloys in correlation with the quasicrystalline (QC) phase formation. The Zr₈₀Pt₂₀ alloy has a high QC-forming ability. It is easily formed in the as-quenched state with a considerably low cooling rate or by annealing the glassy alloy. The radial distribution function (RDF) and extended X-ray absorption fine structure (EXAFS) analysis clearly indicate the existence of icosahedral local structure around Pt atom. The Zr₇₀Cu₃₀ binary and Zr₇₀Al₁₀Ni₂₀ ternary metallic glasses have a QC-forming ability by the addition of a very small amount of noble metals such as Pd. We can also investigate the icosahedral local structure in these alloys. These results are realized that the icosahedral local structure can be applied as a dominant local atomic configuration in the supercooled liquid and/or glassy states in the QC-forming metallic glasses.

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The isothermal relaxation processes of bulk Zr₅₀Cu₄₀Al₁₀ and Pd_42.5Cu₃₀Ni_7.5P₂₀ glasses were examined by density reduction associated with relaxation. Density experiments were carried out by buoyancy method at room temperature. The isothermal relaxation curves were best fitted by a stretched exponential function with a Kohlrausch exponent less than unity. Based on free volume model, the reduced free volume x_f^as=0.0355 and flow defect concentration C_f^as=5.80×10⁻¹³ in as-quenched state was obtained for Pd_42.5Cu₃₀Ni_7.5P₂₀ glass. However, the temperature at which the free volume started to deviate from equilibrium concentration on cooling of the melt was not in accordance with calorimetric glass transition temperature.

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We demonstrate the ability of our cluster expansion approach (CEA) for cohesive energies of alloys, which allows one to study the chemical trends of the relative stability of different atomic structures of alloys, as an example, X dependence of the atomic structures of Al-rich AlX (X = Sc-Zn) alloys, including ordered structures (L1₂(Al₃Sc), DO₂₂ (Al₃V)), a Mackay icosahedron (a local structure in the Al₈₀Mn₂₀ quasicrystal), and precipitate shapes in decomposition phases (Al_1−cCu_c, Al_1−cZn_c; c<0.05). All the terms in the CEA for Al-rich AlX alloy can be determined uniquely and successively from low-order to high-order by using the total energies of isolated Al and X atoms, pure Al and X metals, and X impurities in Al metal. The total energies of impurity systems are calculated accurately by using the all-electron full-potential Korringa-Kohn-Rostoker (FPKKR) Green’s function method, combined with the density-functional theory in the generalized-gradient approximation (GGA). We show: (1) the binding energies of X (X = Cu, Zn) impurities in Al are reproduced very well by the CEA including two- and three-body interaction energies of X impurities; (2) the chemical trends of structural stability among ordered structures (L1₂, DO₂₂, DO₂₃) of Al₃X (X = Sc, Ti, V), being determined by use of the screened-FPKKR and GGA band-structure calculations, are reproduced by the CEA including only two-body (X-X) interaction energies in Al.

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A spray-formed Al₈₉La₆Ni₅ metallic glass matrix composite plate was obtained in thickness of 1 mm and diameter of 200 mm, comprising over 64% primary crystals (e.g. Al₁₁La₃) uniformly dispersed in the glass matrix. The microstructure can not be achieved by annealing corresponding amorphous precursor. The crystals existing in the glass matrix were found to increase the hardness of the composite. Through nanoindentation test, the hardness and modulus of the composite at ambient temperature were found superior than its amorphous ribbon counterpart. The hardness of the composite was estimated with the rule of mixture from the constituents to be 4.4 GPa, which agreed well with the nanoindentation results. From loss modulus measurement and TMA test at elevated temperatures, a weak T_g signal in the range of 213–240°C was revealed in the as-spray-formed composite. Furthermore, the dimension shrinkage of the composite was only 0.5% during the TMA test, which is much smaller than that of amorphous ribbon counterpart by up to 20%. The enhanced hardness by constituent second phases and the dimension stability of the composite are associated with their inherent microstructure, the primary crystals in particular.

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The influence of annealing on the structural changes and the room temperature mechanical properties of a Zr₄₄Ti₁₁Cu_9.8Ni_10.2Be₂₅ bulk metallic glass has been investigated. The structural evolution upon relaxation or crystallization after annealing at a temperature within the supercooled liquid region was studied by thermal analysis, x-ray diffraction, transmission electron microscopy, extended x-ray absorption fine structure and dilatometer measurements. The effects of structural relaxation and nanocrystallization on the mechanical properties were also examined by hardness and compression tests using specimens annealed for various times. The apparent disappearance of plastic strain was found to be due to embrittlement induced by considerable crystallization of the amorphous phase.

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How atoms move in metallic glasses and liquids is an important question in discussing atomic transport, glass formation, structural relaxation and other properties of metallic glasses. While the concept of free-volume has long been used in describing atomic transport, computer simulations and isotope measurements have shown that atomic transport occurs by a much more collective process than assumed in the free-volume theory. We introduce a new approach to describe the atomic dynamics in metallic glasses, in terms of local energy landscapes related to fluctuations in the topology of atomic connectivity. This approach may form the basis for a new paradigm for discussing the structure-properties relationship in metallic glasses.

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We give ab-initio data for the study of the stability of the atomic structures of Zr-rich ZrX (X=Sc-Cu) alloys, such as the cohesive energies and equilibrium Wigner-Seitz radii of elemental metals X (X=Sc-Cu, Zr-Ag) and X-X (X=Sc-Cu) interaction energies in Zr. The calculations are based on the density functional thoery in the generalized gradient approximation and employ the full-potential Korringa-Kohn-Rostoker Green’s function method. Using the calculated results, we elucidate the fundamental features of interatomic interactions of Zr-rich ZrX alloys. Especially, we found that the pair interaction of Cu impurities in Zr becomes strongly attractive around the interatomic distance of 0.45∼0.46 nm. It is shown that this interaction may be important for the stability of icosahedron-like local atomic structures of Zr₁₀Cu₃ and Zr₉Cu₄ clusters in the Zr₇₀Cu₃₀ bulk metallic glass, being proposed experimentally. We also found that the atomic structure of an isolated Zr₁₀X₃ cluster transforms from the hcp structure (initial state) to an icosahedron-like structure (final state) for X=Cu, but not for X=Ni.

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In the present work we propose a new approach for predicting the best glass-former composition(s) in multi-component metallic glasses. By applying the λ criterion, a topological instability criterion proposed to predict the crystallisation behaviour of Al-based systems, we show that it is also successfully possible to reproduce compositional ranges where binary and ternary bulk metallic glasses (BMGs) have recently been obtained. Our results indicate that the good glass-former composition(s) lie(s) within fields of mutual and simultaneous topological instability of all the crystalline phases competing with glassy phase.

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Using microindentation technique, the indentation behavior of a Zr₅₇Ti₅Cu₂₀Ni₈Al₁₀ bulk-metallic glass is studied over a range of the indentation load from 200 mN to 5000 mN. For the indentation load larger than 1000 mN, the indentation load-depth curves during unloading display three regions, a) a fast unloading phase at the onset of unloading, b) a linear phase at which the indentation load is proportional to the indentation depth, and c) a slow unloading phase after the linear phase. The size of the linear region increases with the increase in the indentation load, and the slope is independent of the indentation load. The indentation hardness decreases slightly with the increase in the indentation load. The plastic energy dissipated in an indentation cycle is proportional to the 3/2 power of the indentation load. The effect of the indentation loading rate on the indentation behavior is discussed.

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We investigated the thermal stability and hardness of a Zr₅₅Cu₃₀Al₁₀Ni₅ bulk glassy alloy after isothermal viscous flow deformation in the supercooled liquid region. The influence of deformation temperature, holding time and initial strain rate on the thermal stability and hardness of a Zr₅₅Cu₃₀Al₁₀Ni₅ bulk glassy alloy subjected to the high temperature compression test was examined by differential scanning calorimetry (DSC) and with a Vickers micro-hardness tester. The results showed that the incubation time for isothermal annealing crystallization reduced during the viscous flow deformation. Thermal stability of supercooled liquid decreased after viscous flow deformation. As the deformation temperature increased, the SCL region decreases. At lower temperatures below 713 K the structural relaxation occurred, resulting in a slight increase in hardness. The crystallization at higher temperatures of over 723 K caused a rapid increase in hardness. The supercooled liquid region decreased and the hardness increased with increasing deformation time. Higher strain rate resulted in larger deformation in the same deformation time, and had slight influence on the thermal stability and hardness of the Zr₅₅Cu₃₀Al₁₀Ni₅ glassy alloy. When the Zr₅₅Cu₃₀Al₁₀Ni₅ bulk glassy alloy was compressed for 300 s with an initial strain rate of 3.3×10⁻³ s⁻¹ at the temperatures of 723 K, nanocrystallization occurred, and the grain size was evaluated to be smaller than 5 nm.

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The compression tests were conducted on four Zr-based bulk metallic glasses (BMGs) with different Nb contents. The results show that the addition of few percent Nb did not change the mechanical property. At 77 K, the strength increased notably without embrittlement. Furthermore, it is suggested that the normalized strength changes linearly with the normalized temperature. Current results provided important evidences that BMGs have a great application perspective at cryogenic temperatures. In addition, it is found that at ambient temperature, the BMGs do not exhibit strain rate sensitivity. However, the strength is dependent on the strain rate at high and cryogenic temperatures.

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Internal friction of Zr-based glassy composite alloys containing dispersed-ZrN particles, which were prepared by a powder compact melting and liquid-quenching process using Zr-Al-Ni-Cu glassy alloy and AlN powders as the starting materials, has been investigated using a reed method over the temperature range of ∼90–350 K. It should be noted that a broad multi-composed peak was observed around 260 K. The peak internal friction was about 3×10⁻³. It was also noteworthy that the so-called ΔM effect of the Young’s modulus in its temperature dependence was observed. In addition, the internal friction at the peak temperature depended little on the strain amplitude in the range of about ∼1×10⁻⁶–∼2×10⁻⁴. These results indicate that the observed internal friction peak is related to the relaxation process. Since the hydrogen content in the sample was very low (0.24 at%H), the observed internal friction peak is suggested to be induced by the interstitially doped nitrogen in the glassy phase.

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La₆₄Al₁₄(Cu,Ni)₂₂, La_63.1Al1_5.2(Cu,Ni)_21.7, La_57.6Al_17.5(Cu,Ni)_24.9, and La₅₅Al₂₅Cu₁₀Ni₅Co₅ bulk metallic glasses (BMGs) with low glass transition temperature (T_g) were prepared by copper-mould casting method. The homologous temperature (the ratio of room temperature to T_g) of the four BMGs ranges from 0.64 to 0.73. Plastic deformation behavior of the BMGs at various loading rates was studied by nanoindentation. The results showed that the loading rate dependency of serrated flow, which is related to the nucleation and propagation of shear bands, depends strongly on the homologous temperature. The alloys with relatively high homologous temperature exhibit an increase in flow serration with increasing loading rate, whereas, the alloys with low homologous temperature exhibit prominent serrations at low rates. No distinct shear band is observed around the indents for all alloys after nanoindentation at all the studied loading rates. Alternately, shear band pattern are characterized through macro-indentation, which shows that shear band spacing decreases with the increase of the homologous temperature.

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As a first step in examining a new aspect of inhomogeneous plastic flow in bulk metallic glasses (BMGs) during nanoindentation, a series of nanoindentation experiments were performed on Zr₆₀Cu₃₀Al₁₀ BMG with two pyramidal indenters (Berkovich and cube-corner indenters) having different centreline-to-face angle. It was revealed that the indenter angle can be a new controllable factor affecting the serrated flow behaviour of the BMG during nanoindentation, since a sharper cube-corner indenter induces different stress field under the contact from Berkovich indenter typically used. Results are discussed in terms of preliminary ideas for improving analysis of the shear-band-ruled deformation behaviours in the BMG during nanoindentation.

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Fatigue tests on Zr-based bulk metallic glass were conducted under fully reversed cyclic bending (R=−1), and the surfaces of the fatigued specimen were observed to elucidate the fatigue crack initiation mechanisms. The fracture surface was also observed to examine the crack propagation mechanism. In contrast to most brittle materials, the metallic glass showed fatigue behavior. Its fatigue strength was much lower than its tensile strength, and it had a fatigue limit. In the S-N curve, the number of cycles at the knee point was much lower than that for crystalline metals. The fatigue crack initiation process observed by atomic force microscopy (AFM) showed that cracks were initiated at the bottom of shear steps just after their formation.

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New findings on the inhomogeneous plastic deformation of bulk metallic glasses (BMGs) have shown a disappearance of serrated flow below a critical temperature or above a critical strain rate. This correlates with a change in the strain rate sensitivity (SRS) from negative to positive values, suggesting a change in the deformation mechanism. In addition, a change in the SRS correlating with the increase in the stress drop magnitude is observed with increasing strain. Results on the serration and flow dependence for the binary BMG Cu₅₀Zr₅₀ show close phenomenological similarities with the Portevin - Le Châtelier or dynamic strain aging effect known for crystalline solids. An alternative model for the appearance and disappearance of serrated flow based on the structural relaxation of the atomic configuration of shear transformation zones is described.

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Using the instrumented nanoindentation and differential-scanning calorimetry, the effect of the structural relaxation at the elevated temperature on the Zr_52.5Cu_17.9Ni_14.6Al_10.0Ti_5.0 bulk-metallic glass was investigated. The structural relaxation did not exert a significant influence on the plastic-flow behavior. However, the relaxation enhanced both the hardness and elastic modulus substantially. The decrease in the structural relaxation enthalpy before the glass transition indicates that the relaxation reduced the free volume significantly. The increase in the hardness and elastic modulus is attributed to the reduction in the free volume that resulted from the relaxation.

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An electrolytic polishing technique was used to fabricate micro-sized tensile specimens from two Zr₅₅Al₁₀Ni₅Cu₃₀ bulk metallic glass samples. One sample had a fully amorphous phase, while the other had dendrites with an average size of 33 μm within the amorphous matrix. A scanning electron microscope showed that specimens fabricated by electrolytic polishing had smooth surfaces. The specimens were then subjected to tensile tests at room temperature. The fully amorphous specimen had a fracture strength of 1,640 MPa. This specimen also showed slight plastic deformation after yielding, as well as vein patterns and smooth surface on the fracture surface. Multiple thin shear bands generated from a shear band were observed on the side surface of fractured specimen. The specimen containing dendrites was quite low in strength compared to the fully amorphous specimen, and had yield and fracture strengths of 460 and 600 MPa, respectively. The specimen containing dendrites also showed plastic deformation and work hardening after yielding, as well as vein patterns and a brittle fracture region on the fracture surface.

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The glass-forming ability (GFA) and thermal stability of (Zr₆₅Al_7.5Cu_27.5)_100−xTi_x (x=0∼15; in at%) alloys have been investigated. It was revealed that a certain amount of Ti addition could improve the GFA of Zr₆₅Al_7.5Cu_27.5 alloy effectively. The best bulk metallic glass (BMG) forming composition was found at (Zr₆₅Al_7.5Cu_27.5)₉₃Ti₇. Bulk glassy samples with diameter of 7 mm were made by means of copper mold casting. Further Ti additions deteriorated GFA and led to the precipitation of icosahedral phase, and 3 mm quasicrystalline cylinder was obtained at (Zr₆₅Al_7.5Cu_27.5)₉₀Ti₁₀. Room temperature compression testing showed that the quasicrystalline alloy had a fracture strength of 1875 MPa, being 300 MPa larger than that of the (Zr₆₅Al_7.5Cu_27.5)₉₃Ti₇ monolithic BMG.

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An expression for the temperature dependence of the viscosity and fragility is derived based on a simple model of the melt. According to the model, the fragility is determined by the relaxation of structural units that form the melt, and is described in terms of the bond strength, coordination number, and their fluctuations of the structural units. It is shown that the fragility of some metallic glass forming liquids such as Pd₄₀Ni₄₀P₂₀, La₅₅Al₂₅Ni₂₀ and Zr₆₅Al₁₀Ni₁₀Cu₁₅ are quite well reproduced by the model. The application of the theory to La₅₅Al₂₅Ni₂₀ has revealed that the fluctuation in the bond strength between the structural units is about 6% and that the viscous flow occurs when the bonds in about 8 adjoining structural units are broken.

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Amorphous Mg₆₅Cu₂₀Y₁₀Ag₅/nano ZrO₂ composite alloys are fabricated through mechanical alloying (MA) in the planetary mill, using amorphous matrix alloy prepared by melt spun and 3 vol% spherical nano-sized ZrO₂ particles. The specimens were hot pressed in Ar atmosphere under the pressure of 700 MPa at the temperature of soft point which is determined by TMA (Thermo mechanical Analysis). The hot-pressed composite alloy can reach to a 96% density, the hardness of 315±10 in Hv scale, and the compressive strength of 690 MPa. In addition, the result of mechanical test revealed that the nano-sized ZrO₂ dispersion can obviously increase hardness as well as toughness of the Mg based amorphous alloy. Moreover, after compression test at 426 K (sample has been deformed 60 vol%), the hardness of hot-pressed composite alloy dramatically increases to Hv 400±25. An image of shear band being stopped in front of the ZrO₂ particle was found by the TEM observation. Base on these two evidences, suggests that the strength of amorphous Mg₆₅Y₁₀Cu₂₀Ag₅ with 3 vol% ZrO₂ composite alloy could be potentially improved by healing its residue porosity with hot deformation method within the supercooled liquid temperature region.

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The mechanical behavior of the Mg₆₅Cu₂₅Gd₁₀ bulk metallic glasses (BMGs) in term of compression testing is reported in this study. Room-temperature compression tests are conducted on specimens with various height to diameter ratios (h⁄d) from 2:1, 1:1, 1:2, to 1:4. The failure strength, deformation strain, and the fracture surface morphologies are seen to vary systematically in accordance with the specimen h⁄d ratio. For specimens with h⁄d of 2:1 or 1:1, the compression response is similar to those in most reports. In contrast, for specimens with lower h⁄d ratios, especially at h⁄d=1:4 (or 0.25), the shear band propagation appears to be constrained, resulting in the enhanced ductility. It suggests that different deformation mechanisms are operative for specimens with different h⁄d ratios. The possible deformation mechanisms in specimens of different geometries are discussed.

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To circumvent the limited ductility of bulk metallic glasses (BMGs), heterogeneous materials with glassy matrix and different type and length-scale of heterogeneities (micrometer-sized second phase particles or fibers, nanocrystals in a glassy matrix, phase separated regions, variations in short-range order by clustering) have been developed in order to control the mechanical properties. As example, recent results obtained for Cu- and Ti-base structurally imhomogeneous bulk metallic glasses will be presented. This type of clustered glasses is able to achieve high strength together with pronounced work hardening and large ductility by controlling the instabilities otherwise responsible for early failure. We emphasize the possibilities to manipulate such spatially inhomogeneous glassy structures based on martensitic alloys in favor of either strength and ductility, or a combination of both and also discuss the acquired ability to synthesize such M-glasses in bulk form through inexpensive processing routes.

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Microstructures and mechanical properties of Cu mold-cast Ti₅₀Cu₂₅Ni₁₅Sn₅Ta₅ and Ti₄₅Zr₅Cu₄₄Ni₅Ta₁ alloys were investigated by means of X-ray diffraction, electron microscopy and compressive testing. Ti₅₀Cu₂₅Ni₁₅Sn₅Ta₅ alloys form microscopic composites consisting of Ti-based metallic glass as primary phase and β–Ti phases, while Ti₄₅Zr₅Cu₄₄Ni₅Ta₁ alloys consisting of Ti-based metallic glass matrix and high density of nanocrystals dispersed in the matrix homogeneously. Ti₅₀Cu₂₅Ni₁₅Sn₅Ta₅ bulk composite alloys showed 1.6% of plastic deformation and 2200 MPa of 0.2% of proof stress. The alloys also exhibited work hardening because of the presence of microscopic crystalline phases. Ti₄₅Zr₅Cu₄₄Ni₅Ta₁ bulk alloys also deformed plastically after stress reached 2000 MPa without work hardening.

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We define the Turnbull-Cohen free volume as the critical excess of the Voronoi volume of an atom less its core volume. Using molecular dynamics simulation we calculated the free volume change in two model binary metallic glasses undergoing tension and shear deformation. We show that the free volume change is an integral part of the deformation process; and the shear localization manifested as a shear band is directly related to the inhomogeneous distribution of the free volumes. Shear band formation may consist of two stages: the initial free volume production in the amorphous solids and the liquefaction of the regions with accumulated deformation strains. We show, for the first time, the formation of voids and the “vein” patterns on fracture surfaces at atomic scales; they are the combined result of the free volume change and loading and sample conditions.

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The hydrogen internal friction peak in Zr₅₀-metallic glasses (Zr₅₀Cu₅₀, Zr₅₀Cu₄₀Al₁₀ and Zr₅₀Cu₃₅Al₁₀Ni₅) was studied. The hydrogen internal friction peak was shifted exponentially to lower temperatures with increasing hydrogen concentration similarly to other Zr-Cu base metallic glasses reported in the literature. The peak height increased in proportion to the square-root of hydrogen concentration. These results were discussed in the view point of the hydrogen induced structural relaxation in these metallic glasses.

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