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In this study, high entropy metallic glasses (HEMGs) were developed through a combination of concepts for designing metallic glasses (main element + transition metal + metalloid element) and high-entropy alloys (more than five elements, each element having an atomic concentration between 5 at.% and 35 at.%). The developed metallic glass alloys are composed of Co-Fe-Ni main elements, transition metals (Cr, Mo) and metalloid elements (C, B). Moreover, the present work reports the thermal, mechanical and magnetic properties of (CoFeNi)50(CrMo)50-x(CB)x alloys with x = 20, 25, 30. The developed as-spun HEMGs exhibit typical paramagnetic properties even for a high amount of ferromagnetic elements (Co, Fe, and Ni) and have high elastic modulus (103–160 GPa) and hardness (14–27 GPa), thus possessing mechanical properties similar to well-known Co-based metallic glasses (Co-Cr-Mo-C-B system). In addition, some of the bulk samples prepared with a diameter of 2 mm form bulk metallic glasses with a high compressive strength around 3.5 GPa. The mechanisms determining the stability of the supercooled liquid, as well as the paramagnetic and mechanical properties for the developed non-equiatomic HEMGs, are discussed.

The low-cost β-titanium alloys, Ti-Cr-Al-Si, have been designed by the addition of a commercial Al-based die-cast alloy (ADC12, Al87.38Cu0.95Si10.65Mg0.27Zn0.30Fe0.32Mn0.11Cr0.02 in at.%) containing Si content. The microstructural investigation on Ti84-xCr16(ADC12)x (x = 6, 16 at.%) alloys exhibited that the addition of 6 at.%ADC12 completely dissolved in the β-Ti phase, and exhibited reasonable yield strength by solid solution hardening of the β-Ti phase with large plasticity. The addition of 16 at.%ADC12 effectively reduces the cost of the β-titanium alloys and induces microstructural evolution with formation of Ti-silicide. The β-Ti phase containing high content of solutes and the very fine Ti5Si3 phase that segregated in the interdendritic regions, due to Si solute partitioning during dendritic solidification, mediates outstanding tensile mechanical properties (1015 MPa in yield strength and 17.5% in elongation). These results reveal that the alloy designs using the commercial materials containing various solute elements can facilitate the development of the competitive low-cost β-titanium alloys with excellent mechanical properties.

In this work, we investigated the effect of boron addition on glass-forming ability and mechanical properties of Co-Cr-Mo-C alloys. The starting alloy was (Co0.65Cr0.13Mo0.22)80C20 derived from the Co65Cr13Mo22 ternary eutectic composition. This alloy is almost fully crystalline and exhibits brittle mechanical properties. Replacing carbon with boron allows obtaining bulk metallic glasses (BMGs) and bulk metallic glass composites. The designed alloys show very high strength (∼4100 MPa), wide super-cooled liquid region (∼100 K) and large endothermic enthalpy of the supercooled liquid region (∼35 J/g), indicating high thermal stability. The electronegativity difference and supercooled liquid region of the present alloys are comparable to rare-earth elements containing BMGs. The physical properties of the present alloys corresponded well with the alloy design strategy based on the unified parameter using the glass transition temperature, fracture strength, and molar volume. Furthermore, we propose the optimum compositional condition for glass formation by controlling the carbon-to-boron ratio and the influence of carbon on phase formation in this alloy system is discussed.

Bulk metallic glass composites containing micro-scale B2 particles are subject to investigation with regards to the influence of B2 particles and interfacial stress and strain distribution on the viscous flow behavior at a super-cooled liquid state. An increased volume fraction of B2 particles leads to an increase of minimum viscosity and influences viscous flow behavior before crystallization. In high temperature deformation, the bulk metallic glass shows homogeneous deformation feature. However, the heterogeneous deformation feature is found in thermoplastically deformed bulk metallic glass composite. The strong stain accumulation and sluggish viscous flow occur around B2 particles, which are caused by the heterogeneous stress distribution linked to stress concentration and shear stress impediment around B2 particles. The sluggish viscous flow of super-cooled liquids around B2 particles during high temperature deformation induces an increase of viscosity and strongly affects the viscous flow behavior of Ti-based bulk metallic glass composites containing micro-scale spherical B2 particles.

The as-cast Mg-9Li alloys with difference Al-Si addition were fabricated using induction casting method under the argon atmosphere and then warm rolling process was performed at 473 K. The Al-Si addition to Mg-9Li alloy leads to the formation of Mg2Si intermetallic compounds and microstructural evolutions such as increased volume fraction of α-Mg phases and changed morphology of α-Mg primary phase on the as-cast specimens. Moreover, the addition of 0.05 wt.% Ti elements on Mg-9Li-3(Al-Si) alloy raised the further microstructural evolutions, e.g. volume fraction of α-Mg phases, which bring about change in the microstructure after warm rolling process. The effects of this micro alloying influences the formation of fine microstructure after warm rolling process, which is the main factor in determining the mechanical properties. With these microstructural evolutions, tensile strength was increased from 101.71 MPa to 247.41 MPa by the minor alloying and warm rolling process. Moreover, the remarkably enhanced strength of Mg-9Li-3(Al-Si) alloy was the results of the addition of 0.05 wt.% Ti from 247 MPa to 412 MPa. Furthermore, the warm press-forming tests were carried out at 523 K to evaluate the applicability of this novel alloy for commercial products.

Crystallization and phase transformation behaviors of Ti 45 Cu 40 Ni 7.5 Zr 4 Sn 2.5 Si 1 bulk metallic glass composite with B2 particles were investigated by isothermal heat treatment with systematic TEM analysis. The crystallization of the amorphous phase occurs in two steps with the formation of nanocrystalline followed by the precipitation of γ-TiCu phase. On the one hand, the metastable B2 phase still maintained until crystallization process is completed. However, when the sample was heat treated longer times, the cubic B2 phase are transformed into the tetragonal γ-TiCu phase with highly lattice distortion.

Quaternary Ni-Ti-Hf-Zr high temperature shape memory alloys containing different Zr content (0–15 at.%) were prepared by arc melting and suction casting. The addition of Zr led to change in lattice parameters and monoclinic angle of B19′ martensite phase. The phase transformation temperature as well as yield strength of the alloys gradually increased with increasing the Zr content. Moreover, the alloys exhibited significant changes in phase transition and deformation behaviors. With the addition of Zr up to 7 at.%, the alloys exhibited double yielding and two-step phase transition behaviors. In contrast, alloys containing 10 and 15 at.%Zr revealed single yielding and one-step phase transition behaviors. These distinctions on phase transition and yielding behaviors of the alloys were mainly related to the structural evolution related to twinning mode in martensite phase of as-cast alloys originated from the change of lattice distortion during martensitic transformation by increasing of Zr content. Through detailed investigations on the microstructural features, thermal characteristics, mechanical properties and structural evolution on deformation of the alloys, the influence of Zr content on phase formation, phase transition and deformation behavior of Ni-Ti-Hf-Zr high temperature shape memory alloys was elucidated.

Effects of Ca addition on the microstructure and mechanical properties of as-extruded Mg-11Li-3Al-1Sn-0.4Mn-xCa alloys with x = 0 and 0.8 were investigated. The Ca addition on the Mg-11Li-3Al-1Sn-0.4Mn alloy can lead to no change in the constituent phases, which consist of β -Li, α -Mg, MgLi 2 Al and MgLi 2 Sn. However, the microstructure obtained after the extrusion process clearly exhibits different morphologies, of which Ca free alloy shows homogeneously distributed intermetallic compounds and Ca containing alloy display well-arranged intermetallic compounds along the extrusion direction. From these microstructural evolutions, even though the tensile strength decreased, the tensile elongation was significantly improved from 35.1 to 88.6%. The effect of Ca addition on the microstructural evolution and increased plastic deformability have been discussed using grain refinement, grain boundary sliding and micro crack propagation.

The gradient Al2O3 layer coated bimodal structured composite substrate was fabricated using combined chemical and hydrothermal processes. Selective etching was performed to remove micrometer-sized α-Al dendrites from the ultrafine structured matrix. Simultaneously, a hydrothermal oxidation process was used to grow Al2O3 on the surface of the porous structured substrate. In particular, the architecture of coated metal oxide (Al2O3) can be altered from a rectangular to a pyramidal shape depending on the hydrothermal process time. Keywords: Ultrafine eutectic composite, Porous materials, Dealloying, Hydrothermal process

The microstructure and compressive mechanical properties of squeeze casted Mg 15Li xAl (x = 0, 1, 3 and 5 wt%) alloys have been investigated. With addition of Aluminum (Al) in Mg 15Li alloy, the compressive yield strength is continuously increased and density is slightly decreased. This improved mechanical property is mainly attributed to the precipitation of Al Li intermetallic compounds into the β-phase and grain size refinement of β-phase. Accordingly, lightweight and high specific strength Mg Li Al alloys were developed successfully via proper addition of Al contents, resulted from favorable microstructural evolution.

In this study, we investigate the progress of stress-induced martensitic transformation depending on the stress state on TiCu-based bulk metallic glass composite via systematical transmission electron microscopy analysis. On the stage of elastic deformation (before yielding), the martensitic transformation from austenite B2 phase to martensite B19′ phase occurred from interface between B2 particle and amorphous matrix with ∼50 nm region. Just after yielding, the martensitic transformed region was extended toward B2 particle with distance of ∼130 nm from the interface. Moreover, the deformation twinning of martensite B19′ phase in martensitic transformed region was also observed. When 1% plastic deformation occurred, the martensitic transformed region reached up to ∼600 nm. Based on these results, it is believed that the high level of stress can be concentrated around the interface due to the elastic mismatch of B2 and amorphous phases. As a result, structural gradient morphology originated from phase transition was formed into the B2 particle during early stage of deformation.

Systematic investigations for the influence of the microstructural change derived from compositional tuning in Al-rich corner of Al–Cu–Si system on mechanical properties demonstrate that mechanical characteristic of ultrafine eutectic composites strongly depend on the crystallinity, length scale and volume fraction of constituent phases. Ultrafine eutectic composites can be divided into two categories: 1) whether primary phases exist or not and 2) the types of matrix phases, i.e., single eutectic or bimodal eutectic. The features of primary phases play a principal role on the macroscopic property. Ductile α-Al phase is very effective to improve the plasticity while brittle Al2Cu intermetallic phase deteriorates obviously mechanical performance. In addition, bimodal eutectic matrix alloys composed of eutectics with different length scale and morphology show superior mechanical properties than single eutectic matrix alloys. Based on the microstructural studies, it is believed that high strength is originated from ultrafine scale microstructure and enhanced plasticity is supported by strain gradient plasticity. These results reveal that mechanical properties of the ultrafine eutectic composites can be properly optimized via control of chemical and topological governing factors. Keywords: Ultrafine eutectic composite, Microstructure, Heterogeneity, Deformation mechanism

In this work, the role of individual B2 particles with bimodal length scale on work-hardening and plastic deformation behaviors of Ti-based bulk metallic glass composites has been studied by systemic microstructural and mechanical investigations. At the early stage of plastic deformation, work-hardening characteristic was clearly observed. This work-hardening behavior can be supported by the martensitic transformation and the deformation induced twinning in both small- and large-sized B2 particles during deformation. On progress of plastic deformation after work-hardening, small-sized B2 particles (1–10 μm) were penetrated by propagation of main shear bands while large-sized B2 particles (100–200 μm) were severely interacted with shear bands leading to formation of multiple shear bands and impeding the propagation of principal shear bands. This reveals that each B2 particle with different length scale plays a distinct role on the stage of plastic deformation depending on the particle size.

Porous metallic glass compact (PMGC) using electro-discharge sintering (EDS) process of gas atomized Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 metallic glass powder was developed. The formation of uniform PMGC can only be achieved when low electrical input energy was applied. Functional iron-oxides were formed on the surface of PMGCs by hydrothermal technique. This finding suggests that PMGC can be applied in the new area such as catalyst via hydrothermal technique and offer a promising guideline for using the metallic glasses as a potential functional application.

The influence of cold rolling on the tensile mechanical properties and deformation behavior of Ti-based bulk metallic glass (BMG: Ti40Zr25Ni8Cu9Be18) and β-Ti dendrite reinforced bulk metallic glass matrix composite (BMGMC: Ti40.2Zr18Ni2.85Cu7.65Be12.3Nb19) has been investigated. The cold-rolled BMG and BMGMC samples with 20% thickness reduction ratio exhibit a pronounced tensile plasticity of 0.8% and 4%, respectively. The malleable behavior of the cold-rolled samples originates from the internal structural evolution and modulation of elastic properties.

Tensile mechanical properties and deformation behavior of as-cast and cold-rolled β-Ti dendrite reinforced Ti-based bulk metallic glass matrix composite (BMGMC: Ti40.2Zr18Ni2.85Cu7.65Be12.3Nb19) have been investigated. The tensile test of the pre-strained BMGMC via cold rolling manifests a distinct necking and large plasticity of ∼4%. Such an improvement in tensile mechanical properties of the cold-rolled BMGMC is attributed to the strain-induced change of elastic properties of the glassy matrix, resulting in malleable interaction between the reinforced dendrites and the microstructural evolution derived from pre-introduced multiple shear bands, leading to uniform distribution of shear strain.

The influence of Gd addition on phase separation of rapidly quenched Cu46Zr47−xAl7Gdx metallic glasses (x = 2,5,7) was studied. For low Gd content (x = 2), a homogeneous glass is obtained for the as-quenched state. Annealing leads to cluster formation by nucleation and growth prior to crystallization. For the Gd contents x = 5 and 7, early stages of spinodal decomposition are observed in the as-quenched glasses. Further annealing increases the amplitude of the compositional fluctuations prior to crystallization. Atom probe tomography gives evidence of the presence of Gd-enriched clusters of 2–5 nm size for the Cu46Zr42Al7Gd5 glass. The structure formation as a function of the Gd content is essentially determined by the composition dependence of the miscibility gap of the metastable undercooled melt. Early stages of spinodal decomposition or almost homogeneous glassy states are obtained if the critical temperature of liquid–liquid phase separation is close or below to the glass transition temperature.

The microstructure of carbon nanotube reinforced copper matrix (CNT/Cu) nanocomposites, processed by molecular-level mixing, exhibits CNTs homogeneously dispersed in the Cu matrix. Measured thermal conductivity of the fabricated CNT/Cu nanocomposites decreased as the CNT volume fraction increased from 5% to 10%. A low coefficient of thermal expansion (CTE) was obtained from the 10 vol.% CNT/Cu nanocomposite. These results indicate that embedded CNTs provide CNT/metal interfaces as thermal barriers but also stiffen the metal matrix composites.

The constituent phases, the microstracture, and the mechanical properties of a series of Fe87-xTi7Zr6Bx (x = 0, 2, 4, 6, 8, 10, and 12) alloys produced by copper mold casting were investigated. Partial substitution of iron by boron in the Fe87Ti7Zr6 ultrafine eutectic alloy induces phase/microstructural evolution and simultaneously changes the mechanical properties. In the composition range of 2 ≤ x ≤ 6, the typical lamellar structure slightly changes into a spherical cellular-type eutectic. For 8 ≤ x ≤ 12, multiphase composites containing a glassy phase form. The ultrafine eutectic composites exhibit a high compressive strength of -2.9-3.1 GPa and a distinct plasticity of -2-8%, whereas the glassy matrix composites show a high strength of -3.1-3.3 GPa but no observable macroscopic plasticity before failure. These findings reveal that the plasticity of heterogeneous multiphase composites is strongly related to the length scale variables and the crystallinity of the constituent phases.

A new class of Al-base multi-phase ultrafine composites with multi-scale microstructure, which exhibits high strength and large compressive plasticity at ambient temperature, has been developed in the Al–Cu–Si ternary system. The formation of the favorable multi-phase multi-modal structure can be achieved by proper alloy selection and by controlling the solidification process. The developed hierarchical ultrafine composites exhibit high fracture strength of ∼1 GPa and large compressive plasticity up to ∼25%. The large macroscopic plastic strain is attributed to the combination of dislocation-based slip deformation in the ductile phase and extensive shear banding in the intermetallic phase.

In this study, we developed ductile dendrite-reinforced composites in the Ti–Zr–Ni–Cu–Be–(Nb) system. Although in situ composites have been successfully obtained by optimizing alloy composition and cooling rate, plasticity does not always occur. Only when the size, distribution, and elastic constants of the constituent phases are properly controlled, i.e. by creating homogeneously distributed dendrites with lower shear modulus than the glassy matrix, the composites exhibit large plasticity. By controlling the microstructural length scale and by tuning the intrinsic elastic constants of the constituent phases Ti-based bulk glassy matrix composites with good mechanical performance (high yield strength of ∼1.7 GPa and large plasticity of ∼25%) have been achieved.

In this work, the influence of Al and B concentration on the constituent phases and the mechanical properties of Fe100−x−yAlxBy (0

The compositional dependence of glass formation and thermal and elastic properties was clarified for the ternary La–Al–Co bulk glass-forming system. The existing linear correlation between La concentration and characteristic temperatures, i.e., the glass transition temperature Tg and the onset temperature of crystallization Tx, as well as the elastic moduli in this system can give a useful guideline for the chemical design of desirable bulk metallic glasses (BMGs) with tunable physical properties in advance. The relationship between Tg and elastic constants for the La–Al–Co BMGs can be quantitatively described using a microscopic model proposed by T. Egami.

Center for Non-crystalline Materials, Department of Materials Science and Engineering, Yonsei University, 134 Shinchondong Seodaemungu, Seoul 120-749, Korea Division of Applied Science, Cheongju University, 36 Naedokdong, Cheongju 360-764, Korea IFW Dresden, Institute for Complex Materials, P.O. Box 27 01 16, D-01171 Dresden, Germany TU Dresden, Institute of Materials Science, D-01062 Dresden, Germany

An in situ bulk ultrafine bimodal eutectic Al–Cu–Si composite was synthesized by solidification. This heterostructured composite with microstructural length scale hierarchy in the eutectic microstructure, which combines an ultrafine-scale binary cellular eutectic (α-Al + Al2Cu) and a nanometer-sized anomalous ternary eutectic (α-Al + Al2Cu + Si), exhibits high fracture strength (1.1 ± 0.1 GPa) and large compressive plastic strain (11 ± 2%) at room temperature. The improved compressive plasticity of the bimodal-nanoeutectic composite originates from homogeneous and uniform distribution of inhomogeneous plastic deformation (localized shear bands), together with strong interaction between shear bands in the spatially heterogeneous structure.

The effect of microstructural inhomogeneities with different length scale on the plasticity of (Ti45Zr16Be20Cu10Ni9)100–xTax (x = 0, 5, and 10) bulk glassy alloys has been studied. The formation of specific heterogeneous microstructures with a different type of structural inhomogeneity, i.e., short-/medium-range ordered clusters or micrometer-scale ductile dendrites combined with a glassy matrix, evolved by appropriately tuning the alloy chemistry, improves the room temperature plasticity up to ∼12.5% and ∼15%, respectively. The pronouncedly enhanced plasticity is mainly attributed to the retardation of shear localization and multiplication of shear bands by controlling the plastic and failure instabilities otherwise responsible for premature failure.

The evolution of microstructure and its influence on the mechanical properties of high-strength ultrafine eutectic Fe–(Ti, Zr)–(B, Co) alloys has been studied. The addition of B or Co improves the room temperature compressive plasticity from 1% to ∼8.5% or ∼14%, respectively, due to the formation of a heterogeneous microstructure with distinctly different length scales, which can delay the propagation of shear bands and promotes the activation of multiple shear bands.

An enhancement of plasticity in high strength ultrafine eutectic Fe–Nb composites has been accomplished by introducing heterogeneities in length-scale of the microstructure. Addition of Al acting as a stabilizer for the α-Fe phase in the Fe–Nb composites results in the formation of a larger volume fraction of primary α-Fe phase and an ultrafine eutectic structure with reduced lamellar spacing. As a result, Fe–Nb–Al composites exhibit a good combination of fracture strength and plasticity. Due to the presence of the solution hardened α-Fe phase, the Fe–Nb–Al composites exhibit significantly enhanced work hardening behavior at room temperature.

The present study shows that nanostructure–dendrite composites successfully synthesize in the Fe–Zr binary eutectic system, exhibiting a better combination of strength and plasticity than bulk metallic glass or nanograined materials. The composites composed of microscaled dendritic phases (Fe2Zr or α-Fe) and nanoscaled lamellar eutectic matrix (Fe2Zr + α-Fe) exhibit high compressive strength (1.8–2.6 GPa) and plasticity (2.5–12%) under compression. In particular, the plasticity can be improved when coarsened ductile dendritic phases are reinforced in the fine-scaled lamellar eutectic matrix.

Compressive behavior of Ti45Zr16Ni9Cu10Be20 (numbers indicate at.%) bulk metallic glasses was investigated at strain rates ranging from 10(-4) to 10(-1) s(-1). Little effect of strain rate on the mechanical properties is observed in an amorphous specimen when the strain rates are below 10(-3)s(-1). An appreciable total strain of about 5% is observed and the plastic flow is serrated. However, a positive strain rate dependence of yield strength is found when the strain rate reaches 10(-1) s(-1), which is reported for the first time in metallic glasses under a compressive loading condition. Further, the macroscopic plastic strain distinctly decreases and flow serration vanishes at a high strain rate. A comparison of the significantly different mechanical behavior of Ti45Zr16Ni9Cu10Be20 bulk metallic glass with other bulk metallic glass systems is also presented. (c) 2006 Elsevier B.V. All rights reserved.

The effects of niobium (Nb) addition on the glass-forming ability (GFA), crystallization behavior, and compressive mechanical property of iron (Fe)–boron (B)–yttrium (Y) alloys have been investigated. Among the (Fe71.2B24Y4.8)100−xNbx (x = 0, 2, 4, 6, 8) alloys investigated, (Fe71.2B24Y4.8)96Nb4 exhibits the highest GFA, enabling the formation of glassy rods with a maximum diameter of 7 mm, which is the largest among quaternary Fe-based alloys. The comparison of the crystallization behavior of the alloys shows that the formation of metastable Fe23B6 phase during crystallization in the (Fe71.2B24Y4.8)96Nb4 alloy can suppress the formation of other stable crystalline phases such as α-Fe, enhancing the stability of the glass phase. The present results show that the attainment of a significantly high GFA is possible even in a quaternary Fe-based alloy system by properly tailoring the competing crystalline phase by the modification of liquid chemistry.

The effect of Y addition on the thermal stability and glass forming ability (GFA) has been investigated in (Fe 72 Nb 4 B 20 Si 4 ) 100− x Y x ( x = 0–5) alloys. Addition of 3–5 at.% Y improves the GFA. With increasing the Y content, glass transition temperature ( T g ) and crystallization temperature ( T x ) shifted to the higher temperature region. The (Fe 72 Nb 4 B 20 Si 4 ) 97 Y 3 alloy shows a high thermal stability, with T g of 859 K and the supercooled liquid regions reached maximum value of 56 K. The (Fe 72 Nb 4 B 20 Si 4 ) 97 Y 3 alloy exhibits the largest γ (=0.402) value among the alloy investigated, enabling fabrication of bulk metallic glass (BMG) sample with the diameter of 4 mm.

The plastic strain before failure in as-cast Ti-rich Ti–Zr–Be–Cu–Ni BMGs varies to a large degree depending on the alloy composition, i.e. when the first crystallization product is quasicrystalline phase, higher plastic strain is observed. A possible reason for the enhancement of plasticity is the existence of quenched-in icosahedral nuclei embedded in the amorphous matrix.

Crystallization behavior of melt-spun and injection cast Ti–Zr–Cu–Ni–Be alloys have been studied by using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Ti 40 Zr 28 Cu 9 Ni 7 Be 16 and Ti 34 Zr 31 Cu 10 Ni 8 Be 17 amorphous alloys crystallized through a two step process during heating: Nanoscaled primary I-phase precipitated from an amorphous matrix first and the remaining amorphous phase crystallized into the cubic β-Ti(Zr) phase for Ti 40 Zr 28 Cu 9 Ni 7 Be 16 alloy and to hexagonal Laves phase for Ti 34 Zr 31 Cu 10 Ni 8 Be 17 alloy. The I-phase is stable at lower temperature and transforms into a Laves phase at high temperature through an endothermic reaction. Reversible transformation between the I-phase and Laves phase takes place during cyclic heating and cooling. In-situ composites consisting of I-phase embedded in an amorphous matrix can be fabricated by either heat treatment of fully amorphous phase or by controlling cooling rate during solidification. At lower cooling rate, I-phase forms as primary crystal in undercooled liquid and remaining liquid solidified into a glass.

(x ¼ 10, 15) BMG cylinders with thediameter up to 6mm are successfully fabricated by the injection casting method, exhibiting high Vickers hardness (681–700) and yield strength(2.0–2.1GPa). Ti-Zr-Be-Cu-Ni alloys with >50at% Ti content have higher specific strength than any other Ti-based BMGs reported so far.(Received October 6, 2003; Accepted December 11, 2003)Keywords: bulk metallic glass, glass forming ability, specific strength, titanium-zirconium-beryllium-copper-nickel

The effect of replacement of lanthanide by misch metal (Mm) in La-Al-TM (TM; transition metal, Ni, Cu and Co) alloys has been investigated to evaluate the possibility of fabrication of in-situ glass matrix composites withenhanced properties. For the as-cast cylindrical Mm 5 5 Al 2 5 Ni 1 0 Cu 1 0 alloy ingot with 3 mm diameter, the microstructure is consisted of two kinds of a few μm size crystalline phases (volume fraction: 4.6%) uniformly distributed in the metallic glass matrix. The substitution of La by Mm reduces the glass forming ability (GFA), i.e., lower the reduced glass transition temperature, Trg (= T g /T L , where T L is the liquidus temperature) and smaller superliquid temperature region, ΔT x (= T x - T g , where, Tg is the glass transition temperature and T x the onset temperatures of crystallization), enabling the fabrication of in-situ BMG matrix composite. The Mm 5 5 Al 2 5 Ni 1 0 Cu 1 0 metallic glass matrix composite sample exhibits the compressive fracture strength of 931 MPa, and in particular enhanced the compressive plastic strain of 1.2% before failure. The enhanced strength and ductility was explained by the presence of fine crystalline phases embedded in the BMG matrix, which led to a multiple shear band formation.

The crystallization behavior of bulk amorphous Ti-Zr-Be-Cu-Ni alloys has been studied by using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Detailed thermal analysis showed that Ti-Zr-Be-Cu-Ni amorphous alloys with the wide composition range crystallized through two exothermic reactions followed by one endothermic reaction. At first stage, nanometer scale primary icosahedral phase (I-phase) precipitated from an amorphous matrix and then the remaining amorphous phase crystallized into cubic � -Ti(Zr) phase or hexagonal Laves phase depending on the alloy composition. Finally, I- and � -Ti(Zr) phase or I- and Laves phase mixture transformed into the Laves phase by the high-temperature endothermic reaction, indicating that the I-phase is a thermally stable phase at the lower temperature range. Reversible transformation between the I-phase and Laves phase during cyclic heating and cooling confirmed the thermodynamic stability of the I-phase in Ti-Zr-Be-Cu-Ni system.

Deformation behavior of a Mg 72 Cu 5 Zn 23 alloy containing bimodal eutectic structure has been systematically investigated based on microstructural changes upon different amounts of compressive strain. The microstructural evolution of the sample at the early stage of the deformation up to 3% strain reveals that a large number of twins form homogeneously in the α-Mg phase of the coarse eutectic structure. After further deformation to failure, propagation of cracks takes place along the interface between the fine and coarse eutectic structures forming a typical dimple-like morphology on the fracture surface, indicative of the effective dissipation of the stress.