Present Bulk Metallic Glass Research Articles

Synthesis of Cr50Fe6Co7Mo14C15B6Y2 bulk metallic glass with integrated merits by high-content solvent element substitution and the structural origin

Novel Cr50Fe6Co7Mo14C15B6Y2 bulk metallic glass (BMG) with a critical diameter of about 1.5 mm was developed using high-content solvent element Cr substitution for Fe from the precursor Fe41Cr15Co7Mo14C15B6Y2 BMG. The alloy possesses integrated advantages of superior glass transition temperature of 981 K, extraordinary high onset temperature of crystallization of 1018 K, dramatical high compressive fracture strength of 4.49 GPa and Vickers microhardness of 14.01 GPa, and prominent corrosion resistance of no detectable weight loss in 1 M HCl solution. The structural origin for the decreased glass-forming ability of the present alloy in comparison with its precursor Fe41Cr15Co7Mo14C15B6Y2 BMG results from the lower fraction of icosahedral-type structures (with bond pair indexes of 1551, 1541, and 1431) along with the higher fraction of crystal-like structures (with bond pair indexes of 1421, 1422, 1441 and 1661), and the covalent-like Cr–C and Cr–B bonds are responsible for the superior glass transition temperature, the onset temperature of crystallization, fracture strength and hardness, based on the ab-initio molecular dynamics simulation for the local structures. The present BMG can be a preferable alloy for industrial applications under the harsh environment of high temperature, wear and corrosion.

The role of titanium content in (Ni75Cr15Si10)100−x Ti x bulk metallic glass systems to elevate mechanical and corrosion properties

ABSTRACT Bulk metallic glass (BMG) samples are amalgamated by high-energy ball milling using the general formula (Ni75Cr15Si10)100−x Ti x (labelled as NCST x , where x = 0,4, 8 and 12 at.%). The crystallinity and phase attribution properties of nickel (Ni), chromium (Cr), silicon (Si) and titanium (Ti) are scrutinized using the XRD analysis. The trend related to glass-forming ability (ΔT) and the GFA parameter (γ) is NCST8 > NCST12 > NCST4 > NCST0, which confirms that NCST8 sample shows superior glass-forming ability. The reduced glass transition temperature (T rg) for all the present BMG systems is greater than 0.5, which offers its good thermal stability and glass-forming ability (GFA). Corrosion studies suggested that a sample, having dynamic nature towards corrosion resistance and potential (E c) (NCST8, (Ni75Cr15Si10)92Ti8), exhibits relatively lower values of both i c (4.7 × 10−4 A/cm2) and i p (0.0079 A/cm2), as recommended in potentio-dynamic findings.

Ni-Mo-Si]:Nb Bulk Metallic Glasses: Microstructure, Mechanical and Corrosion Studies

We examine the effect of substituting Niobium (Nb), on the glass-forming abilities (GFA), mechanical and corrosion properties of bulk metallic glasses (BMGs). BMGs are synthesized using the general formula of (Ni75Mo15Si10)100−xNbx (x = 0, 5, 10 and 15 at.%, labeled as NMSNb0, NMSNb5, NMSNb10 and NMSNb15) that are synthesized using high energy mechanical ball milling technique. Thermal, mechanical, and corrosion properties were enhanced significantly with an increase in Niobium (Nb) content of 10 at.% (NMSNb10). Using XRD analysis, the analysis related to phase attribution and crystallizability is scrutinized. Alloying this BMG with Molybdenum (Mo) and Niobium (Nb) helped avoid embrittlement in the sulphuric acid environment, overcoming strain cracking problems caused during welding, preventing pitting, crevice corrosion, and wet corrosion. Applicability of the present BMG system is examined in light of the correlation between morphology, mechanical, and corrosion studies.

Quasi-static and dynamic deformation of an in-situ Ti-based metallic glass composite in supercooled liquid region

The quasi-static and dynamic deformation behaviors of the Ti-based bulk metallic glass (BMG) composite (Ti48Zr20Nb12Cu5Be15) were investigated in the supercooled liquid region. The present BMG composite exhibits homogenous viscous flow under quasi-static deformation, but shear-band dominated inhomogeneous plastic deformation upon dynamic loading. With the increase of the temperature, the flow stress decreases in both quasi-static and dynamic conditions. Due to the effective plastic accommodation of dendrites to the glass matrix, characteristic of the formation of shear steps and multiple dislocations, the remarkable plasticity under dynamic deformation has been obtained in the present BMG composite in SLR. The constitutive equation for the present BMG composite upon quasi-static loading is obtained. Upon dynamic loading, the flow stress approximately follows a linear relationship with the temperature: σ (MPa) ≈ 2,791–2.11T(K).

Saw-tooth-like bulk metallic glass structures with greatly enhanced energy-absorption performance

In this work, saw-tooth-like bulk metallic glass (BMG) structures were developed, exhibiting greatly enhanced energy-absorption performance as compared with existing cellular metals, such as conventional metal foams and BMG foams/honeycombs. The excellent energy absorption capacity is attributed to the change of the deformation modes from bending, buckling and collapse of the structural units in conventional cellular solids to large plastic deformation in the present BMG structures. Additionally, the energy absorption capacity of designed saw-tooth-like BMG structures can also be tuned by tailoring the periodic distribution of the structural units.

Deformation-Induced Martensitic Transformation in Cu-Zr-Zn Bulk Metallic Glass Composites

The microstructures and mechanical properties of (Cu0.5Zr0.5)100−xZnx (x = 0, 1.5, 2.5, 4.5, 7, 10, and 14 at. %) bulk metallic glass (BMG) composites were studied. CuZr martensitic crystals together with minor B2 CuZr and amorphous phases dominate the microstructures of the as-quenched samples with low Zn additions (x = 0, 1.5, and 2.5 at. %), while B2 CuZr and amorphous phases being accompanied with minor martensitic crystals form at a higher Zn content (x = 4.5, 7, 10, and 14 at. %). The fabricated Cu-Zr-Zn BMG composites exhibit macroscopically appreciable compressive plastic strain and obvious work-hardening due to the formation of multiple shear bands and the deformation-induced martensitic transformation (MT) within B2 crystals. The present BMG composites could be a good candidate as high-performance structural materials.

Strain-rate-dependent deformation behavior in a Ti-based bulk metallic glass composite upon dynamic deformation

The deformation behavior of in-situ Ti48Zr20Nb12Cu5Be15 bulk-metallic-glass (BMG) composites was investigated upon dynamic deformation. The present BMG composite exhibits good dynamic mechanical properties, combining high fracture strength (1850MPa) with remarkable plasticity (>10%) at the strain rate of 1.3×103s−1. Ductile to brittle transition occurs with the increase of strain rates, which can be ascribed to the deteriorated ability of dendrites to impede the propagation of shear bands at higher strain rates. An obvious positive to negative transition on strain rate dependence of flow stresses can be observed with the increasing strain rates. Detailed analysis reveals that the variation from the dendrite-dominated mechanism associated with dislocation movement to the matrix-dominated fracture related to thermal softening is responsible for the present transition. The constitutive equations based on their deformation mechanisms are established for describing the present transition.

Temperature dependent dynamic flow behavior of an in-situ Ti-based bulk metallic glass composite

The deformation behavior of in-situ Ti48Zr20Nb12Cu5Be15 bulk metallic glass (BMG) composites was investigated within a wide range of temperature from 77K to 573K upon dynamic loading. The present BMG composites exhibit good plasticity (about 11%) above the ambient temperature, but ductile to brittle transition occurs as the temperature lows. Further studies reveal that the deteriorated ability of dendrites to hinder the propagation of shear bands at low temperature is responsible for the present transition. With the decrease of temperature, the yield stress of the present BMG composite increases dramatically and the lower temperature also yields more obvious temperature rising in the fracture surfaces.

Glass formation, corrosion behavior, and mechanical properties of novel Cr-rich Cr–Fe–Mo–C–B–Y bulk metallic glasses

The glass formation, corrosion behavior, and mechanical properties of novel Cr-rich CrxFe58.8−xMo14.7C14.7B9.8Y2 (x=29.4, 36.75, and 44.1at.%) bulk metallic glasses (BMGs) were evaluated. It is found that the critical diameter for glass formation and supercooled liquid region remarkably decrease from 3mm to 1mm and 68K to 79K, respectively, with the increase in Cr content. Compared with SUS316 stainless steel, those BMGs exhibit more excellent corrosion resistance in 1M HCl solution. However, the corrosion resistance is not significantly improved with increasing Cr content, which may imply that the threshold value of Cr content to efficiently achieve high corrosion resistance for the present alloy system is around 29.4at.%. In addition, the fracture strength, Vickers microhardness, Young’s modulus, shear modulus, and the ratio of hardness to elastic modulus for the present BMGs are up to 4.31GPa, 14.15GPa, 249GPa, 95GPa, and 0.057, respectively.

Fatigue Behaviors of a Ni-free ZrCuFeAlAg Bulk Metallic Glass in Simulated Body Fluid

Fatigue behaviors of a biocompatible Ni-free Zr60.14Cu22.31Fe4.85Al9.7Ag3 Zr-based bulk metallic glass (BMG) have been studied under three-point-bending test in a simulated body fluid (SBF) at 37 °C and compared with those in air at room temperature (RT). The BMG shows a high fatigue limit of approximately 366 MPa in SBF, which was slightly lower than that in air (400 MPa). The fatigue cracks tended to initiate from the defects such as cast-pores, inclusions and corners of the samples and propagate in a similar path in SBF and in air. Three distinct regions, i.e. a crack-initiation region, a stable crack-growth region and an unstable fast-fracture region were clearly observed on the fatigue-fractured surface. Although pitting occurred at the defects where crack initiated, it does not affect significantly the fatigue life of the BMG, because the lifetime in the present BMG is mainly determined by crack propagation. The high corrosion-fatigue limit of the studied BMG results from its excellent corrosion resistance in SBF and intrinsically good toughness.

A Ti36.2Zr30.3Cu8.3Fe4Be21.2 bulk metallic glass with exceptional glass forming ability and remarkable compressive plasticity

The limited glass forming ability (GFA) and deficient plasticity are two longstanding bottlenecks for the applications of bulk metallic glasses (BMGs) as structural materials. In this article, we report a TiZr-based BMG with nominal composition of Ti36.2Zr30.3Cu8.3Fe4Be21.2 (at.%) which possesses exceptional GFA and remarkable compressive plasticity simultaneously. The alloy ingot in weight of 150g can be solidified into an amorphous state, indicating an exceptional GFA – the critical size for glass forming of the current BMG is estimated over 50mm. The plasticity of about 8% was obtained from the as-cast 2-mm-diameter rod with an aspect ratio of 2, concomitant obvious work hardening effect. The present BMG possessing exceptional GFA and remarkable compressive plasticity simultaneously may have a scientific importance on developing BMGs for structural applications.

High-temperature deformation and crystallization behavior of a Cu36Zr48Al8Ag8 bulk metallic glass

The influence of annealing on the crystallization behavior of a Cu36Zr48Al8Ag8 (at.%) bulk metallic glass (BMG) was investigated. In both isochronal and isothermal annealing processes, the effective activation energies of the primary crystallizations were obtained as 295.8 ± 13.4 and 302.7 ± 14.5 kJ/mol by applying the Kissinger and Ozawa methods, respectively. Using the isothermal transformation kinetics described by the Johnson–Mehl–Avrami model, the Avrami exponent n was found to range between 2.56 and 3.25, which indicates that the primary crystallization behavior was three-dimensional diffusion-controlled growth with an increasing nucleation rate. The high-temperature deformation behavior of a Cu36Zr48Al8Ag8 BMG was then investigated by performing a series of compression tests after rapid heating within a supercooled liquid region. It was found that at least 14–17 dense randomly packed atoms are necessary to produce a unit local flow when the present BMG is subjected to non-Newtonian homogeneous deformation, as described by the transition state equation. Deformation and processing maps were also constructed based on the dynamic materials model to predict optimum bulk formability in a Cu36Zr48Al8Ag8 BMG taking warm deformation-induced crystallization within a supercooled liquid into account.

Stress-State Effects on the Fracture of a Zr-Ti-Ni-Cu-Be Bulk Amorphous Alloy

The effects of wide changes in stress state on the flow and fracture behavior of a single Zr-Ti-Ni-Cu-Be bulk metallic glass (BMG) of known chemistry are summarized. Both compression and tension samples were tested with superimposed hydrostatic pressures up to 1230 MPa in addition to notched tension samples tested at 0.1 MPa as well as with 490 MPa superimposed pressure. A wider range of stress states were obtained by including compression experiments conducted in pressure/shear conditions with normal stresses up to 8.7 GPa. The critical shear stress at fracture in the present BMG chemistry and sample dimensions tested is relatively unaffected by these significant changes in stress state, again indicating the normal stress/pressure dependence of flow in this particular BMG chemistry and processing conditions is vanishingly small. The present results are compared to those obtained on other metallic glasses tested under similar conditions and those that exhibit inclusion-initiated failure that demonstrate a much different dependence for similar changes in stress state.

High strain rate response of Zr-based bulk metallic glass in supercooled liquid region

The stress–strain curves of Zr-based bulk metallic glass (BMG) were measured at very high strain rates in the supercooled liquid region (SLR) using a uniaxial compression test. For this purpose, the composite samples consisting of Zr-based metallic glass particles embedded in the crystalline nickel matrix were prepared in order to avoid rapid failure of the BMG alloy. The stress–strain curves of the BMG alloy were calculated using the data of composite samples. The strain rate sensitivity m = ∼0.1 of the present BMG alloy was determined at strain rates ranging from 10 0 to 10 1 s −1.

Ce–Cu–Fe–Al–Si Bulk Metallic Glass Alloys With High Glass Forming Ability

New Ce-Cu-Fe-Al-Si bulk metallic glasses (BMGs) with high glass formation ability (GFA) and large supercooled liquid regions (ΔT x , ΔT x = T x -T g ) were developed. Investigation shows that the addition of Fe and Si elements is very effective to improve the glass formation ability of Ce-based BMGs. For an optimizing composition, the ΔT x value is 95 K and the alloy can be prepared into bulk metallic glass rods with the diameters of at least 10mm. In the Ce-Cu-Al-Fe alloys, the glass transition temperature (Tg), crystallization temperature (T x ) and ΔT x increase with increasing Fe content. The reduced glass transition temperature (T r g = T g /T l ) of the present BMG system is about 0.5-0.6 and is much lower than that of other metal base BMG systems with high GFA. Compressive fracture strength (σ f ) and Young's modulus (E) of the Ce-Cu-Al-Fe BMGs are ∼930 MPa and ∼45 GPa, respectively, and increase with increasing Fe content.

The microprocesses of the quasicrystalline transformation in Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass

The microprocesses of the amorphous-to-quasicrystalline transformation in Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass were studied in detail by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). It was found that the amorphous-to-quasicrystalline transformation in the present system undergoes a series of interprocesses and follows the sequence of the phase transformation of amorphous →FCCZr2Ni→Tetragonal Zr2Ni→Tetragonal Zr2Ni with a domain structure →Quasicrystals. HRTEM indicated that a domain structure with a high density of stacking faults was formed in the sample at the stage just prior to the formation of quasicrystals. This special structure seems to possess the structural symmetries similar to those of icosahedral quasicrystals. Nanobeam energy dispersive x-ray spectrum revealed that atomic diffusion was involved in all interprocesses of the phase transformations. This suggests that the amorphous-to-quasicrystalline transformation in the present bulk metallic glass is a nonpolymorphous reaction.

Deformation behavior and dilatometric measurements of Nd–Fe based bulk metallic glass

Mechanical deformation and thermal expansion behavior of Nd60Fe20Co10Al10 bulk metallic glass (BMG) were studied. A stress overshoot followed by a viscous flow approaching a steady state can be seen in the stress-strain curves within a wide temperature range. Moreover, the flow behavior of the BMG is strongly dependent on the strain rate. The dilatometric measurements of the alloys during continuous heating suggest that the glass transition begins above 470 K, which is accompanied by several weak crystallization processes. The rather unique thermal stability of the Nd-Fe based BMGs is responsible for the difference in homogeneous deformation behavior between the present BMG and other BMGs. (C) 2003 Elsevier B.V. All rights reserved.

A paramagnetic Nd60Cu20Ni10Al10 alloy with high glass-forming ability

A new rare-earth Nd-based bulk metallic glass (BMG) Nd60Cu20Ni10Al10 was prepared in the shape of a rod up to 5 mm in diameter by suction casting. In contrast to the previously reported hard magnetic Nd60Fe20Co10Al10 BMG, the present BMG exhibits a distinct glass transition (GT) with low transition temperature, a stable supercooled liquid region, obvious multi-crystallization, near eutectic melting, a high reduced GT temperature and paramagnetic property.

Quasicrystal Formation in a Zr-based Bulk Metallic Glass

ABSTRACTZr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass with a diameter of 2 mm and a length of 50 mm was prepared by copper-mould casting. The metallic glass obtained follows two-step crystallization reactions with the initial formation of metastable quasicrystals from amorphous phase, followed by the formation of a stable intermetallic Zr2Cu from the post-formed quasicrystals. In this paper, the microprocess of the amorphous-to-quasicrystalline transformation of Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass was studied in detail by TEM and high resolution TEM coupled with nanobeam EDX. It was found that the amorphous-to-quasicrystalline transformation in the present system does not follow the traditional nucleation/growth mechanism. Instead, it undergoes a series of inter-processes and follows the sequence of phase transformation of amorphous → FCC Zr2Ni → Tetragonal Zr2Ni → Quasicrystals. Nanobeam EDX revealed that atomic diffusion was involved in all inter-processes of the phase transformations, suggesting that the amorphous-to-quasicrystalline transformation in the present bulk metallic glass is a non-polymorphous reaction.

Quasicrystal Formation in a Zr-based Bulk Metallic Glass

ABSTRACTZr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass with a diameter of 2 mm and a length of 50 mm was prepared by copper-mould casting. The metallic glass obtained follows two-step crystallization reactions with the initial formation of metastable quasicrystals from amorphous phase, followed by the formation of a stable intermetallic Zr2Cu from the post-formed quasicrystals. In this paper, the microprocess of the amorphous-to-quasicrystalline transformation of Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass was studied in detail by TEM and high resolution TEM coupled with nanobeam EDX. It was found that the amorphous-to-quasicrystalline transformation in the present system does not follow the traditional nucleation/growth mechanism. Instead, it undergoes a series of inter-processes and follows the sequence of phase transformation of amorphous→FCC Zr2Ni →Tetragonal Zr2Ni → Quasicrystals. Nanobeam EDX revealed that atomic diffusion was involved in all inter-processes of the phase transformations, suggesting that the amorphous-to-quasicrystalline transformation in the present bulk metallic glass is a non-polymorphous reaction.