Development and Characterization of Low-Density Ca-Based Bulk Metallic Glasses: An Overview

Ca-based bulk metallic glasses (BMGs) have unique properties and represent a new seventh group of BMGs. Many of them have excellent GFA, which can be related to their efficient atomic packing, low onset driving force for crystallization, and high viscosity (high relaxation time) of the supercooled liquid. The Ca-based glasses have the lowest density and elastic moduli among all BMGs discovered to date. Unfortunately, as many other glasses, Ca-based BMGs are brittle below the glass transition temperature, and they also have marginal oxidation and corrosion resistance. The latter can be improved by proper selection of alloying elements. In this article, we review recent work on the development of low-density Ca-based BMGs and discuss the effect of alloy composition on the thermal, physical, and chemical properties of these glasses. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Self-organized Criticality Behavior in Bulk Metallic Glasses

Serrated flows are known as repeated yielding of bulk metallic glasses (BMGs)during plastic deformation under different loading conditions,which are associated with the operation of shear banding.According to the statis-tics of some parameters,the shear avalanches can display a self-organized critical state,suggesting a large ductility of BMGs.The emergence of the self-organized criticality (SOC)behavior in different BMGs is due to the tempera-ture,strain rate,and chemical compositions.The SOC behavior is accompanied with the following phenomena:the interactions occur in the shear bands;the incubation time is longer than the relaxation time;the time interval is lac-king of typical time scale;and the spatial or temporal parameters should display a power-law distribution.     

Bulk Metallic Glasses VI

Symposium: Bulk Metallic Glasses VI

Bulk Metallic Glasses VI Foreword     

Oxidation and Crystallization Behavior of Quinary Zr-Based Bulk Metallic Glasses

Non-isothermal and isothermal oxidation behavior of four Zr-based bulk metallic glasses (Zr₅₈Cu₂₂Co₄Ag₄Al₁₂, Zr₅₈Cu₂₂Co₂Ag₆Al₁₂, Zr₅₈Cu₂₂Fe₄Ag₄Al₁₂, and Zr₅₈Cu₂₂Fe₂Ag₆Al₁₂ (compositions are in at.%)) has been studied in oxygen environment. Non-isothermal oxidation has been performed at different heating rates up to 1,173 K to understand the effect of progressive crystallization on the oxidation behavior. In addition, crystallization behavior of the glassy alloys has been studied, and activation energies have been calculated in an inert and oxygen environment. Partial replacement of iron with silver and cobalt has a distinct effect on the oxidation and crystallization behavior of the alloys. Oxidation of the glassy alloys starts with the dissolution of oxygen in the amorphous matrix followed by rapid oxidation after crystallization.     

Nanocrystallization in Cu-Zr-Al-Sm Bulk Metallic Glasses

Metallurgical and Materials Transactions A - The effect of rare-earth element (Sm) microalloying on the thermal stability and crystallization kinetics of melt-spun ribbons and suction-cast rods of...     

Tough Hypoeutectic Zr-Based Bulk Metallic Glasses

Significant softening of Zr-based bulk metallic glasses (BMGs) can be seen in a hypoeutectic Zr-enriched composition, which brings about very high toughness (for the Zr₅₅Cu₃₅Al₁₀ and Zr₆₀Cu₃₀Al₁₀ BMGs) and tensile plasticity at room temperature (for the Zr₇₀Ni₁₆Cu₆Al₈ BMG). The unique features of such BMGs include the formation of multiple shear bands and harmonic alternating movements that can immediately accommodate concentrated stresses and avoid accidental catastrophic fracture.     

Thermodynamics and Magnetostriction of Fe-Co-B-Si-Nb-C Bulk Metallic Glasses

Fe-Co-B-Si-Nb-C glassy alloy with the addition of C was prepared by arc melting and copper suck-casting. The thermodynamics and soft magnetic properties were investigated. The casted amorphous alloys were heat-treated at different temperatures. The differential scanning calorimeter (DSC) results and thermal expansion show complete thermodynamics of crystallization. Its magnetostriction properties were studied by capacitance method. Saturation magnetostriction increases to 38×10-6. The amorphous alloy exhibits good soft magnetic properties with low coercivity and high saturation magnetic induction. The results show that minor addition of C is beneficial to enhance the saturation magnetostriction λs, and do not deteriorate the ability of forming amorphous.     

Ti对部分晶化Ni基非晶合金电化学腐蚀性能的影响

采用水冷铜模吸铸法制备出部分晶化的Ni55Nb30Sn5Ti5Zr5和Ni55Nb30Sn5Zr10块体非晶合金,并利用X射线衍射（XRD）分析和示差扫描量热仪分析（DSC）对合金的相组成及热物性参数进行了测量分析。采用极化曲线法研究合金在不同溶液中的腐蚀行为,并利用失重法测定合金在10%HCl溶液中的腐蚀速率,对腐蚀后的显微形貌及表面成分进行了扫描电镜（SEM）观察和能谱分析（EDS）。结果表明,Ni55Nb30Sn5Ti5Zr5合金比Ni55Nb30Sn5Zr10合金具有更宽的过冷液相区和更好的抗腐蚀性能。随着合金晶化相的增多,合金抗腐蚀性能降低。Ti元素的加入可在合金表面形成氧化钛的保护膜,从而使合金的抗腐蚀性能提高。     

Crystallization Kinetics of Misch Metal Based Bulk Metallic Glasses

Bulk metallic glasses (BMGs) have been devel-opedrecentlyin many multi-component metal systems .These BMGs exhibit unique properties such as highstrength,high elastic li mit ,high corrosion resistanceand wear resistance , and low coercivity etc . Sincethe…     

Understanding the Problem of Fatigue in Bulk Metallic Glasses

Early studies suggested there was a severe problem with the fatigue resistance of some bulk metallic glasses (BMGs) and BMG matrix composites, while more recent studies begin to demonstrate a wide variety of fatigue behaviors may be possible for both fully amorphous BMGs and their composites. However, in order to truly understand and control the fatigue behavior of these materials, the role of such factors as thermomechanical processing, the corresponding glass structure, environment, and defects must be understood. Additionally, it is important to understand how these factors relate to the mechanisms of fatigue. This article reviews the current understanding in this regard, and identifies some of the challenges for the future development of fatigue-resistant BMG-based materials.     

Chemical Short-Range-Ordering Effect on Structural Relaxation in Metallic Glasses

A model is proposed to address chemical effects on structural relaxation in metallic glasses. The atomic short range ordering (SRO) is described under the quasi-chemical approximation (QCA). Local chemical deviations from the ideal SRO are considered as an excess enthalpy. The simplified analysis of a disordered region’s evolution is based on the notion of the collective bond exchange between neighboring atoms. The approach suggests a bimolecular mechanism with possibly large apparent activation energy for structural relaxation near the glass transitions. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Ductile Ti-Based Bulk Metallic Glasses with High Specific Strength

Ti-based bulk metallic glasses (BMGs) with large compressive plasticity were developed in the Ti-rich part of Vitreloy series BMGs (Ti_65–x Zr _x Cu₉Ni₈Be₁₈ alloys with x = 0, 5, 10, 15, and 20). The current materials exhibit high fracture strength reaching ~2.3 GPa and plastic strains up to ~8.3 pct after partial substitution of Zr by Ti. The plasticity of the investigated alloys strongly depends on the Zr content, which affects the elastic constants, such as Poisson’s ratio and shear modulus. This, in turn, has an impact on the shear transformation zone (STZ) volume and, hence, on the shear banding of the glasses.     

Ti-Cu-Zr-Fe-Sn-Si-Ag-Pd Bulk Metallic Glasses with Potential for Biomedical Applications

Ti₄₇Cu_38−xZr_7.5Fe_2.5Sn₂Si₁Ag₂Pd_x (x = 1, 2, 3, and 4 atomic percent, at. pct) bulk metallic glasses (BMGs) with potential for biomedical applications were fabricated by copper-mold casting. The Ti-based BMGs exhibited high glass-forming ability (GFA) with critical diameters of 4 to 5 mm and a supercooled liquid region over 50 K, though the high contents of Pd slightly decreased the GFA. The additions of 2 and 3 at. pct Pd benefited the improvement of plasticity, and the resultant BMGs showed the relatively low Young’s modulus of about 100 GPa, high compressive strengths of 2174 to 2340 MPa, and compressive plastic strain of around 4 pct. The addition of Pd also decreased the passive current density and increased the pitting potential of the Ti-based BMGs in the Hank’s solution, leading to the enhanced bio-corrosion resistance of the BMGs. Furthermore, the cell adhesion, viability, and proliferation behaviors revealed that the present Ti-based BMGs possess as good biocompatibility as that of the Ti-6Al-4V alloy. These results demonstrated the potential of the Ti-Cu-Zr-Fe-Sn-Si-Ag-Pd BMGs as biomedical materials.

     

Biocompatibility Study of Zirconium-Based Bulk Metallic Glasses for Orthopedic Applications

Bulk metallic glasses (BMGs) represent an emerging class of materials that offer an attractive combination of properties, such as high strength, low modulus, good fatigue limit, and near-net-shape formability. The BMGs have been explored in mechanical, chemical, and magnetic applications. However, little research has been attracted in the biomedical field. In this work, we study the potential of BMGs for the orthopedic repair and replacement. We report the biocompatibility study of zirconium (Zr)–based solid BMGs using mouse osteoblast cells. Cell attachment, proliferation, and differentiation are compared to Ti-6Al-4V, a well-studied alloy biomaterial. Our in-vitro study has demonstrated that cells cultured on the Zr-based BMG substrate showed higher attachment, alkaline phosphatase activity, and bone matrix deposition compared to those grown on the control Ti alloy substrate. Cytotoxicity staining also revealed the remarkable viability of cells growing on the BMG substrates.     

Designing Zr-Cu-Co-Al Bulk Metallic Glasses with Phase Separation Mediated Plasticity

New Zr-based bulk metallic glasses (BMGs) with improved plasticity were developed in the Zr-Cu-Co-Al system by a combination of Zr₄₅Cu₅₀Al₅ and Zr₅₅Co₂₅Al₂₀ BMGs with a certain concentration ratio. The compressive plasticity of the investigated alloys depends strongly on the concentration ratio of the two BMGs. Because of the positive enthalpy of mixing between Cu and Co (??H_Cu-Co?=?+9?kJ/mol), a strong repulsive interaction between Cu and Co is introduced, whereas an attractive interaction exists among the other constituent elements in the liquid state. When two BMGs are combined at a 1:1 concentration ratio, a maximum compressive plasticity of ~12?pct is achieved for the Zr₅₀Cu₂₅Co_12.5Al_12.5 BMG. The plasticity enhancement is attributed to atomic-scale chemical/structural fluctuations achieved through liquid-phase separation.     

Structural Relaxation, Glass Transition, Viscous Formability, and Crystallization of Zr-Cu–Based Bulk Metallic Glasses on Heating

In this article, we summarize our recent findings on relaxation, glass transition, viscous flow, and crystallization of Zr-Cu?Cbased metallic glasses on heating. At least two processes related to the diffusivities of different alloying elements take place in the glass-transition region of a Zr-Cu-Al-Ni glassy alloy. Also, we report an unusual solidification behavior of the bulk glassy alloy produced using low-purity Zr in which both primary and eutectic-type structural constituents were formed simultaneously during solidification of the melt. In addition, viscous flow and structure changes in the Zr-Cu-Al-Ag glassy alloy are examined in both the glass-transition and supercooled liquid regions. This alloy is found to exhibit localized phase separation leading to nanocrystallization before massive crystallization of the entire sample.     

Preparation and Mechanical Properties of Misch Metal Based Bulk Metallic Glasses

Bulk metallic glasses(BMGs)have been devel-oped in many alloy systems during past decade.Among these systems,rare-earth(RE)metal-basedBMGs are ones of those found earliest and with betterglass forming ability(GFA).For example,La-basedBMGs were the first a…     

Increased Toughness of Zirconium-Based Bulk Metallic Glasses Tested under Mixed Mode Conditions

The effects of mixed mode loading on the fracture behavior of Zr-based bulk metallic glasses (BMGs) (Vitreloy I and Vitreloy 106) were investigated. Mixed mode I/II and mixed mode I/III fracture conditions were tested using both notched and fatigue-precracked specimens. Fully amorphous samples exhibited tremendous increases in fracture energy with the application of mixed mode loading, while partially crystalline samples exhibited more modest increases. A comparison to the behavior of other material systems (e.g., polymers, ceramics, crystalline metals, and composites) illustrates the tremendous increase in fracture energy exhibited by these BMGs under mixed mode loading conditions.