The potential of Zr-based bulk metallic glasses as biomaterials

Zr-based bulk metallic glasses (BMGs) are a new type of metallic materials with disordered atomic structure that exhibit high strength and high elastic strain, relatively low Young’s modulus, and excellent corrosion resistance and biocompatibility. The combination of these unique properties makes the Zr-based BMGs very promising for biomaterials applications. In this review article, the authors give an overview of the recent progress in the study of biocompatibility of Zr-based BMGs, especially the relevant work that has been done in the metallic glasses group in Huazhong University of Science and Technology (HUST), including the development of Ni-free Zr-based BMGs, the mechanical and wear properties, the bio-corrosion resistance, the in vitro and in vivo biocompatibility and the bioactive surface modification of these newly developed BMGs.     

Design of Zr–Al–Ni–Cu bulk metallic glasses with network structures

A series of Zr–Al–Ni–Cu bulk metallic glasses (BMGs) with network structures were carefully designed and their heterogeneous microstructures were investigated by carefully etching the cross sections of these BMGs. It is found that the heterogeneous microstructures of these BMGs can be uncovered by etching with mixed solution of HF and HNO₃. Some of the studied Zr-based BMGs characterize in micrometer network structure. The cell size of the network structure depends on the composition of the BMG and is related with the fractural mode and mechanical property. The found network structure of the Zr-based BMGs benefits for understanding the unique mechanical properties of the Zr-based BMGs.     

Metallic glasses from “alchemy” to pure science: Present and future of design,processing and applications of glassy metals

Metallic glasses, first discovered a half century ago, are currently among the most studied metallic materials. Available in sizes up to several centimeters, with many novel, applicable properties, metallic glasses have also been the focus of research advancing the understanding of liquids and of glasses in general.Metallic glasses (MGs), called also bulk metallic glasses (BMGs) (or glassy metals, amorphous metals, liquid metals) are considered to be the materials of the future. Due to their high strength, metallic glasses have a number of interesting applications, for example as coatings. Metallic glasses can also be corrosion resistant. Metallic glasses, and the crystalline materials derived from them, can have very good resistance to sliding and abrasive wear. Combined with their strength – and now, toughness – this makes them ideal candidates for bio-implants or military applications. Prestigious Journals such as “Nature Materials”, “Nature” frequently publish new findings on these unusual glass materials. Moreover Chinese and Asian scientists have also been showing an interest in the study of metallic glasses.This review paper is far from exhaustive, but tries to cover the areas of interest as it follows: a short history, the local structure of BMGs and the glass forming ability (GFA), BMGs’ properties, the manufacturing and some applications of BMGs and finally, about the future of BMGs as valuable materials.     

Surface features of Zr-based and Ti-based metallic glasses by ion irradiation

Due to a lack of crystalline structures and grain boundaries, metallic glasses exhibit extremely high strength and superior resistance to corrosion. They are also supposed to be resistant against displacive irradiation due to their inherent disordered structure, thereby are potential candidates for applications in irradiation environments. In this work, the irradiation effects of Zr- and Ti- based bulk metallic glasses (BMGs) under heavy ions irradiation were investigated. The results showed that the Zr-based BMG is more resistant to the Cl ion irradiation with no structural transition and distinct damage subjected to high irradiation fluence. In contrast, the Ti-based BMG exhibits unique damage morphology with respect to the Zr-based BMG and other reported metallic glasses material. Two kinds of damage pits in micrometer scale form on the irradiated surface, and distinct viscous flow takes place. The formation mechanism of the unique irradiation damage feature is discussed.     

Crystallization Behaviour and Mechanical Properties of Zr65Cu18Ni9A18 Bulk Metallic Glass

Designing and synthesis of cost effective bulk metallic glasses （BMGs） has been of considerable interest during the last decade so that they can be made commercially viable. Among these, Zr-based BMGs have been reported extensively due to their attractive properties, An alloy having composition Zr65Cu18Ni9A18 was designed and synthesized using 2-3 N pure materials by Cu mould casting. The alloy was characterized by X- ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS） and high temperature differential scanning calorimetry （DSC）. Thermal parameters like supercooled liquid region △Tx, reduced glass transition temperature Trg, γ and δ parameters were evaluated. Mechanical properties like microhardness, nanohardness, elastic modulus and fracture strength were measured. The alloy showed wide supercooled liquid region of 129＋1 K with improved thermal stability. The alloy has considerable fracture strength along with fair amount of ductility.     

Crystallization Behaviour and Mechanical Properties of Zr65Cu18Ni9Al8 Bulk Metallic Glass

Designing and synthesis of cost effective bulk metallic glasses (BMGs) has been of considerable interest during the last decade so that they can be made commercially viable. Among these, Zr-based BMGs have been reported extensively due to their attractive properties. An alloy having composition Zr65Cu18Ni9Al8 was designed and synthesized using 2-3 N pure materials by Cu mould casting. The alloy was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and high temperature differential scanning calorimetry (DSC). Thermal parameters like supercooled liquid region ΔTX, reduced glass transition temperature Trg, γand σ parameters were evaluated. Mechanical properties like microhardness, nanohardness, elastic modulus and fracture strength were measured. The alloy showed wide supercooled liquid region of 129±1 K with improved thermal stability. The alloy has considerable fracture strength along with fair amount of ductility.     

Rapid solidification of zirconium-based alloys

Zr based metal-metal binary and ternary alloys can be obtained in the amorphous state in very wide composition ranges. Several eutectic reactions and intermetallic compounds are present in these alloy systems which provide opportunities for examining the validity of different theories on glass formation. The amorphous phases in these alloys decompose by a variety of crystallization mechanisms. Instances of polymorphic, primary and eutectic crystallization have been encountered in these glasses. Zr-based metallic glasses possess excellent corrosion resistance and mechanical properties. In several studies their properties have been compared with that of their crystalline counterparts and interesting differences have emerged. In the solute lean Zr-based alloys very large freezing ranges are available for studying the liquid to solid transformation. It has been possible to study the formation of some of the low temperature phases directly from the liquid. This paper describes some of the aforementationed studies carried out on Zr-based amorphous and crystalline alloys.     

Plastic deformation of Zr-based bulk metallic glasses under nanoindentation

The plastic deformation of two Zr-based bulk metallic glasses (BMGs), Zr₅₅Cu₃₀Ni₅Al₁₀ and Zr_69.5Cu₁₂Ni₁₁Al_7.5, was investigated by instrumented nanoindentation over a broad range of loading rates. It was found that the plastic flow of the two BMGs exhibited conspicuous serrations at low loading rates. The serrations, however, became less prominent as the rate of indentation increased. AFM showed a significant pile-up of materials around the indents, indicating that a highly localized plastic deformation occurred under nanoindentation. The mechanism governing the plastic deformation in BMGs was tentatively discussed in terms of the mode of strain-induced free volume.     

Zirconium Alloys for Orthopaedic and Dental Applications

Zirconium alloys for biomedical applications are receiving increasing attention due to their two unique properties: 1) the formation of an intrinsic bone‐like apatite layer on their surfaces in body environments, and 2) better compatibility with magnetic resonance imaging (MRI) diagnostics due to their low magnetic susceptibility, as well as their overall excellent biocompatibility, mechanical properties, and bio‐corrosion resistance. In particular, since both of the MRI quality and speed depend on magnetic field strength, there is a compelling drive for use of high magnetic field strength (>3 Tesla) MRI systems. This paper provides a comprehensive review of the characteristics of commercially pure (CP) Zr and Zr‐based alloys as orthopaedic and dental implant materials. These include their 1) phase transformations; 2) unique properties including corrosion resistance, biocompatibility, magnetic susceptibility, shape memory effect, and super‐elasticity; 3) mechanical properties; 4) current orthopaedic and dental applications; and 5) the d‐electron theory for Zr alloy design and novel Zr‐alloys. The mechanical properties of Zr‐based bulk metallic glasses (BMGs) and their application as implant materials are also assessed. Future directions for extending the use of Zr‐alloys as orthopaedic and dental implants are discussed.

     

Simulated body-fluid tests and electrochemical investigations on biocompatibility of metallic glasses

This paper presents the in-vitro and electrochemical investigations of four metallic glasses (MGs) for finding potential MG-based bio-materials. The simulation body-fluid Hanks solution is utilized for testing the corrosion resistance of MGs, and microorganisms of Escherichia coli are used in testing the bio-toxicity. In addition, a simple cyclic voltammetry method is used for rapid verification of the potential electrochemical responses. It is found that the Zr-based MG can sustain in the body-fluid, exhibiting the best corrosion resistance and electrochemical stability. The microbiologic test shows that E. coli can grow on the surface of the Zr-based metallic glass, confirming the low cell toxicity of this Zr-based MG.     

Bulk Metallic Glasses with Functional Physical Properties

In this review, we report on the formation of a variety of novel, metallic, glassy materials that might well have applications as functional materials. The metallic glasses, with excellent glass‐forming ability, display many fascinating properties and features such as excellent wave‐absorption ability, exceptionally low glass‐transition temperatures (～35–60 °C) approaching room temperature, ultralow elastic moduli comparable to that of human bone, high elasticity and high strength, superplasticity and polymer‐like thermoplastic formability near room temperature, an excellent magnetocaloric effect, hard magnetism and tunable magnetic properties, heavy‐fermion behavior, superhydrophobicity and superoleophobicity, and polyamorphism, all of which are of interest not only for basic research but also for technological applications. A strategy based on elastic‐moduli correlations for fabrication of bulk metallic glasses (BMGs) with controllable properties is presented. The work has implications in the search for novel metallic glasses with unique functional properties, for advancing our understanding of the nature and formation of glasses, and for extending the applications of the materials.     

Ultra-high strength Mg-Li based bulk metallic glasses: Preparation and performance research

In this paper, new Mg-Li based bulk metallic glasses (BMGs) are prepared by conventional copper mold injection casting method. The alloys exhibit excellent mechanical properties, such as ultra-high compressive fracture strength (maximal 729 MPa), high Vickers hardness (>2 GPa) and low elastic modulus (∼35 GPa). Compared with the corresponding crystal alloys, the density of the amorphous alloy samples is reduced by about 1.5% due to their free volume. Thus, it is believed that this new BMGs with these outstanding properties will broaden Mg-Li based alloys’ application fields.     

Bulk metallic glass: the smaller the better

Bulk metallic glasses (BMGs) are strong, highly elastic, and resistant to wear but still find limited utility due to their macroscopic brittle nature, high costs, and difficulty of processing, particularly when complex shapes are desired. These drawbacks can be mitigated when BMGs are used in miniature parts (< 1 cm), an application which takes advantage of BMGs' enhanced plasticity at small length scales as well the insignificant material cost associated with such parts. As an alternative to traditional metal processing techniques, thermoplastic forming (TPF)-based microfabrication methods have been developed which can process some BMGs like plastics. In this article, we discuss the properties and fabrication of BMGs on minuscule length scales to explore their prospective application in small-scale devices.     

Mechanical and corrosion behaviour of in situ intermetallic phases reinforced Mg-based glass composite

A (Mg₆₅Cu₁₀Ni₁₀Y₁₀Zn₅)₉₁Zr₉ bulk metallic glass matrix composite, reinforced by in situ formed intermetallic phase, has been fabricated. In contrast to the monolithic Mg-based bulk metallic glasses (BMGs), the composite showed much higher fracture strength of 1039?MPa and a significant plastic strain of more than 5%. Moreover, the effect of in situ formed intermetallic phase on the corrosion behaviour of the composite was also studied. The results indicated that the corrosion resistance of the composite was only slightly lower than that of the monolithic Mg-based BMGs, but still much higher than that of the AZ31 magnesium alloy. This finding gives us a new clue to enhance the mechanical properties and corrosion resistance of Mg-based alloy by designing appropriate metallic glass composites.     

Formation of MgNiPr bulk metallic glasses in air

The Mg–Ni–Pr bulk metallic glasses (BMGs) can be easily cast into glassy rods up to 3 mm in diameter in argon and air atmosphere. The underlying mechanism for the unusual oxygen resistance during the preparation process and high glass forming ability of the alloy are investigated and discussed.     

Fatigue behavior of Zr-based bulk-metallic glasses

The objective of this paper was to study the fatigue characteristics of zirconium (Zr)-based bulk-metallic glasses (BMGs) and to investigate the mechanisms of fatigue-crack initiation, crack propagation, and fracture in BMGs. The fatigue ratios (fatigue limit/tensile strength) (0.30–0.55) of Zr-based BMGs were found to be generally comparable with those of crystalline alloys, such as steel and titanium alloys. Fatigue cracks typically initiate from shear bands, inclusions, and/or porosities. The striations resulting from the blunting and resharpening of the fatigue-crack tip formed in the fatigue-crack-growth region. The fine striation spacing seems to be comparable to that of the crystalline alloys.     

Additive Manufacturing of Advanced Multi‐Component Alloys: Bulk Metallic Glasses and High Entropy Alloys

Bulk metallic glasses (BMGs) and high entropy alloys (HEAs) are both important multi‐component alloys with novel microstructures and unique properties, which make them promising for applications in many industries. However, certain hindrances have been identified in the fabrication of BMGs and HEAs by conventional techniques due to the intrinsic requirements of BMGs and HEAs. With the advent of metal additive manufacturing, new opportunities have been perceived to fabricate geometrically complex BMGs and HEAs with tailorable microstructure theoretically at any site within the specimen, which are not achievable using conventional fabrication techniques. After providing some background and introducing the conventional fabrication techniques for BMGs and HEAs, this review will focus on the current status, development, and challenges in metal additive manufacturing of BMGs and HEAs including different additive manufacturing techniques being used, microstructure design and evolution, as well as properties of the fabricated BMGs and HEAs. A future outlook of metal additive manufacturing of BMGs and HEAs will also be provided at the end.

     

The elastic properties, elastic models and elastic perspectives of metallic glasses

Bulk metallic glass (BMG) provides plentiful precise knowledge of fundamental parameters of elastic moduli, which offer a benchmark reference point for understanding and applications of the glassy materials. This paper comprehensively reviews the current state of the art of the study of elastic properties, the establishments of correlations between elastic moduli and properties/features, and the elastic models and elastic perspectives of metallic glasses. The goal is to show the key roles of elastic moduli in study, formation, and understanding of metallic glasses, and to present a comprehensive elastic perspectives on the major fundamental issues from processing to structure to properties in the rapidly moving field.A plentiful of data and results involving in acoustic velocities, elastic constants and their response to aging, relaxation, applied press, pressure and temperature of the metallic glasses have been compiled. The thermodynamic and kinetic parameters, stability, mechanical and physical properties of various available metallic glasses especially BMGs have also been collected. A survey based on the plentiful experimental data reveals that the linear elastic constants have striking systematic correlations with the microstructural features, glass transition temperature, melting temperature, relaxation behavior, boson peak, strength, hardness, plastic yielding of the glass, and even rheological properties of the glass forming liquids. The elastic constants of BMGs also show a correlation with a weighted average of the elastic constants of the constituent elements. We show that the elastic moduli correlations can assist in selecting alloying components with suitable elastic moduli for controlling the elastic properties and glass-forming ability of the metallic glasses, and thus the results would enable the design, control and tuning of the formation and properties of metallic glasses.We demonstrate that the glass transition, the primary and secondary relaxations, plastic deformation and yield can be attributed to the free volume increase induced flow, and the flow can be modeled as the activated hopping between the inherent states in the potential energy landscape. We then propose an extended elastic model to understand flow in metallic glass and glass-forming supercooled liquid, and the model presents a simple and quantitative mathematic expression for flow activation energy of various glasses. The elastic perspectives, which consider all metallic glasses exhibit universal behavior based on a small number of readily measurable parameters of elastic moduli, are presented for understanding the nature and diverse properties of the metallic glasses.     

Ductile Fe-based bulk metallic glasses at room temperature

In this work, Fe₇₀Ni₁₀P₁₃C₇ and Fe₆₀Ni₂₀P₁₃C₇ bulk metallic glasses (BMGs) with high ductility are synthesised through the appropriate adjustment of flux conditions. Microstructure analyses indicate that the ductility of these two Fe-based BMGs is primarily determined by Fe–Ni and Ni–Ni metal–metal bonds, which enable the glasses to undergo a strain of more than 50% in the absence of fracture, as well as extensive bending ductility, similar to metals such as Fe and Ni. This study aims to find a solution to the brittleness problem in Fe-based BMGs, and the results have implications for understanding the deformation mechanism in Fe-based BMGs.     

Formation and properties of new heavy rare-earth-based bulk metallic glasses

A series of new families of heavy rare-earth (RE) based bulk metallic glasses (BMGs) with excellent glass-forming ability and high thermal stability have been obtained by a copper mold casting method. Compared with the light RE-based BMGs, the heavy RE-based BMGs have much higher glass transition and crystallization temperatures and higher elastic moduli. It is found that the thermal stability is closely correlated with the elastic constants in the RE-based BMGs. The correlations found are useful for guiding BMG-forming alloy design to enhance stability.