Preparation of 16 mm Diameter Rod of Amorphous Zr65Al7.5Ni10Cu17.5 Alloy

Non-Equal Contributions of Different Elements and Atomic Bonds to the Strength and Deformability of a Multicomponent Metallic Glass Zr47Cu46Al7

Multicomponent metallic glasses (MGs) are a fascinating class of advanced alloys known for their exceptional properties such as limit-approaching strength, high hardness and corrosion resistance, and near-net-shape castability. One important question regarding these materials that remains unanswered is how the different elements and atomic bonds within them control their strength and deformability. Here, we present a detailed visual and statistical analysis of the behaviors of various elements and atomic bonds in the Zr47Cu46Al7 (at%) MG during a uniaxial tensile test (in the z-direction) simulated using molecular dynamics. Specifically, we investigate the identities of atoms undergoing significant shear strain, and the averaged bond lengths, projected z-lengths, and z-angles (angles with respect to the z-direction) of all the atomic bonds as functions of increasing strain. We show that, prior to yielding, the Zr element and the intermediate (Zr-Zr, Cu-Al) and stronger (Zr-Al, Zr-Cu) bonds dominate the elastic deformation and strength, while the Cu and Al elements and the weaker Al-Al and Cu-Cu bonds contribute more to the highly localized shear transformation. The significant reconstruction, as signified by the cessation of bond-length increment and bond-angle decrement, of the intermediate and the stronger bonds triggers yielding of the material. After yielding, all the elements and bonds participate in the plastic deformation while the stronger bonds contribute more to the residual strength and the ultimate (fracture) strain. The results provide new insights into the atomic mechanisms underlying the mechanical behavior of multicomponent MGs, and may assist in the future design of MG compositions towards better combination of strength and deformability.

Multi-Scale Traditional and Non-Traditional Machining of Bulk Metallic Glasses (BMGs)-Review of Challenges, Recent Advances, and Future Directions

Bulk metallic glasses (BMGs) are growing in popularity prominently due to their potential in micro-electromechanical systems (MEMSs) and aerospace applications. BMGs have unique mechanical properties, i.e., high strength, hardness, modulus of elasticity, and wear resistance, due to their disordered atomic structure. Due to their unique mechanical properties and amorphous structures, machining of BMGs remains a challenge. This paper aims to carry out a detailed literature review on various aspects of the machining of bulk metallic glasses using both conventional and non-conventional processes, including experimental approaches, modeling, statistical findings, challenges, and guidelines for machining this difficult-to-machine material. Conventional machining processes were found to be challenging for machining bulk metallic glasses due to their high hardness, brittleness, and tendency to convert their amorphous structure into a crystalline structure, especially at the machined surface and sub-surface. Although their high electrical conductivity makes them suitable for machining by non-conventional processes, they impose new challenges such as heat-affected zones and crystallization. Therefore, the successful machining of BMGs requires more in-depth analysis of cutting forces, tool wear, burr formation, surface finish, recast layers or heat-affected zones, crystallization, and mechanical property changes among different varieties of BMGs. This review paper provides guidelines emerging from in-depth analysis of previous studies, as well as offering directions for future research in the machining of BMGs.

Crystallization Kinetics and Consolidation of Al82La10Fe4Ni4 Glassy Alloy Powder by Spark Plasma Sintering

The mechanically alloyed Al82La10Ni4Fe4 glassy powder displays a two-step devitrification characterized by the precipitation of fcc-Al together with small amounts of the intermetallic Al11La3 phase in the first crystallization. The interface-controlled growth mechanism governed the first crystallization event. Calculations of the activation energy, using the methods of Kissinger, Ozawa, and Augis-Bennett gave values of 432.33, 443.2, and 437.76 kJ/mol, respectively. The calculated Avrami exponent (n) for the first crystallization peak was about 1.41, suggesting an almost zero nucleation rate. On the other hand, the value of n for the second peak related to the residual amorphous phase completely transformed into the intermetallic phase Al11La3 was about 3.61, characterizing diffusion controlled three-dimensional crystal growth with an increasing nucleation rate. Samples sintered at 573 K kept an amorphous structure and exhibited a high compressive strength of 650 MPa with a maximum elongation of 2.34% without any plastic deformation. The failure morphology of the sintered sample surface presented a transparticle fracture mechanism, indicating the efficiency of the sintering processing.

A Critical Review on Metallic Glasses as Structural Materials for Cardiovascular Stent Applications

Functional and mechanical properties of novel biomaterials must be carefully evaluated to guarantee long-term biocompatibility and structural integrity of implantable medical devices. Owing to the combination of metallic bonding and amorphous structure, metallic glasses (MGs) exhibit extraordinary properties superior to conventional crystalline metallic alloys, placing them at the frontier of biomaterials research. MGs have potential to improve corrosion resistance, biocompatibility, strength, and longevity of biomedical implants, and hence are promising materials for cardiovascular stent applications. Nevertheless, while functional properties and biocompatibility of MGs have been widely investigated and validated, a solid understanding of their mechanical performance during different stages in stent applications is still scarce. In this review, we provide a brief, yet comprehensive account on the general aspects of MGs regarding their formation, processing, structure, mechanical, and chemical properties. More specifically, we focus on the additive manufacturing (AM) of MGs, their outstanding high strength and resilience, and their fatigue properties. The interconnection between processing, structure and mechanical behaviour of MGs is highlighted. We further review the main categories of cardiovascular stents, the required mechanical properties of each category, and the conventional materials have been using to address these requirements. Then, we bridge between the mechanical requirements of stents, structural properties of MGs, and the corresponding stent design caveats. In particular, we discuss our recent findings on the feasibility of using MGs in self-expandable stents where our results show that a metallic glass based aortic stent can be crimped without mechanical failure. We further justify the safe deployment of this stent in human descending aorta. It is our intent with this review to inspire biodevice developers toward the realization of MG-based stents.

Controlling the Mechanical Properties of Bulk Metallic Glasses by Superficial Dealloyed Layer

Cu₅₀Zr₄₅Al₅ bulk metallic glass (BMG) presents high fracture strength. For improving its plasticity and controlling its mechanical properties, superficial dealloying of the BMG was performed. A composite structure containing an inner rod-shaped Cu-Zr-Al amorphous core with high strength and an outer dealloyed nanoporous layer with high energy absorption capacity was obtained. The microstructures and mechanical properties of the composites were studied in detail. It was found, for the first time, that the mechanical properties of Cu₅₀Zr₄₅Al₅ BMG can be controlled by adjusting the width of the buffer deformation zone in the dealloyed layer, which can be easily manipulated with different dealloying times. As a result, the compressive strength, compressive strain, and energy absorption capacity of the BMGs can be effectively modulated from 0.9 to 1.5 GPa, from 2.9% to 4.7%, and from 29.1 to 40.2 MJ/m³, respectively. The paper may open a door for developing important engineering materials with regulable and comprehensive performances.

Preparing Zr65Al7.5Ni10Cu17.5 bulk metallic glasses based on point-line-face-body theory

Zr₆₅Al_7.5Ni₁₀Cu_17.5 bulk metallic glasses (BMGs) were prepared based on point-line-face-body (PLFB) theory with the pre-laid powder method from laser processing. The thickness of the prepared bulk amorphous alloy was about 1.6 mm. The microstructure evolution, phase composition, chemical component distribution, and corrosion behavior of the bulk amorphous alloy were investigated. The results showed that the amorphization ratio increased with the increase of the thickness of Zr₆₅Al_7.5Ni₁₀Cu_17.5 BMGs; furthermore, the volume fraction of the amorphous phase in the bottom layer (first layer), the middle layer (fourth layer), and the surface layer (seventh layer) was approximately 52%, 66%, and 74%, respectively. Due to different thermal cycles during the PLFB-forming process, the amorphous and crystallization coexisted in the deposited layers. For the corrosion property, the experiments of potentiodynamic polarization plots, Nyquist plots, and the equivalent circuits were performed in 3.5 wt. % sodium chloride solution. The seventh layer exhibits better corrosion-resistance performance than the other layers, which can be attributed to a higher amorphization ratio in the surface layer.

Towards ultrastrong glasses

The development of new glassy materials is key for addressing major global challenges in energy, medicine, and advanced communications systems. For example, thin, flexible, and large-area glass substrates will play an enabling role in the development of flexible displays, roll-to-roll processing of solar cells, next-generation touch-screen devices, and encapsulation of organic semiconductors. The main drawback of glass and its limitation for these applications is its brittle fracture behavior, especially in the presence of surface flaws, which can significantly reduce the practical strength of a glass product. Hence, the design of new ultrastrong glassy materials and strengthening techniques is of crucial importance. The main issues regarding glass strength are discussed, with an emphasis on the underlying microscopic mechanisms that are responsible for mechanical properties. The relationship among elastic properties and fracture behavior is also addressed, focusing on both oxide and metallic glasses. From a theoretical perspective, atomistic modeling of mechanical properties of glassy materials is considered. The topological origin of these properties is also discussed, including its relation to structural and chemical heterogeneities. Finally, comments are given on several toughening strategies for increasing the damage resistance of glass products.

Abrasive Wear Resistance of Bulk Metallic Glasses

This paper reviews work on the wear of metallic glasses in general, as well as reporting recent results on the abrasive wear of bulk metallic glasses. The distinctive mechanical properties of metallic glasses make their wear resistance of fundamental interest. Metallic glasses, and the partially or fully crystalline materials derived from them, can have very good resistance to sliding and abrasive wear. Standard wear laws are followed, with behaviour similar to that of conventional hardened alloys. The microhardness and abrasive wear resistance are measured for four bulk metallic glasses (based on La, Mg, Pd or Zr). The hardness and wear resistance correlate well with the Young's modulus of the glass.

Magnetostriction and Coercivity of Soft Magnetic Fe-(Al, Ga)-(P, C, B, Si) Bulk Glassy Alloys

The relationship between coercivity (Hc) and magnetostriction (λs) of the glassy Fe-(Al, Ga)-(P, C, B, Si) alloys has been discussed. The glassy Fe-(Al, Ga)-(P, C, B, Si) alloys exhibit lower Hc and lower Is compared with the conventional Fe-based amorphous alloys with the same λs and Fe content, respectively. Theoretical analysis on the basis of domain-wall movement suggests that the low Hc results from the long-range homogeneous structure of the glassy alloys, which realizes a low density of pinning centers. The good combination of high glass-forming ability and good soft magnetic properties (especially low Hc) indicates the possibility of future development as new bulk glassy soft magnetic materials.

Metastability and Properties of Metallic Bulk Glass Forming Alloys

Glasses are generally produced from the highly undercooled liquid state by rapid quenching methods or quasi-statically at slow cooling by the effective control of potent heterogeneous nucleation sites. For metallic systems the latter method recently has led to the development of bulk metallic glass with a complex multicomponent chemistry and advanced engineering properties. With these alloys crystallization can be avoided over a broad temperature / time window. As such, the relevant thermodynamic properties of the metastable glassy and undercooled liquid states can be directly measured below and above the glass transition temperature, respectively. The obtained data give new insight into the nature of the glass transition suggesting that it is not a phase transition in the classical sense but kinetic freezing triggered by an underlying entropie instability to avoid crystallization. Further measurements of the mechanical and wear properties point to the unique engineering properties of these highly disordered materials for technological applications.

Bulk Glass-Forming Metallic Alloys: Science and Technology [1998 Mrs Medal Award Lecture, Presented at Symposium Mm]

The paper begins with some brief remarks about the history and background of the field of bulk glass-forming metallic alloys. This is followed by a discussion of multicomponent glass-forming alloys and deep eutectics, the chemical constitution of these new alloys, and how they differ from metallic glasses of a decade ago or earlier. The development of bulk glass forming alloys has led to interesting studies of the deeply undercooled liquid alloys, which are made possible by the exceptional stability with respect to crystallization. Recent advances made in this area will be illustrated by several examples. The paper continues with a discussion of some of the physical properties of bulk metallic glasses. Mechanical properties are specifically discussed. Some interesting potential applications of bulk metallic glasses will be mentioned.

The effect of Nb addition on mechanical properties, corrosion behavior, and metal-ion release of ZrAlCuNi bulk metallic glasses in artificial body fluid

Bulk metallic glasses (BMGs) of Zr(65 - x)Nb(x)- Cu(17.5)Ni(10)Al(7.5) with Nb = 0, 2, and 5 at % were prepared by copper mold casting. Compression tests reveal that the two BMGs containing Nb exhibited superior strength and plasticity to the base alloy. The corrosion behavior of the alloys obtained was investigated in artificial body fluid by electrochemical measurements. It was found that the addition of Nb significantly enhanced the corrosion resistance of the Zr-based BMG, as indicated by a remarkable increase in corrosion potential and pitting potential. XPS analysis revealed that the passive film formed after anodic polarization was enriched in aluminum oxide and depleted in phosphate ions for the BMGs containing Nb, which accounts for the improvement of corrosion resistance. On the other hand, metal-ion release of different BMGs were determined in PPb (ng/mL) level with inductively coupled plasma mass spectrometry (ICP-MS) after being immersed in artificial body fluid at 37 degrees C for 20 days. It was found that the addition of Nb considerably reduced the ion release of all kinds of metals of the base system. This is probably attributed to the promoting effect of Nb on a rapid formation of highly protective film.