Tuning of mechanical properties of Tantalum-based metallic glasses

https://doi.org/10.1016/j.ijmecsci.2021.106546Get rights and content

Highlights

  • The reinforcement of Tantalum monatomic metallic glass (Ta-MG) matrix by Ta monocrystalline fibers increases the ductility and the toughness of the formed nanocomposite and decreases its ultimate tensile stress;

  • The reinforcement of Ta-MG matrix by addition of W reinforces the Ta-MG matrix and increases the maximum strength and the toughness of the nanocomposite;

  • The heterogeneous interface between W monocrystalline fibers and Ta-MG matrix behaves as an obstacle to the propagation of shear bands;

  • The tensile tests have shown that plastic deformations are characterized by the localization of shear bands in amorphous zones.

Abstract

Metallic glasses (MGs) are materials characterized by high performance in terms of their mechanical properties such as excellent elastic behavior and high strength. These famous properties are directly linked to the amorphous structure which is the principal feature behind the absence of atomic order at long range. Nonetheless, MGs usually fail catastrophically by shear localization without showing any synonyms of important plastic deformation under mechanical solicitations and therefore are notoriously brittle, so the reinforcement of MG matrix to form MG-based composite materials is demanded. Molecular dynamics (MD) simulations are of great importance in designing such materials allowing atomic scale insights into the structural-mechanical properties relationship. In this work, we study the effect of adding Ta and W monocrystalline fibers in Ta-MG matrix using MD simulations with the embedded atom method (EAM) to describe the interatomic interactions. In addition, mechanical solicitations have been performed using a tensile test under a strain rate of 107 s−1, the evolutions of stress-strain curves have been compared between four samples (Ta-MG, nanoporous Ta-MG, monocrystalline Ta-reinforced Ta-MG and monocrystalline W-reinforced Ta-MG). Tensile tests have shown that plastic deformations are characterized by the localization of shear bands (SBs) in amorphous zones and the addition of Ta monocrystalline fibers increases the ductility and the toughness of the material and decreases its ultimate tensile stress (UTS); this ductility was found to be a result of the crystal growth inside the glassy matrix triggered by the crystal phase of the fiber. In contrast, the addition of W reinforces the MG matrix and increases the maximum strength and the toughness of the material, this improvement of the mechanical properties was explained by the presence of the heterogeneous interface which behaves as an obstacle to the propagation of SBs.

Introduction

Metallic glasses (MGs) have recently attracted the attention of many experimental and computational scientific researches since their first production in 1960s [1]. They are characterized by a high performance in terms of mechanical and chemical properties which makes them among the principal candidates that meet the needs of the modern industries. They possess a high mechanical strength, good corrosion resistance and a superior abrasion resistance which provide them a high opportunity to be used as a raw mater for the manufacture of various instruments [2], [3], [4]. These important properties are attributed directly to the amorphous structure associated with their metallic bonds. They are characterized by an atomic disorder at long distances and an absence of grains and grain boundaries, which prevents the localization of crystalline defects [5].

The atomic packing of MGs is formed by the so-called icosahedral polyhedrons, which behave as the basic structural element (as skeleton) suggested as an obstacle to the nucleation and growth of long-range crystalline order. Moreover, various experimental and computational techniques were adopted to form MGs with an amorphous structure [6], [7], [8]. All these techniques are based on the rapid cooling process, the main objective of which is to prevent the reorganization of atoms and then to avoid any kind of crystallization. The computational techniques allow to investigate additional details in terms of microstructural behavior of these materials which are difficult to acquire based only on experimental methods. Thus, using molecular dynamics and ab-initio simulations, it was revealed that the icosahedral-like cluster is the fundamental structural unit in which the atoms can be rearranged at the short-range (SRO) [9]. At this level, the atoms are arranged in the predominant Voronoi polyhedral type 〈0,1,10,2〉, 〈0,0,12,0〉 and/or 〈0,2,8,4〉 [10,11]. In addition, the medium-range order (MRO) is constructed by the connection between these icosahedral units/clusters following four principal modes: Vertex-Sharing (VS), Edge-Sharing (ES), Face-Sharing (FS) and Intercross-Sharing (IS) [10], [11], [12]. Furthermore, the glass formation is characterized by the so-called glass forming ability (GFA) which provides a measure of the ease of the material to vitrify. It can be affected by various parameters such as the system composition, the atomic size mismatch between the constituent elements and the cooling rate [13], [14], [15], [16], [17].

The conditions of solicitation are other parameters that affect the mechanical response of MGs and then the underlying mechanism [18], [19], [20]. The mechanical deformation of MGs is characterized by the creation of Shear Transformation Zones (STZs) promoting a macroscopic sliding along localized regions called Shear Bands (SBs) [21]. Moreover, under high stresses and low temperatures (inhomogeneous deformation), the plasticity of MGs is manifested by the movement of these SBs which initiate under several mechanisms modifying their ductility [22]. From where, atomic jumps can be activated favoring nucleation and annihilation of the free volume by activating the STZs. In this context, Greer et al. [22] summarized the formation of SBs in three scenarios: The external stresses lead to a structural disturbance at the atomic level resulting in homogeneous nucleation and a process of combination with the creation of an embryo of SBs and subsequently a fast sliding. The formation of SBs depends significantly on the applied stress field and the introduction of stress concentrators may be beneficial for their initiation processes [23], [24], [25], [26].

MGs are usually brittle materials and fail catastrophically by shear localization without showing any synonyms of important plastic deformation, so the reinforcement of MG matrix to form MG-based composite materials is demanded [27]. The reinforcement of MGs by crystalline metals fibers affects the mechanical response of MGs matrix [28]. However, the high mechanical strength and the metallic nature of the reinforcing phase offers unique possibilities for improving the engineering performance of MG matrix. The amorphous/ crystalline interface plays a vital role for the enhancement of matrix properties [29]. Otherwise, porous metals are materials that have excellent functional and structural properties. They are lightweight materials with properties such as low bulk density, high surface area, low thermal conductivity, etc.… [30]. Glassy phase of these porous metals may improve some physical properties such their corrosion resistance and elastic strain.

In the present work, we focus on the investigation of the mechanical behavior of Tantalum (Ta) monatomic MG and how this behavior is altered by its reinforcement by Ta and W (Tungsten) monocrystalline fibers. This metallic material (Ta) characterized by a bcc crystalline structure, exhibits several important chemical and physical properties, such as its bioactivity which makes it the main candidate for the manufacturing of surgical instruments and implants [3]. Mechanical and chemical performances of this crystalline material can be deteriorated under some environmental circumstances; therefore, the use of its amorphous phase (MG) may provide a key solution to its deterioration. However, this glassy phase is generally brittle [27] and its reinforcement by additive elements to form a Ta MG-based nanocomposite is required. In addition, to our knowledge, there is no study of the mechanical behavior of Ta MG-based nanocomposite using a computational method. The aim of the present study is first to study the mechanical behavior of Ta monatomic MG by means of molecular dynamics (MD) simulations to characterize the evolution of SBs during mechanical loading. On the other hand, we will explore some ways of improving the ductility and mechanical resistance of Ta-MG by designing nanoporous and nanocomposites based on this MG. Nanoporous Ta-MG was first studied to determine the optimal thermally stable pore size, which then was subjected to tensile load. Thus, we will present the behavior of Ta-MG reinforced by two monocrystalline fibers (Ta and W). The paper will be organized as follows: the second section is devoted to the methodology and the modeling technique adopted to achieve this study. In the third section of this manuscript, we present our results by discussing the main differences between the different investigated samples. Finally, the last section contains our concluding remarks.

Section snippets

Methodology

All our investigations are carried out performing MD simulations using the LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) package [31]. Firstly, to form Tantalum (Ta) monatomic MG (Ta-MG), 106 atoms are distributed in a simulation cubic box according to a bcc lattice. This corresponds to sample size of (16.56 × 26.50 × 41.41) nm3. In order to mimic/compute bulk properties, periodic boundary conditions have been applied in the three directions (x, y and z). In addition, to

Formation of vitreous state

We start first by proving that we obtained the formation of Ta monatomic MG after the adopted cooling process. In order to describe the atomic structure during the thermal process, we used the radial distribution function (RDF), which determines the probability of finding the first, the second … the nth neighbors of a referenced atom placed at a distance r from a central atom and leads to deducing the coordination numbers within a certain neighboring shell characterized by a cutoff radius. Its

Discussion

The aim of this study is to investigate the mechanical response of the Ta-MG and nanoporous Ta-MG by adding monocrystalline Ta- and W-fibers. Our discussion will be focused relatively on the four studied samples (gTa, pTa, cTa/gTa and cW/gTa) and we will take the Ta-MG (gTa) as the reference for each comparison. As seen in Table 1, the yield strength for the referenced sample is 1245 MPa reached at 2.8% of strain, from the linear fitting we obtained a Young modulus of 42.01 MPa. However, the

Conclusions

In summary, this work studied the mechanical response of Tantalum (Ta) monatomic metallic glass (Ta-MG) and Ta-MG-based nanocomposites under tensile stress using molecular dynamics simulations. The semi-empirical approach of the embedded atom method (EAM) was adopted to describe the interatomic interactions.

Firstly, the formation of Ta-MG has been confirmed by the splitting of the second peak of the radial distribution function generally attributed to the presence of icosahedral clusters. This

Authorship contributions

Conception and design of study: A. Khmich, A. Hasnaoui,

Acquisition of data: A. Khmich, A. Hassani,

Analysis and/or interpretation of data: A. Khmich, A. Hasnaoui, A. Hassani, K. Sbiaai

Drafting the manuscript: A. Khmich,

Revising the manuscript critically for important intellectual content: A. Hasnaoui, A. Khmich, K. Sbiaai

Approval of the version of the manuscript to be published: A. Khmich, A. Hasnaoui, A. Hassani, K. Sbiaai

Declaration of Competing Interest

This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue. The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript.

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