Class Of Metallic Materials Research Articles

Investigation of the strain rate sensitivity of CoCrFeMnNiTix (x = 0, 0.3) high-entropy alloys using the shear punch test

High entropy alloys (HEAs) are a novel class of metallic materials that exhibit a unique blend of properties due to their chemical composition and atomic arrangement. This research aims to investigate the strain rate sensitivity (SRS) of two HEA CoCrFeMnNiTix (x = 0, 0.3) alloy compositions through the use of shear punch testing. This method has been proven to provide reliable results for both HEA materials, including the CoCrFeMnNiTi0.3 HEA composition which was found to be inherently brittle and contained both σ-phase and Laves phase compounds with a hardness close to 14 GPa and a soft FCC phase. Among all the testing temperatures (room temperature to 400 °C) and deflection rates (0.2, 2 and 10 mm.min−1) used, only the CoCrFeMnNi HEA alloy was found to exhibit SRS at room temperature (m = 0.0333), while for the other HEA alloy variant and testing conditions, the SRS was found to be zero. From empirical correlations and finite element analysis (FEA), the calculated value for m ranged from 0.0333 to 0.0359, thus evidencing that the FEA simulations provide an accurate and suitable means of capturing the deformation behaviour of such alloys when subjected to shearing.

Unprecedented bake hardening responses of interstitial high-entropy alloy by synergistic effect with lattice distortion

High-entropy alloys (HEAs) composed of multiple principal elements have attracted considerable interest in recent decades as a new class of metallic materials. Among them, the equi-atomic CoCrFeMnNi HEA system has great potential for application as a structural material due to its excellent properties in various fields, but it has a drawback of relatively low yield strength (YS) at room temperature. Here, for the first time, we propose the bake hardening (BH) as a breakthrough to overcome the relatively inferior YS of the CoCrFeMnNi HEA system. We found that the carbon-added CoCrFeMnNi HEAs are not only bake-hardenable, but also exhibit unprecedented BH responses than conventional bake-hardenable materials, with BH responses up to 120.0 MPa depending on the carbon concentration in the matrix. It is the outcome of the mutual synergistic effect between the massive solid solution strengthening characteristic from lattice distortion of the HEAs and the Cottrell atmosphere generated during the BH process. This study demonstrates that the carbon-added CoCrFeMnNi HEAs are more advantageous to apply the BH effect than conventional bake-hardenable materials, which suggests the possibility of industrialization of various interstitial HEA systems as well as carbon-added CoCrFeMnNi HEAs.

Tailoring the Microstructure of an AA5754 Aluminum Alloy by Tuning the Combination of Heat Treatment, Friction Stir Welding, and Cold Rolling

Friction stir welding (FSW) has now reached a technological impact and diffusion that makes it a common joining practice for several classes of metallic materials. These include light alloys (aluminum, titanium, magnesium), steels, and other metallic alloys. In addition, the combination of FSW with pre- or post-welding heat treatments or plastic deformation, such as cold rolling (CR), can favor minimal necessary plate thicknesses and induce effective alloy strengthening mechanisms that make the FSW joint lines as plate reinforcing zones. Process parameters, such as pin rotation and transverse speed, can be tuned to optimize the mechanical properties of the resulting joint. This work presents a microstructural study of the mechanical response of different sequences of heat treatment, FSW, and CR in a non-age hardened Al-Mg AA5754 alloy. By using polarized optical microscopy and microhardness tests, two FSW conditions were used to fabricate a joint; and were than subjected to different sequences of heat treatment and cold rolling. The results suggest that FSW conditions have a limited effect on the microstructure, while microhardness profiles show a higher variability of the different datasets related to the low welding speed investigated.

Unquantized anomalies in topological semimetals

Topological semimetals are a new class of metallic materials, which exist at band fillings that ordinarily correspond to insulators or compensated accidental semimetals with zero Luttinger volume. Their metallicity is a result of nontrivial topology in momentum space and crystal symmetry, wherein topological charges may be assigned to point band-touching nodes, preventing gap opening, unless protecting crystal symmetries are violated. These topological charges, however, are defined from noninteracting band eigenstates, which raises the possibility that the physics of topological semimetals may be modified qualitatively by electron-electron interactions. Here we ask the following question: what makes the topological semimetals nontrivial beyond band theory? Alternatively, can strong electron-electron interactions open a gap in topological semimetals without breaking the protecting symmetries or introducing topological order? We demonstrate that the answer is generally no, and what prevents it is their topological response, or quantum anomalies. While this is familiar in the case of magnetic Weyl semimetals, where the topological response takes the form of an anomalous Hall effect, analogous responses in other types of topological semimetals are more subtle and involve crystal symmetry as well as electromagnetic gauge fields. Physically these responses are detectable as fractional symmetry charges induced on certain gauge defects. We discuss the cases of type-I Dirac semimetals and time-reversal invariant Weyl semimetals in detail. For type-I Dirac semimetals, we also show that the anomaly vanishes, in a nontrivial manner, if the momenta of the Dirac nodes satisfy certain exceptional conditions.

HIGH-ENTROPY ALLOYS AS A PROSPECTIVE CLASS OF NEW RADIATION-TOLERANT MATERIALS RESEARCH DEVELOPMENT ANALYSIS BASED ON THE INFORMATION DATABASES

A new class of metallic materials, so-called “high-entropy alloys” (HEAs), was under review. Various definitions of these alloys are given, their main differences from the conventional alloys are indicated and the dynamics of publications in the period from the first publications in 2004 to the end of 2020 are presented. It is noted the almost exponential growth of the article numbers concerning these alloys, and the main reasons of such high interest are discussed. Experimental results of development the radiation-tolerant materials based on the concept of high-entropy alloys and study of the radiation damage mechanisms are summarised.

Dynamic recrystallization-induced temperature insensitivity of yield stress in single-crystal Al1.2CrFeCoNi micropillars

High-entropy alloys, a new class of metallic materials, exhibit excellent mechanical properties at high temperatures. In spite of the worldwide interest, the underlying mechanisms for temperature dependence of mechanical properties of these alloys remain poorly understood. Here, we systemically investigate the mechanical behaviors and properties of Al1.2CrFeCoNi (comprising a body-centered cubic phase) and Al0.3CrFeCoNi (comprising a face-centered cubic phase) single-crystal micropillars with three orientations ([100], [110], and [111]) at temperatures varying from 300 to 675 K by using in situ compression of micropillars inside a scanning electron microscope. The results show that the yield stresses of Al1.2CrFeCoNi micropillars are insensitive to temperature changes, and their flow stresses and work hardening rates increase slightly with increasing temperature from 300 to 550 K, which differs from the typical temperature dependence of yield/flow stresses in metals and alloys. In contrast, Al0.3CrFeCoNi micropillars exhibit typical thermal softening. Furthermore, it is found that the Al1.2CrFeCoNi micropillars exhibit a transition from homogenous deformation to localized deformation at a critical temperature, while the Al0.3CrFeCoNi micropillars always maintain a well-distributed and fine slip deformation. Detailed transmission electron microscopy analyses reveal that dynamic recrystallization (involving dislocation tangles, and formation of dislocation cell structures and sub-grains) plays a key role in the observed temperature insensitivity of the yield stress and increasing flow stress (and work hardening rate) with increasing temperature in the Al1.2CrFeCoNi micropillars, and that thermally activated dislocation slip leads to thermal softening of the Al0.3CrFeCoNi micropillars. The differences in deformation modes and temperature dependence of the mechanical properties between Al1.2CrFeCoNi and Al0.3CrFeCoNi essentially originate from the differences in dislocation activities and slip systems since the two alloys adopt different phases. Our findings provide key insights in the temperature dependence of mechanical properties and deformation behaviors of high-entropy alloys with body-centered cubic and face-centered cubic phases.

Towards understanding the structure–property relationships of heterogeneous-structured materials

Heterogeneous-structured materials are a new class of metallic materials that have recently emerged due to development of advanced processing and structural/architectural design techniques. These materials are made of heterogeneous domains having different constitutive behaviors and achieve superior mechanical properties, such as extra strengthening and work hardening, that are not accessible to conventional homogeneous-structured materials. Here we review recent experimental, theoretical and computational studies on microstructures, mechanical properties and deformation behaviors of heterogeneous-structured metals/alloys, highlighting the relationships between structural heterogeneity and mechanical property improvements, as well as some perspectives towards achieving fundamental understanding of plastic deformation based on strain gradient theory.

Towards superior mechanical properties of hetero-structured high-entropy alloys via engineering multicomponent intermetallic nanoparticles

Dual-phase high-entropy alloys strengthened by multicomponent intermetallic nanoparticles represent a unique class of hetero-structured materials with potentially superior mechanical properties for structural applications. Due to the multicomponent chemistries of both nanoparticles and the matrix, as well as the coherent interfaces between them, these alloys can possess excellent strength-ductility combinations over a wide temperature range. This brief viewpoint article gives an overview of the major developments achieved recently. Advantages over other classes of metallic materials as well as limitations in this field are also carefully discussed. The results provide new insights into the development of high-performance structural materials via multicomponent-nanoparticle engineering.

Phases and compounds composition analyze of ZnMgCa biodegradable alloy

Besides biocompatible materials, a new class of metallic materials with medical applications dedicated to specific traumas is that of biodegradable materials. Zinc-based materials are mentioned as the ‘Calcium of the XXI century’. Zn has been considered as one of the newest promising biodegradable metallic metals together with Mg-based and Fe-based alloys. A new experimental composition of ZnMgCa alloy was obtained using an induction furnace from high purity zinc, magnesium and calcium materials. The material chemical compounds and phases were determined using EDS Bruker detector and XRD X’Pert equipment in molded state of the alloy. Microstructure of the alloy was determined using scanning electron microscopy and the distribution of constituents using VegaTescan software.

Enhanced strength and ductility in a spark plasma sintered CoCrCu0·5NiAl0.5 high-entropy alloy via a double-step ball milling approach for processing powders

High-entropy alloys (HEAs) are a new class of metallic materials that have attracted great attention due to their excellent properties. Spark plasma sintering (SPS), which possesses the combined effects of spark discharge and high temperature/pressure, is a promising method for fabricating high-performance HEAs. However, the low cooling rate after SPS (furnace cooling under vacuum) generally facilitates the formation of stable phases in HEAs, including brittle intermetallic phases, which are detrimental to the deformation abilities and mechanical properties of the SPSed HEAs. Here, we report a double-step ball milling approach for processing raw powders to achieve simultaneous enhancements in both strength and ductility in an SPSed face-centred cubic (FCC) CoCrCu0·5NiAl0.5 HEA. The reasons for enhancing the mechanical properties are that the coarse-scale brittle B2 phase along the grain boundary is replaced by dispersed fine-scale α-Al2O3, which results in a reduction in brittleness and an improvement in strength (via Orowan strengthening and load-transfer strengthening) caused by α-Al2O3. Through this study, a simple and effective approach is proposed that may overcome the strength-ductility trade-off for SPSed Al-containing HEAs.

Study on the hydrogen storage properties of a TiZrNbTa high entropy alloy

High-entropy alloys (HEAs), as a new class of metallic materials, have received more and more attention due to its excellent mechanical properties. In this study, the hydrogen absorption properties, such as hydrogen absorption capacity, thermodynamics, kinetics and cyclic properties, as well as the hydride structure of a newly designed TiZrNbTa HEA were investigated. The results showed that multiple hydrides including ε-ZrH2, ε-TiH2 and β-(Nb,Ta)H were found in the TiZrNbTa HEA after hydrogenation. With the increase of temperature from 293 K to 493 K, the maximum hydrogen absorption capacity decreased from 1.67 wt% to 1.25 wt% and the plateau pressure related with β-(Nb,Ta)H hydrides increased from 1.6 kPa to 14.8 kPa. The formation enthalpy of β-(Nb,Ta)H hydride was determined to be −6.4 kJ/mol, which was less stable than that of NbH and TaH hydrides. The results also showed that the TiZrNbTa HEA exhibited a rapid hydrogen absorption kinetic even at the room temperature with a short incubation time, and the hydrogen absorption mechanism was determined to be the nucleation and growth mechanism. Moreover, the hydrogen absorption capacity at 293 K decreased slowly with the cycle numbers, and remained 86% capacity after 10 cycles. Cracking occurred after hydrogen absorption and became worse with cycles.

Effect of Ternary Addition of Cobalt on Shape Memory Characteristics of Ni–Ti Alloys

Shape memory alloys (SMAs) are a class of metallic materials that exhibit two unique characteristics: shape memory effect and superelasticity. These alloys are capable of responding to stimuli like heat when they are subjected to thermo-mechanical treatment. Therefore, these alloys have proven their utility in many areas and are very common in applications such as sensors and actuators, various life-saving medical devices and stents. Ni–Ti alloys are in the forefront with respect to shape memory materials and have been employed in many practical applications. In recent times, there have been attempts to improve their shape memory characteristics, mechanical properties and corrosion resistance through alloying addition, thermo-mechanical processing, severe plastic deformation, etc. Among these methods, ternary alloying addition seems to have a greater effect in comparison with other methods. In this work, cobalt was added to a binary Ni–Ti alloy and its influence on transformation temperatures and microstructure was studied. Ternary NiTiCo alloys with varying cobalt contents (1, 2, 3 at.%) were prepared by vacuum induction melting, and the alloys were then hot-rolled and homogenized. Various characterization techniques such as differential scanning calorimetry, transmission electron microscopy and X-ray diffraction were employed to study the transformation temperatures, the microstructure and the phase structure of the ternary SMAs. It was seen that cobalt addition decreased the phase transformation temperatures and influenced the functional properties of the binary Ni–Ti alloy. Elaborate results have been discussed in this paper.

A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength.

High-entropy alloys (HEAs) are a class of metallic materials that have revolutionized alloy design. They are known for their high compressive strengths, often greater than 1 GPa; however, the tensile strengths of most reported HEAs are limited. Here, we report a strategy for the design and fabrication of HEAs that can achieve ultrahigh tensile strengths. The proposed strategy involves the introduction of a high density of hierarchical intragranular nanoprecipitates. To establish the validity of this strategy, we designed and fabricated a bulk Fe25Co25Ni25Al10Ti15 HEA to consist of a principal face-centered cubic (fcc) phase containing hierarchical intragranular nanoprecipitates. Our results show that precipitation strengthening, as one of the main strengthening mechanisms, contributes to a tensile yield strength (σ0.2) of ~1.86 GPa and an ultimate tensile strength of ~2.52 GPa at room temperature, which heretofore represents the highest strength reported for an HEA with an appreciable failure strain of ~5.2%.

Biomechanically Inspired Machines, Driven by Muscle Like Acting NiTi Alloys

The Shape of the Memory Alloy (SMA) is a very promising class of metallic materials with interesting non-linear properties such as Pseudo-Elasticity (PE), memory (MEM) and damping capacity due to high mechanical hysteresis and internal friction. Research shows a bioinventory approach to Shape Memory Alloy (SMA) design, a class of intelligent materials capable of reacting to a pulse (thermal for SMA) with shrinkage. Martensitic transformations in shape-effect crystals under the effect of external forces lead to large deformations of an inelastic nature. In some materials, these reversible deformations are in the range from one digit to at least two digits. The recovery of accumulated inelastic deformation and, as a consequence, the return to the original shape of the body can occur both in the process of unloading at a constant temperature (superelastic effect) and in heating (a form memory effect). Both effects are exciting with regard to their application in compact servomotors when heating the effect of shape memory generates stresses in most materials. If the shape memory alloy faces any shape recovery resistance, it can generate reactive force. The importance of this effect in technical applications is that the reactive force significantly exceeds the force that caused the initial change of shape. This can be used to produce a useful mechanical work. The biomechanically inspired machine that is discussed in the paper refers to pairs of muscle antagonists that are part of the skeletal muscles and are usually arranged in opposition so that a group of muscles contractors another group that relaxes or prolongs. The study proposes a model, a solution not only to design a specific application but also to provide an approach to be used for a wide range of adaptive applications (switching windows, intelligent shadows, parking and urban shelters, etc.). The shape changes in response to various external stimuli. The use of pairs of antagonists provides a solution for SMA-optimized systems where the main and proven advantages are: Easier and quicker shape change, the energy requirement for system operation, lower costs for SMA training and lack of overheating problems.

Understanding effect of 3.5 wt.% NaCl on the corrosion of Al0.1CoCrFeNi high-entropy alloy

High entropy alloys are a new class of metallic materials with potential for use in a wide variety of applications including their use in corrosive environment. The present study focused on the corrosion behavior of a single-phase, face-centered cubic high entropy alloy (HEA) Al0.1CoCrFeNi in as-cast condition, and the results are compared with the corrosion behavior of the SS304. The microstructural characterization of the alloys in as-received condition was carried out using optical microscopy, electron backscattered diffraction, energy dispersive spectroscopy, and X-ray diffraction. Corrosion behavior was studied using potentiodynamic polarization test in a 3.5 wt% NaCl solution and electrochemical impedance spectroscopy at room temperature. It was observed that the general corrosion resistance of the HEA was better than that of SS304. Pitting potential of the HEA was found to be superior to that of the SS304. Corrosion pits size was slightly smaller in SS304 than that in the HEA. 3D imaging determined that the pit depths were of the same order in both cases. Overall, the HEA Al0.1CoCrFeNi demonstrated a better resistance to general and pitting corrosion.

Obtaining of Fe-Base Biodegradable Metallic Alloy

Biodegradable metallic materials gain space in implantable materials field based on the applications that can fulfill. Beside Mg-based alloys a new class of metallic materials is under development, alloys based on Fe, in order to improve the corrosion rate, one of the disadvantages of magnesium alloys, and the mechanical properties of the implant. In this article we present the steps took to obtain a biodegradable FeMnSi alloy with metallic additions and few preliminary results about the chemical composition (X-ray dispersive energy analyze EDS) of the sample and the influence of hardening heat treatment on chemical composition. After the melting and pouring stages the new material was analyzed.

Mechanical Properties of High Entropy Alloy Al0.1CoCrFeNi for Peripheral Vascular Stent Application.

High entropy alloys (HEAs) are new class of metallic materials with five or more principal alloying elements. Due to this distinct concept of alloying, the HEAs exhibit unique properties compared to conventional alloys. The outstanding properties of HEAs include increased strength, superior wear resistance, high temperature stability, increased fatigue properties, good corrosion, and oxidation resistance. Such characteristics of HEAs have generated significant interest among the scientific community. However, their applications are yet to be explored. This paper discusses the mechanical behavior and microstructure of Al0.1CoCrFeNi HEA subjected to thermo-mechanical processing, and its potential application in peripheral vascular stent implants that are prone to high failure rates. Results show that Al0.1CoCrFeNi alloy possesses characteristics that compare well against currently used stent materials and it can potentially find use in peripheral vascular stent implants and extend their life-cycle.

Development of a novel high-entropy alloy with eminent efficiency of degrading azo dye solutions.

In addition to its scientific importance, the degradation of azo dyes is of practical significance from the perspective of environmental protection. Although encouraging progress has been made on developing degradation approaches and materials, it is still challenging to fully resolve this long-standing problem. Herein, we report that high entropy alloys, which have been emerging as a new class of metallic materials in the last decade, have excellent performance in degradation of azo dyes. In particular, the newly developed AlCoCrTiZn high-entropy alloy synthesized by mechanical alloying exhibits a prominent efficiency in degradation of the azo dye (Direct Blue 6: DB6), as high as that of the best metallic glass reported so far. The newly developed AlCoCrTiZn HEA powder has low activation energy barrier, i.e., 30 kJ/mol, for the degrading reaction and thus make the occurrence of reaction easier as compared with other materials such as the glassy Fe-based powders. The excellent capability of our high-entropy alloys in degrading azo dye is attributed to their unique atomic structure with severe lattice distortion, chemical composition effect, residual stress and high specific surface area. Our findings have important implications in developing novel high-entropy alloys for functional applications as catalyst materials.

Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures.

High-entropy alloys are an intriguing new class of metallic materials that derive their properties from being multi-element systems that can crystallize as a single phase, despite containing high concentrations of five or more elements with different crystal structures. Here we examine an equiatomic medium-entropy alloy containing only three elements, CrCoNi, as a single-phase face-centred cubic solid solution, which displays strength-toughness properties that exceed those of all high-entropy alloys and most multi-phase alloys. At room temperature, the alloy shows tensile strengths of almost 1 GPa, failure strains of ∼70% and KJIc fracture-toughness values above 200 MPa m1/2; at cryogenic temperatures strength, ductility and toughness of the CrCoNi alloy improve to strength levels above 1.3 GPa, failure strains up to 90% and KJIc values of 275 MPa m1/2. Such properties appear to result from continuous steady strain hardening, which acts to suppress plastic instability, resulting from pronounced dislocation activity and deformation-induced nano-twinning.

Bio-inspired multifunctional metallic glass

As a novel class of metallic materials, bulk metallic glasses (BMGs) have attracted a great deal of attention owing to their technological promise for practical engineering applications. In nature, biological materials exhibit inherent multifunctional integration, which provides some inspiration for scientists and engineers to construct multifunctional artificial materials. In this contribution, inspired by superhydrophobic self-cleaning lotus leaves, multifunctional bulk metallic glasses (BMG) materials have been fabricated through the thermoplastic forming-based process followed by the SiO2/soot deposition. To mimic the microscale papillae of the lotus leaf, the BMG micropillar with a hemispherical top was first fabricated using micro-patterned silicon templates based on thermoplastic forming. The deposited randomly distributed SiO2/soot nanostructures covered on BMG micropillars are similar to the branch-like nanostructures on papillae of the lotus leaf. Micro-nanoscale hierarchical structures endow BMG replica with superhydrophobicity, a low adhesion towards water, and self-cleaning, similar to the natural lotus leaf. Furthermore, on the basis of the observation of the morphology of BMG replica in the Si mould, the formation mechanism of BMG replica was proposed in this work. The BMG materials with multifunction integration would extend their practical engineering applications and we expect this method could be widely adopted for the fabrication of other multifunctional BMG surfaces.