Mechanical Properties Of Metals Research Articles

In Situ Atomic‐Scale Experiments Reveal the Atomistic Mechanisms of Grain Boundary Plasticity

AbstractGrain boundary (GB) plastic deformation is a critical deformation mode that can significantly affect the microstructure and mechanical properties of metals. Given its importance, numerous studies have been conducted over the past few decades to investigate the atomistic mechanism of GB plasticity, which includes GB migration, GB sliding, and grain rotation. These three deformation modes typically occur simultaneously and interact cooperatively. Despite substantial advancements in understanding the atomic‐scale mechanisms of GB plasticity, there is a scarcity of review papers addressing the in situ atomic‐scale mechanisms of GB plasticity. This work aims to provide a comprehensive overview of the atomistic mechanisms of GB plasticity in metals, detailing modes predicted by theoretical models and molecular dynamics (MD) simulations, as well as discussing mechanisms verified by in situ atomic‐scale experiments. Additionally, it examines the factors influencing GB deformation. The authors intend for this review to serve not only as a valuable resource for researchers in the field of nanocrystalline (NC) metals but also as a textbook for educating graduate students.

Effects of multilayer MoS2 coating on the mechanical properties of metals: A competition between external force and interfacial adhesion

Molybdenum disulfide (MoS2) is a two-dimensional material that exhibits unique interfacial interactions with metals, making it potential coating material for improving material properties of metals. In this work, the effects of multilayer MoS2 coating on the mechanical properties and deformation behaviours of copper (Cu) and gold (Au) substrates are investigated by nanoindentation experiments and molecular dynamics (MD) simulations. Specifically, our experimental results indicate that the MoS2 coating greatly increases the Young's modulus and hardness of Au substrate throughout the indentation process. In the MoS2/Cu system, however, the MoS2 coating exhibits inverse effects at diffident indentation depths, which, specifically, has the weakening and enhancing effects at the early and late stages of the indentation process, respectively. MD simulations indicate that the different effects of the MoS2 coating on the mechanical properties of Au and Cu substrates are attributed to the different interfacial adhesion properties between the MoS2/Cu and MoS2/Au systems, as the binding energy of the MoS2/Au system is much larger than that of its MoS2/Cu counterpart. Moreover, it is also revealed in MD simulations that the load-bearing area of metal substrates can be significantly enlarged by the MoS2 coating, which leads to the dense dislocations distributed in metal substrates and thus the strain-hardening in MoS2/metal composites.

DETERMINATION OF CHANGES IN MECHANICAL PROPERTIES OF METAL OF FEEDWATER PIPELINES BENDS AND “HOT” STEAM OF THE SECOND POWER UNIT OF PIVDENNOUKRAINSK NPP FOR THE SECOND 100,000 h OF OPERATION

An analysis of the results of periodic testing of hardness of metal of pipelines bends of power unit No. 2 of Pivdennoukrainsk Nuclear Power Plant (PNPP) after ~100,000 and ~200,000 h of operation was carried out. It is shown that during the operation of feedwater and “hot” steam pipelines during the second 100,000 h of operation, the aging of the metal is observed, which is manifested in a partial, at least in their surface layers, uneven decrease in the strength of the metal. An increased rate of aging of the metal of pipeline bends is observed in areas where the metal was subjected to the greatest plastic deformation during the pipe manufacturing process (compressed and stretched sides of the bends). The critical parameter among the normalized mechanical properties of bending metal is the tensile strength, which is the first to reach a critical level when extrapolating the obtained data. While maintaining the rate of change in the mechanical properties of the metal at the level of the second 100,000 h of operation for post-project operation, the projected residual resource of metal bends of feedwater pipelines and "hot" steam is ~590,000 and ~380,000 h, respectively.

REASONS AND REGULARITIES OF THE INFLUENCE OF MAGNETIC FIELDS ON THE MECHANICAL PROPERTIES AND STRUCTURE OF DEFORMABLE METALS

Background. The strength of metals greatly limits the possibility of obtaining products by plastic deformation. The electromagnetic nature of the processes of structure formation and plastic deformation provided the basis for the application of additional influence of the magnetic field. A fairly large volume of research material has been accumulated on the topic of additional influence of the magnetic field on ferro-, dia- and paramagnetic metals. The researches of recent years have an applied nature of studying the magnetoplasticity of technical alloys. Their generalization will make it possible to move from laboratory research to the development of equipment and technologies for combined pressure processing of metal products in a weak magnetic field. Objective. Generalization and analysis of the results of laboratory and theoretical studies of the additional application of the magnetic field in the processes of mechanical testing of metals and alloys.Methods. Literary review of materials of articles, monographs, dissertations. Results. Reasonable use of a magnetic field for plastic deformation of metals. The explanation of the mechanism of the influence of the magnetic field on the structural elements of metals based on the effect of magnetoplasticity has been made. The description of changes in the mechanical properties of metals and alloys under the additional influence of a magnetic field is given. Conclusions. The phenomenon of magnetoplasticity has been studied for a wide range of materials such as pure metals and their alloys, including industrial steels and alloys. Various types of positive effects of a magnetic field on the mechanical properties of metals have been established: a decrease in the yield strength and deformation resistance, an increase in strain, relaxation of internal stresses, and a decrease in dislocation density. There is also a reverse, negative effect of the influence of a magnetic field: increased rate of hardening, embrittlement, increased creep of metals. What will be the effect of a magnetic field on a specific metal cannot be guaranteed with high accuracy.

Achieving high ductility at medium temperature in a nonequiatomic CoCrNi alloy

The tensile strength and ductility of face-centered cubic (FCC) multi-principal element alloys (MPEAs) typically decline monotonically with increasing temperature. In this work, we conducted tensile tests at different temperatures and characterized deformation microstructures for a nonequiatomic CoCrNi alloy with low stacking fault energy (SFE). Exceptional ductility is obtained at medium temperature, breaking the general sense of monotonic change with temperature. The effect of deformation mechanisms of dislocations, stacking faults and phase transformation on the ductility was discussed. This work reveals the unique temperature effect on the mechanical properties of metals with very low SFE.

The role of grain size in achieving excellent properties in structural materials

Advanced structural materials are expected to display significantly improved mechanical properties and this may be achieved, at least in part, by refining the grain size to the submicrometer or the nanocrystalline range. This report provides a detailed summary of the role of grain size in the mechanical properties of metals. The effect of grain size on the high temperature behavior and the development of superplasticity is illustrated using deformation mechanism maps and the development of exceptional strength through grain refinement hardening at low temperatures is also discussed. It is shown that the deformation mechanism of grain boundary sliding, as developed theoretically, can be used to effectively predict both the high and low temperature behavior of metals having different grain sizes. This analysis explains the increase in strain rate sensitivity in ultrafine-grained metals with low and moderate melting points and the ability to increase both the strength and ductility of these materials to thereby overcome the strength-ductility paradox. The recent development of hybrid materials is also reviewed and it is demonstrated that, although these hybrids have received only limited attention to date, they provide a potential for making significant advances in the production of new structural materials.

Optimizing ball milling parameters for controlling the internal microstructure and tensile characteristics of a laminated carbon nanotube/aluminum-copper-magnesium composite

This research investigates how different ball milling conditions influence the microstructure and mechanical properties of carbon nanotube/aluminum alloys. The study examines varying rotation speeds, specifically 200, 300, and 400 rpm. The results highlight the significant impact of milling conditions on grain size and mechanical properties. Notably, milling at 300 rpm /4 h and at 400 rpm/2 h led to higher tensile strength but lower uniform elongation compared to milling at 200 rpm/6 h. The alloy milled at 300 rpm/4 h displayed a refined microstructure, increased density, and the strongest fiber texture along the (111) direction. At 300 rpm/4 h, the presence of a moderate grain size promoted ductility, resulting in the highest uniform elongation (∼9.1%) combined with high strength (∼515 MPa). This in turn means an increase in UTS by 23% and uniform elongation by 3.4% compared to 400 rpm/2 h. The formation of MgAl2O4 at higher rotational speeds positively influences the CNT–Al interface by alleviating the adverse effects of interfacial oxide (Al2O3), resulting in improved bonding and, consequently, enhanced tensile properties. This study provides valuable insights into the effects of ball milling on the microstructure and mechanical properties of metals and alloys, contributing to the optimization of milling conditions to achieve desired material characteristics.

Metal wire embrittlement monitoring by the measurement of wire oscillation frequency

In the process of irradiation of materials by fluxes of heavy particles (protons, neutrons, alpha particles), damage to material structure is often observed. As a result of the accumulation of such damages, there is a subsequent change in the properties of materials, in particular, its embrittlement and hardening. Monitoring of the embrittlement process is important for nuclear reactor vessels exposed to high neutron fluxes. In this work, to observe the effect of heavy irradiation particles on the mechanical properties of metals, we propose to use vibrating wire resonators, in which the natural frequency of oscillations of the wire strongly depends on its tension. The change in the elastic characteristics of the wire alters the value of the natural frequency of wire oscillations. The natural oscillations are generated by a special circuit. Preliminary experiments to study the embrittlement effect of a stretched wire are performed by heating the wire with an electric current. In the case of short pulses, a significant increase in frequency is achieved, which is explained by the process of hardening of the material as a result of the thermal impact on the wire (rapid heating and cooling).

Optimizing ball milling parameters for controlling the internal microstructure and tensile characteristics of a laminated carbon nanotube/aluminum–copper–magnesium composite

This research investigates how different ball milling conditions influence the microstructure and mechanical properties of carbon nanotube/aluminum alloys. The study examines varying rotation speeds, specifically 200, 300, and 400 rpm. The results highlight the significant impact of milling conditions on grain size and mechanical properties. Notably, milling at 300 rpm/4 h and at 400 rpm/2 h led to higher tensile strength but lower uniform elongation compared to milling at 200 rpm/6 h. The alloy milled at 300 rpm/4 h displayed a refined microstructure, increased density, and the strongest fiber texture along the (111) direction. The presence of a moderate grain size facilitated ductility, resulting in the highest uniform elongation (∼9.1%) while maintaining high strength (∼515 MPa). This study provides valuable insights into the effects of ball milling on the microstructure and mechanical properties of metals and alloys, contributing to the optimization of milling conditions to achieve desired material characteristics.

The Role of Grain Size in the Mechanical Properties of Metals

It is now well established that the grain size is the fundamental microstructural feature of all polycrystalline materials. In practice, a very wide range of grain sizes will be needed in order to fully evaluate the effect of grain size on the mechanical properties of metals. For many years this was a significant limitation because it was not possible to use conventional thermomechanical processing to produce materials with submicrometer or nanometer grain sizes. Recently, this problem has been addressed by developing alternative processing techniques based on the application of severe plastic deformation. This overview demonstrates that, although the flow stress increases with decreasing grain size at low temperatures and decreases with decreasing grain size at high temperatures, this clear dichotomy in behavior may be adequately explained by using a single theoretical flow mechanism based on the occurrence of grain boundary sliding.

Atomic insight into the hydrogen diffusion in Al-doped iron structures

Hydrogen diffusion plays an important role in hydrogen embrittlement, which leads to the degradation of metal's mechanical properties. Understanding the hydrogen diffusion in metal at atomic level is helpful to clarify the mechanism of hydrogen embrittlement. In the present work, hydrogen diffusions in Al-doped iron structures were performed by first-principles calculations. The results show that the doped Al atoms can suppress the hydrogen diffusion, and the diffusion energy barrier initially increased with the doping concentration. With a doping concentration of 11.1 %, the hydrogen remained immobile even the temperature increased up to 600 K.

Application of density functional theory for evaluating the mechanical properties and structural stability of dental implant materials

BackgroundTitanium is a commonly used material for dental implants owing to its excellent biocompatibility, strength-to-weight ratio, corrosion resistance, lightweight nature, hypoallergenic properties, and ability to promote tissue adhesion. However, alternative materials, such as titanium alloys (Ti–Al-2 V) and zirconia, are available for dental implant applications. This study discusses the application of Density Functional Theory (DFT) in evaluating dental implant materials' mechanical properties and structural stability, with a specific focus on titanium (Ti) metal. It also discusses the electronic band structures, dynamic stability, and surface properties. Furthermore, it presents the mechanical properties of Ti metal, Ti–Al-2 V alloy, and zirconia, including the stiffness matrices, average properties, and elastic moduli. This research comprehensively studies Ti metal's mechanical properties, structural stability, and surface properties for dental implants.MethodsWe used computational techniques, such as the CASTEP code based on DFT, GGA within the PBE scheme for evaluating electronic exchange–correlation energy, and the BFGS minimization scheme for geometry optimization. The results provide insights into the structural properties of Ti, Ti–Al-2 V, and zirconia, including their crystal structures, space groups, and atomic positions. Elastic properties, Fermi surface analysis, and phonon studies were conducted to evaluate the tensile strength, yield strength, ductility, elastic modulus, Poisson's ratio, hardness, fatigue resistance, and corrosion resistance.ResultsThe findings were compared with those of Ti–Al-2 V and zirconia to assess the advantages and limitations of each material for dental implant applications. This study demonstrates the application of DFT in evaluating dental implant materials, focusing on titanium, and provides valuable insights into their mechanical properties, structural stability, and surface characteristics.ConclusionsThe findings of this study contribute to the understanding of dental implant material behavior and aid in the design of improved materials with long-term biocompatibility and stability in the oral environment.

Impact and Detection of Hydrogen in Metals

AbstractThe widespread use of hydrogen as an energy carrier is considered one of the most important keys to achieving the decarbonization necessary for the energy transition in numerous areas of technology and society. Not least due to the associated contact of metallic components with (pressurized) hydrogen, there is a latent risk of hydrogen-induced cracking (“hydrogen embrittlement”). The cause of damage is the hydrogen absorbed by the material, which is mobile via interstitial lattice diffusion. In high-strength steels with a tensile strength of more than 800 MPa, even very low diffusive hydrogen contents of less than 1 ppm (parts per million) can have a crack-inducing effect. Hence, dedicated, highly accurate analytical and testing methods are required for the detection of hydrogen and its effect on the mechanical properties of metals. This paper summarizes the current state of knowledge regarding hydrogen embrittlement and reviews the analytical, mechanical, and fractographic investigation methods for detecting hydrogen in metals.

First-principles study of oxygen segregation and its effect on the embrittlement of molybdenum symmetrical tilt grain boundaries

Elemental segregation can pronouncedly affect the cohesion of grain boundary (GB), which shows tremendous potential in altering the thermal stability and mechanical properties of metals. In this work, we systematically investigate the segregation behavior of oxygen (O) atoms at a series of GBs in molybdenum (Mo), using first principles calculations, to reveal the effect of O segregation on the embrittlement of Mo GBs. It is found that O atoms energetically prefer to segregate at sites in both the GB core and the vicinity of the GB plane. The strengthening energy is strongly associated with the GB structure, and it linearly decreases with the continuous deformation of the GB. O segregation can lead to an increase in the volume of polyhedron sites and a decrease in the charge density among adjacent Mo atoms across the GB plane. The weakened Mo-Mo bonds are believed to disrupt the GB cohesion, thereby increasing the intergranular cleavage tendency of Mo. Interestingly, O segregation does not always trigger GB embrittlement. The Σ5(310)[001] symmetric tilt grain boundary (STGB) with an O atom doped at the cap trigonal prism (CTP) site possesses a strength as strong as the clean GB. O segregation promotes the generation of Mo-O bonds across the GB plane, which counteracts the adverse effect of weakened Mo-Mo bonds. This work deepens the understanding of the possible effect of O segregation on GB cohesion of Mo from the atomic and electronic scales, providing guidance for enhancing the mechanical properties of Mo via GB structure optimization.

Understanding phase stability and deformation mechanisms of zirconium under high pressures from generalized stacking fault energy curves: A first-principles study

The mechanical properties of metals are strongly depend on their phase structures, in this work, to understand the phase stability and deformation mechanisms of zirconium(Zr) under high pressures, the generalized planar fault energy(GPFE) curves based on first-principles calculations are utilized to illustrate the deformation processes of α-Zr at high pressures. Firstly, it is found the prismatic slip system is more prominent toward α-Zr at zero pressure, while the slips based on basal plane undertake the main participant during the deformation processes of α-Zr at high pressures. Meanwhile, based on the basal slip, α-Zr phase containing the pre-existing stacking fault is found more favorable to generate twin fault instead of FCC fault at zero pressure; However, the deformation twinning is overwhelmed by the HCP-to-FCC transformation for the α-Zr when the external pressure is higher than 10.4 GPa. It is thus speculated that the slips of partial dislocations for forming FCC fault based on the basal plane (0001) act as a contributing participant during the phase transition processes of Zr under high-pressure. Additionally, the computed elastic constants and the HCP-to-FCC allotropic transformation under specified conditions have revealed the metastable nature of FCC Zr in comparison with HCP Zr.

Developing an analytical bond-order potential for Hf/Nb/Ta/Zr/C system using machine learning global optimization

Despite being effective in unveiling the complicated nanostructure-property relation of (HfNbTaZr)C high-entropy carbide (HEC), applications of atomistic simulations are restricted by the lack of reliable many-body interatomic potentials. In this study, we propose a machine learning (ML) global optimization framework to parameterize an analytical bond-order potential (ABOP) with massive internal parameters for the Hf/Nb/Ta/Zr/C system. The combined distributed breeder genetic algorithm (DBGA), extensive ab initio training data and a normalized objective function markedly accelerate the convergence towards global optimum. By performing a cross-validation for the established potential, we demonstrate that the ABOP can accurately predict fundamental energetic, structural and mechanical properties of metals, intermetallic compounds, alloys and carbides in both the training and test datasets. Moreover, the potential is employed in dynamic simulations such as thermal annealing, simple loadings, nanoindentation and irradiation collision, from which some typical experimental observations are successfully reproduced. This not only further verifies the reliability of ABOP, but also implies its broad future applicability in nanoscale simulations.

First principles study of hydrogen induced the grain boundaries decohesion in fcc Ag

Hydrogen embrittlement (HE) is a pervasive but harmful physical (chemical) phenomenon, and it has a profound effect on the mechanical properties of metals. Although the study of HE began as early as the near century and a half ago, the essential mechanism of HE still cannot be completely figured out yet. The metallic-H atoms interaction at the atomistic scale is considered the essence of the HE. Especially the interaction of interstitial H and host atoms at grain boundaries is crucial for revealing the HE mechanism. Here, the first principles simulation is applied to study the effect of the trapped H atoms on the grain boundaries (GBs) cleavage behavior. We construct the GBs with different orientations of the face-cantered cubic (fcc) Argentum (Ag) and conduct the ab initio tensile test for all the GBs. The strength of GBs during cleavage, the distortion of GBs structure, and the electronic structure variation induced by trapped H atoms are analyzed. We find the GBs cleavage strength is generally decreased by trapping H atoms at GBs. The decohesion mechanism is the GBs distortion induced by the local electron density variation of the GBs trapping H atoms.

A Lie-algebra-based description of disclination densities and the quantification of partial disclinations in deformed polycrystalline metals

Crystalline defects (e.g., dislocations, disclinations and grain boundaries) play a critical role in determining the mechanical and functional properties of metallic materials. From a physical point of view, dislocations and disclinations are the two fundamental types of topological defects in crystals, which originate from the breaking of translational symmetry and rotational symmetry, respectively. In spite of extensive studies on dislocations in the literature, the effects of disclinations on mechanical properties of metals have not been well recognized, partially due to the lack of an appropriate description for the rotational nature of disclinations. Here we suggest a Lie-algebra-based method to quantify the rotational properties of disclinations, which leads to a convenient way to determine disclination density distribution directly from Electron Backscatter Diffraction data. Through quasi-in-situ Electron Backscatter Diffraction characterizations, three major formation mechanisms of disclinations have been identified in deformed polycrystalline Mg alloys, i.e., dislocation-grain boundary interaction, dislocation redistribution and twin-twin reaction, all of which can be treated as topological reactions among various types of defects under a general framework. Our work not only suggests a new mathematical tool to investigate the interactions and reactions among multiple types of crystalline defects, but also provides a new insight to understand the deformation behaviors of metals and alloys based on dislocation/disclination theory.

Ceramic Coating for High Temperature Corrosion Protection of Steel

Abstract: In high temperature environments where oxidation occurs which effects the metal in multiple ways. High temperature corrosion is typically seen in ductile steel. This can cause abrupt failure and reduce a metal's mechanical properties. A variety of ceramic coatings are available that can be applied to enhance functionality and prevent corrosion, particularly at high temperatures. The majority of ceramic coatings are typically electrically nonconducting, making them excellent insulators. It also has a high melting temperature of up to 4000⸰F and remarkable abrasion resistance. Due to these characteristics, they offer exceptional corrosion resistance and strong abrasion resistance in high temperature conditions. In this research, the team synthesize ceramic coating which may provide exceptional abrasion resistant as well high temperature oxidation resistance. Before selecting the ingredients, it needs to be examined the compatibility between mild steel (sample) and constituents of ceramic coating, majorly the thermal expansion characteristics. It must be identical otherwise fractures can be produced on the coated surface of a metal. Samples were made as per demand, following collecting a sample and cleaned accurately to attach the coating appropriately. After application of coating on sample it should place in furnace which promote diffusion on a metal surface and construct protective barrier. Further, dipping the sample in 3.5% NaCl solution for 21 days and execute the OCP and EIS test of naked sample and coated sample correspondingly for 5 days. Potentiostat provides several graphs viz OCP, Bode plot, Nyquist impedance plot and Tafel Extrapolation. High temperature oxidation resistance of the ceramic covering was investigated using TGA analysis. The weight gain of coated sample is roughly 1mg/cm2 compared to about 4 mg/cm2 for plain sample in TGA curve. This illustrates that the ceramic coating is averting oxidation of steel surface at high temperature of 500ºC.

Operational characteristics of steel structures of long term service life

Introduction. The process of natural ageing of metal structures under influence of long-term mechanical loading and environmental factors, leads to changes in physical, chemical and mechanical properties of metals. Nowadays, a considerable number of industrial and civil buildings with metal structures having service life in the range of 30 to 120 years are in operation all over the world. Most of the scientific work on the aging of metals has been done in mechanical engineering, wear resistance of pipelines, machine parts, etc. In this connection, undoubtedly, the development of scientific direction connected with the study of peculiarities of changes in the structure, physical and mechanical characteristics of steel structures of a long period of their operation becomes actual. This is caused by the necessity of safe functioning of these constructions during the whole service life of a building or a structure, and also by the necessity of prediction of their behavior in fire and fire-resistant conditions.
 
 Materials and methods. The results of research concerning a steel structure specimen with a service life of 86 years have been presented. A set of experimental research methods was used: optical emission method to determine the chemical composition; metallographic method to study the microstructure, identify material defects and evaluate non-metallic inclusions in the structure of the sample; static tensile tests to determine the quality and performance characteristics of materials, in particular strength and ductility.
 
 Results. The results show that the chemical composition of the steel in general remains essentially unchanged during operation. A comparative analysis of the microstructure of steel St3 and steel with a lifetime of 86 years indicates slight changes in the structure related to the presence of multi-grain and fragmentary restructuring of structural elements, which may be indicative of the beginning of the destruction of the structure and reduce the strength characteristics of steel. The steel structure revealed the presence of non-metallic inclusions (point oxides and manganese sulfides) which serve as stress and strain concentrators in the matrix, causing local material failure at lower average strain, which may also lead to a reduction in the tensile strength of steel structures. According to the results of metallographic analysis insignificant transformations in the structure characterized by a change in perlite morphology, the presence of heterogeneity as well as the presence of non-metallic inclusions in the form of point oxides and manganese sulfides can be demonstrated. The significant influence of uniform and ulcerous corrosion process flowing into corrosion cracking going deep into the base metal on mechanical characteristics of steel is revealed. The obtained values of operational characteristics of the considered steel structure, having surface corrosion damages shows the lowering of ultimate strength by 15 %, yield strength by 10 % and relative elongation by 12 % from the normative values.
 
 Conclusions. Characteristic changes in the structure of steel with a long service life have been established. A comparative analysis of the results of static tensile tests on specimens from sections of the structure without corrosion damage and specimens cut out at the section acutely affected by corrosion has been made. The influence of corrosion process on reduction of operational characteristics of steel structure is shown. It is supposed that corrosion in course of time turns to a more aggressive type from even corrosion to corrosion cracking and spreads deep into the base metal which leads to considerable loss of mechanical properties of steel structures and to reduction of their fire-resistance limits.