Search

Layered metal composites have been widely used in various industries fields because of their excellent properties and are responsible for mechanical behavior of materials. This paper focuses on analyzing the deformation mechanism of the (110) interface under different loading states by MD. The results show that there are two yield points in the stress–strain curve under both Z- and Y-axis loading states. The first yield is the nucleation of dislocations at the interface, meantime the slip of dislocations and the extension of stacking faults begin at the Al layer. The second one, the dislocation passes through the interface, nucleates and emits toward the Cu layer at the interface, leading to a stress mutation. It is worth noting that during the stable rheological stage, the deformation mechanisms vary under different loading directions. Under Y-axis tensile loading, the phase transformation of FCC–HCP is present due to the interaction of dislocation movement and stacking fault. On the contrary, there are two twin paths A and B, improving the strength, during Z-axis compression loading. For other loading modes, there are three zones, namely the elastic stage, the release of energy, and strain hardening and dynamic softening. The interface plays the role of nucleation, annihilation and penetration of dislocations, and this interface-dislocation mechanism is reflected in the whole stage of plastic deformation. The results have an insight into the design and control in heterointerface. [ABSTRACT FROM AUTHOR]

In this paper, molecular dynamics method was used to design the grain boundary (GB) segregation structure of solute atom Mo in nanocrystalline nickel, and the effect of the segregation structure on the migration and deformation mechanism of nanocrystalline Ni–Mo alloy boundaries was studied. The results indicate that the addition of solute atom Mo can cause segregation at GBs, and the yield strength and tensile strength of nanocrystalline Ni are significantly increased through solid solution strengthening. Mo atoms segregation result in an increase of the GB thickness and stability of the GB. In addition, by labeling GB atoms and tracking their diffusion trajectories, it was found that after adding Mo atoms, the probability of atomic diffusion at GBs decreased. This indicates that Mo atoms reduce GB energy and improve GB stability. Meanwhile, as the Mo content increases, the degree of atomic disorder increases, and the probability of GB migration decreases. This leads to the inability of grains to merge and inhibit their growth, effectively improving the mechanical properties of the material. As the strain increases, the number and length of dislocations increase, and a large amount of entanglement occurs at GBs. With the increase of Mo content, the number of dislocations decreases sharply, with Shockley dislocations having the highest number. Shockley dislocations interact with other dislocations and hinder their generation and movement, forming a more stable dislocation system structure and increasing the strength of the alloy. Our work focuses on observing the influence of GB segregation structure on the mechanical properties and deformation mechanism of nanocrystalline polycrystalline Ni–Mo alloys, establishing the mechanism of the influence of segregation structure on the stability and coarsening of nanocrystalline metal GBs, examining the influence of segregation structure on dislocation motion and GB migration process during deformation, and proposing positive research and development ideas and theoretical basis for designing nanocrystalline metal materials with excellent performance. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were utilized to investigate the mechanical properties of the Al–Co–Cr–Fe–Ni high-entropy alloy and observe atomic microstructure and internal dislocation line changes under different parameter conditions. The findings demonstrate that the mechanical properties of the AlCoCrFeNi3 high-entropy alloy are significantly superior to those of conventional alloys in ambient temperature. During the tensile process, the face-centered structure undergoes interconversion with other structure types, while the internal dislocation lines gradually increase. The presence of grain boundaries impedes dislocation movement, resulting in lower deformation capacity and tensile strength in polycrystals compared to single crystals. Enhancing Ni content, increasing strain rate, and decreasing temperature during tensile process contributes to the enhancement of the mechanical properties of material. Among these factors, the Ni content exerts the most significant influence on the mechanical properties of the material. [ABSTRACT FROM AUTHOR]

This study investigates the impact of initial temperature on the microstructure and mechanical properties of welded components, using molecular dynamics (MD). The stress–strain curves of the welded components, following various initial temperature treatments, revealed a double yielding phenomenon. Notably, there was a significant strain difference of 19.7% between the two yields. When the strain was loaded to the point of doubling yielding, stacking faults and twins covered the aluminum component part, while no such observations were made in the nickel component part. Additionally, tensile cracking occurred in the aluminum component part. The results indicate that treatment at varying initial temperatures alters the internal structure of the welded components. After the material yielded the first time, a significant number of disordered atoms and Shockley partial dislocations emerge, resulting in a substantial buildup of dislocation tangles and reduced dislocation migration rates. Consequently, the material exhibits a phenomenon of double yielding, with dislocation slip and deformation serving as the primary mechanisms. The optimal mechanical properties of the welded components achieved an initial temperature of 200 K. Additionally, the effect of tensile temperature on the mechanical properties of the welded components were analyzed, and similar observations of double yielding were made. The significant number of dislocation tangles served as a barrier to dislocation slip, effectively enhancing the material's mechanical properties. The simulation results provide theoretical support for the development of aluminum–nickel multilayer film self-propagation welding process. [ABSTRACT FROM AUTHOR]

Gradient nanostructured metals have become one of the research hotspots in the field of materials science due to their excellent mechanical properties and unique deformation behavior. In our contributions, the nanotwin gradient was introduced into the nanocrystalline Ni–Co alloy, and the influence of the gradient structure on the shear properties and microscopic deformation behavior was studied in order to reveal the strengthening mechanism. The gradient nanotwin Ni–Co alloy has elastic deformation and work hardening at the initial shear stage. The stress decreases after reaching the stress limit, and the uniform plastic deformation is maintained at the later stage. The excellent stability of fine twin layer and its effective hindrance to dislocation nucleation and movement can improve the strength of the material. In addition, the yield and work hardening of nanotwin gradient Ni–Co alloy are easy to occur at low temperature, and the stress–strain curve fluctuates obviously. At high temperature, the alloy is prone to plastic deformation, and the strength is reduced macroscopically. The higher the temperature is, the more difficult it is to yield. The results provide a solid theoretical basis for the design of Ni‐based alloys. [ABSTRACT FROM AUTHOR]

Nanotwinned exist in crystals as coherent interfaces with low interfacial energy, which can not only improve the strength of metal materials, but also increase the ductility. In this manuscript, we have performed molecular dynamics simulations of the mechanical properties of a nano-columnar crystalline Cu-Ni alloy with different twin boundary spacing. It is found that the model without twin has a stacking fault tetrahedron composed of stair-rod dislocations, which results in a small change in dislocation density at the later stage of deformation, and the average stress after yielding is lower than that of the model with twin. During the deformation process, with the increase of Other atoms, the dislocation slip barrier is enhanced, the tensile strength is increased, and the yield phenomenon is delayed, which is more obvious with the decrease of twin boundary spacing. The dislocation density decreases with the decrease of the spacing of the twin boundary, and the dislocation segments become shorter. When the twin boundary spacing is 0.625 nm, the tensile strength is increased by about 71% compared with the model without twin structure. [ABSTRACT FROM AUTHOR]

Molecular dynamics was used to study the uniaxial tensile process of Ni–Co alloy with gradient nanotwin structure, and the microstructure and deformation mechanism of mechanical properties of gradient nanotwin Ni–Co alloy were studied from the micro perspectives of dislocation, twin layer and grain boundary movement. The results show that when the twin structure Ni–Co alloy is uniaxial stretched along the gradient direction and perpendicular to the gradient direction, the twin layer has different strengthening effects on the structure and strengthening mechanism, the stretching in different directions has greater influence on the dislocation movement and stacking fault nucleation of the nanogradient twin structure. The yield strength of Ni–Co alloy is 11.3 Gpa and 5.5 Gpa, respectively, after stretching along gradient and vertical gradient directions, Young's modulus reaches 221.16 Gpa and 127.90 Gpa. It is found that the gradient twin structure stretched along gradient direction has greater strength and the twin layer breaks into fragments and distributes in the system during the process of strain increase. At different temperatures, it was found that the strength and plasticity of the material decreased sharply with the increase of temperature, the dislocation density in the system also decreased with the increase of temperature, resulting in poor performance of the material. [ABSTRACT FROM AUTHOR]

In this contribution, molecular dynamics method is used to accurately add quantitative Co atoms in the grain boundary (GB) region of nano-polycrystalline Ni to study the effect of solute atoms on the GB and the deformation mechanism of the material. It was found that adding an appropriate amount of Co atoms at the GBs can improve the tensile strength of the material to a certain extent through solid solution strengthening. However, excessive introduction of solute atom will increase the activity of GB atoms, destroy the stability of GBs, and accelerate the appearance of material yielding. At the same time, the Co atoms at the GB gradually detached from the GB region and diffused into the grains. In addition, the dislocations are distributed in a grid at the GBs, and with the increase in strain, the number and length of dislocations gradually increase, forming a large number of entanglements. Moreover, the Shockley dislocation interacts with other dislocations to form a more stable dislocation structure by hindering the generation and movement of other dislocations, which greatly enhances the strength of the system. [ABSTRACT FROM AUTHOR]

The effects of gradient grain size and temperature on the mechanical properties of nanocrystalline nickel were studied by the molecular dynamics method, and the microstructure change process of size gradient nanocrystalline nickel under tensile load was characterized by Common Neighbor Analysis (CNA). The research results show that dislocations tend to generate stress concentration in small-sized grains during stretching, so the plastic deformation of the material always occurs in small-sized grains first. At the same time, through Dislocation Analysis (DXA), it was found that Shockley dislocation is the main factor affecting its mechanical properties, and the interaction between dislocations provides a certain contribution to the strength of the metal. In addition, yield strength, maximum tensile stress, and Young's modulus all decrease with increasing temperature, and the grain boundary atomic content and the degree of disorder are greatly increased. During the stretching process, the number of dislocations is greatly reduced, which leads to a reduction of their interactions, which is the reason for the reduction of the mechanical properties of the material. The above research results have positive meaning for the design of gradient nanocrystalline materials, and provide reference and help for the improvement of nanomaterial properties. [ABSTRACT FROM AUTHOR]

The addition of oxygen atoms in solid solution to α‐Ti alloy can increase not only its hardness but also its brittleness. Herein, the edge dislocation mobility of Ti–O single crystals at oxygen concentrations of 0–2 at% and temperatures of 100–900 K is investigated by molecular dynamics simulations. The results show that the interstitial oxygen atoms have a strong hindering effect on the a/3 [112¯0] edge dislocations on the {1¯100} prismatic planes, which is attributed to the pinning effect of the vacancy clusters on the dislocation movement due to the interstitial oxygen atoms, thus leading to pronounced dislocation strengthening and hardening. The critical resolved shear stress (CRSS) for dislocation movement increases with increasing oxygen content and decreases with increasing temperature. Moreover, the effect of oxygen concentration on dislocation mobility also diminishes with increasing temperature. [ABSTRACT FROM AUTHOR]

Herein, the effects of different Co content and temperature factors on the shear mechanical properties of nano‐polycrystalline nickel–cobalt alloy are analyzed by molecular dynamics (MD) simulations. It is found in the work that the highest shear modulus of 63.03 GPa is obtained when the Co content is 10%, attributed to the lattice distortion caused by the difference in the lattice parameters between two elements. During the shearing process, the multilevel twins are present with intensification of the deformation process, resulting in excellent dynamic shear performance. Shockley dislocations will drive the stacking faults and other partial dislocations to constitute a tetrahedral edge, and finally forms a tetrahedral structure. In addition, as the temperature of the shear environment increases, the highest strain and stress decrease. The grain boundary atoms increase significantly, and the atoms inside the grains decrease accordingly. As the degree of atomic disorder increases, the grain boundaries will melt gradually. The decrease of partial dislocation density can weaken the entanglement effect caused by dislocations. The previous conclusions promote the product development and application of nano‐polycrystalline alloys in the future, and provide important guidance significant for the engineering application of nickel–cobalt alloys. [ABSTRACT FROM AUTHOR]

The stabilization of grain boundaries (GBs) is beneficial for improving the stability and mechanical properties of nanocrystalline (NC) metals. Molecular dynamics (MD) calculations were performed to investigate the shear response of Ni Σ 17 [110](223) symmetrical tilt GB. It was found that under the action of shear, the nucleation and evolution of the GB source Shockley partial dislocations ultimately result in the low-energy-state transformation of the GB structure units (SUs). However, the Ag atom contained in the GB increases the shear stress and strain required for the GB relaxation, and the strain range for the GB relaxation is expanded, indicating the inhibitory effect of the Ag atom on the structural relaxation of Ni Σ 17 [110](223) GB. As the temperature increases from 10 K to 250 K, the structural relaxation of Ni Σ 17 [110](223) GB becomes easier to proceed. In addition to segregation-induced GB stabilization, strain-induced GB relaxation and the roles of foreign atom and temperature clarified in this work could provide several new entry points for stabilizing high-energy GBs. [ABSTRACT FROM AUTHOR]

Ni–Co alloy has great advantages in the fields of micro-electromechanical systems and aerospace, however, the lack of micro-deformation mechanism restricts its industrial application. Herein, the deformation mechanism and microstructure evolution of Ni–Co alloy nanoplate under shear loading are investigated by MD. The yield strength increases gradually with the increase of the velocity, and the highest shear modulus is 111.43 GPa. The stress concentration leads to the nucleation and expansion of the dislocation, and the stacking fault expands with the dislocation motion, swallowing most of the disordered atoms. By Dislocation Extraction Algorithm (DXA), it is found that Shockley and Perfect dislocations make a major role, and the interactions between dislocations are responsible for the high mechanical properties. As the temperature increases, the yield strength decreases significantly, the stress fluctuations in the plastic phase at 100 K and 200 K are greater compared to other temperatures. Meanwhile, the coherence of the dislocations motion decreases, and the atoms in the stacking faults are scattered, leading to the decreasing of area. The above results are helpful for the design and control of nanoelectronic facilities and provide a significant guide for the industrial applications of Ni–Co alloy nanoplate. [ABSTRACT FROM AUTHOR]

The mechanism of plastic deformation under tensile and compressive loading of hexagonal close-packed (HCP)/face-centered cubic (FCC) biphasic titanium (Ti) nanopillars at different temperatures (70 K, 150 K, 300 K and 400 K) and different FCC phase sizes (2 nm, 4 nm, 6 nm and 8 nm) was investigated by molecular dynamics (MD). The plastic deformation is mainly concentrated in the FCC phase during compression loading. The HCP/FCC interface is the main source of 1 6 〈 1 ̄ 2 ̄ 1 〉 Shockley partial dislocations. As the temperature increases, the dislocation nucleation rate increases and the surface dislocation source is activated. During tensile loading, it is more likely that the Shockley partial dislocations react with each other in the FCC phase to form Lomer–Cottrell sessile dislocations and stacking fault (SF) nets. When the temperature is reduced to 70 K, tensile twins are formed at the phase interface. The plastic deformation is dominated by twins and 〈 c + a 〉 dislocation slip occurs in the HCP phase. The effect of the FCC phase size on the plastic deformation mechanism of the nanopillar is strong. The FCC phase is transformed into the HCP phase when the FCC phase size in the nanopillar is reduced to 4 nm under compressive loading. However, twin deformation occurs at the HCP/FCC interface when the FCC phase size is reduced to 2 nm under tensile loading. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations are performed to investigate the nanoscale tribology behavior of Ti-based FeCoNiTi High-entropy alloy (HEA) coating through nanoscratching. Three coating interface models, (001) HEA ||(0001) Ti , (001) HEA ||(11 2 ‾ 0) Ti , and (001) HEA ||(1 1 ‾ 00) Ti , are selected to explore the effects cutting depth (D) and cutting velocity (V) of abrasive particles during the nanoscratching process. The results show that the Ti-based HEA coating with the interface (001) HEA ||(0001) Ti has the smallest coefficient of friction (COF) making it most suitable as the coating interface. The increase in V resulted in the increase of the frictional force influenced by the Other structure composed of disordered atoms. Due to the existence of multiple phase structures in the limited area of the coating, dislocation nucleation is difficult and disordered atoms are formed. This is different from the strengthening caused by dislocation accumulation in the scratching region. The HEA coating plays an effective role in protecting the pure Ti substrate. With the protection of HEA coating, dislocation slip and deformation twinning were not observed in the pure Ti substrate. However, dislocation slip are the main plastic deformation mechanisms of uncoated pure Ti. These findings provide a theoretical reference for upgrading the wear resistance of pure Ti with HEA coating and expands the area of application of pure Ti. [Display omitted] • Cutting of depth and velocity affect the friction behavior of Ti-based HEA coating. • Other structure composed of disordered atoms strongly affects the frictional force. • With the protection of HEA coating, the Ti substrate has no plastic deformation. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were performed with a Finnis-Sinclair many-body potential to investigate the mechanical properties and deformation mechanisms under applied uniaxial tensile and compressive loads in α-titanium (Ti) single-crystal nanopillars oriented along the 〈 1 1  2 ¯  0 〉 direction. The results indicate that the mechanical properties and plastic deformation mechanism display tension–compression asymmetry. The non-linear elastic behavior is attributed to the difference in friction between the neighboring atomic planes at the elastic deformation stage under push and pull loading conditions. Increasing the friction leads to hardening with compression. Decreasing the friction leads to softening with tension. Increasing the friction may also lead to higher yield stress with compression compared with tension. Perfect nanopillars are yielded via the nucleation and propagation of { 1 ¯  0 1 0} 〈1  2 ¯  1 0 〉 dislocations on the surface and corners of the nanopillars. Prismatic slip is the dominant mode of plastic deformation in the Ti nanopillars under compressive loading. However, {1 0  1 ¯  1} 〈1 0  1 ¯ 2 ¯ 〉 twinning is the dominant plastic deformation mechanism together with prismatic slip under tensile loading. Two typical intrinsic stacking faults (SFs) with different propensities exist in the nanopillars. The microstructural evolution of the SFs was also simulated. [ABSTRACT FROM AUTHOR]

The tensile deformation behavior is studied in pure titanium (Ti) nanopillars subjected to loading along the [0 0 0 1] orientation based on molecular dynamics (MD) simulations. The double yielding phenomenon is displayed in stress-strain curves when the deformation temperature is less than 380 K. One new type of deformation-induced phase transformation from the hexagonal close-packed (hcp) to face-centered cubic (fcc) phase has been predicted. The effects of temperature and strain rate on this type of phase transformation are systematically investigated. It is revealed that { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 1 〉 twinning plays an essential role in inducing the phase transformation, which is produced through dislocation glide of multiple Shockley partial dislocations inside the { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 1 〉 twin. A group of high-density stacking faults is accumulated though the continuous glide of multiple Shockley partial dislocations inside the twinning region, eventually leading to the allotropic phase transformation from the hcp to fcc phase. After twinning, two thermally activated dislocation slip processes compete with one another: Shockley partial dislocations and full dislocation slip. The deformation mechanism changes from phase transformation to dislocation slip when the temperature is higher than 380 K or the strain rate is lower than 10 8 s −1 . The dislocation slip on the { 1 0 1 ¯ 1 } pyramidal plane is clearly observed under tensile loading at higher temperatures. Furthermore, our simulations indicate that the nucleation rate has a strong effect on the deformation mechanism on the nanoscale. [ABSTRACT FROM AUTHOR]

Different size effects and deformation mechanisms are revealed in α-titanium (Ti) single crystal nanopillars orientated for [112̄0] and [0001] based on molecular dynamics simulations. The strength–size relationship changes from “smaller is stronger” to “smaller is much weaker” when the width of nanopillars reduces from 19 nm to 3 nm. The “smaller is much weaker” is attributed to that the surface effect caused by a thermal vibration of surface atoms leads to the initiation and growth of surface dislocations. [ABSTRACT FROM AUTHOR]

An inverse “smaller is stronger” trend is predicted on the basis of molecular dynamics simulations of α-titanium (Ti) single-crystal nanopillars orientated for double prismatic slips when the nanopillars are less than 7 nm wide. This trend is attributed to a significant increase in the surface energy due to the nucleation and propagation of edge dislocations on the surface of the pillars. [ABSTRACT FROM AUTHOR]

Mechanical behavior and plastic deformation mechanism of a new type of Co30Fe16.67Ni36.67Ti16.67 high entropy alloys (HEAs) have been calculated by the molecular dynamics method. The results show that the polycrystalline Co30Fe16.67Ni36.67Ti16.67 HEA has remarkable tensile plasticity and anisotropy. When the crystallographic orientation of the grain is <001>, the plastic deformation mechanism is face‐centered cubic (FCC)→body‐centered cubic (BCC) transformation and deformation twins. Grain boundary and vacancy reduce the nucleation energy of FCC→BCC phase transition, making BCC phase nucleation easy and growing in a shear manner, eventually forming deformation twins in the BCC phase. When the crystallographic orientation of grain is <110> and <111>, the plastic deformation mechanism is stacking faults, FCC→hexagonal‐close‐packed (HCP) phase transformation, and deformation twins. The motion of Shockley dislocation leads to the stacking fault, intrinsic stacking fault leads to the FCC→HCP phase transition, extrinsic stratification fault leads to the twin deformation, and the grain refining occurs during the tension process. Temperature and strain rate also have strong effects on tensile strength and elastic modulus. These results will provide a theoretical basis for the development of the HEAs and expand their application. [ABSTRACT FROM AUTHOR]