Short-range Order Effects Research Articles

Effects of chemical short-range order on displacement cascade in medium-entropy CrCoNi alloys

Chemical short-range order (CSRO) is an important structure in high/medium entropy alloys (H/MEAs), which has a significant influence on the mechanical properties of irradiated materials. In this work, molecular dynamics (MD) simulations are performed to investigate the effects of CSRO on the point defect evolution during displacement cascade in medium-entropy CrCoNi alloys. To validate the influence of CSRO on point defects, multi-displacement cascades were initially conducted on the alloy. The results indicate that the CSRO structure can notably diminish dislocation and defect densities. Then, the influence of the CSRO structure on point defects under single displacement cascade was discussed. Both the peak number of point defects and the number of surviving point defects decrease with the increasing degree of CSRO during the single displacement cascade, indicating that the CSRO enhances the irradiation-resistance of irradiated materials. The Ni-rich region in CSRO can inhibit the formation of point defects due to its higher formation energy barrier. While the Co-Cr region in CSRO was found to promote the migration of point defects that can facilitate their recombination due to the lower migration energy. The current work provides new insights into understanding the evolution of irradiation-induced defects and mechanical properties of irradiated M/HEAs.

Atomic simulation for the effect of short-range order and twin boundary on mechanical behavior of FeNiCrCoAl high-entropy alloys

Short-range order (SRO) structure has been considered a potential strengthening method to improve the mechanical properties of high-entropy alloys (HEAs). However, the reinforcement mechanism of SRO structure on the HEA is still unclear. Here, the effect of SRO degree, twin boundary (TB) and temperature on the mechanical properties of the FeNiCrCoAl HEAs with different Al contents under uniaxial tensile is investigated using molecular dynamics/Monte Carlo simulations. The results indicate that the strengthening effect caused by the SRO structure and the softening effect caused by the addition of Al atoms coexist in the HEAs, and their competition determines the mechanical properties of the HEAs. And the softening caused by Al atoms dominates the mechanical properties of the HEAs, and the mechanical properties of the HEAs decrease with the increase of Al content. The results show that Al content has a significant impact on the SRO structure of the HEAs and the degree of SRO decreases in the HEAs with the increase of Al content. It is worth noting that under the same alloy composition, the strengthening effect of the SRO structure on the alloys first increases and then decreases with increasing the degree of SRO. The results indicate that the strengthening effect of the SRO structure and TB together is greater than that of TB or SRO alone. In addition, the results also show that higher temperature is not conducive to the stability of SRO structure, and the strengthening effect of SRO on the HEAs decreases with the increase of temperature.

Research on the effects of chemical short-range order on strengthening and toughening mechanisms of FCC/BCC dual-phase high-entropy alloys at micro/nano-scale

Research on the effects of chemical short-range order on strengthening and toughening mechanisms of FCC/BCC dual-phase high-entropy alloys at micro/nano-scale

The Derivation of CRSS in pure Ti and Ti-Al Alloys

The work focuses on the determination of the critical resolved shear stress (CRSS) in titanium (Ti) and titanium-aluminum (Ti-Al) alloys, influenced by an array of factors such as non-symmetric fault energies and minimum energy paths, dislocation core-widths, short-range order (SRO) effects which alter the local atomic environment, and tension-compression (T-C) asymmetry affected by intermittent slip motion. To address these multifaceted complexities, an advanced theory has been developed, offering an in-depth understanding of the mechanisms underlying slip behavior. The active slip systems in these materials are basal, prismatic, and pyramidal planes, with the latter involving both 〈a〉 and 〈c+a〉 dislocations. Each slip system is characterized by distinct Wigner-Seitz cell configurations for misfit energy calculations, varying partial dislocation separation distances, and unique dislocation trajectories—all critical to precise CRSS calculations. The theoretical CRSS results were validated against a comprehensive range of experimental data, demonstrating a strong agreement and underscoring the model's efficacy.

Inverse design of short-range order arrangement via neural network

Short-range order (SRO) plays a critical role in the mechanical behavior of metallic alloys. The arrangement of atoms at short ranges significantly impacts how the material responds to external forces. Nevertheless, the mechanics of these phenomena remain poorly understood. The identification of SRO in experiments is constrained by the low resolution of intensity distribution and the limitations associated with the direct observation of atomic arrangements in the lattice within the SRO domains. On the other hand, modeling the mechanical properties of short-range-ordered alloys is challenged by computationally expensive density functional theory (DFT)-based Monte Carlo (MC) simulations required to achieve the SRO structure dictated by energy minimization. This study aims to replace these expensive simulations with a trained machine learning (ML) model that yields accurate energy values for a given atomic structure. Further, we train an inverse model to determine the atomic configuration corresponding to the given SRO parameter. We propose a data-driven approach to map out the SRO directly to the atomic arrangements, combining ab initio calculations and a Neural Network (NN) model. We perform DFT-based MC simulations for Ni-V alloys in a wide range of solute compositions. Then, forward and inverse NN models are trained to map the SRO parameters into atomic arrangements or vice-versa. We predict the critical resolved shear stress (CRSS) for slip for all the studied configurations encompassing random and SRO structures and discuss the effect of SRO on the flow stress. The proposed ML methodology provides atomic arrangements from target order parameters with high accuracy, thereby eliminating the need for expensive simulations, and it advances the understanding of SRO at the atomistic scale.

Effect of order-disorder transition and lattice distortion on the mechanical properties of W-X (X = V, Nb, Ta) solid solutions

With the prosperity of high entropy alloys, short-range ordering is getting more and more attentions and regarded as the deciding role in the hardening or softening of solid solutions. In this work, the phase stability and mechanical properties of short-range ordered and disordered body-centered cubic (BCC) structures of W-X solid solutions (X = V, Nb, and Ta) are systematically investigated through a combination of first-principles calculation, cluster expansion and quasi-harmonic Debye formula. Based on the calculated heat of formation (ΔHf), W-X solid solutions show a strong short-range ordering tendency, as those ordered structures have a lower ΔHf than the disordered ones. Generally, short-range ordering results in the decrease of the shear modulus to bulk modulus ratio (G/B) and hardness for W-V and W-Ta systems, while an increase for W-Nb system, manifesting solid-solution softening and hardening effect, respectively. The short-ranged ordered C11b W2X phase exhibits a singularity in mechanical properties characterized by a higher G/B than solid solution phases compared to other ordered phases. The lattice distortion breaks the symmetric W-W bonds and leads to partial covalency in the W2X phases. Besides the increased brittleness, this distortion also causes the increase of ideal strength and the reduction of maximum tensile elongation of W2X. The effect of short-range ordering and lattice distortion on the hardening or softening of the W-X systems disappears after the order-disorder transition. The W-V and W-Ta phases have higher order-disorder transition temperature than W-Nb phase. Nevertheless, the transition temperature is relatively low in comparison to their melting points, signifying the important role in controlling the solute concentration at lower temperature.

A review on recent progress of refractory high entropy alloys: From fundamental research to engineering applications

Refractory high-entropy alloys (RHEAs) have emerged as frontier materials for high-temperature structural applications due to their exceptional mechanical properties and thermal stability. This review aims to provide a comprehensive and in-depth summary of the latest research progress in the field of RHEAs. By systematically analyzing 253 publications since 2022, this review presents a panoramic overview of the current research status in the field of RHEAs, covering aspects from alloy design, microstructure, processing techniques, mechanical behavior, to physicochemical properties. Key strengthening and toughening mechanisms, such as solid solution strengthening, precipitation strengthening, and grain boundary strengthening, are extensively analyzed. The high-temperature mechanical performance, oxidation resistance, and adaptability of RHEAs in extreme environments including corrosion and irradiation, are critically reviewed, and the potential application value of these research findings in aerospace, nuclear energy, biomedical, and other fields is discussed. Simultaneously, the multidisciplinary characteristics of RHEAs research has revealed the trend of the field evolving from fundamental research to practical applications. Furthermore, with the aid of advanced characterization techniques and computational methods, the review elucidates the controlling effects of chemical short-range order, defect structures, and other factors on the performance evolution of RHEAs, highlighting the importance of multi-principal element synergistic effects. Based on summarizing the key scientific issues and technological bottlenecks faced by RHEAs, the article provides a forward-looking perspective on future research directions, emphasizing development strategies that integrate computation and experiments, and accelerate the transformation of fundamental research into engineering applications, thus providing insights and guidance for developing a new generation of high-performance RHEAs.

The effect of chemical short-range order on incipient plastic behavior in FCC structured high entropy alloys

Chemical short-range order (CSRO) was assumed as one of the most important structure feature of high entropy alloys and the influence of CSRO on mechanical properties is a fundamental issue yet to be fully understood. In this work, we performed extensively nanoindentation experiments on CoCrFeNiAlx alloys to study the effect of CSRO on the incipient nanomechanical properties. The statistical nature of strengths at the first pop-in event was analyzed to gain insight of deformation mechanisms. All samples examined here exhibit bimodal distribution which indicate non-unique dislocation nucleation mechanisms. The bimodal distributions can be decomposed into two Gaussian distributions and the activation volumes can be obtained in the range of 0.73–1.38b3. The peaks shift to higher stress level after the development of CSRO. The heterogeneous dislocation nucleation plays a dominant role at low indentation stress with the aid of pre-existing crystalline defects. The homogeneous dislocation nucleation mechanism prevails when indentation stress close to theoretical values. The transmission electron microscopy characterization indicates the presence of chemical ordering in the aged samples. Both the degree of chemical ordering and lattice distortion are much higher in the Al containing HEAs due to the distinctive difference of properties in Al and other transition element atoms.

Chemical short-range order increases the phonon heat conductivity in a refractory high-entropy alloy

We study the effects of the chemical short-range order (SRO) on the thermal conductivity of the refractory high-entropy alloy HfNbTaTiZr using atomistic simulation. Samples with different degrees of chemical SRO are prepared by a Monte Carlo scheme. With increasing SRO, a tendency of forming HfTi and TiZr clusters is found. The phonon density of states is determined from the velocity auto-correlation function and chemical SRO modifies the high-frequency part of the phonon density of states. Lattice heat conductivity is calculated by non-equilibrium molecular dynamics simulations. The heat conductivity of the random alloy is lower than that of the segregated binary alloys. Phonon scattering by SRO precipitates might be expected to reduce scattering times and, therefore, decrease thermal conductivity. We find that, in contrast, due to the increase of the conductivity alongside SRO cluster percolation pathways, SRO increases the lattice heat conductivity by around 12 %. This is expected to be a general result, extending to other HEAs.

Propagation of elastic waves in correlated dispersions of resonant scatterers.

The propagation of coherent longitudinal and transverse waves in random distributions of spherical scatterers embedded in an elastic matrix is studied. The investigated frequency range is the vicinity of the resonance frequencies of the translational and rotational motion of the spheres forced by the waves, where strong dispersion and attenuation are predicted. A technique for making samples made of layers of carbide tungsten beads embedded in epoxy resin is presented, which allows control of the scatterers distribution, induce short-range positional correlations, and minimize the anisotropy of samples. Comparison between phase velocity and attenuation measurements and a model based on multiple scattering theory (MST) shows that bulk effective properties accurately described by MST are obtained from three beads layers. Besides, short-range correlations amplify the effect of mechanical resonances on the propagation of longitudinal and transverse coherent waves. As a practical consequence, the use of short-range positional correlations may be used to enhance the attenuation of elastic waves by disordered, locally resonant, elastic metamaterials, and MST globally correctly predicts the effect of short-range positional order on their effective properties.

Effect of short-range order on lattice distortion, stacking fault energy, and mechanical performance of Co-Fe-Ni-Ti high-entropy alloy at finite temperature

Effect of short-range order on lattice distortion, stacking fault energy, and mechanical performance of Co-Fe-Ni-Ti high-entropy alloy at finite temperature

Nanoindentation into a bcc high-entropy HfNbTaTiZr alloy-an atomistic study of the effect of short-range order.

The plastic response of the Senkov HfNbTaTiZr high-entropy alloy is explored by means of simulated nanoindentation tests. Both a random alloy and an alloy with chemical short-range order are investigated and compared to the well understood case of an elementary Ta crystal. Strong differences in the dislocation plasticity between the alloys and the elementary Ta crystal are found. The high-entropy alloys show only little relaxation of the indentation dislocation network after indenter retraction and only negligible dislocation emission into the sample interior. Short-range order-besides making the alloy both stiffer and harder-further increases the size of the plastic zone and the dislocation density there. These features are explained by the slow dislocation migration in these alloys. Also, the short-range-ordered alloy features no twinning plasticity in contrast to the random alloy, while elemental Ta exhibits twinning under high stress but detwins considerably under stress relief. The results are in good qualitative agreement with our current knowledge of plasticity in high-entropy alloys.

EFFECT OF RANDOM DISTRIBUTION AND SHORT-RANGE ORDERING OF SOLUTES ON THE MECHANICAL PROPERTIES OF NANOCRYSTALLINE Cu–Ag ALLOYS

The effects of solute random distribution (RSS) before relaxation and solute short-range ordering (SRO) after relaxation on the mechanical behavior of nanocrystalline Cu–Ag alloys were analyzed by molecular dynamics simulation. It has been found that the mechanical properties of Cu–Ag alloy mechanics with SRO were better than those of Cu–Ag alloy mechanics with RSS. Specifically, during the whole tensile process, compared with sample #1 with SRO structure, sample #2 with RSS structure has stronger strain–stress response ability, more obvious phase transformation process, and narrower shear strain zone on the grain boundary. Furthermore, when the number of Voronoi seeds is examined concerning the mechanical properties of the nanocrystalline Cu–Ag alloy, it becomes apparent that the average flow stress drops as the quantity of Voronoi seeds increases.

Effects of Chemical Short-Range Order and Temperature on Basic Structure Parameters and Stacking Fault Energies in Multi-Principal Element Alloys

In the realm of advanced material science, multi-principal element alloys (MPEAs) have emerged as a focal point due to their exceptional mechanical properties and adaptability for high-performance applications. This study embarks on an extensive investigation of four MPEAs—CoCrNi, MoNbTa, HfNbTaTiZr, and HfMoNbTaTi—alongside key pure metals (Mo, Nb, Ta, Ni) to unveil their structural and mechanical characteristics. Utilizing a blend of molecular statics and hybrid molecular dynamics/Monte Carlo simulations, the research delves into the impact of chemical short-range order (CSRO) and thermal effects on the fundamental structural parameters and stacking fault energies in these alloys. The study systematically analyzes quantities such as lattice parameters, elastic constants (C11, C12, and C44), and generalized stacking fault energies (GSFEs) across two distinct structures: random and CSRO. These properties are then evaluated at diverse temperatures (0, 300, 600, 900, 1200 K), offering a comprehensive understanding of temperature’s influence on material behavior. For CSRO, CoCrNi was annealed at 350 K and MoNbTa at 300 K, while both HfMoNbTaTi and HfNbTaTiZr were annealed at 300 K, 600 K, and 900 K, respectively. The results indicate that the lattice parameter increases with temperature, reflecting typical thermal expansion behavior. In contrast, both elastic constants and GSFE decrease with rising temperature, suggesting a reduction in resistance to stability and dislocation motion as thermal agitation intensifies. Notably, MPEAs with CSRO structures exhibit higher stiffness and GSFEs compared to their randomly structured counterparts, demonstrating the significant role of atomic ordering in enhancing material strength.

Break the strength and ductility trade-off in novel NbC reinforced Fe40.5(CoCr)25Mn17.5Ni10Si5 high entropy alloy

In this study, a novel NbC reinforced Fe40.5(CoCr)25Mn17.5Ni10Si5 high entropy alloy (HEA) was designed, which exhibits high strength and ductility at room temperature. This alloy was prepared through hot forging and annealing treatments, which exhibited the FCC microstructure with NbC and discrete nano-sized M23C6 carbides precipitation. The studied HEA retained a tensile strength of 863 MPa, and an outstanding ductility of 58 %. The microstructure evolution and deformation mechanisms were further investigated. The deformation mechanism was mainly governed by nano-scale defect heterogeneity of stacking faults (SFs), deformation twins and dislocations. The improved strength-ductility synergy is attributed to the formation of multiple SFs, deformation twining, dislocation cells, and nano-sized NbC precipitation. Moreover, the TEM observation elucidates the presence of chemical short-range order (SRO) domain in the studied HEA, which also has a major contribution in strength and ductility increment. The present findings shed light on developing the HEAs through proper compositional design and heat treatments, resulting in the combine effect of precipitation strengthening, SFs mediated plasticity, twinning induced plasticity (TWIP), and SRO effect.

Effects of Chemical Short-Range Order and Lattice Distortion on Crack-Tip Behavior of Medium-Entropy Alloy by Atomistic Simulations

It is well demonstrated that the complex chemical fluctuations on high/medium-entropy alloys (H/MEAs) play critical roles in their deformation process, but there are few reports related to the effect of such complex chemical fluctuations on the crack behavior. In this paper, the effects of chemical short-range order (CSRO) and lattice distortion (LD) on the crack-tip behavior of CrCoNi MEAs under mode I loading at room temperature are investigated by carrying out molecular dynamics (MD) simulation, hybrid MD/Monte-Carlo (MC) simulation and the J-integral method. The results reveal that CSRO can improve the J-integral value without significant changes in the localized deformation zone size. On the contrary, LD can lower the J-integral value with an increase in the localized deformation zone size. The energetic analysis shows that CSRO improves the activation energy barrier of Shockley partial dislocation from the crack-tip while LD reduces the activation energy barrier. Our work is a step forward in understanding the effects of CSRO and LD on the crack-tip behavior and deformation mechanisms of CrCoNi MEAs.

Effect of Al related chemical short-range order on the irradiation resistance of Al0.5CoCrFeNi multi-principal element alloy: A molecular dynamics simulation

Multi-principal element alloys (MPEAs) have received much attention for future nuclear materials due to their exceptional radiation resistance. This work investigated the effect of Al related chemical short-range ordered (CSRO) which caused by its large atomic size in face-centered cubic (FCC) Al0.5CoCrFeNi alloy on its irradiation damage behavior through mixed molecular dynamics and Monte Carlo simulations. The calculation results indicate that the CSRO structure effectively suppresses the generation of point defects during irradiation in Al0.5CoCrFeNi alloy, and this inhibitory effect increases with increasing irradiation energy. The enhanced radiation resistance of CSRO alloy is attributed to the high vacancy formation energy, interstitial atom formation energy, and vacancy migration energy barrier of Al. Moreover, the Al atoms in CSRO alloy can also act as defect barriers, preventing the migration of vacancy defects; The formation energy of interstitial atoms in the CSRO alloy exhibits a strong element dependence, and there is a significant difference in the formation energy of interstitial atoms between different points, which strengthens the hysteresis diffusion effect of MPEAs and further enhances the radiation resistance of MPEAs.

The shear softening and dislocation glide competition due to the shear-induced short-range order degeneration in CoCrNi medium-entropy alloy

The short-range order (SRO) in multi-principal element alloys (MPEAs) is an intriguing topic in advanced alloy research. The crucial question related to this topic lies in the effect of the local chemical fluctuations on the deformation behavior of MPEAs. In this study, the large-scale molecular dynamics (MD) simulation is used to investigate the dislocation glide behavior and mechanical performance of CoCrNi medium-entropy alloy (MEA) with respect to the SRO and lattice distortion (LD) effects. The slip plane softening and dislocation glide competition are found in the models with SRO. The change of energy barrier caused by SRO degeneration is the dominant reason for the slip plane softening, while the combination of dislocation pinning and slip plane softening leads to the dislocation glide competition, which is the primary mechanism for the shear localization in the CoCrNi MEA with SRO. Moreover, the dislocation glide competition compensates for the strength loss induced by slip plane softening. The results provide a new proposition for the conflicting simulation and experimental results on the topic of the SRO effect in MPEAs.

The influence of short-range molecular order in gelatinized starch on the formation of starch-lauric acid complexes

A model system of gelatinized wheat starch (GWS) and lauric acid (LA) was used to examine the effect of residual short-range molecular order in GWS on the formation of starch-lipid complexes. The extent of residual short-range molecular order, as determined by Raman spectroscopy, decreased with increasing water content or heating duration of gelatinization. The enthalpy changes, crystallinity, short-range molecular order and the in vitro enzymic digestion of GWS-LA complexes increased initially to a maximum and then declined as the short-range molecular order in GWS decreased, showing that there was an optimal amount of residual short-range molecular order in GWS for maximizing GWS-LA complexes formation. Below this optimum amount, the limited disruption of short-range molecular order may constrain the mobility of amylose chains for complexation with LA, whereas with excessive disruption above this amount the amylose chains may be too disorganized or entangled to form complexes with LA. The susceptibility of GWS-LA complexes to enzymatic hydrolysis was influenced by both long- and short-range structural order, and to a lesser extent the amounts of complexes. This study showed clearly the role of short-range molecular order in gelatinized starch in influencing the formation of GWS-LA complexes.

Deformation mechanisms in high entropy alloys: a minireview of short-range order effects.

The complex atomic scale structure of high entropy alloys presents new opportunities to expand the deformation theories of mechanical metallurgy. In this regard, solute-defect interactions have emerged as critical piece in elucidating the operation of deformation mechanisms. While notable progress has been made in understanding solute-defect interactions for random solute arrangements, recent interest in high entropy alloys with short-range order adds a new layer of structural complexity for which a cohesive picture has yet to emerge. To this end, this minireview synthesizes the current understanding of short-range order effects on defect behavior through an examination of the key recent literature. This analysis centers on the nanoscale metallurgy of deformation mechanisms, with the order-induced changes to the relevant defect energy landscapes serving as a touchstone for discussion. The topics reviewed include dislocation-mediated strengthening, twinning and phase transformation-based mechanisms, and vacancy-mediated processes. This minireview concludes with remarks on current challenges and opportunities for future efforts.