arXiv subjects

Huiqiu Deng

Publications and source records attributed to Huiqiu Deng.

8 recordsLinked to original sources

arXiv2026

Thermodynamics of stacking faults and phase stability in cobalt alloys: A combined computational and experimental study

Stacking fault energy dictates phase stability and deformation behavior in Co alloys and WC-Co cemented carbides, yet a quantitative assessment of alloying effects at finite temperatures remains poorly established. By integrating first-principles thermodynamics with microstructural characterization, we provide a rigorous evaluation of these influences across atomic and macroscopic scales. We show that stacking fault energetics at 0K for transition metal solutes are primarily governed by atomic misfit volume. While 4d and 5d elements follow a consistent linear trend, specific 3d solutes exhibit significant deviations due to non-negligible magnetic contributions. By incorporating phonon, electronic, longitudinal spin-fluctuation, and magnetic free-energy contributions, the model accurately captures the fcc-hcp transformation and quantifies how diverse solutes modulate the phase landscape. We demonstrate that V, Ni, Fe, Mo, and W lower the transformation temperature by stabilizing fcc phase, while Cr and C exhibit the opposite effect, consistent with experimental phase diagrams. Furthermore, microscopic analysis confirms that higher W content dissolved in the Co suppresses stacking-fault formation by elevating the stacking fault energy at finite temperatures. This work clarifies the physical mechanisms by which alloying regulates stacking fault energy and phase stability in Co-based systems, providing guidance for the design of Co-based alloys and WC-Co cemented carbides.

cond-mat.mtrl-sci↗

arXiv2026

Atomic-Scale Insights into Solute Drag Effects on Grain Boundary Motion in Mg-Al and Mg-Ca Alloys

The slip behavior of dislocations and grain boundaries critically governs recrystallization and plastic deformation in Mg alloys and can be strongly influenced by solutes. However, the quantitative effects of solute distribution on defect mobility remain unclear. Using molecular dynamics and Monte Carlo simulations, we systematically investigate how Al and Ca solutes affect the motion of dislocations, low-angle grain boundaries (LAGBs), and high-angle grain boundaries (HAGBs) in Mg. Within the idealized framework of random solid-solution, solute drag is dominated by elastic interactions arising from atomic size mismatch, resulting in a stronger resistance from Ca than from Al. In contrast, under the more realistic condition where solute segregation occurs, the dominant mechanism shifts to chemically driven pinning, whose effectiveness is governed by the attainable segregation density. Owing to strong Ca-Ca repulsion, Al achieves substantially higher segregation concentrations than Ca and therefore exerts much stronger pinning effects. Notably, solute-induced retardation is significantly more pronounced for HAGBs than for LAGBs, leading to amplified solute effects during the late stages of recrystallization, where grain growth is controlled primarily by HAGB migration. These results provide atomic-scale insight into experimentally observed grain refinement in Mg alloys.

cond-mat.mtrl-sci↗

arXiv2026

Segregation-Controlled Diffusion-Induced Grain Boundary Migration in Alloy 690

Grain boundary (GB) migration accompanied by Cr depletion is widely observed in Alloy 690 and is closely linked to intergranular degradation and stress corrosion cracking. However, the fundamental driving force for GB migration and its link with Cr depletion remains unclear. In this work, hybrid molecular dynamics and semi-grand canonical Monte Carlo simulations were employed to investigate GB migration in Alloy 690 under coupled solute diffusion and segregation effects across a range of GB characters. The results show that Cr segregation at GBs, while generally considered favorable for GB stability, can facilitate diffusion-induced GB migration and Cr depletion. Cr diffusion along GBs produces localized Cr depletion zones that are energetically incompatible with positively segregating GBs, generating a chemical driving force that drives GB migration toward the Cr-rich matrix, which ultimately results in persistent GB migration accompanied by a Cr depletion. By quantifying solute-GB interaction energetics, we demonstrate that GB migration is quantitively controlled by the coupled effects of solute diffusivity and segregation strength. These mechanistic insights provide a unified framework that rationalizes experimentally observed correlations between GB character, Cr depletion, and GB migration in Cr-containing alloys.

cond-mat.mtrl-sci↗

arXiv2025

Dislocation Transmission Across Tilt Low-Angle Grain Boundaries in BCC Fe: The Role of Elastic Interactions

Low-angle grain boundaries (LAGBs) are often regarded as penetrable interfaces to dislocation motion, yet recent studies suggest they can also act as strong barriers. The origin of this duality remains debated, particularly regarding the role of elastic interactions. Here, large-scale molecular dynamics simulations are employed to investigate dislocation transmission across various tilt LAGBs in BCC Fe. The results show that transmission resistance varies widely with boundary-dislocation geometry. Contrary to the prevailing view that dislocation reactions dominate, elastic interactions between lattice and boundary dislocations emerge as the primary controlling factor. Screw and screw-like dislocations generate shear stresses that bend GB dislocations and produce strong barriers, whereas edge dislocations lack such stresses and transmit more readily. Consequently, barrier strength increases as the dislocation character angle decreases, with screw dislocations experiencing the strongest resistance. From these insights, we develop an analytical model that quantitatively links net transmission stress to dislocation character, boundary inclination, and boundary misorientation, reproducing the simulation results with excellent agreement. These results establish the dominant role of elastic interactions in dislocation-LAGB interactions and provide a predictive basis for designing materials strengthened by controlled boundary architectures.

cond-mat.mtrl-sci↗

arXiv2024

Modulating dislocation reactions through preferential hydrogen segregation in bcc metals

The interaction between dislocations is fundamental to plastic deformation, work hardening, and defect accumulation. While extensive research has focused on the impact of solutes on individual dislocations, how solutes affect dislocation-dislocation reactions remains largely unexplored. Here, using atomistic simulations of iron as a model bcc system, we demonstrate that hydrogen solutes enable two <111>/2 screw dislocations to react and form a <001> edge dislocation junction, a process that is otherwise unfavorable in hydrogen-free environments. This phenomenon arises from the preferential segregation of hydrogen around the <001> dislocation, which reduces the energy of the reaction product. The resulting <001> dislocation demonstrates remarkable stability and transforms into a <001> vacancy-type dislocation loop under strain. These vacancy-type dislocation loops can accumulate during continuous deformation and dislocation reactions, serving as precursors for the initiation of structural damage, such as cracking and blistering. Our findings highlight the pivotal role of hydrogen in dislocation reactions, uncover a novel defect accumulation mechanism crucial for interpreting recent experimental observations, and represent a significant advance in understanding hydrogen-induced damage in bcc metals.

cond-mat.mtrl-sci↗

arXiv2024

Electronic origin of solute effects on the mobility of screw dislocation in bcc molybdenum

In body-centered cubic (bcc) metals such as molybdenum, screw dislocations often exhibit non-Schmid behavior, moving in directions unpredicted by the Schmid law. The mobility of these dislocations is notably influenced by the presence of solute atoms within the alloy matrix. In this study, employing first-principles calculations, we delve into the electronic origins of these influences.Initially, we construct both single atomic column and triple atomic column models to simulate the formation of screw dislocations with solute atoms. Our investigation reveals that tantalum (Ta) and tungsten (W) increase the formation energy of solute-dislocation complexes, in contrast to osmium (Os), iridium (Ir), and platinum (Pt). Subsequently, employing a comprehensive screw dislocation dipole model under shear deformation, we explore the combined effects of solute atoms and deformation on dislocation core movement. Our findings demonstrate that Ta and W, positioned as first nearest neighbors, reduce the stress required to move dislocation cores away from corresponding dislocation dipoles. Conversely, Os, Ir, and Pt exhibit an attractive effect on dislocation cores, lowering the energy barrier for screw dislocation formation and enticing dislocation cores towards these solute atoms.

cond-mat.mtrl-sci↗

arXiv2023

Equilibrium distribution and diffusion of mixed hydrogen-methane gas in gravity field

Repurposing existing natural gas pipelines is a promising solution for large-scale transportation of mixed hydrogen-methane gas. However, it remains debatable whether gravitational stratification can notably affect hydrogen partial pressure in the gas mixture. To address this issue, we combined molecular dynamics simulation with thermodynamic and diffusion theories. Our study systematically examined the equilibrium distribution of hydrogen-methane mixtures in gravity fields. We demonstrated that partial pressures of both gases decrease with altitude, with hydrogen showing slower decrease due to its smaller molar mass. As a result, the volume fraction of hydrogen is maximized at the top end of pipes. The stratification is more favorable at low temperature and large altitude drops, with notable gas stratification only occurring at extremely large drops in altitude, being generally negligible even at a drop of 1500 m. Furthermore, we showed that the diffusion time required to achieve the equilibrium distribution is proportional to gas pressure and the square of pipeline height. This requires approximately 300 years for a 1500 m pipeline at 1 bar. Therefore, temporary interruptions in pipeline gas transportation will not cause visible stratification. Our work clarifies the effect of gravity on hydrogen-methane gas mixtures and provides quantitative insights into assessing the stratification of gas mixtures in pipelines.

cond-mat.stat-mech↗

arXiv2016

Atomistic modeling of the anomalous helium behaviors in vanadium

Ab initio calculations have been performed to clarify the primary behaviors of He atoms in vanadium and to generate the database for the development of the interatomic potential for V-He system within the framework of the"s-band"model.The calculated formation energies of the tetrahedral,octahedral and substitutional He defects,as well as those for He2,He3 and He2V clusters are reasonable when compared with relevant experimental results and ab initio calculations under the same conditions.The applicability of the present V-He potential for atomistic simulations to investigate the moving,clustering,and trapping of interstitial He atoms in vanadium are demonstrated.Similar to the results in iron and tungsten,the interstitial He atoms can migrate quickly in vanadium. However,He atoms aggregate into clusters with low binding energies,and the trapping of He atoms depend much on the pre-existing traps in vanadium.

cond-mat.mtrl-sci↗