Molecular dynamics simulation method for strengthening toughness of Ti / TiAl layered alloy through interface regulation and control

Abstract

The invention discloses a molecular dynamics simulation method for enhancing the toughness of a Ti / TiAl layered alloy through interface regulation and control, and belongs to the technical field of computational material science and molecular dynamics simulation. The molecular dynamics simulation method provided by the invention comprises the following steps: constructing Ti / TiAl layered composite material models with gaps and different interlayer spacing; performing energy minimization processing; performing stretching simulation; the Ti / TiAl layered composite material model in the stretching process is calculated; and drawing a performance diagram, and carrying out mechanical property analysis and microstructure evolution analysis on the Ti / TiAl layered composite material model. According to the method, the influence of different interlayer spacing on the crack propagation behavior of the Ti / TiAl layered alloy is disclosed from the atomic scale, and atomic theoretical support is provided for design and optimization of the Ti / TiAl layered alloy.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of computational materials science and molecular dynamics simulation, and in particular to a molecular dynamics simulation method for interface regulation of strength and toughness enhancement of Ti / TiAl layered alloys. BACKGROUND

[0002] The information disclosed in the background of the application is only intended to increase the understanding of the overall background of the application and should not necessarily be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

[0003] TiAl intermetallic compounds have great application potential in the field of aerospace high-temperature structural materials (such as high-temperature components such as aircraft engine blades and turbine discs) due to their low density, high specific strength and excellent high-temperature oxidation resistance, and are regarded as ideal materials to replace traditional nickel-based high-temperature alloys. However, the room-temperature brittleness and crack sensitivity seriously restrict the engineering application - the plastic deformation ability of TiAl alloy at room temperature is poor, cracks are easy to initiate and quickly expand, leading to brittle fracture of the material during processing and use, which greatly limits its application in complex load environments.

[0004] To improve this problem, researchers propose the strategy of constructing Ti / TiAl laminated composite materials, which alternately arranges the ductile Ti layer and the brittle TiAl layer to coordinate the contradiction between strength and toughness through the interface effect. The interface can hinder crack propagation and stress redistribution to delay fracture, and the ductile Ti layer can absorb energy to improve the anti-fracture ability, thereby significantly improving the comprehensive mechanical properties. However, current research on the fracture behavior of laminated materials mainly focuses on macroscopic mechanical experiments and continuous medium models, which are difficult to reveal the coupling mechanism of interface atomic interaction, dislocation evolution and crack initiation and propagation. Although molecular dynamics (MD) simulation provides a new perspective for studying the stress field evolution at the crack tip, dislocation emission and interface failure process with atomic-level spatial and temporal resolution, existing MD research mainly focuses on the fracture behavior of single interface or homogeneous materials, and the regulation law of the multi-interface synergistic effect of Ti / TiAl laminated materials under different layer spacings and the crack propagation path still lacks in-depth exploration. SUMMARY

[0005] Therefore, the application provides a molecular dynamics simulation method for interface regulation of strength and toughness enhancement of Ti / TiAl layered alloys. The method provided by the application can systematically explore the crack propagation behavior of Ti / TiAl laminated materials under tensile load under different layer spacings, thereby providing a theoretical basis for designing high-toughness TiAl-based laminated materials.

[0006] The application provides a molecular dynamics simulation method for interface regulation of strength and toughness enhancement of Ti / TiAl layered alloys, which comprises the following steps: (1) Construct a Ti / TiAl layered alloy model with different layer spacings, and prefabricate a wedge-shaped notch at the interface between the Ti layer and the TiAl layer to obtain a Ti / TiAl layered alloy model with a notch; (2) Energy minimization processing is performed on the constructed Ti / TiAl layered alloy model with a notch; (3) Under the NPT ensemble, the Ti / TiAl layered alloy model with a notch is brought to thermodynamic equilibrium; (4) Tensile simulation is performed on the Ti / TiAl layered alloy model with a notch; (5) The crystal structure parameters, dislocation characteristics and stress-strain parameters of the Ti / TiAl layered alloy model during the tensile process are calculated; (6) The calculation data of step (5) are processed by using a visualization software to draw stress-strain curves, dislocation density maps and strain distribution maps; by analyzing the interface strain gradient, dislocation-interface interaction and strain concentration characteristics, the influence of different layer spacings on the strength and toughness enhancement of the Ti / TiAl layered alloy and the crack propagation is obtained.

[0007] Compared with the prior art, the present application has the following beneficial effects: (1) The present application builds a Ti / TiAl layered alloy model with a notch and carries out molecular dynamics simulation to systematically study the influence of different layer spacings on the crack propagation behavior of the Ti / TiAl layered alloy, reveals the regulation mechanism of the multi-interface synergistic effect on crack deflection, passivation and propagation path tortuosity from the atomic scale, and makes up for the deficiency that the coupling rules of interface atomic interaction, dislocation evolution and crack initiation and propagation cannot be captured by macroscopic experiments or continuum medium models in the existing research, thereby providing atomic-level theoretical support for the design and optimization of Ti / TiAl layered alloys.

[0008] (2) The present application determines the optimal value (8 nm) of the layer spacing and its toughening mechanism through simulation analysis: the optimal size interface affected zone (IAZ) formed under the layer spacing can effectively enhance the interlayer stress transfer and promote strain homogenization, while the strain concentration factor (SCF) during crack propagation is significantly reduced, delaying the occurrence of unstable fracture and realizing the synergistic optimization of material strength, toughness and crack resistance. These findings provide key theoretical guidance for the design of high-strength and high-toughness TiAl-based composite materials in the aerospace field, and verify the feasibility of synergistically improving the comprehensive mechanical properties of materials by precisely controlling the layer spacing, which has important significance for promoting the engineering application of TiAl alloys from laboratory research to complex load environments. BRIEF DESCRIPTION OF DRAWINGS

[0009] The drawings constituting a part of this application provide further understanding of the present application, the illustrative embodiments of the present application and its description serve to explain the present application, and do not constitute an improper limitation of the present application. Obviously, for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0010] Figure 1 FIG. 1 is a schematic diagram of a Ti / TiAl layered alloy model with a layer spacing of 8 nm constructed in Embodiment 1 of the present application, wherein a is a schematic diagram of a stacked structure, and b is a schematic diagram of a wedge-shaped notch.

[0011] Figure 2 FIG. 2 is (a) stress-strain curves of Ti, TiAl and layered composite models (LMCs) under different layer spacings, and (b) variation of yield stress and average flow stress with layer spacing in Embodiment 2 of the present application.

[0012] Figure 3 FIG. 3 is atomic scale structure evolution under different strain conditions in Embodiment 2 of the present application: (a) TiAl model; (b) LMCs model with a layer spacing of 8 nm; (c) LMCs model with a layer spacing of 12 nm.

[0013] Figure 4 FIG. 4 is (a) evolution curve of free surface area with strain, and (b) evolution graph of dislocation density with strain in Embodiment 2 of the present application.

[0014] Figure 5 FIG. 5 is dislocation analysis results in Embodiment 2 of the present application: (a) TiAl model; (b) LMCs model with a layer spacing of 8 nm; (c) LMCs model with a layer spacing of 12 nm.

[0015] Figure 6 FIG. 6 is (a)-(d) strain distribution cloud maps of the TiAl model under different strain levels, and (e) evolution curves of crack tip shear strain, global average shear strain and strain concentration factor (SCF) with applied strain in Embodiment 2 of the present application.

[0016] Figure 7 FIG. 7 is (a) strain distribution cloud map of the LMCs model with a layer spacing of 4 nm, (b) strain distribution cloud map of the LMCs model with a layer spacing of 8 nm, (c) strain distribution cloud map of the LMCs model with a layer spacing of 12 nm, (d) variation of crack tip shear strain and global average shear strain with applied strain of the LMCs model with a layer spacing of 4 nm, (e) variation of crack tip shear strain and global average shear strain with applied strain of the LMCs model with a layer spacing of 8 nm, (f) variation of crack tip shear strain and global average shear strain with applied strain of the LMCs model with a layer spacing of 12 nm, and (g) evolution curve of SCF with strain of the three models in Embodiment 2 of the present application.

[0017] Figure 8This is Example 2 of the present invention: (a) Schematic diagram of the interface region division method; Evolution curve of strain gradient of LMCs models with different interlayer spacings as strain increases: (b) 4nm; (c) 8nm; (d) 12nm. DETAILED DESCRIPTION

[0018] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0019] The present invention provides a molecular dynamics simulation method for interface-regulated toughness enhancement of Ti / TiAl layered alloys, comprising the following steps: (1) A Ti / TiAl layered alloy model with different interlayer spacings was constructed, and a wedge-shaped notch was prefabricated at the interface between the Ti layer and the TiAl layer to obtain a Ti / TiAl layered alloy model with a notch. (2) Energy minimization of the constructed Ti / TiAl layered alloy model with notches; (3) Under the NPT ensemble, the Ti / TiAl layered alloy model with a notch is brought into thermodynamic equilibrium; (4) Tensile simulation of a Ti / TiAl layered alloy model with a notch; (5) Calculate the crystal structure parameters, dislocation characteristics, and stress-strain parameters of the Ti / TiAl layered alloy model during the tensile process; (6) Visualization software is used to process the calculated data of step (5) and draw stress-strain curves, dislocation density maps and strain distribution maps; by analyzing the interface strain gradient, dislocation-interface interaction and strain concentration characteristics, the effects of different interlayer spacings on the strength and toughness enhancement and crack propagation of Ti / TiAl layered alloys are obtained.

[0020] In the present invention, the term "interlayer spacing" refers to the distance from the middle of the Ti layer to the middle of the TiAl layer. The thickness of the Ti layer and the TiAl layer is the same.

[0021] The above technical solution of the present invention systematically reveals the principles of strength enhancement and crack propagation regulation of Ti / TiAl layered alloys with different interlayer spacings through the full-process design of molecular dynamics simulation: first, a Ti / TiAl layered alloy model with different interlayer spacings is constructed and a wedge-shaped notch is prefabricated at the interface. The core of the scheme is to simulate the difference in interface density in actual materials by setting the variable of interlayer spacing. The wedge-shaped notch serves as a crack source to simulate the inevitable defects in material processing or service, which can trigger the initiation and propagation behavior of cracks in subsequent stretching, providing clear starting conditions for studying the interface synergistic effect.

[0022] Subsequently, the energy minimization process eliminates unreasonable stress in the model by adjusting the initial position of atoms, so that the system is in a stable state with the lowest energy, ensuring that the mechanical behavior of subsequent simulation is based on real interatomic interaction; the thermodynamic equilibrium under the NPT ensemble makes the model stable under the thermodynamic conditions close to the actual service environment, providing a reliable initial structure basis for the tensile simulation. The tensile simulation triggers crack propagation by applying load to the model and using the stress concentration effect of the wedge-shaped notch tip, at which time the interfaces with different layer spacings will change the propagation path through mechanisms such as hindering crack penetration, inducing crack deflection or passivation; at the same time, the alternating arrangement of the ductile Ti layer and the brittle TiAl layer can coordinate deformation through atomic-level behaviors such as stress redistribution at the interface, dislocation emission and absorption, etc., delaying the occurrence of fracture. During the tensile process, the calculation of crystal structure parameters, dislocation characteristics and stress-strain parameters can directly reflect the micro-deformation mechanism of the material.

[0023] Finally, the above micro-parameters are analyzed by visualization software and stress-strain curves, dislocation density maps and strain distribution maps are drawn, which can convert atomic-level micro-behavior into macro-observable performance indicators, so as to quantify the size effect of the interface influence zone, the change rule of the strain concentration coefficient and the uniformity of the dislocation distribution under different layer spacings, and finally clarify the mechanism of the layer spacing on the regulation of the crack propagation path, the stress transmission efficiency and the strain homogenization from the atomic scale, and clarify the influence rule of different layer spacings on the strength and toughness enhancement of Ti / TiAl layered alloy.

[0024] The above technical scheme of the present application utilizes the atomic-level spatiotemporal resolution advantage of molecular dynamics simulation to correlate macro-mechanical properties with micro-atomic behavior, making up for the shortcomings of traditional macro-experiments and continuum medium models in revealing the coupling mechanism of interface atomic interaction, dislocation evolution and crack propagation, and providing micro-theoretical support for the interface design and strength-toughness optimization of Ti / TiAl layered alloy.

[0025] In step (1) of the present application, the layer spacing is set to 4-12 nm, for example, 4 nm, 8 nm or 12 nm; the construction of the Ti / TiAl layered alloy model uses ATOMSK software. The Ti / TiAl layered alloy model can be set to a double-layered structure or a multi-layered structure, and the present application preferably is a multi-layered structure, more preferably a 4-layered structure, with Ti layers and TiAl layers alternately stacked.

[0026] In step (1) of the present application, the Z direction of the Ti / TiAl layered alloy model is parallel to the thickness direction, and the X direction and the Y direction are parallel to the interface direction of the Ti layer and the TiAl layer; the X direction and the Y direction use free boundary conditions, and the Z direction uses periodic boundary conditions.

[0027] Further, the wedge-shaped notch is a triangular prism cavity penetrating in the Z direction, and the cross section in the XOY plane is an isosceles triangle; the base of the isosceles triangle is parallel to the X direction, and the height is parallel to the Y direction. This design simulates the sharp defects (such as micro-cracks or holes) commonly seen at the interface during material processing or service. The isosceles triangular geometry of the notch produces significant stress concentration in the tip region, and the stress increases with the sharpness of the notch, providing clear starting defect conditions for studying the interface-regulated crack propagation behavior. In the present application, the base length of the isosceles triangle is preferably 5 nm, and the vertex angle of the isosceles triangle is 30°.

[0028] In the present application, the load application direction of the tensile simulation process is parallel to the X direction and perpendicular to the height direction (Y direction) of the wedge-shaped notch. Since the stress concentration degree of the notch tip is closely related to the load direction, tensile loading along the X direction can produce the maximum stress concentration in the notch tip region, thereby accurately simulating the crack initiation and propagation behavior under the "notch-interface" coupling effect in the actual service conditions. This load orientation design can ensure that the tensile stress is transmitted along the interlamellar interface direction of the layered alloy, forcing the deformation to mainly concentrate in the Ti / TiAl interface and the notch tip region, thereby amplifying the influence difference of the interlamellar spacing on the interface dislocation blocking, strain gradient regulation and crack deflection effect, and providing clear mechanical boundary conditions for subsequent calculation of micro-parameters (such as dislocation density, stress-strain distribution) to reveal the correlation mechanism between interlamellar spacing and strength and toughness.

[0029] In the present application, steps (2) to (5) are performed in the LAMMPS software, which has high computational efficiency for molecular dynamics simulation of multi-atomic systems, supports various potential functions, and can flexibly set boundary conditions, system types and loading methods. The parallel computing feature of LAMMPS can handle large-scale atomic numbers of Ti / TiAl layered alloy models, ensuring the calculation efficiency and accuracy of energy minimization, thermodynamic equilibrium and tensile simulation. The potential function of the present application uses a multivariate EAM alloy potential.

[0030] In step (2) of the present application, the gradient descent algorithm is used for energy minimization processing, which core is to search for the local minimum value along the negative gradient direction of the potential energy surface by iteratively adjusting the atomic positions, and to eliminate the internal stress generated by unreasonable atomic positions (such as bond length / bond angle distortion) during the initial construction of the model. This step makes the system in a stable state with the lowest energy, ensuring that the mechanical behavior of subsequent thermodynamic equilibrium and tensile simulation is based on the real interatomic interaction (such as the bonding characteristics of metal bonds), avoiding the influence of initial stress interference on the simulation results of crack propagation. The present application does not make special restrictions on the gradient descent algorithm, and the commonly used gradient descent algorithm in the art can be used.

[0031] The method for achieving thermodynamic equilibrium of the Ti / TiAl layered alloy model with a notch in step (3) of the present application is: equilibrating the Ti / TiAl layered alloy model with a notch at 298-308 K and 0-0.1 GPa for 10-30 ps, the purpose of which is to make the model stable under the thermodynamic conditions close to the actual service environment, so as to provide a more consistent initial state with the real material structure for subsequent tensile simulation, and avoid the interference of non-equilibrium state structure on the crack propagation behavior.

[0032] In the present application, the strain rate of the tensile simulation process is 1×10 8 s -1 ~2×10 9 s -1 , which can not only observe the crack propagation process within a reasonable simulation time, but also avoid non-physical deformation caused by too fast loading by controlling the strain rate range. The maximum tensile strain is 30-50%, covering the whole process from elastic deformation (reversible), plastic deformation (dislocation proliferation) to fracture (unstable crack propagation), ensuring to capture the difference in strength and toughness of the material under different layer spacings. In the tensile simulation process, the area of x<5Å at the bottom of the model is fixed as the reference point for load application, avoiding the overall translation of the model, ensuring that the tensile load is effectively transmitted to the notch area, and concentrating energy to drive crack propagation.

[0033] In step (5) of the present application, the crystal structure parameters include the content variation of Ti-containing layer and TiAl layer; the dislocation characteristics include dislocation density, length and type, etc.; and the stress and strain parameters include flow stress, shear stress, etc.

[0034] The visualization software used in step (6) of the present application is OVITO software, which has powerful atomic-level data processing capability. Further, the mechanical property analysis uses the dislocation extraction algorithm and common neighbor analysis in OVITO software. The dislocation extraction algorithm (Dislocation Extraction Algorithm, DXA) can identify and quantify the type (such as edge and screw dislocations), density and length of dislocations, directly reflecting the plastic deformation capacity of the material. The common neighbor analysis (Common Neighbor Analysis, CNA) can distinguish the crystal structure of atoms, revealing the influence of phase transition or structure evolution on crack propagation during the stretching process. By drawing stress-strain curves, dislocation density maps and shear strain distribution maps, the atomic-level micro behavior (such as dislocation emission and interface atomic slip) can be converted into macro-quantifiable performance indicators, and finally the mechanism of interface regulating crack propagation and strength and toughness enhancement under different layer spacings is clarified. The present application does not make special limitation to the dislocation extraction algorithm and common neighbor analysis, and the commonly used dislocation extraction algorithm and common neighbor analysis in the art can be used for data processing and analysis.

[0035] The technical solutions of the present application will be further described below in combination with specific examples. In the following examples, the "interlayer spacing" is defined as the distance from the middle position of the Ti layer to the middle position of the TiAl layer.

[0036] Example 1 In this example, multilayer Ti / TiAl layered alloy is taken as the research object, and the influence of different interlayer spacings on the strength and toughness enhancement and crack propagation of the material is revealed by molecular dynamics simulation. The specific steps are as follows: (1) Constructing a Ti / TiAl layered alloy model with a notch A multilayer Ti / TiAl layered alloy (LMCs) model is constructed using ATOMSK software. The model is a 4-layer stack structure, with Ti layers and TiAl layers arranged alternately. The interlayer spacings of the Ti layers and the TiAl layers are set to 4 nm, 6 nm, 8 nm, 10 nm, and 12 nm. The number of atoms in the 4 nm, 6 nm, 8 nm, 10 nm, and 12 nm models is 1.6 × 10 5 , 3.6 × 10 5 , 6.4 × 10 5 , 1 × 10 6 , and 1.44 × 10 6 , respectively. Taking an interlayer spacing of 8 nm as an example, the multilayer Ti / TiAl layered alloy (LMCs) model is shown in Figure 1 a, which has a length of 40 nm, a width of 32 nm, and a height of 32 nm. The Ti layers and the TiAl layers have the same thickness.

[0037] The model coordinate system is defined as follows: the Z direction is parallel to the thickness direction (perpendicular to the layer interface), and the X and Y directions are parallel to the interface direction of the Ti layers and the TiAl layers. The boundary conditions are set as follows: the X and Y directions use free boundary conditions, and the Z direction uses periodic boundary conditions.

[0038] A wedge-shaped notch is pre-prepared at the interface between the Ti layer and the TiAl layer. The notch is a three-prism-shaped cavity that penetrates in the Z direction. Its cross-section in the XOY plane is an isosceles triangle, with the base parallel to the X direction and the height parallel to the Y direction. In this example, the three-prism-shaped cavity has a column height of 32 nm (Z direction length), an isosceles triangle base length of 5 nm (X direction), and a wedge angle of 30°, to ensure that the notch tip produces a significant stress concentration effect. The schematic diagram is shown in Figure 1 b (taking an interlayer spacing of 8 nm as an example).

[0039] (2) Energy minimization The Ti / TiAl layered alloy model with a notch constructed in step (1) is imported into the LAMMPS software, and the gradient descent algorithm is used for energy minimization. The potential function uses a multivariate EAM alloy potential.

[0040] (3) Thermodynamic equilibrium treatment The model was relaxed in the NPT ensemble in the LAMMPS software to make the system reach equilibrium under the thermodynamic conditions close to the actual service environment. The specific parameter settings are as follows: temperature 300 K, pressure 0 GPa, and equilibrium time 20 ps.

[0041] (4) Tensile simulation The tensile simulation was performed on the model after thermodynamic equilibrium, and the load application direction was parallel to the X direction to maximize the stress gradient at the notch tip. The specific parameter settings are as follows: strain rate 10 9 s -1 , and cutoff of uniform plastic deformation stage 40%; during the tensile process, the area of x<5Å at the bottom of the model was fixed to avoid overall translation of the model and ensure effective transmission of the load to the notch area.

[0042] (5) Microscopic parameter calculation During the tensile simulation, the following microscopic parameters were calculated in real time by the LAMMPS software combined with atomic-scale analysis algorithms, and the interface effect characteristics were associated: Crystal structure parameters: based on the common neighbor analysis (CNA) algorithm, the phase content changes of Ti layer (HCP structure) and TiAl layer (B2 or γ phase) were quantitatively identified through dynamic tracking of atomic coordinates and bonding relationships, focusing on the induction effect of atomic rearrangement and phase transition behavior in the interface region on crack propagation; Dislocation parameters: the dislocation extraction algorithm (DXA) was used to calculate the dislocation density (unit volume dislocation length), total dislocation length, and dislocation type (such as edge dislocation and screw dislocation), and the spatial distribution characteristics of dislocations (proportion of interface dislocations and matrix dislocations, dislocation entanglement network density) were analyzed synchronously to quantify the interaction strength between dislocations and interfaces (such as dislocation storage capacity and strain energy dissipation efficiency); Stress-strain parameters: the overall flow stress of the model, local shear stress (focusing on the crack tip and interface region), and atomic strain (ε tip : average strain of atoms within 1 nm range of the crack tip; ε0: global average atomic strain) were recorded, which provided data support for the calculation of the subsequent strain concentration factor (SCF=ε tip / ε0).

[0043] (6) Mechanical property analysis and result output The OVITO software was used for multidimensional visual analysis of the tensile simulation data, focusing on revealing the correlation between interlayer spacing, interface effect, and high-toughness performance, including: Dislocation evolution analysis: Based on the dislocation coordinate data output by DXA algorithm, the evolution curve of dislocation density with strain is drawn, and the spatial distribution of dislocations (such as interface dislocation decomposition, dislocation tangle network formation) is visualized combined with atomic structure snapshot, and the dislocation activity characteristics of different interlayer spacing models (such as uniform distribution of dislocations in 8nm model, localization of dislocations in 12nm model) are compared; Crystal structure evolution analysis: Through the visualization results of CNA algorithm, the atomic crystal structure types of interface and matrix are distinguished, and the regulation effect of atomic rearrangement (such as HCP→B2 phase transition) or phase separation behavior at the interface on the crack propagation path (such as crack deflection, interface debonding inhibition) is analyzed; Strain feature analysis: Based on the atomic strain calculation results, the strain distribution cloud map (intuitively show the strain localization area, such as the strain concentration of cleavage plane in TiAl model, the interface strain gradient in LMCs model), the SCF evolution curve (quantify the change law of strain concentration degree with strain, distinguish the stable and accelerated crack propagation stages) and the interface strain gradient distribution diagram (statistic the size of interface affected zone IAZ, reveal the negative correlation between interlayer spacing and IAZ width) are drawn.

[0044] Example 2 This example provides the model simulation and calculation result analysis of example 1.

[0045] (1) Mechanical property characterization Figure 2 The (a) in the above table shows the stress-strain curve comparison results of pure Ti, pure TiAl and different interlayer spacing Ti / TiAl layered metal composite (LMCs) models. In the initial elastic deformation stage, the stress-strain linear relationship of all LMCs models is highly consistent, and there is no significant difference in the strain value of the yield starting point; after entering the plastic deformation and crack propagation stage, its mechanical response shows significant differentiation from pure Ti and pure TiAl - the yield process of pure Ti model is significantly lagged behind the LMCs model, and the flow stress after yield shows a sharp fluctuation, reflecting the disorder of dislocation multiplication and movement in the single metal structure; the pure TiAl model shows typical brittle characteristics, with the lowest yield strength and the stress rapidly decaying to zero after yield, without showing obvious plastic deformation; while the LMCs model, with the alternating laminated structure of Ti layer (toughness) and TiAl layer (brittleness) and the interface regulation effect, shows a more gentle stress evolution trend in the elastic-plastic transition stage, with a significantly lower flow stress fluctuation amplitude than the pure Ti model.

[0046] To quantitatively characterize the plastic deformation ability of LMCs model, the "average flow stress" is defined as: the arithmetic mean of flow stress in the interval from the yield strain to the total strain of 0.4 (each interlayer spacing model is simulated three times independently, and the mean value is taken to reduce statistical error). Combined with the stress-strain curve, the average flow stress of different interlayer spacing models is calculated as follows: Figure 2The evolution of (b) in FIG. 6 shows that when the layer spacing is in the range of 4-8 nm, the yield stress and the average flow stress of the LMCs model both show a gentle upward trend, and reach a peak at a layer spacing of 8 nm; when the layer spacing increases to 12 nm, both mechanical properties decrease significantly. Based on the corresponding parameters of pure Ti (dashed line in the figure), the yield strength of the LMCs model is basically the same as that of pure Ti when the layer spacing is 4-8 nm; only when the layer spacing increases to 12 nm, the average flow stress is slightly lower than that of pure Ti. It is worth emphasizing that the average flow stress, compared with the instantaneous yield stress, can better reflect the mechanical response characteristics of the actual polycrystalline material - due to the complexity of grain orientation and interface distribution in the actual material, the deformation behavior is essentially a multi-scale and multi-mechanism collaborative process, and the average flow stress, by statistically averaging the stress in the plastic deformation zone, is more in line with the macroscopic mechanical performance of the material in the experiment. Based on the above results, the Ti / TiAl LMCs model realizes the synergistic optimization of strength (yield stress) and plasticity (average flow stress) through layer spacing regulation (the optimal interval is 4-8 nm).

[0047] (2) Microstructure evolution during crack propagation To further reveal the micro-regulation mechanism of crack propagation, the microstructure evolution of the model was systematically analyzed by atomic-scale characterization techniques, focusing on crystal structure transformation, dislocation configuration evolution, and dynamic behavior of planar defects (such as stacking faults and twin boundaries). Figure 3 The atomic-scale structure evolution characteristics of the pure TiAl model and the LMCs model with layer spacings of 8 nm and 12 nm at different strain stages are shown.

[0048] The yield behavior of the pure TiAl model is mainly driven by the dislocation emission mechanism at the crack tip (as shown in (a) of FIG. 7). Figure 3 As a typical intermetallic compound, TiAl exhibits intrinsic brittleness: the crack propagates rapidly along a nearly straight path, and the propagation rate is significantly higher than that of the LMCs model; at the intersection area of the cleavage planes, the nucleation and growth of nanoholes are particularly obvious, ultimately leading to early material fracture.

[0049] In sharp contrast to the TiAl model, the LMCs model exhibits a synergistic toughening mechanism due to the alternating layer structure of Ti layers (high plasticity) and TiAl layers (brittleness) and the interface regulation effect. During the entire crack propagation process, the stacking fault content of the LMCs model is significantly higher than that of the TiAl model (as shown in (b) of FIG. 7). Figure 3and the crack propagation behavior of the TiAl model presents typical plastic fracture characteristics due to the plastic deformation ability of the Ti layer—the crack does not propagate linearly along a single cleavage plane, but rather zigzags to consume strain energy. This path evolution allows more strain energy to be converted into new free surface energy, thereby improving the material toughness; the increase in the final fracture strain further verifies this toughening effect.

[0050] It is observed in the LMCs model with a layer spacing of 8 nm that nanoholes are generated inside the model, which are converted into surface energy by absorbing strain energy and merged with the crack in the subsequent process, further inducing the zigzag of the crack propagation path. Statistics of the free surface area change in the crack propagation process of the three models Figure 4 indicates that the free surface area of the TiAl model presents a nearly linear rapid growth trend, with a significantly higher growth rate than the LMCs model; while the free surface area growth of the LMCs model exhibits a stage feature—after the material yields, it enters a crack steady-state expansion period, during which the free surface area growth rate is slower, corresponding to the consumption of strain energy by the interaction of dislocations, stacking faults, and other planar defects; then the free surface area grows exponentially, corresponding to the crack unstable expansion period. It is worth noting that the crack unstable expansion timing of the LMCs model with a layer spacing of 8 nm is significantly lagging behind that of the LMCs model with a layer spacing of 12 nm, which is consistent with the observed results.

[0051] Figure 4 (b) of FIG. 1 is a diagram of the dislocation density evolution of the three models with strain, which shows that the dislocation evolution curves of the two LMCs models are significantly different from that of the TiAl model, and the dislocation density of the TiAl model is always significantly lower than that of the LMCs models throughout the deformation process. The dislocation density evolution of the TiAl model presents typical characteristics of brittle materials: when the initial state is dislocation-free, the stress concentration at the crack tip induces dislocation nucleation, and the density rapidly rises to a saturation value, and the dislocations are always localized near the cleavage plane. This limited dislocation activity directly leads to brittle cleavage fracture of the material (as shown in (a) of FIG. 1). Figure 5

[0052] In contrast, the LMCs models exhibit completely different dislocation behavior characteristics: due to the existence of two-phase structure in the system, a large number of interface dislocations are gathered at the two-phase interface region, and the yield process begins with the decomposition of the interface dislocations and shearing of the two phases. When the strain is less than 25%, the dislocation density of the LMCs model continuously increases and dislocation entanglement occurs, and the LMCs model with a layer spacing of 8 nm exhibits a higher dislocation density and a more uniform dislocation distribution, as shown in (b) of FIG. 1. Figure 5 ​The difference is attributed to the promotion effect of smaller interlayer spacing on the interaction between interface and dislocation, which is embodied in the denser dislocation tangle network, higher dislocation storage capacity and more effective strain energy dissipation mechanism. With the further increase of strain, the crack propagation promotes the movement of dislocations to the free surface, and the dislocation density gradually decreases; but the 8 nm model always maintains better dislocation stability, which corresponds to the higher failure strain of this model.

[0053] In the layered alloy system, local stress-strain analysis is of great significance to elucidate the micro-mechanical behavior of materials, optimize material design and predict failure mechanism. The interface transition zone, as the core functional area of stress transfer and deformation coordination, is particularly important to accurately characterize its mechanical behavior. Through local stress-strain analysis techniques, the quantitative analysis of three-dimensional stress field gradient distribution and dynamic strain response in the interface region can be realized, providing key experimental evidence for revealing the evolution law of macro-micro mechanical properties of materials under external load. Studies have shown that during plastic deformation, due to the significant differences in crystal orientation and mechanical properties between each component layer, layered materials often exhibit non-coordinated deformation characteristics. Local stress-strain analysis helps to better understand the independent deformation mechanisms of each single layer and their interactions, such as dislocation emission, stacking fault formation and subsequent expansion in the interface. Based on this, the local atomic strain analysis of crack propagation process in LMCs models with different interlayer spacing and TiAl model was carried out, and the specific calculation formula of atomic strain is as follows: ; where, η αβ ( α , β = x, y, z) is the local Lagrangian strain matrix component.

[0054] To further reveal the local mechanical response characteristics of materials under load, the strain concentration factor (SCF) under different strain conditions was calculated. SCF, as an important indicator to characterize the inhomogeneity of local deformation, reflects the regulation mechanism of microstructure on macroscopic mechanical behavior. By quantitatively analyzing the evolution law of SCF, not only can the stress / strain distribution characteristics of materials or structures under load be effectively characterized, but also important theoretical basis and engineering guidance for understanding material failure mechanism, predicting fatigue life and optimizing structure strength can be provided.

[0055] SCF is defined as the ratio of local strain to global strain, and its mathematical expression is: . Where, ε tipAtomic strain at the crack tip region, which is obtained by calculating the average atomic strain of atoms within a 1 nm radius of the crack tip. It is worth noting that, in order to eliminate the influence of surface effects on the calculation results, the atoms within 10 A from the surface are excluded in this study. ε0 represents the overall average strain obtained by calculating the average of all atomic strain, which reflects the macroscopic deformation characteristics of the material.

[0056] Figure 6 Figures (a)-(d) in the present disclosure show the strain distribution contour of the TiAl model under different strain conditions. According to the analysis of dislocation evolution characteristics, it can be seen that when the crack propagates, the strain is mainly localized in the cleavage plane region. This strain localization phenomenon is closely related to the brittle fracture characteristics of the material. In addition, other secondary strain concentration regions are also observed in the model, which mainly correspond to the positions of crystal defects such as stacking faults; it is worth noting that the strain concentration degree of these defect regions is significantly lower than that of the cleavage plane region, which may be related to the strain release effect of dislocation motion. Figure 6 Figure (e) quantitatively analyzes the relationship between the shear strain at the crack tip and the overall average shear strain with the strain, and gives the evolution law of the strain concentration factor (red curve). The study shows that: in the low strain stage, since the crack has not been significantly expanded, the strain at the crack tip is basically consistent with the overall average strain, resulting in a low level of strain concentration factor; as the strain increases, the crack begins to expand, the strain at the crack tip shows a rapid upward trend, while the overall average strain remains approximately linear growth, eventually leading to a significant increase in the strain concentration factor until the material breaks.

[0057] In contrast, the LMCs model exhibits significantly different strain distribution characteristics from the TiAl model. Figure 7 Figures (a)-(c) in the present disclosure show the strain distribution contour of the LMCs model with interlayer spacing of 4 nm, 8 nm, and 12 nm, respectively, under an applied strain of 10%. At this strain level, all models are in the uniform plastic deformation stage and have not yet shown localized instability, which can clearly reveal the regulation of interlayer spacing on the deformation characteristics before strain localization. The results show that all models exhibit significant strain concentration at the crack tip, and there are widely distributed high strain regions in the model, among which the model with an interlayer spacing of 12 nm has the worst strain uniformity. Figure 7 Figures (d)-(f) in the present disclosure show the relationship between the shear strain at the crack tip and the overall average shear strain with the applied strain for LMCs models with different interlayer spacings. It can be seen that before the model loses stability and the crack accelerates to expand, the strain at the crack tip is basically consistent with the overall average strain level; when the crack enters the rapid expansion stage, the strain at the crack tip increases rapidly. Figure 7The evolution of SCF with strain in (g) of FIG. 6 shows a clear two-stage feature: when the strain is less than 35%, the SCF fluctuates in the range of 1-1.5, corresponding to the stable crack propagation stage; then the SCF increases rapidly, and the crack propagation rate accelerates. It is worth noting that the LMCs model with a layer spacing of 8 nm has the lowest SCF value, which corresponds to the higher flow stress and fracture strain described earlier.

[0058] The strain gradient distribution in the interfacial region is a key factor affecting the strength, toughness, and failure mechanism of materials. In layered metal composites (LMCs), the uneven distribution of strain gradients can cause stress concentration, dislocation accumulation, or interfacial debonding, and other failure behaviors. In this study, a partitioned quantitative analysis method was used to divide multiple calculation regions along the Z direction centered on the interface (as shown in (a) of FIG. 6), and the evolution law of strain gradient of LMCs with different layer spacings was systematically studied. Figure 8 Figure 8 (b)-(d) of FIG. 6 presents the average shear strain spatial distribution characteristics of LMCs models with different layer spacings at different strain levels. At the initial stage of deformation when the strain is less than 35%, all three models show a typical strain distribution law of layered composites: the strain intensity reaches a peak value at the interface region, and then decreases gradually along the vertical interface direction (Z direction) to both sides of the matrix. This strain gradient distribution is mainly due to the difference in mechanical properties of the constituent materials: the soft phase (such as the Al layer) maintains a high strain level due to its excellent plastic deformation ability; the hard phase (such as the Ti layer) shows a relatively low strain intensity. Based on this, the region with a significant strain gradient regulated by the interfacial effect is defined as the interfacial affected zone (IAZ), and its characteristics directly affect the load transfer efficiency and interfacial bonding strength of LMCs and other key properties.

[0059] By systematically comparing the deformation behavior of the three models, it is found that the size of the interfacial affected zone (IAZ) and the layer spacing show a significant negative correlation (R2=0.99) Figure 8 ​). Specifically, the IAZ range gradually expands as the interlayer spacing decreases from 12 nm to 4 nm, indicating that the interface effect significantly enhances with the decrease of the interlayer spacing. It is worth noting that the model with an interlayer spacing of 4 nm exhibits an abnormal deformation characteristic when the strain reaches 45%: the strain level of the Ti layer and the interface region tends to be consistent, and the material loses the typical layered strain distribution characteristics, thus the heterogeneous deformation-induced (HDI) strengthening effect is significantly weakened. In contrast, the model with an interlayer spacing of 8 nm exhibits the best interface regulation efficiency, which indicates that the expansion of the interface stress transfer range significantly enhances the regulation effect of the interface effect on the overall deformation behavior of the material. As the strain increases, the IAZ gradually widens, which helps to more evenly distribute the strain and alleviate local stress concentration, thus improving the material deformation uniformity and anti-instability ability. The IAZ region of the LMCs model with an interlayer spacing of 12 nm remains small throughout the deformation process, which weakens the regulation effect of the interface mechanism on the material deformation behavior, reduces the stress transfer efficiency, and ultimately affects the overall mechanical properties of the material. Therefore, a moderate interlayer spacing can effectively balance the interface strengthening and plastic deformation ability, thus optimizing the comprehensive mechanical properties of the material. By reasonably regulating the interlayer spacing, the strength, toughness, and local instability resistance of the LMCs can be significantly improved.

[0060] In this study, the crack propagation behavior and interface toughening mechanism of Ti / TiAl layered metal composites (LMCs) were systematically studied by molecular dynamics simulation method, focusing on revealing the influence of interlayer spacing on material performance. The results show that Ti / TiAl layered metal composites (LMCs) successfully break through the bottleneck of the difficulty in simultaneously improving the strength and toughness of traditional TiAl alloys through unique interface design; among them, the material with an interlayer spacing of 8 nm exhibits the best strength-toughness synergy effect. The LMC structure effectively compensates for the intrinsic low plasticity of TiAl through crack deflection, nano-hole induced plasticity, and strong interaction between dislocations and interfaces, significantly improving the crack propagation resistance of the material; among them, the introduction of the plastic Ti layer promotes the tortuosity of the crack propagation path and realizes the uniform distribution of dislocations. Atomic strain analysis further shows that the interlayer spacing regulates the interface strain gradient to dominate the macroscopic mechanical behavior of the material; among them, the 8 nm interlayer spacing sample exhibits the best interface affected zone (IAZ) characteristics, which can effectively alleviate strain localization and reduce the crack tip strain concentration factor, thus significantly delaying the instability fracture of the material. This study successfully builds a bridge between atomic-scale deformation mechanisms and macroscopic performance, providing a systematic theoretical guidance and technical path for the design of high-toughness TiAl composite materials.

[0061] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A molecular dynamics simulation method for interface regulation of strength and toughness enhancement of Ti / TiAl layered alloys, characterized in that: The steps include: (1) A Ti / TiAl layered alloy model with different interlayer spacings was constructed, and a wedge-shaped notch was prefabricated at the interface between the Ti layer and the TiAl layer to obtain a Ti / TiAl layered alloy model with a notch. (2) Energy minimization of the constructed Ti / TiAl layered alloy model with notches; (3) Under the NPT ensemble, the Ti / TiAl layered alloy model with a notch is brought into thermodynamic equilibrium; (4) Tensile simulation of a Ti / TiAl layered alloy model with a notch; (5) Calculate the crystal structure parameters, dislocation characteristics, and stress-strain parameters of the Ti / TiAl layered alloy model during the tensile process; (6) Visualization software is used to process the calculated data of step (5) and draw stress-strain curves, dislocation density maps and strain distribution maps; by analyzing the interface strain gradient, dislocation-interface interaction and strain concentration characteristics, the effects of different interlayer spacings on the strength and toughness enhancement and crack propagation of Ti / TiAl layered alloys are obtained.

2. The molecular dynamics simulation method according to claim 1, wherein In step (1), the interlayer spacing is set to 4-12 nm; the Ti / TiAl layered alloy model is constructed using ATOMSK software.

3. The molecular dynamics simulation method according to claim 1, wherein In step (1), the Z direction of the Ti / TiAl layered alloy model is parallel to the thickness direction, and the X and Y directions are parallel to the interface direction of the Ti layer and the TiAl layer; the X and Y directions adopt free boundary conditions, and the Z direction adopts periodic boundary conditions.

4. The molecular dynamics simulation method according to claim 3, wherein The wedge-shaped notch is a triangular prism-shaped cavity penetrating along the Z direction, and its cross section is located in the XOY plane and is an isosceles triangle; the base of the isosceles triangle is parallel to the X direction, and the height is parallel to the Y direction.

5. The molecular dynamics simulation method according to claim 4, wherein The load application direction of the stretching simulation process is parallel to the X direction.

6. The molecular dynamics simulation method according to claim 1, wherein Steps (2) to (5) are performed in the LAMMPS software.

7. The molecular dynamics simulation method according to claim 1, wherein In step (2), the energy minimization process is performed using the gradient descent algorithm.

8. The molecular dynamics simulation method according to claim 1, wherein In step (3), the method for making the Ti / TiAl layered alloy model with a notch reach thermodynamic equilibrium is: equilibrating the Ti / TiAl layered alloy model with a notch at 298~308 K and 0~0.1 GPa for 10~30 ps.

9. The molecular dynamics simulation method according to claim 1, wherein The strain rate of the stretching simulation process is 1×10 8 s -1 ~2×10 9 s -1 , the maximum tensile strain is 30~50%; during the tensile simulation, the area at the bottom of the model with x<5Å is fixed.

10. The molecular dynamics simulation method according to claim 1, wherein The visualization software used in step (6) is OVITO software.

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