A method for predicting fracture behavior at the brazing interface of high-nitrogen steel-molybdenum-niobium alloy based on multi-element coupling modeling
By using multi-element coupled modeling and first-principles calculations, the fracture behavior of the brazed interface between high-nitrogen steel and molybdenum-niobium alloy is predicted, solving the problem of difficult process optimization in traditional methods and achieving efficient fracture mode prediction and joint strength improvement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NORTH CHINA UNIV OF WATER RESOURCES & ELECTRIC POWER
- Filing Date
- 2026-03-24
- Publication Date
- 2026-06-26
AI Technical Summary
Existing technologies are insufficient to effectively predict the fracture behavior of the brazed interface between high-nitrogen steel and molybdenum-niobium alloy. Traditional methods rely on trial and error and lack theoretical support, failing to reveal the interfacial bonding evolution mechanism under multi-element segregation at the atomic scale, which leads to difficulties in process optimization.
A multi-element coupled modeling method was used to construct a realistic model of the brazing interface between high-nitrogen steel and molybdenum-niobium alloy. The interface adhesion work and electronic structure were calculated and analyzed using first-principles calculations to predict the fracture location and mode. Combined with experiments, the optimized process parameters were verified.
It achieves cross-scale mapping from micro to macro, rapidly predicts fracture modes, shortens R&D cycles, reduces costs, provides theoretical basis for process optimization, and improves joint reliability.
Smart Images
Figure CN122290818A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of dissimilar material joining technology, specifically to a method for predicting the fracture behavior of brazing interfaces in high-nitrogen steel-molybdenum-niobium alloys based on multi-element coupling modeling. Background Technology
[0002] Nitrogen in high-nitrogen steel strengthens stainless steel through mechanisms such as grain refinement and solid solution strengthening, while maintaining the good ductility and toughness of stainless steel. It also exhibits high hardness, high wear resistance, high strength, and excellent corrosion resistance, making it a promising material for high-end equipment manufacturing. Molybdenum-niobium alloys, as high-performance refractory metals, combine the high melting point and high strength of molybdenum with the excellent toughness and processing properties of niobium. They also possess excellent resistance to high-temperature creep and corrosion, making them widely used in critical structural components for extreme environments, such as aerospace engine nozzles and nuclear reactor core components. However, molybdenum-niobium alloys are expensive and have a high density, often requiring dissimilar material joining with high-strength steel in practical engineering applications to construct composite structural components. Therefore, achieving high-quality joining between high-nitrogen steel and molybdenum-niobium alloys has significant engineering application value.
[0003] However, high-nitrogen steel and molybdenum-niobium alloys exhibit significant differences in thermophysical properties, leading to substantial residual stress at the interface during brazing cooling. Furthermore, dissimilar metal brazing involves complex metallurgical processes with strong multi-element coupling; the segregation and interaction of elements at the interface can easily induce the formation of a brittle reaction layer, which becomes a source of cleavage fracture under macroscopic stress. Current brazing material development largely relies on traditional trial-and-error methods, which are not only time-consuming and costly but also fail to reveal the interfacial bonding evolution mechanism and failure causes under multi-element segregation at the atomic scale, resulting in a lack of theoretical support for process optimization.
[0004] First-principles calculations, based on quantum mechanics, can simulate and calculate material properties at the atomic scale. However, in related patents on high-nitrogen steel dissimilar brazing calculations, existing models are mostly limited to ideal pure metals or simple binary interfaces, failing to realistically reproduce the complex metallurgical environment of multi-component solid solutions and compound formation. Furthermore, existing research largely focuses on superficial comparisons of interfacial binding energies, lacking a systematic mapping and evaluation standard from electronic structure characteristics to macroscopic fracture behavior. Therefore, there is an urgent need to establish a method for predicting the fracture behavior of brazing interfaces based on multi-element coupling modeling. By constructing a realistic interface model with multi-element synergistic doping at the atomic scale, the electronic localization characteristics of the new phase at the interface can be analyzed, and stress concentration regions, preferential fracture locations, and fracture modes can be predicted, providing theoretical support for process parameter optimization and joint reliability design. Summary of the Invention
[0005] The purpose of this invention is to solve the above-mentioned technical problems existing in the prior art and to provide a method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling.
[0006] To address the shortcomings of the aforementioned technical problems, the present invention employs the following technical solution: a method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling, comprising the following steps: S1. Construct initial crystal structure models of pure metals with high-nitrogen steel principal components, molybdenum-niobium alloy principal components, and brazing filler metal principal components; S2. Based on preset parameters, the geometric structure of the initial crystal structure model is optimized using first-principles calculation methods to obtain the optimized high-nitrogen steel principal element pure metal model, molybdenum-niobium alloy principal element pure metal model and brazing filler metal principal element pure metal model. S3. Cut the optimized model along the preset crystal plane index to construct multiple crystal plane plate models with different atomic layer thicknesses. S4. Convergence tests were performed on multiple crystal plane plate models. Based on the test results, the optimal number of atomic layers that each crystal plane can exhibit bulk phase characteristics was determined, and stable surface models of high nitrogen steel main element pure metal, molybdenum-niobium alloy main element pure metal and brazing filler metal main element pure metal were obtained. S5. Based on the stable surface model, construct the pure metal interface model of high nitrogen steel principal element / brazing filler metal principal element and the pure metal interface model of molybdenum-niobium alloy principal element / brazing filler metal principal element according to the principle of minimizing lattice mismatch. S6. Based on the chemical composition of real high-nitrogen steel, molybdenum-niobium alloy and brazing filler metal, multi-element components are introduced into the interface model through atomic substitution to construct a real brazing interface composite model with multi-element metallurgical interaction characteristics, and the composite model is geometrically optimized. S7. Based on the optimized real brazing interface composite model, calculate the interface adhesion work data and electronic structure data. Quantitatively determine the theoretical bonding strength of the interface through the interface adhesion work data. Qualitatively evaluate the degree of weakening of the bonding rigidity and charge delocalization ability of the multi-element segregated new phase by analyzing the electronic structure data. Based on the above information, determine the preferred fracture location and fracture mode of the joint under macroscopic stress.
[0007] Specifically, the interface with the minimum adhesion work in the calculation results is identified as the region with the weakest theoretical bonding. Observing the electronic structure data, if the multi-element agglomeration region of the interface exhibits charge localization transfer and a significant increase in the electron localization function, it is determined that the covalent bonding rigidity of the region is enhanced, the charge delocalization ability is weakened, and lattice dislocation slip is hindered. Combining the above, the interface region with the minimum adhesion work and the weakest charge delocalization ability is inferred as the preferred fracture location under macroscopic stress of the joint.
[0008] Fracture modes are predicted using electronic structure data such as charge density, differential charge density, and electron localization function.
[0009] Fracture modes are classified into brittle fracture and ductile fracture; The electronic structure characteristics of brittle fracture are: high overlap of charge density, significant charge localization transfer, significantly increased ELF value and electron depletion region on the periphery; Electronic structure characteristics of ductile fracture: There is a continuous and uniform charge distribution, no obvious faults or localized aggregations are observed, and the ELF value is close to 0.5.
[0010] As a further optimization of the method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling of the present invention, the preset parameters in step S2 include: exchange-correlated functional, pseudopotential, plane wave cutoff energy, Brillouin zone K-point grid density, energy convergence threshold, maximum stress threshold and maximum displacement threshold.
[0011] As a further optimization of the method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling of the present invention: the preset crystal plane indices in step S3 include (111), (100), (001) and (010).
[0012] As a further optimization of the method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling of the present invention: the convergence test in step S4 includes surface energy convergence test and interlayer relaxation test.
[0013] As a further optimization of the method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling of the present invention: the specific method for determining the optimal number of atomic layers in step S4 is as follows: calculate the surface energy and the rate of change of atomic layer spacing of different atomic layer thickness models. When the surface energy fluctuation is less than the preset energy threshold, or the rate of change of atomic layer spacing is less than the preset percentage, the corresponding atomic layer thickness is determined to be the optimal atomic layer thickness.
[0014] As a further optimization of the method for predicting the fracture behavior of high-nitrogen steel / molybdenum-niobium alloy brazing interface based on multi-element coupling modeling of the present invention: the specific method for constructing the high-nitrogen steel / brazing filler metal interface model and the molybdenum-niobium alloy / brazing filler metal interface model in step S5 is as follows: The lattice constants and included angles of each stable surface were statistically analyzed. Calculate the lattice mismatch under different surface combinations; A pure metal interface model is constructed by establishing crystal plane combinations with lattice mismatch below a preset threshold through cell expansion or lattice reconstruction methods.
[0015] As a further optimization of the method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling in this invention: the interface mismatch degree of the two surfaces is ≤8%.
[0016] As a further optimization of the method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling of the present invention: the atomic substitution in step S6 specifically involves: introducing N atoms to replace some metal atoms on the high-nitrogen steel side, introducing alloying active elements to replace some principal atoms on the brazing filler metal side, and introducing Nb atoms to replace some Mo atoms on the molybdenum-niobium alloy side.
[0017] As a further optimization of the method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling of the present invention: the electronic structure data includes charge density, differential charge density and electronic localization function.
[0018] As a further optimization of the method for predicting the fracture behavior of high-nitrogen steel / molybdenum-niobium alloy brazing interface based on multi-element coupling modeling of the present invention, the prediction method also includes process closed-loop verification: the preferential fracture location determined in step S7 is compared with the fracture morphology of the actual brazed joint of high-nitrogen steel / molybdenum-niobium alloy. If the experimental fracture occurs in the region corresponding to the calculation result, the heating temperature range and holding time of the actual brazing process are reverse-optimized based on the calculation model to improve the joint strength.
[0019] Specifically: If the calculation shows that the preferential fracture site is caused by a brittle phase induced by multi-element segregation, it can be inferred that the active elements at the interface have diffused excessively. Reverse optimization can reduce the brazing heating temperature or shorten the holding time to inhibit the excessive diffusion and segregation of active elements to the interface. If the calculation shows that the adhesion work at the preferential fracture site is low, but there is no obvious charge transfer, it can be inferred that the interfacial metallurgical bonding is insufficient. Reverse optimization can increase the brazing temperature or extend the holding time to promote the interfacial metallurgical reaction.
[0020] The present invention has the following beneficial effects: 1. This invention breaks through the limitations of traditional first-principles calculation of ideal interface models, and constructs a real brazing interface model with multi-element coupling and doping. It can simulate element segregation and phase transformation in actual brazing, quickly infer stress concentration areas and predict fracture modes, significantly shorten the research and development cycle and reduce costs. 2. This invention breaks through the limitations of traditional methods for analyzing microstructure. By combining interfacial adhesion work and electronic structure, it quantifies the bonding characteristics of new phases at the interface, establishes a cross-scale mapping from microscopic charge delocalization to macroscopic dislocations and stress concentration, reveals the brittle mechanism of alloying elements, and provides a theoretical basis for the regulation of interfacial strength and toughness. 3. The multi-element coupling modeling and fracture prediction of the present invention can be extended to brazing systems of various complex heterogeneous materials. Its prediction results can form a closed loop with macroscopic mechanical testing and fracture morphology characteristics, and can reversely guide the optimization of core process parameters such as temperature and holding time, thus having high engineering practical value. Attached Figure Description
[0021] Figure 1Flowchart for predicting the brazing mechanical properties of high-nitrogen steel / molybdenum-niobium alloy; Figure 2 The crystal structures are Fe, Mo, and Ni; Figure 3 To construct the interface structure of high-nitrogen steel / nickel-based brazing filler metal and molybdenum-niobium alloy / nickel-based brazing filler metal; Figure 4 Charge density diagrams at the interfaces of high-nitrogen steel / nickel-based solder and molybdenum-niobium alloy / nickel-based solder; Figure 5 Differential charge density diagrams of the interfaces between high-nitrogen steel / nickel-based solder and molybdenum-niobium alloy / nickel-based solder; Figure 6 Electron localization function diagrams of the interfaces of high-nitrogen steel / nickel-based solder and molybdenum-niobium alloy / nickel-based solder; Figure 7 The fracture path of the high-nitrogen steel / molybdenum-niobium alloy joint. Detailed Implementation
[0022] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.
[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the accompanying drawings in this application are for illustrative and descriptive purposes only and are not intended to limit the scope of protection of this application. Furthermore, it should be understood that the schematic drawings are not drawn to scale. The flowcharts used in this application illustrate operations implemented according to some embodiments of this application. It should be understood that the operations in the flowcharts may not be implemented in sequence, and steps without logical contextual relationships may be reversed or implemented simultaneously. In addition, those skilled in the art, guided by the content of this application, may add one or more other operations to the flowcharts, or remove one or more operations from the flowcharts.
[0024] Furthermore, the described embodiments are merely some, not all, of the embodiments of this application. The components of the embodiments of this application described and illustrated herein can typically be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.
[0025] It should be noted that the term "comprising" will be used in the embodiments of this application to indicate the presence of the features declared thereafter, but does not exclude the addition of other features.
[0026] This embodiment provides a method for predicting the brazing mechanical properties of high-nitrogen steel / molybdenum-niobium alloys based on first-principles calculations. The process is as follows: Figure 1 As shown. In this embodiment, high-nitrogen austenitic stainless steel is used as the first base material, molybdenum-niobium alloy is used as the second base material, and Ni-based solder is used as the intermediate connecting layer.
[0027] This method is based on density functional theory and uses the CASTEP module in VASP or MaterialsStudio for calculations. The specific steps are as follows: Step S1: Construct the initial crystal model like Figure 2 As shown, the high-nitrogen steel matrix model uses a face-centered cubic Fe cell as the initial matrix model; the molybdenum-niobium alloy matrix model uses a body-centered cubic Mo cell as the initial matrix model; and the solder model uses a face-centered cubic Ni cell as the nickel-based solder model.
[0028] Step S2: Cell structure optimization Based on the first preset parameters, the geometric structure of the above unit cell model was optimized until the system energy converged. The parameters used were a GGA-PBE functional; an ultrasoft pseudopotential; a plane wave cutoff energy of 500 eV; and an 8×8×8 Brillouin zone K-point grid. The energy convergence threshold was 1.0 × 10⁻⁶. -5 eV / atom, maximum stress threshold is 0.03 eV / Å, maximum displacement threshold is 1.0 × 10⁻⁶ eV / Å. -3 Å.
[0029] Step S3: Crystal facet cutting The optimized unit cell model was cut along the low-index crystal planes (100), (110), and (111) to construct a flat plate model containing a 15Å vacuum layer.
[0030] Step S4: Convergence Test Surface energy calculations were performed on pure metallic plate models with varying atomic layer thicknesses. The surface energy calculation formula was used. ; Formula for calculating interatomic spacing ; It was determined that when the thickness of the Fe plate was 7 layers, the thickness of the Mo plate was 7 layers, and the thickness of the Ni plate was 7 layers, the surface energy tended to converge and the internal atomic interlayer spacing was close to that of the bulk phase. and These correspond to the total energy of the single cell and surface models, respectively. and These correspond to the number of atoms in a single unit cell and a surface model, respectively, while A corresponds to the area of the surface model. and These represent the distances between the i-th and j-th layers before and after relaxation of the surface model, respectively.
[0031] Step S5: Build the interface model Interface matching was performed using the surface parameters obtained after convergence testing to construct interface models for pure metals. By rotating crystal planes or constructing supercells, Fe / Ni interfaces were constructed by selecting 7 Fe(100) planes and 7 Ni(100) planes, and Mo / Ni interfaces were constructed by selecting 7 Mo(001) planes and 7 Ni(100) planes. The lattice mismatch of the interfaces was calculated to be ≤8%.
[0032] Step S6: Multi-element coupling doping and optimization Based on the existing Fe / Ni and Mo / Ni pure metal interfaces, multi-element substitution doping was performed within three atomic layers from the interface. At the high-nitrogen steel / solder alloy interface, N atoms were used to replace some Fe atoms on the high-nitrogen steel side, and B atoms were used to replace some Ni atoms on the solder side. At the molybdenum-niobium alloy / solder alloy interface, Nb atoms were used to replace some Mo atoms on the molybdenum-niobium alloy side, and B atoms were used to replace some Ni atoms on the solder side. This was done to realistically simulate the actual brazing environment of high-nitrogen steel, molybdenum-niobium alloy, and solder. Figure 3 As shown. After doping, 2-3 layers of atoms far from the interface are fixed, and then their geometry is finally optimized.
[0033] Step S7: Interface Combination Analysis and Fracture Behavior Prediction The final interface model after relaxation is analyzed and calculated.
[0034] Through formula Calculate the adhesion work at the interface and compare the magnitudes of adhesion work at different interfaces. Where E... X E y E represents the energy of the flat plate layers on both sides of the interface. interface Let A be the total energy of the interface structure. interface The interface area is given. The adhesion work at the molybdenum-niobium alloy / nickel-based solder interface is 3.72 J / m. 2 The adhesion work at the high-nitrogen steel / nickel-based solder interface is 2.75 J / m. 2 From a thermodynamic perspective, this quantitatively demonstrates that the energy required to separate the interface of high-nitrogen steel / nickel-based brazing filler metal is lower, and its interfacial bonding force is relatively weaker.
[0035] Figure 4The images show the charge density at the interfaces of high-nitrogen steel / nickel-based solder and nickel-based solder / molybdenum-niobium alloy. At the high-nitrogen steel side interface, there is a high degree of charge density overlap between N atoms and diffused B atoms on the solder side. This charge accumulation indicates a strong chemical bond between N and B, macroscopically corresponding to the BN reaction layer generated in the experiment. Although the BN phase has strong internal bonding, its charge distribution lacks the continuous and diffuse characteristics of pure metallic bonds, exhibiting typical hard and brittle phase properties, unable to resist macroscopic deformation through electron cloud ionization. At the molybdenum-niobium alloy / nickel-based solder interface, the charge distribution between Mo and Nb atoms and Ni atoms on the solder side is continuous and uniform, without obvious charge discontinuities or extreme localization, exhibiting good metallic bonding characteristics.
[0036] Figure 5 The differential charge density maps show the interfaces of high-nitrogen steel / nickel-based brazing filler metal and nickel-based brazing filler metal / molybdenum-niobium alloy. Red areas represent electron accumulation, and blue areas represent electron dissipation. At the high-nitrogen steel side interface, significant charge localization transfer is observed around N and B atoms, indicating typical covalent bond characteristics between N and B, microscopically corresponding to the formation of a hard and brittle BN phase. Because such strongly localized covalent bonds lack pure electron slip and deformation capabilities, this region is highly brittle, easily leading to stress concentration and crack initiation, ultimately causing the joint to fracture at the BN interface on the high-nitrogen steel side. In contrast, the charge recombination distribution at the molybdenum-niobium alloy side interface is more diffuse and continuous, without obvious charge transfer faults, indicating that this interface retains the delocalization characteristics of metallic bonds, possesses superior plastic deformation and stress absorption capabilities, and exhibits higher crack propagation resistance.
[0037] Figure 6 The image shows the electron localization function (ELF) at the interfaces of high-nitrogen steel / nickel-based solder and molybdenum-niobium alloy / nickel-based solder. In the base material region far from the interface, the ELF value is close to 0.5, exhibiting typical metallic bond charge delocalization characteristics. However, in the multi-element segregated interface region, the ELF value increases significantly, accompanied by a distinct electron depletion region. This phenomenon indicates that strong orbital hybridization occurs between the segregating elements, generating a directional rigid covalent bond reaction phase. Under macroscopic stress, this highly rigid covalent bond, lacking electron recombination buffering capacity, strongly hinders lattice dislocation slip, preventing energy release through plastic deformation and leading to increased local stress. Therefore, this highly electron-localized region is determined to be the preferential initiation site for brittle cleavage fracture at the joint.
[0038] Figure 7 The image shows a scanning electron microscope (SEM) image of the fracture path of the brazed high-nitrogen steel / molybdenum-niobium alloy joint actually prepared. The image shows that the crack extends and fractures along the BN reaction layer at the interface between the high-nitrogen steel side and the brazing filler metal. The brazing filler metal and the molybdenum-niobium alloy interface are tightly bonded, which verifies the above calculation results.
[0039] Based on the above calculations and experimental results, a reverse optimization strategy can be adopted in the subsequent brazing process to reduce the brazing temperature and shorten the holding time, thereby suppressing the excessive diffusion of interfacial active elements, reducing the thickness of the brittle reaction layer, and improving the joint strength and toughness.
[0040] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.
Claims
1. A method for predicting the fracture behavior of brazed interfaces in high-nitrogen steel-molybdenum-niobium alloys based on multi-element coupling modeling, characterized in that, Includes the following steps: S1. Construct initial crystal structure models of pure metals with high-nitrogen steel principal components, molybdenum-niobium alloy principal components, and brazing filler metal principal components; S2. Based on preset parameters, the geometric structure of the initial crystal structure model is optimized using first-principles calculation methods to obtain the optimized high-nitrogen steel principal element pure metal model, molybdenum-niobium alloy principal element pure metal model and brazing filler metal principal element pure metal model. S3. Cut the optimized model along the preset crystal plane index to construct multiple crystal plane plate models with different atomic layer thicknesses. S4. Convergence tests were performed on multiple crystal plane plate models. Based on the test results, the optimal number of atomic layers that each crystal plane can exhibit bulk phase characteristics was determined, and stable surface models of high nitrogen steel main element pure metal, molybdenum-niobium alloy main element pure metal and brazing filler metal main element pure metal were obtained. S5. Based on the stable surface model, construct the pure metal interface model of high nitrogen steel principal element / brazing filler metal principal element and the pure metal interface model of molybdenum-niobium alloy principal element / brazing filler metal principal element according to the principle of minimizing lattice mismatch. S6. Based on the chemical composition of real high-nitrogen steel, molybdenum-niobium alloy and brazing filler metal, multi-element components are introduced into the interface model through atomic substitution to construct a real brazing interface composite model with multi-element metallurgical interaction characteristics, and the composite model is geometrically optimized. S7. Based on the optimized real brazing interface composite model, calculate the interface adhesion work data and electronic structure data. Quantitatively determine the theoretical bonding strength of the interface through the interface adhesion work data. Qualitatively evaluate the degree of weakening of the bonding rigidity and charge delocalization ability of the multi-element segregated new phase by analyzing the electronic structure data. Based on the above information, determine the preferred fracture location and fracture mode of the joint under macroscopic stress.
2. The method for predicting the fracture behavior of the brazing interface of high nitrogen steel molybdenum niobium alloy based on multi-element coupling modeling according to claim 1, characterized in that: The preset parameters in step S2 include: exchange-correlated functional, pseudopotential, plane wave cutoff energy, Brillouin zone K-point grid density, energy convergence threshold, maximum stress threshold, and maximum displacement threshold.
3. The method for predicting the fracture behavior of the brazing interface of high nitrogen steel molybdenum niobium alloy based on multi-element coupling modeling according to claim 1, characterized in that: The preset crystal plane indices in step S3 include (111), (100), (001), and (010).
4. The method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling as described in claim 1, characterized in that: The convergence test in step S4 includes surface energy convergence test and interlayer relaxation test.
5. The method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling as described in claim 1, characterized in that: The specific method for determining the optimal number of atomic layers in step S4 is as follows: calculate the surface energy and the rate of change of atomic layer spacing for different atomic layer thickness models. When the surface energy fluctuation is less than a preset energy threshold or the rate of change of atomic layer spacing is less than a preset percentage, the corresponding atomic layer thickness is determined to be the optimal atomic layer thickness.
6. The method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling as described in claim 1, characterized in that: The specific methods for constructing the high-nitrogen steel / brazing filler metal interface model and the molybdenum-niobium alloy / brazing filler metal interface model in step S5 are as follows: The lattice constants and included angles of each stable surface were statistically analyzed. Calculate the lattice mismatch under different surface combinations; A pure metal interface model is constructed by establishing crystal plane combinations with lattice mismatch below a preset threshold through cell expansion or lattice reconstruction methods.
7. The method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling as described in claim 6, characterized in that: The interface mismatch between the two surfaces is ≤8%.
8. The method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling as described in claim 1, characterized in that: The atomic substitution in step S6 specifically involves: introducing N atoms to replace some metal atoms on the high-nitrogen steel side, introducing alloying active elements to replace some principal atoms on the solder side, and introducing Nb atoms to replace some Mo atoms on the molybdenum-niobium alloy side.
9. The method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling as described in claim 1, characterized in that: The electronic structure data includes charge density, differential charge density, and electron localization function.
10. The method for predicting the fracture behavior of high-nitrogen steel-molybdenum-niobium alloy brazing interface based on multi-element coupling modeling as described in claim 1, characterized in that: The prediction method also includes process closed-loop verification: the preferential fracture location determined in step S7 is compared with the fracture morphology of the actual brazed joint of high nitrogen steel / molybdenum-niobium alloy. If the experimental fracture occurs in the region corresponding to the calculation result, the heating temperature range and holding time of the actual brazing process are optimized in reverse based on the calculation model to improve the joint strength.