A laser cladding repair method for interface damage in titanium-steel composite plates based on a copper interlayer

Abstract

This invention discloses a laser cladding repair method for interface damage in titanium-steel composite plates based on a copper interlayer, belonging to the field of metal material remanufacturing. It constructs an evaluation system based on the sufficiency of copper-steel interface fusion, copper layer remelting rate, and interface residual stress. The optimal process window is determined using multi-layer dissimilar material multi-physics coupled finite element simulation to guide the repair. The process parameters for the copper interlayer are: laser power 2400-2800W, spot diameter 3.8-4.2mm, and scanning speed 400-500mm / min; the process parameters for the titanium filler layer are: laser power 1100-1300W, spot diameter 1.6-2.0mm, and scanning speed 700-750mm / min. This process blocks excessive diffusion of Fe-Ti elements, avoids the formation of brittle intermetallic compounds, and results in a dense interface structure with a shear strength of 270MPa, superior to the original titanium-steel composite plate shear strength and related standards.

Description

Technical Field

[0001] This invention belongs to the field of metal material welding and additive manufacturing technology, specifically relating to a laser cladding repair method for interface damage of titanium-steel composite plates based on a copper interlayer. Background Technology

[0002] Titanium-steel composite plates are widely used due to their excellent comprehensive performance, but their interfaces are easily damaged during service. Because of the significant differences in the physicochemical properties of titanium and steel, brittle Fe-Ti intermetallic compounds (including TiFe, TiFe2, etc.) readily form near the interface at high temperatures, significantly reducing the interfacial bonding strength. During the service of pressure vessels, damage or defects in the interface area of ​​the composite plate directly threaten the safety and service life of the equipment. Traditional welding repair methods easily lead to interface embrittlement, while laser cladding remanufacturing technology, with its advantages of concentrated heat input, low dilution rate, and high forming precision, provides a new approach for the repair of titanium-steel composite plates.

[0003] In existing technologies, there are methods for laser additive manufacturing of titanium-steel composite plates using pure copper as an intermediate layer (such as the powder-feeding laser additive manufacturing method for titanium-steel composite plates with pure Cu as a transition layer disclosed in CN113199025A). These methods, by optimizing laser powder feeding process parameters, suppress the formation of Fe-Ti brittle compounds to some extent. However, this method mainly targets the manufacturing process of newly manufactured composite plates and does not address the repair of interface damage in already in-service composite plates. There are also methods for repairing interface defects in titanium-steel composite plates using high-energy beam additive manufacturing (such as the high-energy beam additive repair method for interface defects in titanium / steel layered composite materials disclosed in CN114990545A). However, these methods only address the bevel angle, transition layer, and repair layer thickness, without considering the impact of key laser repair process parameters (such as laser power and spot size) on the repair effect, and do not clearly define the critical process window.

[0004] The technological window for laser cladding repair of titanium-steel composite plate interfaces is extremely narrow: for the copper interlayer, insufficient laser energy will result in ineffective metallurgical bonding between the copper and the steel substrate, leading to cracks and incomplete fusion defects; while for the titanium filler layer, insufficient laser energy will cause incomplete melting of the titanium powder and the formation of pores, while excessive laser energy will cause "overheating" of the copper interlayer—that is, the laser heat flow penetrates the copper layer, causing large-area remelting, allowing Fe elements to penetrate the liquid copper layer and diffuse into the titanium layer, forming a hard and brittle iron-titanium intermetallic compound. Existing parameter exploration relies heavily on trial and error, lacking systematic theoretical guidance. While existing technologies include methods for guiding laser cladding process parameters through finite element simulation (such as Chinese patent CN121278990A, "A Method for Determining Laser Cladding Process Parameters Based on Finite Element Simulation"), the evaluation criteria guided by finite element simulation in these methods only focus on stress and strain, failing to provide effective guidance for the repair process of multilayer dissimilar materials. Furthermore, these methods model cladding scenarios for open flat surfaces, neglecting the influence of constraint geometry on heat dissipation behavior and failing to address the complex thermo-mechanical coupling problem of multilayer dissimilar material deposition in a V-shaped constrained bevel. The repair scenario for a titanium / copper / steel three-layer dissimilar material system differs fundamentally from single-layer cladding: First, the thermophysical properties of the three materials differ significantly, leading to drastically different heat transfer behaviors between layers; second, the difference in thermal expansion coefficients between layers results in complex interlayer thermal stress during cooling; third, the copper intermediate layer needs to simultaneously meet the metallurgical bonding requirements with the upper and lower materials while maintaining sufficient thickness to prevent Fe diffusion, and whether the copper layer "overheats" during the titanium layer cladding process directly determines the success or failure of the repair.

[0005] Therefore, there is an urgent need for a repair method specifically designed for titanium / copper / steel multilayer dissimilar material systems, capable of systematically revealing the evolution of multilayer molten pools and the formation mechanism of interface defects under different laser energies, and accurately determining the optimal combination of process parameters for each layer. Summary of the Invention

[0006] This invention proposes a laser cladding repair method for interface damage of titanium-steel composite plates based on a copper interlayer. A multiphysics coupled finite element simulation model is established for a three-layer dissimilar material system of titanium / copper / steel in a V-shaped constrained groove. The birth and death element technique is used to simulate the layer-by-layer deposition process in the order of "copper first, then titanium". An interlayer cooling control stage is set between the deposition of copper and titanium layers. The interlayer waiting temperature is determined through simulation iteration. A multi-objective evaluation criterion including metallurgical fusion sufficiency, copper layer remelting rate and interface residual stress is proposed, which realizes the accurate determination of the process window.

[0007] To achieve the above objectives, the present invention proposes the following technical content: A laser cladding repair method for interface damage in titanium-steel composite plates based on a copper interlayer includes the following steps: S1: Beveling preparation; removing damaged areas of the titanium-steel composite plate and processing a V-shaped beveling; the depth of the V-shaped beveling penetrates the titanium coating and extends into the interior of the steel substrate to completely remove the original damaged interface; grinding and cleaning the beveling surface. S2: Cladding preparation; pure copper powder is selected as the intermediate transition layer material of titanium / steel heterogeneous interface, and TA2 titanium powder is selected as the cladding filler material. The above powders are dried. S3: Finite element modeling and process window determination for multilayer dissimilar materials; specifically including the following steps: S3.1: Geometric modeling; Based on the actual dimensions of the V-shaped bevel to be repaired in step S1, a three-dimensional multilayer dissimilar material finite element geometric model including a steel substrate, V-shaped bevel cavity, copper intermediate layer and titanium filling layer is established using finite element analysis software, and mesh is generated. S3.2: Assigning multiple material properties; Assigning non-linear material properties that vary with temperature to the steel substrate, copper interlayer, and titanium filler layer respectively; S3.3: Layered sequential activation of heat source loading and interlayer cooling control; the layer-by-layer deposition process is simulated using dead and alive cells. At the initial moment of the simulation, all cells of the copper intermediate layer and titanium filler layer are inactive. First, the copper intermediate layer cells are activated sequentially according to the preset scanning path, and a moving Gaussian heat source is applied to complete the copper layer temperature field-stress field coupling calculation. After the copper layer deposition is completed, a natural cooling simulation stage is set. In this stage, no heat source is applied, and only the thermal convection and thermal radiation boundary conditions are retained. By monitoring the change of the copper layer surface node temperature over time, it is determined whether the copper layer surface temperature has dropped to less than or equal to the preset interlayer waiting temperature. When the copper layer surface temperature drops to the interlayer waiting temperature, the titanium filler layer cells are activated sequentially, and a moving Gaussian heat source is applied to perform the titanium layer temperature field-stress field coupling calculation. The Gaussian heat source parameters of the copper layer and titanium layer are set independently according to the actual spot diameter and laser power of each layer. S3.4: Multi-objective evaluation and process window determination; Parametric scanning calculations were performed on multiple different combinations of copper layer laser power-spot diameter and titanium layer laser power-spot diameter. For the simulation results of each combination of process parameters, the following evaluation indicators were extracted: Evaluation index 1 – Sufficient metallurgical fusion at the copper-steel interface: Whether the peak temperature of the steel substrate surface at the copper-steel interface reaches the solidus temperature of the steel during the copper layer deposition process. Evaluation index two – Copper layer remelting rate η The maximum depth of the region within the copper interlayer where the temperature exceeds the melting point of copper during titanium deposition. h re Total thickness of copper interlayer δ Cu The ratio,

[0008] Evaluation index three – residual stress at the copper-steel interface: residual Von Mises equivalent stress at the copper-steel interface after each layer has cooled to room temperature, and the distribution of residual stress components in the scanning path direction and the interface normal direction at the cladding interface. S4: Copper interlayer cladding; Based on the optimal process parameters of the copper layer determined in S3, a copper interlayer is deposited on the bevel surface of the steel substrate to achieve metallurgical bonding and eliminate interfacial stress concentration; S5: Interlayer cooling; After the copper intermediate layer is clad, wait until the surface temperature of the copper layer drops to less than or equal to the interlayer waiting temperature determined in step S3 before proceeding with the subsequent titanium layer deposition. S6: Titanium filler layer cladding; Based on the optimal process parameters of the titanium layer determined in S3, a titanium filler layer is deposited on the copper intermediate layer, and a protective gas is used throughout the cladding process of the copper and titanium layers.

[0009] Further, in step S3.3, the heat flux density distribution function of the moving Gaussian heat source is:

[0010] In the formula, P This indicates laser power, measured in W. A The absorption rate of laser energy by the metal powder; r The radius of the light spot is in mm. η The laser penetration depth is expressed in mm. x 0, y 0) represents the current coordinates of the heat source center; Q ( x,y,z ) represents spatial coordinates ( x,y,z The heat flux density at ().

[0011] Further, in step S3.3, the value of the interlayer waiting temperature is determined as follows: Subsequent titanium layer deposition simulations are performed for multiple candidate interlayer waiting temperatures, and the temperature that results in the highest copper layer remelting rate is selected. η The highest interlayer waiting temperature not exceeding a preset threshold is taken as the final interlayer waiting temperature; it is finally determined through repeated iterations, and the interlayer waiting temperature is set to be less than or equal to 200℃.

[0012] Furthermore, step S3.4 must satisfy the following conditions: the peak temperature of the steel substrate surface at the copper-steel interface during copper deposition reaches the solidus temperature of the steel; and the copper layer remelting rate... η The residual Von Mises equivalent stress at the copper-steel interface is the lowest after each layer is cooled to room temperature, and the residual stress components in the scanning path direction and interface normal direction at the cladding interface are low.

[0013] Furthermore, in step S4, the process parameters for cladding the copper intermediate layer are: laser power 2400-2800W, spot diameter 3.8-4.2mm, and scanning speed 400-500mm / min.

[0014] Furthermore, in step S6, the process parameters for cladding the titanium filler layer are: laser power 1100-1300W, spot diameter 1.6-2.0mm, and scanning speed 700-750mm / min.

[0015] Furthermore, the pure copper powder and TA2 titanium powder are prepared using a plasma rotating electrode process, with a particle size range of 75-150 μm; before cladding, the powder is placed in a vacuum drying oven for drying at a temperature of 80-120°C for 1-3 hours.

[0016] Furthermore, during the copper intermediate layer cladding and titanium filler layer cladding processes, the scanning path is planned as a serpentine reciprocating scanning method parallel to the long side of the V-shaped bevel; at the same time, high-purity argon is used as the protective gas throughout the process, with a gas flow rate of 15-25 L / min.

[0017] The beneficial effects that can be achieved by adopting the above technologies are: 1. An interlayer cooling control strategy was proposed; a cooling waiting stage guided by finite element simulation was inserted between the deposition of copper and titanium layers, which effectively avoided secondary remelting of the copper layer due to heat accumulation and ensured the continuous barrier function of the copper layer to Fe element diffusion; and through simulation analysis, it was found that 200℃ is the optimal interlayer cooling temperature, providing theoretical guidance for actual repair work.

[0018] 2. A multi-objective process evaluation criterion was established: by comprehensively considering the constraints of three dimensions—metallurgical fusion sufficiency, copper layer remelting rate, and interfacial residual stress—the process window was accurately determined; this ensured that the copper layer was fully clad, and the molten copper was fully spread and wetted within the steel substrate bevel; it also ensured the complete melting of titanium powder and avoided excessive remelting of the copper layer; the overall repair performance was significantly improved, and the interfacial shear strength after repair reached 270 MPa, meeting the national standard requirements; and it was higher than the shear strength of the copper-titanium interface mentioned in the background technology (approximately 224 MPa).

[0019] 3. A dedicated finite element simulation method for a three-layer dissimilar material system of titanium / copper / steel was established: Unlike the existing flat plate cladding model of a single material system, this invention models a special scenario of three dissimilar materials being deposited layer by layer in a V-shaped constrained bevel, which fully considers the huge differences in thermophysical properties among the three materials, making the simulation results more realistic and reliable. Attached Figure Description

[0020] Figure 1It is the initial material morphology; Figure 1 (a) in the figure represents the macroscopic morphology of the titanium-steel interface. Figure 1 (b) in the figure shows the microstructure of the titanium-steel interface. Figure 1 (c) in the figure represents the substrate structure furthest from the interface. Figure 1 In the diagram, (d) represents the cladding layer located away from the interface.

[0021] Figure 2 This is a diagram showing the dimensions of the test block and the V-groove dimensions for the repair test.

[0022] Figure 3 It is the finite element model and constraints; Figure 3 (a) in the figure is the finite element model. Figure 3 (b) in the equation represents a three-point constraint.

[0023] Figure 4 These are cloud maps showing the temperature field distribution of the molten pool under different process parameters; Figure 4 (a) shows the temperature distribution of the copper-steel molten pool when the copper layer is at 1600W. Figure 4 (b) shows the temperature distribution of the copper-steel molten pool at 2600W copper layer. Figure 4 (c) in the figure represents the temperature distribution of the molten pool in the titanium layer melting zone when the titanium layer is heated to 1000W. Figure 4 (d) in the figure represents the temperature distribution of the titanium-copper molten pool when the titanium layer is 1000W. Figure 4 (e) in the figure represents the temperature distribution of the molten pool in the titanium layer melting zone when the titanium layer is heated to 1400W. Figure 4 (f) in the figure represents the temperature distribution of the titanium-copper metallurgical molten pool when the titanium layer is at 1400W.

[0024] Figure 5 These are cloud maps showing the stress field distribution of the copper layer under different process parameters; Figure 5 (a) shows the residual Von Mises equivalent stress distribution at 1600W for the copper layer. Figure 5 (b) shows the stress distribution of S22 in the copper layer at 1600W. Figure 5 (c) shows the stress distribution of S33 in the copper layer at 1600W. Figure 5 In the figure, (d) represents the residual Von Mises equivalent stress of the copper layer at 2600W. Figure 5 (e) in the figure represents the stress distribution of S22 when the copper layer is at 2600W. Figure 5 (f) in the figure represents the stress distribution of S33 when the copper layer is at 2600W.

[0025] Figure 6 This is a schematic diagram of the scanning path.

[0026] Figure 7 The microstructures of different areas after repair in Example 1 (optimal process, copper layer 2600W / 4mm + titanium layer 1200W / 1.8mm) are shown. Figure 7(a) in the image represents a titanium / copper / steel composite layer. Figure 7 (b) in the diagram represents the copper / steel interface region. Figure 7 (c) in the diagram represents the titanium / copper bonding interface region. Figure 7 (d) in the figure represents the bevel interface region of the cladding zone.

[0027] Figure 8 This is a hardness distribution diagram of the steel / copper / titanium interface at different locations in Example 1.

[0028] Figure 9 This is the fracture morphology of the sheared sample repaired using the optimal process in Example 1. Figure 9 (a) in the figure shows the macroscopic morphology of the fracture surface. Figure 9 (b) in Figure 9 shows the microscopic morphology of the overall fracture surface, and (c) in Figure 9 shows a magnified view of a local area.

[0029] Figure 10 This is a metallographic diagram of the repaired interface in Comparative Example 1 (copper layer power 1600W is too low, first repair). Figure 10 (a) in the figure represents the overall morphology. Figure 10 (b)-(d) in the figure represent cracks in different areas of the copper layer. Figure 11 This is a metallographic diagram of the repair interface in Comparative Example 2 (titanium layer power 1000W too low, second repair); Figure 11 (a) in the image represents a titanium / copper / steel composite layer. Figure 11 (b) in the diagram represents the copper / steel interface region. Figure 11 (c) in the diagram represents the titanium / copper bonding interface region. Figure 11 (d) in the diagram represents the titanium / copper transition region. Figure 11 (e) in the diagram represents the titanium-coated region. Figure 11 (f) in the figure represents the bevel interface region of the cladding zone.

[0030] Figure 12 The fracture morphology of the shear specimen in Comparative Example 2 is shown. Figure 12 (a) in the figure shows the macroscopic morphology of the fracture surface. Figure 12 (b) in the figure shows the microstructure of the overall fracture surface. Figure 12 (c) in the image represents a porosity defect. Figure 12 (d) in the figure represents unmelted powder.

[0031] Figure 13 This is a metallographic diagram of the repair interface in Comparative Example 3 (titanium layer power 1400W too high, fourth repair). Figure 13 (a) in the image represents a titanium / copper / steel composite layer. Figure 13 (b) in the figure represents the titanium / copper bonding interface region.

[0032] Figure 14 The results are EDS test results for the composite layer in Comparative Example 3. Figure 14 (a) in the image represents the EDS line scan result. Figure 14 (b) in the image is a point scan electronic image. Figure 14 (c) in the spectrum Figure 1 The element concentration ratio, Figure 14 (d) in the spectrum Figure 2 The element concentration ratio, Figure 14 (e) in the diagram represents the surface scan result; Figure 15 This is the flowchart of this solution. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] like Figure 15 As shown, a laser cladding repair method for interface damage in titanium-steel composite plates based on a copper interlayer includes the following steps: S1: Beveling preparation and pretreatment.

[0035] In this embodiment and all comparative examples, TA2 / S30408 ​​titanium-steel composite plates prepared by explosive welding were used as the repair objects. The overall dimensions of the model were 120×20×15mm, and the thickness of the 304 stainless steel substrate was 12mm. Figure 1 As shown in (a), the initial material interface is well bonded, and its interface exhibits a typical wavy characteristic. The microstructure along the thickness direction from the cladding to the substrate can be divided into: cladding side deformation structure, titanium / steel interface layer (… Figure 1 (b) of the basal fibrous deformed tissue area Figure 1 (c) and the original microstructure region. The original microstructure of the substrate is uniform equiaxed austenite, and the TA2 pure titanium cladding is far from the interface region ( Figure 1 (d) in the figure represents equiaxed α-phase grains.

[0036] The titanium-steel composite plate to be repaired is fixed on the worktable, and the damaged area is removed by wire cutting or machining. Specifically, a V-shaped bevel with an angle between 55° and 65° and a depth of 0.3-0.5mm is machined in the thickness direction. The actual dimensions of the V-shaped bevel on the repair test block are as follows: Figure 2 As shown: a V-groove with an angle of 60° and a depth of 3.5mm; this depth ensures that the bottom of the groove extends into the steel substrate. The groove surface is then polished and cleaned with alcohol and dried to remove oil and scale.

[0037] S2: Preparation of cladding materials.

[0038] Both TA2 titanium powder and pure copper powder were prepared using the plasma rotating electrode method. Pure copper powder was used as the intermediate transition layer material, with a designed thickness of approximately 1 mm. TA2 titanium powder was selected as the cladding filler material to fill the remaining thickness area. The particle size of both powders ranged from 75 to 150 μm, exhibiting good sphericity. Before the cladding test, the pure copper powder and TA2 titanium powder were placed in a vacuum drying oven and dried at 80-120°C for 1-3 hours, preferably at 100°C for 2 hours, to remove adsorbed moisture from the powder surface and prevent the formation of porosity defects during the cladding process.

[0039] S3: Finite element modeling and process window determination for multilayer dissimilar materials. This step is the core innovation of this invention, and specifically includes the following sub-steps: S3.1: Geometric Modeling. Based on the actual dimensions of the V-shaped bevel to be repaired (including bevel angle, depth, bottom width, and top width), a three-dimensional multilayer dissimilar material finite element geometric model is established using finite element analysis software (such as ABAQUS). This model includes a steel substrate, the V-shaped bevel cavity, a copper intermediate layer, and a titanium filling layer. The model is then meshed non-uniformly, with local mesh refinement in the V-shaped cladding area and appropriate coarsening in areas far from the cladding area. Eight-node hexahedral thermo-coupled elements are selected (C3D8RT is used in ABAQUS as an example). Direct thermo-coupling analysis is employed in the calculations. In this embodiment, the meshed model is as follows: Figure 3 (a) contains a total of 18,720 grid cells. Mesh independence verification showed that the selected grid density ensured both computational accuracy and efficiency.

[0040] S3.2: Assignment of Multiple Material Properties. Nonlinear material properties varying with temperature, as shown in Tables 1-3, are assigned to the steel substrate, copper interlayer, and titanium filler layer, respectively. These properties include at least: density, thermal conductivity, specific heat capacity, elastic modulus, Poisson's ratio, yield strength, coefficient of thermal expansion, and latent heat. Each material property data covers a temperature range from room temperature to above the melting point of each material. Convection and radiation boundary conditions are set in the simulation: the surface emissivity of the materials is set to 0.85, the convective heat transfer coefficient is set to 10 W / (m²•K), and the ambient temperature is room temperature. To simulate the laser cladding process under actual unconstrained conditions, a boundary condition is applied to the bottom of the substrate as shown in Tables 1-3. Figure 3 The three-point constraint shown in (b) is used to eliminate rigid displacement.

[0041] The steel substrate is 304 stainless steel, with a density of 7830 kg / m³, a melting point of 1450°C, a Poisson's ratio of 0.29, a latent heat of 268000 J / kg, a solidus temperature of 1400°C, and a liquidus temperature of 1455°C. Other material properties of 304 stainless steel as a function of temperature are shown in Table 1.

[0042] Table 1 Material parameters of 304 stainless steel

[0043] Pure copper has a density of 8940 kg / m³, a melting point of 1084°C, a specific heat of 390 J / (kg•K), a Poisson's ratio of 0.34, a latent heat of 210000 J / kg, a solidus temperature of 1080°C, and a liquidus temperature of 1085°C. Other material properties of pure copper as a function of temperature are shown in Table 2.

[0044] Table 2 Material parameters of copper

[0045] TA2 pure titanium has a density of 4320 kg / m³, a melting point of 1667°C, a Poisson's ratio of 0.34, a latent heat of 400,000 J / kg, a solidus temperature of 1660°C, and a liquidus temperature of 1670°C. Other material properties of TA2 titanium as a function of temperature are shown in Table 3.

[0046] Table 3 Material parameters of titanium

[0047] S3.3: Layered sequential activation of heat source loading and interlayer cooling control.

[0048] In finite element analysis software, the stiffness matrix of a specified element is multiplied by a minimum factor while its mass, load, and other related properties are set to zero, making the element's contribution to the overall stiffness negligible, thus achieving element "failure." At the initial moment of the simulation, all elements in the copper intermediate layer and titanium filler layer within the V-groove region are treated as "failures."

[0049] The layer-by-layer deposition process was simulated using the cell birth and death technique. The simulation flow was: "copper layer deposition → interlayer cooling → titanium layer deposition → final cooling to room temperature".

[0050] First, a copper intermediate layer deposition simulation is performed: During the copper layer deposition process, copper layer cells are activated sequentially along a serpentine reciprocating path. In each analysis step, a set of cells is activated and a moving Gaussian heat source is applied; the heat flux density distribution function of the moving Gaussian heat source is:

[0051] In the formula, P This indicates laser power, measured in W.A The absorption rate of laser energy by the metal powder; r The radius of the light spot is in mm. η The laser penetration depth is expressed in mm. x 0, y 0) represents the current coordinates of the heat source center; Q ( x,y,z ) represents spatial coordinates ( x,y,z The heat flux density at point ( ). The application of the heat source model is achieved by writing a subroutine.

[0052] After the entire copper layer has been deposited, a natural cooling simulation phase is inserted. In this phase, no heat source is applied; only thermal convection and thermal radiation boundary conditions are maintained, allowing the model to cool naturally. By monitoring the temperature change of the central node on the copper layer surface over time, the point at which the copper layer surface temperature drops to less than or equal to a preset interlayer waiting temperature (e.g., 200°C) is determined. In actual repair operations, the criterion for initiating subsequent titanium layer deposition is using the copper layer surface temperature dropping to less than or equal to this interlayer waiting temperature.

[0053] Then, after the interlayer cooling stage, the deposition simulation of the titanium filling layer is performed: the titanium layer units are activated sequentially according to the same preset serpentine reciprocating scanning path, and a moving Gaussian heat source is applied, the heat source parameters of which are independently set according to the actual spot diameter of the titanium layer and the laser power.

[0054] The interlayer waiting temperature was determined as follows: Subsequent titanium layer deposition simulations were performed for multiple candidate interlayer waiting temperatures, and the temperature that resulted in the highest copper layer remelting rate was selected. η The highest interlayer waiting temperature not exceeding a preset threshold is used as the final interlayer waiting temperature, determined through iterative processes. In practice, five candidate interlayer waiting temperatures are set for the copper layer surface to cool to 300℃, 250℃, 200℃, 150℃, and 100℃, respectively, and titanium layer deposition simulations are performed for each. The maximum depth of the region where the temperature in the copper interlayer exceeds the copper melting point during titanium layer deposition at each candidate temperature is extracted, and the copper remelting rate is calculated. η, Simulation results show that when the interlayer waiting temperature is 300℃, insufficient heat dissipation due to the V-groove constraint results in a high residual temperature of the copper layer and a high copper remelting rate during titanium layer deposition. η Far exceeding the 50% threshold; when the interlayer waiting temperature drops to 250℃, η Still over 50%; when the interlayer waiting temperature drops to 200℃, η It drops to approximately 35%, falling within the optimal range of 20%-40%; when the interlayer waiting temperature further decreases to 150℃ and 100℃, ηThe remelting rates were reduced to approximately 25% and 20% respectively, both within safe limits, but the waiting time was significantly extended. Therefore, 200℃ was selected as the final interlayer waiting temperature to ensure the copper layer remelting rate. η The shortest inter-floor waiting time was achieved while remaining within a safe range.

[0055] The purpose of interlayer cooling control is to prevent the copper interlayer from being in an excessively preheated state due to residual heat from the previous layer during titanium deposition. This prevents unintended secondary full-thickness remelting (i.e., "overheating") of the copper layer during titanium cladding, ensuring that the copper layer can continuously and effectively block the diffusion of Fe from the steel substrate to the titanium layer. When the copper layer remelting rate... η When the content exceeds 50%, the Fe element in the steel substrate will penetrate the liquid copper layer and diffuse into the titanium layer, forming a brittle Fe-Ti intermetallic compound at the titanium / copper interface, which severely reduces the interfacial bonding strength.

[0056] S3.4: Multi-objective evaluation and process window determination.

[0057] For each set of process parameter combinations, the following evaluation indicators are extracted: Evaluation criterion one—Determining the sufficiency of metallurgical fusion at the copper-steel interface by adjusting the laser power, scanning speed, and spot diameter of the copper layer: Checking whether the peak temperature of the steel substrate surface at the copper-steel interface reaches the solidus temperature of the steel during the copper layer deposition process. If it does, it is determined that the copper-steel interface can form sufficient metallurgical bonding; if not, it is determined that the copper layer process parameters result in insufficient heat input, and there may be unfusion defects between the copper and steel, inducing cracks. Figure 4 As shown in (a), when the laser power of the copper layer is 1600W, the temperature distribution of the copper-steel molten pool shows that the molten pool depth is shallow, and the peak temperature of the steel substrate surface does not reach the solidus temperature of 304 stainless steel, indicating insufficient metallurgical fusion; Figure 4 As shown in (b), when the laser power of the copper layer is increased to 2600W and the spot diameter is increased to 4mm, the depth of the molten pool increases significantly, achieving good metallurgical fusion at the copper / steel interface.

[0058] Evaluation index two – Adjusting the copper layer remelting rate by adjusting the laser power, scanning speed, and spot diameter of the titanium layer. η During the titanium layer deposition process, the maximum depth to which the temperature in the copper interlayer exceeds the melting point of copper (approximately 1084°C) was extracted. h re Calculate the copper layer remelting rate in, The total thickness of the copper interlayer is designed to be 1 mm in this embodiment. Copper layer remelting rate. η It should not exceed 50%, and preferably be controlled within the range of 20% to 40%. For example... Figure 4As shown in (c) and (d), when the laser power of the titanium layer is 1000W, the molten pool temperature in the titanium layer melting zone is insufficient to completely melt the titanium layer. The copper layer remelting rate is low, but there is a risk of incomplete melting defects. Figure 4 As shown in (e) and (f), when the laser power of the titanium layer is increased to 1400W, the titanium layer is fully melted, but the depth of the titanium-copper molten pool increases significantly, causing large-area melting of the lower copper layer. The remelting rate of the copper layer far exceeds the safety threshold, resulting in "overburning" and Fe element penetration and diffusion.

[0059] Evaluation index three – residual stress at the copper-steel interface: such as Figure 5 As shown, after the model cooled to room temperature, the residual Von Mises equivalent stress at the copper-steel interface, the residual stress component distribution along the scanning path and the interface normal direction at the cladding interface were extracted. High residual stress reduces shear strength and tensile strength, and also easily leads to interface microcracks. Figure 5 (a) shows the residual Von Mises equivalent stress distribution at 1600W for the copper layer. Figure 5 (b) shows the S22 stress distribution when the copper layer is at 1600W. Figure 5 (c) shows the stress distribution of S33 in the copper layer at 1600W. Figure 5 In the figure, (d) represents the residual Von Mises equivalent stress distribution of the copper layer at 2600W. Figure 5 (e) in the figure represents the stress distribution of S22 when the copper layer is at 2600W. Figure 5 (f) in the figure represents the stress distribution of S33 when the copper layer is at 2600W.

[0060] With all the above evaluation indicators meeting the corresponding safety criteria as constraints, all feasible combinations of process parameters (laser power, scanning speed, and spot diameter for copper and titanium layers) were selected. From all feasible parameter combinations, the combination that minimizes the residual Von Mises equivalent stress at the interface, has low residual stress components in the scanning path direction and interface normal direction at the cladding interface, and achieves the highest copper layer remelting rate was chosen. η The combination within the optimal range (20%~40%) is taken as the optimal process parameter.

[0061] S4: Copper interlayer cladding.

[0062] The forming path is imported into the control system. To improve the stability of the cladding process, given the narrow width of the bottom edge of the repair tank, if a scanning method parallel to the short side of the test block is used, the reciprocating frequency of the deposition head will be high, which can easily lead to a decrease in powder feeding stability. Therefore, the scanning path planning adopts a serpentine reciprocating scanning method parallel to the long side of the test block (e.g., ...). Figure 6 As shown in the figure, based on the optimal process parameters of the copper layer (copper layer laser power, scanning speed and spot diameter) determined in step S3, a pure copper intermediate layer is deposited on the bevel surface of the steel substrate.

[0063] S5: Interlayer cooling.

[0064] After the copper intermediate layer is completely deposited, wait until the surface temperature of the copper layer drops to no higher than the interlayer waiting temperature determined in step S3 (200℃ in this embodiment) before proceeding with the subsequent titanium layer deposition. In actual operation, the surface temperature of the copper layer can be monitored in real time using an infrared thermometer.

[0065] S6: The cladding of the titanium filler layer.

[0066] Based on the optimal process parameters for the titanium layer determined in step S3 (laser power, scanning speed, and spot diameter), a TA2 titanium filler layer is deposited on the prepared copper intermediate layer. Under these process parameters, the titanium powder is completely melted, and only moderate fusion occurs at the titanium-copper interface. The copper layer remelting rate is controlled within a safe range, avoiding the problem of Fe element penetrating the copper layer and diffusing into the titanium layer due to excessive remelting of the copper layer. High-purity argon is used as the protective gas throughout the process, with a gas flow rate of 15-25 L / min, to effectively suppress the oxidation reaction of titanium during the cladding process.

[0067] Performance testing: After repair, metallographic and mechanical property tests were performed on the workpiece. Interface quality inspection was conducted on the repaired titanium-steel composite plate. Inspection items included metallographic observation and shear strength testing. The shear strength test was performed according to GB / T6396-2008 "Test Methods for Mechanical and Technological Properties of Composite Steel Plates," requiring the shear strength of the repaired interface to be no less than the lower limit of shear strength (196 MPa) for high-bonding-strength composite plates specified in GB / T8547-2019 "Titanium-Steel Composite Plates."

[0068] Example 1: Preferred process of the present invention.

[0069] Based on the guidance of the above finite element simulation, this embodiment uses optimized process parameters for repair.

[0070] Copper interlayer cladding: The laser power was set to 2600W, the spot diameter to 4.0mm, the scanning speed to 450mm / min, and the scanning path to be a serpentine reciprocating scanning method parallel to the long side of the test block (e.g., Figure 6 As shown in the figure, under the action of this high power and large spot size, the copper liquid achieved full spreading and wetting in the bevel of the steel substrate.

[0071] Interlayer cooling: After copper layer deposition, wait until the copper layer surface temperature drops below 200℃. In actual operation, the copper layer surface temperature is monitored in real time using an infrared thermometer.

[0072] Titanium filler cladding: The laser power was set to 1200W, the spot diameter to 1.8mm, and the scanning speed to 720mm / min. High-purity argon gas was used throughout the process at a flow rate of 20L / min. This power was within the optimal window determined by simulation, ensuring complete melting of the titanium powder while avoiding excessive remelting of the copper layer.

[0073] The results of the repaired macroscopic and microscopic tests are as follows: Microscopic morphology: such as Figure 7 As shown, metallographic microstructure observation indicates that, Figure 7 (a) No macroscopic cracks were observed at the intact titanium / copper / steel composite interface; Figure 7 (b) At the copper / steel interface, a good metallurgical bond is formed between the copper layer and the steel substrate; Figure 7 (c) The titanium / copper interface in the middle has good bonding; Figure 7 There are no obvious defects in the bevel interface area of ​​the cladding zone (d) in the middle.

[0074] Mechanical properties: such as Figure 8 As shown, the steel layer exhibits a uniform hardness distribution, averaging approximately 210 HV; the copper layer has the lowest hardness at approximately 108 HV; the titanium / copper interface shows a significant increase in hardness due to the incorporation of titanium and the formation of copper-titanium intermetallic compounds, reaching approximately 510 HV; the hardness of the titanium layer, located away from the copper / titanium interface, gradually decreases to approximately 203 HV. Shear tests revealed an average shear strength of up to 270 MPa for the joint, meeting the standard requirement of 196 MPa for high-bonding-strength composite plates in GB / T 8547-2019 "Titanium-Steel Composite Plates".

[0075] Fracture characteristics: such as Figure 9 As shown, shear failure occurs at the steel / copper interface, and the fracture surface is generally smooth (see...). Figure 9 (a) and Figure 9 (b)). Numerous uniformly distributed and elongated dimples were observed on the fracture surface, exhibiting good plasticity and typical characteristics of ductile fracture (see 9(c) in the figure), indicating that the repaired joint has excellent plasticity reserve.

[0076] Comparative Example 1: Copper layer power too low (first repair test).

[0077] This comparative example aims to verify the effect of insufficient heat input to the copper layer, and at the same time verify the predictions of "insufficient metallurgical fusion" and "interfacial tensile stress concentration" in the finite element simulation.

[0078] Process parameters: Laser power of 1600W for copper intermediate layer, spot diameter of 2mm, scanning speed of 480mm / min; laser power of 1000W for titanium filler layer, spot diameter of 1.6mm, scanning speed of 720mm / min.

[0079] Test results: such as Figure 10As shown, due to insufficient laser power, the heat of the molten pool was inadequate to maintain good wettability of liquid copper on the stainless steel surface. Obvious cracks existed between the copper layer and the steel substrate, failing to achieve effective metallurgical bonding (see...). Figure 10 (a) to (d)). This result is consistent with the prediction in the finite element simulation that "the peak temperature of the steel substrate surface at 1600W did not reach the solidus temperature, and there was obvious tensile stress concentration at the interface".

[0080] Comparative Example 2: The titanium layer power is too low (second repair test).

[0081] This comparative example aims to verify the porosity and unmelted defects caused by insufficient heat input to the titanium layer.

[0082] Process parameters: The copper intermediate layer uses optimized parameters (2600W, 4mm spot size). The titanium layer is deposited after the interlayer is cooled to below 200℃. The titanium filling layer has a laser power of 1000W, a spot diameter of 1.6mm, and a scanning speed of 720mm / min.

[0083] Test results: such as Figure 11 As shown, Figure 11 (a) in the figure represents a titanium / copper / steel composite layer, with good bonding at the copper / steel interface (see...). Figure 11 (b)), but the titanium / copper interface transition zone contains fine dendrites and a certain number of incompletely melted TA2 spherical powder particles (see (b)). Figure 11 (c) and (d) in the text). This is because during the cladding process, the molten titanium liquid cools rapidly after contacting the lower-temperature copper layer. The large supercooling inhibits grain growth, while the low heat input allows some of the titanium powder to completely melt. Figure 11 (e) in the figure represents the titanium-coated region, where a small number of porosity defects still exist at the titanium / copper interface at the bevel edge (see...). Figure 11 (f) in the middle.

[0084] The shear test yielded an average shear strength of 185 MPa. The fracture surface was located at the titanium / copper interface, exhibiting brittle fracture. The fracture surface was uneven (see...). Figure 12 (a) and (b) show river patterns and cleavage steps, exhibiting typical cleavage brittle fracture as a whole (see [reference]). Figure 12 (c) in the middle), and pores and spherical unmelted powder particles were found on the fracture surface (see (c) in the middle). Figure 12 (d)). This result is consistent with the prediction in the finite element simulation that "the molten pool temperature in the titanium layer melting zone at 1000W is insufficient to completely melt the titanium layer".

[0085] Comparative Example 3: Excessive power in the titanium layer caused overheating (fourth repair test).

[0086] This comparative example aims to verify the destructive effect of excessive heat input to the titanium layer on the barrier effect of the copper layer, that is, to verify the "overburning" phenomenon predicted in the finite element simulation and the consequences after the copper layer remelting rate η exceeds the safety threshold.

[0087] Process parameters: The copper intermediate layer uses optimized parameters (2600W, 4mm spot size). The titanium layer is deposited after the interlayer is cooled to below 200℃. The laser power of the titanium filling layer is increased to 1400W, while the other parameters remain unchanged.

[0088] Test results: such as Figure 13 As shown, although no pores or unmelted powder were observed in the titanium / copper interface region, the overall metallic luster of the interface layer was weakened, indicating overheating (see...). Figure 13 (a)). Numerous microcracks were clearly observed at the titanium-copper interface (see [reference]). Figure 13 (b)). With further increases in the power of the titanium layer, the heat input to the molten pool increases significantly, leading to an increase in the dilution rate and consequently causing local overburning of the copper layer. This overburning phenomenon exacerbates the diffusion of Fe elements from the copper layer into the titanium molten pool and the penetration of Ti elements into the copper layer, causing the formation of a large number of brittle Fe-Ti intermetallic compounds at the titanium / copper interface, which induces the initiation of microcracks under thermal stress.

[0089] like Figure 14 As shown, EDS testing was performed on the composite layer interface after the fourth repair. The EDS line scan results are shown (see...). Figure 14 In (a) of the diagram, Fe no longer exhibits a significant abrupt change at the copper / steel interface, but rather shows a continuous distribution in both the copper and titanium layers. This indicates that the copper layer underwent significant overheating under these process conditions, leading to a large influx of Fe from the steel matrix into the copper layer and further diffusion into the titanium layer. EDS point analysis results further confirm this phenomenon (see [reference]). Figure 14 (b)~(d)) shows that the Fe content in the copper layer is as high as 28.21 at%. Figure 14 (d) in the middle; while the Fe content in the titanium / copper transition region still reaches 19.75 at% (see...) Figure 14 (c) in the middle. EDS surface scan results show ( Figure 14 In (e) of the figure, a transition region composed of Fe, Ti, and Cu elements is formed at the titanium / copper interface, indicating that the three elements undergo strong interdiffusion in this region. This result is consistent with the prediction in the finite element simulation that "the remelting rate of the copper layer at 1400W far exceeds the 50% safety threshold".

[0090] The simulation and experimental results show that the finite element model can effectively reproduce the thermodynamic evolution of the laser cladding process under different process parameters, thus providing a theoretical basis for explaining the interface forming phenomena observed in different repair experiments. The experimental defects in each comparative example are highly consistent with the failure modes predicted by the finite element simulation, fully verifying the effectiveness and accuracy of the multi-objective evaluation criterion proposed in this invention.

[0091] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for laser cladding repair of interface damage in titanium-steel composite plates based on a copper interlayer, characterized in that, Includes the following steps: S1: Beveling preparation; removing damaged areas of the titanium-steel composite plate and processing a V-shaped beveling; the depth of the V-shaped beveling penetrates the titanium coating and extends into the interior of the steel substrate to completely remove the original damaged interface; grinding and cleaning the beveling surface. S2: Cladding preparation; pure copper powder is selected as the intermediate transition layer material of titanium / steel heterogeneous interface, and TA2 titanium powder is selected as the cladding filler material. The above powders are dried. S3: Finite element modeling and process window determination for multilayer dissimilar materials; specifically including the following steps: S3.1: Geometric modeling; Based on the actual dimensions of the V-shaped bevel to be repaired in step S1, a three-dimensional multilayer dissimilar material finite element geometric model including a steel substrate, V-shaped bevel cavity, copper intermediate layer and titanium filling layer is established using finite element analysis software, and mesh is generated. S3.2: Assigning multiple material properties; Assigning non-linear material properties that vary with temperature to the steel substrate, copper interlayer, and titanium filler layer respectively; S3.3: Layered sequential activation of heat source loading and interlayer cooling control; the layer-by-layer deposition process is simulated using dead and alive cells. At the initial moment of the simulation, all cells of the copper intermediate layer and titanium filler layer are inactive. First, the copper intermediate layer cells are activated sequentially according to the preset scanning path, and a moving Gaussian heat source is applied to complete the copper layer temperature field-stress field coupling calculation. After the copper layer deposition is completed, a natural cooling simulation stage is set. In this stage, no heat source is applied, and only the thermal convection and thermal radiation boundary conditions are retained. By monitoring the change of the copper layer surface node temperature over time, it is determined whether the copper layer surface temperature has dropped to less than or equal to the preset interlayer waiting temperature. When the copper layer surface temperature drops to the interlayer waiting temperature, the titanium filler layer cells are activated sequentially, and a moving Gaussian heat source is applied to perform the titanium layer temperature field-stress field coupling calculation. The Gaussian heat source parameters of the copper layer and titanium layer are set independently according to the actual spot diameter and laser power of each layer. S3.4: Multi-objective evaluation and process window determination; Parametric scanning calculations were performed on multiple different combinations of copper layer laser power-spot diameter and titanium layer laser power-spot diameter. For the simulation results of each combination of process parameters, the following evaluation indicators were extracted: Evaluation index 1 – Sufficient metallurgical fusion at the copper-steel interface: Whether the peak temperature of the steel substrate surface at the copper-steel interface reaches the solidus temperature of the steel during the copper layer deposition process. Evaluation index two – Copper layer remelting rate η The maximum depth of the region within the copper interlayer where the temperature exceeds the melting point of copper during titanium deposition. h re Total thickness of copper interlayer δ Cu The ratio, ; Evaluation index three – residual stress at the copper-steel interface: residual Von Mises equivalent stress at the copper-steel interface after each layer has cooled to room temperature, and the distribution of residual stress components in the scanning path direction and the interface normal direction at the cladding interface. S4: Copper interlayer cladding; Based on the optimal process parameters of the copper layer determined in S3, a copper interlayer is deposited on the bevel surface of the steel substrate to achieve metallurgical bonding and eliminate interfacial stress concentration; S5: Interlayer cooling; After the copper intermediate layer is clad, wait until the surface temperature of the copper layer drops to less than or equal to the interlayer waiting temperature determined in step S3 before proceeding with the subsequent titanium layer deposition. S6: Titanium filler layer cladding; Based on the optimal process parameters of the titanium layer determined in S3, a titanium filler layer is deposited on the copper intermediate layer, and a protective gas is used throughout the cladding process of the copper and titanium layers.

2. The method for laser cladding repair of interface damage in titanium-steel composite plates based on a copper interlayer according to claim 1, characterized in that, In step S3.3, the heat flux density distribution function of the moving Gaussian heat source is: ； In the formula, P This indicates laser power, measured in W. A The absorption rate of laser energy by the metal powder; r The radius of the light spot is in mm. η The laser penetration depth is expressed in mm. x 0, y 0) represents the current coordinates of the heat source center; Q ( x,y,z ) represents spatial coordinates ( x,y,z The heat flux density at ().

3. The laser cladding repair method for interface damage of titanium-steel composite plates based on a copper interlayer according to claim 1, characterized in that, In step S3.3, the value of the interlayer waiting temperature is determined as follows: Subsequent titanium layer deposition simulations are performed for multiple candidate interlayer waiting temperatures, and the temperature that results in the highest copper layer remelting rate is selected. η The highest interlayer waiting temperature, not exceeding a preset threshold, is taken as the final interlayer waiting temperature and is determined through repeated iterations; and the interlayer waiting temperature is set to be less than or equal to 200℃.

4. The laser cladding repair method for interface damage of titanium-steel composite plates based on a copper interlayer according to claim 1, characterized in that, Step S3.4 must meet the following requirements: the peak temperature of the steel substrate surface at the copper-steel interface during copper deposition must reach the solidus temperature of the steel; the copper remelting rate must be [missing information]. η The residual Von Mises equivalent stress at the copper-steel interface is the lowest after each layer is cooled to room temperature, and the residual stress components in the scanning path direction and interface normal direction at the cladding interface are low.

5. The laser cladding repair method for interface damage of titanium-steel composite plates based on a copper interlayer according to claim 1, characterized in that, In step S4, the process parameters for cladding the copper intermediate layer are: laser power 2400-2800W, spot diameter 3.8-4.2mm, and scanning speed 400-500mm / min.

6. The laser cladding repair method for interface damage of titanium-steel composite plates based on a copper interlayer according to claim 1, characterized in that, In step S6, the process parameters for cladding the titanium filler layer are: laser power 1100-1300W, spot diameter 1.6-2.0mm, and scanning speed 700-750mm / min.

7. The laser cladding repair method for interface damage of titanium-steel composite plates based on a copper interlayer according to claim 1, characterized in that, The pure copper powder and TA2 titanium powder were prepared using a plasma rotating electrode process, with a particle size range of 75-150 μm. Before cladding, the powder was placed in a vacuum drying oven for drying at a temperature of 80-120°C for 1-3 hours.

8. The laser cladding repair method for interface damage of titanium-steel composite plates based on a copper interlayer according to claim 1, characterized in that, During the copper intermediate layer cladding and titanium filler layer cladding processes, the scanning path is planned as a serpentine reciprocating scanning method parallel to the long side of the V-shaped bevel; at the same time, high-purity argon is used as the protective gas throughout the process, with a gas flow rate of 15-25 L / min.

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