A deep-sea equipment coating with macro-bionic-micro-gradient composite structure and a preparation method thereof

Abstract

The application discloses a deep-sea equipment coating with macroscopic bionic-microscopic gradient composite structure and a preparation method thereof. The coating is formed by laser cladding technology on the surface of a base material in one scanning to reach the overall coating with a preset thickness. The coating has a periodic arrangement of bionic structures which are macroscopically optimized in structure design. The microstructure is a gradient structure with equiaxed crystals as the main part on the top and columnar crystals as the main part on the bottom which is spontaneously formed in the cladding process. The application actively designs the macrostructure based on thermal stress, spontaneously regulates the microstructure, adopts an integrated manufacturing process, and the three synergies not only simplify the process, reduce the cost, but also improve the comprehensive performance of the coating, and effectively control the negative effects in the preparation process, thereby providing an innovative and practical technical path for long-life protection of equipment in deep-sea extreme environment.

Description

Technical Field

[0001] This invention relates to a surface strengthening coating for key components of deep-sea equipment and its preparation method, specifically belonging to the field of metal material surface treatment and laser additive manufacturing technology. Background Technology

[0002] Key components of deep-sea equipment (such as the legs of submersibles) operate for extended periods in the high-pressure, corrosive, and highly abrasive deep-sea environment. Taking TC4 titanium alloy as an example, its wear resistance is poor, and its surface is easily worn when subjected to friction from seabed sand and rock fragments. Seawater erosion triggers electrochemical corrosion, and high pressure accelerates metal fatigue and microcrack propagation, exacerbating structural fatigue and localized deformation, severely impacting component lifespan and equipment safety. Therefore, there is an urgent need to develop efficient wear- and corrosion-resistant coating technologies to improve the overall service performance of key materials.

[0003] Currently, preparing biomimetic gradient coatings on titanium alloy surfaces using laser cladding technology is a common method for surface strengthening. Existing methods mainly fall into two categories: one is to form a gradient structure through multiple laser cladding processes using powders of different compositions (e.g., CN104480464A); the other is to achieve a gradient structure using different compositional systems under certain process parameters through processes such as powder mixing, hot pressing sintering, cutting thin sheets, and pre-layer cladding (e.g., CN115011831A). In addition, laser carburizing and nitriding processes are also used to prepare composition-gradient wear-resistant coatings (e.g., CN113529008B). Although the above methods improve the bonding strength, wear resistance, and corrosion resistance of the coating to the substrate to some extent, and reduce thermal deformation, their gradient structures require deliberate construction through multiple layers and multiple process steps, resulting in complex processes, low preparation efficiency, and high costs, making it difficult to meet the requirements of production efficiency and economy for large-scale engineering applications.

[0004] Furthermore, laser cladding technology inherently presents a contradiction between heat input and metallurgical bonding: sufficient energy input is a prerequisite for ensuring metallurgical bonding between powder and substrate, but high heat input inevitably leads to an expansion of the heat-affected zone and intensified thermal deformation of the substrate, affecting component precision and substrate performance. How to effectively control the heat-affected zone and suppress deformation while ensuring bonding quality remains a key challenge for this technology.

[0005] Therefore, how to efficiently combine biomimetic structural design with laser cladding to simplify the process, reduce costs, and simultaneously optimize coating performance and control thermal deformation is a pressing technical challenge. If a biomimetic gradient structure with an upper equiaxed crystal layer and a lower columnar crystal layer can be spontaneously formed during a single laser cladding process through the coordinated design of biomimetic structures, coating composition, and process parameters, it is hoped that the aforementioned problems of complex processes, large heat-affected zones, and insufficient performance can be solved simultaneously, providing a more promising engineering solution for surface strengthening of key components in deep-sea equipment. Summary of the Invention

[0006] To address the challenges of complex and costly processes in existing biomimetic gradient coating fabrication technologies, which hinder engineering applications, and the inherent contradiction between heat input and deformation control in laser cladding technology, this invention provides a coating for deep-sea equipment with a macroscopic biomimetic-microscopic gradient composite structure and its preparation method. This method synergistically combines the active optimization design of the macroscopic biomimetic structure with in-situ control of the microscopic gradient organization, achieving both low-stress forming and performance improvement of the coating through single-pass laser cladding.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A deep-sea equipment coating with a macroscopic biomimetic-microscopic gradient composite structure is characterized in that the coating is formed by laser cladding technology on the surface of a substrate in one scan to achieve a predetermined thickness. The coating has a macroscopically optimized biomimetic structure with periodic arrangement, and the microstructure is a gradient structure formed spontaneously during the cladding process, with equiaxed crystals on the top and columnar crystals on the bottom.

[0008] Furthermore, the biomimetic structure includes at least linear, square, wavy, and arc-shaped structures.

[0009] Furthermore, the geometry of the biomimetic structure is determined by the height of the unit side. a Unit side width b , Element base length c, radius of curvature r definition.

[0010] Note: In this invention, the side height of the unit is... a This refers to the height of the side of the smallest structural unit in a biomimetic structure, and the width of the unit's side. b Let be the width of the side of the smallest structural unit of the biomimetic structure, and let c be the length of the base of the smallest structural unit of the biomimetic structure, and let be the radius of curvature. r This is the radius of the circle tangent to the side and bottom edges.

[0011] Furthermore, the coating comprises a titanium or titanium alloy matrix and a ceramic reinforcing phase dispersed in the matrix and generated in situ; wherein the ceramic reinforcing phase accounts for 1% to 10% by mass in the coating, and the titanium or titanium alloy matrix accounts for 90% to 99% by mass in the coating.

[0012] Furthermore, the ceramic reinforcing phase is selected from one or more of TiB2, TiC, BN, and B4C.

[0013] The coating mentioned above is prepared by the following method, specifically including the following steps: S1. Bionic Structure Optimization Design: For the target service conditions, a basic periodic wave-like bionic structure is first preset as the design prototype. Based on this, parametric geometric models of different bionic structures are established. Under a preset set of fixed laser power and scanning speed parameters, the parametric geometric models of different bionic structures are imported into finite element analysis software to simulate and analyze the thermal stress distribution of different bionic structures. From the simulation results, the bionic structure type and parameters with the least thermal impact on the substrate are selected. S2. Powder preparation: Nanoscale ceramic powder is mixed with micron-sized titanium or titanium alloy powder in a predetermined ratio to prepare composite powder; S3. Process parameter optimization: The various biomimetic structure types with the least thermal impact on the substrate, as optimized in step S1, are respectively used as target biomimetic structures. The molten pool temperature field under multiple combinations of laser power and scanning speed is simulated by finite element method. The combination of laser power and scanning speed parameters that satisfies the nucleation density of the upper layer of the coating is greater than that of the lower layer is selected as the optimized laser power and scanning speed of the target biomimetic structure. S4. Laser Additive Manufacturing: Under a protective atmosphere, using a laser cladding device, the composite powder is clad onto the substrate surface in one step according to the path of the target biomimetic structure optimized in step S1, the laser power and scanning speed optimized in step S3, and the matching powder feeding parameters, to form the coating.

[0014] The reason why this invention uses a periodic, wave-like biomimetic structure as the preset design prototype in step S1 is that the uneven surface texture of many organisms in the biological world can protect them from external erosion and damage. For example, pangolins, dung beetles, and mole crickets have a special pattern of non-smooth outer skin, which has excellent desorption, drag reduction, and wear resistance properties, while also having stress dispersion and stress relief effects. Drawing inspiration from this uneven structure, a wave-like periodic biomimetic structure is preset.

[0015] Furthermore, the specific process of step S1 is as follows: 1.1: For the area to be strengthened on the workpiece surface, a wave-like biomimetic cladding path model composed of repeated periodic units is constructed. The periodic units are parameterized using four parameters: unit side height a, unit side width b, unit side length c, and radius of curvature r. By adjusting the values ​​of the geometric parameters, a variety of alternative biomimetic structures can be generated. 1.2: Calculate the length shape factor λ and curvature shape factor for quantitatively evaluating the thermodynamic effects of each candidate biomimetic structure. η The calculation formula is: , Where: L is the length of the single-cycle cladding trajectory, d is the projected length of L, and Lc is the total length of the single-cycle cladding trajectory curve (circular arc) segment; 1.3: Import the parameterized models of each candidate biomimetic structure into the finite element analysis software. Under the premise of ensuring that the total heat input of different structures on the same area remains consistent, a set of fixed laser power and scanning speed combinations are preset to simulate and analyze the thermal stress distribution of different biomimetic structure types, and obtain the thermodynamic results of each candidate biomimetic structure. The thermodynamic results include thermal stress and the depth of the heat-affected zone. 1.4: Based on the λ and η calculated in step 1.2 and the thermodynamic results obtained from the simulation in step 1.3, a comprehensive evaluation function is constructed. By comparing the comprehensive evaluation function values ​​of each candidate biomimetic structure, the biomimetic structure model and its parameters a, b, c, and r with the least thermal impact on the substrate under the premise of meeting the requirements of wear resistance and corrosion resistance are selected, providing a quantitative design basis for subsequent process optimization.

[0016] It should be noted that, during the optimization of the structure, although different preset laser power and scanning speed will affect thermal stress, the influence of the biomimetic structure on thermal stress under different parameter combinations is similar. Therefore, as long as a fixed combination of laser power and scanning speed is used, the influence of different biomimetic structures on thermal stress can be reflected. Thus, there is no limitation on the preset laser power and scanning speed. Of course, the preset parameter values ​​are premised on ensuring good metallurgical adhesion of the coating.

[0017] Furthermore, the comprehensive evaluation function Ji in step 1.4 is... , Where α, β, γ, and δ are weighting coefficients, representing the influence of length, curvature, thermal stress, and heat-affected zone depth on the comprehensive evaluation, respectively. Suggested ranges are: α: 0.3-0.5, β: 0.2-0.3, γ: 0.15-0.25, δ: 0.15-0.25; σ max,i The maximum residual equivalent stress; H HAZ,i The maximum residual equivalent stress and the depth of the heat-affected zone are used to evaluate the degree of thermal impact and residual stress level of different biomimetic paths on the substrate.

[0018] Furthermore, the specific process of step S3 is as follows: 3.1. For the various biomimetic structures with the least thermal impact on the substrate selected in step S1, set multiple sets of different laser powers and scanning speeds as alternative parameters; 3.2. For each set of candidate parameters, the laser cladding process is simulated using the finite element method to obtain the transient temperature field of the molten pool; based on the temperature field results of the finite element simulation, the temperatures of the upper layer (the layer in contact with air) and the lower layer (the layer in contact with the substrate) of the coating are read, and the temperature gradient G of the upper and lower layers of the coating as a function of time is calculated respectively. 3.3. Based on the relationship between nucleation density N0 and temperature gradient G, the nucleation density N0 of the upper layer of the coating under different combinations of laser power and scanning speed can be obtained. 0上 and the nucleation density N in the lower layer 0下 ; 3.4. Filter out those that satisfy N 0上 Greater than N 0下 The alternative parameter combinations for this condition serve as the laser power and scanning speed combination for the target biomimetic structure. The larger N0 is, the more nucleation sites there are and the smaller the grain size.

[0019] The microhardness of the coating prepared using the optimized structure and process parameters of this invention was measured using a micro Vickers hardness tester under a 0.20 kg load for 15 s. A series of tribological corrosion experiments were conducted using a wear testing machine (Rtec, MFT-5000) and an electrochemical workstation (Gamry 3000). Under a positive load of 30 N, the sample slid 5 mm at a frequency of 1 Hz. Electrochemical experiments were performed in a 3.5 wt.% NaCl solution, with a three-electrode system including a working electrode (coating), a reference electrode (Ag / AgCl electrode (0.199 V vs. standard hydrogen electrode), and a counter electrode (platinum wire electrode). The potentiodynamic polarization curves ranged from -0.3 V. OCP Up to 2.0 V Ag / AgCl The scan rate was 0.5 mV / s at the beginning.

[0020] The advantages of this invention are: (1) On a macroscopic level, this invention designs a periodic biomimetic structure through parametric modeling. The core purpose of biomimicry is to actively control the heat input and thermal stress distribution during the laser cladding process, thereby suppressing substrate deformation and preventing any impact on key components of deep-sea equipment. Moreover, the coating thickness is controllable, and the coating material is metallurgically bonded to the substrate. On a microscopic level, by precisely matching powder composition and process parameters, a microstructure gradient of upper equiaxed crystals and lower columnar crystals is spontaneously formed during a single-pass cladding process. This achieves integrated design and spontaneous formation of macroscopic biomimicry and microscopic gradient. Through corrosion channel blocking effect and crack deflection effect, corrosion and wear resistance are improved. The formed equiaxed crystal layer of the coating is wear-resistant and crack propagation-resistant, while the columnar crystal layer is firmly bonded to the substrate and impact-resistant. This overcomes the traditional method of constructing gradients through multi-layer cladding or complex prefabrication processes.

[0021] (2) In the optimization design process, this invention introduces quantitative indicators such as length shape factor (λ) and curvature shape factor (η) to link the geometric characteristics of the biomimetic structure with the cladding thermal process. Using finite element analysis software, the thermal stress distribution of different biomimetic structures is simulated and analyzed, predicting the depth of the heat-affected zone and residual stress, thereby quantitatively selecting the optimal structural parameters (a, b, c, r). This significantly improves the design success rate and reduces R&D costs.

[0022] (3) When optimizing process parameters, the present invention takes the control of temperature gradient distribution during the solidification process of the molten pool as the core objective. By the relationship between nucleation density and temperature gradient, the temperature gradient is converted into nucleation density that can dominate the grain morphology, so that the upper region of the coating has the conditions of low temperature gradient and high nucleation density to promote the formation of equiaxed crystals; and the lower region of the coating adjacent to the substrate maintains the conditions of high temperature gradient and low nucleation density to form columnar crystals.

[0023] In summary, this invention, based on the active design of macroscopic structure by thermal stress, the spontaneous regulation of microstructure, and the adoption of an integrated manufacturing process, not only simplifies the process and reduces costs, but also improves the overall performance of the coating and effectively controls the negative effects in the preparation process. It provides a highly innovative and practical technical path for long-life protection of equipment in extreme deep-sea environments. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. The accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a design drawing of the bio-control structure of the present invention.

[0026] Figure 2 A diagram showing the key locations of the pile legs in an embodiment of the present invention.

[0027] Figure 3 This is a schematic diagram of the formulas for the length shape factor λ and the curvature shape factor η constructed in an embodiment of the present invention.

[0028] Figure 4 The results are finite element simulations of the coating of the triangular wave biomimetic structure of this invention at a certain time, where 4a is the temperature field and 4b is the thermal stress distribution diagram.

[0029] Figure 5This is a biomimetic structure diagram prepared by the present invention using 2wt.%TiB2+98wt.%Ti6Al4V titanium-based composite material as cladding powder, where 5(a) is the macroscopic structure and 5(b) is the microstructure.

[0030] Figure 6 This is a cross-sectional view of the microstructure of the coating prepared by this invention.

[0031] Figure 7 yes Figure 5 The coating performance diagrams are shown, where 7(a) represents the hardness diagram, 7(b) represents the corrosion resistance diagram, and 7(c) represents the wear resistance diagram.

[0032] In the diagram: 1 - First critical part, 2 - Second critical part, 3 - Third critical part. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0034] The following section uses the leg, one of the key components of a deep-sea submersible, as an example to explain in detail the implementation process of the entire process of this invention.

[0035] S1. Biomimetic structural optimization design Piling legs face challenges such as wear, corrosion, and impact when operating on the seabed. Surface strengthening of the piling legs varies depending on the location and the specific challenges encountered (see...). Figure 2 The specific optimization process is as follows: 1.1: For high-impact wear scenarios (see...) Figure 2 (The first key part 1, the second key part 2, and the third key part 3) In this invention, a wave-like strip is preferred as the design prototype (see the first key part 1, the second key part 2, and the third key part 3). Figure 1 The left figure shows that, at this point C=0, the wavy trough and crest structure provides redundant stress paths, allowing stress redistribution in dynamic operations (such as collisions with rocks), avoiding single-point failure, and allowing for parameterization of the waveform to optimize impact resistance. 1.2: Calculate the length shape factor λ and curvature shape factor η used to quantitatively evaluate the thermodynamic effects of each candidate biomimetic structure; the calculation formula is: , In the formula: L is the length of the single-cycle cladding trajectory, d is the projected length of L, and Lc is the total length of the single-cycle cladding trajectory curve (circular arc) segment.

[0036] Specifically, in this embodiment, the construction process of the formulas for the length shape factor λ and the curvature shape factor η is as follows: Reference Figure 3During the construction process, the wave-shaped structure adopts a triangular wave trajectory. Let the coordinates of the trough point within one cycle be (0,0), the peak point be (b,a), and the next trough point be (2b,0). That is, each cycle consists of two straight lines of equal length. Ignoring the first-order effect of the fillet radius r on the length, the length l of each straight line segment is:

[0037] The length of a single-cycle cladding trajectory is:

[0038] The corresponding length shape factor is:

[0039] To avoid stress concentration caused by sharp corners, this invention preferably sets a fillet radius r at the crests and troughs. After each bend is replaced by a fillet, the total length of the cut-off straight line is approximately 2r, and the newly added arc length is approximately πr / 2. Therefore, the length increment of each bend is:

[0040] One cycle contains two bends, therefore the length of the corrected single-cycle cladding trajectory is approximately:

[0041] The corresponding length shape factor is:

[0042] The total length of the curve segment is approximately the sum of two quarter-circle arcs, that is:

[0043] Therefore, the curvature shape factor is approximately:

[0044] By adjusting a, b, and the radius of curvature r, the periodic element can be parameterized. By adjusting a / b and r / b, different parameterized geometric models can be obtained, achieving a balance between trajectory length amplification and local curvature concentration, thereby optimizing the thermal stress distribution.

[0045] 1.3: Importing different parametric geometric models into the finite element analysis software, while ensuring that the total heat input of different models on the same area remains consistent, a set of fixed laser power and scanning speed combinations is preset to simulate and analyze the thermal stress distribution of different biomimetic structural types; the specific process of controlling the initial conditions of the finite element analysis is as follows: 1.3.1 Construction of the temperature field In the finite element analysis stage of this invention, a thermo-mechanical coupling model of the computational domain consisting of the substrate and coating was established using the transient heat conduction equation and the linear elastic mechanical equilibrium equation as the governing equations. The temperature field of this model is described as follows: At any point x = (x, y, z) and at time t, the temperature field satisfies

[0046] The boundary conditions are convective-radiative combined heat transfer conditions. , Where: ρ is the density of the cladding material; c is the specific heat capacity; k is the thermal conductivity; Q i (x,t) is the energy density function of the heat source moving along the i-th type of biomimetic scanning path; It is the spatial gradient vector of the temperature field, representing the rate of change of temperature along each coordinate direction; σ is the rate of change of temperature of the cladding material over time; h is the convective heat transfer coefficient; ε is the surface emissivity; σ SB T is the Stefan-Boltzmann constant; ∞ The ambient temperature; It is the temperature difference between the surface of the cladding material and the environment, which is the driving force for convective heat transfer. This represents the temperature difference that indicates radiative heat transfer between the surface of the cladding material and the environment. This represents the thermal flux density in the normal direction of the boundary surface.

[0047] 1.3.2 Construction of the thermal stress field

[0048] After the temperature field is solved, it is applied as a known load to the structural field for stress analysis. The structural field satisfies the following equilibrium equations and thermoelastic constitutive relations: , Where σ is the stress tensor, f is the body force, D is the elastic stiffness matrix, and ε is the total strain tensor. th Represents thermal strain. It represents the divergence of the stress tensor.

[0049] The above constitutive relation Thermal strain has been taken into account, and it expresses stress as a function of the total strain tensor and temperature. The thermal strain is determined by the temperature field, and the calculation formula is: , Where k is the coefficient of linear expansion, T0 is the initial temperature of the cladding powder, and T t This is the current local temperature field, where I is the unit tensor; Substituting the constitutive relation into the equilibrium equation and solving it yields the equivalent stress σ under various biomimetic scanning paths. eq(x,t) and the final residual stress distribution.

[0050] 1.3.3 Finite Element Simulation Input Control To describe different biomimetic scanning paths, this invention parameterizes the midline of the i-th type of biomimetic structure with an arc length parameter s, obtaining a trajectory function. , Where L i Let z0 be the total arc length of the biomimetic scanning path, z0 be the height of the coating surface, and Γ be the total arc length of the biomimetic scanning path. i (s) represents the trajectory function. From the aforementioned geometric derivation, we can obtain... , d is the projected length of L, λ i This is the length shape factor corresponding to the biomimetic structure.

[0051] Let the cladding scanning speed be defined as v i Then the motion of the heat source center along this trajectory satisfies , In the formula, t represents any moment from the start to the end of laser cladding.

[0052] To ensure consistent total energy input across different biomimetic paths on the same area, this invention uses energy input E per unit area. A As a normalization metric. For laser power P, channel width w, and total path length L. i The i-th type of biomimetic structure has , Where η th For overall thermal efficiency, E A,i This represents the energy input per unit surface area for the i-th type of biomimetic structure.

[0053] Assuming that the energy input per unit area is the same for all biomimetic structures, i.e.: E A,i =E A,0 And taking a linear structure as the reference structure, its length shape factor and scanning speed are λ respectively. ref v ref Then there is

[0054] This allows us to obtain the scanning speed of different biomimetic structures.

[0055] As can be seen from the above formula, when the length shape factor λ i When the value is large, the corresponding scanning speed increases accordingly, thereby ensuring that the four biomimetic paths obtain the same energy input level in the same surface area.

[0056] Regarding the heat source model, this invention preferably uses a Gaussian surface heat source, whose heat flux density q at any time t is... i (x,y,t) can be written as , Where: R is the equivalent spot radius, which is also the radius of the Gaussian heat source; q i (x,y,t) represents the surface heat flux density acting on the surface point (x,y,z0) at time t of the i-th type of biomimetic path; x and y represent the planar coordinates of a fixed spatial point (corresponding to any point on the workpiece surface), t is a time variable (the laser scanning time), and η th For overall thermal efficiency, P represents laser power.

[0057] To simulate the internal thermal field generated by surface heat flow applied at z=z0, an equivalent volumetric heat source can be used to model the thermally affected region. The energy density function of this volumetric heat source can be derived from the surface heat flow using the principle of energy equivalence, i.e.: the energy density function of the volumetric heat source is, , In the formula: Z is the Dirac function, z is the vertical coordinate in the three-dimensional coordinate system, which is the third spatial variable in the heat conduction model, and z0 is the height of the upper surface of the workpiece.

[0058] In the specific numerical implementation, the path L is discretized into a series of points with a fixed arc length step size Δs: , Where N s =L i / Δs,s k This represents the arc length parameter value at the k-th discrete point. This represents the spatial coordinate vector of the k-th discrete point on the i-th type of biomimetic path. This represents the time corresponding to when the heat source center moves along the i-th path to the k-th discrete point.

[0059] Will and Export to an external path file, and set the Gaussian heat source center at the k-th time step via a user subroutine or secondary development interface. This allows for one-click simulation switching between four biomimetic paths—linear, semi-circular, wavy, and trapezoidal—on the same finite element mesh. The simulation results of the temperature and thermal stress fields at time t for the biomimetic structure using the triangular wave form are shown below. Figure 4 As shown, the temperature field simulation results are shown in [the image / reference]. Figure 4 a. The simulation results of the thermal stress field are shown in [the table]. Figure 4 b.

[0060] 1.4 Constructing a comprehensive evaluation function Based on λ and η calculated in step 1.2 and the boundary conditions of the finite element input control in step 1.3, the following comprehensive evaluation function is constructed; to evaluate the thermal effects of different biomimetic paths on the substrate and the residual stress level, this invention defines the maximum thermal stress σ. max,i for:

[0061] and the depth H of the heat-affected zone HAZ,i for , Where t end When cooling to near ambient temperature, t peak T represents the peak temperature during the cladding process. crit The critical temperature at which the microstructure of the cladding material undergoes a significant change.

[0062] Combining the aforementioned geometric shape factor λ i ,η i The comprehensive evaluation function is constructed as follows: , Wherein, α, β, γ, δ are weighting coefficients, and in the embodiment, α, β, γ, δ are taken as 0.35, 0.30, 0.20, and 0.15, respectively.

[0063] By comparing the comprehensive evaluation function values ​​J of each candidate biomimetic structure i We selected the biomimetic structural model and its parameters a, b, c, and r that minimized the thermal impact on the substrate and the maximum thermal stress while meeting the requirements for wear resistance and corrosion resistance, providing a quantitative design basis for subsequent process optimization.

[0064] Figure 1 On the right are four biomimetic models and their parameters optimized from the wavy strip design prototype, including linear (a=0), square (b=0), wavy (c=0), and semi-circular (b=c=0).

[0065] S2: Coating Composition Design This invention can use various metal material powders and ceramic reinforcement powders. For key components of titanium alloy pile legs, TC4 micron-sized titanium alloy powder and nano-sized ceramic powders such as TiB2, TiC, BN, and B4C are preferred. 1%-10% of the ceramic reinforcement powder and 90%-99% of the titanium and titanium alloy powder are mixed by wet ball milling with alcohol for 4-6 hours by weight. In this embodiment, micron-sized Ti6Al4V titanium alloy powder (approximately 40 μm) and nano-sized (approximately 40 nm) TiB2 ceramic powder are used. 2% of the TiB2 ceramic powder and 98% of the Ti6Al4V titanium alloy powder are mixed by wet ball milling with alcohol for 4 hours by weight. The powder is then placed in a vacuum drying oven at 40 degrees Celsius and dried for 24 hours.

[0066] S3: Optimization of cladding parameters The optimization process of cladding parameters is illustrated below using the optimized wave-shaped biomimetic structure as an example.

[0067] The cladding parameters include laser power, scanning speed, spot diameter, and powder feed rate. Since the purpose of optimizing the process parameters in this invention is to control the microstructure of the coating to form a gradient structure, and based on solidification characteristics, the melt pool temperature gradient is a key factor determining the grain morphology, which mainly depends on the laser power and scanning speed controlling the heat input, this embodiment fixes the spot diameter at 2 mm to optimize the laser power and scanning speed. The optimization process is as follows: 3.1: For the wave-shaped biomimetic structure, multiple sets of different laser powers and scanning speeds were set as alternative parameters; 3.2: For each set of candidate parameters, based on the temperature field results obtained in step 1.4 above, read the temperatures of the upper and lower layers of the coating cross section, and then calculate the temperature gradient G; 3.3: Based on the relationship between the nucleation density N0 and the cooling rate G, the nucleation density N of the upper layer of the coating under different combinations of laser power and scanning speed can be obtained. 0上 and the nucleation density N in the lower layer 0下 ; , In the formula, G represents the temperature gradient, and v s θ is the scanning speed, θ is the angle between the scanning direction and the normal direction of the solid / liquid interface, m is the cooling rate exponent, N0 is the nucleation density, and k is the material growth kinetic coefficient. 3.4: Screening for nucleation density N that satisfies the requirements of the upper coating layer 0上 The nucleation density N is greater than that of the underlying coating layer. 0下The alternative parameter combinations under this condition ultimately yielded a laser power of 1000 W - 2000 W and a cladding speed of 6 mm / s - 12 mm / s. This combination, along with a spot diameter of 2 mm and a powder feeding speed of 0.6 kg / h - 0.8 kg / h (the powder feeding speed is selected based on the coating composition), were used as the cladding parameters.

[0068] S4: Coating cladding The oxide film on the surface of the titanium and titanium alloy substrate was removed with sandpaper, and the surface oil film and stains were cleaned with anhydrous ethanol in an ultrasonic cleaner. Under argon protection, the polished titanium and titanium alloy were placed in a high-speed laser cladding system, with a spot diameter of 2 mm, a laser power of 1600 W, a cladding speed of 12 mm / s, and a powder feed rate of 0.8 kg / h. Figure 2 Laser cladding of titanium-based composite materials is performed on the first key part 1, the second key part 2, and the third key part 3.

[0069] Figure 5 This invention relates to a wavy coating prepared on a substrate, from... Figure 5 The microscopic image in (b) shows that the coating of the present invention has a network of TiB fibers. Figure 6 The microstructure of the coating shows a gradient structure with columnar structures underneath and isocrystalline structures on top. The performance of the titanium-based composite coating prepared by this invention was tested, and the test results are shown in the figure. Figure 7 The Vickers hardness of the coating is from 320 HV. 0.2 (TC4) increased to 480 HV 0.2 The surface hardness is approximately 1.5 times higher than that of substrates without laser cladding. Compared to TC4 titanium alloy, the corrosion current density during the corrosion process of the 2wt.% TiB2+98wt.%Ti6Al4V titanium-based composite material is basically the same as that of TC4, while the wear resistance is improved by more than 3 times. The biomimetic titanium-based composite coating obtained under the preparation conditions of this invention has both high hardness and corrosion resistance, thereby improving the service life of titanium alloys under complex working conditions.

[0070] The above is merely an example of the present invention and is not intended to limit the technical solution of the present invention. Any modifications and refinements made on the basis of the present invention without creative effort should be within the protection scope of the present invention, and the specific protection scope shall be determined by the claims.

Claims

1. A method for preparing a coating for deep-sea equipment with a macroscopic biomimetic-microscopic gradient composite structure, characterized in that the coating is formed on the surface of a substrate in a single scan using laser cladding technology to achieve a predetermined thickness. The coating macroscopically possesses a periodically arranged biomimetic structure with optimized structural design, and the microstructure is a gradient structure spontaneously formed during the cladding process, with equiaxed crystals predominating on the upper surface and columnar crystals predominating on the lower surface. The preparation method includes the following steps: S1. Bionic Structure Optimization Design: For the target service conditions, a basic, periodic, wave-like bionic structure is first pre-designed as a prototype. Based on this, parametric geometric models of different bionic structures are established. Under a pre-set set of fixed laser power and scanning speed parameters, the parametric geometric models of different bionic structures are imported into finite element analysis software to simulate and analyze the thermal stress distribution of different bionic structures. From the simulation results, the bionic structure type and parameters with the least thermal impact on the substrate are selected. The specific process is as follows: 1.1: For the area to be strengthened on the surface of the workpiece, a wave-like biomimetic cladding path model composed of repeated periodic units is constructed. The periodic units are parameterized using four parameters: unit side height a, unit side width b, unit bottom length c, and radius of curvature r. By adjusting the values ​​of the geometric parameters, a variety of alternative biomimetic structures are generated. 1.2: Calculate the length shape factor λ and curvature shape factor for quantitatively evaluating the thermodynamic effects of each candidate biomimetic structure. η ; The calculation formula is: In the formula: L The length of a single-cycle cladding trajectory ，d for L The projected length, L c This represents the total length of the single-cycle cladding trajectory curve segment. 1.3: Import the parametric models of each candidate biomimetic structure into the finite element analysis software. Under the premise of ensuring that the total heat input of different structures on the same area remains consistent, simulate and analyze the thermal stress distribution of different biomimetic structure types to obtain the thermodynamic results of each candidate biomimetic structure. The thermodynamic results include thermal stress and the depth of the heat-affected zone. 1.4: Based on λ calculated in step 1.2 and η Based on the thermodynamic results obtained from the simulation in step 1.3, a comprehensive evaluation function is constructed. By comparing the comprehensive evaluation function values ​​of each candidate biomimetic structure, the biomimetic structure model and its parameters that have the least thermal impact on the substrate while meeting the requirements for wear resistance and corrosion resistance are selected. a , b , c , r This provides a quantitative design basis for subsequent process optimization; S2. Powder preparation: Nanoscale ceramic powder is mixed with micron-sized titanium or titanium alloy powder in a predetermined ratio to prepare composite powder; S3. Process parameter optimization: The various biomimetic structure types with the least thermal impact on the substrate, as optimized in step S1, are respectively used as target biomimetic structures. The molten pool temperature field under multiple combinations of laser power and scanning speed is simulated by finite element method. The combination of laser power and scanning speed parameters that satisfies the nucleation density of the upper layer of the coating is greater than that of the lower layer is selected as the optimized laser power and scanning speed of the target biomimetic structure. S4. Laser Additive Manufacturing: Under a protective atmosphere, using a laser cladding device, the composite powder is clad onto the substrate surface in one step according to the path of the target biomimetic structure optimized in step S1, the laser power and scanning speed optimized in step S3, and the matching powder feeding parameters, to form the coating.

2. The method for preparing a deep-sea equipment coating with a macroscopic biomimetic-microscopic gradient composite structure as described in claim 1, characterized in that, The biomimetic structures described include at least linear, square, wavy, and arc-shaped structures.

3. The method for preparing a deep-sea equipment coating with a macroscopic biomimetic-microscopic gradient composite structure as described in claim 2, characterized in that, The coating comprises a titanium or titanium alloy matrix and a ceramic reinforcing phase dispersed in the matrix by in-situ generation; wherein the ceramic reinforcing phase accounts for 1% to 10% by mass in the coating, and the titanium or titanium alloy matrix accounts for 90% to 99% by mass in the coating.

4. The method for preparing a deep-sea equipment coating with a macroscopic biomimetic-microscopic gradient composite structure as described in claim 3, characterized in that, The ceramic reinforcing phase is selected from one or more of TiB2, TiC, BN, and B4C.

5. The method for preparing a deep-sea equipment coating with a macroscopic biomimetic-microscopic gradient composite structure as described in claim 1, characterized in that, The comprehensive evaluation function in step 1.4 for: ; in: These are weighting coefficients, representing the degree of influence of length, curvature, thermal stress, and heat-affected zone depth on the comprehensive evaluation. For the maximum residual equivalent stress, The depth of the heat-affected zone; the depth of the heat-affected zone and the maximum residual equivalent stress are used to evaluate the degree of thermal impact and residual stress level of different biomimetic paths on the substrate.

6. The method for preparing a deep-sea equipment coating with a macroscopic biomimetic-microscopic gradient composite structure as described in claim 1, characterized in that, The specific process of step S3 is as follows: 3.

1. For the various biomimetic structures with the least thermal impact on the substrate selected in step S1, set multiple sets of different laser powers and scanning speeds as alternative parameters; 3.

2. For each set of candidate parameters, the laser cladding process is simulated using the finite element method to obtain the transient temperature field of the molten pool; based on the temperature field results of the finite element simulation, the temperatures of the upper and lower layers of the coating are read, and the temperature gradient G of the upper and lower layers of the coating over time is calculated respectively. 3.

3. Based on the relationship between nucleation density N0 and temperature gradient G, the nucleation density N0 of the upper layer of the coating under different combinations of laser power and scanning speed is obtained. 0上 and the nucleation density N in the lower layer 0下 ; 3.

4. Filter out those that satisfy N 0上 Greater than N 0下 The alternative parameter combinations for this condition serve as the laser power and scanning speed combination for the target biomimetic structure.

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