Crack inhibition method for laser cladding composite coating based on pre-deformed substrate

Abstract

The invention discloses a crack inhibition method for a laser cladding composite coating based on a pre-deformed substrate, and relates to the technical field of laser additive manufacturing. The method comprises the following steps: firstly, predicting a deformation field and a residual stress field of a substrate during laser cladding of a specific coating material under non-rigid constraint through numerical simulation, and calculating the required pre-deformation compensation amount according to the deformation field and the residual stress field; then, the pre-deformation compensation amount is applied to the deformable substrate, so that the deformable substrate is in a pre-bending or pre-torsional deformation state. And laser cladding is carried out on the pre-deformed substrate, and thermal stress generated in the cladding process and preset deformation energy of the substrate can offset each other, so that effective release of residual stress and accurate control of macroscopic deformation of the component are synchronously realized. According to the method, the coating stress can be reduced, crack initiation can be inhibited, and the industrial problem that stress control and shape precision in traditional laser cladding are difficult to consider at the same time is solved.

Description

Technical Field

[0001] This invention belongs to the field of laser additive manufacturing and surface engineering technology, specifically relating to an advanced process method for optimizing the laser cladding process, reducing residual stress, and suppressing cracks by controlling substrate deformation. Background Technology

[0002] Laser cladding technology, as an advanced surface modification and additive manufacturing technology, has been widely used in the repair and remanufacturing of critical components. However, due to the intense unbalanced heating and cooling during laser processing, significant residual stress is introduced into the cladding layer and the substrate. This residual stress can cause component warping and deformation, affecting dimensional accuracy; in severe cases, it can lead to cracks and peeling of the cladding layer, directly resulting in product scrap.

[0003] Currently, methods for reducing residual stress mainly include process parameter optimization, substrate preheating, post-heat treatment, and the addition of rare earth elements. While these methods have some effect, they all have limitations: process optimization has limited effect; preheating increases equipment complexity and energy consumption; post-treatment cannot prevent deformation and may impair performance; and adding elements complicates the process and increases costs.

[0004] Research has shown that using a non-rigidly constrained substrate, allowing for elastic or plastic deformation during laser cladding, provides deformation space for the release of thermal stress, thereby effectively reducing residual stress and suppressing the generation of cracks in the cladding layer. This mechanism indicates that actively controlling the constraint state of the substrate and guiding it to undergo controllable deformation during processing is an effective way to achieve coating stress control. However, this method faces a key contradiction in engineering applications: stress release is often accompanied by macroscopic deformation of the component, making it difficult to simultaneously ensure shape accuracy. To resolve this contradiction, this invention proposes an innovative pre-deformation compensation method, which achieves coordinated control of residual stress and component morphology by applying precise pre-deformation to the substrate before cladding. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To overcome the industry challenge of controlling both cracking of the cladding layer and macroscopic deformation of the component due to high residual stress in traditional laser cladding technology, this invention provides a method for suppressing cracks in laser cladding composite coatings based on pre-deformed substrates.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] S1. Modeling and Prediction: First, a three-dimensional "thermo-mechanical coupling" finite element model of the laser cladding process is established. The implementation of this model is as follows:

[0010] Step 1: In finite element analysis software (such as ANSYS, Abaqus, etc.), establish the geometric model (length, width, height, etc.) of the single-pass or multi-pass laser cladding layer and the substrate. Select hexahedral mesh generation, refine the mesh of the cladding layer and heat-affected zone, and reduce the mesh density of the rest of the substrate.

[0011] Step 2: The laser cladding process is simulated using the "death and death cell" technique. Cells not scanned by the laser are considered "killed," and their material properties are weakened by a tiny factor, thus ignoring their impact on the model. Once the laser scans the cell, the cell is immediately "activated" and its complete material properties are restored.

[0012] Step 3: A Gaussian body heat source model is selected as the laser heat source, and the movement trajectory of the heat source is programmed through the software's command flow interface to accurately reproduce the actual scanning path;

[0013] Step 4: Apply convective heat transfer boundary conditions to all surfaces of the substrate to simulate heat exchange with the surrounding air; at the same time, apply additional thermal radiation boundary conditions to the laser-scanned cladding area to consider radiative heat dissipation in the high-temperature area; to simulate a non-rigid constraint mechanical environment, apply a fixed constraint to a local square area at the bottom of the substrate instead of completely restricting the entire substrate.

[0014] Step 5: All thermophysical parameters (such as thermal conductivity, specific heat capacity, and density) and mechanical property parameters (such as elastic modulus, yield strength, and coefficient of thermal expansion) of the material are set as nonlinear functions that change with temperature, which can usually be calculated using professional software such as JMatPro; the total simulation time covers the entire laser cladding process (such as the first 2 seconds) and the subsequent air cooling stage (such as the last 1 second), and finally outputs the transient deformation field of the substrate, the final residual deformation, and the residual stress field distribution inside the coating and the substrate throughout the process;

[0015] S2. Determine the pre-deformation amount: Based on the final residual deformation field of the substrate obtained from the S1 simulation (including its specific deformation shape and displacement at each point), a geometric inverse method is used for compensation design. Specifically, the deformation result predicted by the simulation is regarded as the final state of the system under thermal stress. An initial deformation field of equal magnitude and opposite direction is obtained by analytical calculation or iterative optimization algorithm. This initial deformation field is the pre-deformation amount that needs to be applied, which can be directly quantified as the radius of curvature of the pre-bending or the preset displacement at a specific location. Its purpose is to enable the component to accurately restore to the target flatness or designed geometry after the cladding stress is released.

[0016] S3. Apply pre-deformation: Based on the precise pre-deformation amount calculated in S2, pre-process the deformable substrate using a controllable mechanical loading method (including but not limited to bending machines, hydraulic systems, and custom fixtures).

[0017] S4. Laser Cladding: The pre-deformed substrate is clamped onto the worktable using a non-rigid constraint. This non-rigid constraint can be achieved through simple beam support, elastic support, or localized bottom fixation. Subsequently, a composite coating is laser-clad onto the substrate. The cladding material can be titanium-based, nickel-based, cobalt-based, iron-based alloys, or their corresponding metal-based composite materials.

[0018] (III) Beneficial Effects

[0019] Compared with existing technologies, this invention, through an active control strategy of "pre-deformation followed by cladding," can significantly reduce or even eliminate residual stress and deformation in laser-clad components, fundamentally suppressing the generation of cracks in the cladding layer. This method can greatly improve the dimensional accuracy and yield of components, reduce subsequent straightening and processing steps, and its process is highly versatile, applicable to various materials and complex-shaped components, with outstanding advantages of significant effect, low cost, and ease of promotion. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the 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.

[0021] Figure 1 It is a laser cladding geometric model;

[0022] Figure 2 This is a deformation field cloud map after laser cladding;

[0023] Figure 3 a represents a substrate (thin plate) with a thickness of 5mm. Figure 3 b represents a substrate (thick plate) with a thickness of 10mm. Figure 3 c represents the surface morphology of the thin plate laser cladding. Figure 3 d represents the surface morphology of the thick plate after laser cladding. Because the thin plate deformed and released residual stress, no cracks were generated. However, the thick plate did not deform and could not release residual stress, resulting in a network of cracks. This indicates that deformation can release residual stress and effectively inhibit crack initiation.

[0024] Figure 4 This is a schematic diagram of a three-roll bending mill.

[0025] Figure 5 This is a flowchart of the pre-deformation process applied to a non-rigid substrate;

[0026] Figure 6 This is a schematic diagram of laser cladding on a pre-deformed substrate.

[0027] 1-Upper roll, 2-Lower roll, 3-Drive motor, 4-Base, 5-Base plate, 6-Pre-deformed substrate, 7-Powder feeding trough, 8-Powder feeding nozzle, 9-Laser, 10-Substrate bottom constraint. Detailed Implementation

[0028] The embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the present invention.

[0029] The pre-deformation loading device applicable to the embodiments of the present invention is as follows: Figure 4 As shown, it includes: an upper roller 1, a lower roller 2, a drive motor 3, and a base 4. The laser cladding device is as follows: Figure 6 As shown, it includes: base plate 5, pre-deformed substrate 6, powder feeding trough 7, powder feeding nozzle 8, laser 9, and substrate bottom constraint 10.

[0030] A method for suppressing cracks in laser cladding composite coatings based on pre-deformed substrates includes:

[0031] S1, Modeling and Prediction

[0032] Step 1: Use the thermal coupling module of ANSYS Workbench to create a 3D geometric model of the substrate and the single-pass cladding layer. The substrate dimensions are 50mm × 50mm × 5mm, and the cladding layer dimensions are 40mm × 2mm × 1mm. Hexahedral elements are used for meshing. The mesh of the cladding layer and the heat-affected zone directly below it (approximately 1mm deep) is refined with an element size of 0.1mm; the remaining areas of the substrate use a gradually sparser mesh with a minimum element size of 0.5mm.

[0033] Step 2: Employ the "death and death unit" technique to simulate the layer-by-layer addition of cladding material. Initially, all units in the cladding layer are "killed." During laser scanning, as the heat source moves, the corresponding cladding layer units are sequentially "activated."

[0034] Step 3: The laser heat source is a Gaussian body heat source model with a power of 1200W and a spot diameter of 2mm. A moving heat source is applied to the surface of the cladding layer using the APDL command, controlling the heat source to move uniformly along the length of the cladding layer (40mm) at a scanning speed of 8mm / s.

[0035] Step 4: Apply a convective heat transfer coefficient of 20 W / (m²) to all external surfaces. 2 The ambient temperature was set to 25℃. Convective radiation was applied to the laser-scanned cladding area, with an emissivity of 0.4. To simulate actual fixture conditions, all degrees of freedom (completely fixed) of a 10mm × 10mm square area at the center of the bottom of the substrate were constrained, while the remaining areas remained free.

[0036] Step 5: The thermophysical parameters (thermal conductivity, specific heat capacity, density) and mechanical property parameters (elastic modulus, yield strength, coefficient of thermal expansion) of the substrate and cladding material are all set as nonlinear functions from 25 to 1500℃, and the data are obtained through calculation using JMatPro software. The total simulation time is 3 seconds (2 seconds for cladding and 1 second for cooling). After the calculation is completed, the final residual deformation field of the substrate and the residual stress field inside the cladding layer are output.

[0037] S2. Determine the pre-deformation amount

[0038] According to the simulation results, the substrate underwent upward warping deformation after cladding, with the maximum deformation located at both ends of the substrate. Using a geometric inverse compensation method, the simulated deformation field data was imported into a post-processing program. Through analytical calculation or iterative optimization algorithms, the required pre-deformation was determined to be an initial pre-bending that produces a deformation pattern opposite to the predicted deformation and with the same maximum displacement.

[0039] S3, Apply pre-deformation

[0040] Based on the calculated pre-deformation amount, the following is adopted: Figure 4 The three-roll bending mill shown pre-processes the substrate. In this equipment, a bending structure is formed above the two lower rolls, and feed is achieved by a drive motor. The pre-deformation process is as follows: Figure 5 As shown: During operation, the upper roller, under pressure Fn, causes the substrate between the rollers to bend in a controllable manner. Precise control of the pre-deformation is achieved by adjusting the amount of pressure applied by the upper roller.

[0041] S4, Laser Cladding

[0042] The pre-deformed substrate is fixed and constrained in the middle region of its bottom. On the pre-deformed substrate, single-pass laser cladding of titanium-based alloy powder is performed according to the process parameters used in the simulation (laser power 1200W, scanning speed 8mm / s, spot diameter 2mm).

Claims

1. A method of crack suppression in laser cladding composite coatings based on pre-deformed substrates, characterized in that, The method comprises the following steps: S1, modeling and prediction: by establishing a three-dimensional "thermal-mechanical coupling" finite element model of the laser cladding process, the transient deformation field and the final residual deformation of the substrate during the laser cladding process and after cooling to room temperature are predicted, and the residual stress field distribution inside the coating and the substrate is obtained; S2, determining the pre-deformation: based on the final residual deformation field of the substrate predicted by step S1, the final deformation state of the substrate obtained by simulation is taken as the target geometric morphology, and through the geometric inverse method, the initial deformation field which is equal in size and opposite in direction to the target flatness that the substrate needs to recover after stress release is inversely calculated, so as to accurately quantify the key parameters of pre-deformation; S3, applying pre-deformation: according to the pre-deformation determined in step S2, a controllable mechanical loading method is used to apply pre-deformation to the deformable substrate, so that the substrate generates an initial geometric morphology with target curvature or specific deflection; S4, laser cladding: on the substrate with pre-deformation, laser cladding of the composite coating is carried out under non-rigid constraint condition, so that the thermal stress generated in the cladding process and the pre-set deformation of the substrate can offset each other, thereby realizing the release of residual stress and the collaborative control of macroscopic deformation of the component.

2. The method of claim 1, wherein, The key parameters in step S2 include the curvature radius of pre-bending or the pre-set displacement amount of specific position points.

3. The method of claim 1, wherein, The "geometric inverse method" in step S2 is realized by analytical calculation or iterative optimization algorithm.

4. The method of claim 1, wherein, The three-dimensional "thermal-mechanical coupling" finite element model in step S1 sets the thermal physical parameters and mechanical performance parameters of the material as nonlinear functions varying with temperature.

5. The method of claim 1, wherein, The deformable substrate is a planar, curved or revolved thin-walled component with a thickness of 1-10 mm.

6. The method of claim 1, wherein, The "controllable mechanical loading method" in step S3 is to make the substrate produce elastic-plastic pre-deformation by mechanical force, hydraulic pressure or support clamps with predetermined profile.

7. The method of claim 1, wherein, The "non-rigid constraint condition" in step S4 refers to the clamping method of supporting the substrate as a simply supported beam, elastic support or only applying fixed constraint in the local area at the bottom of the substrate.

8. The method of claim 1, wherein, The cladding material used in the laser cladding step is titanium-based, nickel-based, cobalt-based, iron-based alloy or metal matrix composite material.

9. The method of claim 1, wherein, The laser cladding in step S4 is single or multi-pass cladding.

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