Laser cladding process method of thermal fatigue resistant multi-scale structure iron-based coating

Abstract

The invention discloses a laser cladding process method of a thermal fatigue resistant multi-scale structure iron-based coating. Comprising the following steps: (1) carrying out surface cleaning on a mold material by using a PA-EH dispersing agent, and removing dirt such as oil dirt on the surface; (2) weighing 12wt%-18wt% of tungsten carbide powder, 2wt% of oxide powder and the balance of iron-based alloy material powder; (3) ball-milling the mixed powder and drying; (4) setting process parameters, and carrying out laser cladding of a coating material on the surface of the mold; and (5) solid solution aging treatment. The method has the advantages that the mode that WC particles are wrapped with rare earth oxide YO is used, cladding is conducted on the surface of a mold through the rare earth oxide YO and an iron-based alloy material in a laser mode, a particle-grain boundary multi-scale crack propagation resisting structure is constructed, and transverse and longitudinal communicating pores are avoided; the thermal fatigue resistance of the surface of the coating grinding tool material is improved; and the high mixed entropy effect inhibits the formation of intermetallic compounds, so that the laser-cladded coating is compact in structure and stable in property.

Description

Technical Field

[0001] This invention relates to a laser cladding process for a multi-scale structured iron-based coating that resists thermal fatigue, belonging to the field of surface protection and additive repair technology for metallic materials. Background Technology

[0002] Traditional hot-working dies (such as die-casting dies and forging dies) are prone to thermal fatigue cracks under cyclic thermal shock at temperatures above 800℃, leading to coating peeling and insufficient lifespan. Existing improved iron-based cladding layers often employ single micron-sized carbides (such as WC) for reinforcement, making crack propagation along grain boundaries difficult to suppress. One existing improvement method involves directly changing the die material; however, this means replacing all existing dies made of the same material, which is too costly. Furthermore, the variety of die styles and the quality of the finished products require further verification. Laser cladding technology, as a highly efficient and reliable surface modification technique, is used for component surface treatment and protective coating preparation, achieving metallurgical bonding between the coating and the substrate. However, applying the coating material to the die surface is problematic. Because general coating materials contain a large amount of brittle hard phases, the rapid melting and solidification process of laser cladding makes them highly susceptible to cracking when applying multiple layers over a large area, limiting its application in practical improvement projects.

[0003] Furthermore, it has been found that in the field of laser cladding strengthening of mold surfaces, tungsten carbide (WC), with its ultra-high melting point (2870℃), extreme hardness (2200HV), and excellent wear resistance, forms an ideal composite structure with the alloy matrix, endowing the cladding layer with excellent resistance to high-temperature softening (>900℃) and abrasive wear, making it particularly suitable for high-temperature and high-pressure working environments such as die-casting molds and hot extrusion molds. However, this composite coating faces severe crack control challenges in large-area mold repair applications. Due to the significant difference in thermal expansion coefficients between the mold steel matrix (e.g., H13) and the cladding layer (Δα≈4×10-6 / K), the rapid laser melting process (cooling rate>10) presents significant challenges. 3 The high residual stress induced by K / s accumulates exponentially in multilayer stacking. When the repair area exceeds 100 mm², this becomes particularly pronounced. 2 When the mold collapses, repeated thermal cycling exacerbates the stress concentration effect between layers.

[0004] Simultaneously, the high-temperature environment of the laser (>1400℃) causes partial dissolution of WC particles, forming a brittle η phase (such as Fe6W6C, M) at the interface. 12(Type C carbides). These micron-sized brittle phases become preferential nucleation sites for cracks, and with the increase of the number of cladding layers, the interfacial reaction layer continues to expand, leading to a significant increase in crack susceptibility. In engineering practice, when the WC content increases to above 35 wt%, the crack incidence rate of the cladding layer in complex curved molds (such as deep cavity structures) soars to 70%, and the crack propagation depth can reach 80% of the layer thickness, severely restricting the overall reinforcement application of large molds. Current technologies are mostly limited to local repairs such as ejector pin holes. To achieve large-area crack-free cladding in mold cavities, it is necessary to overcome the dual constraints of thermal stress and interfacial reaction. Therefore, how to solve the above-mentioned technical problems has become an urgent technical challenge. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a laser cladding process for a multi-scale structured iron-based coating that can achieve complete surface strengthening of molds and resist thermal fatigue while ensuring wear resistance.

[0006] To solve the above-mentioned technical problems, the laser cladding process method for a multi-scale structure iron-based coating resistant to thermal fatigue of the present invention includes the following steps:

[0007] (1) Use PA-EH dispersant to clean the surface of the mold material to remove dirt such as oil stains;

[0008] (2) Weigh 12wt% to 18wt% of tungsten carbide powder, 2wt% of oxide powder and the balance of iron-based alloy material powder;

[0009] (3) Ball milling and drying the mixed powder; In this step, the metal element added to the iron-based alloy material also makes the surface of the tungsten carbide particles have an oxide layer of a certain thickness. The thickness of the oxide layer on the surface of the WC particles is 0.05μm to 1μm, and the tungsten carbide particles are spherical with an ellipticity of 1.2 to 1.8.

[0010] (4) Set process parameters and perform laser cladding of coating material on the mold surface;

[0011] (5) Solution aging treatment.

[0012] The oxide powder is rare earth oxide Y2O3, the particle size of which is 180-220 nm, and the particle size of which is tungsten carbide is 3-7 μm.

[0013] The iron-based alloy powder is FeCrNiCo, and the content of each element in the iron-based alloy powder FeCrNiCo is between 10% and 35%.

[0014] The metal element added to the iron-based alloy material is at least one of copper (Cu) or aluminum (Al).

[0015] The amount of the added metal element is 1-2% of the original alloy ratio.

[0016] In step (3), the weighed tungsten carbide powder and iron-based alloy powder FeCrNiCo are uniformly mixed using a ball mill. The mass ratio of ball to powder is 6:1, the mixing time is 1.2-1.5h, the ball mill speed is 500rpm, the environment is vacuum, and finally it is dried at 120℃ for 25min.

[0017] In step (4), the powder spreading and laser cladding on the mold surface are carried out simultaneously. The diameter of the light spot and the overlap are adjusted so that the powder spreading focal point and the laser focal point coincide. The powder spreading speed is adjusted to be synchronized with the laser scanning speed. The cooling gas flow rate and the cleaning gas flow rate are adjusted to carry out mixed powder cladding.

[0018] In step (4), the laser scanning speed is 5-10 mm / s, the powder spreading speed is 0.8-1.2 r / min, the cooling gas flow rate is 10-20 L / min, the cleaning gas flow rate is 5-15 L / min, the overlap rate between layers is 30%, the cladding thickness of each layer is ≤1.5 mm, and the laser power density is controlled at 80-120 J / mm². 2 Interlayer temperature ≤200℃.

[0019] In step (5), after cladding, the temperature is heated to 1050-1100℃; then cooled by water quenching or oil quenching; and aged for 620℃×1.5h.

[0020] The beneficial effects of this invention are:

[0021] (1) In this invention, rare earth oxide Y2O3 is used to encapsulate WC particles and clad the surface of the mold with iron-based alloy material under laser treatment to construct a multi-scale anti-crack propagation structure of particles-grain boundaries without transverse and longitudinal interconnected pores; the coating is crack-free and the surface of the coated abrasive material is improved in terms of thermal fatigue resistance.

[0022] (2) The high mixing entropy effect inhibits the formation of intermetallic compounds, promotes a single solid solution phase, and imparts a uniform microstructure and elemental distribution to the material, making the coating structure after laser cladding compact and the properties stable.

[0023] (3) Each cladding layer is ultrasonically treated and then subjected to solution aging treatment to finish. In this way, even if there are multiple layers, there is no residual stress, the thermal fatigue resistance is improved by more than 40%, and the wear resistance of the grinding wheel is enhanced.

[0024] (4) By overcoming thermal stress and interface reaction, it is possible to achieve large-area crack-free cladding of mold cavities with multiple sizes and structures. Attached Figure Description

[0025] Figure 1 A magnified schematic diagram showing that the WC particles coated with rare earth oxide are round or elliptical without sharp corners.

[0026] Figure 2 The result of PT non-destructive testing—crack detection—on the coating prepared on the aluminum-magnesium alloy surface in Example 3 (no cracks were generated);

[0027] Figure 3 This is a schematic diagram of the grain-grain boundary crack propagation resistant structure formed by the parameters in Example 1;

[0028] Figure 4 Comparison of fracture morphology of bent copper alloy substrate specimens after laser cladding and without laser cladding in Example 1; Detailed Implementation

[0029] The present invention will be further described below through specific embodiments. To make the inventive objectives, technical solutions, and beneficial technical effects of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the embodiments described in this specification are merely for explaining the present invention and are not intended to limit the present invention.

[0030] Unless otherwise stated, all films and reagents used in the examples are commercially available or synthesized using conventional methods and can be used directly without further processing. The instruments used in the examples are also commercially available. Molds used in common hot forging, extrusion, and die-casting applications are mostly made of copper alloys or aluminum-magnesium alloys; therefore, the substrate material selected for cladding in the following examples is one of these alloys.

[0031] The laser cladding process for a thermal fatigue-resistant multi-scale structured iron-based coating of the present invention includes the following steps:

[0032] (1) Use PA-EH dispersant to clean the surface of the mold material to remove dirt such as oil stains;

[0033] (2) Weigh 12wt% to 18wt% of tungsten carbide powder, 2wt% of oxide powder and the balance of iron-based alloy material powder; wherein, the oxide powder is rare earth oxide Y2O3, the particle size of Y2O3 is 180-220nm, and the particle size of tungsten carbide is 3-7μm.

[0034] (3) Ball mill the mixed powder and dry it;

[0035] In this step, the metal element added to the iron-based alloy material simultaneously gives the tungsten carbide particles a certain thickness of oxide layer on the surface. The thickness of the oxide layer on the surface of the WC particles is 0.05μm to 1μm, and the tungsten carbide particles are spherical with an ellipticity of 1.2 to 1.8.

[0036] In this iron-based alloy material, the added metallic element is at least one of copper (Cu) or aluminum (Al), and the amount of the added metallic element (Cu or Al) is 1-2% of the original alloy proportion (i.e., with the total amount unchanged, the proportion of the original alloy decreases accordingly when the metallic element increases). The iron-based alloy powder is FeCrNiCo, and the content of each element in the FeCrNiCo iron-based alloy material is 10%-35%, preferably Fe35Cr25Ni25Co15. Using the above technical solution, the multiple components of the alloy material can form a high mixing entropy, which is conducive to the formation of simple solid solutions. When metallic elements are added to the FeCrNiCo iron-based alloy material, its crystal structure will transform from face-centered cubic (FCC) to body-centered cubic (BCC), and the hardness will also increase accordingly. In addition, this addition can significantly improve the stacking fault energy of the alloy, thus having an important impact on the deformation mechanism of the alloy. When metallic elements (such as copper (Cu) or aluminum (Al) replace some elements in the original alloy, and the amount added is between 1% and 2%, the crystal structure of the alloy remains unchanged, but the yield strength and fracture strength are significantly improved. This is because Fe, Ni, Co, and Cr have similar atomic radii, while Cu or Al have larger atomic radii, thus resulting in substitution solid solution strengthening in the alloy.

[0037] During laser cladding, the iron-based alloy FeCrNiCo is sintered to form a high-entropy alloy. Due to the presence of multiple main elements, FeCrNiCo exhibits complex short-range order. During solidification, this short-range order causes "friction strengthening," which continuously affects the entire process of plastic deformation, thereby increasing the alloy's yield strength without reducing its plasticity. Furthermore, the varying atomic sizes of the elements result in severe lattice distortion in FeCrNiCo, leading to solid solution strengthening and giving it high hardness and strength.

[0038] (4) Set process parameters and perform laser cladding of coating material on the surface of iron-based mold substrate. In this step, the powder spreading and laser cladding on the mold surface are carried out simultaneously. Adjust the spot diameter and overlap to make the powder spreading focus position coincide with the laser focus position. Adjust the powder spreading speed and laser scanning speed to synchronize. Adjust the cooling gas flow rate and cleaning gas flow rate to perform mixed powder cladding. After each layer of cladding, ultrasonic impact treatment is used to eliminate residual stress.

[0039] (5) Solution aging treatment; In this step, after cladding, the temperature is heated to 1050-1100℃; the temperature is cooled by water quenching or oil quenching; the aging time is 620℃×1.5h; By adopting the above technical solution, the heating after cladding is a solution treatment, which can dissolve coarse carbides; then the temperature is rapidly cooled and maintained at 620℃ for 1.5h, which improves the thermal fatigue resistance by 40% and significantly enhances the wear resistance.

[0040] Using the above-described process, a laser cladding coating is applied to the surface of an iron-based alloy substrate. This coating consists of an iron-based alloy material and tungsten carbide (WC) particles. The iron-based alloy material undergoes aging treatment after the addition of metallic elements to form a certain number of small-angle grain boundaries. The WC particles are uniformly distributed within the iron-based alloy material as a dispersed strengthening phase. (That is, after adding metallic elements to the iron-based alloy material, mixing it with tungsten carbide (WC) powder, and performing laser cladding, further aging treatment is carried out, resulting in WC particles being uniformly distributed within the iron-based alloy material as a dispersed strengthening phase.) A certain number of small-angle grain boundaries are formed in the iron-based alloy material containing metallic elements, constructing a multi-scale anti-crack propagation structure of grains and grain boundaries; the pores in the coating are spherical, with a maximum pore size ≤10μm, and there are no transverse and longitudinal connected pores; the coating is crack-free, and the surface of the coated abrasive material has improved thermal fatigue resistance; among them, the WC particles are spherical to eliminate stress concentration caused by sharp corners, and the surface of the tungsten carbide WC particles has an oxide layer of a certain thickness to avoid excessive dissolution of the tungsten carbide WC particles by the molten iron-based alloy and cracking caused by carbonization of the binder phase.

[0041] Furthermore, in step (3), a ball mill is used to uniformly mix the weighed tungsten carbide powder (containing a rare earth oxide Y2O3 layer on the surface) and the iron-based alloy material powder FeCrNiCo. The mass ratio of ball to powder is 6:1, the mixing time is 1.2-1.5h, the ball mill speed is 500rpm, the environment is vacuum, and finally it is placed at 120℃ to dry for 25min.

[0042] Furthermore, in step (4), the laser scanning speed is 5-10 mm / s, the powder spreading speed is 0.8-1.2 r / min, the cooling gas flow rate is 10-20 L / min, the cleaning gas flow rate is 5-15 L / min, the overlap rate between passes (multi-pass cladding, referring to the overlap rate between each cladding layer) is 30%, the thickness of each cladding layer is ≤1.5 mm, and the laser power density is controlled at 80-120 J / mm². 2 Interlayer temperature ≤200℃.

[0043] The following examples illustrate its effectiveness:

[0044] Application Example 1:

[0045] (1) Use PA-EH dispersant to clean the surface of the copper alloy mold material to remove dirt such as oil stains.

[0046] (2) Weigh out 15wt% tungsten carbide WC powder, 2wt% rare earth oxide Y2O3 powder and the balance of iron-based alloy material FeCrNiCo powder;

[0047] (3) Tungsten carbide WC powder with a rare earth oxide Y2O3 layer on its surface was ball-milled and dried with iron-based alloy material FeCrNiCo powder; the ball-to-powder mass ratio was 6:1, the mixing time was 1.5h, the ball mill speed was 500rpm, the environment was vacuum, and finally it was dried at 120℃ for 25min; the surface of tungsten carbide WC particles had an oxide layer of a certain thickness, the thickness of the rare earth oxide Y2O3 layer on the surface of WC particles was 0.2μm, the WC particles were spherical, and the ellipticity was 1.2~1.8; the particle size of oxide Y2O3 was 200nm, and the particle size of tungsten carbide WC was 5μm; aluminum Al was added to the iron-based alloy material FeCrNiCo powder, and the amount added was 2% of the original alloy ratio;

[0048] (4) Set process parameters and perform laser cladding of coating material on the surface of the iron-based mold substrate; the powder spreading and laser cladding on the mold surface are carried out simultaneously. Adjust the spot diameter and overlap to make the powder spreading focal point coincide with the laser focal point. Adjust the powder spreading speed and laser scanning speed synchronously. Adjust the cooling gas flow rate and cleaning gas flow rate to perform mixed powder cladding. After each layer of cladding, ultrasonic impact treatment is used to eliminate residual stress. The laser scanning speed is 5-10 mm / s, the powder spreading speed is 0.8-1.2 r / min, the cooling gas flow rate is 10-20 L / min, the cleaning gas flow rate is 5-15 L / min, the overlap rate between layers is 30%, the thickness of each cladding layer is ≤1.5 mm, and the laser power density is controlled at 80-120 J / mm. 2 Interlayer temperature ≤200℃.

[0049] (5) After cladding, heat to 1050℃; cool by oil quenching; age at 620℃ for 1.5h.

[0050] Application Example 2:

[0051] (1) Use PA-EH dispersant to clean the surface of the copper alloy mold material to remove dirt such as oil stains;

[0052] (2) Weigh out 15wt% tungsten carbide WC powder, 2wt% rare earth oxide Y2O3 powder and the balance of iron-based alloy material FeCrNiCo powder;

[0053] (3) Tungsten carbide WC powder with a rare earth oxide Y2O3 layer on its surface was ball-milled and dried with iron-based alloy material FeCrNiCo powder; the ball-to-powder mass ratio was 6:1, the mixing time was 1.2 h, the ball mill speed was 500 rpm, the environment was vacuum, and finally it was dried at 120℃ for 25 min; the surface of tungsten carbide WC particles had an oxide layer of a certain thickness, the thickness of the rare earth oxide Y2O3 layer on the surface of WC particles was 0.2 μm, the WC particles were spherical, and the ellipticity was 1.2 to 1.8; the particle size of oxide Y2O3 was 200 nm, and the particle size of tungsten carbide WC was 5 μm; copper Cu was added to the iron-based alloy material FeCrNiCo powder, and the amount added was 1% of the original alloy ratio.

[0054] (4) Set process parameters and perform laser cladding of coating material on the mold surface; powder spreading and laser cladding on the mold surface are carried out simultaneously. Adjust the spot diameter and overlap to make the powder spreading focal point coincide with the laser focal point. Adjust the powder spreading speed and laser scanning speed synchronously. Adjust the cooling gas flow rate and cleaning gas flow rate to perform mixed powder cladding. After each layer of cladding, ultrasonic impact treatment is used to eliminate residual stress. The laser scanning speed is 5-10 mm / s, the powder spreading speed is 0.8-1.2 r / min, the cooling gas flow rate is 10-20 L / min, the cleaning gas flow rate is 5-15 L / min, the overlap rate between passes is 30%, the thickness of each cladding layer is ≤1.5 mm, and the laser power density is controlled at 80-120 J / mm. 2 Interlayer temperature ≤200℃.

[0055] (5) After cladding, heat to 1100℃; cool by water quenching; age at 620℃ for 1.5h.

[0056] Application Example 3:

[0057] (1) Use Henkel's BONDERITE C-AK305 to clean the surface of aluminum-magnesium alloy mold materials to remove oil and other dirt.

[0058] (2) Weigh out 15wt% tungsten carbide WC powder, 2wt% rare earth oxide Y2O3 powder and the balance of iron-based alloy material FeCrNiCo powder;

[0059] (3) Tungsten carbide WC powder with a rare earth oxide Y2O3 layer on its surface was ball-milled and dried with iron-based alloy material FeCrNiCo powder; the ball-to-powder mass ratio was 6:1, the mixing time was 1.4 h, the ball mill speed was 500 rpm, the environment was vacuum, and finally it was dried at 120℃ for 25 min; the surface of the tungsten carbide WC particles had an oxide layer of a certain thickness, the thickness of the rare earth oxide Y2O3 layer on the surface of the WC particles was 0.5 μm, the WC particles were spherical with an ellipticity of 1.2 to 1.8; the particle size of the oxide Y2O3 was 200 nm, and the particle size of the tungsten carbide WC was 5 μm; aluminum Al was added to the iron-based alloy material FeCrNiCo powder, and the amount added was 1% of the original alloy ratio;

[0060] (4) Set process parameters and perform laser cladding of coating material on the mold surface; powder spreading and laser cladding on the mold surface are carried out simultaneously. Adjust the spot diameter and overlap to make the powder spreading focal point coincide with the laser focal point. Adjust the powder spreading speed and laser scanning speed synchronously. Adjust the cooling gas flow rate and cleaning gas flow rate to perform mixed powder cladding. After each layer of cladding, ultrasonic impact treatment is used to eliminate residual stress. The laser scanning speed is 5-10 mm / s, the powder spreading speed is 0.8-1.2 r / min, the cooling gas flow rate is 10-20 L / min, the cleaning gas flow rate is 5-15 L / min, the overlap rate between passes is 30%, the thickness of each cladding layer is ≤1.5 mm, and the laser power density is controlled at 80-120 J / mm. 2 Interlayer temperature ≤200℃.

[0061] (5) After cladding, heat to 1100℃; cool by water quenching; age at 620℃ for 1.5h.

[0062] Application Example 4:

[0063] (1) Use Henkel's BONDERITE C-AK 305 to clean the surface of aluminum-magnesium alloy mold materials to remove oil and other dirt.

[0064] (2) Weigh out 15wt% tungsten carbide WC powder, 2wt% rare earth oxide Y2O3 powder and the balance of iron-based alloy material FeCrNiCo powder;

[0065] (3) Tungsten carbide WC powder with a rare earth oxide Y2O3 layer on its surface was ball-milled and dried with iron-based alloy material FeCrNiCo powder; the ball-to-powder mass ratio was 6:1, the mixing time was 1.3 h, the ball mill speed was 500 rpm, the environment was vacuum, and finally it was dried at 120℃ for 25 min; the surface of the tungsten carbide WC particles had an oxide layer of a certain thickness, the thickness of the rare earth oxide Y2O3 layer on the surface of the WC particles was 0.05 μm, the WC particles were spherical, and the ellipticity was 1.2 to 1.8; the particle size of the oxide Y2O3 was 200 nm, and the particle size of the tungsten carbide WC was 5 μm; copper Cu was added to the iron-based alloy material FeCrNiCo powder, and the amount added was 2% of the original alloy ratio.

[0066] (4) Set process parameters and perform laser cladding of coating material on the mold surface; powder spreading and laser cladding on the mold surface are carried out simultaneously. Adjust the spot diameter and overlap to make the powder spreading focal point coincide with the laser focal point. Adjust the powder spreading speed and laser scanning speed synchronously. Adjust the cooling gas flow rate and cleaning gas flow rate to perform mixed powder cladding. After each layer of cladding, ultrasonic impact treatment is used to eliminate residual stress. The laser scanning speed is 5-10 mm / s, the powder spreading speed is 0.8-1.2 r / min, the cooling gas flow rate is 10-20 L / min, the cleaning gas flow rate is 5-15 L / min, the overlap rate between passes is 30%, the thickness of each cladding layer is ≤1.5 mm, and the laser power density is controlled at 80-120 J / mm. 2 Interlayer temperature ≤200℃.

[0067] (5) After cladding, heat to 1050℃; cool by oil quenching; age at 620℃ for 1.5 hours.

[0068] In Application Examples 1-4, the thickness of the rare earth oxide Y2O3 layer on the surface of tungsten carbide (WC), the ball milling mixing time, the solution aging treatment method after cladding, different mold materials (such as aluminum-magnesium alloys and copper alloys), and the addition of copper or aluminum to the iron-based alloy FeCrNiCo, with adjustments to the amount added, were investigated to examine the effects of these parameters on the properties. The results are shown in the table below:

[0069]

[0070] Data from Application Examples 1-4 show that the mold substrate treated with laser cladding has a thermal fatigue resistance that is improved by more than 40%, a crack resistance that is significantly improved, and an impact hardness resistance that is also significantly improved.

[0071] In addition, from Figure 1 As can be seen, the surface of tungsten carbide (WC) particles has a certain thickness of rare earth oxide (Y2O3) layer, and the WC particles are spherical, which can eliminate stress concentration caused by sharp corners. Figure 2 The results show that after the laser cladding process of the present invention, no cracks were generated when the coating on the surface of the mold was subjected to PT non-destructive testing - crack detection, and the crack resistance was improved.

[0072] Figure 3 Iron-based alloy matrix: Light gray area, showing the contours of small-angle grain boundaries formed after the addition of metallic elements and aging treatment. Small-angle grain boundaries: Fine black lines, indicating that cracks are easily deflected or branched when they encounter grain boundaries, effectively inhibiting straight propagation. WC particles: Dark gray spherical dispersed phase, the spherical shape avoids stress concentration, and the particle surface is covered with an oxide layer to prevent excessive dissolution by the molten matrix. Spherical pores (≤10um): White circles, with a maximum size not exceeding 10μm, and not connected laterally or longitudinally, reducing straight crack propagation channels. Crack propagation path: Black zigzag lines, indicating the repeated deflection and passivation process of cracks around multi-scale interfaces and particles.

[0073] This structure, through the multi-scale interaction between particles and grain boundaries, continuously deflects the crack propagation path and dissipates energy, thereby significantly improving the coating's resistance to thermal fatigue.

[0074] from Figure 4 It can be seen that the fracture surface of the mold alloy substrate treated with laser cladding coating has a large number of dimples and a small number of cleavage facets. Both indicate a micropore aggregation fracture, suggesting good alloy plasticity. In contrast, the fracture surface of the alloy substrate without laser cladding coating shows numerous cleavage surfaces with tearing edges, and small, shallow dimples around these surfaces. Therefore, the fracture type of both is generally classified as quasi-cleavage fracture. This indicates that the plasticity of the mold alloy substrate treated with laser cladding coating is reduced compared to that without, but it still retains a certain degree of plasticity. Furthermore, the improved mold alloy substrate exhibits increased hardness without sacrificing toughness.

[0075] In summary, the laser cladding process for the thermal fatigue resistant multi-scale structure iron-based coating disclosed in this invention has the advantages of convenient process steps, effective stress elimination, promotion of a single solid solution phase, imparting uniform microstructure and elemental distribution to the material, and significantly improving the performance of the resulting mold substrate in all aspects.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser cladding process for a thermal fatigue-resistant multi-scale iron-based coating, comprising the following steps: (1) Use PA-EH dispersant to clean the surface of the mold material to remove dirt such as oil stains; (2) Weigh 12wt% to 18wt% of tungsten carbide powder, 2wt% of oxide powder and the balance of iron-based alloy material powder; (3) Ball milling and drying the mixed powder; In this step, the metal element added to the iron-based alloy material also makes the surface of the tungsten carbide particles have an oxide layer of a certain thickness. The thickness of the oxide layer on the surface of the WC particles is 0.05μm to 1μm, and the tungsten carbide particles are spherical with an ellipticity of 1.2 to 1.

8. (4) Set process parameters and perform laser cladding of coating material on the mold surface; (5) Solution aging treatment.

2. The laser cladding process for a thermal fatigue-resistant multi-scale iron-based coating according to claim 1, characterized in that: The oxide powder is rare earth oxide Y2O3, the particle size of which is 180-220 nm, and the particle size of which is tungsten carbide is 3-7 μm.

3. The laser cladding process for a thermal fatigue-resistant multi-scale iron-based coating according to claim 1, characterized in that: The iron-based alloy powder is FeCrNiCo, and the content of each element in the iron-based alloy powder FeCrNiCo is between 10% and 35%.

4. The laser cladding process for a thermal fatigue-resistant multi-scale iron-based coating according to claim 1, characterized in that: The metal element added to the iron-based alloy material is at least one of copper (Cu) or aluminum (Al).

5. The laser cladding process for a thermal fatigue-resistant multi-scale iron-based coating according to claim 1, characterized in that: The amount of the added metal element is 1-2% of the original alloy ratio.

6. The laser cladding process for a thermal fatigue-resistant multi-scale iron-based coating according to claim 1, characterized in that: In step (3), the weighed tungsten carbide powder and iron-based alloy powder FeCrNiCo are uniformly mixed using a ball mill. The mass ratio of ball to powder is 6:1, the mixing time is 1.2-1.5h, the ball mill speed is 500rpm, the environment is vacuum, and finally it is dried at 120℃ for 25min.

7. The laser cladding process for a thermal fatigue-resistant multi-scale iron-based coating according to claim 1, characterized in that: In step (4), the powder spreading and laser cladding on the mold surface are carried out simultaneously. The diameter of the light spot and the overlap are adjusted so that the powder spreading focal point and the laser focal point coincide. The powder spreading speed is adjusted to be synchronized with the laser scanning speed. The cooling gas flow rate and the cleaning gas flow rate are adjusted to carry out mixed powder cladding.

8. The laser cladding process for a thermal fatigue-resistant multi-scale structured iron-based coating according to claim 7, characterized in that: In step (4), the laser scanning speed is 5-10 mm / s, the powder spreading speed is 0.8-1.2 r / min, the cooling gas flow rate is 10-20 L / min, the cleaning gas flow rate is 5-15 L / min, the overlap rate between layers is 30%, the cladding thickness of each layer is ≤1.5 mm, and the laser power density is controlled at 80-120 J / mm². 2 Interlayer temperature ≤200℃.

9. The laser cladding process for a thermal fatigue-resistant multi-scale iron-based coating according to claim 1, characterized in that: In step (5), after cladding, the temperature is heated to 1050-1100℃; the temperature is cooled by water quenching or oil quenching; and the aging time is 620℃×1.5h.

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