High wear-resistant chromium oxide-nanodiamond composite coating and laser remelting preparation method thereof

Abstract

This invention provides a high-wear-resistant chromium oxide-nanodiamond composite coating and its laser remelting preparation method, relating to the field of thermal spray coatings. The method includes: Step 1, preparing a porous framework: using thermal spraying technology, a chromium oxide-based coating is deposited on the substrate surface, achieving a porosity of 8%-20%, with interconnected pores predominating; Step 2, nanodiamond infiltration: the coating obtained in Step 1 is immersed in a nanodiamond suspension, and vacuum-assisted or pressure-assisted infiltration is applied to fill the pores of the coating with nanodiamonds; Step 3, laser remelting and densification: a laser beam is used to scan and remelt the infiltrated coating, causing localized melting and densification of the coating surface, thereby constructing a porous chromium oxide underlayer and a dense composite surface layer. This method overcomes the technical bias of diamond ablation caused by high laser temperature, achieves the retention and interfacial bonding of nanodiamonds, and solves the problem of easy cracking in traditional dense coatings.

Description

Technical Field

[0001] This invention relates to the field of thermal spray coating technology, and in particular to a high wear-resistant chromium oxide-nanodiamond composite coating and its laser remelting preparation method. Background Technology

[0002] Chromium oxide (Cr2O3) coatings, due to their high hardness, excellent wear resistance, and good corrosion resistance, are widely used for surface protection of critical friction components such as mechanical seals and printing rollers. Currently, industrial applications primarily employ thermal spraying technologies such as atmospheric plasma spraying to prepare chromium oxide-based coatings. In traditional coating design, porosity is generally considered the main defect weakening the coating's mechanical properties and protective function. Therefore, in existing technologies, most efforts in this field focus on controlling the coating porosity to a low level of 1%–5% by optimizing spraying process parameters, selecting fine-grained powders, or adding specific modifying phases, thereby obtaining a dense microstructure.

[0003] However, in practical applications, existing technologies have gradually revealed the following technical bottlenecks: First, obtaining low-porosity coatings is highly dependent on equipment precision and operational experience, making production difficult. Second, excessively dense coatings often accumulate significant thermal and residual stresses, easily triggering the initiation and propagation of microcracks, leading to coating cracking or large-area peeling and a short service life. Third, relying solely on component control (such as adding TiO2, SiO2, etc. to form a Cr2O3-based multi-component system) to improve hardness and wear resistance has reached its limit, making it difficult to further enhance these properties. Furthermore, existing post-sealing techniques treat pores as defect channels that need to be sealed, often using chemical reagents such as chromates, phosphates, or organic resins for surface sealing to block the penetration path of corrosive media. This results in weak adhesion between the sealing layer and the substrate, making it prone to premature failure under harsh wear conditions.

[0004] Finally, although nanodiamonds have extremely high hardness, excellent thermal conductivity and self-lubricating properties, making them an ideal coating reinforcement phase, existing technologies usually use them to directly mix into spray powder or to form composite coatings in one step by laser cladding.

[0005] The applicant has discovered at least the following problems in the prior art: On the one hand, the nanoparticles are prone to agglomeration in the high-temperature plasma flame or molten pool, making it difficult to achieve uniform dispersion; on the other hand, the high-temperature thermal process of laser or plasma can easily cause diamond to be graphitized or oxidized and ablated, failing to meet the dual requirements of effective preservation of the nanophase and densification of the coating, which seriously restricts the realization of its wear resistance enhancement potential.

[0006] In summary, existing chromium oxide-based coating technologies are generally limited by the traditional understanding that "the lower the porosity, the better," resulting in significant shortcomings in terms of process stability and internal stress control. How to break through the traditional mindset of densification and develop new coating preparation methods with high hardness and good wear resistance has become a pressing technical challenge in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a high wear-resistant chromium oxide-nanodiamond composite coating and its laser remelting preparation method, so as to solve the technical problem that the preparation methods of chromium oxide-based coatings in the prior art are difficult to obtain coatings with high hardness and good wear resistance. The various technical effects of the preferred technical solutions provided by this invention are described in detail below.

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

[0009] The present invention provides a laser remelting method for preparing a high wear-resistant chromium oxide-nanodiamond composite coating, the method comprising: Step 1, preparing a porous framework: using thermal spraying technology, a chromium oxide-based coating is deposited on the substrate surface, so that the porosity of the chromium oxide-based coating is 8%-20%, and the pores are mainly interconnected pores; Step 2, nanodiamond infiltration: Immerse the coating obtained in Step 1 in a nanodiamond suspension, and apply vacuum-assisted infiltration or pressure-assisted infiltration to allow the nanodiamonds to fill the pores of the coating. Step 3, laser remelting and densification: A laser beam is used to scan and remelt the penetrated coating, causing localized melting and densification of the coating surface, thereby constructing a porous chromium oxide underlayer and a dense composite surface layer. The porous chromium oxide substrate has a connected pore structure, and the dense composite surface layer is disposed on the porous chromium oxide substrate. The dense composite surface layer includes a chromium oxide matrix and nanodiamond particles. The interior of the chromium oxide matrix has a porous structure, and the nanodiamond particles fill the porous structure. The porosity of the dense composite surface layer is less than that of the porous chromium oxide substrate.

[0010] Preferably, the chromium oxide-based coating in step one is a Cr2O3 coating, or a composite coating composed of Cr2O3 and at least one modified oxide, wherein the modified oxide is selected from one or more of TiO2, SiO2, and ZrO2.

[0011] Preferably, the substrate is pretreated by sandblasting before step one; In step one, the thermal spraying is atmospheric plasma spraying, and the spraying process parameters are: spraying power 30-45kW, spraying distance 80-120mm, main gas flow rate 40-60L / min, auxiliary gas flow rate 5-15L / min, and powder feeding rate 30-60g / min.

[0012] Preferably, in step one, the porosity of the interconnected pore structure is 10%-15%, and the pore diameter is 50nm-500nm.

[0013] Preferably, in step two, the particle size of the nanodiamond particles is 10-50 nm; the components of the suspension include nanodiamond, dispersant and deionized water, wherein the mass percentage of nanodiamond is 5%-15% and the mass percentage of dispersant is 0.5%-2%.

[0014] Preferably, the dispersant is one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, or polyethylene glycol.

[0015] Preferably, in step two, the vacuum degree of the vacuum-assisted permeation is -0.08MPa to -0.1MPa, and the pressure holding time is 10-30 minutes; the pressure of the pressure-assisted permeation is 0.2-0.6MPa, and the pressure holding time is 5-20 minutes.

[0016] Preferably, in step three, the laser remelting is carried out under the protection of an inert gas, which is argon or nitrogen. The laser remelting parameters are: laser power 200-800W, scanning speed 5-20mm / s, spot diameter 1-3mm, and overlap rate 30%-50%.

[0017] Preferably, in step three, the depth of the dense composite surface layer is controlled to be 30%-70% of the total coating thickness.

[0018] The present invention also provides a high wear-resistant chromium oxide-nanodiamond composite coating, which is prepared by the laser remelting preparation method of the above-mentioned high wear-resistant chromium oxide-nanodiamond composite coating.

[0019] The high wear-resistant chromium oxide-nanodiamond composite coating and its laser remelting preparation method provided by this invention have the following advantages compared with existing technologies: This laser remelting preparation method overturns the traditional understanding that "the lower the porosity, the better," combining the three-step process of "pore formation, penetration, and laser remelting," and overcomes the technical bias of diamond ablation caused by high laser temperature, achieving effective retention and interfacial bonding of nanodiamonds. The high wear-resistant chromium oxide-nanodiamond composite coating structure prepared by this method has a dense composite surface containing nanodiamond particles, resulting in a coating hardness of over 1700 HV and improved wear resistance compared to traditional chromium oxide coatings. In the overall structure, the dense composite surface provides high hardness and high wear resistance, while the porous chromium oxide underlayer provides toughness buffering, effectively solving the problem of easy cracking in traditional dense coatings. The porosity change between the porous chromium oxide underlayer and the dense composite surface can effectively release internal stress in the coating, improving the service life of the coating. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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 This is a flowchart of a laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating; Figure 2 This is a schematic cross-sectional view of the high wear-resistant chromium oxide-nanodiamond composite coating structure; Figure 3 This is a schematic diagram of a dense composite surface.

[0022] In the figure: 1. Substrate; 2. Porous chromium oxide bottom layer; 21. Circulating pore structure; 3. Transition layer; 4. Dense composite surface layer; 41. Chromium oxide matrix; 42. Porous structure; 5. Nanodiamond particles. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] In the description of this invention, it should be understood that the terms "center," "length," "width," "height," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and "side," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0025] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] While nanodiamonds possess extremely high hardness, excellent thermal conductivity, and self-lubricating properties, making them ideal coating reinforcement phases, current technologies typically employ direct mixing with spray powders or one-step laser cladding to prepare composite coatings. However, these existing methods suffer from two main drawbacks. First, nanoparticles readily agglomerate in high-temperature plasma flames or molten pools, making uniform dispersion difficult. Second, the high-temperature thermal processes of lasers or plasmas easily lead to graphitization or oxidative ablation of the diamond, failing to simultaneously address the dual requirements of effective preservation of the nanophase and coating densification, thus severely limiting their potential for wear-resistant enhancement.

[0027] In summary, existing chromium oxide-based coating technologies are generally limited by the traditional understanding that "the lower the porosity, the better," resulting in significant shortcomings in terms of process stability and internal stress control. How to break through the traditional mindset of densification and develop new coating preparation methods with high hardness and good wear resistance has become a pressing technical challenge in this field.

[0028] To address the above problems, embodiments of the present invention provide a high wear-resistant chromium oxide-nanodiamond composite coating and its laser remelting preparation method.

[0029] The following is combined Figures 1-3 The technical solution provided by this invention will be described in more detail below.

[0030] Example 1 like Figures 1-3As shown, this invention provides a laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating. The method comprises: Step 1, preparing a porous framework: using thermal spraying technology, depositing a chromium oxide-based coating on the surface of a substrate 1, such that the porosity of the chromium oxide-based coating is 8%-20%, and the pores are mainly interconnected pores; Step 2, nanodiamond infiltration: immersing the coating obtained in Step 1 into a nanodiamond suspension, applying vacuum-assisted infiltration or pressure-assisted infiltration to allow the nanodiamonds to fill the pores of the coating; Step 3, laser remelting densification: using laser... The infiltrated coating is scanned and remelted, causing localized melting and densification of the coating surface, thereby constructing a porous chromium oxide underlayer 2 and a dense composite surface layer 4. The porous chromium oxide underlayer 2 has a connected pore structure 21, and the dense composite surface layer 4 is disposed on the porous chromium oxide underlayer 2. The dense composite surface layer 4 includes a chromium oxide matrix 41 and nanodiamond particles 5. The interior of the chromium oxide matrix 41 is provided with a porous structure 42, and the nanodiamond particles 5 fill the porous structure 42. The porosity of the dense composite surface layer 4 is less than that of the porous chromium oxide underlayer 2.

[0031] The aforementioned porous framework refers to a chromium oxide-based coating with a certain porosity and interconnected pore structure 21, which is pre-prepared on the surface of the substrate 1 using thermal spraying technology, and serves as a carrier for the subsequent infiltration of nanodiamond particles 5.

[0032] Nanodiamond suspension refers to a stable dispersion system formed by uniformly dispersing diamond particles with a particle size at the nanoscale in a liquid medium, which is used to introduce nanodiamonds into the interior of a porous framework.

[0033] The porous chromium oxide underlayer 2 refers to the layer in the composite coating that is close to the substrate 1. It retains the interconnected pore structure 21 of the original porous skeleton and is mainly composed of chromium oxide.

[0034] See Figure 1 This invention reverses the technical bias of existing technologies that "pursue low porosity" and adopts a reverse process route of "first constructing a porous framework, then infiltrating with nano-functional materials, and then laser remelting for densification". It transforms pores from "defects" into "functional carriers" and achieves coating densification and interface metallurgical bonding through laser remelting, ultimately obtaining a composite coating with high hardness, high wear resistance and good bonding strength.

[0035] See Figure 2 and Figure 3The high wear-resistant chromium oxide-nanodiamond composite coating structure prepared by this method contains nanodiamond particles 5 in the dense composite surface layer 4, which enables the coating hardness to reach above 1700 HV and improves wear resistance compared with traditional chromium oxide coatings. In the overall structure, the dense composite surface layer 4 provides high hardness and high wear resistance, while the porous chromium oxide bottom layer 2 provides toughness buffer, effectively solving the problem of easy cracking of traditional dense coatings. The porosity change between the porous chromium oxide bottom layer 2 and the dense composite surface layer 4 can effectively release the internal stress of the coating and improve the service life of the coating.

[0036] As an optional implementation, the chromium oxide-based coating in step one is a Cr2O3 coating, or a composite coating composed of Cr2O3 and at least one modified oxide, wherein the modified oxide is selected from one or more of TiO2, SiO2, and ZrO2.

[0037] Cr2O3 possesses high hardness and wear resistance. Introducing modified oxides further optimizes the coating's toughness, thermal shock resistance, and interfacial bonding with nanodiamonds. This makes the porous framework less prone to structural damage when subjected to nanodiamond suspension infiltration, and allows for localized melting and densification during laser remelting. This facilitates the formation of a highly wear-resistant chromium oxide-nanodiamond composite coating with excellent mechanical properties, high density, and a longer service life.

[0038] The laser remelting method for preparing a high wear-resistant chromium oxide-nanodiamond composite coating in this embodiment involves first depositing a chromium oxide-based coating on the surface of a substrate 1 using thermal spraying technology to form a porous framework with a specific porosity and interconnected pore structure 21. Then, the coating is immersed in a nanodiamond suspension for infiltration, allowing the nanodiamonds to fill the pores of the coating. Finally, a laser beam is used to scan and remelt the infiltrated coating to achieve local melting and densification of the coating surface, thereby constructing a porous chromium oxide underlayer 2 and a dense composite surface layer 4.

[0039] However, if the spraying process parameters are not properly selected during the preparation of the porous skeleton using thermal spraying technology, it may lead to uneven pore structure and poor pore connectivity in the coating, and even affect the bonding strength between the coating and the substrate 1, thus affecting the effective penetration of the subsequent nanodiamond particles 5 and the performance of the final composite coating.

[0040] As an optional implementation, see Figure 1 Before step one, the substrate 1 is pretreated by sandblasting to roughen it. In step one, the thermal spraying is atmospheric plasma spraying. The spraying process parameters are: spraying power 30-45kW, spraying distance 80-120mm, main air flow rate 40-60L / min, auxiliary air flow rate 5-15L / min, and powder feeding rate 30-60g / min.

[0041] The aforementioned parameters enable the preparation of a chromium oxide-based coating with a specific porosity (8%-20%) and predominantly interconnected pores on the surface of substrate 1. This results in a more uniform and interconnected pore structure within the coating, facilitating improved filling efficiency and uniformity of subsequent nanodiamond deposition. Furthermore, these spraying parameters also contribute to enhanced bonding strength between the coating and substrate 1, reducing coating defects.

[0042] As an optional implementation, see Figure 1 In step one, the porosity of the coating is 10%-15%, and the pore size of the pores in the interconnected pore structure 21 is 50nm-500nm.

[0043] If the porosity is below 10%, the interconnected pore structure 21 inside the coating may not be sufficient to accommodate a adequate amount of nanodiamond suspension, affecting the penetration and filling of nanodiamond particles 5, resulting in a low nanodiamond content in the final composite coating and failing to fully exert its structural reinforcement effect. Conversely, if the porosity is above 15%, although it is beneficial for the penetration of nanodiamond suspension, it may weaken the mechanical strength and integrity of the porous framework, making it prone to structural collapse or cracking during subsequent processing (such as laser remelting), affecting the quality and performance of the final coating. Therefore, controlling the porosity within the range of 10%-15% can ensure sufficient penetration space while maintaining the necessary strength of the coating framework.

[0044] When the pore size of the interconnected pore structure 21 is <50nm, capillary resistance increases dramatically and it is easily blocked by nanoparticle aggregates, resulting in insufficient penetration depth. When the pore size of the interconnected pore structure 21 is >500nm, the specific surface area drops sharply, and the mechanical interlocking force between the particles and the pore wall and the subsequent metallurgical bonding area are significantly weakened. The pore size of the interconnected pore structure 21 in the range of 50nm-500nm can ensure the deep and uniform filling of the nanodiamond suspension under vacuum / pressure assistance.

[0045] As an optional implementation, see Figure 1 In step two, the nanodiamond particles 5 have a particle size of 10-50 nm. Overly large nanodiamond particles 5 may have difficulty penetrating the smaller interconnected pores in the porous framework, leading to insufficient penetration; overly small particles may easily agglomerate in the suspension or be difficult to maintain stability in subsequent processing. The 10-50 nm particle size of the nanodiamond particles ensures that the nanodiamond particles 5 can effectively penetrate into the porous structure 42 while maintaining good dispersibility and stability, facilitating the formation of a uniform and dense composite coating.

[0046] The suspension in this embodiment comprises nanodiamonds, a dispersant, and deionized water, wherein the mass percentage of nanodiamonds is 5%-15% and the mass percentage of the dispersant is 0.5%-2%.

[0047] Deionized water, as a solvent, provides the medium for the dispersion and transport of nanodiamonds. The dispersant's role is to reduce the van der Waals forces between nanodiamond particles, preventing their aggregation and sedimentation, thereby improving the stability of the suspension and the uniform dispersion of nanodiamonds in the liquid, ensuring that nanodiamonds can effectively penetrate into the coating pores in the form of single particles or small clusters.

[0048] As an optional implementation, the dispersant is one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, or polyethylene glycol.

[0049] The aforementioned dispersant can improve the dispersion uniformity and stability of nanodiamond particles 5 in suspension. By providing effective electrostatic repulsion or steric hindrance, the dispersant inhibits the aggregation and sedimentation of nanodiamond particles 5, ensuring that nanodiamonds can penetrate into the porous structure 42 more quickly, thereby improving the filling efficiency and distribution uniformity of nanodiamond particles 5.

[0050] As an optional implementation, in step two, the vacuum degree of vacuum-assisted permeation is -0.08MPa to -0.1MPa, and the pressure holding time is 10-30 minutes; the pressure of pressure-assisted permeation is 0.2-0.6MPa, and the pressure holding time is 5-20 minutes.

[0051] By generating a sufficient negative pressure difference, the nanodiamond suspension is effectively drawn into the porous structure 42, while the air trapped in the pores is expelled at the same time, which facilitates the full penetration of the nanodiamond particles 5.

[0052] As an optional implementation, in step three, laser remelting is carried out under the protection of an inert gas, which is argon or nitrogen; the laser remelting parameters are: laser power 200-800W, scanning speed 5-20mm / s, spot diameter 1-3mm, and overlap rate 30%-50%.

[0053] Laser remelting under inert gas protection effectively prevents the coating from reacting with reactive gases such as oxygen and nitrogen in the air during high-temperature melting, thereby inhibiting the formation of oxides and the graphitization or decomposition of nanodiamond particles 5, ensuring the chemical stability and structural integrity of the composite coating.

[0054] As an optional implementation, in step three, the depth of the dense composite surface layer 4 is controlled to be 30%-70% of the total coating thickness.

[0055] The aforementioned depth of the dense composite surface layer 4 ensures that the coating surface has a sufficiently thick, dense, and high-hardness composite layer, thereby providing excellent wear resistance and effectively extending the service life of the coating. Furthermore, it avoids excessive thermal stress caused by an excessively thick dense layer, significantly reducing the risk of coating cracking and peeling, and improving the integrity and reliability of the coating.

[0056] In addition, a sufficiently thick porous chromium oxide underlayer 2 is retained, which allows it to continue to play a stress buffering role, further enhancing the bonding strength and fatigue resistance between the coating and the substrate 1.

[0057] The above structure allows the composite coating to maintain high wear resistance while also taking into account good toughness and adhesion.

[0058] For details, see Figure 1 This embodiment provides a method for preparing a high wear-resistant chromium oxide-nanodiamond composite coating, including the following steps: Step 1: Preparation of the porous framework. 45# steel was used as the substrate 1, and the surface was roughened by sandblasting. Atmospheric plasma spraying equipment was used, with Cr2O3 powder as the spraying powder. The spraying process parameters were: power 38kW, spraying distance 100mm, main gas (Ar) flow rate 50L / min, auxiliary gas (H2) flow rate 10L / min, and powder feed rate 45g / min. The resulting coating thickness was approximately 200μm, with a porosity of 12%, and the pores were interconnected, with a pore size of approximately 100-300nm.

[0059] Step Two: Nanodiamond Infiltration. A suspension was prepared by mixing 20nm nanodiamond powder with sodium carboxymethyl cellulose and deionized water at a mass ratio of 10:1:89, and ultrasonically dispersed for 30 minutes. The coating obtained in Step One was then immersed in the suspension, and a vacuum was drawn to -0.09MPa and maintained for 20 minutes to allow the nanodiamonds to fully infiltrate the coating pores. After removal, it was dried at 80℃ for 1 hour.

[0060] Step 3: Laser remelting and densification. A fiber laser is used to scan and remelt the penetrated coating under argon protection. Laser parameters: power 500W, scanning speed 12mm / s, spot diameter 2mm, overlap rate 40%. The remelted layer depth is approximately 80μm (accounting for 40% of the coating thickness).

[0061] Performance testing: The coating porosity was determined to be 0.8% using image analysis; the hardness was measured using a Vickers hardness tester with a load of 300g and a holding time of 15s, yielding an average hardness of 1720HV; the bond strength was determined to be 85MPa using the tensile method; and wear testing was conducted using a pin-disc friction and wear testing machine with GCr15 steel balls as the wear material, a load of 50N, a rotation speed of 200r / min, and a time of 30min, resulting in a wear amount that was 23% of that of a traditional dense chromium oxide coating (porosity 3%, hardness 1200HV).

[0062] Example 2 This embodiment is basically the same as Embodiment 1, except that the powder sprayed in step one is a Cr2O3-5%TiO2 composite powder. The spraying process parameters are adjusted as follows: power 35kW, spraying distance 90mm, main gas flow rate 45L / min, auxiliary gas flow rate 8L / min, and powder feed rate 40g / min. The porosity of the resulting coating is 15%.

[0063] After undergoing the same infiltration and laser remelting, the coating porosity is 0.9%, the hardness is 1750 HV, the bonding strength is 82 MPa, and the wear is 21% of that of traditional dense coatings.

[0064] Example 3 This embodiment is basically the same as Embodiment 1, except that in step three, the laser power is adjusted to 300W, the scanning speed is adjusted to 10mm / s, and the remelted layer depth is approximately 60μm. The final coating has a porosity of 1.0%, a hardness of 1680HV, a bonding strength of 78MPa, and a wear rate of 28% compared to traditional dense coatings.

[0065] Comparative Example 1 A dense Cr2O3 coating was prepared using a traditional process with a spraying power of 45 kW, a spraying distance of 80 mm, a main gas flow rate of 40 L / min, an auxiliary gas flow rate of 12 L / min, and a powder feed rate of 35 g / min. The resulting coating had a porosity of 3%, a hardness of 1200 HV, a bonding strength of 45 MPa, and a wear rate of 100% as a baseline.

[0066] Comparative Example 2 Using the same porous framework as in Example 1, but without nanodiamond infiltration, laser remelting was performed directly (parameters same as in Example 1). The resulting coating had a porosity of 0.7%, a hardness of 1350 HV, a bonding strength of 70 MPa, and a wear rate of 65% compared to traditional dense coatings.

[0067] Comparative Example 3 Using the same porous framework as in Example 1, nanodiamond infiltration was performed (same as in Example 1), but without laser remelting, only low-temperature curing (500°C, 2 hours). The resulting coating had a porosity of 5.2%, a hardness of 1420 HV, a bonding strength of 48 MPa, and a wear rate of 58% compared to traditional dense coatings.

[0068] See the table below for specific comparison data.

[0069] Table 1. Comparison of specific parameters between Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3

[0070] As can be seen from the above embodiments and comparative examples, the present invention successfully prepared a composite coating with a porosity ≤1%, hardness ≥1680HV, and bonding strength ≥78MPa through a three-step method of "pore-forming-penetration-laser remelting," reducing wear by more than 70% compared to traditional dense chromium oxide coatings. Compared with simple laser remelting (Comparative Example 2) or only penetration low-temperature curing (Comparative Example 3), the synergistic effect of the present invention is significant, fully demonstrating the superiority and inventiveness of the technical solution.

[0071] See Figure 2 and Figure 3 As shown, this embodiment provides a high wear-resistant chromium oxide-nanodiamond composite coating, which is prepared by the laser remelting preparation method of the high wear-resistant chromium oxide-nanodiamond composite coating of the above embodiment.

[0072] The high wear-resistant chromium oxide-nanodiamond composite coating of this embodiment not only has excellent overall bonding strength, but also forms a high-hardness and high-wear-resistant composite layer on the surface, which significantly improves the coating's ability to resist abrasive wear and erosion wear, extends its service life, and broadens its application range under harsh working conditions.

[0073] like Figure 1 and Figure 2 As shown, a transition layer 3 is provided between the porous chromium oxide underlayer 2 and the dense composite surface layer 4. The porosity of the transition layer 3 is between that of the porous chromium oxide underlayer 2 and the dense composite surface layer 4, and the porosity of the transition layer 3 gradually decreases along the direction close to the dense composite surface layer 4.

[0074] The porous chromium oxide bottom layer 2, the transition layer 3, and the dense composite surface layer 4 gradually transition from 12% porosity in the bottom layer to less than 1% porosity in the surface layer, forming a gradient structure to achieve a smooth transition in mechanical properties and avoid abrupt changes in the hard-brittle interface.

[0075] The formation mechanism of transition layer 3 is as follows: During laser remelting, the laser beam energy decays exponentially along the coating depth direction, and the molten pool boundary is not a knife-cut flat interface; the surface layer completely absorbs the laser energy, undergoes full melting and rapid solidification, forming a dense composite layer. The bottom layer is minimally affected by heat, retaining the original porous skeleton structure of the plasma spraying, i.e., the porous chromium oxide bottom layer 2. The intermediate region is in a thermodynamic non-equilibrium state of partial melting, partial sintering, and local metallurgical bonding, thus naturally transitioning to form transition layer 3.

[0076] The transition layer 3 serves three main purposes: First, it acts as a stress buffer and crack preventer, mitigating residual stress caused by the difference in thermal expansion coefficients and rapid laser cooling and contraction between the dense composite surface layer 4 (high hardness, low toughness) and the porous chromium oxide underlayer 2 (low hardness, high toughness), thus preventing interfacial peeling or transverse crack propagation. Second, it achieves a smooth transition between hardness and toughness (due to the porous underlayer absorbing energy), making the coating less prone to hard and brittle layer peeling under impact or alternating loads. Third, it ensures bonding strength by gradually transitioning from metallurgical bonding to mechanical bonding, resulting in an overall coating bonding strength ≥80MPa, far exceeding that of traditional physical adhesion or simple chemical sealing processes.

[0077] The specific features, structures, or characteristics described in this specification may be combined in any suitable manner in one or more embodiments or examples.

[0078] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0079] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating, characterized in that, The method includes: Step 1, preparing a porous framework: using thermal spraying technology, a chromium oxide-based coating is deposited on the substrate surface, so that the porosity of the chromium oxide-based coating is 8%-20%, and the pores are mainly interconnected pores; Step 2, nanodiamond infiltration: Immerse the coating obtained in Step 1 in a nanodiamond suspension, and apply vacuum-assisted infiltration or pressure-assisted infiltration to allow the nanodiamonds to fill the pores of the coating. Step 3, laser remelting and densification: A laser beam is used to scan and remelt the penetrated coating, causing localized melting and densification of the coating surface, thereby constructing a porous chromium oxide underlayer and a dense composite surface layer. The porous chromium oxide substrate has a connected pore structure, and the dense composite surface layer is disposed on the porous chromium oxide substrate. The dense composite surface layer includes a chromium oxide matrix and nanodiamond particles. The interior of the chromium oxide matrix has a porous structure, and the nanodiamond particles fill the porous structure. The porosity of the dense composite surface layer is less than that of the porous chromium oxide substrate.

2. The laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating according to claim 1, characterized in that, The chromium oxide-based coating in step one is a Cr2O3 coating, or a composite coating composed of Cr2O3 and at least one modified oxide, wherein the modified oxide is selected from one or more of TiO2, SiO2, and ZrO2.

3. The laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating according to claim 1, characterized in that, Before step one, the substrate is subjected to sandblasting roughening pretreatment; In step one, the thermal spraying is atmospheric plasma spraying, and the spraying process parameters are: spraying power 30-45kW, spraying distance 80-120mm, main gas flow rate 40-60L / min, auxiliary gas flow rate 5-15L / min, and powder feeding rate 30-60g / min.

4. The laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating according to claim 1, characterized in that, In step one, the porosity of the interconnected hole structure is 10%-15%, and the pore diameter is 50nm-500nm.

5. The laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating according to claim 1, characterized in that, In step two, the nanodiamond particles have a particle size of 10-50 nm; the suspension consists of nanodiamonds, a dispersant, and deionized water, wherein the mass percentage of nanodiamonds is 5%-15% and the mass percentage of the dispersant is 0.5%-2%.

6. The laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating according to claim 5, characterized in that, The dispersant is one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, or polyethylene glycol.

7. The laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating according to claim 1, characterized in that, In step two, the vacuum degree of the vacuum-assisted permeation is -0.08MPa to -0.1MPa, and the pressure holding time is 10-30 minutes; the pressure of the pressure-assisted permeation is 0.2-0.6MPa, and the pressure holding time is 5-20 minutes.

8. The laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating according to claim 1, characterized in that, In step three, the laser remelting is carried out under the protection of an inert gas, which is argon or nitrogen. The laser remelting parameters are: laser power 200-800W, scanning speed 5-20mm / s, spot diameter 1-3mm, and overlap rate 30%-50%.

9. The laser remelting method for preparing a high-wear-resistant chromium oxide-nanodiamond composite coating according to claim 1, characterized in that, In step three, the depth of the dense composite surface layer is controlled to be 30%-70% of the total coating thickness.

10. A high-wear-resistant chromium oxide-nanodiamond composite coating, characterized in that, It is prepared by laser remelting of the high wear-resistant chromium oxide-nanodiamond composite coating according to any one of claims 1-9.

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