A method for preparing a high content WC particle reinforced composite coating by laser cladding

Abstract

The application discloses a laser cladding preparation method of a high-content WC particle reinforced composite coating, and comprises the following steps: (1) taking NiCr21Mo9Cu8 nickel-based alloy powder as a binder phase, mixing the same with WC powder as a hard reinforcing phase to obtain WC / Ni composite powder; (2) selecting stainless steel as a substrate, and performing degreasing, oil removal and polishing treatment on the surface of the substrate; (3) laying the nickel-based superalloy on the surface of the stainless steel, performing laser cladding treatment, and cooling and solidifying to obtain a nickel-based transition layer; and (4) laying the WC / Ni composite powder on the nickel-based transition layer, performing laser cladding treatment, and cooling and solidifying to obtain a Ni-WC functional layer, so that a ceramic reinforced metal-based composite cladding layer which is metallurgically combined with the substrate is obtained. The composite structure of the transition layer and the functional layer is constructed, the transition layer releases stress and improves toughness, the functional layer provides high wear resistance and corrosion resistance, the difference in thermal physical properties between the heterogeneous materials is effectively relieved, the residual stress and cracking sensitivity of the coating are significantly reduced, and the unification of high bonding strength and excellent forming quality is realized.

Description

Technical Field

[0001] This invention belongs to the field of surface strengthening technology of metal materials, and specifically relates to a laser cladding method for preparing a composite coating with high WC particle content. Background Technology

[0002] 15-15HS MAX high-nitrogen austenitic stainless steel possesses excellent properties such as high strength, high toughness, and non-magnetic properties, meeting the requirements of deep-sea drilling equipment under complex loads and deep-well conditions. Its body hardness can reach 350–430 BHN. However, in actual service, the surface of this material is subjected to severe abrasive wear from high-hardness rock formations, fluid erosion, and seawater corrosion over long periods. The original surface wear resistance is insufficient, making it prone to premature failure and affecting the continuous operation of the equipment.

[0003] Current common technologies for improving the surface properties of stainless steel include thermal spraying, electroplating, welding, and chemical heat treatment, but they generally have the following drawbacks: 1. The coating and the substrate are mainly mechanically bonded, resulting in low interfacial bonding strength and easy peeling. 2. The process is cumbersome, highly polluting, and has poor environmental performance; 3. The coating has low density, and its wear resistance and corrosion resistance are only slightly improved, making it difficult to adapt to high load and strong corrosion conditions.

[0004] Laser cladding, as a highly efficient surface modification technology, can prepare high-performance composite coatings that are metallurgically bonded to the substrate, making it an ideal solution for addressing surface failures in marine equipment. Traditional cladding coatings often use Ni-based, Fe-based, or Co-based alloys as the binder phase, with ceramic particles such as WC, TiC, and Al2O3 added as reinforcing phases. However, in corrosive environments, problems such as uneven distribution of reinforcing phases, poor interfacial bonding, and significant microgalvanic corrosion effects can significantly reduce the overall performance of the coating.

[0005] Existing wear-resistant cladding coatings for stainless steel surfaces mostly employ a single alloy system, resulting in a simple strengthening mechanism and limited improvement in hardness and wear resistance. Furthermore, ceramic particles are prone to burn-off, agglomeration, and interfacial debonding during the cladding process, severely impacting coating quality. Therefore, developing a high-WC-content reinforced composite coating preparation technology that offers stable forming, uniform microstructure, and excellent synergistic wear and corrosion resistance has become a critical issue urgently needing to be addressed in the field of marine equipment surface strengthening. Summary of the Invention

[0006] This invention aims to address the early failure problem of 15-15HS MAX high-nitrogen austenitic stainless steel components in marine oil equipment under coupled high-pressure friction and corrosion conditions. While this material possesses excellent mechanical properties, its original surface still exhibits insufficient wear resistance when facing the severe abrasion and extreme erosion environment of high-hardness rock strata in the deep sea. Therefore, one objective of this invention is to provide a laser cladding method for preparing a composite coating reinforced with high WC particles.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a laser cladding method for preparing a high-WC particle-reinforced composite coating, comprising the following steps: (1) Take NiCr21Mo9Cu8 nickel-based alloy powder as the binder phase and WC powder as the hard reinforcing phase, mix the two to obtain WC / Ni composite powder; (2) Substrate pretreatment: Stainless steel is selected as the substrate. The surface needs to be degreased, deoiled and polished to remove oxide scale and improve surface roughness to ensure the bonding quality of the cladding layer; (3) Preparation of transition layer: A nickel-based superalloy is laid on the surface of stainless steel, laser cladding is performed, and the surface is cooled and solidified to obtain a nickel-based transition layer; (4) Functional layer preparation: WC / Ni composite powder is laid in the transition layer, laser cladding is performed, and the layer is cooled and solidified to obtain Ni-W functional layer, thus obtaining ceramic-reinforced metal matrix composite cladding layer that is metallurgically bonded to the matrix.

[0008] This invention proposes a dual laser cladding structure design, which involves first cladding a nickel-based transition layer on the substrate surface, followed by cladding a Ni-WC functional layer, to significantly improve the surface properties of components and extend their service life.

[0009] The stainless steel is 15-15HS MAX high-nitrogen austenitic stainless steel. The nickel-based superalloy is Inconel 625 alloy powder.

[0010] In step (1), the NiCr21Mo9Cu8 nickel-based alloy powder has the following composition by mass percentage: Ni 55-60%, Cr 20-22%, Mo 8-10%, Cu 6-8%, with the remainder being unavoidable impurities. The composition design of this invention aims to utilize the high Cu content in the NiCr21Mo9Cu8 nickel-based alloy to significantly improve corrosion resistance, reduce the coefficient of friction, improve wettability and formability, while refining the microstructure and reducing the tendency for coating cracking. It can effectively wet and coat WC particles, thereby enhancing the coating's resistance to pitting corrosion, crevice corrosion, and intergranular corrosion.

[0011] Preferably, the composition of NiCr21Mo9Cu8 nickel-based alloy powder is: Ni 57.19 wt.%, Cr 21.3 wt.%, Mo 9 wt.%, and Cu 7.5 wt.%. In step (1), the volume fraction of spherical pure WC powder is 30-50 vol%.

[0012] In step (3), the laser cladding process parameters for the nickel-based transition layer are: laser power 1.2~2kW, scanning speed 6~10mm / s, and powder feeding rate 0.2~0.5r / min. The preferred process parameters are: laser power 1.6kW, scanning speed 8mm / s, and powder feeding rate 0.5r / min.

[0013] In step (3), the thickness of the nickel-based transition layer is controlled between 0.3 and 1.5 mm, preferably 0.8 mm.

[0014] In step (4), the laser cladding process parameters for the Ni-WC functional layer are: laser power 1~1.2kW, scanning speed 6~10mm / s, and powder feeding rate 0.2~0.6r / min. The preferred process parameters are: laser power 1.1kW, scanning speed 8mm / s, and powder feeding rate 0.5r / min.

[0015] In step (4), the thickness of the Ni-WC functional layer is controlled between 1.5 and 2.7 mm. Preferably, it is 1.6 mm.

[0016] Argon gas must be introduced as a protective gas throughout the cladding process.

[0017] In step (1), the mixing of NiCr21Mo9Cu8 nickel-based alloy powder and WC powder is preferably carried out using a three-dimensional motion powder mixer.

[0018] In step (1), when loading materials into the three-dimensional motion powder mixer, a layered feeding method is adopted: a layer of NiCr21Mo9Cu8 alloy powder and a layer of WC ceramic powder are alternately stacked into the mixing cylinder. After all the powder materials are filled in layers, the machine is started to mix as a whole.

[0019] Mixing parameters: dry mixing without grinding balls, cylinder rotation speed 12 r / min, continuous mixing for 60 min. This invention does not use grinding balls to avoid powder particle breakage and damage to the spherical shape of the powder due to excessive ball milling impact force.

[0020] The second objective of this invention is to provide a WC / Ni composite powder.

[0021] To achieve the above objectives, the present invention adopts the following technical solution: a WC / Ni composite powder, mainly composed of NiCr21Mo9Cu8 nickel-based alloy powder and WC ceramic powder, wherein the NiCr21Mo9Cu8 nickel-based alloy powder has the following powder composition by mass percentage: Ni 55~60%, Cr 20~22%, Mo 8~10%, Cu 6~8%, and the remainder being unavoidable impurities.

[0022] Preferably, the composition of NiCr21Mo9Cu8 nickel-based alloy powder is: Ni 57.19 wt.%, Cr 21.3 wt.%, Mo 9 wt.%, and Cu 7.5 wt.%.

[0023] The WC ceramic powder is spherical pure WC powder, and its volume fraction in the WC / Ni composite powder is 30-50 vol.

[0024] The preferred method for mixing NiCr21Mo9Cu8 nickel-based alloy powder and WC powder is a three-dimensional motion powder mixer.

[0025] The specific operation is as follows: When loading materials into the three-dimensional motion powder mixer, the material is laid in layers: one layer of NiCr21Mo9Cu8 alloy powder and one layer of WC ceramic powder are alternately stacked into the mixing cylinder. After all the powders are filled in layers, the machine is started to mix them as a whole.

[0026] Mixing parameters: dry mixing without grinding balls, cylinder rotation speed 12 r / min, continuous mixing for 60 min. This invention does not use grinding balls to avoid powder particle breakage and damage to the spherical shape of the powder due to excessive ball milling impact force.

[0027] A third objective of this invention is to provide nickel-based alloy powder.

[0028] To achieve the above objectives, the present invention adopts the following technical solution: nickel-based alloy powder, specifically NiCr21Mo9Cu8 nickel-based alloy powder, with the following powder composition by mass percentage: Ni 55~60%, Cr 20~22%, Mo 8~10%, Cu 6~8%, and the remainder being unavoidable impurities.

[0029] The beneficial effects of this invention are: This invention constructs a composite structure of a transition layer and a functional layer through a dual-layer laser cladding process. The transition layer releases stress and improves toughness, while the functional layer provides high wear and corrosion resistance. This effectively alleviates the differences in thermophysical properties between heterogeneous materials, significantly reduces residual stress and cracking sensitivity of the coating, and achieves a balance between high bonding strength and excellent molding quality.

[0030] The functional layer uses WC / Ni composite powder composed of NiCr21Mo9Cu8 alloy and WC. NiCr21Mo9Cu8 alloy exhibits excellent wettability on WC particles, ensuring strong interfacial bonding between particles and preventing them from falling off. Combined with the dry mixing process to protect the sphericity of the powder, it further ensures the stability of powder feeding and the uniformity and density of the coating structure.

[0031] The coating prepared by this invention has a microhardness of up to 2800HV0.2, and has both extremely high wear resistance and corrosion resistance. It can perfectly adapt to the harsh working conditions of marine oil equipment, and significantly reduce the failure frequency and the total life cycle maintenance cost of the equipment. Attached Figure Description

[0032] Figure 1 Here is a SEM image of the WC / Ni powder described in this invention; Figure 2 Samples of coatings with different WC contents as described in this invention were prepared. Figure 3 This invention provides EDS line and area scans of 30 vol% WC volume fraction. Figure 4 This invention provides EDS line and area scans of 35 vol% WC volume fraction. Figure 5 This invention provides EDS line and area scans of 40 vol% WC volume fraction. Figure 6 EDS line scan and area scan of 45 vol% WC volume fraction (30 vol.% to 50 vol.%) of the present invention; Figure 7 EDS line scan and area scan of the present invention with a 50 vol% WC volume fraction (30 vol.% to 50 vol.%); Figure 8 The XRD diffraction patterns of the coatings with different WC contents described in this invention are shown below. Figure 9 Microhardness tests were performed on samples with different WC contents as described in this invention. Detailed Implementation

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

[0034] Cladding process: Substrate pretreatment: 15-15HS MAX high-nitrogen austenitic stainless steel is selected as the substrate. The surface is degreased, deoiled and polished to remove oxide scale and improve surface roughness to ensure the bonding quality of the cladding layer.

[0035] Powder pre-placement: The thickness of the Inconel 625 alloy powder pre-placement layer is controlled at 0.3-1.5 mm using the pre-placement powder method, serving as a transition layer; then the mixed WC / Ni composite powder is laid on the transition layer, with the layer thickness controlled at 1.5-2.7 mm.

[0036] Laser cladding: A dual-layer laser cladding process is employed. A transition layer buffers stress and reduces cracking, achieving a combination of bottom-layer toughness and surface wear and corrosion resistance, thus improving coating bonding strength and forming quality. The process parameters for the transition layer are: laser power 1.2~2kW, scanning speed 6~10mm / s, powder feed rate 0.2~0.5r / min; the process parameters for the functional layer are: laser power 1~1.2kW, scanning speed 6~10mm / s, powder feed rate 0.2~0.6r / min. Argon gas is required as a protective gas throughout the cladding process.

[0037] Cooling and forming: After the cladding is completed, the cladding layer solidifies under natural cooling conditions, and finally a ceramic-reinforced metal matrix composite cladding layer with metallurgical bonding with the substrate is obtained.

[0038] Preferably, the thickness of the cladding powder pre-layer transition layer is controlled to be 0.8 mm, and the thickness of the functional layer is controlled to be 1.6 mm. The optimal process parameters for the transition layer are: laser power 1.6 kW, scanning speed 8 mm / s, and powder feeding rate 0.5 r / min; the optimal process parameters for the functional layer are: laser power 1.1 kW, scanning speed 8 mm / s, and powder feeding rate 0.5 r / min.

[0039] Preparation of WC / Ni composite powder: When loading materials into the three-dimensional motion powder mixer, a layered feeding method is adopted: a layer of NiCr21Mo9Cu8 alloy powder and a layer of WC ceramic powder are alternately stacked into the mixing cylinder. After all the powders are filled in layers, the machine is started for overall mixing.

[0040] Mixing parameters: dry mixing without grinding balls, cylinder rotation speed 12 r / min, continuous mixing for 60 min. This invention does not use grinding balls to avoid powder particle breakage and damage to the spherical shape of the powder due to excessive ball milling impact force.

[0041] This invention introduces NiCr21Mo9Cu8 nickel-based alloy powder into a composite laser cladding layer system, the specific chemical composition of which is shown in Table 1-1. Through multiple adjustments of the content, the alloy is based on Ni (57.19 wt.%) and is rich in alloying elements such as Cr (21.30 wt.%), Mo (9.00 wt.%), and Cu (7.50 wt.%). The Ni-based alloy powder exhibits good toughness, impact resistance, heat resistance, oxidation resistance, and corrosion resistance. The high content of Cr and Mo significantly improves the coating's resistance to pitting and crevice corrosion in marine environments. The addition of Cu further enhances the overall corrosion resistance of the material in corrosive media such as seawater, reducing spatter during powder laser additive manufacturing and minimizing deformation and stress cracking of the printed parts. The presence of an appropriate amount of Nb (3.51 wt.%) helps refine the grains and inhibit intergranular corrosion. Using this alloy, which has excellent toughness and extremely high corrosion resistance, as a binder phase can not only provide good wetting and coating of hard WC particles during laser cladding, but also effectively meet the corrosion and wear resistance requirements of marine drilling equipment components such as the Xuanji system under harsh service conditions.

[0042] Table 1.1 Chemical composition (wt.%) of NiCr21Mo9Cu8 nickel-based alloy powder

[0043] NiCr21Mo9Cu8 nickel-based alloy powder was then mixed with WC ceramic powder, the composition of which is shown in Table 1-2. The high W content of 57.1% aims to form a high volume fraction of tungsten carbide hard phase in the cladding layer, which serves as an anti-wear skeleton support and gives the coating excellent anti-abrasive wear performance. Inconel625 (containing 21.3% Cr and 9% Mo) was used as the alloy matrix, and its excellent resistance to pitting corrosion and crevice corrosion was utilized to ensure the chemical stability of the coating in corrosive media such as high salt spray, hydrogen sulfide and carbon dioxide. In addition, the addition of 3.9% Cu not only improves the toughness of the matrix through solid solution strengthening, but also improves the wettability and fluidity of the molten pool, further promoting composition homogenization and reducing crack sensitivity.

[0044] Table 1.2 Chemical composition of WC / Ni powder

[0045] The microstructure of the mixed WC / Ni composite powder is as follows: Figure 1As shown in the figure, scanning electron microscopy (SEM) analysis revealed two types of particles with significantly different contrasts in the mixed powder system. The particles exhibiting high contrast, smooth surfaces, and extremely high sphericity are pure WC reinforcing phase powder; while the particles exhibiting gray contrast, predominantly spherical or near-spherical morphology, with a small amount of "satellite powder" adhering to their local surfaces are NiCr21Mo9Cu8 alloy matrix phase powder. From an overall perspective, after mechanical mixing, particles of different sizes are interspersed, and the WC particles and nickel-based alloy particles are uniformly dispersed, with no obvious particle agglomeration or severe segregation observed. The composite powder maintains an excellent spherical morphology. This uniform dispersion and high sphericity effectively reduce the friction between powder particles, ensuring excellent flowability and a continuous and stable powder feed rate during laser cladding. This provides a solid material foundation for preparing functional coatings with uniform structure and no obvious pores or crack defects.

[0046] Then, laser cladding was performed according to the optimized process parameters. A German LDF6000-60 fiber laser was selected as the light source, with a power adjustable between 100-6000W. The system primarily uses coaxial powder feeding, with a 4mm diameter laser plate, a processing distance of 18mm, and 99.9% pure argon as the protective gas at a pressure of 20L / min, while the powder feeding gas pressure is 2.5L / min. A series of laser cladding layers were prepared through laser cladding.

[0047] Figure 2 To prepare samples with coatings of different WC contents, five groups of Ni-WC composite powders with WC volume fractions of 30 vol%, 35 vol%, 40 vol%, 45 vol%, and 50 vol% were prepared by mechanical ball milling. These powders were then subjected to multi-pass overlapping laser cladding on the surface of 15-15HSMAX high-nitrogen austenitic stainless steel samples. After cladding, the coating was cut into 15 mm × 15 mm × 10 mm pieces using wire cutting. The cross-sections were then polished with sandpaper of different grits and polished to a mirror finish using polishing paste, providing samples for subsequent testing.

[0048] 1. Microscopic morphology and phase distribution characteristics like Figure 3-7 As shown in the microstructure and EDS surface scan results of each group of samples, WC particles are dispersed in the nickel-based alloy matrix in spherical or near-spherical shapes, with a relatively uniform overall distribution. With the increase of the initial WC content, the distribution density of the hard phase in the cladding layer significantly increases. Under the action of the high-energy laser beam, a slight micro-dissolution phenomenon occurred on the surface of the WC particles, which is beneficial for forming a good metallurgical bond between the particles and the matrix.

[0049] 2. EDS line scan analysis and interface diffusion like Figure 3-7 As shown, by observing the line scan curves of each group of samples (black curve represents W, blue represents Ni, and red represents Cr), the elemental gradient changes between WC particles and the matrix can be clearly identified: Abrupt changes in elemental concentration: When the scan line enters the interior of WC particles, the W element signal rapidly rises to a peak value, while the matrix main elements Ni and Cr show obvious trough characteristics.

[0050] Interfacial transition layer: At the particle edges, the W curve intersects with the Ni and Cr curves at a certain slope, rather than abruptly changing vertically. This confirms that during the existence of the molten pool, W and C atoms in the WC particles diffuse into the molten pool, while elements such as Cr and Ni in the matrix also penetrate towards the particle edges, forming a compositional transition zone of a certain width. This micro-diffusion behavior can effectively reduce the interfacial stress between the particles and the matrix, and enhance the peeling resistance of the interface.

[0051] 3. Elemental distribution and matrix dilution rate The surface scan results further confirmed the spatial distribution of the components: W element (red area): accurately anchors the position of the WC hard phase, with clear particle outline.

[0052] Ni, Cr, Mo, and other matrix elements are mainly enriched in the matrix region between particles. Notably, the overall intensity of Fe (purple curve) remained at a low level during online scanning. This indicates that under optimized laser process parameters, the dilution rate of the substrate to the cladding layer was strictly controlled, effectively preventing excessive Fe from the high-nitrogen steel substrate from mixing into the coating and reducing its hardness and corrosion resistance.

[0053] 4. Comparison of tissues with different WC contents Low content stage (30-35 vol.%): The matrix phase is relatively abundant, and the WC particles are completely wrapped by the matrix. The coating has good toughness reserves, but the spacing between the hard phases is large, and the shielding and protection effect on the matrix is ​​limited.

[0054] In the high-content stage (45-50 vol.%), the WC particle density increases significantly, forming a denser, harder skeleton. However, with the increase in WC content, the viscosity of the molten pool increases, and Marangoni convection is suppressed to some extent, posing higher process requirements for porosity control and interfacial stress release in the coating.

[0055] 1. Composition of the main phase of the coating and the pyrolysis behavior of WC Depend on Figure 8It is evident that the most prominent diffraction peaks in all coatings with different WC volume fractions correspond to the face-centered cubic γ-Ni solid solution. This constitutes the matrix phase that provides macroscopic toughness support for the composite coating. Furthermore, the characteristic diffraction peaks of simple hexagonal WC (labeled 3) and close-packed hexagonal W2C (labeled 2) are clearly identified in the spectra. With the gradual increase of WC content in the original composite powder (from 30 vol% to 50 vol%), the intensity of the characteristic diffraction peaks of WC and W2C in the spectra shows a significant and regular increase. The abundant presence of the W2C phase directly confirms, from a crystallographic perspective, the dramatic thermodynamic evolution during the interaction between the high-energy laser beam and matter: under extremely high laser heat input, the surface of the original WC particles absorbs heat and undergoes local melting and decarburization reactions (2WC = W2C + C). The precipitated W2C has higher hardness than WC, but its brittleness also increases; the strengthening of its peak indicates a simultaneous increase in hardness and crack sensitivity in coatings with high WC content.

[0056] 2. In-situ precipitation and multiple peak overlap of complex secondary carbides In combination with the multi-element characteristics of the Ni-WC composite powder of the present invention, which contains Cr, Mo, Cu, Nb and other elements, a complex in-situ alloying reaction occurs in the laser molten pool during the rapid solidification process.

[0057] In the XRD pattern, the overlap between the chromium-rich carbide and the Cu phase masks the chromium phase: at the strongest principal diffraction peak near 44°, in addition to the (111) crystal plane diffraction of γ-Ni, there is also Cr. 23 The diffraction phases include C6, Cr7C3, and Cu. Cr in the powder exhibits a strong carbon affinity, readily combining with free carbon released during the thermal decomposition of WC to precipitate chromium-rich carbides at grain boundaries. While Cu is mostly dissolved in Ni, localized micro-segregation is possible. The main characteristic peaks of these phases exhibit perfect crystallographic overlap with γ-Ni, collectively contributing to the broadening and enhanced asymmetry of the diffraction peaks at this location.

[0058] Precipitation of complex η-phase carbides and NbC: In the temperature range of 39°~41°, in addition to the characteristic peaks of W2C, Ni2W4C (M6C type phase) and NbC are also present. Nb first combines with carbon in the molten pool to form high-melting-point NbC as a non-spontaneous nucleation core; as the temperature of the molten pool decreases, supersaturated W and C undergo peritectic or eutectic reactions with the Ni matrix at the dendrites, precipitating complex Ni2W4C carbides.

[0059] 3. Crystallographic confirmation of solid solution strengthening mechanism Although the phase composition of the coatings remains largely consistent across different WC contents, close observation of the position of the main Ni peak reveals a significant distortion and expansion of the matrix lattice due to the supersaturated solid solution of multiple alloying elements (especially those with large atomic radii such as W, Cr, and Mo). This distortion is caused by a large number of dissolved atoms and the dispersed precipitation of complex nanoscale carbides, such as Cr. 23 C6 and Ni2W4C strongly hinder dislocation movement. This significant synergistic mechanism of solid solution strengthening and precipitation dispersion strengthening lays a solid crystallographic and phase foundation for the substantial improvement of the microhardness and wear resistance of subsequent coatings.

[0060] In summary, as the WC volume fraction increased from 30 vol% to 50 vol%, the distribution density of the hard phase in the coating significantly improved, and the WC particles were uniformly distributed in the matrix. EDS analysis confirmed that the WC particles underwent micro-dissolution under the action of a high-energy laser beam, and W and C elements diffused bidirectionally with the matrix Ni and Cr elements at the interface, forming a compositional transition zone and effectively reducing interfacial stress. XRD analysis showed that the coating mainly consisted of γ-Ni solid solution, unmelted WC, thermally desorbed W2C, and in-situ generated complex carbides (such as Cr). 23 The composition is C6, Ni2W4C, and NbC. The high WC content exacerbates the precipitation of W2C and lattice distortion, providing a strong solid solution and dispersion strengthening effect.

[0061] 1. Overall hardness gradient distribution characteristics of the coating system Depend on Figure 9 It can be intuitively observed that all samples, from the surface WC / Ni functional layer and the Inconel625 transition layer to the 15-15HS MAX stainless steel substrate, exhibit an extremely significant step-like gradient distribution of microhardness, successfully constructing an ideal mechanical structure of "extremely hard surface, soft middle, and strong and tough substrate".

[0062] Substrate and HAZ: The average microhardness of the 15-15HS MAX high-nitrogen austenitic stainless steel matrix remains at approximately 350 HV. 0.2 Approximately. In the heat-affected zone (2.7mm~3.6mm range), due to the effect of laser thermal cycling, the hardness fluctuates slightly but remains generally similar to that of the substrate.

[0063] Transition layer region: After crossing the matrix interface and entering the Inconel 625 transition layer (1.5mm ~ 2.7mm range), the hardness curves of each group of samples highly overlap, and the average hardness drops to approximately 250~300 HV. 0.2This hardness value is lower than that of the matrix and much lower than that of the surface layer, fully leveraging its buffering role as a high-ductility and high-toughness "soft isolation zone". It can effectively absorb and release the huge residual thermal stress generated during the rapid solidification process of the surface WC / Ni functional layer, and provide excellent toughness support to resist the strong alternating impact loads during the service of marine drilling tools, fundamentally preventing the propagation of cracks into the matrix.

[0064] 2. The Influence of WC Content on the Microhardness of Functional Layers In the Ni-WC functional layer region (0.3~1.5mm), the microhardness of the coating exhibits a sharp and precipitous increase, and shows a strong positive correlation with the volume fraction of WC in the composite powder.

[0065] Hardness with increasing content: When the WC content is at a low level (30 vol%), the hardness of the functional layer is 1700~2200 HV. 0.2 Fluctuations between these ranges; as the WC content increases to 45 vol% of the original formula, the overall hardness jumps to 2100~2600 HV. 0.2 When the WC content reaches the limit of 50 vol%, the local peak hardness of the coating even approaches 2800 HV0. .2 .

[0066] Strengthening Mechanism Analysis: The significant increase in hardness of the Ni-WC functional layer is mainly attributed to the synergistic effect of multiple strengthening mechanisms. First, there is second-phase strengthening (composite strengthening). Unmelted WC particles with high hardness and high elastic modulus act as a framework in the γ-Ni matrix, and the increase in WC content significantly reduces the path of freedom of the matrix, greatly enhancing its resistance to micro-indentation deformation. Second, there is solid solution and dispersion strengthening. Combined with XRD and microstructure analysis, the high-heat input of the laser causes some WC to dissolve, and the supersaturated solid solution of free large atomic radius W and C elements in the nickel matrix causes severe lattice distortion. At the same time, the in-situ precipitated W2C and complex secondary carbides (such as the η phase) dispersedly further play a strong role in pinning dislocations.

[0067] Microscopic Explanation of Hardness Fluctuations: In the functional layer region, the hardness curves of all sample groups exhibited drastic sawtooth-like fluctuations, especially in the high-content (45 vol%) and 50 vol%) groups. This dispersion is a typical mechanical characteristic of metal matrix composites. This is because the indenter size of the microhardness tester is extremely small. During the indentation process, if the indenter directly hits the hard phase WC particles or their dense areas, an extremely high hardness peak is measured; if the indenter falls on the relatively soft γ-Ni solid solution matrix region, the hardness value is relatively low. Furthermore, when the WC content reaches 50 vol%, particle agglomeration and micropore defects easily occur within the coating, which is also an important reason for the further aggravation of the dispersion of its hardness curves.

[0068] In summary, the microhardness test results fully validate the rationality and superiority of the double-layer laser cladding structure design. The Inconel 625 transition layer provides crucial flexible buffering; while the addition of an appropriate amount of WC, such as 40 vol%~45 vol%, imparts extremely high macrohardness to the surface layer without causing serious defects. This gradient performance distribution of "hard on the outside and tough on the inside" lays a solid mechanical foundation for the wear-resistant sleeve of deep-sea directional drilling tools to withstand friction and wear under extreme working conditions.

[0069] The above description is not intended to limit the present invention in any way. Any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention using the disclosed technical content are equivalent embodiments of the present invention. At the same time, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A laser cladding method for preparing a composite coating reinforced with high WC particle content, characterized in that, Includes the following steps: (1) Take NiCr21Mo9Cu8 nickel-based alloy powder as the binder phase and WC powder as the hard reinforcing phase, mix the two to obtain WC / Ni composite powder; (2) Substrate pretreatment: Stainless steel is selected as the substrate. The surface needs to be degreased, deoiled and polished to remove oxide scale and improve surface roughness to ensure the bonding quality of the cladding layer; (3) Preparation of transition layer: A nickel-based superalloy is laid on the surface of stainless steel, laser cladding is performed, and the layer is cooled and solidified to obtain a nickel-based transition layer; (4) Functional layer preparation: WC / Ni composite powder is laid in the transition layer, laser cladding is performed, and the mixture is cooled and solidified to obtain a Ni-WC functional layer, thus obtaining a ceramic-reinforced metal matrix composite cladding layer that is metallurgically bonded to the matrix.

2. The laser cladding method for preparing a high-WC particle-reinforced composite coating according to claim 1, characterized in that, In step (1), the NiCr21Mo9Cu8 nickel-based alloy powder has the following composition by mass percentage: Ni 55~60%, Cr 20~22%, Mo 8~10%, Cu 6~8%, and the remainder being unavoidable impurities.

3. The laser cladding method for preparing a high-WC particle-reinforced composite coating according to claim 2, characterized in that, The composition of NiCr21Mo9Cu8 nickel-based alloy powder is as follows: Ni 57.19 wt.%, Cr 21.3 wt.%, Mo 9 wt.%, and Cu 7.5 wt.%.

4. The laser cladding method for preparing a high-WC particle-reinforced composite coating according to claim 1, characterized in that, In step (1), the volume fraction of WC powder is 30-50 vol%.

5. The laser cladding method for preparing a high-WC particle-reinforced composite coating according to claim 1, characterized in that, In step (3), the laser cladding process parameters of the nickel-based transition layer are: laser power 1.2~2kW, scanning speed 6~10mm / s, powder feeding rate 0.2~0.5r / min; the thickness of the transition layer is controlled at 0.3-1.5mm; in step (4), the laser cladding process parameters of the Ni-WC functional layer are: laser power 1~1.2kW, scanning speed 6~10mm / s, powder feeding rate 0.2~0.6r / min, and the thickness of the Ni-WC functional layer is controlled at 1.5-2.7mm.

6. The laser cladding method for preparing a high-WC particle-reinforced composite coating according to claim 5, characterized in that, The laser cladding process parameters for the nickel-based transition layer are: laser power 1.6kW, scanning speed 8mm / s, powder feeding rate 0.5r / min; the thickness of the nickel-based transition layer is controlled to be 0.8mm.

7. The laser cladding method for preparing a high-WC particle-reinforced composite coating according to claim 5, characterized in that, In step (4), the laser cladding process parameters of the Ni-WC functional layer are: laser power 1.1kW, scanning speed 8mm / s, powder feeding rate 0.5r / min; the thickness of the Ni-WC functional layer is controlled to be 1.6mm.

8. A WC / Ni composite powder, characterized in that, It is mainly composed of NiCr21Mo9Cu8 nickel-based alloy powder and WC ceramic powder. The NiCr21Mo9Cu8 nickel-based alloy powder has the following composition by mass percentage: Ni 55~60%, Cr 20~22%, Mo 8~10%, Cu 6~8%, and the remainder being unavoidable impurities.

9. The WC / Ni composite powder according to claim 8, characterized in that, The composition of the NiCr21Mo9Cu8 nickel-based alloy powder is as follows: Ni 57.19 wt.%, Cr 21.3 wt.%, Mo 9 wt.%, and Cu 7.5 wt.%.

10. Nickel-based alloy powder, characterized in that, It is a NiCr21Mo9Cu8 nickel-based alloy powder, with the following powder composition by mass percentage: Ni 55~60%, Cr 20~22%, Mo 8~10%, Cu 6~8%, and the remainder being unavoidable impurities.

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