Laser cladding method for preparing interface-optimized machine tool guide rail nanoceramic coating

Abstract

This invention discloses a laser cladding method for preparing an interface-optimized nano-ceramic coating for machine tool guideways, relating to the field of ceramic coatings. This method comprehensively solves the key bottlenecks of traditional coating technologies. Its core advantage lies in the creative introduction of a composition-gradient nano-transition layer prepared by the sol-gel method. This finely structured intermediate layer effectively alleviates thermal stress caused by the difference in thermal expansion coefficients between the ceramic coating and the metal substrate, thereby enhancing the interfacial bonding strength to an extremely high level and fundamentally eliminating the risk of coating cracking and peeling. The nano-ceramic particles and tough metal-based composite powder system used in the process form a composite coating structure with dispersion strengthening and metallurgical bonding under laser action. This allows it to maintain extremely high hardness and excellent wear resistance while also possessing good toughness, sufficient to withstand severe impacts under heavy-load conditions.

Description

Technical Field

[0001] This invention relates to ceramic coating technology, specifically to a laser cladding method for preparing an interface-optimized nano-ceramic coating for machine tool guideways. Background Technology

[0002] As a core moving component and precision benchmark of a machine tool, the performance of the machine tool guideway directly determines the machining accuracy, stability, and lifespan of the entire machine. During long-term service, the guideway surface is subjected to high-frequency sliding friction, periodic heavy-load impacts, and environmental erosion from cutting fluids and debris. Therefore, extremely stringent comprehensive requirements are placed on its surface coating: it must possess excellent wear resistance to resist wear and maintain precision; it needs extremely high bonding strength to ensure the coating does not peel off under complex stress; it must possess excellent impact toughness to buffer alternating loads; simultaneously, the coating process itself and subsequent treatments must strictly guarantee dimensional accuracy, and thermal deformation and other issues must not affect the geometric accuracy and assembly of the guideway. Among many advanced nano-ceramic coating preparation processes, such as plasma spraying and physical vapor deposition, laser cladding, after comprehensive evaluation, is considered the most suitable choice to meet the above core requirements. Its fundamental advantage lies in the fact that the high-energy-density laser beam can instantly melt and rapidly solidify the pre-placed or synchronously delivered ceramic composite powder and the guideway substrate surface, forming a strong metallurgical bond at the interface. This bond strength is far higher than that of spraying techniques that primarily rely on mechanical bonding. Meanwhile, the rapid cooling of the molten pool results in an extremely dense coating structure with almost no pores and high hardness, thus giving the coating excellent load-bearing and impact resistance, which is key to dealing with heavy-load and repeated impact conditions of machine tool guideways.

[0003] However, traditional single laser cladding processes still face a fundamental technical bottleneck in the preparation of ceramic coatings. Ceramic materials (such as Al2O3 and ZrO2) and the steel substrates commonly used in machine tool guideways differ significantly in their physical properties, with the mismatch in thermal expansion coefficients being the most prominent issue. The thermal expansion coefficient of ceramics is typically much lower than that of metals. When the high-temperature heat source of the laser cladding process disappears, the coating and substrate experience significant internal thermal stress due to their different degrees of shrinkage during cooling and solidification, as well as subsequent temperature changes. This stress exists within the coating and at the bonding interface, significantly weakening the effective adhesion of the coating. During actual operation of the machine tool guideway, repeated thermal cycles caused by frictional heat generation and ambient temperature fluctuations cause this thermal stress to accumulate and release continuously, ultimately easily leading to microcracks or even macroscopic cracks in the coating. The propagation of these cracks not only directly damages the integrity of the coating, leading to wear resistance failure, but in more severe cases, it can cause large-scale peeling of the coating or deformation of the substrate, seriously threatening the operational safety and accuracy of the machine tool. Therefore, although laser cladding has a promising future, it is necessary to systematically improve and innovate the existing process to address its inherent thermal stress problem in order to truly meet the stringent application requirements of high-end machine tool guideways. Summary of the Invention

[0004] The purpose of this invention is to provide a laser cladding method for preparing an interface-optimized nano-ceramic coating for machine tool guideways, in order to solve the problem that the ceramic coating prepared by existing laser cladding technology has internal thermal stress during preparation and operation, resulting in weak coating adhesion and easy cracking and peeling.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a laser cladding method for preparing an interface-optimized nano-ceramic coating for machine tool guideways, comprising: The machine tool guide rail substrate is pretreated by sandblasting roughening, two-phase cleaning, laser cleaning and preheating treatment to obtain the pretreated substrate. A multilayer gradient transition layer is prepared on the surface of a pretreated substrate; A nanocomposite cladding layer was prepared on the surface of the gradient transition layer; A fish-scale-like array of micro-pits was constructed on the surface of the nanocomposite cladding layer, and a solid lubricant was filled inside the pits of the micro-pit array and then heat-treated to cure the solid lubricant. Post-processing and finishing of machine tool guideways include stress-relieving annealing, precision grinding, and polishing.

[0006] Preferably, the sandblasting roughening process uses 80-100 mesh brown corundum sand, the air pressure is 0.6-0.8MPa, the spray angle is set to 75°, and the surface roughness of the machine tool guide rail substrate is processed to Ra3.2-4.5μm; The two-phase cleaning process includes ultrasonic cleaning with acetone for 15 minutes and cleaning with ethanol for 10 minutes. The laser cleaning process uses a wavelength of 1064nm and an energy density of 5-8J / cm². 2 Pulsed fiber laser scanning removes the oxide layer; The preheating treatment involves preheating the machine tool guideway substrate to 300-350℃ in an inert gas protective atmosphere.

[0007] Preferably, the fabrication steps of the multilayer gradient transition layer include: Tetraethyl orthosilicate, aluminum isopropoxide, and zirconium acetylacetonate were mixed in a molar ratio of 4:3:1 to prepare a sol, and 0.5 wt% of silane coupling agent was added. Sol was coated onto the pretreated substrate surface using a dip-coating method at a dip-coating speed of 200 mm / min. After each coating, the substrate was dried at 150°C for 10 minutes. This process was repeated three times to form a transition layer of 0.8–1.2 μm. By adjusting the sol composition, a continuous compositional transition is achieved from the substrate side to the coating side. The coating inside the substrate is a Si- and Al-rich layer, while the coating outside the substrate is a Zr- and Ti-rich layer. The coefficient of thermal expansion of the coating decreases from 12 x 10⁻⁶ to 12 x 10⁻⁶.-6 / ℃ gradually increases to 8x10 -6 / ℃.

[0008] Preferably, the preparation steps of the nanocomposite cladding layer include: Composite powder was prepared by mixing matrix powder and reinforcing phase. The matrix powder was a Co-based alloy with a particle size of 45-75μm, accounting for 75wt%. The reinforcing phase was a mixture of nano-Al2O3 and submicron TiC in a 2:1 ratio, accounting for 25wt%. The mixture was prepared by mixing with a three-dimensional powder mixer for 4 hours. The beam diameter of the fiber laser was adjusted to 2.5 mm, and the power density was adjusted to 250-300 W / mm². 2 The scanning speed was adjusted to 8-12 mm / s, the overlap rate was 40%, the powder feeding rate was 18-22 g / min, and the protective gas was argon gas with a flow rate of 15-20 L / min. Infrared thermal imagers are used to monitor the molten pool temperature in real time and control it between 1850-2100℃, while the substrate temperature is controlled to not exceed 600℃.

[0009] Preferably, the micro-pits in the micro-pit array have a diameter of 150 μm, a depth of 60 μm, an array spacing of 300 μm, and an arrangement angle of 45°; the micro-pits are processed by a picosecond laser with a pulse width of 10 ps and a wavelength of 532 nm, a single pulse energy of 0.8 mJ, a repetition frequency of 50 kHz, and a scanning speed of 500 mm / s.

[0010] Preferably, the solid lubricant filling the micro-pits is a polymer-based solid lubricant containing 10% molybdenum disulfide, and is cured by heat treatment at 200°C.

[0011] Preferably, the post-processing and finishing steps include: Hold at 550℃ for 2 hours, then cool in the furnace to 300℃ and air cool to complete stress-relief annealing; The substrate was ground using a 400# diamond grinding wheel with a grinding depth ≤ 0.01 mm / pass, and the final surface roughness Ra ≤ 0.4 μm. Polishing with diamond polishing paste resulted in a top Ra of ≤0.1μm for the micro-protrusions between the micro-pits.

[0012] Compared with existing technologies, the laser cladding preparation method for interface-optimized machine tool guide nano-ceramic coatings provided by this invention comprehensively solves the key bottlenecks of traditional coating technologies. Its core advantage lies in the creative introduction of a composition gradient nano-transition layer prepared by the sol-gel method. This microstructured intermediate layer can effectively alleviate the thermal stress caused by the difference in thermal expansion coefficients between the ceramic coating and the metal substrate, thereby improving the interfacial bonding strength to an extremely high level and fundamentally eliminating the risk of coating cracking and peeling.

[0013] The process utilizes a composite powder system of nano-ceramic particles and tough metal matrix, which, under laser irradiation, forms a composite coating structure that combines dispersion reinforcement and metallurgical bonding. This allows the coating to maintain extremely high hardness and excellent wear resistance while also possessing good toughness, making it capable of withstanding severe impacts under heavy-duty conditions.

[0014] This innovative process combines laser in-situ biomimetic microtexturing technology to form a regular microstructure on the coating surface that can store lubricant, thereby achieving a significant reduction in the coefficient of friction and long-term stability of the lubrication state, greatly improving the guide rail's anti-seize and anti-scratch capabilities.

[0015] The entire process chain is also highly controllable. Through precise heat input management and subsequent precision machining, it can ensure that the coating is uniform and dense, and control the workpiece deformation within an extremely low range, perfectly meeting the stringent requirements of machine tool guideways for dimensional accuracy and surface integrity. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0017] Figure 1 This is a flowchart of the preparation method provided in an embodiment of the present invention; Figure 2 This is a flowchart of a preprocessing method provided in an embodiment of the present invention; Figure 3 A flowchart illustrating the method for preparing a multilayer gradient transition layer according to an embodiment of the present invention; Figure 4 This is a flowchart of the preparation method provided in an embodiment of the present invention. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0019] As attached Figure 1-4 As shown: This invention provides a laser cladding method for preparing an interface-optimized nano-ceramic coating on machine tool guideways, comprising: The machine tool guide rail substrate is pretreated by sandblasting roughening, two-phase cleaning, laser cleaning and preheating treatment to obtain the pretreated substrate. A multilayer gradient transition layer is prepared on the surface of a pretreated substrate; A nanocomposite cladding layer was prepared on the surface of the gradient transition layer; A fish-scale-like array of micro-pits was constructed on the surface of the nanocomposite cladding layer, and a solid lubricant was filled inside the pits of the micro-pit array and then heat-treated to cure the solid lubricant. Post-processing and finishing of machine tool guideways include stress-relieving annealing, precision grinding, and polishing.

[0020] As can be seen from the above, the key bottlenecks of traditional coating technology have been comprehensively solved. Its core advantage lies in the creative introduction of a composition gradient nano-transition layer prepared by the sol-gel method. This ingeniously structured intermediate layer can effectively alleviate the thermal stress caused by the difference in thermal expansion coefficients between the ceramic coating and the metal substrate, thereby improving the interfacial bonding strength to an extremely high level and fundamentally eliminating the risk of coating cracking and peeling.

[0021] The process utilizes a composite powder system of nano-ceramic particles and tough metal matrix, which, under laser irradiation, forms a composite coating structure that combines dispersion reinforcement and metallurgical bonding. This allows the coating to maintain extremely high hardness and excellent wear resistance while also possessing good toughness, making it capable of withstanding severe impacts under heavy-duty conditions.

[0022] This innovative process combines laser in-situ biomimetic microtexturing technology to form a regular microstructure on the coating surface that can store lubricant, thereby achieving a significant reduction in the coefficient of friction and long-term stability of the lubrication state, greatly improving the guide rail's anti-seize and anti-scratch capabilities.

[0023] The entire process chain is also highly controllable. Through precise heat input management and subsequent precision machining, it can ensure that the coating is uniform and dense, and control the workpiece deformation within an extremely low range, perfectly meeting the stringent requirements of machine tool guideways for dimensional accuracy and surface integrity.

[0024] The sandblasting roughening process uses 80-100 mesh brown corundum abrasive, with an air pressure of 0.6-0.8 MPa and a spray angle of 75° to process the surface roughness of the machine tool guide rail substrate to Ra3.2-4.5 μm, thereby enhancing the mechanical bonding points of the coating. The two-phase cleaning process includes ultrasonic acetone cleaning for 15 minutes and ethanol cleaning for 10 minutes to remove oil and particles from the substrate surface. The laser cleaning process uses a wavelength of 1064nm and an energy density of 5-8J / cm². 2 Pulsed fiber laser scanning removes the oxide layer, forming an active surface; Preheating treatment involves preheating the machine tool guide rail substrate to 300-350℃ in an inert gas protective atmosphere to reduce thermal stress during the cladding process.

[0025] The fabrication steps of the multilayer gradient transition layer include: Tetraethyl orthosilicate, aluminum isopropoxide, and zirconium acetylacetonate were mixed in a molar ratio of 4:3:1 to prepare a sol, and 0.5 wt% of silane coupling agent was added. Sol was coated onto the pretreated substrate surface using a dip-coating method at a dip-coating speed of 200 mm / min. After each coating, the substrate was dried at 150°C for 10 minutes. This process was repeated three times to form a transition layer of 0.8–1.2 μm. By adjusting the sol composition, a continuous compositional transition is achieved from the substrate side to the coating side. The coating inside the substrate is a Si- and Al-rich layer, while the coating outside the substrate is a Zr- and Ti-rich layer. The coefficient of thermal expansion of the coating decreases from 12 x 10⁻⁶ to 12 x 10⁻⁶. -6 / ℃ gradually increases to 8x10 -6 / ℃.

[0026] The sol consists of, from the inside out, a bottom layer of bonding adhesive, an intermediate gradient adhesive, and a top layer of compatible adhesive.

[0027] The bottom adhesive tightly bonds the matrix and is prepared from tetraethyl orthosilicate (TEOS) and aluminum isopropoxide (AIP) in a molar ratio of 4:1, with ethanol as the solvent; dilute nitric acid as the catalyst; and 1.5 wt% silane coupling agent (KH550) is added to form a Si-Al-O-rich amorphous network. Its coefficient of thermal expansion is ~11 × 10⁻⁶. -6 / ℃) close to the steel substrate (12×10 -6 It can form strong chemical bonds with the matrix metal oxide through silane coupling agents ( / ℃).

[0028] An intermediate gradient adhesive, used for transitioning between composition and properties, is prepared in a molar ratio of TEOS:AIP:zirconium acetylacetonate (Zr(acac)4) = 2:1:1, with ethanol as the solvent and dilute nitric acid as the catalyst, forming a Si-Al-Zr-O composite oxide. The introduction of Zr allows the coefficient of thermal expansion to transition to approximately 9.5 × 10⁻⁶. -6 / ℃, achieving a buffer from metal to ceramic.

[0029] A top-layer compatible adhesive is used to bond the ceramic coating. The adhesive is prepared in a molar ratio of Zr(acac)4:tetrabutyl titanate (TBT) = 2:1, with ethylene glycol methyl ether as the solvent and acetylacetone as the chelating agent, forming a Zr-Ti-O-rich precursor. Its structure and properties are closest to the top-layer Al2O3-TiC ceramic coating, with a coefficient of thermal expansion of approximately 8.5 × 10⁻⁶. -6 / ℃, ensuring good compatibility.

[0030] The preparation steps of the nanocomposite cladding layer include: Composite powder was prepared by mixing matrix powder and reinforcing phase. The matrix powder was a Co-based alloy (Co-28Cr-6Mo-2Si) with a particle size of 45-75μm, accounting for 75wt%. The reinforcing phase was a mixture of nano-Al2O3 (50nm) and submicron TiC (0.8μm) in a 2:1 ratio, accounting for 25wt%. The mixture was prepared by mixing the two phases using a three-dimensional powder mixer for 4 hours. The beam diameter of the fiber laser was adjusted to 2.5 mm, and the power density was adjusted to 250-300 W / mm². 2 The scanning speed was adjusted to 8-12 mm / s, the overlap rate was 40%, the powder feeding rate was 18-22 g / min, and the protective gas was argon gas with a flow rate of 15-20 L / min. Infrared thermal imagers are used to monitor the molten pool temperature in real time and control it between 1850-2100℃, while the substrate temperature is controlled to not exceed 600℃.

[0031] The micro-pit array has a diameter of 150 μm, a depth of 60 μm, an array spacing of 300 μm, and an arrangement angle of 45°. The micro-pits are processed by a picosecond laser with a pulse width of 10 ps and a wavelength of 532 nm, a single pulse energy of 0.8 mJ, a repetition frequency of 50 kHz, and a scanning speed of 500 mm / s.

[0032] The solid lubricant filling the micro-pits is a polymer-based solid lubricant containing 10% molybdenum disulfide, and is cured by heat treatment at 200°C.

[0033] The post-processing and finishing steps include: Hold at 550℃ for 2 hours, then cool in the furnace to 300℃ and air cool to complete stress-relief annealing; The substrate was ground using a 400# diamond grinding wheel with a grinding depth ≤ 0.01 mm / pass, and the final surface roughness Ra ≤ 0.4 μm. Polishing with diamond polishing paste resulted in a top Ra of ≤0.1μm for the micro-protrusions between the micro-pits.

[0034] The gradient transition layer enables complete metallurgical bonding between the coating and the substrate, without cracks or voids, with an interfacial bonding strength ≥85MPa. The total coating thickness is 0.8-1.2mm, the cladding layer is 0.7-1.0mm, and the transition layer is 0.8-1.2μm.

[0035] Coating surface hardness HV 0.3 The hardness of the heat-affected zone of the matrix decreases gradually from the surface to the substrate, ranging from 1250 to 1450. The hardness of the substrate heat-affected zone is ≤HV 400. Under a load of 10N and a sliding speed of 0.2m / s (dry friction), the wear rate is ≤2.5×10⁻⁶. -6 mm 3 / N·m, which is 4 times higher than that of traditional plasma spraying coatings; the coefficient of friction is 0.18-0.22 in the initial stage, and decreases to 0.12-0.15 after stable operation (it can be reduced to 0.06-0.08 under lubrication conditions); it can withstand ≥5J / cm 2 The impact energy was absorbed without spalling (drop hammer impact test).

[0036] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A laser cladding method for preparing an interface-optimized machine tool guideway nano-ceramic coating, characterized in that, include: The machine tool guide rail substrate is pretreated by sandblasting roughening, two-phase cleaning, laser cleaning and preheating treatment to obtain the pretreated substrate. A multilayer gradient transition layer is prepared on the surface of a pretreated substrate; A nanocomposite cladding layer was prepared on the surface of the gradient transition layer; A fish-scale-like array of micro-pits was constructed on the surface of the nanocomposite cladding layer, and a solid lubricant was filled inside the pits of the micro-pit array and then heat-treated to cure the solid lubricant. Post-processing and finishing of machine tool guideways include stress-relieving annealing, precision grinding, and polishing.

2. The laser cladding method for preparing the interface-optimized machine tool guideway nano-ceramic coating according to claim 1, characterized in that: The sandblasting roughening process uses 80-100 mesh brown corundum abrasive, with an air pressure of 0.6-0.8 MPa and a spray angle of 75° to process the surface roughness of the machine tool guide rail substrate to Ra3.2-4.5 μm; The two-phase cleaning process includes ultrasonic cleaning with acetone for 15 minutes and cleaning with ethanol for 10 minutes. The laser cleaning process uses a wavelength of 1064nm and an energy density of 5-8J / cm². 2 Pulsed fiber laser scanning removes the oxide layer; The preheating treatment involves preheating the machine tool guide rail base to 300-350℃ in an inert gas protective atmosphere.

3. The laser cladding method for preparing the interface-optimized machine tool guideway nano-ceramic coating according to claim 1, characterized in that, The fabrication steps of the multilayer gradient transition layer include: Tetraethyl orthosilicate, aluminum isopropoxide, and zirconium acetylacetonate were mixed in a molar ratio of 4:3:1 to prepare a sol, and 0.5 wt% of silane coupling agent was added. Sol was coated onto the pretreated substrate surface using a dip-coating method at a dip-coating speed of 200 mm / min. After each coating, the substrate was dried at 150°C for 10 minutes. This process was repeated three times to form a transition layer of 0.8–1.2 μm. By adjusting the sol composition, a continuous compositional transition is achieved from the substrate side to the coating side. The coating inside the substrate is a Si- and Al-rich layer, while the coating outside the substrate is a Zr- and Ti-rich layer. The coefficient of thermal expansion of the coating decreases from 12 x 10⁻⁶ to 12 x 10⁻⁶. -6 / ℃ gradually increases to 8x10 -6 / ℃.

4. The laser cladding method for preparing the interface-optimized machine tool guideway nano-ceramic coating according to claim 1, characterized in that, The preparation steps of the nanocomposite cladding layer include: Composite powder was prepared by mixing matrix powder and reinforcing phase. The matrix powder was a Co-based alloy with a particle size of 45-75μm, accounting for 75wt%. The reinforcing phase was a mixture of nano-Al2O3 and submicron TiC in a 2:1 ratio, accounting for 25wt%. The mixture was prepared by mixing with a three-dimensional powder mixer for 4 hours. The beam diameter of the fiber laser was adjusted to 2.5 mm, and the power density was adjusted to 250-300 W / mm². 2 The scanning speed was adjusted to 8-12 mm / s, the overlap rate was 40%, the powder feeding rate was 18-22 g / min, and the protective gas was argon gas with a flow rate of 15-20 L / min. Infrared thermal imagers are used to monitor the molten pool temperature in real time and control it between 1850-2100℃, while the substrate temperature is controlled to not exceed 600℃.

5. The laser cladding method for preparing the interface-optimized machine tool guideway nano-ceramic coating according to claim 1, characterized in that, The micro-pit array has a diameter of 150 μm, a depth of 60 μm, an array spacing of 300 μm, and an arrangement angle of 45°. The micro-pits are processed by a picosecond laser with a pulse width of 10 ps and a wavelength of 532 nm, a single pulse energy of 0.8 mJ, a repetition frequency of 50 kHz, and a scanning speed of 500 mm / s.

6. The laser cladding method for preparing an interface-optimized machine tool guideway nano-ceramic coating according to claim 1, characterized in that, The solid lubricant filling the micro-pits is a polymer-based solid lubricant containing 10% molybdenum disulfide, and is cured by heat treatment at 200°C.

7. The laser cladding method for preparing the interface-optimized machine tool guideway nano-ceramic coating according to claim 1, characterized in that, The post-processing and finishing steps include: Hold at 550℃ for 2 hours, then cool in the furnace to 300℃ and air cool to complete stress-relief annealing; The substrate was ground using a 400# diamond grinding wheel with a grinding depth ≤ 0.01 mm / pass, and the final surface roughness Ra ≤ 0.4 μm. Polishing with diamond polishing paste resulted in a top Ra of ≤0.1μm for the micro-protrusions between the micro-pits.

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