Titanium alloy valve based on composite ceramic coating

Abstract

This invention relates to the field of surface strengthening technology for automotive parts, and provides a titanium alloy valve based on a composite ceramic coating. The valve includes a valve stem and a valve assembly mounted at the bottom of the valve stem. A connector is fixedly connected to the top of the valve assembly, and a valve stem insertion hole is provided at the bottom of the valve stem. The size of the connector and the valve stem insertion hole are matched by an interference fit. The valve assembly is coated with a composite ceramic coating. This device improves the valve's high-temperature resistance and wear resistance. By applying a composite ceramic coating to the valve, it effectively resists oxidation, deformation, and wear caused by high temperatures under the harsh conditions of high-pressure diesel engines, significantly extending the valve's service life and meeting the requirements for long-term stable operation.

Description

Technical Field

[0001] This invention relates to the field of surface strengthening technology for parts and components, and provides a titanium alloy valve based on a composite ceramic coating. Background Technology

[0002] Valve and valve stem are crucial components of an internal combustion engine, primarily used to control the intake and exhaust of gases within the engine cylinders. Valve controls the intake and exhaust processes of the cylinders, ensuring the engine's normal operation. The valve stem is the core component of the valve, supporting its opening and closing movements through its connection with the valve seat. The valve stem typically works in conjunction with other valve components to control the gases entering the cylinder, ensuring the engine's performance and efficiency under various operating conditions.

[0003] Valve and valve stem structures are typically cylindrical, with the length and diameter of the valve stem varying depending on the engine type and design requirements. Valve stems are usually made of high-strength alloy materials, requiring good mechanical properties, corrosion resistance, and high-temperature resistance. The manufacturing process for valves typically includes material selection, precision casting, machining, and heat treatment. Valve stem machining involves turning, grinding, and heat treatment to ensure precision and durability. During manufacturing, special attention must be paid to the valve stem's hardness, surface finish, and wear resistance to ensure it can withstand the harsh operating conditions of the engine, including high temperature, high pressure, and high speed.

[0004] However, in the operating environment of high-boost diesel engines, especially at temperatures exceeding 800°C, valve cores face extremely severe challenges. Under high temperatures, the wear resistance of valve stems and related components decreases significantly, making them prone to high-temperature corrosion, oxidation, and wear, thus affecting engine performance and service life. For example, the density of traditional steel valve stems is 7.8 g / cm³. 3 This results in excessive inertial force, limiting engine speed increases. In contrast, titanium-aluminum alloys and titanium alloy valves offer superior performance with a density of 4-4.43 g / cm³. 3 The surface hardness is insufficient (HV330), resulting in a high coefficient of friction of 0.35-0.45 with cast iron conduits (HV450-550). To avoid this, existing coating technologies typically employ either PVD-TiN coatings with a thickness <5μm (PVD-TiN coatings have significantly shortened lifespan and gradually lose effectiveness at temperatures >400℃) or plasma-sprayed Al2O3, which has a bonding strength <50MPa and poor thermal shock resistance.

[0005] Therefore, the existing valve technology and valve processing technology are still insufficient and cannot meet the long-term stable operation requirements of high-boost diesel engines under harsh conditions such as high temperature and high pressure. There is an urgent need for a new technology that can significantly improve the high temperature and wear resistance of valve stems in order to extend the service life of valves. Utility Model Content

[0006] To address the aforementioned deficiencies, the present invention aims to provide a titanium alloy valve based on a composite ceramic coating, in order to solve the problems raised in the background art. This includes a valve stem utility model and a valve utility model mounted at the bottom of the valve stem utility model. The top of the valve utility model is fixedly connected to a connector utility model, and the bottom of the valve stem utility model is provided with a valve stem insertion hole utility model. The size of the connector utility model and the valve stem insertion hole utility model are matched by an interference fit. The valve utility model is coated with a composite ceramic coating.

[0007] Furthermore, the plug-in part is a cylindrical structure; when the valve stem is heated, the inner diameter of the valve stem insertion hole at its bottom allows the plug-in part to be inserted, and when the temperature returns to normal, the valve stem insertion hole and the plug-in part can fit together tightly.

[0008] Furthermore, the bottom of the valve stem utility model is provided with an embedding part utility model, the embedding part utility model is a frustum-shaped structure, the top of the frustum-shaped structure is integrally connected with the valve stem utility model, the valve stem insertion hole utility model is provided at the bottom of the embedding part utility model, and the top of the valve utility model is provided with a valve insert hole utility model that matches the embedding part utility model.

[0009] Furthermore, the valve stem utility model is provided with a valve stem screw hole utility model, and the insertion part utility model is provided with an insertion part screw hole utility model corresponding to the valve stem screw hole utility model.

[0010] This invention utilizes a titanium alloy valve based on a composite ceramic coating, which improves the valve's high-temperature resistance and wear resistance compared to existing technologies. By applying a composite ceramic coating to the valve, it effectively resists oxidation, deformation, and wear caused by high temperatures under the harsh conditions of high-boost diesel engines, thus significantly extending the valve's service life and meeting the requirements for long-term stable operation. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the valve structure;

[0012] Figure 2 This is a cross-sectional view of the valve structure;

[0013] Figure 3This is a schematic diagram of the inflatable mounting cavity structure;

[0014] In the diagram: 1-Valve; 11-Connection part; 111-Connection part screw hole; 12-Valve insert hole; 2-Valve stem; 201-Valve stem screw hole; 202-Reinforcing rib; 21-Valve stem insertion hole; 22-Embedded part; 3-Lower valve spring seat ring groove; 4-Inflation mounting cavity; 41-Inlet end; 42-Outlet end; 5-Heating coil; 6-Clamping mechanism; 7-Lifting platform; 71-Valve tooling. Detailed Implementation

[0015] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments.

[0016] It should be noted that, in the description of this utility model, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model 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 this utility model. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0017] Furthermore, in the description of this utility model, unless otherwise explicitly specified and limited, the terms "connected" and "linked" 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. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0018] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the scope of the present utility model.

[0019] See Figure 1-3This utility model provides a titanium alloy valve based on a composite ceramic coating, including a valve stem 2 and a valve 1 mounted at the bottom of the valve stem 2; the top of the valve 1 is fixedly connected to a connector 11, and the bottom of the valve stem 2 is provided with a valve stem insertion hole 21, the size of the connector 11 and the valve stem insertion hole 21 being matched by an interference fit. The valve 1 is coated with a composite ceramic coating.

[0020] Specifically, the insertion part 11 has a cylindrical structure. At room temperature, the outer diameter of the insertion part 11 is slightly larger than the inner diameter of the valve stem insertion hole 21. When the valve stem 2 is heated, the inner diameter of the valve stem insertion hole 21 at the bottom of the valve stem 2 allows the insertion part 11 to be inserted. When the temperature returns to room temperature, the valve stem insertion hole 21 and the insertion part 11 can fit together tightly.

[0021] Preferably, the bottom of the valve stem 2 is provided with an insert portion 22, which has a frustoconical structure. The top (smaller diameter end) of the frustoconical structure of the insert portion 22 is integrally connected to the valve stem 2, and the valve stem insertion hole 21 is located at the bottom of the insert portion 22. The top of the valve 1 is provided with a recessed valve mounting hole 12, which matches the insert portion 22. During installation, the insert portion 22 can be inserted into the valve mounting hole 12, thereby achieving a more stable connection and fixation.

[0022] Preferably, the valve stem 2 is provided with a valve stem screw hole 201, and the insertion part 11 is provided with an insertion part screw hole 111 corresponding to the valve stem screw hole 201. When the insert part 22 can be inserted into the valve insert hole 12, the two can be further fixed by the screw, thereby ensuring further structural reinforcement.

[0023] Furthermore, based on the structure of the titanium alloy valve with the above composite ceramic coating, this utility model also provides a manufacturing process for the titanium alloy valve with the composite ceramic coating.

[0024] The manufacturing process proposed in this utility model improves the performance of titanium-aluminum alloy and titanium alloy valve stems by using titanium-aluminum alloy or titanium alloy as the base material for the valve stem, a preliminary processing flow for the base material, a special material combination, and post-processing assembly of several parts. This primarily meets the usage requirements under harsh conditions of high temperature and high wear, such as in high-power automotive engines and high-boost diesel engines.

[0025] The manufacturing process of titanium alloy valves based on composite ceramic coatings mainly involves the following steps. To make the technical concept of this utility model clearer, the technology of each step is described in detail below.

[0026] This invention pre-processes the valve 1 and the valve stem 2 near the valve 1 (the outer surface of the embedded part 22) using laser equipment to create a roughened layer. Specifically, this production line utilizes a continuous wave laser system (IPGYLS-5000 fiber laser), preferably with parameters of 400W power, 100ns pulse width, and 20kHz frequency, to process the surface of the alloy substrate; that is, a high-energy laser beam is used to scan the substrate surface, making the originally smooth and flat surface rough, forming a peak-valve micro-texture.

[0027] Specifically, the average surface roughness (Ra) of the surface-treated parts is controlled within the range of 5-10 μm. This provides better "adhesion points" for subsequent coatings, enhancing the adhesion between the coating and the substrate.

[0028] Specifically, through parameter control of the laser equipment, a micro-pit array of a texturing layer is formed on all parts of the valve 1 except for the outer surface of the embedded part 22. The micro-pit diameter is 50-80 μm, the aspect ratio is 0.4, and the density reaches 150±20 pits / mm. 2 The micro-pit array structure ensures that subsequent coating materials can fill the interior of the micro-pit structure, improving bonding strength. Furthermore, the optimized size and distribution of the micro-pits minimize the mismatch in thermal expansion coefficients (d) between the coating and the substrate. For example, TC4 and ZrO2 have different thermal expansion coefficients; when combined, they are prone to tearing or loosening under microscopic mechanical conditions, leading to cracks and delamination between the coating and the substrate.

[0029] This invention employs a NiCrAlY-20%TiN transition layer to coat the substrate. Specifically, NiCrAlY is a commonly used high-temperature alloy coating material with excellent resistance to high-temperature oxidation and corrosion. This invention incorporates 20% TiN (titanium nitride) nanoparticles into the NiCrAlY material, with the TiN nanoparticles having a size of 50-100 nm.

[0030] Meanwhile, this invention employs high-speed oxygen fuel spraying (HVOF spraying process) to create a gradient distribution of TiN nanoparticles within the NiCrAlY matrix. Specifically, the TiN content gradually changes from the side closer to the laser-textured layer to the side closer to the surface layer. This alleviates stress concentration issues caused by differences in the thermal expansion coefficients of different materials, achieving a smooth transition from the matrix to the surface layer and preventing cracks or warping due to excessive material differences.

[0031] This invention uses a ZrO2-8Y2O3-5%SiC coating to coat the bottom surface of valve 1:

[0032] The ZrO2-8Y2O3-5%SiC surface layer utilizes zirconium oxide (ZrO2), yttrium oxide (Y2O3), and silicon carbide (SiC) materials, exhibiting excellent high-temperature performance, thermal insulation, and wear resistance. The addition of 8% Y2O3 (yttrium oxide) to the ZrO2-8Y2O3-5%SiC surface layer stabilizes the ZrO2 phase structure, improving its high-temperature and thermal stability. SiC possesses high hardness, high wear resistance, and good corrosion resistance; the addition of 5% SiC (silicon carbide) enhances the wear and corrosion resistance of the entire surface layer while maintaining excellent thermal insulation.

[0033] Furthermore, the ZrO2-8Y2O3-5%SiC surface layer used in this invention incorporates a transition metal boron-nitrogen ceramic synergistic phase (HfB2-HfN). This effectively inhibits crack propagation, further improves toughness, and optimizes stress distribution.

[0034] Both HfB2 and HfN introduced in this scheme are high-melting-point ceramics (>3300℃). However, HfB2 has a melting point of 3250℃ but poor oxidation resistance, while HfN will oxidize above 1200℃. The coefficients of thermal expansion of both are about 30% higher than those of the matrix. The addition amount must be controlled below the percolation threshold, otherwise the coating will crack. The HfB2 / HfN addition amount proposed in this invention is ≤8wt%, while the SiC component is reduced to 4% to balance the total composition.

[0035] For the powder pretreatment process of HfB2 and HfN, a high-energy ball mill under argon protection is used for mixing (the mixture contains YSZ, SiC, HfB2, and HfN), and the ball milling time is ≤4h (to prevent grain coarsening). Therefore, the ZrO2-8Y2O3-5%SiC surface layer used in this invention provides wear resistance, ultra-high temperature strengthening, and creep resistance, with a hardness retention rate >80% at 1100℃ and a 60% improvement in thermal shock life. The HfB2 and HfN doping can remain stable in harsh exhaust environments >1000℃, and provides stronger resistance to oxidation and molten salt corrosion when low-ash engine oil additives are present in the engine.

[0036] For HVOF (High-Voltage Oxygen Fuel Spraying), the particle velocity is set to 750 m / s. During HVOF spraying, powder particles are accelerated to extremely high speeds (750 m / s), controlled with an accuracy of ±25 m / s. These high-speed particles collide with the laser-textured substrate surface, rapidly depositing to form a dense coating. The high-speed impact helps improve the coating's bonding strength and density; imagine a high-speed bullet hitting a wall—the bullet will embed firmly in the wall. Similarly, high-speed particles more easily bond tightly to the substrate.

[0037] Equipment parameter correspondence: Using the Praxair JP-8000 equipment, the kerosene flow rate is set to 25L / min, and the powder feed rate to 35g / min, thereby achieving the required particle velocity control. Kerosene, as fuel, provides energy; its flow rate affects the flame intensity and temperature, which in turn affects the particle acceleration and heating degree. The powder feed rate determines the amount of powder entering the spray gun per unit time, and in conjunction with the kerosene flow rate, ensures that the powder particles achieve a suitable flight velocity.

[0038] In this invention, valve 1, as a complete valve assembly, directly participates in the intake and exhaust process of the engine and needs to withstand high temperature, high pressure, and frequent mechanical friction. Therefore, valve 1 has very high requirements for the comprehensive performance of its coating, such as wear resistance, heat resistance, and corrosion resistance. Valve stem 2, as part of the valve assembly, mainly plays a guiding and supporting role and does not directly contact high-temperature gases or withstand high-intensity friction; therefore, its requirements for some extreme performance characteristics are relatively lower.

[0039] This utility model relates to a pretreatment process for valve 1 and valve stem 2 using different technological steps, specifically including the following steps:

[0040] As a complete valve assembly, valve 1 undergoes the following process steps:

[0041] 1. Laser texturing: Using an IPGYLS-5000 fiber laser with parameters of 400W power, 100ns pulse width, and 20kHz frequency, the surface of valve 1 (including the head and stem) is laser texturized to form a laser texturing layer with an average roughness (Ra) of 5-10μm, and a micro-pit array structure (diameter 50-80μm, aspect ratio 0.4, density 150±20 pits / mm). 2 The above steps provide a good bonding foundation for subsequent coatings, ensuring that the coating can adhere firmly to the surface of valve 1.

[0042] 2. HVOF Spraying: Using a Praxair JP-8000 machine, with a kerosene flow rate of 25L / min and a powder feed rate of 35g / min, powder particles impact the laser-textured valve 1 surface at a velocity of 750±25m / s, and a NiCrAlY-20%TiN transition layer is sprayed on. The transition layer has a gradient distribution of TiN nanoparticles (50-100nm), which can achieve good matching with the substrate and the surface layer, alleviate problems such as differences in thermal expansion coefficients, and improve the overall performance of the coating.

[0043] 3. Plasma Spraying: A ZrO2-8Y2O3-5%SiC topcoat is plasma sprayed onto the surface of valve 1. The porosity of the coating is strictly controlled to be below 1.5%, and the porosity is monitored in real time using online CT detection to ensure the density and quality of the coating. The topcoat provides valve 1 with excellent heat insulation, wear resistance, and corrosion resistance, enabling it to better adapt to harsh operating conditions such as high temperature and wear.

[0044] As a component of the valve assembly, valve stem 2's main function is to connect the valve head and the valve drive mechanism. Compared to valve 1, its working environment is relatively simple, mainly subjecting it to friction and wear along the stem and a certain degree of temperature change. Therefore, its requirements for comprehensive performance such as heat insulation and wear resistance are relatively low, and some processes can be omitted. The specific processes are as follows:

[0045] 1. Laser texturing: The laser texturing process for valve bores is omitted. Other parts are texturized by laser to increase the surface roughness of the valve and form a micro-pit array, which can improve the adhesion between the coating and the rod substrate and prevent the coating from peeling off.

[0046] 2. HVOF Coating: The coating of the valve stem 2 and valve bores on valve 1 is omitted. Since valve stem 2 primarily bears the force transmission, its requirements for the high-temperature performance and overall protective performance of the coating are not as high as those for valve 1. Omitting the HVOF coating step allows for the direct application of a relatively simple coating that meets the usage requirements of valve stem 2, such as some common wear-resistant coatings. This simplifies the process, reduces production costs, and does not affect the normal performance of valve stem 2.

[0047] Similarly, valve bores do not require coating.

[0048] 3. Plasma spraying: This can be omitted. Valve stem 2 does not need to withstand the direct impact of high-temperature combustion gases and complex thermal stress changes like valve stem 1; therefore, its requirements for thermal insulation performance are not high. Omitting the plasma spraying ZrO2-8Y2O3-5%SiC topcoat not only reduces process steps and costs but also avoids unnecessary performance redundancy that this coating might have on valve stem 2, without affecting the basic function of valve stem 2.

[0049] In the above steps, the HVOF spraying step needs to be performed under certain temperature conditions. When HVOF spraying is performed under certain high temperature conditions, the surface temperature of the substrate material will rise appropriately, allowing the sprayed particles to undergo better plastic deformation upon impact with the substrate surface. At the same time, because the high temperature reduces the yield strength of the substrate surface material, making it more prone to deformation, HVOF spraying under these conditions allows the high-speed impacting powder particles to embed more deeply into the micro-pits and rough textures of the substrate surface, forming a stronger mechanical bond and ensuring that the coating is less prone to peeling off during subsequent use.

[0050] For coating and substrate systems composed of different materials, thermal stress will be generated due to the difference in thermal expansion coefficients during operation. However, HVOF spraying under high-temperature conditions allows the coating to gradually adapt to the thermal expansion state of the substrate during deposition, helping to alleviate the thermal stress concentration between the coating and the substrate during operation. In the existing valve 1 processing procedure, the valve 1 needs to be heated and sprayed before it can be installed with the valve stem 2. This directly leads to more severe peeling between the coating and the substrate system due to the difference in thermal expansion coefficients, which will accelerate the damage to the valve 1.

[0051] Therefore, in addition to providing a method for HVOF spraying via thermal spraying, this utility model also proposes an interference fit assembly device for valves and a pre-processing step for thermal spraying.

[0052] The equipment includes a clamping mechanism 6 capable of holding the upper end of the valve stem 2, and a valve fixture 71 capable of installing the valve 1. The valve fixture is mounted on a lifting platform 7, which is mounted on a turntable device, enabling the processed valve components to be moved to other processes. The equipment also includes an inflation mounting cavity 4, inside which a heating coil 5 is installed. The heating coil 5 utilizes the principle of electromagnetic induction heating; that is, when the bottom of the metal valve stem 2 is inserted into the alternating magnetic field of the heating coil 5, an induced electromotive force is generated inside the metal, thereby forming eddy currents. Due to the resistivity of the metal material, a large amount of heat is generated, causing the end of the valve stem 2 to heat up and deform rapidly. At this time, the clamping mechanism 6 drives the valve stem 2 to descend, completing the insertion with the valve 1.

[0053] The inflatable mounting cavity 4 is equipped with an air inlet 41 and an air outlet 42. The air inlet 41 and the air outlet 42 are connected to an external ventilation system, which can discharge the residual heat inside the continuously operating equipment.

[0054] Under the action of heating coil 5, the heat will increase the diameter of valve stem insertion hole 21 to complete the insertion process. In the subsequent cooling process, the diameter will shrink to complete the interference fit. At the same time, due to the heat diffusion between valve 1 and valve stem 2, the outer surface of valve 1 will be further heated. At this time, clamping mechanism 6 releases the clamp, and lifting platform 7 drives valve fixture 71 and valve stem 2 to descend and enter the next HVOF spraying process. At this time, due to heat diffusion, valve 1 is heated and the spraying process is directly carried out in the HVOF spraying process, which greatly improves the processing speed.

[0055] Of course, there may be other embodiments of this utility model. Without departing from the spirit and essence of this utility model, those skilled in the art can make various corresponding changes and modifications based on this utility model, but these corresponding changes and modifications should all fall within the protection scope of the appended claims of this utility model.

Claims

1. A titanium alloy valve based on a composite ceramic coating, characterized in that, It includes a valve stem (2) and a valve (1) mounted on the bottom of the valve stem (2); the top of the valve (1) is fixedly connected to a plug part (11), the bottom of the valve stem (2) is provided with a valve stem insertion hole (21), the size of the plug part (11) is matched with the valve stem insertion hole (21) by interference fit, and the valve (1) is provided with a composite ceramic coating.

2. The titanium alloy valve based on a composite ceramic coating according to claim 1, characterized in that, The plug-in part (11) has a cylindrical structure; when the valve stem (2) is heated, the inner diameter of the valve stem insertion hole (21) at its bottom allows the plug-in part (11) to be inserted. When the temperature returns to normal, the valve stem insertion hole (21) and the plug-in part (11) can fit together tightly.

3. The titanium alloy valve based on a composite ceramic coating according to claim 1, characterized in that, The bottom of the valve stem (2) is provided with an insert (22), the insert (22) is a frustum structure, the top of the frustum structure is integrally connected with the valve stem (2), the valve stem insertion hole (21) is provided at the bottom of the insert (22), and the top of the valve (1) is provided with a valve insert hole (12) that matches the insert (22).

4. The titanium alloy valve based on a composite ceramic coating according to claim 1, characterized in that, The valve stem (2) is provided with a valve stem screw hole (201), and the plug part (11) is provided with a plug part screw hole (111) corresponding to the valve stem screw hole (201).

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