A nitriding method for Ti-6Ai-4V titanium alloy valves for unmanned aerial vehicles

Abstract

This invention belongs to the field of metal material surface treatment technology, and discloses a nitriding method for Ti-6Ai-4V titanium alloy valves of unmanned aerial vehicles (UAVs). It employs a combined process of ion nitriding and gas nitriding: first, ion nitriding is performed at 550℃ to remove the TiO2 passivation film on the valve surface using ion bombardment; then, gas nitriding is performed at 680℃±5℃ to obtain the desired nitriding hardness and layer depth. A three-stage temperature control curve is used during the ion nitriding process to control deformation. After treatment, the valve surface hardness is ≥600HV. 0.1 The effective hardened layer depth is ≥0.01mm, and the runout of the outer circle of the rod and the arc surface of the disc is ≤0.01mm. This invention solves the problems of large deformation and high equipment requirements in the existing high-temperature ion nitriding process (860℃~900℃), and overcomes the difficulty of TiO2 passivation film obstruction in low-temperature simple gas nitriding. It is suitable for mass production of Ti-6Al-4V titanium alloy valves for UAVs.

Description

Technical Field

[0001] This invention belongs to the field of metal material surface treatment technology, and relates to a nitriding method for Ti-6Ai-4V titanium alloy valves of unmanned aerial vehicles. Background Technology

[0002] Ti-6Al-4V titanium alloy is an α+β type titanium alloy with comprehensive advantages such as high specific strength, excellent corrosion resistance, and good high-temperature mechanical properties, and is widely used in aerospace, shipbuilding, chemical, and medical fields. In recent years, with the rapid development of UAV technology, the performance requirements for key engine components have been increasing. As a core component in the valve train of UAV engines, the valve is subjected to the scouring of high-temperature and high-pressure combustion gases and repeated opening and closing impact loads during operation. There is high-frequency reciprocating friction between the valve stem and the guide, and there is periodic sealing impact contact between the upper arc surface of the valve disc and the valve seat. Therefore, the valve surface is required to have high hardness and good wear resistance. Ti-6Al-4V titanium alloy has been selected as the manufacturing material for UAV valves due to its excellent comprehensive properties. However, the surface hardness of this alloy itself is relatively low, which is difficult to meet the wear resistance requirements of the valve under working conditions. Therefore, surface strengthening treatment is needed to improve its surface hardness and wear resistance.

[0003] Nitriding is a crucial surface engineering technique for improving the surface hardness and wear resistance of metal parts. For titanium alloys, nitriding can form a nitride layer with extremely high hardness on the surface, significantly improving surface hardness and wear resistance. However, Ti-6Al-4V titanium alloys readily form a dense and stable TiO2 passivation film on their surface under natural conditions. This passivation film effectively blocks the diffusion of nitrogen atoms into the substrate. In conventional gas nitriding processes, the active nitrogen atoms generated by the decomposition of ammonia gas have difficulty penetrating this TiO2 passivation film, resulting in ineffective gas nitriding at lower temperatures, poor adhesion between the nitride layer and the substrate, and unsatisfactory nitriding results.

[0004] To address the obstacle that the TiO2 passivation film poses to nitriding, existing technologies typically employ high-temperature ion nitriding to treat Ti-6Al-4V titanium alloys. This process utilizes the physical sputtering effect of ion bombardment to remove the TiO2 passivation film from the surface and achieves nitriding at high temperatures ranging from 860°C to 900°C. Although high-temperature ion nitriding can solve the problem of TiO2 passivation film to some extent and obtain a certain nitriding layer depth and surface hardness, this process has the following prominent technical problems: First, under high temperature conditions of 860℃ to 900℃, the yield strength of Ti-6Al-4V titanium alloy is significantly reduced. Under the combined action of its own weight, thermal stress, and ion bombardment force, the parts are prone to plastic deformation. For slender rod-shaped valve parts, the roundness and straightness of the outer circle of the rod and the dimensional accuracy of the upper arc surface of the disc are difficult to control, and the deformation often exceeds the design tolerance requirements of the parts. Second, the high temperature of 860℃ to 900℃ places high demands on the temperature resistance of the ion nitriding equipment. However, in actual production, the limit operating temperature of some ion nitriding equipment is only 650℃, which cannot meet the requirements of this temperature range, thus limiting the applicability of the process. Third, prolonged high-temperature treatment may lead to coarsening of the titanium alloy matrix structure, affecting mechanical properties.

[0005] Furthermore, while the temperature of a simple gas nitriding process is controllable, the presence of a TiO2 passivation film makes it difficult to perform gas nitriding effectively at lower temperatures, failing to achieve the required nitriding layer depth and surface hardness. Therefore, effectively removing the TiO2 passivation film from the surface of Ti-6Al-4V titanium alloy at lower temperatures, while ensuring that the nitrided parts meet comprehensive requirements regarding surface hardness, hardened layer depth, and heat treatment deformation, is a pressing technical problem to be solved in this field. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to solve the above problems and provide a nitriding method for Ti-6Ai-4V titanium alloy valves of unmanned aerial vehicles.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A nitriding method for Ti-6Al-4V titanium alloy valves for unmanned aerial vehicles includes the following steps: S1. Ion nitriding: The Ti-6Al-4V titanium alloy valve is placed in an ion nitriding device and ion nitrided at 550°C to remove the TiO2 passivation film on the valve surface. S2. Gas nitriding: The valve treated in step S1 is placed in a gas nitriding furnace and gas nitrided at a temperature of 680℃±5℃.

[0008] Further, in step S1, the valve is placed vertically on the cathode plate or tooling plate of the ion nitriding equipment, and the cathode plate or tooling plate is adjusted to be in a horizontal state so that the valve is kept in a vertically mounted posture.

[0009] Furthermore, in step S1, the vacuum degree of ion nitriding is 270~280 Pa, the glow thickness is 4~5 mm, and the nitriding time is 10~12 hours.

[0010] Furthermore, in step S1, the heating process of ion nitriding is divided into three stages: Low temperature heating stage: First, heat up to 200℃ at a rate of 5℃ / minute and maintain the temperature uniformly for 5 minutes, then heat up to 320℃ at a rate of 4℃ / minute and maintain the temperature uniformly for 5 minutes; Medium-temperature heating stage: Heat to 430℃ at a rate of 2℃ / minute and maintain uniform temperature for 30 minutes; High-temperature heating stage: The temperature is increased to 550℃ at a rate of 1℃ / minute, and ion nitriding is carried out at 550℃.

[0011] Furthermore, in step S2, the valve is vertically mounted in the circular groove of the gas nitriding apparatus, with the lower end of the valve plate placed in the circular groove. The apparatus is adjusted to be horizontal so that the valve maintains a vertical posture during the gas nitriding process.

[0012] Furthermore, in step S2, the ammonia flow rate for gas nitriding is 0.75 m³ / h, the furnace pressure is ≥50 mm water column, and the nitriding time is 12~15 hours.

[0013] Furthermore, after the ion nitriding treatment in step S1, the TiO2 passivation film on the valve surface is removed, allowing nitrogen atoms to diffuse into the valve substrate during gas nitriding in step S2.

[0014] Furthermore, the valves obtained after steps S1 and S2 meet the following performance requirements: surface hardness ≥ 600 HV. 0.1 The effective hardened layer depth is ≥0.01mm, the runout of the outer circle of the rod is ≤0.01mm, and the runout of the upper arc surface of the disc is ≤0.01mm.

[0015] The beneficial effects of this invention are as follows: First, by performing ion nitriding at a relatively low temperature of 550℃, the TiO2 passivation film on the surface of the Ti-6Al-4V titanium alloy valve is effectively removed through ion bombardment. This allows nitrogen atoms to diffuse into the valve substrate during subsequent gas nitriding, improving the adhesion between the nitrided layer and the substrate, and enhancing the overall nitriding effect. Since the ion nitriding temperature is only 550℃, far lower than the existing ion nitriding temperatures of 860℃ to 900℃, it is suitable for ion nitriding equipment with a maximum operating temperature of 650℃, thus broadening the equipment applicability of the process.

[0016] Secondly, by performing gas nitriding at a temperature of 680℃±5℃, the required nitriding hardness and hardened layer depth were obtained. After treatment, the valve surface hardness reached 640HV. 0.1 Around, satisfying ≥600HV 0.1 The hardness requirement is met; the effective hardened layer depth reaches 0.013mm, satisfying the layer depth requirement of ≥0.01mm. Its performance is similar to that of imported Ti-6Al-4V titanium alloy valves, and it can meet the need to replace imported parts.

[0017] Third, by using a three-stage temperature control curve and precisely controlling the gas nitriding temperature within the range of 680℃±5℃, the heat treatment deformation of the valve was effectively controlled. After treatment, the outer diameter runout of the valve stem was approximately 0.007mm, and the upper arc surface runout of the valve disc was approximately 0.006mm, both meeting the deformation control requirement of ≤0.01mm. Compared to the potentially large deformation caused by the existing high-temperature ion nitriding process of 860℃ to 900℃, the deformation control effect of this invention is significantly superior.

[0018] Fourth, this invention employs a two-step process combining ion nitriding to remove the passivation film and gas nitriding. This process uses a relatively low overall processing temperature, which avoids equipment limitations and deformation problems caused by high temperatures. Furthermore, the synergistic effect of the two nitriding methods ensures the final nitriding quality. The process is stable and controllable, and is suitable for the mass production of Ti-6Al-4V titanium alloy valves for UAVs.

[0019] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the Ti-6Al-4V titanium alloy valve part involved in the present invention.

[0021] Figure 2 This is a schematic diagram of the tooling used in the gas nitriding step of the present invention.

[0022] Figure 3 This is a schematic diagram of the process curve for the ion nitriding step of the present invention. Detailed Implementation

[0023] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0024] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0025] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0026] Example 1 like Figure 1 As shown, the Ti-6Al-4V titanium alloy valve of this invention has a slender rod-like structure, including a rod portion and a disc portion located at the lower end of the rod portion, the upper end surface of the disc portion being an arc surface. There is reciprocating frictional motion between the valve rod portion and the guide, and there is a sealing impact contact between the arc surface of the upper end of the disc portion and the valve seat; therefore, the valve needs to be nitrided to improve its surface hardness and wear resistance. The nitriding method for the Ti-6Al-4V titanium alloy valve of this UAV includes the following steps: Step S1, Ion nitriding: The Ti-6Al-4V titanium alloy valve is placed vertically on the cathode plate or tooling plate of the ion nitriding equipment. The cathode plate or tooling plate is adjusted to ensure it is horizontal, guaranteeing the valve's vertical mounting and preventing deformation of the valve stem and upper arc surface during subsequent nitriding due to tilting. Ion nitriding is performed at 550℃ to remove the TiO2 passivation film on the valve surface. The vacuum degree of ion nitriding is 270~280Pa, the glow discharge thickness is 4~5mm, and the nitriding time is 10~12 hours.

[0027] The heating process of ion nitriding is as follows Figure 3 As shown, it is divided into three stages: (1) Low temperature heating stage: The heating rate to 200℃ is 5℃ / minute, and the temperature is evenly distributed for 5 minutes; the heating rate to 320℃ is 4℃ / minute, and the temperature is evenly distributed for 5 minutes. The low temperature stage is to ensure heating efficiency.

[0028] (2) Medium temperature heating stage: The heating rate to 430℃ is 2℃ / minute, and the temperature is uniform for 30 minutes. The temperature is raised at a low rate and uniformly heated to control deformation.

[0029] (3) High temperature heating stage: The temperature is increased to 550℃ at a rate of 1℃ / minute, and ion nitriding is carried out at 550℃.

[0030] The purpose of ion nitriding is to remove the TiO2 passivation film on the surface of Ti-6Al-4V titanium alloy, improve the adhesion between the nitrided layer and the substrate, and enhance the nitriding effect. During production, the ion nitriding stage is limited by the extreme temperature of the ion nitriding equipment (650℃), serving as both a passivation film removal stage and an auxiliary nitriding stage for titanium alloy valves.

[0031] Step S2, Gas Nitriding: like Figure 2 As shown, the valve, after being processed in step S1, is vertically installed in the circular groove of the gas nitriding apparatus. The lower end of the valve's disc is placed in the groove, and the apparatus is adjusted to be horizontal to ensure that the valve maintains a vertical posture as much as possible during the gas nitriding process. Gas nitriding is carried out at a temperature of 680℃±5℃, with an ammonia flow rate of 0.75 m³ / h, a furnace pressure ≥50 mm water column, and a nitriding time of 12~15 hours.

[0032] In particular, the gas nitriding temperature is closely related to the nitriding effect and deformation control. When the temperature is ≤670℃, the nitriding hardness does not meet the requirements; when the temperature is ≥690℃, the deformation is large; when the temperature exceeds 720℃, the deformation reaches more than 0.10mm. Therefore, controlling the gas nitriding temperature at 680℃±5℃ is a key process parameter that balances nitriding hardness and deformation control.

[0033] After the ion nitriding treatment in step S1, the TiO2 passivation film on the valve surface is removed, allowing nitrogen atoms to diffuse into the valve substrate during gas nitriding in step S2, thereby achieving effective nitriding treatment.

[0034] Processing result: After gas nitriding, the part body is inspected. The valve obtained after steps S1 and S2 meets the following performance requirements: (1) Surface hardness is 640HV. 0.1 Approximately, meeting the surface hardness requirement of ≥600HV. 0.1 The requirements are: (2) The effective hardened layer depth is 0.013mm, which meets the requirement that the effective hardened layer depth is ≥0.01mm; (3) The runout of the outer circle of the rod is about 0.007mm, and the runout of the upper arc surface of the disc is about 0.006mm, which both meet the requirements that the runout of the outer circle of the rod is ≤0.01mm and the runout of the upper arc surface of the disc is ≤0.01mm.

[0035] Compared to the commonly used ion nitriding process for Ti-6Al-4V titanium alloy parts, which has a temperature of 860℃~900℃, this process uses a combination of ion nitriding at a lower temperature of 550℃ and gas nitriding at 680℃±5℃. This achieves the required hardness and other performance characteristics of the parts while controlling the minimum deformation.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A nitriding method for Ti-6Al-4V titanium alloy valves of unmanned aerial vehicles, characterized in that, Includes the following steps: S1. Ion nitriding: The Ti-6Al-4V titanium alloy valve is placed in an ion nitriding device and ion nitrided at 550°C to remove the TiO2 passivation film on the valve surface. S2. Gas nitriding: The valve treated in step S1 is placed in a gas nitriding furnace and gas nitrided at a temperature of 680℃±5℃.

2. The nitriding method according to claim 1, characterized in that, In step S1, the valve is placed vertically on the cathode plate or tooling plate of the ion nitriding equipment, and the cathode plate or tooling plate is adjusted to be in a horizontal state so that the valve is kept in a vertically mounted position.

3. The nitriding method according to claim 1, characterized in that, In step S1, the vacuum degree of ion nitriding is 270~280 Pa, the glow discharge thickness is 4~5 mm, and the nitriding time is 10~12 hours.

4. The nitriding method according to claim 3, characterized in that, In step S1, the heating process of ion nitriding is divided into three stages: Low temperature heating stage: First, heat up to 200℃ at a rate of 5℃ / minute and maintain the temperature uniformly for 5 minutes, then heat up to 320℃ at a rate of 4℃ / minute and maintain the temperature uniformly for 5 minutes; Medium-temperature heating stage: Heat to 430℃ at a rate of 2℃ / minute and maintain uniform temperature for 30 minutes; High-temperature heating stage: The temperature is increased to 550℃ at a rate of 1℃ / minute, and ion nitriding is carried out at 550℃.

5. The nitriding method according to claim 1, characterized in that, In step S2, the valve is vertically mounted in the circular groove of the gas nitriding fixture, with the lower end of the valve plate placed in the groove. The fixture is adjusted to be horizontal so that the valve remains vertical during the gas nitriding process.

6. The nitriding method according to claim 1, characterized in that, In step S2, the ammonia flow rate for gas nitriding is 0.75 m³ / h, the furnace pressure is ≥50 mm water column, and the nitriding time is 12~15 hours.

7. The nitriding method according to claim 1, characterized in that, After the ion nitriding treatment in step S1, the TiO2 passivation film on the valve surface is removed, allowing nitrogen atoms to diffuse into the valve substrate during gas nitriding in step S2.

8. The nitriding method according to claim 1, characterized in that, The valves obtained after steps S1 and S2 meet the following performance requirements: surface hardness ≥ 600 HV 0.1 The effective hardened layer depth is ≥0.01mm, the runout of the outer circle of the rod is ≤0.01mm, and the runout of the upper arc surface of the disc is ≤0.01mm.

Images