Gear and method for local reinforcement and ultra-fine crystallization of tooth surface of gear

Abstract

The invention discloses a gear and a method for local reinforcement and ultra-fine grain of the tooth surface of the gear, and belongs to the field of metal material precision machining, the core of the method is that firstly, a gradient structure prefabricated blank composed of a core base body and an external nano-particle reinforcement layer is prepared; and then through a precisely-controlled plastic forming process, by means of the metal flowing rule, a reinforcing layer material in the preformed blank is selectively migrated and finally precisely fixed to the tooth surface area of the gear, and therefore a nano-particle and ultra-fine grain composite material layer is formed on the tooth surface. According to the invention, excellent combination of high hardness and high wear resistance of the tooth surface and high toughness of the tooth body on a single gear component is realized, the performance contradiction of the traditional technology is solved, and the material utilization rate is high.

Description

Technical Field

[0001] This application belongs to the field of metal material processing, and specifically relates to a method for local strengthening and ultrafine crystallization of gears and their tooth surfaces. Background Technology

[0002] As a core component of power transmission, gears directly determine the reliability, efficiency, and lifespan of the transmission system. Due to alternating contact stress and sliding friction, gear teeth are highly susceptible to pitting, wear, and scuffing failures. Traditional methods for improving gear performance fall into two main categories: one is to use high-strength homogeneous materials, such as carburized steel, high-strength aluminum alloys, or titanium alloys, but this faces the inherent contradiction of balancing tooth surface hardness and tooth root toughness; the other is to perform post-treatments on the tooth surface, such as carburizing, nitriding, and plating, but these methods create thin reinforcing layers, typically less than 0.5 mm, which pose risks of weak adhesion to the substrate, high brittleness, and easy peeling, and also fail to form a stable ultrafine-grained structure on the tooth surface.

[0003] Nanoparticle-reinforced metal matrix composites have attracted attention due to their excellent specific strength and wear resistance. For example, existing technologies uniformly disperse TiC nanoparticles in 7075 aluminum alloy, which improves the overall strength and stiffness of the material. However, directly applying this technology to gears has obvious drawbacks: First, the expensive nanoparticles are uniformly dispersed throughout the component, resulting in material waste and a surge in costs; second, uniform reinforcement may lead to a decrease in toughness in non-working areas of the gear (such as the tooth core and spokes), which is not conducive to withstanding impact loads.

[0004] Intense plastic deformation methods such as equal diameter angular extrusion (ECAP) of titanium alloys can achieve overall ultrafine crystallization, but the equipment is complex and the cost is high. It also severely sacrifices the subsequent processing plasticity of the material, making it difficult to directly form complex tooth shapes and unable to achieve local selective strengthening.

[0005] In summary, existing technologies cannot achieve the synergistic optimization of deep tooth surface strength, high wear resistance, and high tooth body toughness and high fatigue strength in a single gear component in an economical and efficient manner. Therefore, there is an urgent need to develop an innovative manufacturing method that can "strengthen as needed" according to the stress distribution of the gear during service. Summary of the Invention

[0006] To address the aforementioned problems, this application provides a method for localized strengthening and ultrafine graining of gear tooth surfaces, comprising: A reinforcing layer is coated onto the surface of the core matrix to obtain a preform; The preform is plastically formed to obtain a gear blank; The teeth of the gear blank are cold extruded or cold precision forged to obtain the formed gear; The formed gears are finished and heat-treated to obtain the finished gears.

[0007] Furthermore, a reinforcing layer is coated on the surface of the core substrate, including: A reinforcing layer is constructed on the surface of the core matrix by wrapping composite material strips, heat-fitting composite material sleeves, plasma spraying, or pre-placed powder sintering. The thickness of the reinforcing layer is determined according to the preset tooth height of the gear, and the distribution area of ​​the reinforcing layer is determined according to the preset tooth surface area of ​​the gear.

[0008] Furthermore, the reinforcement layer coated on the surface of the core substrate also includes: The reinforcing layer is bonded to the core matrix by hot isostatic pressing or hot pressing sintering.

[0009] Furthermore, the core substrate is made of aluminum alloy, titanium alloy, magnesium alloy or copper alloy.

[0010] Furthermore, the reinforcing layer is a composite material, comprising an alloy matrix and nanoparticles.

[0011] Furthermore, the nanoparticles are one or more of TiC, TiB2, Al2O3, and SiC.

[0012] Furthermore, the average particle size of the nanoparticles is 20-100 nm.

[0013] Further, the preform undergoes plastic forming processing, including: The reinforcing layer is extruded and wrapped around the pitch circle to the tip circle of the gear blank.

[0014] This application also discloses a gear with locally strengthened and ultra-finely crystallized tooth surface, which is prepared by the above method.

[0015] Furthermore, the gear includes a tooth surface strengthening layer, which comprises an alloy matrix and nanoparticles; From the tooth surface towards the tooth center of the gear, the grain size gradually increases, while the concentration of nanoparticles gradually decreases.

[0016] Compared with the prior art, this application has the following advantages: 1. The method of this application can manufacture gears with performance gradients. The tooth surface is a composite material layer of "nanoparticles + ultrafine crystals". It has extremely high hardness, wear resistance and contact fatigue strength. The core maintains the excellent toughness of the matrix and has good impact and bending fatigue resistance. It solves the performance contradiction of traditional homogeneous materials or surface treatment technology.

[0017] 2. The method of this application uses expensive nanoparticles only in key stress areas that occupy a small part of the component volume, achieving "precise delivery" of material properties. The cost is far lower than that of the overall reinforcement scheme, and the cost-effectiveness is extremely high.

[0018] 3. The method of this application organically integrates the three processes of material modification (nano-reinforcement), structural forming (gear forging), and surface strengthening (ultrafine crystallization) into a continuous and compact manufacturing process, which has high production efficiency and avoids quality fluctuations and energy consumption caused by multiple heating and process changes.

[0019] 4. The method of this application can customize a local reinforcement scheme for gears with different working conditions and different failure modes by adjusting the composition, thickness and distribution of the reinforcing layer in the preform, so as to achieve personalized performance design.

[0020] 5. The method of this application overturns the traditional ideas of homogeneous reinforcement or post-processing, and pioneers an integrated method for actively constructing gear performance that combines "design-materials-process".

[0021] Other features and advantages of this application will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A flowchart illustrating a method for local strengthening and ultrafine crystallization of gear tooth surfaces according to an embodiment of the application is shown. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] To achieve synergistic optimization of deep tooth surface properties, high strength, and high wear resistance with high toughness and high fatigue strength of the tooth body in an economical and efficient manner, such as... Figure 1 As shown, this application discloses a method for local strengthening and ultrafine crystallization of gear tooth surfaces, including: S1: A reinforcing layer is constructed on the surface of the core matrix by wrapping composite material strips, heat-fitting composite material sleeves, plasma spraying, or pre-placed powder sintering. The thickness of the reinforcing layer is determined according to the preset tooth height of the gear, and the distribution area of ​​the reinforcing layer corresponds to the preset tooth surface area. Subsequently, through hot isostatic pressing or hot pressing sintering, the reinforcing layer and the core matrix achieve a good metallurgical or mechanical bond, forming an integrated gradient preform. The core matrix uses the base alloy of the target gear as the material, such as aluminum alloy, titanium alloy, magnesium alloy, or copper alloy. The reinforcing layer is a composite material, including an alloy matrix and nanoparticles. The alloy matrix is ​​the same as or compatible with the material of the core matrix, and the nanoparticles are one or more of TiC, TiB2, Al2O3, and SiC, with an average particle size of 20-100 nm. Before gear forming, by pre-planting reinforcing materials containing nanoparticles at specific locations on the blank, the material properties can be "precisely applied," reducing production costs. Furthermore, local reinforcement schemes with different reinforcing layer compositions, thicknesses, and distributions can be customized for gears under different working conditions and failure modes, achieving personalized performance design.

[0026] S2: The preform is plastically formed by heating it to a warm working temperature and then forging it to obtain a gear blank. The warm working temperature is lower than the recrystallization temperature, but sufficient to reduce the deformation resistance. By controlling the metal flow, the reinforcing layer is extruded and wrapped around the pitch circle to the addendum circle of the gear blank, rather than flowing to non-target areas such as spokes or webs, and an ultrafine crystalline structure is formed during the deformation process.

[0027] S3: At room temperature or low temperature, the gear blank is cold-extruded or cold-forged to obtain the formed gear. This stage is crucial for achieving localized ultrafine crystallization and performance leap. Under intense triaxial compressive stress, the reinforcing layer located in the tooth surface region undergoes extreme plastic strain. Nanoparticles strongly pin dislocations and hinder grain boundary migration, causing the surrounding alloy matrix grains to be repeatedly sheared and broken, thus forming an ultrafine or even nanocrystalline structure. At the same time, the extrusion pressure further densifies the material, making the bond between the nanoparticles and the alloy matrix stronger.

[0028] S4: After forming, the tooth surface is finished (e.g., roll forming, polishing) to reduce surface roughness and introduce beneficial residual compressive stress. Finally, low-temperature stress-relief annealing (for titanium alloys) or aging treatment (for aluminum alloys) is performed to stabilize the ultrafine grain structure and eliminate processing stress without causing excessive grain growth.

[0029] This application also discloses a gear with localized tooth surface strengthening and ultrafine crystallization, which is prepared by the above-described method. The gear includes a tooth surface strengthening layer, which comprises an alloy matrix and nanoparticles; the grain size gradually increases from the tooth surface towards the tooth center, while the concentration of nanoparticles gradually decreases.

[0030] To better illustrate this solution, the following embodiments and comparative examples are provided.

[0031] Example 1 S1: Commercial 7075 aluminum alloy bars are machined to φ58mm to serve as the core matrix. TiC powder with an average particle size of 50nm is mixed with 7075 aluminum alloy powder at a mass ratio of 1.5:98.5, and a binder is added to roll it into a continuous strip with a thickness of 1.2mm and a width of 50mm as a reinforcing layer. The strip is spirally and tightly wrapped around the surface of the core matrix, with two layers wrapped in total. Under argon protection, it is hot-pressed and sintered at 450℃ and 50MPa pressure for 40 minutes to densify the strip and bond it with the core matrix, forming a preform with an outer diameter of approximately φ60.5mm.

[0032] S2: The preform is heated to 380°C and then forged in a closed die on an 800-ton hydraulic press to form a gear blank. The die design ensures that the reinforcing layer material completely covers the pitch circle to the tip circle of the gear blank.

[0033] S3: At room temperature, the teeth of the gear blank are cold-extruded using a special tooth-shaped extrusion die to obtain the formed gear. The extrusion force per tooth is approximately 55 tons, and the tooth surface profile is clear after extrusion.

[0034] S4: The tooth surface of the formed gear is rolled and polished, and then subjected to T73 heat treatment: solution treatment at 465℃ for 1 hour, water quenching, holding at 110℃ for 8 hours + holding at 160℃ for 6 hours, two-stage aging, to obtain the finished gear.

[0035] Performance testing: Metallographic and electron microscopic observations show that the tooth surface of the finished gear has a gradient reinforcement layer with a thickness of about 1.0 mm, the outermost grain size is <1 μm, and TiC particles are uniformly distributed.

[0036] The tooth surface has a microhardness of 205HV, and the core hardness is 135HV, with a smooth transition.

[0037] Bench tests show that the tooth surface contact fatigue life (L) of the finished gears is... 10 It improves by about 180% compared to unreinforced 7075 aluminum alloy gears prepared by the same process, and by about 40% compared to gears uniformly reinforced with 1.5wt% TiC, and its bending fatigue limit is significantly better than the latter.

[0038] Example 2 S1: A commercially available Ti-6Al-4V alloy rod was machined to φ48mm to serve as the core matrix. TiB2 particles (average particle size 80nm) with an outer diameter of φ55mm and an inner diameter of φ48.2mm were prepared using powder metallurgy to reinforce Ti-6Al-4V composite tubes (TiB2 content 1.0wt%) as the reinforcing layer. The composite tubes were heated to 550℃ and hot-fitted onto the core. After cooling, an interference fit was formed. The tubes were then hot isostatically pressed (pressure 100MPa) at 920℃ under vacuum for 2 hours to achieve complete diffusion bonding at the interface, resulting in a preform.

[0039] S2: The preform is heated to 700℃ and formed into the basic tooth shape of the herringbone gear through a positive extrusion process. The reinforcing layer flows evenly and covers the pitch circle to the tip circle of the gear blank.

[0040] S3: Cool the gear blank to below 150℃ and perform cold precision forging of the tooth profile to further improve the tooth surface accuracy and density, thus obtaining the formed gear.

[0041] S4: The tooth surface of the formed gear is rolled and polished, then vacuum annealed at 600℃ for 2 hours, and then furnace cooled to obtain the finished gear.

[0042] Performance testing: Metallographic and electron microscopic observations show that the depth of the reinforcing layer on the tooth surface is about 1.5 mm, and the grain size gradually changes from 0.8 μm to 5 μm from the surface to the inside.

[0043] The wear resistance of the tooth surface is about 3 times higher than that of the base Ti-6Al-4V gear.

[0044] The 350℃ contact fatigue test showed that its life was about twice that of the traditional forged nitrided gears, and the failure mode was normal wear with no spalling.

[0045] Comparative Example 1 Gears were manufactured using a monolithic 1.5wt% TiC / 7075 aluminum alloy composite rod with the same composition as in Example 1, employing the same warm forging and cold extrusion processes. The tooth surface hardness was 185HV, lower than the finished gear of Example 1; its tooth core impact toughness was 32J / cm², significantly lower than the 145J / cm² of the finished gear of Example 1, and the cost was high.

[0046] Comparative Example 2 Using ordinary 7075 aluminum alloy, without a reinforcing layer, the gear was manufactured using the same process as in Example 1, and then subjected to gas nitriding treatment. The resulting gear tooth surface hardness exceeded 650 HV, but the hardened layer thickness was only about 0.15 mm. Four-point bending fatigue tests showed that the fatigue cracks in the gear of Comparative Example 2 mostly originated from the interface between the hard nitrided layer and the softer substrate, and the bending fatigue limit was about 15% lower than that of the gear in Example 1.

[0047] In summary, the method of this application can manufacture gears with performance gradients. The tooth surface is a composite material layer of "nanoparticles + ultrafine crystals", which has extremely high hardness, wear resistance and contact fatigue strength. The core maintains the excellent toughness of the matrix and has good impact and bending fatigue resistance, thus solving the performance contradiction of traditional homogeneous materials or surface treatment technologies.

[0048] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for local strengthening and ultrafine crystallization of gear tooth surfaces, characterized in that, include: A reinforcing layer is coated onto the surface of the core matrix to obtain a preform; The preform is subjected to plastic forming to obtain a gear blank; The teeth of the gear blank are cold extruded or cold precision forged to obtain a shaped gear; The formed gear is then finished and heat-treated to obtain the finished gear.

2. The method for local strengthening and ultrafine crystallization of gear tooth surfaces according to claim 1, characterized in that, The process of coating the core substrate with a reinforcing layer includes: The reinforcing layer is constructed on the surface of the core matrix by wrapping composite material strips, heat-fitting composite material sleeves, plasma spraying, or pre-placed powder sintering. The thickness of the reinforcing layer is determined according to the preset tooth height of the gear, and the distribution area of ​​the reinforcing layer is determined according to the preset tooth surface area of ​​the gear.

3. The method for local strengthening and ultrafine crystallization of gear tooth surfaces according to claim 2, characterized in that, The method of coating the core substrate with a reinforcing layer further includes: The reinforcing layer is bonded to the core matrix by hot isostatic pressing or hot pressing sintering.

4. The method for local strengthening and ultrafine crystallization of gear tooth surfaces according to claim 1, characterized in that, The core substrate is made of aluminum alloy, titanium alloy, magnesium alloy or copper alloy.

5. The method for local strengthening and ultrafine crystallization of gear tooth surfaces according to claim 1, characterized in that, The reinforcing layer is a composite material, comprising an alloy matrix and nanoparticles.

6. The method for local strengthening and ultrafine crystallization of gear tooth surfaces according to claim 5, characterized in that, The nanoparticles are one or more of TiC, TiB2, Al2O3, and SiC.

7. The method for local strengthening and ultrafine crystallization of gear tooth surfaces according to claim 5, characterized in that, The average particle size of the nanoparticles is 20-100 nm.

8. The method for local strengthening and ultrafine crystallization of gear tooth surfaces according to claim 1, characterized in that, The preform is subjected to plastic forming processing, including: The reinforcing layer is extruded and wrapped around the pitch circle to the tip circle of the gear blank.

9. A gear with locally strengthened and ultra-finely crystallized tooth surface, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. A gear with locally strengthened and ultra-finely crystallized tooth surface according to claim 9, characterized in that, The gear includes a tooth surface reinforcement layer, which comprises an alloy matrix and nanoparticles; The grain size of the gear gradually increases from the tooth surface to the tooth center, while the concentration of nanoparticles gradually decreases.

Images