Construction method of gradient nanostructure on surface of variable-diameter thin-wall shaft

Abstract

The invention belongs to the technical field of material surface mechanical strengthening, and particularly relates to a construction method of a variable-diameter thin-wall shaft surface gradient nanostructure, which is suitable for surface strengthening machining of key parts of high-end equipment such as a gas turbine transmission shaft and a wind power main shaft. A gradient nanostructure layer with a certain depth is formed on the surface of the variable-diameter thin-wall shaft part through the surface nanocrystallization technology, and the surface of the variable-diameter thin-wall shaft part is remarkably strengthened. The core of the method is that a tool platform for conducting surface nanometer strengthening on the large-size and complex-shape shaft piece is built; and meanwhile, in the surface severe plastic deformation treatment process, rigidity compensation is provided for supporting the thin-wall structure, and the thin-wall shaft piece is prevented from deforming and losing efficacy. And finally, the gradient nanostructure layer with the obvious strengthening characteristic is completely obtained on the surface of the thin-wall shaft piece. According to the method, the problem of keeping the structural stability of the variable-diameter thin-wall shaft part in the surface machining process can be solved, and meanwhile a machining platform and a solving mode are provided for surface nanocrystallization treatment of large-size complex devices.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material surface mechanical strengthening, and particularly relates to a method for constructing a surface gradient nanostructure of a variable-diameter thin-walled shaft, which is suitable for surface strengthening processing of key parts of high-end equipment such as a gas turbine transmission shaft and a wind power main shaft. BACKGROUND

[0002] A low-temperature high-load transmission shaft component of a gas turbine is mainly subjected to torsion and tension-compression fatigue loads during service. Since the surface notch sensitivity of the material of the structural component is relatively high, surface mechanical processing is usually required to introduce a residual compressive stress layer to improve the service safety of the material. The commonly used surface mechanical processing is surface shot peening, which has the defect that the introduced residual stress layer is relatively shallow and cannot effectively reduce the surface roughness. The surface roughness is a key factor affecting the fatigue performance.

[0003] With the development of surface mechanical processing technology, significant progress has been made in surface nanocrystallization of transmission shaft materials: during surface nanocrystallization processing of C250 steel (transmission shaft steel), local severe plastic deformation occurs on the surface, the surface layer grain size is greatly reduced (from 350 nm to 20 nm), Ni and Mo atoms are segregated at the interface of the nanosheet structure on the surface of the C250 steel, the surface hardness is greatly improved (from 6.5 GPa to 8.5 GPa), and the thickness of the gradient strengthening layer of the C250 steel reaches 200 pm, the surface residual compressive stress is greater than 1500 MPa. After the C250 steel is processed by the invention, the fatigue limit is improved from 650 MPa to 850 MPa, and the rotating bending fatigue performance is significantly improved.

[0004] However, the application of surface nanocrystallization technology to transmission shaft components still faces many technical challenges: the transmission shaft component has a relatively complex outer surface; at the same time, due to the need for weight reduction and mechanical design, the transmission shaft component is usually a hollow thin-walled part, and surface nanocrystallization technology needs to apply a large shear stress on the surface to achieve effective grain refinement and introduction of a large residual stress, which may cause dimensional changes of the transmission shaft component or even structural damage to the thin-walled part; at the same time, the transmission shaft component generally has a large outer size, which puts higher requirements on the traditional surface nanocrystallization platform. The lubrication system, heating system and tool machining system of the nanocrystallization technology platform need to be integrated to effectively connect and cooperate between the functions during the processing of large-size samples, so as to improve the processing efficiency.

[0005] The patent with publication number CN110605403A discloses a method for preparing a gradient nanostructured metal material by using liquid nitrogen environment diamond turning to prepare a gradient nanostructure, but the deformation is difficult to control, resulting in a shape and position tolerance of the thin-walled part exceeding 0.1 mm under the action of radial load.

[0006] In summary, it is very difficult to realize surface treatment of large-size variable-diameter thin-wall shafts by using existing surface nanocrystallization technology. It is necessary to integrate surface nanocrystallization technology to provide rigidity compensation, introduce temperature parameters, and optimize processing platform, so as to effectively obtain gradient nano-structured thin-wall shafts with deep deformation layer, good grain refinement effect, and obvious surface strengthening. SUMMARY

[0007] The present application aims to provide a method for constructing surface gradient nano-structure of variable-diameter thin-wall shafts, and solve the problem of maintaining the structural stability of variable-diameter thin-wall shafts during surface processing, and provide a processing platform and solution for surface nanocrystallization treatment of large-size complex devices.

[0008] The technical solution of the present application is as follows:

[0009] A method for constructing surface gradient nano-structure of variable-diameter thin-wall shafts, comprising the following steps:

[0010] (1) Clamping the variable-diameter thin-wall shaft on the processing platform, assembling a rigidity compensation device inside the variable-diameter thin-wall shaft, making the rigidity compensation device pass through the variable-diameter thin-wall shaft, and adjusting to make it tightly fit with the inner wall of the variable-diameter thin-wall shaft, and stabilizing the geometric shape of the variable-diameter thin-wall shaft during severe deformation through the rigidity compensation device;

[0011] (2) Carrying out surface mechanical deformation treatment on the variable-diameter thin-wall shaft obtained in step (1), so that the surface roughness of the variable-diameter thin-wall shaft is obviously improved, the structure is obviously refined, and the cross-sectional hardness presents a gradient distribution characteristic;

[0012] (3) Immediately applying a temperature field to the surface of the variable-diameter thin-wall shaft after mechanical deformation treatment, and heat treating at 200-400℃ for 10-60min to promote the segregation of alloying elements to the nanocrystalline grain boundaries.

[0013] The method for constructing surface gradient nano-structure of variable-diameter thin-wall shafts, in step (2), the rigidity compensation device is used to compensate the rigidity inside the shaft during surface mechanical deformation treatment of the variable-diameter thin-wall shaft.

[0014] The method for constructing surface gradient nano-structure of variable-diameter thin-wall shafts, in step (2), nanocrystallization treatment is carried out on the surface of the variable-diameter thin-wall shaft with complex shape, a hardened layer with a depth of 200μm or more is formed, the surface grains are significantly refined to the nanometer level, the distribution, size and morphology of precipitated phases are simultaneously changed, the surface strengthening effect of the variable-diameter thin-wall shaft is realized through fine-grain strengthening and interface segregation structure regulation, and the microhardness after surface strengthening is improved.

[0015] The construction method of the surface gradient nanostructure of the variable-diameter thin-wall shaft maintains the shape of the variable-diameter thin-wall shaft not to be damaged through the precise support of the internal rigidity compensation device in the surface nanocrystallization process.

[0016] In the mechanical deformation processing in step (2), the cutting head of the machining tool is pressed into the surface of the variable-diameter thin-wall shaft; at the same time, the cutting head of the machining tool is fed along the axial direction of the variable-diameter thin-wall shaft or the direction perpendicular to the rotary surface of the variable-diameter thin-wall shaft.

[0017] In step (1), the machining platform is integrated with an oil lubrication system, a surface nanocrystallization machining system and a surface heating system to improve the surface machining efficiency of the variable-diameter thin-wall shaft.

[0018] In the construction method of the surface gradient nanostructure of the variable-diameter thin-wall shaft, the material of the variable-diameter thin-wall shaft is maraging steel, the depth of the surface hardening layer reaches 200 mu m, and the surface grain size of the maraging steel is greatly reduced from 350 nm to below 100 nm.

[0019] The construction method of the surface gradient nanostructure of the variable-diameter thin-wall shaft is suitable for the construction of the surface gradient nanostructure of the variable-diameter thin-wall shaft and large-size structural devices.

[0020] The design idea of the present application is:

[0021] The present application adopts multi-pass surface plastic deformation processing on the material surface, and provides rigidity compensation and temperature field (200 DEG C to 400 DEG C) in situ. Among them, through the rigidity compensation, the surface deformation is increased under the premise of maintaining the thin-wall structure, and the gradient nanostructure layer with a relatively thick depth is formed. The temperature field makes the interface diffusion accelerate and the grain boundary structure adjust, and further enhances the mechanical properties of the material.

[0022] Further, the plastic deformation processing on the surface of the thin-wall shaft includes surface mechanical rolling technology, surface mechanical rolling technology and other surface mechanical deformation processing, and the gradient nanostructure of the maraging steel is constructed by combining the rigidity compensation device and the temperature field in situ.

[0023] Further, the key to the rigidity compensation is to ensure that the geometric shape of the variable-diameter thin-walled shaft does not change due to the surface plastic deformation treatment, which specifically includes the following details: the rigidity compensation device is nested in the numerical control machine tool (in the thin-walled device) to ensure the stability during machining, and the material deformation caused by the surface plastic deformation (surface mechanical rolling technology, surface mechanical rolling technology, etc.) during the nanocrystallization treatment causes more severe surface deformation of the variable-diameter thin-walled shaft. The key technology of the in-situ temperature field treatment is temperature field control, which specifically includes the following details: the temperature field can be applied during the entire plastic deformation nanocrystallization treatment, and / or after the plastic deformation nanocrystallization treatment. First, the plastic deformation nanocrystallization treatment is used to refine the grain, and when the grain is refined to the nanometer level, the increase in the interface volume fraction is beneficial to the rapid diffusion of elements, and the subsequent plastic deformation treatment is used to apply the in-situ temperature field treatment to cause interface segregation and interface structure adjustment, realize obvious surface strengthening, and the temperature selection range is 200-400°C.

[0024] The advantages and beneficial effects of the present application are:

[0025] 1. The construction method of the present application mainly uses surface nanocrystallization technology on thin-walled transmission shaft devices with complex surfaces to form a gradient nanostructure layer with a certain depth, and significantly strengthen the surface. The core of the method is to build a tooling platform for surface nanostrengthening of large-size complex-shaped shafts, and to provide rigidity compensation support for the thin-walled structure during the surface severe plastic deformation process, prevent deformation failure of the thin-walled shaft, maintain the shape of the device and intensify the degree of surface plastic deformation, provide a temperature field to accelerate interface segregation and interface structure adjustment, and finally obtain a gradient nanostructure layer with obvious strengthening characteristics on the surface of the thin-walled shaft.

[0026] 2. The construction method of the present application integrates surface nanocrystallization technology to provide rigidity compensation, introduces temperature parameters, obtains a gradient nanostructure variable-diameter thin-walled shaft with a deeper deformation layer, better grain refinement effect and obvious surface strengthening, and improves the service performance through the construction of gradient nanostructure technology. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a schematic diagram of the variable-diameter thin-walled shaft in the embodiment.

[0028] Figure 2 It is a schematic diagram of the rigidity compensation device in the embodiment.

[0029] Figure 3 It is a display diagram of the large-size gradient nanostructure construction platform.

[0030] Figure 4It is a microhardness distribution diagram of the strengthening layer of the gradient nanostructure variable-diameter thin-wall shaft. In the diagram, the horizontal coordinate Depth is depth (μm), and the vertical coordinate Hardness is hardness (GPa).

[0031] Figure 5 It is a whole structure diagram of the large-size nanometer processing platform. In the diagram, 1 is a lathe top, 2 is a shaft rigidity compensation device, 3 is a variable-diameter thin-wall shaft, 4 is an integrated tool device (41 is a tool handle, 42 is a rotatable integrated tool seat, and 43 is a detachable tool head), 5 is a temperature control device (51 is a heating air cylinder, 52 is a temperature measuring element, and 53 is a temperature control platform), 6 is an oil circuit lubrication system (61 is an oil guide pipe, 62 is a lubricating oil recovery disc, 63 is an oil pump, and 64 is an oil storage tank). DETAILED DESCRIPTION

[0032] In the implementation process, the present application mainly solves the structural stability problem in the process of constructing the gradient nanostructure on the surface of the variable-diameter thin-wall shaft. At the same time, aiming at the surface strengthening demand of the transmission shaft component, after the nanometer treatment and the grain refinement to the nanocrystalline, the temperature field is provided in situ to realize the surface hardening of the metal material.

[0033] Further, the plastic deformation treatment on the surface of the variable-diameter thin-wall shaft includes the surface mechanical rolling technology, the surface mechanical rolling technology, and the like, which realizes the gradient nanostructure construction technology in combination with the in-situ temperature field. The above technical implementation methods have been embodied in the patents of the applicant, and the present application will not be described in detail. The technical core of the present application is to realize the fastener design and assembly for rigidity compensation in the gradient nanostructure construction method and the integrated platform for large-size sample nanometer processing; the rigidity compensation device is nested in the numerical control machine tool to control the stability of the variable-diameter thin-wall shaft in the surface nanometerization process; the temperature field can be applied to the whole process of the plastic deformation nanometerization treatment and / or after the plastic deformation nanometerization treatment. The temperature selection range is 200℃-400℃. Under the temperature field, the atoms in the nanostructure have a faster short-range diffusion rate, and thus the strength and hardness of the metal material are further improved. The integrated platform for large-size sample nanometer processing is beneficial to efficiently and stably realize the surface nanometerization of the large-size sample.

[0034] In the following, the present application is further described in detail through examples and comparative examples.

[0035] Example 1

[0036] Taking the variable-diameter thin-wall shaft (material: C250 maraging steel) as an example, the gradient nanostructure construction is carried out to realize the surface strengthening effect. The specific steps are as follows:

[0037] 1) The C250 steel ingot is machined to obtain the required variable-diameter thin-wall shaft. The size of the variable-diameter thin-wall shaft is as follows: the wall thickness is 5mm, the length is 220mm, the small end hole diameter is 85mm, and the large end hole diameter is 102mm, as shown inFigure 1 as shown in the drawings;

[0038] 2) Assembling the rigidity compensation device, Figure 2 , making the rigidity compensation device pass through the variable-diameter thin-walled shaft, and adjusting to make it tightly fit with the inner wall of the variable-diameter thin-walled shaft. Figure 3 Then, the variable-diameter thin-walled shaft obtained in step 1) is subjected to surface mechanical deformation treatment, so that the surface roughness of the C250 steel is significantly improved, Figure 3 the structure is significantly refined, and the cross-sectional hardness presents a gradient distribution characteristic.

[0039] Specifically, the surface nanocrystallization technology adopted is surface mechanical rolling treatment technology (SMRT). The SMRT machining tool performs high-speed rolling on the surface of the C250 steel, and the specific process parameters are as follows: the rotating speed V1 of the variable-diameter thin-walled shaft is 50 revolutions / min, the horizontal moving speed V2 of the SMRT machining tool is 3 mm / min, and 4-6 passes are repeated, so that the surface of the C250 steel to be treated is subjected to high-speed plastic shear deformation, a gradient nano-structure layer with a relatively thick depth is formed on the surface of the C250 steel, and the surface grains are significantly refined to the nanometer level.

[0040] The rigidity compensation device stabilizes the sample geometry during severe deformation to provide more severe surface deformation capability and expand the influence layer depth of surface treatment. During the first pass treatment, the tool head of the SMRT machining tool is pressed into the surface of the C250 steel; at the same time, the tool head of the SMRT machining tool is fed along the axial direction of the variable-diameter thin-walled shaft or the direction perpendicular to the revolution surface of the variable-diameter thin-walled shaft; after the SMRT treatment, the variable-diameter thin-walled shaft after treatment is subjected to hot air blowing on the surface of the variable-diameter thin-walled shaft using a hot air blowing device, so as to stabilize the surface temperature at 400℃ for 10 min. The high-temperature environment can promote the segregation of Ni and Mo atoms at the interface, and greatly improve the hardness of the surface of the variable-diameter thin-walled shaft.

[0041] As shown in the drawings, Figure 3 , Figure 5 The nanocrystallization machining platform of the present application is embedded in a numerical control surface nanocrystallization machining equipment (numerical control machine tool), and mainly comprises a lathe center 1, a shaft rigidity compensation device 2, a variable-diameter thin-walled shaft 3, an integrated tool device 4, a temperature control device 5 and an oil circuit lubrication system 6, and the specific structure is as follows:

[0042] The shaft stiffness compensation device 2 is tightly fitted in the inner cavity of the variable-diameter thin-wall shaft 3, the shaft stiffness compensation device 2 and the variable-diameter thin-wall shaft 3 are combined and installed horizontally on the lathe center 1 of the numerical control machine tool, the integrated tool device 4, the temperature control device 5 and the oil lubrication system 6 are arranged around the combined structure of the shaft stiffness compensation device 2 and the variable-diameter thin-wall shaft 3. The integrated tool device 4 comprises tool shanks 41 of different angles, a rotatable integrated tool holder 42 and detachable tool heads 43, the tool shanks 41 of different angles are installed on the rotatable integrated tool holder 42, and the detachable tool heads 43 corresponding to the surface of the variable-diameter thin-wall shaft 3 are arranged on each tool shank 41. The temperature control device 5 comprises a heating air cylinder 51, a temperature measuring element 52 and a temperature control platform 53, the heating air cylinder 51 and the temperature measuring element 52 corresponding to the surface of the variable-diameter thin-wall shaft 3 are installed on the temperature control platform 53. The oil lubrication system 6 comprises an oil guide pipe 61, an oil recovery disc 62, an oil pump 63 and an oil storage tank 64, the oil outlet of the oil storage tank 64 is connected with the oil pump 63, the output end of the oil pump 63 is connected with the surface of the variable-diameter thin-wall shaft 3 through the oil guide pipe 61, and the oil recovery disc 62 is arranged below the variable-diameter thin-wall shaft 3 and connected with the oil return port of the oil storage tank 64 through a pipeline.

[0043] The working process of the nanometer processing platform is as follows: firstly, the shaft stiffness compensation device 2 is arranged in the variable-diameter thin-wall shaft 3, and the variable-diameter thin-wall shaft 3 and the shaft stiffness compensation device 2 are tightly fitted through the tension nut. Then the shaft stiffness compensation device 2 and the variable-diameter thin-wall shaft 3 are fixed on the lathe center 1 of the numerical control machine tool. The integrated tool device 4 (SMRT machining tool) is located above the variable-diameter thin-wall shaft 3 and moves horizontally at a speed V2. At different positions, different curved surfaces are machined by selecting different angles of the tool shanks 41 and the detachable tool heads 43 through the rotatable integrated tool holder 42. During the machining, the oil lubrication system 6 is continuously opened, the lubricating oil is dripped on the machining surface of the variable-diameter thin-wall shaft 3 under the driving of the oil pump 63 through the oil guide pipe 61, and is collected into the oil storage tank 64 through the oil recovery disc 62 to realize the recycling of the oil circuit. After machining, the variable-diameter thin-wall shaft 3 after surface nanometerization treatment is heated by the heating air cylinder 51, the temperature of the surface of the variable-diameter thin-wall shaft 3 is measured by the temperature measuring element 52, and the temperature of the surface of the variable-diameter thin-wall shaft 3 is maintained at 400 DEG C for 10 min by the temperature control platform 53. The nanometer processing platform is optimized, the oil lubrication system, the surface heating system (temperature control device) and the surface nanometerization machining system (integrated tool device) are reasonably and effectively integrated in modules, and the machining efficiency of the large-size variable-diameter thin-wall shaft in the surface nanometerization process is improved.

[0044] As shown in Figure 4 The microhardness distribution of the strengthening layer of the gradient nanostructure variable-diameter thin-wall shaft. As can be seen from the figure, the surface of the shaft is hardened to 7.2 GPa after blowing hot air, and the hardening effect is obvious.

[0045] Comparative Example 1

[0046] The same as the material of the example, except that no surface treatment is used; the variable thin-walled shaft maintains the machined state, and the roughness Ra is 1.6 microns.

[0047] Comparative Example 2

[0048] The same as the material of the example, except that surface shot peening treatment is used; the surface roughness Ra of the variable thin-walled shaft is 1.1 microns.

[0049] Comparative Example 3

[0050] The same as the material of the example and the surface nanocrystallization processing method, except that no integrated large-size surface nanocrystallization platform is used; the final variable thin-walled shaft has the same processing quality, but the processing efficiency is only half of the integrated platform.

[0051] As can be seen from the results of the example, the surface nanocrystallization technology provided by the present application causes local severe plastic deformation of the surface of the variable thin-walled shaft during the surface nanocrystallization processing of the variable thin-walled shaft, and the size of the crystal grains in the surface layer is greatly reduced; at the surface of the shaft, Ni and Mo atoms are segregated at the interface of the nanosheet structure, greatly improving the hardness of the surface (5.5 GPa to 7.2 GPa). And due to the introduction of the stiffness compensation device, the thickness of the strengthened layer of the thin-walled shaft reaches 200 microns, and the surface residual compressive stress is greater than 1500 MPa, so this method can effectively construct a gradient nanostructure on the surface of a large-size variable thin-walled shaft.

Claims

1. A method for constructing surface gradient nanostructures of a variable-thickness thin-walled shaft, characterized in that, The method comprises the following steps: (1) clamping the variable-diameter thin-wall shaft on a machining platform, assembling a rigidity compensation device inside the variable-diameter thin-wall shaft, making the rigidity compensation device pass through the variable-diameter thin-wall shaft, and debugging to make it tightly fit with the inner wall of the variable-diameter thin-wall shaft, and stabilizing the geometric shape of the variable-diameter thin-wall shaft during severe deformation through the rigidity compensation device; (2) performing surface mechanical deformation treatment on the variable-diameter thin-wall shaft obtained in step (1), so that the surface roughness of the variable-diameter thin-wall shaft is obviously improved, the structure is obviously refined, and the cross-sectional hardness presents a gradient distribution characteristic; (3) immediately applying a temperature field to the surface of the variable-diameter thin-wall shaft after mechanical deformation treatment, and heat treating at 200-400℃ for 10-60 min to promote the segregation of alloy elements to the nanocrystalline boundary.

2. The method of claim 1, wherein the method further comprises: In step (2), the internal rigidity compensation device is used to compensate the rigidity of the shaft during surface mechanical deformation treatment of the variable-diameter thin-wall shaft.

3. The method of claim 1, wherein the method further comprises: In step (2), the nanocrystallization treatment is performed on the surface of the variable-diameter thin-wall shaft with complex shape, a hardened layer with a depth of 200μm or more is formed, the surface grains are significantly refined to the nanometer level, the distribution, size and morphology of precipitated phases are simultaneously changed, the surface strengthening effect of the variable-diameter thin-wall shaft is realized through fine-grain strengthening and interface segregation structure regulation, and the microhardness after surface strengthening is improved.

4. The method of claim 3, wherein the method further comprises: In the surface nanocrystallization process, the internal rigidity compensation device is used to maintain the shape of the variable-diameter thin-wall shaft without being damaged.

5. The method of claim 1, wherein the method further comprises: In step (2), during mechanical deformation treatment, the cutting tool head is pressed into the surface of the variable-diameter thin-wall shaft, and at the same time, the cutting tool head is fed along the axial direction of the variable-diameter thin-wall shaft or the direction perpendicular to the rotary surface of the variable-diameter thin-wall shaft.

6. The method of claim 1, wherein the method further comprises: In step (1), the machining platform is integrated with an oil lubrication system, a surface nanocrystallization processing system and a surface heating system to improve the surface processing efficiency of the variable-diameter thin-wall shaft.

7. The method of claim 1, wherein the method further comprises: When the material of the variable-diameter thin-wall shaft is maraging steel, the depth of the surface hardened layer reaches 200μm, and the surface grain size of the maraging steel is greatly reduced from 350nm to less than 100nm.

8. The method of claim 1, wherein the method further comprises: The method is suitable for constructing surface gradient nanostructure of variable-diameter thin-wall shafts and large-size structural devices.

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