Local ion nitriding method for titanium alloy barrel

Abstract

The invention provides a local ion nitriding method for a titanium alloy barrel, and belongs to the technical field of titanium alloy surfaces.The local ion nitriding method comprises the steps that an anti-seepage tool is prepared according to the size and shape of a non-nitriding area of the titanium alloy barrel; carrying out micro-arc oxidation treatment on the attached shielding surface of the anti-seepage tool; performing hole sealing treatment on the anti-seepage tool subjected to micro-arc oxidation treatment; and the hole-sealed anti-seepage tool is installed in a non-nitriding area of the titanium alloy barrel, ion nitriding treatment is conducted on the titanium alloy barrel where the anti-seepage tool is installed, the anti-seepage tool is dismantled, the titanium alloy barrel subjected to local ion nitriding is obtained, and micro-arc oxidation and hole sealing treatment are conducted on the attached shielding face of the anti-seepage tool, so that the anti-seepage performance of the titanium alloy barrel is improved. Boron nitride with a lubricating effect is generated on the surface of the porous oxidation film, the situation that the anti-seepage tool and the workpiece cannot be detached due to adhesion is prevented, the anti-seepage tool is beneficial to reducing the deformation tendency of the barrel, and the anti-seepage method is convenient to operate, environmentally friendly, free of pollution and wide in applicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of titanium alloy surface, in particular to a method for local ion nitriding of titanium alloy cylinder. BACKGROUND

[0002] Titanium alloy cylinder is widely used in aerospace, ship, rail transportation and other fields as a precision component of hydraulic control system. In order to meet the requirements of high reliability and high precision control of the hydraulic control system, the inner wall and the two end faces subjected to reciprocating friction and impact should have good wear resistance and dimensional accuracy. However, the titanium alloy surface has low hardness and poor wear resistance, so local ion nitriding technology is needed to form a high-hardness nitrided layer on the easily-worn surface to improve the wear resistance, avoid unnecessary impact on the performance of other areas, and ensure that the deformation of the cylinder as a whole is controlled within ±0.02 mm.

[0003] Current local ion nitriding mostly adopts shielding method by coating anti-permeation agent and mechanical shielding method. Titanium alloy ion nitriding temperature is relatively high, and the protective layer formed by coating anti-permeation agent is prone to cracking, bubbling and falling off during the nitriding process, resulting in anti-permeation failure. The mechanical shielding method blocks active nitrogen ions from hitting by tightly bonding the part and the anti-permeation tool to achieve local nitriding, but the thermal expansion of the part and the anti-permeation tool at high temperature causes the workpiece and the anti-permeation tool to stick together and cannot be disassembled, or the workpiece deforms due to uneven stress, and the surface of the anti-permeation tool is also bombarded by active nitrogen ions at high temperature, which causes impurity ions to sputter onto the surface of the workpiece, affecting the surface quality of the workpiece. SUMMARY

[0004] In view of the shortcomings of the mechanical shielding method in the background art, the present application provides a method for local ion nitriding of titanium alloy cylinder, which can effectively reduce the deformation of the cylinder after nitriding treatment and achieve local ion nitriding strengthening. Specifically, the bonding and shielding surface of the anti-permeation tool can be subjected to micro-arc oxidation and sealing treatment, boron oxide and urea can be loaded in the porous micro-arc oxidation film, and the bonding and shielding surface of the anti-permeation tool is almost bonded with the non-nitriding surface of the titanium alloy cylinder. As the nitriding temperature increases, on the one hand, the pores in the micro-arc oxidation film are in a relatively closed state, and these pores act as reaction containers. Boron nitride formed by the chemical reaction of boron oxide and urea at high temperature has good lubricity and can be used as a release agent to prevent the anti-permeation tool and the workpiece from sticking together and being disassembled; on the other hand, the thermal expansion coefficient of the ceramic micro-arc oxidation film is significantly smaller than that of the titanium alloy substrate, which reduces the compressive stress applied to the cylinder by the thermal expansion of the anti-permeation tool and improves the precision stability of the nitriding cylinder. At the same time, the non-bonding and shielding surface of the anti-permeation tool can still glow discharge during ion nitriding, which helps to improve the temperature uniformity of the titanium alloy cylinder and reduce the deformation tendency of the cylinder.

[0005] The application provides a method for local ion nitriding of a titanium alloy cylinder, comprising the following steps: Step one, preparing an anti-permeation tool according to the size and shape of the non-nitriding area of the titanium alloy cylinder; the outer wall of the anti-permeation tool has a plurality of longitudinal grooves, the width of the grooves is 10-20 mm, and the depth of the grooves is half of the wall thickness of the anti-permeation tool; Step two, performing micro-arc oxidation treatment on the fitting shielding surface of the anti-permeation tool; a micro-arc oxidation film is prepared on the fitting shielding surface of the anti-permeation tool by the micro-arc oxidation method, the thickness of the obtained micro-arc oxidation film is 15-30 μm, and the surface porosity is 25%-40%; Step three, immersing the anti-permeation tool after the micro-arc oxidation treatment into a sealing solution for sealing treatment; the sealing solution is composed of boron oxide, urea and polyvinyl alcohol, the concentration of the polyvinyl alcohol is 50-100 g / L, the content of the boron oxide in the solution is 72-180 g / L, the content of the urea is 144-360 g / L, and the concentration ratio of the urea to the boron oxide is greater than or equal to 2:1; Step four, installing the anti-permeation tool after the sealing treatment on the non-nitriding area of the titanium alloy cylinder, and performing ion nitriding treatment on the titanium alloy cylinder with the installed anti-permeation tool in a segmented heating mode to obtain the titanium alloy cylinder after local ion nitriding.

[0006] Preferably, the material of the anti-permeation tool in step one is titanium alloy, and the wall thickness of the anti-permeation tool is the same as that of the titanium alloy cylinder.

[0007] Preferably, in step two, the non-fitting shielding surface of the anti-permeation tool is pasted with an insulating tape during the micro-arc oxidation treatment, the insulating tape pasted on the non-fitting shielding surface is torn off after the micro-arc oxidation treatment, and the anti-permeation tool is cleaned.

[0008] Preferably, the electrolyte selected for the micro-arc oxidation treatment in step two is composed of 10 g / L sodium hexametaphosphate, 10 g / L sodium metaaluminate, 4 g / L sodium tetraborate and 1 g / L potassium hydroxide; the voltage of the micro-arc oxidation treatment is 500-650 V, the frequency is 1000-2000 Hz, the duty cycle is 30-50%, and the treatment time is 20-40 min.

[0009] Preferably, in step three, the sealing treatment is that the sealing solution with the anti-permeation tool is placed in a vacuum heating box, and after standing for 1 h under the conditions of negative pressure and 60-100℃, the anti-permeation tool is taken out and dried.

[0010] Preferably, in the ion nitriding process in step four, the titanium alloy cylinder is first heated at a stepwise heating rate, raised to 400 DEG C at a heating rate of 5 DEG C / min, then raised to 600 DEG C at a heating rate of 3 DEG C / min, then raised to 700 DEG C at a rate of 2 DEG C / min, and finally raised to the holding temperature at a heating rate of 1 DEG C / min, the holding temperature is 750-830 DEG C, the volume ratio of nitrogen and argon in the furnace during the holding stage is 5:0-5:1, the holding time is 5-8h, and after the holding is completed, the furnace is cooled to below 100 DEG C and then the titanium alloy cylinder is taken out.

[0011] Compared with the prior art, the present application has the following beneficial effects: 1. The local ion nitriding method for the titanium alloy cylinder provided by the present application can form a nitriding layer with a hardness of 900HV or more at the nitriding part of the workpiece, and the remaining parts are protected by the anti-permeation tool and do not form a nitriding layer, thereby avoiding unnecessary influence on the performance of the non-nitriding area, and ensuring that the deformation amount of the whole cylinder is controlled within ±0.02 mm.

[0012] 2. The present application utilizes the following chemical reaction of boron oxide and urea at high temperature: B2O3+2CO(NH2)2=2BN+2CO2+3H2O+2NH3 The formed boron nitride has good lubricity and can be used as a release agent to prevent the anti-permeation tool and the workpiece from being unable to be disassembled due to adhesion, and the anti-permeation method is easy to operate, environmentally friendly, pollution-free and widely applicable.

[0013] 3. On the one hand, the non-adhesion shielding surface of the anti-permeation tool can still glow discharge during the ion nitriding process, and the non-adhesion shielding surface of the anti-permeation tool is provided with a groove with a width of 10-20 mm, more heat can be generated by utilizing the hollow cathode effect, and the temperature uniformity of the titanium alloy cylinder can be improved, on the other hand, the micro-arc oxidation layer formed on the surface of the shielding surface has a small thermal expansion coefficient, and the synergistic effect of the two helps to improve the precision stability of the nitriding cylinder. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a schematic diagram of the titanium alloy cylinder and the anti-permeation tool provided by the present application.

[0015] Figure 2 is the surface morphology of the micro-arc oxidation layer of the anti-permeation tool adhesion shielding surface of the present application.

[0016] Figure 3 is the surface morphology of the anti-permeation tool adhesion shielding surface of the present application after micro-arc oxidation and sealing treatment.

[0017] Figure 4 is the surface morphology of the inner wall of the anti-permeation tool after ion nitriding of the present application.

[0018] Figure 5 is the cross-sectional morphology of the nitrided surface of the titanium alloy cylinder of embodiment 1 of the present application.

[0019] Figure 6 is the cross-sectional morphology of the non-nitrided surface of the titanium alloy cylinder of embodiment 1 of the present application.

[0020] Figure 7 is the surface morphology of the shielding surface of the anti-permeation tooling of embodiment 2 of the present application after micro-arc oxidation.

[0021] Figure 8 is the surface morphology of the shielding surface of the anti-permeation tooling of embodiment 2 of the present application after micro-arc oxidation and sealing treatment.

[0022] Figure 9 is the surface morphology of the inner wall of the anti-permeation tooling of embodiment 2 of the present application after ion nitriding.

[0023] Figure 10 is the cross-sectional morphology of the nitrided surface of the titanium alloy cylinder of embodiment 2 of the present application.

[0024] Figure 11 is the cross-sectional morphology of the non-nitrided surface of the titanium alloy cylinder of embodiment 2 of the present application. Specific implementation method

[0025] In order to make the purpose, technical scheme and advantages of the embodiments of the present disclosure clearer, the technical scheme of the embodiments of the present disclosure will be described clearly and completely below in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by a person skilled in the art without any inventive effort also belong to the scope of protection of the present disclosure.

[0026] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this present subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0027] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. A person of ordinary skill in the art will readily recognize from the disclosure herein, given the total volume of this application that one or more passages that are described as an embodiment is / are also an embodiment of another embodiment.

[0028] The application provides a method for locally ion nitriding a titanium alloy cylinder, comprising the following steps: Step one, selecting the same material as the titanium alloy cylinder as the material for manufacturing the anti-permeation tooling, preparing the anti-permeation tooling according to the size and shape of the non-nitriding area of the titanium alloy cylinder, the wall thickness of the anti-permeation tooling being the same as that of the titanium alloy cylinder, and the outer wall of the anti-permeation tooling having a plurality of longitudinal grooves (such as Figure 1 ), the width of the grooves being preferably 10-20 mm, for example, 10 mm, 15 mm or 20 mm, and the groove depth being half the wall thickness of the anti-permeation tooling; Step two, performing micro-arc oxidation treatment on the fitting shielding surface of the anti-permeation tooling; preparing a micro-arc oxidation film on the fitting shielding surface of the anti-permeation tooling by the micro-arc oxidation method, and the thickness of the obtained micro-arc oxidation film being preferably 15-30 μm, for example, 15 μm, 20 μm, 25 μm or 30 μm, and the surface porosity being preferably 25%-40%, for example, 25%, 30%, 35% or 40%; In the micro-arc oxidation treatment, the non-fitting shielding surface of the anti-permeation tooling is pasted with an insulating tape, the micro-arc oxidation electrolyte is composed of 10 g / L sodium hexametaphosphate, 10 g / L sodium metaaluminate, 4 g / L sodium tetraborate and 1 g / L potassium hydroxide, the voltage of the micro-arc oxidation treatment is 500-650 V, the frequency is 1000-2000 Hz, the duty cycle is 30-50%, the treatment time is 20-40 min, and after the micro-arc oxidation treatment, the insulating tape pasted on the non-fitting shielding surface is torn off and the anti-permeation tooling is cleaned; Step three, performing sealing treatment on the anti-permeation tooling after the micro-arc oxidation treatment, placing the sealing solution containing the anti-permeation tooling in a vacuum heating box, standing for 1 h under the conditions of negative pressure and 60-100℃, and then taking out and drying, the sealing solution being composed of boron oxide, urea and polyvinyl alcohol, the concentration of the polyvinyl alcohol being preferably 50-100 g / L, for example, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L or 100 g / L, the content of the boron oxide in the solution being preferably 72-180 g / L, for example, 72 g / L, 80 g / L, 100 g / L, 120 g / L, 150 g / L, 160 g / L or 180 g / L, the content of the urea being preferably 144-360 g / L, for example, 144 g / L, 180 g / L, 200 g / L, 220 g / L, 250 g / L, 270 g / L, 300 g / L, 330 g / L or 360 g / L, and the concentration ratio of the urea and the boron oxide being ensured to be greater than or equal to 2:1; Step four, install the anti-infiltration tooling after the sealing treatment on the non-nitriding area of the titanium alloy cylinder, and conduct ion nitriding treatment on the titanium alloy cylinder with the installed anti-infiltration tooling. First, heat the titanium alloy cylinder at a stepwise heating rate, increase the temperature to 400℃ at a heating rate of 5℃ / min, then increase the temperature to 600℃ at a heating rate of 3℃ / min, then increase the temperature to 700℃ at a rate of 2℃ / min, and finally increase the temperature to the holding temperature at a heating rate of 1℃ / min. The holding temperature is preferably 750℃ to 830℃, for example, it can be 750℃, 770℃, 790℃, 810℃, or 830℃. The volume ratio of nitrogen and argon in the furnace during the holding stage is preferably 5:0 to 5:1, for example, it can be 5:0 or 5:1. The holding time is preferably 5 to 8 hours, for example, it can be 5 hours, 6 hours, 7 hours, or 8 hours. After the holding is completed, cool the workpiece to below 100℃ in the furnace, remove the anti-infiltration tooling, and obtain the titanium alloy cylinder after local ion nitriding.

[0029] The application will be further described below through specific examples.

[0030] Example 1 In this example, the inner wall and the two end faces of a TA15 titanium alloy cylinder with an outer diameter of 90mm, an inner diameter of 50mm, and a height of 120mm are subjected to ion nitriding. Step one, according to the size and shape of the TA15 titanium alloy cylinder, an anti-infiltration tooling is made, as shown in FIG. 1, the wall thickness of the anti-infiltration tooling is 20mm, and the outer wall has 8 longitudinal grooves (as shown in FIG. 2), the width of the grooves is 10mm, the groove depth is 10mm, and the inner diameter of the anti-infiltration tooling is 32μm larger than the outer diameter of the TA15 titanium alloy cylinder, so that the TA15 titanium alloy cylinder can be fitted into the cylinder-shaped anti-infiltration tooling after micro-arc oxidation and sealing treatment. Figure 1 Figure 1

[0031] Since the temperature of the titanium alloy cylinder is high during ion nitriding, the inner wall does not easily dissipate heat, making the inner wall temperature higher than the outer wall temperature, which leads to easy deformation of the cylinder. The cylinder-shaped tooling not only plays a shielding role, on the one hand, the non-adhesion shielding surface of the anti-infiltration tooling can still glow discharge during ion nitriding, and the grooves on the outer wall increase the glow discharge area, increasing the temperature of the outer layer, thereby enhancing the temperature uniformity of the titanium alloy cylinder; on the other hand, since the inner wall is a ceramic coating after micro-arc oxidation treatment, the thermal expansion coefficient is small, after fitting the anti-infiltration tooling into the titanium alloy cylinder, a uniform constraint can be applied to the cylinder as the temperature rises, and the synergistic effect of the two helps to improve the precision stability of the nitriding cylinder.

[0032] ​​Step two, the inner wall of the cylinder type anti-seepage tool is treated by micro-arc oxidation. Before the micro-arc oxidation treatment, the positions of the cylinder type anti-seepage tool except the inner wall are pasted with insulating tape. The micro-arc oxidation electrolyte is composed of 10 g / L sodium hexametaphosphate, 10 g / L sodium metaaluminate, 4 g / L sodium tetraborate and 1 g / L potassium hydroxide. The voltage of the micro-arc oxidation treatment is 650 V, the frequency is 1000 Hz, the duty cycle is 50%, and the treatment time is 20 min. Then, the micro-arc oxidation film with a thickness of 15 μm is obtained. The pasted insulating tape is torn off, and the cylinder type anti-seepage tool is cleaned.

[0033] Figure 2 The surface morphology of the inner wall of the anti-seepage tool treated by micro-arc oxidation can be seen. A large number of micropores with a diameter of about 5-10 μm are distributed on the surface. The porosity of the oxidation film is about 40%. The larger the micropore diameter, the higher the porosity, which is more conducive to the loading of boron oxide and urea, resulting in more boron oxide generated, which is more conducive to the release of the film.

[0034] Step three, the cylinder type anti-seepage tool is treated by sealing. The sealing solution is composed of 180 g / L boron oxide, 360 g / L urea and 100 g / L polyvinyl alcohol. The cylinder type anti-seepage tool is immersed in the sealing solution and placed in a vacuum heating box. After being placed at negative pressure and 100℃ for 1 h, it is taken out and dried.

[0035] Under the environment of 100℃, the dissolution of boron oxide, urea and polyvinyl alcohol is facilitated, and under the action of negative pressure, they completely penetrate into the pores on the surface of the micro-arc oxidation film, Figure 3 The surface morphology of the inner wall of the cylinder type anti-seepage tool treated by micro-arc oxidation and then by sealing treatment. The sealing agent basically fills the surface pores. The white blocky substance is boron oxide and urea after drying and precipitation.

[0036] Step four, the cylinder type anti-seepage tool is installed on the non-nitriding area of the TA15 titanium alloy cylinder. The TA15 titanium alloy cylinder is treated by ion nitriding. First, the titanium alloy cylinder is heated at a stepwise heating rate. The heating rate is 5℃ / min to 400℃, then 3℃ / min to 600℃, then 2℃ / min to 700℃, and finally 1℃ / min to 750℃. The volume ratio of nitrogen to argon in the furnace during the holding stage is 5:1, and the holding time is 8 h. After the holding is completed, the furnace is cooled to below 100℃, the workpiece is taken out, the cylinder type anti-seepage tool is removed, and the TA15 titanium alloy cylinder with ion nitriding on the inner wall and both end faces is obtained. The surface hardness of the nitriding layer is 920 HV, the deformation of the cylinder is not more than 0.01 mm, and the dimensional accuracy meets the requirements.

[0037] Figure 4To show the surface morphology of the inner wall of the anti-seepage tool after ion nitriding, the blocky material distributed on the surface before nitriding is transformed into granular material. Combined with the element content of the inner wall surface of the anti-seepage tool after nitriding given in Table 1, boron and nitrogen are present, and their atomic percentages are close to 1:1, indicating that boron nitride has been generated on the surface.

[0038] Table 1. Element content of the inner wall surface of the seepage prevention equipment after nitriding

[0039] like Figure 5 and Figure 6 These are the nitrided and non-nitrided cross sections of the TA15 titanium alloy cylinder after ion nitriding, respectively. The nitrided and non-nitrided areas can be clearly distinguished. The non-nitrided area does not form a nitrided layer under the protection of the anti-seepage tooling.

[0040] Example 2 Unlike Example 1, in this example, the cylinder is made of TC6 titanium alloy.

[0041] In step one, the width of the groove on the outer wall of the anti-seepage tooling is 20mm; In step two, the voltage of the micro-arc oxidation treatment is 500 V, the frequency is 2000 Hz, the duty cycle is 30%, and the treatment time is 40 min, which yields a micro-arc oxidation film with a thickness of 30 μm. In step three, the sealing solution consists of 72 g / L boron oxide, 144 g / L urea and 50 g / L polyvinyl alcohol. The cylindrical anti-seepage tool is immersed in the sealing solution and placed in a vacuum heating box. After standing for 1 hour under negative pressure and 60°C, it is taken out and dried. In step four, during the heat preservation stage, the volume ratio of nitrogen to argon in the furnace is 5:0 (pure nitrogen), the heat preservation temperature is 830℃, and the heat preservation time is 5h. After the heat preservation is completed, the furnace is cooled to below 100℃ and the workpiece is taken out. The cylindrical anti-seepage tooling is removed to obtain a TC6 titanium alloy cylinder with ion nitriding on the inner wall and both end faces. The surface hardness of the nitrided layer is 1100HV, and the deformation of the cylinder does not exceed 0.02 mm, which meets the required dimensional accuracy. The rest is the same as in Example 1.

[0042] Figure 7 The surface morphology of the inner wall of the anti-seepage tooling after micro-arc oxidation treatment shows that there are a large number of micropores with a diameter of about 3~5μm distributed on the surface, and the porosity of the oxide film is about 25%. Figure 8 The image shows the surface morphology of the inner wall of the cylindrical anti-seepage tool after micro-arc oxidation treatment and sealing treatment. The sealing agent basically fills the surface pores, and the white blocky substances are boron oxide and urea that have been dried and precipitated.

[0043] Figure 9To prevent the surface morphology of the inner wall after ion nitriding of the anti-seepage tool, the block-shaped substance distributed on the surface before nitriding is converted into granular substance. In combination with the element content on the inner wall surface after nitriding of the anti-seepage tool given in Table 2, there are boron element and nitrogen element, and the atomic percentage of the two is close to 1:1, indicating that boron nitride is generated on the surface. Compared with Example 1, although the contents of surface boron element and nitrogen element are reduced, but from Figure 9 It can be seen that the generated granular boron nitride still uniformly covers the surface, which can play a lubricating and demolding role.

[0044] Table 2 Element content on the inner wall surface after nitriding of the anti-seepage tool

[0045] As Figure 10 and Figure 11 are the nitriding surface section and non-nitriding section of the TC6 titanium alloy cylinder after ion nitriding, respectively, which can obviously distinguish the nitriding zone and non-nitriding zone, and the non-nitriding zone does not form a nitriding layer under the protection of the anti-seepage tool.

[0046] Example 3 Different from Example 1, in this embodiment, the cylinder is TC18 titanium alloy.

[0047] In step one, the groove width of the outer wall of the anti-seepage tool is 15 mm; In step two, the voltage of the micro-arc oxidation treatment is 600 V, the frequency is 1500 Hz, the duty cycle is 40%, and after 30 min of treatment, a micro-arc oxidation film with a thickness of 20 μm and a porosity of 30% can be obtained; In step three, the pore sealing solution is composed of 100 g / L of boron oxide, 250 g / L of urea and 75 g / L of polyvinyl alcohol, the cylinder-shaped anti-seepage tool is immersed in the pore sealing solution and placed in a vacuum heating box, and after standing at negative pressure and 80℃ for 1 h, it is taken out and dried; In step four, the volume ratio of nitrogen and argon in the furnace during the holding stage is 5:0.5, the holding temperature is 800℃, and the holding time is 7 h. After the holding is completed, the workpiece is taken out when the furnace is cooled to below 100℃, the cylinder-shaped anti-seepage tool is removed, and a TC6 titanium alloy cylinder after ion nitriding of the inner wall and both end faces is obtained. The surface hardness of the nitriding layer is 1000 HV, the deformation of the cylinder is not more than 0.015 mm, and the size accuracy meets the requirements; the rest is the same as Example 1.

[0048] Comparative Example 1 Different from Example 1, in this comparative example, the local ion nitriding process of the TA15 titanium alloy cylinder does not include step two and step three.

[0049] The TA15 titanium alloy cylinder and the anti-permeation tool of the present comparative example are expanded by heat during the ion nitriding process, and are extruded with each other, which not only causes the TA15 titanium alloy cylinder to be bonded with the anti-permeation tool, and the anti-permeation tool to be unable to be removed, but also causes the deformation amount of the cylinder to be 0.03 mm, which is higher than 0.02 mm, and the size precision to be unable to meet the requirement.

[0050] Comparative Example 2 The present comparative example is different from Example 1 in that, in the present comparative example, the outer wall of the anti-permeation tool is free of grooves in the step one.

[0051] Although the cylinder-type anti-permeation tool can be removed after the ion nitriding of the TA15 titanium alloy cylinder of the present comparative example is completed, the anti-permeation tool has a reduced heating area, and loses the hollow cathode effect brought by the grooves, and the auxiliary heating effect of the anti-permeation tool is insufficient, which causes the temperature distribution to be uneven during the ion nitriding of the TA15 titanium alloy cylinder, and the deformation amount of the cylinder to be 0.04 mm, which is higher than 0.02 mm, and the size precision to be unable to meet the requirement.

[0052] Comparative Example 3 The present comparative example is different from Example 1 in that, in the present comparative example, the inner diameter of the anti-permeation tool is 22 μm larger than the outer diameter of the TA15 titanium alloy cylinder in the step one, and the anti-permeation tool is treated by micro-arc oxidation to obtain a micro-arc oxidation film with a thickness of 10 μm and a porosity of 20% in the step two.

[0053] The thickness and the surface porosity of the micro-arc oxidation film of the present comparative example are smaller than those of Example 1, and the micro-arc oxidation film has a smaller load of boron oxide and urea, and after the ion nitriding treatment, the TA15 titanium alloy cylinder is bonded with the anti-permeation tool, and the anti-permeation tool is unable to be removed. Meanwhile, the deformation amount of the cylinder is 0.025 mm, which is higher than 0.02 mm, and the size precision is unable to meet the requirement.

[0054] Comparative Example 4 The present comparative example is different from Example 1 in that, in the present comparative example, the inner diameter of the anti-permeation tool is 82 μm larger than the outer diameter of the TA15 titanium alloy cylinder in the step one, and the anti-permeation tool is treated by micro-arc oxidation to obtain a micro-arc oxidation film with a thickness of 40 μm and a porosity of 50% in the step two.

[0055] The thickness and the surface porosity of the micro-arc oxidation film of the present comparative example are significantly larger than those of Example 1, and due to the limitation of the micro-arc oxidation technology itself, the higher the thickness is, the looser the surface micro-arc oxidation layer is, and under the action of the high temperature of the ion nitriding, the micro-arc oxidation layer is damaged or even cracked and falls off, and loses the protection effect, and after the ion nitriding treatment, the TA15 titanium alloy cylinder is still bonded with the anti-permeation tool, and the anti-permeation tool is unable to be removed.

[0056] Comparative Example 5 The difference between the present comparative example and example 1 is that, in the present comparative example, the pore sealing solution in step three is composed of 180 g / L of boron oxide, 360 g / L of urea and 20 g / L of polyvinyl alcohol.

[0057] The pore sealing solution in the present comparative example has too little polyvinyl alcohol added compared with example 1, and the polyvinyl alcohol plays the role of an adhesive. Therefore, too little polyvinyl alcohol leads to too low contents of deposited boron oxide and urea after the micro-arc oxidation pore sealing treatment, and it is impossible to form sufficient boron nitride. After the ion nitriding treatment, the TA15 titanium alloy cylinder and the anti-seepage tooling still stick together and cannot be removed.

[0058] Comparative example 6 The difference between the present comparative example and example 1 is that, in the present comparative example, the pore sealing solution in step three is composed of 180 g / L of boron oxide, 360 g / L of urea and 500 g / L of polyvinyl alcohol.

[0059] The pore sealing solution in the present comparative example has too much polyvinyl alcohol added compared with example 1, which leads to a sharp increase in the viscosity of the pore sealing solution. In step three, it is impossible to discharge the gas in the micro-arc oxidation pores by immersing the cylinder-shaped anti-seepage tooling in the pore sealing solution and placing it in a vacuum heating box. The boron oxide and urea only distribute on the surface of the micro-arc oxidation film and cannot enter the pores of the micro-arc oxidation film. After drying at the end of the pore sealing, a large amount of boron oxide and urea are agglomerated on the inner wall surface of the cylinder-shaped anti-seepage tooling, which leads to too high a thickness of the pore sealing layer. This not only makes it difficult to assemble the anti-seepage tooling with the titanium alloy cylinder, but also, after forced assembly, the boron oxide and urea in the gap are unevenly distributed, and the lubricating effect is limited. After the ion nitriding treatment, the TA15 titanium alloy cylinder and the anti-seepage tooling still stick together and cannot be removed.

[0060] Comparative example 7 The difference between the present comparative example and example 1 is that, in the present comparative example, the temperature is increased to 750℃ at a constant rate of 10℃ / min in step four.

[0061] The ion nitriding process in the present comparative example has a faster temperature increasing rate compared with example 1, which leads to uneven temperature distribution of the cylinder, and the deformation of the cylinder reaches 0.05mm, which does not meet the required dimensional accuracy.

[0062] The above examples are preferred examples for implementing the present application, and the present application is not limited to the above examples. Any non-essential addition, replacement made by a person skilled in the art according to the technical features of the technical solution of the present application all belong to the protection scope of the present application.

Claims

1. A method of locally ion nitriding a titanium alloy cylinder, characterized in that, The method comprises the following steps: Step one, preparing an anti-permeation tool according to the size and shape of the non-nitriding area of the titanium alloy cylinder; the anti-permeation tool has a plurality of longitudinal grooves on the outer wall, the width of the grooves is 10-20 mm, and the depth of the grooves is half of the wall thickness of the anti-permeation tool; Step two, performing micro-arc oxidation treatment on the shielding surface of the anti-permeation tool; A micro-arc oxidation film is prepared on the shielding surface of the anti-permeation tool by the micro-arc oxidation method, the thickness of the micro-arc oxidation film is 15-30 μm, and the surface porosity is 25%-40%; Step three, immersing the anti-permeation tool after the micro-arc oxidation treatment into a sealing solution for sealing treatment; The sealing solution is composed of boron oxide, urea and polyvinyl alcohol, the concentration of the polyvinyl alcohol is 50-100 g / L, the content of the boron oxide in the solution is 72-180 g / L, the content of the urea is 144-360 g / L, and the concentration ratio of the urea to the boron oxide is greater than or equal to 2:1; Step four, installing the anti-permeation tool after the sealing treatment on the non-nitriding area of the titanium alloy cylinder, and performing ion nitriding treatment on the titanium alloy cylinder with the installed anti-permeation tool by a segmented heating mode to obtain a titanium alloy cylinder after local ion nitriding.

2. A method of localised plasma nitriding of a titanium alloy cylinder according to claim 1, characterised in that, The material of the anti-permeation tool in step one is titanium alloy, and the wall thickness of the anti-permeation tool is the same as that of the titanium alloy cylinder.

3. A method of localised plasma nitriding of a titanium alloy cylinder according to claim 1, characterised in that, In the micro-arc oxidation treatment in step two, the non-shielding surface of the anti-permeation tool is pasted with an insulating tape, the insulating tape pasted on the non-shielding surface is torn off after the micro-arc oxidation treatment, and the anti-permeation tool is cleaned.

4. The method of claim 1 wherein the titanium alloy cylinder is locally plasma nitrided. The micro-arc oxidation electrolyte for the micro-arc oxidation treatment is composed of 10 g / L sodium hexametaphosphate, 10 g / L sodium metaaluminate, 4 g / L sodium tetraborate and 1 g / L potassium hydroxide; the voltage for the micro-arc oxidation treatment is 500-650 V, the frequency is 1000-2000 Hz, the duty cycle is 30-50%, and the treatment time is 20-40 min.

5. The method of claim 1 wherein the titanium alloy cylinder is locally ion nitrided by, In step three, the sealing solution with the anti-permeation tool is placed in a vacuum heating box, and after standing for 1 h under the conditions of negative pressure and 60-100 ℃, the anti-permeation tool is taken out and dried.

6. A method of localised plasma nitriding of a titanium alloy cylinder according to claim 1, characterised in that, In step four, during the ion nitriding treatment, the titanium alloy cylinder is first heated at a stepped heating rate, the temperature is raised to 400 ℃ at a heating rate of 5 ℃ / min, then the temperature is raised to 600 ℃ at a heating rate of 3 ℃ / min, then the temperature is raised to 700 ℃ at a rate of 2 ℃ / min, and finally the temperature is raised to the holding temperature at a heating rate of 1 ℃ / min, the holding temperature is 750-830 ℃, the volume ratio of nitrogen to argon in the furnace during the holding stage is 5:0-5:1, the holding time is 5-8 h, and after the holding is completed, the titanium alloy cylinder is taken out after being cooled to below 100 ℃ in the furnace.

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