Method for preparing multilayer and multiphase strengthening layer on surface of titanium alloy

Abstract

The application discloses a preparation method of a multilayer and multiphase reinforcing layer on a titanium alloy surface, which comprises the following steps: uniformly cladding a niobium-titanium alloy layer on the surface of the pretreated titanium alloy by using an automatic wire feeding plasma cladding device, then performing solid solution treatment, then performing electroplating iron treatment on the surface of the solid solution preform, burying and sealing the iron-plated preform in a crucible by using solid carburizing agent powder, then placing the preform in a graphite carbon tube heating furnace and heating to 900-1100 DEG C, keeping heat for 2-8 hours, taking out the preform after cooling to room temperature, and performing pickling and iron removal on the carburized composite material in concentrated hydrochloric acid, so as to obtain the titanium alloy with the (NbTi)C carburized layer and the niobium-titanium alloy cladding layer as the reinforcing layer. By plating iron on the cladded niobium-titanium alloy layer and then carburizing, the application effectively avoids the oxidation of the alloy layer during carburizing, so that the loose and peeling of the carburized layer are avoided, and the prepared composite carbide (NbTi)C layer has higher deformation resistance.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy surface strengthening technology, and relates to a method for preparing multilayer multiphase strengthening layers on the surface of titanium alloys. Background Technology

[0002] Titanium alloys are a class of alloys formed by alloying titanium with other metallic elements. Their advantages include high strength, lightweight, good corrosion resistance, and biocompatibility. However, titanium alloys have relatively low surface hardness and poor wear resistance, which severely limits their application in abrasive environments. To improve their hardness and wear resistance, surface strengthening treatments are typically performed on titanium alloys to enhance their hardness and wear resistance.

[0003] Traditional titanium alloy surface strengthening technologies are diverse, including ultrasonic rolling, plasma or laser cladding, vapor deposition, ion implantation, and surface carburizing or nitriding. Among these, surface carburizing is a simple and effective method to improve the surface properties of titanium alloys. Commonly used titanium alloy surface carburizing processes include two types: gas carburizing and solid carburizing. During gas carburizing, the infiltration of hydrogen can easily lead to hydrogen embrittlement. Taking measures to prevent hydrogen embrittlement increases the difficulty and cost of preparation, greatly limiting the application of gas carburizing in titanium alloys. For example, Chinese patent CN105420663B proposes a low-pressure vacuum gas carburizing and nitriding composite technology, which combines intermittent periodic gas filling and evacuation with the carburizing and nitriding process to prepare titanium carbides, nitrides, and Ti(N,C) on the titanium alloy surface, avoiding the hydrogen embrittlement problem. However, this process is complex and difficult to prepare, making it difficult to apply in actual production. Solid carburizing, as illustrated in Chinese Patent CN1044328376B, uses a solid carburizing method to prepare a titanium carbide ceramic layer on the surface of TC4 titanium alloy. This method improves the hydrogen embrittlement problem caused by traditional gas carburizing and enhances the wear resistance of the titanium alloy. However, the prepared TiC layer exhibits high brittleness, leading to easy cracking and even peeling. Therefore, how to improve the solid carburizing method, solve the problem of high brittleness and low toughness of the carbide layer on the titanium alloy surface, and improve the stability of the carbide layer on the titanium alloy surface is a pressing technical challenge that needs to be addressed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a multi-layer, multi-phase reinforcing layer on the surface of titanium alloys, which solves the problem of high brittleness and low toughness of the carbide layer formed on the surface of titanium alloys by existing solid carburizing methods.

[0005] The technical solution adopted in this invention is a method for preparing a multilayer multiphase strengthening layer on the surface of a titanium alloy, comprising the following steps:

[0006] Step 1: Pre-treat the titanium alloy to remove the surface oxide layer and impurities;

[0007] Step 2: Using niobium-titanium alloy wire as raw material, an automatic wire feeding plasma cladding equipment is used to uniformly clad a niobium-titanium alloy layer on the pretreated titanium alloy surface. The cladding is a single-layer multi-pass plasma cladding.

[0008] Step 3: The titanium alloy with a niobium-titanium alloy layer fused to its surface is placed in an inert atmosphere heating furnace for solution treatment, and then rapidly cooled at 60-100℃ / min to obtain a solution preform.

[0009] Step 4: Electroplating iron is performed on the surface of the solution-treated preform to obtain an iron-plated preform;

[0010] Step 5, solid carburizing: Place the iron-plated preform in a crucible, cover and seal it with solid carburizing agent powder, then place it in a graphite carbon tube heating furnace and heat it to 900-1100℃, hold it for 2-8 hours, and then take it out after cooling to room temperature with the furnace.

[0011] Step 6: Place the carburized composite material in concentrated hydrochloric acid for pickling to remove iron, thereby obtaining a titanium alloy with a (NbTi)C carburized layer and a niobium-titanium alloy cladding layer as the reinforcing layers.

[0012] In step 1, the titanium alloy is pretreated, including grinding the surface of the titanium alloy to be clad with sandpaper in stages, polishing after grinding to 1000 grit, ultrasonic cleaning with anhydrous ethanol, and finally drying for later use.

[0013] The niobium content in the niobium-titanium alloy wire used in step 2 is 40-80 wt.%, and the diameter of the niobium-titanium alloy wire is 1 mm-6 mm.

[0014] In step 2, an automatic wire-feeding plasma cladding equipment is used to uniformly clad a niobium-titanium alloy layer on the pretreated titanium alloy surface. The plasma cladding power is 19–24 kW, the plasma arc column diameter is 5 mm–10 mm, the wire is fed by a side-feeding method, the wire feeding speed is 50–90 mm / s, the scanning speed is 20–50 mm / s, argon is used as the protective gas and plasma gas, the protective gas flow rate is 25–30 SCFH, the plasma gas flow rate is 1.5–3.0 SCFH, and the thickness of the clad niobium-titanium alloy layer is 1 mm–7 mm.

[0015] In step 3, the solution treatment temperature is 600–800℃ and the solution treatment time is 3 hours.

[0016] In step 4, before iron plating, the surface of the cladding layer is polished and the non-electroplating surface is treated with water-based paint for anti-plating. After the coating material is air-dried for 1 hour, a pure iron plate is used as the anode and the solid solution preform is used as the cathode. The preform is electroplated in a ferrous chloride aqueous solution for a period of time to obtain the iron plating preform.

[0017] In step 4, the pH value of the ferrous chloride aqueous solution is 1-5, the electroplating current is 0.05A-5A, and the electroplating time is 20min-150min.

[0018] In step 5, before solid carburizing, the non-carburized surface is coated with refractory coating to prevent seepage. After the coating material is air-dried for 24 hours, the iron-plated preform is placed in a crucible, buried and sealed with solid carburizing agent powder, and then placed in a graphite carbon tube heating furnace and heated to 900-1100℃ at a heating rate of 5℃ / min-10℃ / min.

[0019] The solid carburizing agent consists of: 5-20 wt.% sodium carbonate, with the balance being carbon black.

[0020] The titanium alloy is TC4 titanium alloy, and the thickness of the surface carbide layer obtained by solid carburizing is 15μm to 100μm.

[0021] The beneficial effects of this invention are as follows:

[0022] (1) A multiphase carbide layer was formed on the surface of titanium alloy by plasma cladding and solid carburizing. The multiphase carbide (NbTi)C is a core-shell structure with Ti-rich phase as the core and Nb-rich phase as the shell. The particle size of the carburized layer shows a gradient distribution from the surface to the inside, which is large → small → large. This gradient change in composition and grain size makes the carbide layer have both high hardness and good toughness. In terms of performance, (NbTi)C has better fracture toughness than TiC and NbC alone, and has higher deformation resistance.

[0023] (2) A niobium-titanium alloy layer is clad on the surface of the titanium alloy. Nb and Ti are two metal elements with good compatibility. They can form an infinite solid solution. During the cladding process, Nb and Ti can fully dissolve each other to form a uniform alloy layer without obvious interface separation. This infinite solid solution characteristic improves the bonding force between the titanium alloy matrix and the cladding layer, and also improves the stability of the material under different working conditions.

[0024] (3) By plating iron on the clad niobium-titanium alloy layer and then carburizing, the loose and peeling of the carbide layer caused by oxidation during the carburizing of the alloy layer is effectively avoided, the preparation efficiency of the carbide layer is improved, and the iron plating carburizing process can be applied to the surface modification of complex parts. Compared with the traditional hot pressing interstitial atomic carburizing method, it is simpler, more efficient and has a wider range of applications.

[0025] (4) The thickness of the composite carbide layer prepared by the method of the present invention is controllable. In the temperature range of 900 to 1100°C, the thickness of the carbide ceramic layer increases with the increase of temperature and the film thickness increases with the extension of the holding time. By controlling the appropriate cooling rate, the matrix grains can be made fine, which effectively ensures the mechanical properties of the titanium alloy matrix. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the multilayer multiphase reinforcement layer on the surface of the titanium alloy in this invention;

[0027] Figure 2 This is a SEM image of the multilayer multiphase reinforcement layer on the surface of the titanium alloy prepared in Example 1;

[0028] Figure 3 This is a SEM image of the multilayer multiphase reinforcement layer on the surface of the titanium alloy prepared without iron plating in Comparative Example 1.

[0029] In the figure, 1. Titanium alloy substrate, 2. Niobium-titanium alloy layer, 3. Surface carbide layer, 4. Iron plating layer. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0031] The present invention discloses a method for preparing a multilayer multiphase reinforcement layer on the surface of a titanium alloy, comprising the following steps:

[0032] Step 1: Titanium alloy pretreatment to remove surface oxide layer and impurities, including using sandpaper to grind the surface of the titanium alloy to be clad step by step, grinding to 1000 grit and then polishing, then using anhydrous ethanol for ultrasonic cleaning, and finally drying for later use.

[0033] Step 2, cladding coating: Using niobium-titanium alloy wire as raw material, the niobium content in the niobium-titanium alloy wire is 40-80 wt.%, and the diameter of the niobium-titanium alloy wire is 1 mm-6 mm. An automatic wire feeding plasma cladding equipment is used to uniformly clad the niobium-titanium alloy layer on the pretreated titanium alloy surface. The cladding is a single-layer multi-pass plasma cladding, with a plasma cladding power of 19-24 kW and a plasma arc column diameter of 5 mm-10 mm. The wire is fed by a side feeding method with a wire feeding speed of 50-90 mm / s and a scanning speed of 20-50 mm / s. Argon is used as the protective gas and plasma gas. The protective gas flow rate is 25-30 SCFH, and the plasma gas flow rate is 1.5-3.0 SCFH. The thickness of the clad niobium-titanium alloy layer is 1 mm-7 mm.

[0034] Step 3, solution treatment: The titanium alloy with the niobium-titanium alloy layer fused to the surface is placed in an inert atmosphere heating furnace, the furnace temperature is raised to 600-800℃ and held for 3 hours, and then rapidly cooled at a cooling rate of 60-100℃ / min to obtain the solution preform.

[0035] Step 4, surface iron plating treatment: The surface of the cladding layer of the solution preform is polished and coated with water-based paint to prevent plating on the non-electroplating surface. After the coating material is air-dried for 1 hour, a pure iron plate is used as the anode and the solution preform is used as the cathode. In a ferrous chloride aqueous solution with a pH of 1 to 5, the electroplating current is I = 0.05A to 5A for 20 to 150 minutes to obtain the iron-plated preform.

[0036] Step 5, solid carburizing: First, apply a refractory coating to the non-carburized surface for anti-carburizing treatment. After the coating material has dried in the shade for 24 hours, place the iron-plated preform in a crucible, cover it with solid carburizing agent powder and seal it. The solid carburizing agent composition is: 5-20 wt.% sodium carbonate, 5-20 wt.% sodium carbonate, and the balance is carbon black. Then place it in a graphite carbon tube heating furnace and heat the furnace temperature to 900-1100℃ at a heating rate of 5-10℃ / min, hold it at that temperature for 2-8 hours, and then cool it to room temperature with the furnace before taking it out. A (NbTi)C carburized layer, i.e., a surface carbide layer, is formed on the surface of the niobium-titanium alloy layer. The thickness of this surface carbide layer is 15μm-100μm.

[0037] Step 6: The carburized composite material is placed in concentrated hydrochloric acid for pickling to remove iron, thus obtaining a titanium alloy with a (NbTi)C carburized layer and a niobium-titanium alloy cladding layer as the reinforcing layers. Its structure is as follows: Figure 1 The bottom is a titanium alloy substrate 1, and on the titanium alloy substrate 1 are a niobium titanium alloy layer 2 and a surface carbide layer 3 in sequence.

[0038] Example 1

[0039] A method for preparing a multilayer multiphase reinforcement layer on the surface of a titanium alloy includes the following steps:

[0040] Step 1, titanium alloy pretreatment, including selecting TC4 plate with length × width × height = 25mm × 25mm × 8mm as the substrate, using sandpaper to grind the surface of the titanium alloy to be clad step by step, grinding to 1000 grit and then polishing, then using anhydrous ethanol for ultrasonic cleaning for 10 minutes, and finally drying for later use.

[0041] Step 2, cladding coating: Using Nb40Ti60 wire with a diameter of 1mm as raw material, an automatic wire feeding plasma cladding equipment is used to uniformly clad a niobium-titanium alloy layer on the pretreated titanium alloy surface. The cladding is a single-layer, multi-pass plasma cladding with a plasma cladding power of 19kW and a plasma arc column diameter of 5mm. The wire is fed by a side feeding method with a wire feeding speed of 50mm / s and a scanning speed of 20mm / s. Argon is used as both the protective gas and the plasma gas. The protective gas flow rate is 25SCFH, and the plasma gas flow rate is 1.5SCFH. The thickness of the clad niobium-titanium alloy layer is 1mm.

[0042] Step 3, solution treatment: The titanium alloy with the niobium-titanium alloy layer fused to the surface is placed in an inert atmosphere heating furnace, the furnace temperature is raised to 600℃ and held for 3 hours, and then rapidly cooled at a cooling rate of 60℃ / min to obtain the solution preform.

[0043] Step 4, surface iron plating treatment: The surface of the cladding layer of the solution preform is polished and coated with water-based paint to prevent plating on the non-electroplating surface. After the coating material is air-dried for 1 hour, a pure iron plate is used as the anode and the solution preform is used as the cathode. In a ferrous chloride aqueous solution with a pH of 1, the plating current is I = 0.05A and the plating time is 20 minutes to obtain the iron-plated preform.

[0044] Step 5, solid carburizing: First, apply a refractory coating to the non-carburized surface for anti-seepage treatment. After the coating material has dried in the shade for 24 hours, place the iron-plated preform in a crucible, cover it with solid carburizing agent powder and seal it. The solid carburizing agent composition is: 5 wt.% sodium carbonate, 5 wt.% sodium carbonate, and the balance is carbon black. Then place it in a graphite carbon tube heating furnace, heat the furnace temperature to 900℃ at a heating rate of 5℃ / min, hold it at that temperature for 2 hours, and then cool it to room temperature with the furnace before taking it out.

[0045] The microstructure of the extracted titanium alloy sheet was observed using a scanning electron microscope, such as... Figure 2 As shown in the figure, the TC4 titanium alloy substrate has a clad niobium-titanium alloy layer 2 on its surface. The surface of the niobium-titanium alloy layer 2 is a (NbTi)C carburized layer, i.e., a surface carbide layer 3, with a thickness of about 15μm. This surface carbide layer has a dense structure, no obvious pores, fine grains, and good bonding with the niobium-titanium alloy layer interface. The (NbTi)C particles show a gradient distribution from the surface to the inside, from large to small to large. The surface of the (NbTi)C carburized layer is an iron plating layer 4.

[0046] Step 6: At room temperature, the carburized composite material is placed in concentrated hydrochloric acid for pickling to remove the iron plating layer 4 on the surface of the (NbTi)C carburized layer, thus obtaining TC4 titanium alloy sheet with (NbTi)C carburized layer and niobium titanium alloy cladding layer as reinforcement layers.

[0047] The fracture toughness of the surface carbide layer of the TC4 titanium alloy prepared in Example 1 was tested, and the fracture toughness value was approximately 3.67 MPa·m. 1 / 2 .

[0048] Comparative Example 1

[0049] A method for preparing a multilayer multiphase reinforcement layer on the surface of a titanium alloy includes the following steps:

[0050] Step 1, titanium alloy pretreatment, is the same as in Example 1;

[0051] Step 2, cladding coating, is the same process as in Example 1.

[0052] Step 3, solution treatment, is the same as the process in Example 1;

[0053] Step 4, solid carburizing, is the same process as in Example 1.

[0054] The microstructure of the extracted titanium alloy sheet was observed using a scanning electron microscope, such as... Figure 3 As shown in the figure, the multi-layer multiphase strengthening layer on the surface of the titanium alloy prepared in Comparative Example 1 consists of a clad niobium-titanium alloy layer 2 and a surface carbide layer 3. The surface carbide layer is a (NbTi)C carburized layer, which has a loose structure and is easy to peel off.

[0055] The fracture toughness of the surface carbide layer of the TC4 titanium alloy plate prepared in Comparative Example 1 was tested, and its fracture toughness value was approximately 2.94 MPa·m. 1 / 2 .

[0056] Example 2

[0057] A method for preparing a multilayer multiphase reinforcement layer on the surface of a titanium alloy includes the following steps:

[0058] Step 1, titanium alloy pretreatment, including selecting TC4 plate with length × width × height = 35mm × 35mm × 8mm as the substrate, using sandpaper to grind the surface of the titanium alloy to be clad step by step, grinding to 1000 grit and then polishing, then using anhydrous ethanol for ultrasonic cleaning for 10 minutes, and finally drying for later use.

[0059] Step 2, cladding coating: Using Nb50Ti50 wire with a diameter of 2mm as raw material, an automatic wire feeding plasma cladding equipment is used to uniformly clad a niobium-titanium alloy layer on the pretreated titanium alloy surface. The cladding is a single-layer, multi-pass plasma cladding with a plasma cladding power of 20kW and a plasma arc column diameter of 6mm. The wire is fed by a side feeding method with a wire feeding speed of 50mm / s and a scanning speed of 20mm / s. Argon is used as both the protective gas and the plasma gas. The protective gas flow rate is 30SCFH and the plasma gas flow rate is 2.0SCFH. The thickness of the clad niobium-titanium alloy layer is 2mm.

[0060] Step 3, solution treatment: The titanium alloy with niobium-titanium alloy layer fused to the surface is placed in an inert atmosphere heating furnace, the furnace temperature is raised to 620℃ and held for 3 hours, and then rapidly cooled at a cooling rate of 75℃ / min to obtain the solution preform.

[0061] Step 4, surface iron plating treatment: The surface of the cladding layer of the solution preform is polished and coated with water-based paint to prevent plating on the non-electroplating surface. After the coating material is air-dried for 1 hour, a pure iron plate is used as the anode and the solution preform is used as the cathode. In a ferrous chloride aqueous solution with a pH of 2, the plating current is I = 0.8A and the plating time is 50 minutes to obtain the iron-plated preform.

[0062] Step 5, solid carburizing: First, apply a refractory coating to the non-carburized surface for anti-seepage treatment. After the coating material has dried in the shade for 24 hours, place the iron-plated preform in a crucible, cover it with solid carburizing agent powder and seal it. The solid carburizing agent composition is: 10 wt.% sodium carbonate, 10 wt.% sodium carbonate, and the balance is carbon black. Then place it in a graphite carbon tube heating furnace, heat the furnace temperature to 950℃ at a heating rate of 8℃ / min, hold it at that temperature for 5 hours, and then cool it to room temperature with the furnace before taking it out.

[0063] The microstructure of the extracted titanium alloy sheet was observed using a scanning electron microscope. The TC4 titanium alloy substrate had a clad niobium-titanium alloy layer on its surface, and a (NbTi)C carburized layer, i.e., a surface carbide layer, with a thickness of about 45 μm. This surface carbide layer had a dense structure, no obvious pores, fine grains, and good interfacial bonding with the niobium-titanium alloy layer. The (NbTi)C particles showed a gradient distribution from the surface to the interior, from large to small to large. The surface of the (NbTi)C carburized layer was an iron plating layer.

[0064] Step 6: At room temperature, the carburized composite material is placed in concentrated hydrochloric acid for pickling to remove the iron plating layer on the surface of the (NbTi)C carburized layer, thus obtaining TC4 titanium alloy sheet with (NbTi)C carburized layer and niobium titanium alloy cladding layer as reinforcement layers.

[0065] The fracture toughness of the surface carbide layer of the TC4 titanium alloy prepared in Example 2 was tested, and its fracture toughness value was approximately 4.28 MPa·m. 1 / 2 .

[0066] Example 3

[0067] A method for preparing a multilayer multiphase reinforcement layer on the surface of a titanium alloy includes the following steps:

[0068] Step 1, titanium alloy pretreatment, including selecting TC4 plate with length × width × height = 50mm × 50mm × 8mm as the substrate, using sandpaper to grind the surface of the titanium alloy to be fused step by step, grinding to 1000 grit and then polishing, then using anhydrous ethanol for ultrasonic cleaning for 10 minutes, and finally drying for later use.

[0069] Step 2, cladding coating: Using Nb60Ti40 wire with a diameter of 3mm as raw material, an automatic wire feeding plasma cladding equipment is used to uniformly clad a niobium-titanium alloy layer on the pretreated titanium alloy surface. The cladding is a single-layer, multi-pass plasma cladding with a plasma cladding power of 21kW and a plasma arc column diameter of 6mm. The wire is fed by a side feeding method with a wire feeding speed of 60mm / s and a scanning speed of 30mm / s. Argon is used as both the protective gas and the plasma gas. The protective gas flow rate is 25SCFH and the plasma gas flow rate is 2.5SCFH. The thickness of the clad niobium-titanium alloy layer is 4mm.

[0070] Step 3, solution treatment: The titanium alloy with niobium-titanium alloy layer fused to the surface is placed in an inert atmosphere heating furnace, the furnace temperature is raised to 680℃ and held for 3 hours, and then rapidly cooled at a cooling rate of 80℃ / min to obtain the solution preform.

[0071] Step 4, surface iron plating treatment: polish the surface of the cladding layer of the solution preform, and apply anti-plating treatment to the non-electroplating surface with water-based paint. After the coating material has dried in the shade for 1 hour, use a pure iron plate as the anode and the solution preform as the cathode. Electroplating is carried out in a ferrous chloride aqueous solution with a pH of 2 for 60 minutes at an electroplating current of I = 2A to obtain the iron-plated preform.

[0072] Step 5, solid carburizing: First, apply a refractory coating to the non-carburized surface to prevent seepage. After the coating material has dried in the shade for 24 hours, place the iron-plated preform in a crucible, cover it with solid carburizing agent powder and seal it. The solid carburizing agent composition is: 15 wt.% sodium carbonate, 15 wt.% sodium carbonate, and the balance is carbon black. Then place it in a graphite carbon tube heating furnace, heat the furnace temperature to 980℃ at a heating rate of 8℃ / min, hold it at that temperature for 4 hours, and then cool it to room temperature with the furnace before taking it out.

[0073] The microstructure of the extracted titanium alloy sheet was observed using a scanning electron microscope. The TC4 titanium alloy substrate had a clad niobium-titanium alloy layer on its surface, and a (NbTi)C carburized layer, i.e., a surface carbide layer, with a thickness of about 55 μm, on its surface. This surface carbide layer had a dense structure, no obvious pores, fine grains, and good interfacial bonding with the niobium-titanium alloy layer. The (NbTi)C particles showed a gradient distribution from large to small to large from the surface to the interior. The surface of the (NbTi)C carburized layer was an iron plating layer.

[0074] Step 6: At room temperature, the carburized composite material is placed in concentrated hydrochloric acid for pickling to remove the iron plating layer on the surface of the (NbTi)C carburized layer, thus obtaining TC4 titanium alloy sheet with (NbTi)C carburized layer and niobium titanium alloy cladding layer as reinforcement layers.

[0075] The fracture toughness of the surface carbide layer of the TC4 titanium alloy prepared in Example 3 was tested, and the fracture toughness value was approximately 4.57 MPa·m. 1 / 2 .

[0076] Example 4

[0077] A method for preparing a multilayer multiphase reinforcement layer on the surface of a titanium alloy includes the following steps:

[0078] Step 1, titanium alloy pretreatment, including selecting TC4 plate with length × width × height = 65mm × 65mm × 8mm as the substrate, using sandpaper to grind the surface of the titanium alloy to be clad step by step, grinding to 1000 grit and then polishing, then using anhydrous ethanol for ultrasonic cleaning for 10 minutes, and finally drying for later use.

[0079] Step 2, cladding coating: Using Nb70Ti30 wire with a diameter of 5mm as raw material, an automatic wire feeding plasma cladding equipment is used to uniformly clad a niobium-titanium alloy layer on the pretreated titanium alloy surface. The cladding is a single-layer, multi-pass plasma cladding with a plasma cladding power of 22kW and a plasma arc column diameter of 8mm. The wire is fed by a side feeding method with a wire feeding speed of 50mm / s and a scanning speed of 25mm / s. Argon is used as both the protective gas and the plasma gas. The protective gas flow rate is 28SCFH and the plasma gas flow rate is 2.5SCFH. The thickness of the clad niobium-titanium alloy layer is 5mm.

[0080] Step 3, solution treatment: The titanium alloy with the niobium-titanium alloy layer fused to the surface is placed in an inert atmosphere heating furnace, the furnace temperature is raised to 760℃ and held for 3 hours, and then rapidly cooled at a cooling rate of 90℃ / min to obtain the solution preform.

[0081] Step 4, surface iron plating treatment: polish the surface of the cladding layer of the solution preform, and apply anti-plating treatment to the non-electroplating surface with water-based paint. After the coating material has dried in the shade for 1 hour, use a pure iron plate as the anode and the solution preform as the cathode. Electroplating is carried out in a ferrous chloride aqueous solution with a pH of 3 for 120 minutes at an electroplating current of I = 3A to obtain the iron-plated preform.

[0082] Step 5, solid carburizing: First, apply a refractory coating to the non-carburizing surface to prevent seepage. After the coating material has dried in the shade for 24 hours, place the iron-plated preform in a crucible, cover it with solid carburizing agent powder and seal it. The solid carburizing agent composition is: 15 wt.% sodium carbonate, 15 wt.% sodium carbonate, and the balance is carbon black. Then place it in a graphite carbon tube heating furnace, heat the furnace temperature to 1050℃ at a heating rate of 10℃ / min, hold it at that temperature for 6 hours, and then cool it to room temperature with the furnace before taking it out.

[0083] The microstructure of the extracted titanium alloy sheet was observed using a scanning electron microscope. The TC4 titanium alloy substrate had a clad niobium-titanium alloy layer on its surface, and a (NbTi)C carburized layer, i.e., a surface carbide layer, with a thickness of about 75 μm. This surface carbide layer had a dense structure, no obvious pores, fine grains, and good interfacial bonding with the niobium-titanium alloy layer. The (NbTi)C particles showed a gradient distribution from large to small to large from the surface to the interior. The surface of the (NbTi)C carburized layer was an iron plating layer.

[0084] Step 6: At room temperature, the carburized composite material is placed in concentrated hydrochloric acid for pickling to remove the iron plating layer on the surface of the (NbTi)C carburized layer, thus obtaining TC4 titanium alloy sheet with (NbTi)C carburized layer and niobium titanium alloy cladding layer as reinforcement layers.

[0085] The fracture toughness of the surface carbide layer of the TC4 titanium alloy prepared in Example 4 was tested, and the fracture toughness value was approximately 6.45 MPa·m. 1 / 2 .

[0086] Example 5

[0087] A method for preparing a multilayer multiphase reinforcement layer on the surface of a titanium alloy includes the following steps:

[0088] Step 1, titanium alloy pretreatment, including selecting TC4 plate with length × width × height = 80mm × 80mm × 8mm as the substrate, using sandpaper to grind the surface of the titanium alloy to be fused step by step, grinding to 1000 grit and then polishing, then using anhydrous ethanol for ultrasonic cleaning for 10 minutes, and finally drying for later use.

[0089] Step 2, cladding coating: Using 6mm diameter Nb80Ti20 wire as raw material, an automatic wire feeding plasma cladding equipment is used to uniformly clad a niobium-titanium alloy layer on the pretreated titanium alloy surface. The cladding is a single-layer, multi-pass plasma cladding with a plasma cladding power of 24kW and a plasma arc column diameter of 10mm. The wire is fed by a side feeding method at a wire feeding speed of 90mm / s and a scanning speed of 50mm / s. Argon is used as both the protective gas and the plasma gas. The protective gas flow rate is 30SCFH and the plasma gas flow rate is 3.0SCFH. The thickness of the clad niobium-titanium alloy layer is 7mm.

[0090] Step 3, solution treatment: The titanium alloy with the niobium-titanium alloy layer fused to the surface is placed in an inert atmosphere heating furnace, the furnace temperature is raised to 800℃ and held for 3 hours, and then rapidly cooled at a cooling rate of 100℃ / min to obtain the solution preform.

[0091] Step 4, surface iron plating treatment: polish the surface of the cladding layer of the solution preform, and apply anti-plating treatment to the non-electroplating surface with water-based paint. After the coating material has dried in the shade for 1 hour, use a pure iron plate as the anode and the solution preform as the cathode. Electroplating is carried out in a ferrous chloride aqueous solution with a pH of 5 for 150 minutes at an electroplating current of I = 5A to obtain the iron-plated preform.

[0092] Step 5, solid carburizing: First, apply a refractory coating to the non-carburizing surface to prevent seepage. After the coating material has dried in the shade for 24 hours, place the iron-plated preform in a crucible, cover it with solid carburizing agent powder and seal it. The solid carburizing agent composition is: 20 wt.% sodium carbonate, 20 wt.% sodium carbonate, and the balance is carbon black. Then place it in a graphite carbon tube heating furnace, heat the furnace temperature to 1100℃ at a heating rate of 10℃ / min, hold it at that temperature for 8 hours, and then cool it to room temperature with the furnace before taking it out.

[0093] The microstructure of the extracted titanium alloy sheet was observed using a scanning electron microscope. The TC4 titanium alloy substrate had a clad niobium-titanium alloy layer on its surface, and a (NbTi)C carburized layer, i.e., a surface carbide layer, with a thickness of about 100 μm. This surface carbide layer had a dense structure, no obvious pores, fine grains, and good bonding with the niobium-titanium alloy layer. The (NbTi)C particles showed a gradient distribution from the surface to the interior, from large to small to large. The surface of the (NbTi)C carburized layer was an iron plating layer.

[0094] Step 6: At room temperature, the carburized composite material is placed in concentrated hydrochloric acid for pickling to remove the iron plating layer on the surface of the (NbTi)C carburized layer, thus obtaining TC4 titanium alloy sheet with (NbTi)C carburized layer and niobium titanium alloy cladding layer as reinforcement layers.

[0095] The fracture toughness of the surface carbide layer of the TC4 titanium alloy prepared in Example 5 was tested, and the fracture toughness value was approximately 5.88 MPa·m. 1 / 2 .

Claims

1. A method for preparing a multilayer multiphase strengthening layer on the surface of a titanium alloy, characterized in that, Includes the following steps: Step 1: Pre-treat the titanium alloy to remove the surface oxide layer and impurities; Step 2: Using niobium-titanium alloy wire as raw material, an automatic wire feeding plasma cladding equipment is used to uniformly clad a niobium-titanium alloy layer on the pretreated titanium alloy surface. The cladding is a single-layer multi-pass plasma cladding. The niobium content in the niobium-titanium alloy wire used in step 2 is 40-80 wt.%, and the diameter of the niobium-titanium alloy wire is 1 mm-6 mm. Step 3: The titanium alloy with a niobium-titanium alloy layer fused to its surface is placed in an inert atmosphere heating furnace for solution treatment, and then rapidly cooled at 60~100℃ / min to obtain a solution preform. In step 3, the solution treatment temperature is 600~800℃ and the solution treatment time is 3h; Step 4: Electroplating iron is performed on the surface of the solution-treated preform to obtain an iron-plated preform; Step 5, solid carburizing: Place the iron-plated preform in a crucible, cover and seal it with solid carburizing agent powder, then place it in a graphite carbon tube heating furnace and heat it to 900~1100℃, hold it for 2h~8h, and then take it out after cooling to room temperature with the furnace. Step 6: Place the carburized composite material in concentrated hydrochloric acid for pickling to remove iron, thereby obtaining a titanium alloy with a (NbTi)C carburized layer and a niobium-titanium alloy cladding layer as the reinforcing layers.

2. The method for preparing a multilayer multiphase strengthening layer on the surface of a titanium alloy according to claim 1, characterized in that, In step 1, the titanium alloy is pretreated by using sandpaper to grind the surface of the titanium alloy to be clad step by step, polishing it after grinding to 1000 grit, ultrasonically cleaning it with anhydrous ethanol, and finally drying it for later use.

3. The method for preparing a multilayer multiphase strengthening layer on the surface of a titanium alloy according to claim 1, characterized in that, In step 2, an automatic wire-feeding plasma cladding equipment is used to uniformly clad a niobium-titanium alloy layer on the pretreated titanium alloy surface. The plasma cladding power is 19~24 kW, the plasma arc column diameter is 5mm~10mm, the wire is fed by a side feeding method, the wire feeding speed is 50~90mm / s, the scanning speed is 20~50mm / s, argon is used as the protective gas and plasma gas, the protective gas flow rate is 25~30SCFH, the plasma gas flow rate is 1.5~3.0SCFH, and the thickness of the niobium-titanium alloy layer obtained by cladding is 1mm~7mm.

4. The method for preparing a multilayer multiphase strengthening layer on the surface of a titanium alloy according to claim 3, characterized in that, In step 4, before iron plating, the surface of the cladding layer is polished and the non-electroplating surface is treated with water-based paint to prevent plating. After the coating material is air-dried for 1 hour, a pure iron plate is used as the anode and the solid solution preform is used as the cathode. The preform is electroplated in a ferrous chloride aqueous solution for a period of time to obtain the iron plating preform.

5. The method for preparing a multilayer multiphase strengthening layer on the surface of a titanium alloy according to claim 4, characterized in that, In step 4, the pH value of the ferrous chloride aqueous solution is 1~5, the electroplating current is 0.05A~5A, and the electroplating time is 20min~150min.

6. The method for preparing a multilayer multiphase strengthening layer on the surface of a titanium alloy according to claim 5, characterized in that, In step 5, before solid carburizing, the non-carburized surface is coated with refractory coating to prevent seepage. After the coating material is air-dried for 24 hours, the iron-plated preform is placed in a crucible, buried and sealed with solid carburizing agent powder, and then placed in a graphite carbon tube heating furnace and heated to 900~1100℃ at a heating rate of 5℃ / min~10℃ / min.

7. The method for preparing a multilayer multiphase strengthening layer on the surface of a titanium alloy according to claim 1, characterized in that, The titanium alloy is TC4 titanium alloy, and the thickness of the surface carbide layer obtained by solid carburizing is 15μm~100μm.

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