A method for realizing rapid boronization of a titanium metal surface by using electric field-induced nano-assembly in molten salt

Abstract

The present application relates to the technical field of metal surface treatment, and particularly relates to a method for realizing rapid boronization of titanium metal surface by using electric field induced nano-assembly in molten salt, wherein titanium dioxide powder, boron powder, inorganic salt and nano-particle coating agent are mixed and heated to obtain molten salt containing nano-TiB2. Graphite and titanium metal parts are put into the molten salt containing nano-TiB2, graphite serving as anode and titanium metal parts serving as cathode, the surface area ratio of anode to cathode being 3-10:1, nano-TiB2 in the molten salt being assembled to form boronized layer on the surface of titanium metal parts under the action of electric field, and the boronization speed being 60-500 microns / hour. In the present application, nano-TiB2 is used as the constituent unit of boronized layer, compared with the existing high-temperature boronization technology using active boron atom as the constituent unit, the boronization speed can be significantly improved, and the high-temperature boronization treatment time of titanium metal can be reduced, so that the negative influence of high-temperature environment on the organization structure and mechanical properties of titanium metal parts can be eliminated while energy saving and cost reduction are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal surface treatment, in particular to a method for realizing rapid boronization of titanium metal surface by using electric field induced nano-assembly in molten salt. BACKGROUND

[0002] Industrial pure titanium and titanium alloys have been widely used in the fields of aerospace, petroleum and chemical industry, automobile manufacturing, and biomedical technology due to their low thermal expansion coefficient, excellent corrosion resistance, and superior specific strength and specific stiffness. However, titanium metal itself has some inherent limitations, such as low hardness and insufficient wear resistance, which limit its potential in certain applications. To overcome these limitations, researchers have developed a series of surface modification techniques, including carburizing, oxidizing, nitriding, and boronizing treatment on the surface of titanium metal. These techniques aim to improve the surface properties of titanium metal to make it more suitable for diverse industrial needs.

[0003] Titanium borides have high hardness, excellent thermal conductivity, and low resistivity, which make the formation of a boronized layer on the surface of titanium metal an effective means to improve its performance and broaden its application. Currently, titanium metal surface boronizing treatment techniques mainly include solid powder boronizing, salt bath boronizing, and molten salt electrolysis. However, these methods generally have a problem that they require high-temperature treatment at 800-1200℃ for a long time, usually 5-20h. This not only leads to high energy consumption costs, but also causes changes in the microstructure of the titanium metal matrix material, thereby negatively affecting its mechanical properties. Therefore, how to improve the boronization speed of titanium metal has become a key problem to be solved in the field of titanium metal surface boronization.

[0004] In view of the above-mentioned defects, the present inventors have finally obtained the present application after a long period of research and practice. SUMMARY

[0005] The present application aims to solve the problem that the existing titanium metal surface boronization technology principle is that active boron atoms diffuse to the surface of titanium metal and react with titanium to form a boride layer in a high-temperature environment, however, the diffusion speed of boron atoms is slow, which limits the realization of rapid boronization. The present application provides a method for realizing rapid boronization of titanium metal surface by using electric field induced nano-assembly in molten salt. The technical principle of the present application is to use nano-TiB2 as an assembly unit and utilize electric field to accelerate the migration and deposition of TiB2.

[0006] To achieve the above-mentioned purpose, the present application discloses a method for realizing rapid boronization of titanium metal surface by using electric field induced nano-assembly in molten salt, comprising the following steps:

[0007] S1, mix titanium dioxide powder, boron powder, inorganic salt, nanoparticle coating agent, and obtain molten salt containing nano TiB2 after heating reaction;

[0008] S2, put graphite and titanium metal parts into the molten salt containing nano TiB2, graphite as the positive electrode, titanium metal parts as the negative electrode, nano TiB2 in the molten salt is assembled on the surface of the titanium metal parts to form a boronized layer under the action of the electric field.

[0009] In the step S1, the inorganic salt is a combination of any two or three of NaCl, KCl, MgCl2, NaF, LiF, KF and AlF3.

[0010] In the step S1, the concentration of nano TiB2 in the molten salt containing nano TiB2 is 100-200 g / L, and the size of TiB2 particles is 2-20 nm.

[0011] In the step S1, the nanoparticle coating agent is any one or two of di boron trioxide, silicon dioxide, tin dioxide and aluminum trioxide, and the concentration of the nanoparticle coating agent in the molten salt is 3-8wt%.

[0012] In the step S2, the material of the titanium metal part is any one of industrial pure titanium, Ti-6Al-4V, Ti-5Al-2.5Sn and Ti-6Al-6V-2Sn.

[0013] In the step S2, the surface area ratio of the positive electrode to the negative electrode is 3-10:1.

[0014] In the step S2, the electric field intensity is 0.3-1.2 V / cm.

[0015] In the step S2, the boronized layer includes a transition layer TiB and a working layer TiB2.

[0016] In the step S2, the boronized layer formation speed is 60-500 μm / h.

[0017] Compared with the prior art, the beneficial effects of the present application are:

[0018] 1. The present application provides a boronizing method based on a new principle, which has simple operation method, short boronizing time, low energy consumption, and small influence on the microstructure and mechanical properties of titanium metal matrix material;

[0019] 2. The boronized layer formed by the present application has the characteristics of full densification and uniform thickness, and the transition layer TiB does not contain acicular structure, which not only reduces the brittleness of the boronized layer, but also makes the hardness reach more than 4000HV;

[0020] 3、The boronized layer formed by the application has a certain thickness of TiB transition layer, which ensures the bonding strength of the boronized layer and the substrate to be above 100N (using scratch method as the test standard), and can meet the use under various severe conditions;

[0021] 4、The molten salt medium used in the application has a purifying effect on the surface of titanium metal parts, and only simple treatment is required before boronization, without the need for complex surface pretreatment such as polishing. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 TEM image of the solid salt obtained after cooling of the molten salt containing nano-TiB2;

[0023] Figure 2 SEM image of the boronized layer section obtained by rapid boronization of industrial pure titanium;

[0024] Figure 3 Local high magnification SEM image of the boronized layer section obtained by rapid boronization of industrial pure titanium;

[0025] Figure 4 Experimental result graph of the scratch test bonding strength of the surface boronized industrial pure titanium;

[0026] Figure 5 Hardness test result of the surface boronized layer of industrial pure titanium;

[0027] Figure 6 Friction coefficient test result of the surface boronized layer of industrial pure titanium;

[0028] Figure 7 SEM image and corresponding mapping analysis of the boronized layer section obtained by rapid boronization of TC4 titanium alloy;

[0029] Figure 8 TEM image of the transition layer of the boronized layer section obtained by rapid boronization of TC4 titanium alloy;

[0030] Figure 9 SEM image of the solid salt obtained after cooling of the molten salt containing nano-TiB2 in Comparative Example 1;

[0031] Figure 10 SEM image of the boronized layer section obtained in Comparative Example 1;

[0032] Figure 11 SEM image of the boronized layer section obtained in Comparative Example 2;

[0033] Figure 12 SEM image of the agglomerated TiB2 sheet in the solid salt in Comparative Example 2. DETAILED DESCRIPTION

[0034] The above and other technical features and advantages of the present invention are described in more detail below with reference to the accompanying drawings.

[0035] Example 1

[0036] Rapid boronization was performed on the surface of commercially pure titanium. A molten salt containing nano-TiB2 was synthesized. B powder (average particle size 1 μm) and TiO2 powder (average particle size 100 nm) were mixed in a molar ratio of 4:1 to obtain a raw material mixture. The inorganic salts consisted of NaF and AlF3 salts in a molar ratio of 1:1.2. The nanoparticle coating agent was Al2O3 (average particle size 5 μm). The raw material mixture, inorganic salt, and nanoparticle coating agent were mixed uniformly in a mass ratio of 1:10:0.5 and placed in a graphite crucible. The crucible was heated to 900°C and held for 2 hours to obtain TiB2 particles with a particle size of 3 nm. Then, electric field-induced nanoassembly was performed in the molten salt containing nano-TiB2. A graphite positive electrode and a commercially pure titanium negative electrode were inserted into the molten salt, with a positive electrode to negative electrode surface area ratio of 5:1. A voltage of 1.2 V was applied, corresponding to an electric field strength of 0.6 V / cm, and the assembly time was 50 minutes. The industrial pure titanium after boronization treatment was taken out and placed in molten NaCl-KCl at 690°C for cleaning for 5 minutes to remove the residual solid salt on the surface of the boronized layer. It was then washed with water and dried to obtain a fully dense boronized layer with a thickness of 70 μm.

[0037] Figure 1 The TEM test results of the solid salt obtained after cooling the molten salt containing nano-TiB2 are shown in Figure 1. Figure 1 It can be seen that TiB2 particles with a particle size of about 3 nanometers were synthesized by reaction in the molten salt; Figure 2 and Figure 3 The low-magnification and local high-magnification SEM analysis results of the cross-section of the borided layer obtained by rapid boriding of industrial pure titanium show that the average thickness of the borided layer is 70 μm, the boriding rate is 84 μm / h, and the borided layer is composed of TiB and TiB2. Figure 4 The bonding strength test results of industrial pure titanium with surface boronization were tested by scratch method. The results show that the bonding strength is greater than 100N. Figure 5 and Figure 6 The test results for the hardness and friction coefficient of the boride layer on the surface of industrial pure titanium are as follows: The average hardness is 4007 HV and the average friction coefficient is 0.13. The bonding strength, hardness, and friction coefficient of the boride layer fully meet the application requirements.

[0038] Example 2

[0039] Rapid boronization treatment was performed on the surface of TC4 titanium alloy (Ti-6Al-4V). First, a molten salt containing nano-TiB2 was synthesized. B powder (average particle size 1 μm) and TiO2 powder (average particle size 100 nm) were mixed in a molar ratio of 4.2:1 to obtain a mixed raw material for the reactants. The inorganic salts were NaCl, KCl, and AlF3 salts in a molar ratio of 1:1:0.5. The nanoparticle coating agent was SiO2 (average particle size 0.8 μm). The mixed raw material, inorganic salt, and nanoparticle coating agent were mixed uniformly in a mass ratio of 1:11:0.4 and placed in a graphite crucible. The graphite crucible was heated to 930°C and held at this temperature for 3 hours to obtain TiB2 particles with a particle size of 10 nm. Then, electric field-induced nanoassembly was performed in the molten salt containing nano-TiB2. A graphite positive electrode and a TC4 titanium alloy negative electrode were inserted into the molten salt, with a positive-to-negative electrode surface area ratio of 6:1. A voltage of 1.3V was applied, corresponding to an electric field strength of 0.5V / cm, and the assembly time was 60 minutes. The borided TC4 titanium alloy was removed and washed in molten NaCl-KCl at 700°C for 6 minutes to remove any residual solid salt on the surface of the borided layer. The layer was then washed and dried to obtain a fully dense borided layer with a thickness of 110μm.

[0040] Figure 7 The following is a cross-sectional SEM image of the boronized layer obtained after rapid boronization treatment on the surface of TC4 titanium alloy (Ti-6Al-4V) and the corresponding mapping analysis. The results show that the average thickness of the boronized layer is 110μm and the boronization rate is 110μm / h. TEM analysis of the interface between the substrate and the coating is as follows: Figure 8 As shown. Figure 8 It can be seen that there is a 1 μm thick TiB layer at the coating interface, which forms a transition layer between the boride layer and the TC4 titanium alloy substrate, forming a metallurgical bond and ensuring that the boride layer and the substrate have a bonding strength that meets the use requirements.

[0041] Example 3

[0042] Rapid boronizing treatment was carried out on the surface of TA7 titanium alloy (Ti-5Al-2.5Sn). First, the molten salt containing nano-TiB2 was synthesized. B powder (average particle size 1 μm) and TiO2 powder (average particle size 100 nm) were mixed according to the molar ratio of 4.5:1 to obtain the mixed raw material of reactants. The inorganic salt was KF, NaF and AlF3 salt with the molar ratio of 1:1:1.2. The nano-particle encapsulating agent was SnO2 (average particle size 2 μm). The mixed raw material of reactants, inorganic salt and nano-particle encapsulating agent were mixed uniformly according to the mass ratio of 1:12:0.2 and then put into a graphite crucible. The graphite crucible was heated to 890 °C and kept for 5 hours to obtain TiB2 particles with a particle size of 12 nm. Then, the electric field induced nano-assembly was carried out in the molten salt containing nano-TiB2. The graphite anode and TA7 titanium alloy cathode were inserted into the molten salt, the surface area ratio of anode to cathode was 9:1, a voltage of 1.4 V was applied, the corresponding electric field intensity was 0.9 V / cm, and the assembly time was 40 min. After the boronized TA7 titanium alloy was taken out, it was put into molten NaCl-KCl at 700 °C for 7 min to remove the residual solid salt on the surface of the boronized layer, and then washed with water and dried to obtain a full dense boronized layer with a thickness of 150 μm.

[0043] Comparative Example 1

[0044] An industrial pure titanium surface boronized coating was prepared by electric field induced nano-assembly in molten salt according to the same steps as in Example 1, except that no nano-particle encapsulating agent Al2O3 was added. The SEM of the obtained solid salt containing nano-TiB2 is shown in Figure 9 From Figure 9 it can be seen that, under the condition of no nano-particle encapsulating agent, TiB2 particles with a size of 50-100 nm were formed in the molten salt. After the electric field induced assembly of the molten salt containing large TiB2 particles, the SEM analysis of the cross section of the coating is shown in Figure 10 From Figure 10 it can be seen that the coating is not a single dense boronized coating, but is composed of two dense boronized layers sandwiching a solid salt layer. This indicates that TiB2 particles with a size of 50-100 nm in the molten salt are not conducive to the realization of rapid boronization.

[0045] Comparative Example 2

[0046] An industrial pure titanium surface boronized coating was prepared by electric field induced nano-assembly in molten salt according to the same steps as in Example 1, except that no nano-particle encapsulating agent Al2O3 was added, and the surface area ratio of anode to cathode was adjusted to 9. The SEM analysis of the cross section of the finally obtained coating is shown in Figure 11 From Figure 11 it can be seen that only a solid salt layer rich in TiB2 particles was adhered to the surface of the electrode, and no boronized layer was formed. At the same time, the SEM analysis of the solid salt after the boronization treatment was carried out, as shown inFigure 12 As shown in the figure, a large number of agglomerated TiB2 sheets exist in the solid salt, which indicates that when the ratio of the positive electrode to the negative electrode surface area is adjusted to 9, the nano TiB2 is easy to lose stability during migration, to gather to form TiB2 sheets in the molten salt, and to fail to reach the titanium substrate surface to form a boronized layer. Figure 12

[0047] The nanoparticle size and coating cross-section morphology obtained in Example 1 and Comparative Examples 1-2 were observed, and the results are shown in Table 1.

[0048] Table 1 Comparison of key process parameters and implementation effects of Examples and Comparative Examples 1-2

[0049]

[0050] As shown in Table 1, the nanoparticle coating agent plays a key role, that is, it can assist in achieving the synthesis of TiB2 with a size of less than 20 nm in the molten salt, and the nano TiB2 with such a size can achieve the preparation of a flat and fully dense boronized layer at a high positive electrode to negative electrode area ratio, thereby achieving a high boronizing speed. Without the nanoparticle coating agent, the size of the nano particles can only be in the range of 50-100 nm, and when a higher positive electrode to negative electrode area ratio is used, large-size nano TiB2 is easy to agglomerate and sink during the electric field-induced migration process, and a normal boronized layer cannot be obtained.

[0051] The above description is merely preferred embodiments of the present application, which are only illustrative, but not limiting. It is understood by those skilled in the art that many changes, modifications, and even equivalent can be made to the present application within the spirit and scope of the present application defined in the claims, and all shall fall within the protection scope of the present application.​

Claims

1. A method for rapid boronization of titanium metal surface by electric field-induced nanoassembly in molten salt, characterized in that: The following steps are involved: S1, titanium dioxide powder, boron powder, inorganic salt, and nanoparticle coating agent are mixed and heated to react to obtain a molten salt containing nano-TiB2; S2, placing graphite and titanium metal parts in a molten salt containing nano-TiB2, with graphite serving as the positive electrode and the titanium metal parts serving as the negative electrode. Nano-TiB2 in the molten salt assembles on the surface of the titanium metal parts under the action of an electric field to form a boronized layer; In step S1, the inorganic salt is a combination of any two or three of NaCl, KCl, MgCl2, NaF, LiF, KF and AlF3; In step S1, the nanoparticle encapsulating agent is any one or two of boron trioxide, silicon dioxide, tin dioxide and aluminum trioxide, and the concentration of the nanoparticle encapsulating agent in the molten salt is 3-8 wt %; In step S2, the surface area ratio of the positive electrode to the negative electrode is 3 to 5:1; In step S2, the boronized layer includes a transition layer TiB and a working layer TiB2.

2. The method for realizing rapid boronization of titanium metal surface by using electric field induced nanoassembly in molten salt according to claim 1, characterized in that: In the step S1, the concentration of nano-TiB2 in the molten salt containing nano-TiB2 is 100-200 g / L, and the TiB2 particle size is 2-20 nm.

3. The method for realizing rapid boronization of titanium metal surface by using electric field induced nanoassembly in molten salt according to claim 1, characterized in that: In step S2, the material of the titanium metal part is any one of industrial pure titanium, Ti-6Al-4V, Ti-5Al-2.5Sn and Ti-6Al-6V-2Sn.

4. The method for realizing rapid boronization of titanium metal surface by electric field induced nanoassembly in molten salt according to claim 1, characterized in that: In step S2, the electric field strength is 0.3-1.2 V / cm.

5. The method for realizing rapid boronization of titanium metal surface by using electric field induced nanoassembly in molten salt according to claim 1, characterized in that: In step S2, the boride layer is formed at a speed of 60-500 μm / h.

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