A multiphase boride boronizing layer on the surface of TC4 titanium alloy

Abstract

This invention discloses a multiphase boride boronizing layer on the surface of TC4 titanium alloy, belonging to the field of surface treatment technology. The multiphase boride boronizing layer on the TC4 titanium alloy surface involved in this invention comprises, from the surface to the substrate, a WB2 / TiB2 dual-phase boride outer layer and a TiB whisker inner layer, with a boronizing layer thickness of not less than 45 μm and a surface hardness of not less than 800 HV and not more than 1200 HV. The multiphase boride boronizing layer formed on the TC4 titanium alloy surface is tightly bonded to the substrate, reducing stress concentration at the bonding point between the boronizing layer and the substrate, improving the surface hardness of the TC4 titanium alloy, and enhancing its wear resistance.

Description

Technical Field

[0001] This invention relates to a multiphase boride boronizing layer on the surface of TC4 titanium alloy, belonging to the field of surface treatment technology. Background Technology

[0002] TC4 titanium alloy (Ti6Al4V alloy) is widely used in automotive engineering, aerospace, marine vessels, and biomedicine due to its high melting point, high specific strength, good corrosion resistance, strong high-temperature stability, and excellent biocompatibility. It is currently the most widely used titanium alloy. However, TC4 titanium alloy has relatively low hardness and poor wear resistance, making it prone to adhesive wear during sliding, which can lead to workpiece seizure. These drawbacks severely limit the wider engineering applications of TC4 titanium alloy.

[0003] Boronizing technology is one of the important surface modification technologies for improving the surface properties of titanium and its alloys that has developed rapidly in recent years. By boronizing the surface of TC4 titanium alloy, a two-phase boronized layer of TiB2 outer layer + TiB whisker inner layer is formed, which effectively improves the surface hardness of TC4 titanium alloy, allowing the boronized TC4 titanium alloy to still meet the requirements of wear resistance and corrosion resistance. Patent document CN101608296A discloses a method for boronizing the surface of titanium alloy using boron carbide as a boronizing agent, obtaining a two-phase boronized layer of TiB2 and TiB, with a boronized layer thickness generally not exceeding 20μm. To further increase the thickness of the boronized layer, patent document CN101608295B discloses a method for using a powdered boronizing agent for boronizing the surface of titanium alloy. The TiB2 outer layer hardness reaches 3000HV~3800HV, and the TiB whisker microhardness reaches 800HV~1500HV, which can increase the boronized layer thickness by more than 30%, reaching 26μm. Patent document CN104233180B discloses a method for obtaining a boride diffusion layer on the surface of a titanium alloy. The obtained boride diffusion layer is composed of a two-phase boride of TiB and TiB2, which improves the wear resistance of the titanium alloy to a certain extent. However, after 20 minutes of wear, the friction pair penetrates the boride diffusion layer and reaches the substrate.

[0004] This indicates that the current boronizing layer consists of TiB2 and TiB dual-phase borides, with a thickness of less than 40 μm. In the TiB2 and TiB dual-phase boronizing layer, the outer TiB2 layer has a hardness of up to 3000 HV, approximately nine times that of the TC4 alloy (~340 HV). This easily leads to stress concentration at the interface between the boronizing layer and the substrate, resulting in poor bonding. When the TC4 titanium alloy boronized workpiece is subjected to a certain load, the TiB2 and TiB dual-phase boronizing layer is easily worn away, exhibiting spalling and pitting corrosion, thus eliminating its protective effect on the substrate and significantly reducing the service stability of the TC4 titanium alloy. Summary of the Invention

[0005] This invention addresses the problems existing in the TiB2 and TiB dual-phase boronizing layer on the surface of TC4 titanium alloy by providing a multiphase boride boronizing layer on the surface of TC4 titanium alloy.

[0006] The multiphase boride boronizing layer involved in this invention comprises, from the surface to the substrate, a WB2 / TiB2 dual-phase boride outer layer and a TiB whisker inner layer. The thickness of the boronizing layer is not less than 45 μm, and the surface hardness is not less than 800 HV and not more than 1200 HV. The thickness of the WB2 / TiB2 dual-phase boride outer layer is 5 to 10 μm, and the length of the TiB whiskers is 40 to 120 μm.

[0007] Preferably, the multiphase boride boronizing layer is prepared by a multiphase boride boronizing agent, which comprises the following substances by mass percentage: 10%-15% aluminum powder, 5%-10% potassium chloride, 10%-20% tungsten oxide powder, and 50%-65% anhydrous borax, wherein the total mass percentage of aluminum powder, potassium chloride, tungsten oxide powder, and anhydrous borax is 100%.

[0008] Preferably, boron carbide powder may also be added to the multiphase boride boronizing agent, with an addition amount of 10%-15% by mass, and the total mass percentage of aluminum powder, potassium chloride, tungsten oxide powder, anhydrous borax, and boron carbide powder is 100%.

[0009] Invention principle: During the tungsten-boron co-diffusion process of TC4 alloy, the following reaction occurs:

[0010] (1) Ti + B → TiB;

[0011] (2) Ti + 2B → TiB2;

[0012] (3) W+2B→WB2;

[0013] The formation free energies of TiB2, TiB, and WB2 are all less than zero, with the formation free energy of reaction (2) being the smallest and the formation free energy of reaction (3) being the largest. This indicates that a TiB2 layer was first formed during the tungsten-boron co-diffusion process, and then TiB whiskers were formed on one side of the TC4 matrix. Finally, due to the high concentrations of W and B in the boronizing agent in the tungsten-boron co-diffusion, WB2 was formed on the outer layer of the TiB2, ultimately forming a WB2 / TiB2 dual-phase boride outer layer and a TiB whisker inner layer.

[0014] The beneficial effects of this invention are:

[0015] (1) The multiphase boride layer formed on the surface of TC4 titanium alloy is tightly bonded to the substrate, which reduces stress concentration at the junction of the boride layer and the substrate, improves the surface hardness of TC4 titanium alloy, and improves the wear resistance of TC4 titanium alloy.

[0016] (2) The hardness of the multiphase boride boronizing layer on the surface of the TC4 titanium alloy described in this invention is not less than 800 HV and not more than 1200 HV. This not only effectively reduces the stress concentration at the junction of the boronizing layer and the substrate, making the boronizing layer and the substrate bond well, but also improves the surface hardness of the TC4 titanium alloy, improves the wear resistance of the TC4 titanium alloy, and significantly reduces the coefficient of friction.

[0017] (3) The thickness of the multiphase boride boronizing layer on the surface of the TC4 titanium alloy described in this invention is not less than 50 μm, which improves the service life of the TC4 titanium alloy workpiece and increases its service safety. Attached Figure Description

[0018] Figure 1 The image shows a scanning electron microscope (SEM) image of the cross-sectional morphology of the multiphase boride boronizing layer on the surface of TC4 titanium alloy in Example 1.

[0019] Figure 2 This is a scanning electron microscope (SEM) image of the cross-sectional morphology of the multiphase boride boronizing layer on the surface of TC4 titanium alloy in Example 2.

[0020] Figure 3 This is a scanning electron microscope (SEM) image of the cross-sectional morphology of the multiphase boride boronizing layer on the surface of TC4 titanium alloy in Example 3.

[0021] Figure 4 This is a scanning electron microscope (SEM) image of the cross-sectional morphology of the multiphase boride boronizing layer on the surface of TC4 titanium alloy in Example 4.

[0022] Figure 5 The XRD pattern of the multiphase boride boronizing layer on the surface of TC4 titanium alloy in Example 4 is shown.

[0023] Figure 6 The cross-sectional microstructure of the TiB2 outer layer + TiB whisker inner layer of 1TC4 titanium alloy is shown in (a) and the worn surface is shown in ((b) and (c)). Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0025] Example 1

[0026] The specific preparation steps of the multiphase boride boronizing layer on the surface of TC4 titanium alloy are as follows:

[0027] (1) The TC4 titanium alloy substrate was pretreated by the following methods: the TC4 titanium alloy was degreased, cleaned with deionized water for 15 min, polished with 400# and 2000# sandpaper, polished with 0.5μm Al2O3 polishing powder, cleaned with acetone (common commercial acetone) for 10 min, and ultrasonically cleaned with deionized water for 20 min. Then it was sealed in anhydrous ethanol for later use.

[0028] (2) Preparation of tungsten-boron co-diffusion boronizing agent: 10% aluminum powder, 10% potassium chloride, 15% tungsten oxide powder and 65% anhydrous borax were mixed by mass percentage and ball-milled for 30 min to obtain tungsten-boron co-diffusion boronizing agent.

[0029] (3) The TC4 titanium alloy matrix pretreated in step (1) is embedded in the tungsten-boron co-diffusion boronizing agent obtained in step (2), sealed in a corundum crucible, placed in a box-type muffle furnace, and treated with tungsten-boron co-diffusion at a high temperature of 1000℃ for 10h. Then the sample is taken out, cooled to room temperature, and boiled in hot water at 90~100℃ for 3~5 hours to remove the residual boronizing agent and impurities on the surface, and WB2 / TiB2 dual-phase boride outer layer and TiB whisker inner layer and inner TiB whisker are obtained.

[0030] In this implementation case, the surface hardness of the multiphase boride-infiltrated layer on the TC4 titanium alloy surface was 1157 HV, which is 3 times higher than that of the substrate. The UMT-3 tribometer was set with a test force of 10 N, a rotation speed of 200 r / min, and a time of 30 min. The friction pair was a Ф6 mm Al2O3 ball. The friction coefficient of the sample surface was 0.22, which is significantly lower than that of the substrate, and the friction pair did not penetrate the multiphase boride-infiltrated layer.

[0031] The cross-sectional morphology of the multiphase boride boronizing layer on the TC4 titanium alloy surface in this embodiment is shown in the scanning electron microscope image. Figure 1 .from Figure 1 It can be seen that the outer layer of the WB2 / TiB2 dual-phase boride is 6 μm, and the length of the TiB whiskers reaches 120 μm.

[0032] Example 2

[0033] The specific preparation steps of the multiphase boride boronizing layer on the surface of TC4 titanium alloy are as follows:

[0034] (1) Pretreatment of TC4 titanium alloy substrate: TC4 titanium alloy is subjected to surface degreasing, deionized water cleaning, sandpaper polishing, acetone cleaning, and deionized water ultrasonic cleaning in sequence, and then sealed in anhydrous ethanol for later use.

[0035] (2) Preparation of tungsten-boron co-diffusion boronizing agent: 10% aluminum powder, 10% potassium chloride, 15% tungsten oxide powder, 50% anhydrous borax and 15% carbon boride were ball-milled for 30 min to obtain tungsten-boron co-diffusion boronizing agent by mass percentage.

[0036] (3) The TC4 titanium alloy matrix pretreated in step (1) is embedded in the tungsten-boron co-diffusion boronizing agent obtained in step (2), sealed in a corundum crucible, placed in a box-type muffle furnace, and boronized at a high temperature of 1000℃ for 10 hours. Then the sample is taken out, cooled to room temperature, and boiled in hot water at 90-100℃ for 3-5 hours to remove the residual boronizing agent and impurities on the surface, and the outer and inner TiB whiskers of WB2 / TiB2 dual-phase boride are obtained.

[0037] In this implementation case, the surface hardness of the multiphase boride-infiltrated layer on the TC4 titanium alloy surface reached 838 HV, which is twice that of the substrate. The UMT-3 tribometer was used with a test force of 10 N, a rotation speed of 200 r / min, and a test time of 30 min. The friction pair consisted of Ф6 mm Al2O3 balls. The coefficient of friction on the sample surface was 0.28, significantly lower than that of the substrate, and the friction pair did not penetrate the multiphase boride-infiltrated layer.

[0038] The cross-sectional morphology of the multiphase boride boronizing layer on the TC4 titanium alloy surface in this embodiment is shown in the scanning electron microscope image. Figure 2 .from Figure 2 It can be seen that the outer layer of the WB2 / TiB2 dual-phase boride is 5 μm, and the length of the TiB whiskers reaches 43 μm.

[0039] Example 3

[0040] The specific preparation steps of the multiphase boride boronizing layer on the surface of TC4 titanium alloy are as follows:

[0041] (1) Pretreatment of TC4 titanium alloy substrate: TC4 titanium alloy is subjected to surface degreasing, deionized water cleaning, sandpaper polishing, acetone cleaning, and deionized water ultrasonic cleaning in sequence, and then sealed in anhydrous ethanol for later use.

[0042] (2) Preparation of tungsten-boron co-diffusion boronizing agent: 10% aluminum powder, 10% potassium chloride, 15% tungsten oxide powder and 65% anhydrous borax were ball-milled for 30 min to obtain tungsten-boron co-diffusion boronizing agent by mass percentage.

[0043] (3) The TC4 titanium alloy substrate pretreated in step (1) is embedded in the tungsten-boron co-diffusion boronizing agent obtained in step (2), sealed in a corundum crucible, placed in a box-type muffle furnace, and subjected to high-temperature boronizing treatment at 1100℃ for 10h. The sample is taken out, cooled to room temperature, and then boiled in hot water at 90-100℃ for 3-5 hours to remove the residual boronizing agent and impurities on the surface, and a WB2 / TiB2 dual-phase boride outer layer is obtained; at the same time, TiB whiskers are also generated by surface tungsten-boron co-diffusion.

[0044] In this implementation case, the surface hardness of the multiphase boride-infiltrated layer on the TC4 titanium alloy surface reached 1159 HV, which is four times higher than that of the substrate. The UMT-3 tribometer was used with a test force of 10 N, a rotation speed of 200 r / min, and a test time of 30 min. The friction pair consisted of Ф6 mm Al2O3 balls. The coefficient of friction on the sample surface was 0.20, which is more than 50% lower than that of the substrate, and the friction pair did not penetrate the multiphase boride-infiltrated layer.

[0045] The cross-sectional morphology of the multiphase boride boronizing layer on the TC4 titanium alloy surface in this embodiment is shown in the scanning electron microscope image. Figure 3 .from Figure 3 It can be seen that the outer layer of the WB2 / TiB2 dual-phase boride is 10 μm, and the length of the TiB whiskers reaches 40 μm.

[0046] Example 4

[0047] The specific preparation steps of the multiphase boride boronizing layer on the surface of TC4 titanium alloy are as follows:

[0048] (1) Pretreatment of TC4 titanium alloy substrate: TC4 titanium alloy is subjected to surface degreasing, deionized water cleaning, sandpaper polishing, acetone cleaning, and deionized water ultrasonic cleaning in sequence, and then sealed in anhydrous ethanol for later use.

[0049] (2) Preparation of tungsten-boron co-diffusion boronizing agent: 13% aluminum powder, 8% potassium chloride, 17% tungsten oxide powder, 12% B4C powder and 50% anhydrous borax were ball-milled for 30 min to obtain tungsten-boron co-diffusion boronizing agent by mass percentage.

[0050] (3) The TC4 titanium alloy substrate pretreated in step (1) is embedded in the tungsten-boron co-diffusion boronizing agent obtained in step (2), sealed in a corundum crucible, placed in a box-type muffle furnace, and subjected to high-temperature boronizing treatment at 1000℃ for 10h. The sample is taken out, cooled to room temperature, and then boiled in hot water at 90-100℃ for 3-5 hours to remove the residual boronizing agent and impurities on the surface, and a WB2 / TiB2 dual-phase boride outer layer is obtained. At the same time, TiB whiskers are also generated by tungsten-boron co-diffusion on the surface.

[0051] In this embodiment, the surface hardness of the multiphase boride-infiltrated layer on the TC4 titanium alloy surface was 1013 HV. The UMT-3 tribometer was set with a test force of 10 N, a rotation speed of 200 r / min, and a time of 30 min. The friction pair consisted of Ф6 mm Al2O3 balls. The friction coefficient of the sample surface was 0.23, which was significantly lower than that of the substrate, and the friction pair did not penetrate the multiphase boride-infiltrated layer.

[0052] The cross-sectional morphology of the multiphase boride boronizing layer on the TC4 titanium alloy surface in this embodiment is shown in the scanning electron microscope image. Figure 4 .from Figure 4It can be seen that the outer layer of the WB2 / TiB2 dual-phase boride is 6 μm, and the length of the TiB whiskers reaches 62 μm.

[0053] The XRD pattern of the multiphase boride boronizing layer on the surface of the TC4 titanium alloy in this embodiment is shown below. Figure 5 .from Figure 5 It can be seen that the multiphase boride boronizing layer is composed of WB2, TiB2 and TiB.

[0054] Comparative Example 1

[0055] In this comparative example, the boron-diffused layer is a two-phase boride layer consisting of an outer TiB2 layer and an inner TiB whisker layer. The thickness of this two-phase boride layer is 28 μm. The hardnesses of the outer TiB2 layer, TiB, and TC4 alloy are 2800 HV, 1900 HV, and 343 HV, respectively. The microhardness of the boron-diffused layer on the TC4 titanium alloy surface is more than 8 times that of the substrate, and the hardness gradient from the boron-diffused layer to the substrate is large. Using a UMT-3 tribometer with a test force of 10 N, a rotation speed of 200 r / min, and a time of 30 min, the friction pair consisted of Ф6 mm Al2O3 balls, and the coefficient of friction on the sample surface was 0.35. The boron-diffused layer was worn away, exhibiting peeling and pitting corrosion, thus eliminating its protective effect on the substrate and significantly reducing the service stability of the TC4 titanium alloy. Figure 6 The cross-sectional microstructure of the TiB2 outer layer + TiB whisker inner layer of 1TC4 titanium alloy is shown in (a) and the worn surface is shown in ((b) and (c)).

[0056] Compared with the comparative examples, the boronized layer obtained in Examples 1 to 4 has a smaller hardness gradient, with a hardness between 800 HV and 1200 HV. Within this hardness gradient range, stress concentration is less likely to occur at the interface between the boronized layer and the substrate. Compared with the comparative examples, the boronized layer obtained in Examples 1 to 4 has a smaller friction coefficient, and the friction pair does not penetrate the boronized layer. Therefore, the multiphase boride boronized layer of the present invention can reduce the surface hardness gradient of TC4 titanium alloy and improve the wear resistance of TC4 titanium alloy.

[0057] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A multiphase boride boronizing layer on the surface of TC4 titanium alloy, characterized in that: The multiphase boride boronizing layer consists of a WB2 / TiB2 dual-phase boride outer layer and a TiB whisker inner layer from the surface to the substrate, and the thickness of the boronizing layer is not less than 45 μm.

2. The multiphase boride boronizing layer on the surface of TC4 titanium alloy according to claim 1, characterized in that: The outer layer thickness of WB2 / TiB2 dual-phase borides is 5~10μm, and the length of TiB whiskers is 40~120μm.

3. The multiphase boride boronizing layer on the surface of TC4 titanium alloy according to claim 1, characterized in that: The multiphase boride boronizing layer is prepared from a multiphase boride boronizing agent, which comprises the following substances by mass percentage: A multiphase boride boronizing agent is obtained by ball milling 10%-15% aluminum powder, 5%-10% potassium chloride, 10%-20% tungsten oxide powder, and 50%~65% anhydrous borax. The total mass percentage of aluminum powder, potassium chloride, tungsten oxide powder, and anhydrous borax is 100%.

4. The multiphase boride boronizing layer on the surface of TC4 titanium alloy according to claim 3, characterized in that: The multiphase boride boronizing agent also contains boron carbide powder, which is added at a mass percentage of 10%-15%, and the total mass percentage of aluminum powder, potassium chloride, tungsten oxide powder, anhydrous borax, and boron carbide powder is 100%.

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