Diffusion welding method for dissimilar high-strength titanium alloys

Abstract

This invention provides a diffusion welding method for dissimilar high-strength titanium alloys, comprising the following steps: (1) Sample surface cleaning: Grinding and polishing the surfaces of the two titanium alloys to be welded to a roughness Ra≤1.0μm, then removing the oxide film on the surface to be welded with acid, wiping the surface to be welded with alcohol before welding to remove surface impurities, and drying with cold air; (2) Sample loading into the furnace: Butt-jointing the two titanium alloys obtained in step (1) with cleaned surfaces; (3) Diffusion welding: Placing the sample obtained in step (2) between the upper and lower pressure heads of a vacuum hot press furnace, and then performing diffusion welding, maintaining good axial alignment between the sample and the pressure head, applying a pressure of 5-25MPa to the sample to be welded through the upper pressure head to ensure close contact between the metals, and then depressurizing; performing three heat preservation and pressure preservation cycles, after which depressurizing, first slow cooling, and then cooling with the furnace. This fills a domestic gap and provides a new design solution for high-strength laminated titanium alloys.

Description

Technical Field

[0001] This invention belongs to the field of diffusion welding technology for dissimilar high-strength metals, specifically involving a diffusion welding method for dissimilar high-strength titanium alloys made of two materials: titanium alloy TC4 and titanium alloy Ti80. Background Technology

[0002] Armored vehicles, as one of the most important land-based weapons, are the main combat force of the army. The principle of "one generation of materials, one generation of equipment" highlights the importance of lightweighting and improving the protective performance of armor materials in recent years, which is crucial for enhancing the combat performance of armored vehicles. To resolve the contradiction between lightweighting and high survivability in armored vehicles, major military powers worldwide have placed great emphasis on the research of titanium alloys for armor.

[0003] Lightweighting is a key development direction and research focus for armored vehicles, significantly improving their mobility and combat capabilities. Besides being lightweight, the base armor metal materials of armored vehicles should also possess excellent ballistic resistance, processability, and environmental adaptability. Common metal base armor materials include armor steel, armor aluminum alloy, armor magnesium alloy, and armor titanium alloy. Titanium alloy is a lightweight, high-strength armor material with advantages such as low density, high specific strength, resistance to high and low temperatures, and corrosion resistance. Therefore, armor titanium alloys offer the best overall performance, simultaneously meeting the requirements for ballistic resistance, processability, and environmental adaptability.

[0004] Currently, both domestic and international armored vehicles have begun to adopt high-strength titanium alloys as alternatives to steel and aluminum. This not only reduces weight but also provides excellent ballistic resistance and strong resistance to seawater and salt spray corrosion. With the widespread application of titanium alloys in armored vehicles, a consensus has been largely reached in my country's defense industry, establishing TC4 as the primary material for the development of first-generation armor titanium alloys. Meanwhile, research over the past decade has shown that using single-material titanium alloys as armor offers limited performance improvements and cannot meet the future needs of armored vehicle development. High-strength laminated titanium alloys offer a new design solution. Compared to traditional low-strength, high-elongation laminated metal composites, high-strength laminated titanium alloys are prepared using high-strength, low-elongation dissimilar titanium alloy materials, significantly increasing the complexity of the composite process. Currently, this is a blank area in China, lacking research and breakthroughs in key technologies and mechanisms, requiring further technological breakthroughs.

[0005] Chinese patent CN107030367A discloses a dissimilar metal diffusion welding method for titanium alloy and stainless steel. The welding method includes the following steps: grinding and polishing the surfaces of the titanium alloy and stainless steel to be welded; removing the oxide film on the surfaces of the titanium alloy and copper foil using an acid solution; then, alternately stacking the metal materials in the following order: titanium alloy-niobium foil-copper foil-stainless steel-copper foil-niobium foil-titanium alloy; then placing the stacked sample between the upper and lower pressure heads of a vacuum hot press furnace, applying a pressure of 15-30 MPa, depressurizing, first slowly cooling, and then cooling with the furnace.

[0006] Chinese patent CN111299796A discloses a vacuum diffusion welding method for dissimilar metals, TC4 titanium alloy and 316L stainless steel. The method mainly involves cleaning the sample surface, then stacking the samples in the following order: TC4 titanium alloy-vanadium foil-copper foil-cobalt foil-316L stainless steel, or 316L stainless steel-cobalt foil-copper foil-vanadium foil-TC4 titanium alloy. The stacked samples are placed between the upper and lower pressure heads of a vacuum hot press furnace, and diffusion welding is performed. A pressure of 15-30 MPa is applied. After the vacuum hot press furnace is evacuated to 1×10⁻² Pa, the pressure is released after heat and pressure holding, and the temperature is reduced to 700℃ at a rate of 7℃ / min, followed by furnace cooling.

[0007] Chinese patent CN112548414A discloses an environmentally friendly copper-aluminum welding process, including a copper part and an aluminum part welded to the copper part. The welding process includes: forming the aluminum part and cleaning its surface; spraying a copper powder layer onto the cleaned surface; welding the aluminum part to the copper part by means of the sprayed copper layer; forming a welding coating by spraying before welding, which is more stable during the welding process, especially suitable for aluminum-to-copper and aluminum-to-aluminum welding. Under the action of the solder pad coating, the aluminum part does not need to undergo nickel plating surface treatment before welding, and the spraying method is more efficient. The original aluminum part needs to be nickel plated before welding. The spraying method of this invention is more environmentally friendly than electroplating.

[0008] Currently, there is a lack of domestic methods for producing high-strength laminated titanium alloys. Therefore, how to weld high-strength laminated titanium alloys is an urgent problem to be solved in this field. Summary of the Invention

[0009] In view of this, the present invention aims to propose a diffusion welding method for dissimilar high-strength titanium alloys to solve the problems of dissimilar high-strength titanium alloys failing to bond and cracking during hot rolling in the prior art.

[0010] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0011] A diffusion welding method for dissimilar high-strength titanium alloys includes the following steps:

[0012] (1) Sample surface cleaning: The surfaces of the two titanium alloys to be welded were ground and polished to make their roughness Ra≤1.0μm. Then, acid was used to remove the oxide film on the surface to be welded. Before welding, the surface to be welded was wiped with alcohol to remove surface impurities and dried with cold air.

[0013] (2) Sample loading: The two titanium alloys obtained in step (1) with cleaned surfaces are joined together;

[0014] (3) Diffusion welding: Place the sample obtained in step (2) between the upper and lower pressure heads of the vacuum hot press furnace, and then perform diffusion welding. Maintain good axial alignment between the sample and the pressure head. Apply pressure of 5-25 MPa to the sample to be welded through the upper pressure head to make the metals in close contact. Then depressurize. Perform three heat preservation and pressure preservation. After the heat preservation and pressure preservation is completed, depressurize, cool slowly first, and then cool with the furnace.

[0015] Furthermore, the acid solution in (1) is a mixed solution of hydrofluoric acid and nitric acid.

[0016] Furthermore, the two titanium alloys in (1) and (2) are titanium alloy TC4 and titanium alloy Ti80.

[0017] Furthermore, the three-stage heat preservation and pressure holding method in (3) is as follows: the true hot press furnace is evacuated until the vacuum degree reaches 1.0 × 10⁻⁶. -2 When Pa, the temperature is raised to 850℃ for the first heat preservation and pressure holding, and the pressure is maintained at 15MPa; after the first heat preservation and pressure holding is completed, the temperature is raised to 950℃, which is close to the phase change point, and the heat preservation and pressure holding time is 2.5h; after the second heat preservation and pressure holding is completed, the temperature is lowered to 850℃ for the third heat preservation and pressure holding.

[0018] Furthermore, the heating rate before reaching 850℃ is 7℃ / min.

[0019] Furthermore, after the second heat preservation and pressure holding is completed, the temperature is lowered to 850℃ at a rate of 10℃ / min for the third heat preservation and pressure holding.

[0020] Furthermore, after the third heat preservation and pressure holding is completed, the pressure is released, and the temperature is reduced to 700℃ at a rate of 10℃ / min, and then cooled with the furnace.

[0021] Furthermore, after diffusion welding is completed, slow cooling is performed at a rate of 7°C / min.

[0022] Furthermore, when the sample obtained in (3) is placed between the upper and lower pressure heads of the vacuum hot press furnace, it is ensured that the gap between the two titanium alloys is less than 0.1 mm.

[0023] Furthermore, the thickness of both titanium alloys is 1 to 10 mm.

[0024] Compared with existing technologies, the diffusion welding method for dissimilar high-strength titanium alloys described in this invention has the following advantages: a high-strength laminated titanium alloy production method is developed using a vacuum hot press furnace, filling a domestic gap and providing a new design solution for high-strength laminated titanium alloys.

[0025] (1) Compared with the traditional hot rolling process, the diffusion welding method was used to composite dissimilar high-strength titanium alloys, and the composite between dissimilar high-strength titanium alloys was successfully realized.

[0026] (2) The present invention employs three heat preservation and pressure preservation methods to ensure close contact between metal interfaces, guarantee atomic diffusion, and effectively eliminate thermal stress after diffusion to prevent sample deformation.

[0027] (3) The present invention employs a slow cooling method after vacuum diffusion welding, which helps to eliminate interfacial welding stress.

[0028] (4) The method of the present invention is simple and can be widely applied to the composite of various high-strength titanium alloys. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the vacuum diffusion welding temperature-time process of the present invention;

[0030] Figure 2 This is the interface morphology of the weld area in Example 1. Detailed Implementation

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0032] A method for dissimilar metal diffusion welding of titanium alloy TC4 and titanium alloy Ti80, the specific steps of which are as follows:

[0033] (1) Sample surface cleaning: The surfaces of titanium alloy TC4 and titanium alloy Ti80 to be welded were ground and polished to a roughness Ra≤1.0μm. Then, a mixed acid solution of hydrofluoric acid and nitric acid in a certain proportion was used to remove the oxide film on the surface to be welded, so that the surfaces to be welded can make good contact. Before welding, the surface to be welded was wiped with alcohol to remove surface impurities and dried with cold air;

[0034] (2) Sample loading: The titanium alloy TC4 and titanium alloy Ti80 obtained in step (1) with their surfaces cleaned are connected in sequence, in the order of: titanium alloy TC4-titanium alloy Ti80, or titanium alloy Ti80-titanium alloy TC4.

[0035] (3) Diffusion welding: Place the stacked samples obtained in step (2) between the upper and lower pressure heads of the vacuum hot press furnace. Then perform diffusion welding, maintaining good axial alignment between the sample and the pressure head. Apply pressure of 5-25 MPa to the sample to be welded through the upper pressure head to ensure close contact between the metals, and then release the pressure; perform three heat preservation and pressure holding cycles. After the heat preservation and pressure holding are completed, release the pressure, cool slowly first, and then cool with the furnace.

[0036] Through extensive experimentation, the inventors of this application selected a three-stage heat preservation and pressure holding method as follows:

[0037] The hot press furnace was evacuated. When the vacuum level reached 1.0 × 10⁻² Pa, the temperature was raised to 850 °C at a rate of 7 °C / min for the initial heat preservation and pressure holding, while maintaining the pressure at 15 MPa. This ensured close contact and plastic deformation of the titanium alloy TC4-titanium alloy Ti80 interface. After the initial heat preservation and pressure holding, a second heat preservation and pressure holding was performed, raising the temperature to 950 °C, close to the phase transformation point, for 2.5 hours. After the second heat preservation and pressure holding, the temperature was lowered to 850 °C at a rate of 10 °C / min for the third heat preservation and pressure holding. After the third heat preservation and pressure holding, the pressure was released, and the temperature was simultaneously lowered to 700 °C at a rate of 10 °C / min, and then cooled along with the furnace.

[0038] After diffusion welding, slow cooling is performed at a rate of 7℃ / min. This slower cooling rate avoids stress caused by uneven shrinkage during cooling due to the different coefficients of thermal expansion of the two titanium alloys. Once the furnace temperature reaches 700℃, furnace cooling can be used directly.

[0039] By rationally matching the diffusion temperature, temperature range, holding time, pressure range, and holding time, atoms at the contact surfaces are fully diffused, resulting in a high bonding strength at the interface. This invention's method is simple, efficient, and can be successfully applied to the lamination and composite bonding of dissimilar high-strength titanium alloys.

[0040] Example 1

[0041] The surfaces of 4mm thick TC4 titanium alloy and 4mm thick Ti80 titanium alloy to be welded were mechanically ground and polished to achieve a roughness Ra ≤ 1.0μm. Then, a mixture of hydrofluoric acid and nitric acid in a certain proportion was used to remove the oxide film on the surfaces to be welded, ensuring good contact between the surfaces. Before welding, the surfaces to be welded were wiped with alcohol to remove any residual impurities, and then dried with cold air to prevent impurities from seeping into the weld and damaging its performance.

[0042] The cleaning methods described above are all existing technologies known in the art;

[0043] After cleaning the surfaces, place the titanium alloy TC4 and titanium alloy Ti80 together. Fix them between the upper and lower pressure heads in the furnace chamber of the vacuum diffusion furnace, ensuring the gap is less than 0.1mm;

[0044] After securing the workpiece, proceed according to the standard procedure. First, apply a pre-pressure of 10 MPa to the workpiece using the upper and lower pressure heads to stably fix it between the pressure heads. Then, perform vacuuming until the vacuum level reaches 1.0 × 10⁻⁶. -2 When the pressure is 5 MPa, the vacuum diffusion welding process is carried out. In this embodiment, the diffusion time is 2.5 hours, the diffusion welding pressure is 5 MPa, the diffusion welding temperature is 950°C, and a vacuum diffusion machine is used for diffusion welding.

[0045] The specific operation is as follows: First, the temperature is raised to 850℃ at a rate of 7℃ / min for the initial heat preservation and pressure holding, and then held at 15MPa for 45 minutes to ensure close contact and plastic deformation of the titanium alloy TC4-titanium alloy Ti80 interface. After the initial heat preservation and pressure holding, a second heat preservation and pressure holding is performed, raising the temperature to 950℃, close to the phase transformation point, and holding for 2.5 hours. After the second heat preservation and pressure holding, the temperature is lowered to 850℃ at a rate of 10℃ / min, and then held at 15MPa for the third heat preservation and pressure holding. After the third heat preservation and pressure holding, the pressure is released, and the temperature is simultaneously lowered to 700℃ at a rate of 10℃ / min, and then cooled in the furnace. After welding, the sample is allowed to cool to room temperature before the furnace is opened and the sample is removed, resulting in an 8mm titanium alloy TC4 and titanium alloy Ti80 composite plate.

[0046] Example 2

[0047] The same diffusion welding composite of 4mm titanium alloy TC4 and 4mm titanium alloy Ti80 was performed using the same process as in Example 1, except that the diffusion welding temperature (i.e., the secondary heat preservation temperature) was 960℃, and the other conditions were the same as in Example 1.

[0048] Example 3

[0049] The same diffusion welding composite of 4mm titanium alloy TC4 and 4mm titanium alloy Ti80 was performed using the same process as in Example 1, except that the diffusion welding temperature (i.e., the secondary heat preservation temperature) was 970℃, and the other conditions were the same as in Example 1.

[0050] Examples 1-3 compare the effects of different diffusion welding temperatures on the weld properties between vacuum diffusion welds of dissimilar high-strength titanium alloys. The results are shown in Table 1 below. In this invention, the welded specimens were subjected to tensile tests at room temperature and the loading rate was 0.5 mm / min, in accordance with the national standard GB / T228-2002.

[0051] Table 1 shows the mechanical properties of welded components made of titanium alloy TC4 and titanium alloy T803.

[0052] Example 1 (Diffusion welding temperature: 950℃) 646 490 Example 2 (Diffusion welding temperature is 960℃) 704 603 Example 3 (Diffusion welding temperature: 970℃) 698 520

[0053] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A diffusion welding method for dissimilar high-strength titanium alloys, characterized in that, Includes the following steps: (1) Sample surface cleaning: The surfaces of titanium alloy TC4 and titanium alloy Ti80 to be welded are ground and polished to make their roughness Ra≤1.0μm. Then, acid is used to remove the oxide film on the surface to be welded. Before welding, the surface to be welded is wiped with alcohol to remove surface impurities and dried with cold air. (2) Sample docking: The titanium alloy TC4 and titanium alloy Ti80 obtained in step (1) with their surfaces cleaned are docked. (3) Diffusion welding: Place the sample obtained in step (2) between the upper and lower pressure heads of the vacuum hot press furnace, and then perform diffusion welding. Maintain good axial alignment between the sample and the pressure head. Apply pressure of 5-25 MPa to the sample to be welded through the upper pressure head to make the metals in close contact. Then depressurize. Perform three heat preservation and pressure preservation. After the heat preservation and pressure preservation is completed, depressurize, cool slowly first, and then cool with the furnace. The three-stage heat preservation and pressure holding method involves: evacuating the vacuum hot press furnace until the vacuum level reaches 1.0 × 10⁻⁶. -2 When Pa, the temperature is raised to 850℃ for the first heat preservation and pressure holding, and the pressure is maintained at 15MPa; after the first heat preservation and pressure holding is completed, the temperature is raised to 950℃, which is close to the phase change point, and the heat preservation and pressure holding time is 2.5h; after the second heat preservation and pressure holding is completed, the temperature is lowered to 850℃ for the third heat preservation and pressure holding.

2. The diffusion welding method for dissimilar high-strength titanium alloys according to claim 1, characterized in that, The acid solution in (1) is a mixed solution of hydrofluoric acid and nitric acid.

3. The diffusion welding method for dissimilar high-strength titanium alloys according to claim 1, characterized in that, The heating rate before reaching 850℃ is 7℃ / min.

4. The diffusion welding method for dissimilar high-strength titanium alloys according to claim 1, characterized in that, After the second heat preservation and pressure holding is completed, the temperature is lowered to 850℃ at a rate of 10℃ / min for the third heat preservation and pressure holding.

5. The diffusion welding method for dissimilar high-strength titanium alloys according to claim 1, characterized in that, After the third heat preservation and pressure holding is completed, the pressure is released and the temperature is reduced to 700℃ at a rate of 10℃ / min, and then cooled with the furnace.

6. The diffusion welding method for dissimilar high-strength titanium alloys according to claim 1, characterized in that, After diffusion welding is completed, slow cooling is performed at a rate of 7℃ / min.

7. The diffusion welding method for dissimilar high-strength titanium alloys according to claim 1, characterized in that, When the sample obtained in (3) is placed between the upper and lower pressure heads of the vacuum hot press furnace, ensure that the gap between the two titanium alloys is less than 0.1 mm.

8. The diffusion welding method for dissimilar high-strength titanium alloys according to claim 1, characterized in that, Both titanium alloys have a thickness of 1~10mm.

Images