A method for welding and forming a titanium-steel dissimilar metal composite member

Abstract

This invention relates to a welding and forming method for titanium-steel dissimilar metal composite components, belonging to the field of dissimilar metal welding and forming. It solves the problems of easy defects in titanium alloy casting, low strength of titanium / steel welded joints, and lengthy process flow in existing technologies. The method includes: surface treatment of the alloy steel workpiece; preparation of a Ni-V alloy composite intermediate layer on the alloy steel surface; use of titanium alloy atomized powder; placing the alloy steel part in a steel cladding, filling it with titanium alloy powder, and sealing it; after vacuum degassing, performing integrated forming and welding using a three-stage hot isostatic pressing process: low-temperature pre-connection, high-temperature high-pressure densification, and cooling in-situ stress relief; finally, removing the cladding. This invention effectively suppresses the formation of the Fe-Ti brittle phase through the diffusion-blocking effect of the Ni-V intermediate layer and the synergistic control of the three-stage hot isostatic pressing, resulting in high interfacial strength. It is suitable for the preparation of various high-strength composite components of titanium alloys and alloy steels.

Description

Technical Field

[0001] This invention relates to the field of dissimilar metal welding and forming technology, and in particular to a welding and forming method for titanium-steel dissimilar metal composite components. Background Technology

[0002] Titanium alloys possess advantages such as high specific strength, high temperature resistance, and corrosion resistance, making them widely used in aerospace, petrochemical, and other fields. However, titanium alloys are expensive, have poor creep resistance, and are difficult to process and form. Titanium alloys are primarily formed through casting, but the forming process is prone to casting defects such as shrinkage porosity, cracking, and segregation, leading to product scrap. Alloy steels offer excellent mechanical properties, lower cost, and better formability, but their high-temperature strength and specific strength are relatively low. Combining titanium alloys with alloy steels can combine the advantages of both, improving material economy and meeting the weight reduction requirements of modern equipment.

[0003] Currently, the composite bonding of titanium alloys and alloy steels mainly employs brazing or electron beam welding technologies. Brazing involves joining titanium alloy and alloy steel parts using filler metal, but welding must be performed above the liquidus line of the filler metal. This process easily leads to the formation of large brittle phases (such as TiFe and TiFe2) at the joint, resulting in low joint strength, typically not exceeding 250 MPa. Electron beam welding avoids the addition of filler metal, but it is also a liquid-state welding process, which easily produces large intermediate brittle phases, resulting in low weld strength. Furthermore, both processes require pre-casting of the titanium alloy parts, leading to lengthy processes and unavoidable casting defects.

[0004] Therefore, existing technologies suffer from problems such as difficulty in forming titanium alloys, low strength of titanium / steel welded joints, and lengthy process flows. There is an urgent need for an integrated process that can simultaneously achieve high-quality forming of titanium alloys and high-strength welding of titanium / steel. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a welding and forming method for titanium-steel dissimilar metal composite components, in order to solve the problems of easy defects in titanium alloy casting, low strength of titanium / steel welded joints, and lengthy process flow in the prior art.

[0006] The objective of this invention is mainly achieved through the following technical solutions: This invention provides a welding and forming method for titanium-steel dissimilar metal composite components, comprising the following steps: S1: Surface treatment of alloy steel workpieces; S2: A modified nickel-based composite intermediate layer is prepared on the surface of alloy steel; S3: Prepare titanium alloy powder for later use; S4: Design the shape of the sheath according to the shape of the target titanium alloy, and prepare the sheath; S5: Place the alloy steel workpiece with completed surface treatment and composite intermediate layer preparation into a sleeve, fill it with titanium alloy powder, and then perform argon arc sealing welding; S6: Place the package into a heat preservation furnace for vacuum degassing; S7: Ultrasonic testing is used to inspect the casing to ensure that there are no porosity defects in the casing; S8: The three-stage hot isostatic pressing process is used for the integrated forming and welding of titanium and steel dissimilar metals. S9: Remove the cladding on the surface of titanium alloy and alloy steel by machining to obtain a titanium-steel dissimilar metal composite component of the target shape.

[0007] Furthermore, in step S2, the modified nickel-based composite intermediate layer is made of Ni-V alloy, wherein the mass content of V is ≤20%, and the thickness of the modified nickel-based composite intermediate layer is 800-1800 nm.

[0008] Furthermore, in step S3, the titanium alloy powder is titanium alloy atomized powder with an oxygen content ≤1500ppm and a powder particle size range of 15-150 μm.

[0009] Furthermore, in step S5, the rate at which the titanium alloy powder is filled is ≤500g / s; The parameters for the argon arc sealing welding are: current 50-80A, voltage 9-10V, welding speed 5-10mm / s, argon flow rate 6-10L / min, and no less than 2 weld passes.

[0010] Furthermore, in step S6, the vacuum degassing temperature is 100-300℃, and the vacuum degree is less than 1×10⁻⁶. - Degassing was stopped after 2 Pa.

[0011] Further, step S8 includes: S81: Place the package in a hot isostatic pressing furnace, slowly introduce nitrogen or argon gas to the first specified pressure, heat to the first specified temperature, and hold at the temperature; S82: Slowly heat to the second specified temperature, pressurize to the second specified pressure, and maintain the temperature; S83: Slowly cool down to the third specified temperature, reduce pressure to the third specified pressure, and maintain the temperature; S84: Slowly release the gas. After the gas is completely released, remove the sheath and perform visual inspection and ultrasonic testing on the sheath. The second specified temperature is higher than the first specified temperature, the second specified pressure is higher than the first specified pressure, and the first specified pressure is less than or equal to the third specified pressure.

[0012] Further, in step S81, the heating rate is ≤10℃ / min, the first specified temperature is 550-750℃, the first specified pressure is 100-150MPa, and the holding time is 2-6h.

[0013] Further, in step S82, the heating rate is ≤10℃ / min, the second specified temperature is 940-1100℃, the second specified pressure is 180-260MPa, and the holding time is 2-6h.

[0014] Further, in step S83, the cooling rate is ≤10℃ / min, the third specified temperature is 600-850℃, the third specified pressure is 150-200MPa, and the heat preservation time is 1-5h.

[0015] The present invention also provides a titanium-steel dissimilar metal composite component, which is prepared by the above-described welding forming method.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. This invention employs a sputtering process to deposit a Ni-V alloy intermediate layer on the surface of alloy steel. Utilizing the excellent wettability of nickel, it bonds firmly to the substrate. Simultaneously, it leverages the diffusion-blocking effect of vanadium during hot isostatic pressing (forming a V-Ti compound layer). A three-stage hot isostatic pressing process is used for diffusion bonding. This "solid-state welding" mechanism effectively suppresses large-scale interdiffusion between Fe and Ti, preventing the formation of brittle phases such as large-size TiFe and TiFe2, thereby improving interfacial strength.

[0017] 2. This invention employs a three-stage hot isostatic pressing process and powder-solid co-packing method: "low-temperature pre-bonding—high-temperature and high-pressure densification—cooling and in-situ stress relief." Specifically: the first stage (550-750℃, 100-150MPa) pre-sintersects the titanium alloy powder, while optimizing the interface bonding between the Ni-V interlayer and the alloy steel; the second stage (940-1100℃, 180-260MPa) causes the titanium alloy powder to undergo isotropic and uniform shrinkage, achieving full densification sintering (relative density ≥99.5%) and completing sufficient diffusion bonding at the titanium / steel interface; the third stage (600-850℃, 150-200MPa) involves in-situ stress-relieving annealing during cooling to eliminate residual welding stress. This three-stage synergistic process completely avoids defects such as shrinkage porosity, gas porosity, segregation, and cracking that are easily generated in traditional casting processes, and the mechanical properties (strength and plasticity) of the sintered titanium alloy are superior to those of cast alloys of the same composition.

[0018] 3. This invention utilizes an integrated process of "powder-solid co-packing + multi-stage hot isostatic pressing" to simultaneously complete the densification of titanium alloy powder, diffusion welding of titanium / steel dissimilar metals, and in-situ stress relief after welding (third stage: 600-850℃ heat preservation for stress relief) within the same hot isostatic pressing cycle. Compared to existing technologies, this invention eliminates numerous intermediate steps involved in titanium alloy casting, such as mold preparation, melting, pouring, riser cutting, casting surface treatment, non-destructive testing, heat treatment, and pre-welding surface activation treatment of titanium alloy castings. This significantly shortens the process flow and reduces manufacturing costs.

[0019] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0020] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0021] Figure 1 is a schematic diagram of the planar design of the titanium alloy and stainless steel composite pipe of Example 1; Figure 2 This is a microstructure diagram of the titanium alloy and stainless steel composite pipe of Example 1; Figure 3 This is a microstructure diagram of the titanium alloy and stainless steel composite pipe of Example 2; Figure 4 The image shows the microstructure of the titanium alloy and stainless steel composite pipe of Comparative Example 1. Detailed Implementation

[0022] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0023] This invention provides a welding and forming method for titanium-steel dissimilar metal composite components, comprising the following steps: S1: Surface treatment of alloy steel workpieces; Specifically, the alloy steel workpieces undergo surface treatment, including mechanical grinding, pickling, ultrasonic cleaning, and vacuum drying. The specific operation is as follows: After mechanical grinding, a 5%-10% dilute hydrochloric acid solution is used to remove the surface oxide film. If the concentration of the dilute hydrochloric acid solution is too low, the film removal will be incomplete, the steel surface will not be sufficiently activated, and the bonding strength between the intermediate layer and the alloy steel will be affected. If the concentration is too high, it will easily cause over-corrosion. After pickling, anhydrous ethanol is used directly for ultrasonic cleaning to remove residual acid from the alloy steel surface. The parameters for ultrasonic cleaning are: frequency of 30-60kHz (exemplary, 30kHz, 35kHz, 40kHz, 45kHz, 50kHz, 55kHz, 60kHz), and time of 10-20min (exemplary, 10min, 12min, 14min, 15min, 16min, 18min, 20min). If the frequency is too low (<30kHz), cavitation corrosion will easily occur and damage the surface. If the frequency is too high (>60kHz), the cleaning ability will decrease. If the cleaning time is too short (<10min), the residue will not be completely removed. If the time is too long (>20min), the surface finish may be damaged due to cavitation. Subsequently, the alloy steel is dried in a vacuum oven to remove surface moisture and residual ethanol. The drying temperature is 150-200℃ (exemplary values: 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃), the vacuum degree is ≤100Pa, and the drying time is 2-6 hours (exemplary values: 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours). If the drying temperature is too low or the drying time is too short... If the time is too short, the moisture cannot be completely removed, and the residual moisture will vaporize in the subsequent high-temperature hot isostatic pressing stage, resulting in interface voids; if the temperature is too high or the time is too long, it may cause slight surface oxidation or softening of the alloy steel during tempering; a vacuum degree of ≤100Pa can accelerate the evaporation of moisture and ethanol and avoid oxidation; the temperature range of 150-200℃ can quickly desorb surface moisture and ethanol without causing changes in the structure of the coating or substrate; after completing the above surface treatment, the surface finish of the alloy steel workpiece plate should not be less than 3μm (i.e., Ra≤3μm).

[0024] S2: A modified nickel-based composite intermediate layer is prepared on the surface of alloy steel; Specifically, the modified nickel-based composite intermediate layer is a Ni-V alloy, wherein the V content in the modified nickel-based alloy is ≤20%. The alloy steel surface is coated using a sputtering process, and the thickness of the intermediate layer is controlled between 800-1800 nm (exemplary values: 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, 1050 nm, 1100 nm, 1150 nm, 1200 nm, 1250 nm, 1300 nm, 1350 nm, 1400 nm, 1450 nm, 1500 nm, 1550 nm, 1600 nm, 1650 nm, 1700 nm, 1750 nm, 1800 nm). During the sputtering process, a vacuum degree of less than 1×10⁻⁶ is required. -4 Pa (for example, 0.1 × 10⁻⁶) -4 Pa, 0.2×10 -4 Pa, 0.3×10 -4 Pa, 0.4×10 - 4 Pa, 0.5×10 -4 Pa, 0.6×10 -4 Pa, 0.7×10 -4 Pa, 0.8×10 -4 Pa, 0.9×10 -4 Pa), power 300-400W (exemplary, 300W, 320W, 340W, 360W, 380W, 400W), deposition rate 80-200nm / min (exemplary, 80nm / min, 100nm / min, 120nm / min, 140nm / min, 150nm / min, 160nm / min, 180nm / min, 200nm / min).

[0025] Magnetron sputtering, as a dry coating process, avoids the chemical waste generated by wet processes such as electroplating, making it environmentally friendly. From an industrial production perspective, it is easier to ensure the uniformity of large-size film layers, thereby guaranteeing the uniformity of the weld interface strength.

[0026] The modified nickel-based composite interlayer is a Ni-V alloy coating. Compared to a pure nickel layer, the addition of V allows for the formation of a stable vanadium-rich thin film during sputtering and subsequent hot isostatic pressing. This layer acts as a diffusion barrier, further suppressing interdiffusion between Fe and Ti. Simultaneously, the addition of V improves sputtering efficiency and reduces energy loss. The nickel alloy layer adheres firmly to the alloy steel surface, while the addition of V refines the grain size, mitigating the columnar crystal penetration structure that may exist in pure nickel layers and reducing the internal stress of the interlayer itself, thereby improving the bonding strength with the substrate and preventing delamination. Vanadium also refines the grain size, significantly reducing the grain size of interfacial reaction layers (such as Ni-Ti intermetallic compounds), thus improving interfacial strength and toughness and preventing the initiation of brittle cracks. The sputtering process does not generate chemical waste and produces a uniform coating thickness on large workpieces without edge effects, further ensuring the uniformity of the weld interface strength.

[0027] The thickness of the modified nickel-based composite interlayer is controlled between 800-1800 nm. If the thickness is too small (<800 nm), the interlayer cannot continuously block the interdiffusion of Fe and Ti during the subsequent hot isostatic pressing process, and the diffusion barrier effect of V is insufficient, resulting in the formation of a large-sized brittle phase at the interface. At the same time, an excessively thin interlayer may be discontinuous or locally fractured, leading to local direct contact between the alloy steel and the titanium alloy, reducing the joint strength. If the thickness is too large (>1800 nm), the deposition time is prolonged, affecting the preparation efficiency. Furthermore, excessive thickness will cause excessive internal stress in the interlayer, making it prone to peeling during the preparation process and cracking during the subsequent hot isostatic pressing cooling stage. In addition, an excessively thick interlayer will lead to the formation of an excessively thick Ni-Ti intermetallic compound layer at the interface, which will make the joint brittle.

[0028] The vacuum level must be less than 1×10⁻⁶ during sputtering. -4 High vacuum (Pa) removes residual oxygen, water vapor, and other impurities from the chamber, preventing film oxidation or oxide inclusions and ensuring the purity and bonding strength of the Ni-V alloy layer to the substrate. A sputtering power of 300-400W maintains stable glow discharge, ensuring a moderate deposition rate. Too low a power results in a slow deposition rate and poor film density; too high a power leads to excessive bombardment energy, potentially damaging the substrate surface or increasing internal stress in the film. A deposition rate of 80-200 nm / min produces a uniform Ni-V alloy layer with few defects. Too high a rate leads to a loose film and reduced adhesion; too low a rate results in low efficiency and may introduce excessive impurities.

[0029] S3: Prepare titanium alloy powder for later use; Specifically, the titanium alloy powder is atomized titanium alloy powder, which can be prepared by gas atomization, plasma rotation, or electrode induction, preferably by electrode induction gas atomization, with a purity of 99% or higher. The oxygen content of the powder is ≤1500ppm (exemplary, 1500ppm, 1400ppm, 1300ppm, 1200ppm, 1100ppm, 1000ppm, 900ppm, 800ppm, 700ppm, 600ppm, 500ppm), and the particle size range is 15-150 μm (exemplary, 15-53μm, 15-105μm, 53-105μm, 105-150μm). The oxygen content of the powder should be ≤1500ppm. Oxygen plays a role in solid solution strengthening in titanium alloys, but excessive oxygen content will significantly reduce the plasticity and toughness of titanium alloys, making the titanium alloy layer brittle and prone to brittle fracture under stress. Excessive oxygen content will form a thick oxide film (TiO2) on the surface of the titanium alloy powder. This oxide film is difficult to completely remove during subsequent hot isostatic pressing, hindering the metallurgical bonding between titanium alloy powder particles and affecting the diffusion bonding between the titanium alloy and the intermediate layer (Ni-V alloy), leading to a decrease in interfacial bonding strength. Controlling the oxygen content to ≤1500ppm ensures that the oxide film thickness on the powder surface is within an acceptable range, ensuring good wettability and diffusion bonding. When the oxygen content is too high, the oxide on the powder surface may decompose at high temperatures to produce gas, or react with carbon in the titanium alloy to generate CO / CO2, which remains at the grain boundaries, forming pores and reducing density.

[0030] The powder particle size range is 15-150 μm. A wider particle size distribution (15-150 μm) allows coarse and fine particles to fill gaps, resulting in a higher tap density. This high tap density helps form a stable powder buildup in the initial stages of hot isostatic pressing, reducing volume shrinkage during densification and preventing excessive deformation or cracking of the titanium alloy layer. If the particle size is too fine, the powder has a large specific surface area, easily adsorbing gas and causing a decrease in tap density. If the particle size is too coarse, the gaps between coarse particles are large, resulting in a low tap density, high shrinkage after molding, and potentially leading to dimensional deviations or cracks in the component. Powder with a particle size of 15-150 μm has good flowability, allowing it to smoothly fill the complex gaps between the alloy steel workpiece and the cladding in the subsequent encapsulation process, preventing bridging or void formation. If the particle size is too fine, the flowability deteriorates, and it easily agglomerates; if the particle size is too coarse, it is difficult to penetrate narrow gaps.

[0031] This invention preferably uses electrode induction gas atomization (EIGA) powder. The EIGA method employs crucibleless induction melting, which avoids contamination of the titanium alloy melt by crucible materials. The resulting powder has high purity, low oxygen content, and good sphericity, which is beneficial for subsequent sintering and welding. Gas atomization and plasma rotating electrode methods can also be used, but it is necessary to ensure that the final powder meets the requirements for oxygen content and particle size.

[0032] S4: Design the shape of the sheath according to the shape of the target titanium alloy, and prepare the sheath; Specifically, the sheath can be a steel sheath, and the sheath material is 316 stainless steel. 316 stainless steel has moderate strength and is easy to remove, making it more widely applicable. It can be formed through various processes and has greater advantages in forming complex-shaped components. The sheath can be prepared by 3D printing or welding.

[0033] S5: Place the alloy steel workpiece with completed surface treatment and composite intermediate layer preparation into a sleeve, fill it with titanium alloy powder, and then perform argon arc sealing welding; Specifically, the alloy steel workpiece with completed surface treatment and composite intermediate layer preparation is placed in a sleeve, and titanium alloy powder is slowly filled at a rate not exceeding 500g / s (exemplary, 500g / s, 450g / s, 400g / s, 350g / s, 300g / s, 250g / s, 200g / s, 150g / s, 100g / s, 50g / s). During the filling process, the outer wall of the sleeve is gently tapped 3 times every 5-10mm in height to avoid powder bridging or segregation, followed by argon arc sealing. The parameters for argon arc welding are as follows: current 50-80A (exemplary, 50A, 55A, 60A, 65A, 70A, 75A, 80A), voltage 9-10V (exemplary, 9V, 9.2V, 9.4V, 9.5V, 9.6V, 9.8V, 10V), welding speed 5-10mm / s (exemplary, 5mm / s, 6mm / s, 7mm / s, 8mm / s, 9mm / s, 10mm / s), argon flow rate 6-10L / min (exemplary, 6L / min, 6.5L / min, 7L / min, 7.5L / min, 8L / min, 8.5L / min, 9L / min, 9.5L / min, 10L / min), and at least two weld passes. After sealing, the casing should be leak-tested using helium mass spectrometry; the leak rate should be ≤2×10⁻⁶. - 7 Pa·m³ / s, ensuring the airtightness of the casing.

[0034] It should be noted that the rate at which titanium alloy powder is filled into the cladding should be ≤500g / s. A rate that is too high can lead to uneven powder accumulation within the cladding, causing bridging or segregation, affecting subsequent densification and interfacial bonding quality; a rate that is too low will reduce efficiency. During the filling process, the outer wall of the cladding should be lightly tapped three times every 5-10mm. Regular tapping helps the powder settle naturally and eliminates voids. Too large an interval will not effectively break up bridging, while too small an interval will be cumbersome and may damage the cladding. The argon arc welding current should be 50-80 A and the voltage 9-10 V. This parameter range ensures a stable weld pool, guaranteeing moderate weld penetration and good airtightness. Too low a current can easily result in incomplete fusion or porosity; too high a current may burn through the thin wall of the cladding or cause an excessively large heat-affected zone. A welding speed of 5-10mm / s ensures uniform weld formation while avoiding overheating deformation due to excessively slow speed or incomplete penetration due to excessively fast speed. An argon flow rate of 6-10 L / min ensures a sufficient protective atmosphere to prevent weld oxidation. Too low a flow rate results in insufficient protection, while too high a flow rate can cause turbulence and introduce air. The weld should be passed at least twice; multiple passes reduce residual stress in individual welds, lower the risk of cracking, and improve the sealing reliability of the enclosure. Helium mass spectrometry leak detection rate ≤2×10⁻⁶. -7 Pa·m³ / s ensures that the cladding will not leak under subsequent hot isostatic pressure high-pressure conditions. If the leakage rate is higher than this value, gas may enter the cladding, leading to oxidation of titanium alloy powder or contamination of the welding interface.

[0035] S6: Place the package into a heat preservation furnace for vacuum degassing; Specifically, the degassing temperature is 100-300℃ (exemplary values: 120℃, 140℃, 150℃, 160℃, 180℃, 200℃, 220℃, 240℃, 250℃, 260℃, 280℃, 300℃), and the vacuum degree is less than 1×10⁻⁶. - Degassing should be stopped after 2 Pa. Degassing temperatures within the range of 100-300℃ can effectively remove adsorbed gases (such as H2O, O2, N2) and residual moisture from the surface of titanium alloy powder, preventing porosity defects during subsequent high-temperature hot isostatic pressing stages. To ensure the sintering activity of the powder, the degassing temperature should not be too high, otherwise it may lead to pre-oxidation of the powder surface or reduced activity, affecting the densification effect; if the temperature is too low, the degassing efficiency will be insufficient, and residual gases will still cause interfacial porosity or oxidation contamination. Vacuum levels below 1×10⁻⁶ Pa are acceptable. - A vacuum level of 2 Pa ensures extremely low residual gas pressure within the casing, allowing for complete desorption and extraction of the adsorbed gas. If the vacuum is too high (i.e., higher absolute pressure), degassing will be incomplete, and the remaining gas may not fully compress and dissolve under subsequent hot isostatic pressure (HIP) conditions, or may form high-pressure pores, damaging the density of the titanium alloy layer and the performance of the welded joint. Achieving 1×10⁻⁶ Pa is recommended. - Stopping degassing after 2 Pa ensures effective degassing while avoiding unnecessary evacuation time.

[0036] S7: Ultrasonic testing is used to inspect the casing to ensure that there are no defects such as pores in the casing; S8: The three-stage hot isostatic pressing process is used for the integrated forming and welding of titanium and steel dissimilar metals. Specifically, step S8 includes: S81: Place the package in a hot isostatic pressing furnace, slowly introduce nitrogen or argon gas to increase the pressure to the first specified pressure, heat to the first specified temperature, and hold at the temperature; Specifically, nitrogen or argon gas is slowly introduced, and the temperature is increased to a first specified temperature of 550-750℃ (exemplary, 550℃, 560℃, 580℃, 600℃, 620℃, 640℃, 650℃, 660℃) at a rate of ≤10℃ / min (exemplary, 10℃ / min, 9℃ / min, 8℃ / min, 7℃ / min, 6℃ / min, 5℃ / min, 4℃ / min, 3℃ / min, 2℃ / min, 1℃ / min) at a rate of ≤10℃ / min (exemplary, 10℃ / min, 9℃ / min, 8℃ / min, 7℃ / min, 6℃ / min, 5℃ / min, 4℃ / min, 3℃ / min, 2℃ / min, 1℃ / min) The temperature is set at 680℃, 700℃, 720℃, 740℃, and 750℃, with a first specified pressure of 100-150MPa (exemplary values: 100MPa, 110MPa, 115MPa, 120MPa, 125MPa, 130MPa, 135MPa, 140MPa, 145MPa, and 150MPa), and held for 2-6 hours (exemplary values: 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, and 6 hours). During this stage, the interface properties between the intermediate layer and the steel are optimized to improve the welding strength between the composite intermediate layer and the alloy steel; the density of the barrier layer V is improved to prevent violent reactions between localized areas of the titanium alloy powder and the alloy steel during the high-temperature stage; the titanium alloy powder is pre-sintered to shorten the sintering time in the high-temperature stage; and preliminary densification of the titanium alloy powder and pre-diffusion bonding between the composite intermediate layer and titanium and iron are achieved.

[0037] It should be noted that a heating rate ≤10℃ / min can prevent uneven heating of the powder inside the cladding or excessive thermal stress leading to deformation due to excessive heating. The first specified temperature is 550-750℃, below the β-phase transformation point of titanium alloy, which allows for pre-sintering while preventing excessive diffusion of the interlayer. If the temperature is too low, the pre-sintering effect will be insufficient; if it is too high, brittle phases may be generated prematurely. The first specified pressure is 100-150MPa, which provides appropriate pressure to promote the interfacial bonding between the interlayer and the steel matrix, but is lower than the second specified pressure to avoid early excessive densification affecting subsequent diffusion. Holding time of 2-6 hours ensures sufficient and uniform interfacial reaction between the interlayer and the steel; too short a time will result in insufficient optimization, while too long a time will reduce efficiency.

[0038] S82: Slowly heat to the second specified temperature, pressurize to the second specified pressure, and maintain the temperature; Specifically, the heating rate does not exceed 10℃ / min (exemplary, 10℃ / min, 9℃ / min, 8℃ / min, 7℃ / min, 6℃ / min, 5℃ / min, 4℃ / min, 3℃ / min, 2℃ / min, 1℃ / min), the second specified temperature is 940-1100℃ (exemplary, 940℃, 950℃, 960℃, 980℃, 1000℃, 1020℃, 1040℃, 1050℃, 1060℃, 1080℃, 1100℃), and the second specified pressure is 180-260MPa (exemplary, 180MPa, 185 ... The pressures are set at 190MPa, 195MPa, 200MPa, 205MPa, 210MPa, 215MPa, 220MPa, 225MPa, 230MPa, 235MPa, 240MPa, 245MPa, 250MPa, 255MPa, and 260MPa, and held at these temperatures for 2-6 hours (exemplary times: 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, and 6 hours). This stage completes the full densification sintering of the titanium alloy powder (relative density ≥ 99.5%) and the full diffusion bonding of the titanium / steel interface.

[0039] Controlling the heating rate to no more than 10℃ / min prevents microcracks from forming at the interface between the titanium alloy powder and the intermediate layer due to differences in thermal expansion at high temperatures, while also ensuring temperature uniformity. The second specified temperature of 940-1100℃ is higher than the β-phase transformation point of the titanium alloy (approximately 995℃), promoting plastic flow and full densification of the powder, while avoiding excessive growth of brittle phases due to excessively high temperatures (>1100℃). The second specified pressure is 180-260MPa; high pressure promotes atomic diffusion and pore closure, ensuring sufficient densification of the titanium alloy powder. Holding at this temperature for 2-6 hours ensures complete sintering of the titanium alloy powder and sufficient interfacial diffusion; too short a time results in insufficient density, while too long a time leads to grain coarsening.

[0040] S83: Slowly cool down to the third specified temperature, reduce pressure to the third specified pressure, and maintain the temperature; Specifically, the cooling rate shall not exceed 10℃ / min (exemplary, 10℃ / min, 9℃ / min, 8℃ / min, 7℃ / min, 6℃ / min, 5℃ / min, 4℃ / min, 3℃ / min, 2℃ / min, 1℃ / min), the third specified temperature shall be 600-850℃ (exemplary, 600℃, 620℃, 640℃, 650℃, 660℃, 680℃, 700℃, 720℃, 740℃, 750℃, 760℃, 780℃, 800℃, 820℃, 840℃, 850℃), and the third specified pressure shall be 150-200MPa (exemplary, 150MPa, 155MPa, 160MPa, 165MPa, 170MPa, 175MPa, 180MPa, 185MPa, 190MPa, 195MPa, 200MPa). (MPa), and hold at that temperature for 1-5 hours (exemplary times: 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours). During this stage, in-situ stress-relief annealing is performed during cooling to eliminate residual welding stress, reduce internal stress in the titanium alloy, and avoid a separate heat treatment process. Simultaneously, pressure control prevents uneven expansion and localized deformation.

[0041] The cooling rate should be controlled to ≤10℃ / min to avoid excessive thermal stress caused by the difference in thermal expansion coefficients between titanium and steel, thus preventing interface cracking. The third specified temperature is 600-850℃. Within this temperature range, atoms still possess a certain diffusion capacity, effectively releasing stress while avoiding sensitive areas for the precipitation of harmful phases (such as TiFe and TiNi3). Annealing effects are weakened below 600℃. The third specified pressure is 150-200MPa. Maintaining a certain pressure can suppress uneven shrinkage of the workpiece, preventing local warping or deformation, while also promoting stress release. Holding at this temperature for 1-5 hours ensures sufficient elimination of residual stress; too short a time results in incomplete stress relief, while too long a time affects production efficiency.

[0042] S84: Slowly release the gas. After the gas is completely released, remove the sheath and perform visual inspection and ultrasonic testing on the sheath. Specifically, the deflation rate should not be too fast to avoid deformation or cracking of the cladding. Visual inspection includes observing whether there are obvious abnormalities such as deformation, bulging, and cracking of the cladding. If the deformation amount exceeds 2 mm or visible cracks or bulges appear, it is determined that the appearance is abnormal. Ultrasonic flaw detection is used to detect whether there are internal defects or local failures in the cladding. During ultrasonic flaw detection inspection, if there is no single discontinuity defect signal exceeding the equivalent of a Φ2 mm flat-bottomed hole and no multiple discontinuity defect signals exceeding the equivalent of a Φ1.2 mm flat-bottomed hole, the ultrasonic flaw detection is qualified; otherwise, the ultrasonic flaw detection is abnormal. If the appearance of the cladding is intact and ultrasonic flaw detection does not find local failure, it is determined that the cladding has not failed during hot isostatic pressing, and the next step can be entered; if it is found that the cladding has abnormalities or failures, for visible cracks, repairs can be made (such as repair welding), and if it passes the ultrasonic re-inspection after repair, it can be used continuously; for severe deformation, bulging or internal defects that cannot be repaired, it is determined that the products of this batch are unqualified, and subsequent processing is stopped, and the hot isostatic pressing process parameters (such as heating rate, pressure stability, holding time, etc.) are traced to find the cause.

[0043] S9: Remove the cladding on the surfaces of the titanium alloy and the alloy steel by machining to obtain a titanium-steel dissimilar metal composite component with the target shape.

[0044] The present invention uses a sputtering process to deposit a Ni-V alloy intermediate layer (V content ≤ 20%, thickness 800 - 1800 nm) on the surface of the alloy steel. The good wettability of nickel is used to firmly bond with the substrate, and at the same time, the diffusion barrier effect of vanadium during hot isostatic pressing (forming a V-Ti compound layer) is utilized, and diffusion bonding is carried out under a high pressure of 180 - 260 MPa at a temperature below the liquidus of the Ni-V alloy (940 - 1100 °C in the second stage of hot isostatic pressing). This "solid-phase welding" mechanism effectively inhibits the large-scale interdiffusion of Fe and Ti and avoids the formation of large-size brittle phases such as TiFe and TiFe2, thereby improving the interface strength.

[0045] The present invention adopts a three-stage hot isostatic pressing process of "low-temperature pre-bonding - high-temperature high-pressure densification - cooling in-situ stress relief" and a powder-solid co-packing method. Specifically: in the first stage (550 - 750 °C, 100 - 150 MPa), the titanium alloy powder is pre-sintered, and at the same time, the interfacial bonding between the Ni-V intermediate layer and the alloy steel is optimized; in the second stage (940 - 1100 °C, 180 - 260 MPa), the titanium alloy powder undergoes isotropic uniform shrinkage to achieve full densification sintering (relative density ≥ 99.5%), and sufficient diffusion bonding of the titanium / steel interface is completed; in the third stage (600 - 850 °C,

[0046] This invention utilizes an integrated process of "powder-solid co-packing + multi-stage hot isostatic pressing" to simultaneously complete the densification of titanium alloy powder, diffusion welding of titanium / steel dissimilar metals, and in-situ stress relief of residual welding (third stage: stress relief by holding at 600-850℃) within the same hot isostatic pressing cycle. Compared to existing technologies, this invention eliminates numerous intermediate steps involved in titanium alloy casting, such as mold preparation, melting, pouring, riser cutting, casting surface treatment, non-destructive testing, heat treatment, and pre-welding surface activation treatment of titanium alloy castings. This significantly shortens the process flow and reduces manufacturing costs.

[0047] The mechanical properties of the titanium-steel dissimilar metal composite components prepared by this invention are superior to those of cast titanium alloys of the same composition. When TC4 titanium alloy powder is used, the tensile strength of the titanium-steel dissimilar metal composite components prepared by this invention is ≥850 MPa (e.g., 890-920 MPa), the yield strength is ≥780 MPa (e.g., 820-830 MPa), and the elongation is ≥10% (e.g., 17-20%), which is significantly better than that of cast TC4 titanium alloys. When TA15 titanium alloy powder is used, the tensile strength of the titanium-steel dissimilar metal composite components prepared by this invention is ≥600 MPa (e.g., 660 MPa), the yield strength is ≥500 MPa (e.g., 520 MPa), and the elongation is ≥20% (e.g., 29%). The titanium / steel interface strength of the titanium-steel dissimilar metal composite components prepared by this invention is ≥300 MPa (e.g., 320-480 MPa), which is far higher than that of existing brazing techniques (≤250 MPa).

[0048] Example 1 This embodiment provides a welding and forming method for titanium-steel dissimilar metal composite components, wherein the alloy steel is 304 stainless steel, and a titanium alloy and stainless steel composite pipe is to be prepared. Figure 1 is a schematic diagram of the planar design of the titanium alloy and stainless steel composite pipe of this embodiment.

[0049] Includes the following steps: S1: Surface treatment of alloy steel workpieces; Specifically, the surface treatment of 304 stainless steel workpieces includes mechanical grinding, pickling, ultrasonic cleaning, and vacuum drying. The specific procedures are as follows: after mechanical grinding, an 8% (w / w) dilute hydrochloric acid solution is used to remove the surface oxide film; after pickling, anhydrous ethanol is used for ultrasonic cleaning to remove residual acid from the alloy steel surface; the ultrasonic cleaning parameters are: frequency 40kHz, time 15min; subsequently, the alloy steel surface is dried in a vacuum oven to remove moisture, with a drying temperature of 160℃, a vacuum degree ≤100Pa, and a drying time of 2h; after completing the above surface treatment, the required surface finish of the stainless steel sheet is 1.6μm.

[0050] S2: A modified nickel-based composite intermediate layer is prepared on the surface of alloy steel; Specifically, the modified nickel-based composite interlayer is a Ni-7V alloy (i.e., the V content in the modified nickel-based composite interlayer alloy is 7%), and the alloy steel surface is coated using a sputtering process. The thickness of the interlayer is 1000 nm, and the vacuum degree during the sputtering process is 0.5 × 10⁻⁶. -4 Pa, power 400W, deposition rate 150 nm / min.

[0051] S3: Uses commercially available electrode-induction gas atomization TC4 powder with a purity ≥99%, an oxygen content of 1200ppm, and a particle size range of 15-105μm; S4: Based on the shape of the target titanium alloy, design the shape of the 316 stainless steel cladding, and prepare a tubular cladding with a shape similar to that of the target titanium alloy by welding. S5: Place the alloy steel workpiece with completed surface treatment and composite intermediate layer preparation into a sleeve, fill it with TC4 titanium alloy powder, and then perform argon arc sealing welding; Specifically, the alloy steel part, after surface treatment and composite intermediate layer preparation, is placed in a casing, and titanium alloy powder is slowly filled at a rate of 400 g / s. During the filling process, the outer wall of the casing is gently tapped three times every 8 mm in height to avoid powder bridging or segregation. Then, argon arc welding is performed. The welding parameters are: current 60A, voltage 10V, welding speed 8mm / s, argon flow rate 8L / min, and at least two weld passes. After sealing, the casing is subjected to helium mass spectrometry leak testing; the leak rate is ≤2×10⁻⁶. -7 Pa·m³ / s ensures the airtightness of the enclosure.

[0052] S6: Place the package into a heat preservation furnace for vacuum degassing; Specifically, the degassing temperature is 200℃, and the vacuum degree is less than 1×10⁻⁶. - Degassing was stopped after 2 Pa.

[0053] S7: Ultrasonic testing is used to inspect the casing to ensure that there are no defects such as pores in the casing; S8: The three-stage hot isostatic pressing process is used for the integrated forming and welding of titanium and steel dissimilar metals. Specifically, step S8 includes: S81: Place the package in a hot isostatic pressing furnace, slowly introduce argon gas, heat to the first specified temperature of 600℃ at a rate of 8℃ / min, and the first specified pressure of 120MPa, and hold for 4 hours; S82: Heat to the second specified temperature of 1000℃ at a rate of 5℃ / min, maintain the temperature for 4 hours at the second specified pressure of 195MPa; S83: Cool down to the third specified temperature of 800℃ at a rate of 5℃ / min, maintain the temperature for 2 hours at the third specified pressure of 170MPa; S84: Slowly release the gas. After the gas is completely released, remove the sheath and perform visual inspection and ultrasonic testing on the sheath to confirm that the sheath does not have obvious deformation, bulge, cracks, internal defects or local failures.

[0054] S9: Remove the cladding on the surface of titanium alloy and alloy steel by machining to obtain a titanium-steel dissimilar metal composite component of the target shape.

[0055] In this embodiment, a titanium alloy and stainless steel composite pipe is prepared, wherein the thickness of the titanium alloy is 25 mm, the thickness of the stainless steel is 25 mm, and the interfacial strength between the titanium alloy and stainless steel is 340 MPa. Figure 2 This is a microstructure diagram of the titanium alloy and stainless steel composite pipe in this embodiment. As can be seen from the diagram, the interface between 304 stainless steel and TC4 titanium alloy is completely welded without any microcracks.

[0056] The titanium alloy and stainless steel composite pipe obtained in this embodiment has excellent mechanical properties, with a tensile strength of 900 MPa, a yield strength of 830 MPa, and an elongation of 19%. Its comprehensive mechanical properties are better than those of the cast state (the tensile strength of the cast-4TC4 is 835 MPa, the yield strength is 765 MPa, and the elongation is 5%), as shown in Table 1.

[0057] Example 2 This embodiment provides a welding and forming method for titanium-steel dissimilar metal composite components, wherein the alloy steel is 40CrMo mold steel. The steps are similar to those in Embodiment 1, except that: S1: Surface treatment of alloy steel workpieces Specifically, the 40CrMo mold steel workpiece undergoes surface treatment, including mechanical grinding, pickling, ultrasonic cleaning, and vacuum drying. The specific procedures are as follows: after mechanical grinding, a 5% (w / w) dilute hydrochloric acid solution is used to remove the surface oxide film; after pickling, anhydrous ethanol is used for ultrasonic cleaning to remove residual acid from the alloy steel surface. The ultrasonic cleaning parameters are: frequency 35kHz, time 15min; subsequently, the alloy steel is dried in a vacuum oven to remove surface moisture at a temperature of 160℃, a vacuum degree ≤100Pa, and a drying time of 2h. After completing the above surface treatment, the required surface finish of the steel is 1.6μm.

[0058] S2: A modified nickel-based composite intermediate layer is prepared on the surface of alloy steel; the intermediate layer is a Ni-7V alloy, and the coating is applied to the alloy steel surface using a sputtering process. The thickness of the intermediate layer is controlled at 900 nm, and the vacuum degree during sputtering is 0.5 × 10⁻⁶. -4 Pa, power 400W, deposition rate 180 nm / min.

[0059] S81: Place the package in a hot isostatic pressing furnace, slowly introduce nitrogen or argon gas, heat to the first specified temperature of 700℃ and the first specified pressure of 150MPa at a rate of 8℃ / min, and hold for 2 hours. S82: Heat to the second specified temperature of 1050℃ at a rate of 5℃ / min and the second specified pressure of 220MPa, and hold for 3.5h; S83: Cool down to the third specified temperature of 780℃ at a rate of 5℃ / min, maintain the temperature at the third specified pressure of 175MPa for 2.5h.

[0060] The remaining steps and process parameters are the same as in Example 1.

[0061] In this embodiment, a composite pipe of titanium alloy and mold steel is prepared, wherein the thickness of titanium alloy is 25 mm, the thickness of 40CrMo mold steel is 25 mm, and the interface strength between titanium alloy and stainless steel is 400 MPa. Figure 3 The image shows the microstructure of the titanium alloy and mold steel composite pipe in this embodiment. As can be seen from the image, the interface between the 40CrMo mold steel and the TC4 titanium alloy is completely welded without any microcracks.

[0062] The titanium alloy obtained in this embodiment has excellent mechanical properties, with a tensile strength of 890 MPa, a yield strength of 820 MPa, and an elongation of 20%. Its comprehensive mechanical properties are better than those of the cast state, as shown in Table 1.

[0063] Example 3 This embodiment provides a welding and forming method for titanium-steel dissimilar metal composite components, wherein the alloy steel is 40CrMo mold steel. The welding and forming method for titanium-steel dissimilar metal composite components is similar to that in Embodiment 2, except that: S2: A modified nickel-based composite intermediate layer is prepared on the surface of alloy steel; the intermediate layer is a Ni-10V alloy, and the coating is applied to the alloy steel surface using a sputtering process. The thickness of the intermediate layer is controlled at 1500 nm, and the vacuum degree during sputtering is 0.5 × 10⁻⁶. - 4 Pa, power 400W, deposition rate 180 nm / min.

[0064] S3: Uses commercially available electrode-induction gas atomization TC4 powder, with an oxygen content of 1300ppm and a particle size range of 53~150μm; S81: Place the package in a hot isostatic pressing furnace, slowly introduce nitrogen or argon gas, raise the temperature to the first specified temperature of 650℃ and the first specified pressure of 145MPa at a rate of 6℃ / min, and hold for 2 hours. S82: Heat to the second specified temperature of 1020℃ and the second specified pressure of 240MPa at a rate of 5℃ / min, and hold for 3 hours; S83: Cool down to the third specified temperature of 750℃ at a rate of 5℃ / min, maintain the temperature for 4 hours at the third specified pressure of 165MPa.

[0065] This embodiment yields a titanium alloy and mold steel composite pipe, wherein the titanium alloy has a thickness of 20 mm, the 40CrMo mold steel has a thickness of 30 mm, and the interface strength between the titanium alloy and stainless steel is 380 MPa. The interface between the 40CrMo mold steel and the TC4 titanium alloy is completely welded without any microcracks.

[0066] The titanium alloy obtained in this embodiment has excellent mechanical properties, with a tensile strength of 920 MPa, a yield strength of 820 MPa, and an elongation of 17%. Its comprehensive mechanical properties are better than those of the cast state, as shown in Table 1.

[0067] Example 4 This embodiment prepares a titanium alloy and mold steel composite plate. The welding and forming method of the titanium-steel dissimilar metal composite component is similar to that in Example 1. The difference is that the nickel-based composite intermediate layer used in this embodiment is Ni-8V (i.e., the V content is 8%), and the remaining steps and process parameters are the same as in Example 1.

[0068] This embodiment yields a titanium alloy and mold steel composite plate, wherein the titanium alloy has a thickness of 50 mm, the 40CrMo mold steel has a thickness of 60 mm, and the interface strength between the titanium alloy and stainless steel is 320 MPa. Ultrasonic testing of the 40CrMo mold steel and TC4 titanium alloy confirmed that the interface is completely welded.

[0069] The titanium alloy obtained in this embodiment has excellent mechanical properties, with a tensile strength of 900 MPa, a yield strength of 830 MPa, and an elongation of 19%. Its comprehensive mechanical properties are better than those of the cast state, as shown in Table 1.

[0070] Example 5 This embodiment prepares a titanium alloy and mold steel composite plate. The welding and forming method of the titanium-steel dissimilar metal composite component is similar to that in Example 4, except that: S2: A modified nickel-based composite intermediate layer is prepared on the surface of alloy steel; the intermediate layer is a Ni-6V alloy, and the alloy steel surface is coated by sputtering. The thickness of the intermediate layer is controlled at 1600 nm, and the vacuum degree during sputtering is 0.5 × 10⁻⁶. -4 Pa, power 380W, deposition rate 180 nm / min.

[0071] S3: TA15 powder is atomized using a commercially available plasma rotating electrode. The oxygen content of the powder is 1000ppm and the particle size range is 25-105μm.

[0072] This embodiment yields a titanium alloy and mold steel composite plate, wherein the titanium alloy is 30 mm thick, the 40CrMo mold steel is 10 mm thick, and the interface strength between the titanium alloy and stainless steel is 480 MPa. Ultrasonic testing results of the 40CrMo mold steel and TA5 titanium alloy confirm that their interface is completely welded.

[0073] The titanium alloy obtained in this embodiment has excellent mechanical properties, with a tensile strength of 660 MPa, a yield strength of 520 MPa, and an elongation of 29%. Its comprehensive mechanical properties are better than those of the cast state (the tensile strength of the cast-TA5 is 590 MPa, the yield strength is 490 MPa, and the elongation is 10%), as shown in Table 1.

[0074] Comparative Example 1 This comparative example prepares a titanium alloy and stainless steel composite pipe similar to that in Example 1. The welding and forming method for the titanium-steel dissimilar metal composite component is similar to that in Example 1, except that: S8: Place the package in a hot isostatic pressing furnace, introduce argon gas, and then heat it to the specified temperature of 1300℃ at a rate of 8℃ / min, with a pressure of 150MPa, and maintain the temperature and pressure for 4 hours.

[0075] This comparative example prepared a titanium alloy and stainless steel composite pipe, wherein the thickness of the titanium alloy is 25 mm, the thickness of the stainless steel is 25 mm, and the interfacial strength between the titanium alloy and stainless steel is 120 MPa. Figure 4 The image shows the microstructure of the titanium alloy and stainless steel composite pipe in this comparative example. As can be seen from the image, cracks initiate at the interface between 304 stainless steel and TC4 titanium alloy. Comparative Example 2 This comparative example prepares a titanium alloy and stainless steel composite pipe similar to that in Example 1. The welding and forming method for the titanium-steel dissimilar metal composite component is similar to that in Example 1, except that: S81: Place the package in a hot isostatic pressing furnace, slowly introduce argon gas, heat to the first specified temperature of 800℃ at a rate of 8℃ / min, and the first specified pressure of 80MPa, and hold for 3 hours; S82: Heat to the second specified temperature of 1200℃ at a rate of 5℃ / min, maintain the temperature at the second specified pressure of 140MPa for 3.5h; S83: Cool down to the third specified temperature of 900℃ at a rate of 5℃ / min, maintain the temperature at the third specified pressure of 120MPa for 1 hour; The remaining steps and process parameters are the same as in Example 1.

[0076] This comparative example prepared a titanium alloy and stainless steel composite pipe with a titanium alloy wall thickness of 25 mm and a stainless steel wall thickness of 25 mm. The interfacial strength between the titanium alloy and stainless steel was 180 MPa. Cracks initiated at the interface between 304 stainless steel and TC4 titanium alloy.

[0077] Comparative Example 3 This comparative example prepares a titanium alloy and stainless steel composite pipe similar to that in Example 1. The welding and forming method of the titanium-steel dissimilar metal composite component is similar to that in Example 1, except that step S81 is not performed, and the temperature is directly raised to the second specified temperature.

[0078] The remaining steps and process parameters are the same as in Example 1.

[0079] This comparative example yielded a titanium alloy and stainless steel composite pipe with a titanium alloy wall thickness of 25 mm and a stainless steel wall thickness of 25 mm. The interface had virtually no strength and cracked during processing.

[0080] Comparative Example 4 This comparative example prepares a titanium alloy and mold steel composite plate similar to that in Example 5. The welding and forming method for the titanium-steel dissimilar metal composite component is similar to that in Example 5, except that: S2: A modified nickel-based composite intermediate layer is prepared on the surface of alloy steel; the intermediate layer is a Ni-6V alloy, and the coating is applied to the alloy steel surface using a sputtering process. The thickness of the intermediate layer is controlled at 600 nm, and the vacuum degree during sputtering is 0.5 × 10⁻⁶. -4 Pa, power 340W, deposition rate 100 nm / min.

[0081] S3: TA15 powder is atomized using a commercially available plasma rotating electrode. The oxygen content of the powder is 1600ppm and the particle size range is 0-15μm.

[0082] The remaining steps and process parameters are the same as in Example 5.

[0083] This comparative example prepared a titanium alloy and mold steel composite plate, wherein the titanium alloy has a thickness of 30 mm, with relatively severe original powder boundaries in some areas, the 40CrMo mold steel has a thickness of 10 mm, and the interface strength between the titanium alloy and the mold steel is 80 MPa.

[0084] The titanium alloy has a tensile strength of 670 MPa, a yield strength of 480 MPa, and an elongation of 9%, which does not meet the requirements for titanium alloy castings and is relatively brittle.

[0085] Comparative Example 5 This comparative example prepares a titanium alloy and stainless steel composite plate similar to that in Example 5. The welding and forming method for the titanium-steel dissimilar metal composite component is similar to that in Example 5, except that: S2: A modified nickel-based composite intermediate layer is prepared on the surface of alloy steel; the intermediate layer is a pure nickel layer.

[0086] The remaining steps and process parameters are the same as in Example 5.

[0087] This comparative example yielded a titanium alloy and 304 stainless steel composite plate, with the titanium alloy having a thickness of 30 mm and the stainless steel having a thickness of 10 mm. The titanium alloy exhibited excellent mechanical properties, which were essentially similar to those of Example 5, and its overall mechanical properties were superior to those of the cast state. However, the interfacial strength between the titanium alloy and stainless steel obtained in this comparative example was extremely low, at 10 MPa.

[0088] Table 1 shows the mechanical properties of the titanium-steel dissimilar metal composite components of the examples and comparative examples, and Table 2 shows the thickness and interface strength of the titanium-steel dissimilar metal composite components of the examples and comparative examples.

[0089] Table 1. Mechanical properties of titanium-steel dissimilar metal composite components in the examples and comparative examples.

[0090] Table 2. Thickness and interfacial strength of titanium-steel dissimilar metal composite components in the examples and comparative examples.

[0091] The as-cast TC4 has a tensile strength of 835 MPa, a yield strength of 765 MPa, and an elongation of only 5%. In contrast, Examples 1-4 (using TC4 titanium alloy powder) exhibit tensile strengths of 890-920 MPa, yield strengths of 820-830 MPa, and elongations of 17%-20%. Example 5 (using TA15 titanium alloy powder) shows superior mechanical properties compared to as-cast TA15. This demonstrates that the welding and forming method for titanium-steel dissimilar metals of the present invention achieves finer grains and fewer casting defects, thereby realizing an excellent strength-ductility match between titanium and steel dissimilar metals. The tensile strength of Comparative Example 4 was 670 MPa, the yield strength was 480 MPa, and the elongation was only 9%, which was lower than that of the as-cast TA5 (590 / 490 / 10%). The elongation was also much lower than that of Example 5 (29%). This is because the oxygen content in Comparative Example 4 exceeded the standard (1600 ppm > the upper limit of 1500 ppm in this invention), resulting in an excessively thick oxide film on the powder surface, which hindered sintering and densification. The particle size was too fine (0-15 μm), which made it easy to agglomerate and produce low tap density, resulting in original powder boundary defects.

[0092] The interfacial strength of the titanium alloy and steel in Examples 1-5 is significantly higher than that of existing brazing techniques (≤250MPa). Comparative Example 1, using a single-stage 1300℃ hot isostatic pressing (HIP), does not meet the requirements of the three-stage HIP of this invention, resulting in an interfacial strength of only 120MPa and the appearance of cracks. Comparative Example 2, although using a three-stage HIP, has some parameters that do not meet the requirements of this invention, resulting in an interfacial strength lower than that of Example 1. Comparative Example 3, using a two-stage HIP, does not meet the requirements of this invention, resulting in processing cracks and virtually no interfacial strength. Compared to Example 5, Comparative Example 4 has an excessively thin interlayer, excessive oxygen content, and excessively fine particle size, failing to meet the requirements of this invention, and its interfacial strength is lower than that of Example 5. Comparative Example 5 uses a pure nickel interlayer, and compared to Example 5, its interfacial strength is reduced, indicating that the addition of V significantly improves the interfacial strength in this invention, and pure nickel cannot effectively prevent Fe-Ti interdiffusion.

[0093] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of welding forming a titanium-steel dissimilar metal composite member, characterized by, Includes the following steps: S1: Surface treatment of alloy steel workpieces; S2: A modified nickel-based composite intermediate layer is prepared on the surface of alloy steel; S3: Prepare titanium alloy powder for later use; S4: Design the shape of the sheath according to the shape of the target titanium alloy, and prepare the sheath; S5: Place the alloy steel workpiece with completed surface treatment and composite intermediate layer preparation into a sleeve, fill it with titanium alloy powder, and then perform argon arc sealing welding; S6: Place the package into a heat preservation furnace for vacuum degassing; S7: Ultrasonic testing is used to inspect the casing to ensure that there are no porosity defects in the casing; S8: The three-stage hot isostatic pressing process is used for the integrated forming and welding of titanium and steel dissimilar metals. S9: Remove the cladding on the surface of titanium alloy and alloy steel by machining to obtain a titanium-steel dissimilar metal composite component of the target shape.

2. The method of welding forming of claim 1, wherein, In step S2, the modified nickel-based composite intermediate layer is made of Ni-V alloy, wherein the mass content of V is ≤20%, and the thickness of the modified nickel-based composite intermediate layer is 800-1800 nm.

3. The method of claim 1, wherein, In step S3, the titanium alloy powder is titanium alloy atomized powder with an oxygen content ≤1500ppm and a particle size range of 15-150 μm.

4. The method of claim 1, wherein, In step S5, the rate at which the titanium alloy powder is filled is ≤500g / s; The parameters for the argon arc sealing welding are: current 50-80A, voltage 9-10V, welding speed 5-10mm / s, argon flow rate 6-10L / min, and no less than 2 weld passes.

5. The method of claim 1, wherein, In step S6, the vacuum degassing temperature is 100-300°C, and the vacuum degree is lower than 1x10 - Pa, and then the degassing is stopped.

6. The method of claim 1, wherein, Step S8 includes: S81: Place the package in a hot isostatic pressing furnace, slowly introduce nitrogen or argon gas to the first specified pressure, heat to the first specified temperature, and hold at the temperature; S82: Slowly heat to the second specified temperature, pressurize to the second specified pressure, and maintain the temperature; S83: Slowly cool down to the third specified temperature, reduce pressure to the third specified pressure, and maintain the temperature; S84: Slowly release the gas. After the gas is completely released, remove the sheath and perform visual inspection and ultrasonic testing on the sheath. The second specified temperature is higher than the first specified temperature, the second specified pressure is higher than the first specified pressure, and the first specified pressure is less than or equal to the third specified pressure.

7. The method of welding forming of claim 6, wherein, In step S81, the heating rate is ≤10℃ / min, the first specified temperature is 550-750℃, the first specified pressure is 100-150MPa, and the holding time is 2-6h.

8. The welding forming method according to claim 7, characterized in that, In step S82, the heating rate is ≤10℃ / min, the second specified temperature is 940-1100℃, the second specified pressure is 180-260MPa, and the holding time is 2-6h.

9. The welding forming method according to claim 8, characterized in that, In step S83, the cooling rate is ≤10℃ / min, the third specified temperature is 600-850℃, the third specified pressure is 150-200MPa, and the heat preservation time is 1-5h.

10. A titanium-steel dissimilar metal composite component, characterized in that, It is prepared by the welding forming method according to any one of claims 1-9.

Images