Titanium / steel dissimilar metal brazing method and application

Abstract

The application provides a titanium / steel heterogeneous metal brazing method and application, and relates to the technical field of brazing. Specifically, the method comprises the following steps: laying metal powder on the surface of a steel base to be welded, combining the metal powder with the steel base by laser cladding to obtain the steel base with a surface configuration; and then assembling the steel base with a titanium base to be welded and a filler metal, and then performing vacuum brazing. The method can effectively improve the formation and distribution of brittle intermetallic compounds in the joint by constructing the surface of the heterogeneous steel base, and can customize the preparation of a non-flat, non-continuous and multi-phase interface structure, so that the strength and toughness of the titanium / steel brazing joint are improved, high-quality titanium / steel brazing metallurgical connection is realized, and the method has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of brazing, in particular to a brazing method for titanium / steel dissimilar metals and application. BACKGROUND

[0002] Titanium alloy has the advantages of high strength, good corrosion resistance, good low-temperature performance, low thermal conductivity and elasticity. Steel is one of the most cost-effective and widely used metals. Titanium / steel composite components are typical representatives of dissimilar metal composite components, which fully combine the performance advantages of the two materials, can overcome the problems of difficult processing and high cost of titanium alloy and large weight of steel in actual production, realize lightweight structure, and have good mechanical properties and corrosion resistance. It is an indispensable key component of high-end equipment such as aerospace power system guide pipe structure, energy chemical reactor, nuclear reactor, etc.

[0003] However, the linear thermal expansion coefficient of titanium and steel is very different, and a large residual stress is often generated in the joint between the two, which seriously damages the performance of the joint. Compared with other welding methods, brazing can heat the entire welded structure, effectively relieving residual stress from a physical level. However, the chemical incompatibility of Fe and Ti at room temperature is more significant, and the solid solubility between them is less than 0.1% at room temperature. Brittle intermetallic compounds such as FeTi and Fe2Ti are easily generated in the titanium / steel brazed joint. There is a mismatched lattice structure and mismatched brittle performance between FeTi and Fe2Ti. The continuous interface of flat mismatched FeTi / Fe2Ti and the brittle reaction layer thus form a weak area for crack initiation and propagation in the titanium / steel brazed joint, which directly leads to brittle fracture of the joint and seriously restricts the improvement of the strength and toughness of the joint.

[0004] Therefore, the present application is proposed. SUMMARY

[0005] The first object of the present application is to provide a brazing method for titanium / steel dissimilar metals, which solves the technical problem that the two different welded parts of titanium and steel are prone to cause low strength and toughness and poor joint performance after welding, and provides a titanium / steel dissimilar metal (alloy) vacuum brazed joint to avoid the formation of a continuous flat mismatched interface and a brittle intermetallic compound reaction layer. In order to achieve the above object of the present application, the following technical scheme is adopted:

[0006] A brazing method for titanium / steel dissimilar metals includes the following steps: laying a metal powder on the surface of a steel base to be welded, combining the metal powder with the steel base by laser micro-scale cladding to obtain the steel base with a surface configuration; and then assembling the steel base with a titanium base to be welded and a filler metal, and then performing vacuum brazing.

[0007] The present application adopts laser micro-scale cladding manufacturing technology; it is a kind of technology using femtosecond laser as heat source to heat and melt powder to realize cladding manufacturing, with the advantages of micro local heating, high energy density, size precision etc.The present application clads a certain geometric structure of metal powder on the surface of steel matrix by laser micro-scale cladding manufacturing technology, prepares heterogeneous structure steel matrix surface, and based on the metallurgical reaction between heterogeneous structure steel matrix surface and titanium-based filler metal, constructs non-flat, non-continuous multi-phase interface structure, so as to improve the strength and toughness of titanium / steel heterogeneous brazing joint.

[0008] Preferably, the surface configuration includes dot matrix and row matrix;

[0009] More preferably, the surface configuration can optionally include the following features: (a) the height of the surface configuration is 30-50 μm; (b) the dot spacing of the dot matrix is 35-75 μm; (c) the row spacing of the row matrix is 35-75 μm;

[0010] Further preferably, for feature (a), the height of the surface configuration includes but is not limited to 30 μm, 32 μm, 35 μm, 40 μm, 45 μm, 50 μm; (b) the dot spacing of the dot matrix includes but is not limited to 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm; (c) the row spacing of the row matrix includes but is not limited to 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm.

[0011] It should be noted that during actual operation, the laying of metal powder and the laser cladding usually need to be repeated several times until the preset surface configuration is obtained; that is, the thickness or morphology of the dot matrix or the row matrix cannot be achieved by one-time cladding, and those skilled in the art can adjust the number of specific operations and the process parameters of each implementation according to the above surface configuration parameter characteristics.

[0012] Preferably, the metal powder is nanoscale; the metal powder can be selected as independent nanoscale copper powder or nanoscale nickel powder, or a mixture of nanoscale copper powder and nanoscale nickel powder in any ratio;

[0013] More preferably, the purity of the metal powder is ≥99.9%, and further preferably, the metal powder with a purity of 99.99% is used;

[0014] More preferably, the particle size of the metal powder includes but is not limited to 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm.

[0015] Preferably, the laser micro-scale cladding is performed by a femtosecond laser processing device; in particular, the steel substrate is fixed on a 3D displacement platform, the displacement platform is adjusted to the focal length position of the femtosecond laser, the laid cladding metal powder is focused and cladded by the femtosecond laser processing platform, and the cladding metal powder is combined with the steel substrate.

[0016] The femtosecond laser processing platform comprises a femtosecond laser amplification system, a confocal microscopic system, a 3D displacement platform and a control system, wherein: the femtosecond laser amplification system comprises a half-wave plate, a polarization beam splitter prism and an electronic shutter, and provides a light source for the processing platform; the confocal microscopic system is composed of an electronic coupling device, a light-emitting diode and an objective lens, and is used for real-time observation of the processing platform; the femtosecond laser amplification system, the confocal microscopic system and the 3D displacement platform are connected with the control system, and the distance between the focusing elements in the laser lens and the laser single-pulse energy are adjusted by the control system to control the laser spot diameter and the cladding metal size, thereby completing the precise positioning cladding of the steel substrate.

[0017] More preferably, the femtosecond laser comprises the following characteristics: a central wavelength of 1040 nm, a power of 8 W, a pulse width of 200 fs, a repetition frequency of 50 MHz, and a spot diameter of 16 μm to 18 μm.

[0018] More preferably, the laser cladding is performed in an argon atmosphere; the gas pressure of the laser cladding is standard atmospheric pressure, and the oxygen content is ≤10 ppm.

[0019] Preferably, the surface configuration further comprises a pretreatment of the steel substrate before the brazing, and the pretreatment comprises polishing, washing and drying in sequence; more preferably, the steel substrate is polished flat with 600-mesh sandpaper, then ultrasonically cleaned in acetone for 15 min, and then dried.

[0020] Preferably, the brazing further comprises a second pretreatment of the titanium substrate and the steel substrate before the brazing, and the second pretreatment comprises polishing, polishing, washing and drying in sequence; more preferably, the surfaces to be welded of the two substrates are polished flat by 600-mesh water-resistant sandpaper, and then polished by diamond grinding liquid, and then ultrasonically cleaned in acetone for 15 min, and finally dried.

[0021] Preferably, the steel substrate comprises 316L stainless steel, 316 stainless steel or 304 stainless steel.

[0022] Preferably, the titanium substrate comprises TC4 titanium alloy (Ti6Al4V, wt.%) or TiAl alloy (Ti-48Al-2Cr-2Nb, at.%).

[0023] Preferably, the filler material comprises a titanium-based filler material, preferably, the titanium-based filler material comprises Ti 33.3 Zr 16.7 Cu 39 Ni 11 。

[0024] Preferably, the pressure of the vacuum brazing is ≤ 5 × 10 -3 Pa;

[0025] Preferably, the temperature control of the vacuum brazing comprises a first stage and a second stage, wherein the first stage is heated to 750-800℃ at a speed of 10℃ / min, and then kept for 3-10min, the second stage is heated to 930-990℃ at a speed of 3-8℃ / min, and then kept for 3-60min.

[0026] More preferably, after the keeping of the second stage, the welding piece is restored to room temperature with the furnace temperature.

[0027] Preferably, the assembling comprises: assembling the steel base, the filler material and the titanium base from bottom to top, wherein the configuration surface of the steel base is the welding surface.

[0028] More preferably, a pressing piece is arranged on the titanium base, and the welding interface is tightly contacted by applying downward pressure to the welding piece.

[0029] The second object of the present application is to provide a titanium / steel composite welding piece prepared by the brazing method of the titanium / steel heterogeneous metal.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] (1) The present application prepares copper-steel, nickel-steel and copper-steel-nickel three types of "steel base + cladding metal" periodic heterogeneous structure microsurfaces by laser microscale cladding surface configuration of the steel base, and generates Ti-Cu(Ni) and Fe-Cu(Ni) multi-element products based on the metallurgical reaction between the steel base configuration surface and the titanium-based filler material, thereby constructing a non-flat and non-continuous stable interface structure and improving the strength and toughness of the titanium / steel brazing joint, and realizing high-quality brazing metallurgical connection of titanium / steel.

[0032] (2) The present application uses femtosecond laser with short pulse, high energy density and high precision, and nanoscale metal powder, and can accurately control the structure size of the cladding metal by adjusting the parent material walking path, laser energy, spot diameter, powder thickness and other parameters. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the accompanying drawings needed to be used in the description of the specific embodiments or the prior art will be briefly introduced. Obviously, the accompanying drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0034] Figure 1 A schematic diagram of the femtosecond laser technician platform used in the embodiments of the present application;

[0035] Figure 2 A schematic diagram of the steel substrate after laser cladding in the embodiments of the present application; wherein, Figure 2 (a) corresponds to Example 1, Figure 2 (b) corresponds to Example 2;

[0036] Figure 3 A schematic diagram of vacuum brazing in Example 1 of the present application; wherein, Figure 3 (a) corresponds to the apparent state, Figure 3 (b) corresponds to the microscopic state;

[0037] Figure 4 The weld strength curve of Example 2 of the present application. DETAILED DESCRIPTION

[0038] The technical solutions of the present application will be described clearly and completely in the following description in combination with the accompanying drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort are within the scope of protection of the present application. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased on the market.

[0039] Example 1

[0040] The surface of the 316L steel substrate is polished flat with 600 grit sandpaper, ultrasonically cleaned in acetone for 15 minutes, and then dried. Copper powder with a purity of 99.99% and a particle size of 50 nm is laid on the surface of the 316L steel substrate, and the powder thickness is 50 μm. The laying method is as follows: a 50 μm adhesive tape is fixed at the edge of the steel substrate to determine the thickness of the metal powder attached to the steel substrate; then anhydrous alcohol is added dropwise into the metal powder, and the mixture is stirred thoroughly to form a uniform suspension, which is then transferred to the surface of the steel substrate, and the steel substrate is gently shaken to evenly distribute the suspension; then the steel substrate is placed on a horizontal surface and left to dry, at which time the metal powder has been attached to the steel substrate with a thickness slightly greater than a film. The part of the film that is higher than the film thickness is gently scraped off with a wafer, so that the powder left on the steel substrate has the same thickness as the film; finally, the film is removed, and a thin layer of the nano-powder with a thickness of 50 μm is obtained.

[0041] A femtosecond laser processing platform is used for laser cladding of the steel substrate, as shown in Figure 1 The steel substrate is fixed on a 3D displacement platform, the displacement platform is adjusted to the focal length position of the femtosecond laser, and the row-column protruding structure is introduced into the control system of the platform. The femtosecond laser amplification system, the confocal microscopic system, and the 3D displacement platform are connected to the control system, and the laid metal powder is focused and cladded in an argon atmosphere to form a metallurgical bond between the metal powder and the steel substrate, thereby preparing a "cladded metal + steel substrate" periodic heterogeneous structure surface. The argon atmosphere pressure is standard atmospheric pressure, the oxygen content is less than 10 ppm, the central wavelength of the femtosecond laser is 1040 nm, the power is 8 W, the pulse width is 200 fs, the repetition frequency is 50 MHz, and the spot radius is 16 μm to 18 μm. The copper metal powder is sequentially and repeatedly cladded until the metal powder is cladded on the surface of the steel substrate to form a row-column protruding structure, as shown in Figure 2 (a), wherein the cladded metal height reaches 35 μm, and the row-column spacing is 50 μm.

[0042] The cladded 316L steel substrate and the TC4 titanium substrate are assembled, the titanium base filler metal Ti 33.3 Zr 16.7 Cu 39 Ni 11 (at.%) is placed between the two metal substrates to form a "sandwich" structure of the welded piece, as shown in Figure 3 (a). A pressing block is placed on the surface of the titanium alloy substrate to press the welded surface. The assembled welded sample is placed in a vacuum brazing furnace, and the vacuum is drawn to 5 × 10 - 3After 30 Pa, the brazing starts, and the brazing temperature is: the first stage, the temperature is raised to 800℃ at the speed of 10℃ / min, and the temperature is kept for 5 min to make the temperature of the welding part uniform; the second stage, the temperature is raised to 960℃ at the speed of 5℃ / min and kept for 10 min; the third stage, the welding part is cooled to room temperature with the furnace.

[0043] The schematic diagram of the brazing seam structure after the brazing is completed is shown in Figure 3 (b), the Ti-Cu(Ni), Ti-Fe, Fe-Cu(Ni) multi-element products are generated on the steel matrix side, forming a non-flat and non-continuous multi-phase interface, improving the situation of brittle fracture along the flat interface of the joint, and thus improving the strength and toughness of the titanium / steel brazed joint.

[0044] Example 2

[0045] The surface of the 316L steel matrix is polished flat with 600 mesh sandpaper, ultrasonically cleaned in acetone for 15 min, and then dried. The metal copper powder with a purity of 99.99% and a powder particle size of 50 nm is laid on the surface of the 316L steel matrix, and the powder laying thickness is 50 μm. The laying method is the same as that of Example 1.

[0046] The steel matrix is laser cladded using the same femtosecond laser processing platform as in Example 1. The steel matrix is fixed on the 3D displacement platform, the displacement platform is adjusted to the focal length position of the femtosecond laser, the dot array distribution structure is introduced into the control system of the platform, and the femtosecond laser amplification system, the confocal microscopic system and the 3D displacement platform are connected with the control system. The laid metal powder is focused and cladded in an argon atmosphere to form a metallurgical bond between the metal powder and the steel matrix, and a periodic heterogeneous structure surface of “cladded metal + steel matrix” is prepared. The argon atmosphere pressure is standard atmospheric pressure, the oxygen content is less than 10 ppm, the central wavelength of the femtosecond laser is 1040 nm, the power is 8 W, the pulse width is 200 fs, the repetition frequency is 50 MHz, and the spot radius is 16 μm-18 μm. The copper metal powder is sequentially and repeatedly cladded until the metal powder is cladded on the surface of the steel matrix to form a dot array distribution structure, as shown in Figure 2 (b), wherein the cladded metal thickness reaches 35 μm, and the horizontal and vertical spacing of the dots is 50 μm.

[0047] The cladded 316L steel matrix and the TC4 are assembled, the titanium-based filler metal Ti 33.3 Zr 16.7 Cu 39 Ni 11 (at.%) is placed between the two metal matrices to form a “sandwich” structure of the welded part. The pressing block is placed on the titanium alloy matrix to press the welded surface. The assembled welded sample is placed in a vacuum brazing furnace, and the vacuum is extracted to 5×10 -3After 30 s, the brazing starts, and the brazing temperature is: first stage, the temperature is raised to 800℃ at the speed of 10℃ / min, and the brazing part is kept at this temperature for 5 min to make the temperature of the brazing part uniform; second stage, the temperature is raised to 960℃ at the speed of 5℃ / min and kept for 10 min; third stage, the brazing part is cooled to room temperature with the furnace.

[0048] The joint strength of the present example is tested, Figure 4 The real-time strength value and deformation of the joint during the test are given.

[0049] Example 3

[0050] The present example is basically the same as example 1, and the only difference is that the metal nickel powder is used as the cladding metal on the surface of the steel substrate.

[0051] Example 4

[0052] The present example is basically the same as example 2, and the only difference is that the metal nickel powder is used as the cladding metal on the surface of the steel substrate.

[0053] Comparative example

[0054] The 316L steel substrate and the titanium substrate are assembled, and the titanium-based filler metal Ti 33.3 Zr 16.7 Cu 39 Ni 11 (at.%) is placed between the two metal substrates to form a "sandwich" structure of the to-be-welded part and is vacuum brazed; the specific parameter conditions of the vacuum brazing are completely consistent with those of example 1.

[0055] The joint strength of each example and the comparative example is tested, as shown in Table 1 below.

[0056] Table 1

[0057] Joint strength / MPa Example 1 318 Example 2 324 Example 3 320 Example 4 312 Comparative Example 216

[0058] Although the present application has been illustrated and described with specific embodiments, it should be realized that the above examples are only used to illustrate the technical solutions of the present application, and are not limiting; those skilled in the art should understand that the technical solutions described in the above examples can be modified, or some or all of the technical features can be replaced with equivalents, without departing from the spirit and scope of the present application; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application; therefore, this means that all these replacements and modifications within the scope of the present application are included in the appended claims.

Claims

1. A brazing method of titanium / steel dissimilar metals, characterized by, It comprises the following steps: laying metal powder on the surface of a steel substrate to be welded, combining the metal powder with the steel substrate by laser cladding to obtain the steel substrate with a surface configuration; and then assembling the steel substrate with a titanium substrate to be welded and a filler metal and performing vacuum brazing. The surface configuration comprises a dot array and a row-column array. The height of the surface configuration is 30-50 μm. The dot spacing of the dot array is 35-75 μm. The row spacing of the row-column array is 35-75 μm. The metal powder is nanoscale; the metal powder comprises at least one of copper powder and nickel powder; the purity of the metal powder is ≥99.9%, and the particle size of the metal powder is 25-75 nm. The vacuum brazing pressure is < 5 x 10 -3 Pa; The temperature control of the vacuum brazing comprises a first stage and a second stage, wherein the first stage is heated to 750-800 ℃ at a speed of 10 ℃ / min, and then held for 3-10 min, the second stage is heated to 930-990 ℃ at a speed of 3-8 ℃ / min, and then held for 3-60 min; after the holding of the second stage ends, the welding piece is restored to room temperature with the furnace temperature.

2. The method of brazing titanium / steel dissimilar metals according to claim 1, characterized in that, The laser cladding is performed by a femtosecond laser processing device. The femtosecond laser comprises the following features: central wavelength 1040 nm, power 8 W, pulse width 200 fs, repetition frequency 50 MHz, and spot diameter 16-18 μm.

3. The method of brazing titanium / steel dissimilar metals according to claim 1, wherein The laser cladding is performed in an argon atmosphere.

4. The method of brazing titanium / steel dissimilar metals according to claim 1, wherein Before the surface configuration is performed, the steel substrate is also subjected to pretreatment. The pretreatment comprises polishing, washing and drying in sequence; the washing is performed by acetone.

5. The method of brazing titanium / steel dissimilar metals of claim 1, wherein, Before the vacuum brazing is performed, the titanium substrate and the steel substrate are also subjected to second pretreatment. The second pretreatment comprises polishing, polishing, washing and drying in sequence; the polishing is performed by diamond grinding liquid, and the washing is performed by acetone.

6. The method of brazing titanium / steel dissimilar metals of claim 1, wherein, The steel substrate comprises 316L stainless steel, 316 stainless steel or 304 stainless steel. The titanium substrate comprises TC4 titanium alloy or TiAl alloy. And / or, the filler material includes a titanium-based filler material including Ti 33.3 Zr 16.7 Cu 39 Ni 11 .

7. The method of brazing titanium / steel dissimilar metals of claim 1, wherein, The assembly comprises assembling the steel substrate, the filler metal and the titanium substrate from bottom to top, wherein the configuration surface of the steel substrate is the welding surface.

8. The method of brazing titanium / steel dissimilar metals according to claim 7, wherein A pressing piece is arranged on the titanium substrate.

9. A welding piece prepared by the brazing method of titanium / steel dissimilar metal according to any one of claims 1-8.

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