High-entropy alloy titanium alloy gradient structure and preparation method thereof

Abstract

The invention discloses a high-entropy alloy titanium alloy gradient structure and a preparation method thereof, and belongs to the technical field of metal material additive manufacturing. According to the method, NbZrTi medium-entropy alloy is adopted as a middle layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure, and the high-entropy alloy / titanium alloy gradient structure with better interface bonding performance is prepared by using a TIG multi-wire additive manufacturing system and a CNC machine tool, so that the problem that cracks and air holes are easily caused in the process of preparing the high-entropy alloy / titanium alloy gradient structure is solved; according to the method, the high-entropy alloy / titanium alloy gradient structure with good surface forming quality and excellent interface bonding performance can be prepared, so that the mechanical property of the high-entropy alloy / titanium alloy gradient structure is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing of metal materials, and particularly to a high-entropy alloy titanium alloy gradient structure and a preparation method thereof. Background Art

[0002] As a metal material with characteristics such as high specific strength, good corrosion resistance, and high temperature resistance, titanium alloys are highly favored in the aerospace field. However, there are still many engineering application problems that are difficult to solve. For example, the "thermal barrier" temperature of high-temperature titanium alloys (i.e., the service temperature of titanium alloys is difficult to exceed 600 °C), and the "titanium fire" that occurs in titanium alloys used in aeroengines under high-speed friction (i.e., the burning event of titanium alloys). Moreover, with the development of the aerospace industry, the severe aerodynamic heating environment has put forward requirements for the thermal protection system of aircraft, such as lightweight, low ablation, and high-efficiency heat insulation. At present, the existing macroscopic thermal protection theory and the existing types of superalloys (Co-based, Ni-based, Ti-based superalloys, etc.) are already difficult to meet the increasingly stringent service environment of the aerospace industry.

[0003] Compared with traditional single-component alloys, high-entropy alloys have advantages such as high strength, high hardness, wear resistance, corrosion resistance, and high temperature resistance. However, due to the high melting point, high room-temperature brittleness, and relatively high density of high-entropy alloys, the preparation of large-size high-entropy alloys is a difficult problem in research, which is also the fundamental reason restricting the large-scale application of high-entropy alloys. Therefore, combining high-entropy alloys and titanium alloys can solve the problems of high density of high-entropy alloys and insufficient high-temperature strength of titanium alloys.

[0004] Although high-entropy alloys and titanium alloys have good functionality and practical value, due to the differences in their thermophysical properties, especially the large differences in melting point, linear expansion coefficient, specific heat capacity, thermal conductivity, density, etc., cracks and pores are likely to appear during the preparation of high-entropy alloy / titanium alloy gradient structures. The TaMoNbZrTi high-entropy alloy is a high-entropy alloy composed of five refractory metal elements, Ta, Mo, Nb, Zr, and Ti, which has a relatively high melting point and good high-temperature stability, but has a relatively high density. TA15 titanium alloy is a titanium alloy with Ti and Al elements as the main components, which has a relatively low density, and has a relatively high specific strength and specific stiffness. Because of the large property differences between high-entropy alloys and titanium alloys, it is difficult to prepare a high-entropy alloy / titanium alloy gradient structure with good interfacial bonding by existing methods.

[0005] At present, the preparation methods of high-entropy alloys include vacuum arc melting, powder metallurgy, laser cladding, etc. Among them, the processes of vacuum arc melting and powder metallurgy are complex, and it is difficult to ensure that the alloy is not contaminated. The high-entropy alloys prepared by laser cladding have strong cracking sensitivity. The arc additive manufacturing technology is a kind of additive manufacturing technology. It uses an arc as the heat source, and conveys metal wire materials to the nozzle through a wire feeding system to heat and melt the metal wire materials. The molten metal drops on the path set by the program and is rapidly formed by layer-by-layer stacking. It is suitable for the low-cost, high-efficiency and rapid forming of large-size complex components, and can realize multi-material additive manufacturing by freely replacing multiple nozzles or various material wire materials.

[0006] Therefore, how to prepare a high-entropy alloy / titanium alloy gradient structure with good surface forming quality and excellent interface bonding performance through arc additive manufacturing technology is a technical problem to be solved in this technical field. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a high-entropy alloy titanium alloy gradient structure and its preparation method. The NbZrTi medium-entropy alloy is used as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure, and a TIG multi-wire additive manufacturing system is used to obtain a high-entropy alloy / titanium alloy gradient structure with better interface bonding performance.

[0008] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0009] On the one hand, the present invention first provides a preparation method of a high-entropy alloy titanium alloy gradient structure. First, pure Ta wire, pure Mo wire, pure Zr wire and TiNb wire are deposited layer by layer on a preheated titanium substrate by using a TIG multi-wire additive manufacturing system to obtain a TaMoNbZrTi high-entropy alloy deposition layer; then pure Nb wire, pure Zr wire, and TA0 pure Ti wire are deposited layer by layer on the upper surface of the TaMoNbZrTi high-entropy alloy deposition layer to obtain a NbZrTi medium-entropy alloy deposition layer; then TA15 titanium alloy wire is deposited layer by layer on the upper surface of the NbZrTi medium-entropy alloy deposition layer to obtain a TA15 titanium alloy deposition layer, and a high-entropy alloy titanium alloy gradient structure with the NbZrTi medium-entropy alloy as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure is obtained.

[0010] Further, the diameters of the pure Ta wire, pure Nb wire, pure Zr wire, TA0 pure Ti wire, and TA15 titanium alloy wire are 1.4 mm to 1.8 mm, and the diameter of the pure Mo wire is 1.0 mm to 1.4 mm.

[0011] Further, the above method is carried out by using a TIG multi-wire additive manufacturing system (tungsten inert gas shielded welding multi-wire additive manufacturing system) and a CNC machine tool (computer numerical control machine tool), and includes the following steps:

[0012] S1. Establish a three-dimensional model of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure to be manufactured, and prepare a processing path program according to the three-dimensional model;

[0013] S2. Feed pure Ta wire, pure Mo wire, pure Zr wire, and TiNb wire to the lower part of the welding torch through different wire feeding mechanisms. Under the action of the wire feeding mechanisms, the four wire materials are melted by the arc. Through the CNC machine tool, the nozzle moves with the welding torch along the processing path described in step S1, and the four wire materials are simultaneously stacked layer by layer on the preheated titanium substrate to obtain a TaMoNbZrTi high-entropy alloy deposition layer;

[0014] S3. Replace the four wire materials in step S2 with pure Nb wire, pure Zr wire, TA0 pure Ti wire, and TA15 titanium alloy wire, and feed them to the lower part of the welding torch through different wire feeding mechanisms. Close the wire feeding mechanism of the TA15 titanium alloy wire. The three wire materials of pure Nb wire, pure Zr wire, and TA0 pure Ti wire are melted by the arc under the control of the wire feeding mechanism. Through the CNC machine tool, the nozzle moves with the welding torch along the processing path described in step S1, and the three wire materials are simultaneously stacked layer by layer on the TaMoNbZrTi high-entropy alloy deposition layer to obtain a NbZrTi medium-entropy alloy deposition layer on the TaMoNbZrTi high-entropy alloy deposition layer;

[0015] S4. Close the wire feeding mechanisms of the three wire materials of pure Nb wire, pure Zr wire, and TA0 pure Ti wire, and open the wire feeding mechanism of the TA15 titanium alloy wire. The TA15 titanium alloy wire is melted by the arc under the control of the wire feeding mechanism. Through the CNC machine tool, the nozzle moves with the welding torch along the processing path described in step S1, and the TA15 titanium alloy wire is stacked layer by layer on the NbZrTi medium-entropy alloy deposition layer to obtain a TA15 titanium alloy deposition layer on the NbZrTi medium-entropy alloy deposition layer, and finally obtain a high-entropy alloy titanium alloy gradient structure with the NbZrTi medium-entropy alloy as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure.

[0016] Further, the moving speed of the welding torch controlled by the CNC machine tool is 80 mm / min to 120 mm / min, and the arc types of the welding torch are all DC pulsed arcs.

[0017] Further, the arc additive deposition processes in steps S2, S3, and S4 are all carried out in a protective gas atmosphere. The protective gas is argon, and the argon gas flow rate is 18 L / min to 22 L / min.

[0018] Further, the welding machine thermal input parameters of the TaMoNbZrTi high-entropy alloy deposition layer in step S2 are as follows: peak current is 280A - 300A; peak duty cycle is 30% - 36%; pulse frequency is 0.8Hz - 1.2Hz; base current is 90A - 110A; wire feeding speeds of pure Ta wire and TiNb wire are: 0.3m / min - 0.5m / min, and wire feeding speeds of pure Mo wire and pure Zr wire are: 0.4m / min - 0.6m / min;

[0019] The welding machine thermal input parameters of the NbZrTi medium-entropy alloy deposition layer in step S3 are as follows: peak current is 265A - 295A; peak duty cycle is 33% - 37%; pulse frequency is 0.8Hz - 1.2Hz; base current is 40A - 60A; wire feeding speeds of pure Nb wire and TA0 pure Ti wire are: 0.3m / min - 0.5m / min, and wire feeding speed of pure Zr wire is: 0.4m / min - 0.6m / min;

[0020] The welding machine thermal input parameters of the TA15 titanium alloy deposition layer in step S4 are as follows: peak current is 270A - 290A; peak duty cycle is 43% - 47%; pulse frequency is 1.6Hz - 2.0Hz; base current is 20A - 40A; wire feeding speed of TA15 titanium alloy wire is: 1.6m / min - 2.0m / min.

[0021] The peak duty cycle is the percentage of the peak current time in the entire pulse current time.

[0022] The pure Ta wire, pure Mo wire, pure Nb wire, pure Zr wire, TA0 pure Ti wire, and TA15 titanium alloy wire have auxiliary heating equipment in the wire feeding mechanism for preheating.

[0023] Further, in the wire feeding mechanism, a hot wire power supply auxiliary heating equipment is adopted. The hot wire current for preheating the pure Ta wire and pure Mo wire is a DC power supply of 300A - 400A; the hot wire current for preheating the pure Nb wire and pure Zr wire is a DC power supply of 150A - 250A; the hot wire current for preheating the TA15 titanium alloy wire is 100A - 140A, and the frequency is an AC power supply of 200Hz.

[0024] Further, in step S2, the titanium substrate uses a TC4 titanium alloy substrate with a thickness of 5mm - 10mm. The welding machine thermal input parameters for preheating the titanium substrate are: peak current is 280A - 320A; peak duty cycle is 28% - 32%; pulse frequency is 1.0Hz; base current is 90A - 110A, and the number of preheating passes of the titanium substrate is 2 passes.

[0025] Further, the height of a single layer of the TaMoNbZrTi high-entropy alloy deposition layer is 1.8 mm to 2.2 mm; the height of a single layer of the NbZrTi medium-entropy alloy deposition layer is 1.5 mm to 1.9 mm; and the height of a single layer of the TA15 titanium alloy deposition layer is 1.9 mm to 2.1 mm.

[0026] On the other hand, the present invention also provides a high-entropy alloy-titanium alloy gradient structure prepared by using the method described in any one of the above.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The preparation method of the high-entropy alloy-titanium alloy gradient structure provided by the present invention adopts the "entropy reduction transition" method of arc additive manufacturing, uses the NbZrTi medium-entropy alloy as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure, and uses a TIG multi-wire additive manufacturing system to obtain a high-entropy alloy / titanium alloy gradient structure with good interfacial bonding performance, simplifies the preparation process, and improves the working efficiency.

[0029] 2. The preparation method of the high-entropy alloy-titanium alloy gradient structure provided by the present invention is based on the principle of layer-by-layer stacking. The previous deposition layer plays a good preheating role for the subsequent deposition layer, and the subsequent deposition layer plays a good heat treatment role for the previous layer, making the structures of the high-entropy alloy and the titanium alloy more uniform and finer. At the same time, the mechanical properties at the interfaces between the high-entropy alloy and the medium-entropy alloy and between the medium-entropy alloy and the titanium alloy are also improved, solving the problems of cracks and pores easily caused during the preparation of the high-entropy alloy / titanium alloy gradient structure. This method can obtain a high-entropy alloy / titanium alloy gradient structure with good surface forming quality and excellent interfacial bonding performance. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings.

[0031] Figure 1 It is a macroscopic morphology diagram of the high-entropy alloy-titanium alloy gradient structure prepared in Example 1 of the present invention.

[0032] Figure 2 It is a microscopic morphology diagram of the interface between the high-entropy alloy and the medium-entropy alloy in the high-entropy alloy-titanium alloy gradient structure prepared in Example 1 of the present invention.

[0033] Figure 3Microstructure diagram and EDS element distribution diagram of high-entropy alloy dendrites in the high-entropy alloy titanium alloy gradient structure prepared in Example 1 of the present invention. (a) is the microstructure diagram of high-entropy alloy dendrites; (b) is the Ta element distribution diagram of high-entropy alloy; (c) is the Mo element distribution diagram of high-entropy alloy; (d) is the Nb element distribution diagram of high-entropy alloy; (e) is the Zr element distribution diagram of high-entropy alloy; (f) is the Ti element distribution diagram of high-entropy alloy. Detailed implementation manners

[0034] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the drawings and embodiments. Among them, the methods are all conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels or prepared according to the literature unless otherwise specified.

[0035] In order to solve the defects such as cracks when the TaMoNbZrTi high-entropy alloy and the TA15 titanium alloy are combined, the present invention provides a preparation method of a high-entropy alloy titanium alloy gradient structure, which uses the NbZrTi medium-entropy alloy as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure. This medium-entropy alloy has good compatibility with both the high-entropy alloy and the titanium alloy, and can effectively relieve the stress concentration problem caused by the composition difference in the gradient structure, and improve the reliability of the combination.

[0036] At the same time, through a large number of experimental studies, it is confirmed that using the NbZrTi medium-entropy alloy as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure has the best material properties compared with other medium-entropy alloys. For example, using Mo element instead of Nb element will cause the plasticity of the material to decrease and the brittleness to increase. Using Hf instead of Zr will cause the grains to be coarse, the plasticity to decrease, and at the same time increase the material cost. Therefore, the present invention selects the NbZrTi medium-entropy alloy as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure.

[0037] Specifically, the present invention is carried out by using a TIG multi-wire additive manufacturing system and a CNC machine tool, and the method steps are as follows:

[0038] (1) Establish a three-dimensional model of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure to be manufactured, and compile a processing path program according to the three-dimensional model;

[0039] (2) According to the target composition of the TaMoNbZrTi high-entropy alloy, pure Ta wire, pure Mo wire, pure Zr wire, and TiNb wire are transported to below the welding torch through different wire feeding mechanisms. Through the wire feeding mechanisms, the four wires are melted under the action of the arc at different or the same wire feeding speeds. Through the CNC machine tool, the nozzle moves with the welding torch along the processing path described in step (1), and the four wires are simultaneously stacked layer by layer on the preheated titanium substrate to obtain a TaMoNbZrTi high-entropy alloy deposition layer;

[0040] (3) Replace the four wires in step (2) with pure Nb wire, pure Zr wire, TA0 pure Ti wire, and TA15 titanium alloy wire, and transport them to below the welding torch through different wire feeding mechanisms. Close the wire feeding mechanism of the TA15 titanium alloy wire. The three wires of pure Nb wire, pure Zr wire, and TA0 pure Ti wire are melted under the action of the arc at different or the same wire feeding speeds under the control of the wire feeding mechanism. Through the CNC machine tool, the nozzle moves with the welding torch along the processing path described in step (1), and the three wires are simultaneously stacked layer by layer on the TaMoNbZrTi high-entropy alloy deposition layer to obtain a NbZrTi medium-entropy alloy deposition layer on the TaMoNbZrTi high-entropy alloy deposition layer;

[0041] (4) Close the wire feeding mechanisms of the three wires of pure Nb wire, pure Zr wire, and TA0 pure Ti wire, and open the wire feeding mechanism of the TA15 titanium alloy wire. The TA15 titanium alloy wire is melted under the action of the arc at a certain wire feeding speed under the control of the wire feeding mechanism. Through the CNC machine tool, the nozzle moves with the welding torch along the processing path described in step (1), and the TA15 titanium alloy wire is stacked layer by layer on the NbZrTi medium-entropy alloy deposition layer to obtain a TA15 titanium alloy deposition layer on the NbZrTi medium-entropy alloy deposition layer, and finally obtain a "entropy reduction transition" part with the NbZrTi medium-entropy alloy as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure.

[0042] Among them, in step (3), elemental wires (pure Nb wire, pure Zr wire, TA0 pure Ti) or NbZrTi alloy wires can be used. In the present invention, using elemental wires can achieve the regulation of any composition by the multi-wire arc additive manufacturing equipment, which is simpler. If NbZrTi pre-alloyed wires are used, the cost is high and the composition regulation is complex. Therefore, the present invention uses elemental wires.

[0043] In the present invention, the three-dimensional model of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure manufactured is a single-channel thin wall with a length of 120 mm. The detailed G code of the processing path program is preferably as follows:

[0044] G92 X0 Y0 Z0

[0045] G91

[0046] M14

[0047] M36

[0048] M38

[0049] M40

[0050] M42

[0051] G01 X120 F100

[0052] M37

[0053] M39

[0054] M41

[0055] M43

[0056] M15

[0057] G01 Z2.0

[0058] G01 X-120F2000

[0059] M02

[0060] Among them, M14 is the welding machine start code, M36, M38, M40, and M42 are the wire feeding mechanism start codes, M15 is the welding machine stop code, and M37, M39, M41, and M43 are the wire feeding mechanism stop codes. By repeatedly executing the above G codes in the present invention, it can be ensured that the manufactured single-pass thin wall conforms to the designed three-dimensional model.

[0061] In the present invention, the purity of the pure Ta wire and the pure Mo wire is preferably not less than 99.95%; the purity of the pure Nb wire, the pure Zr wire, and the TA0 pure Ti wire is preferably not less than 99.99%; the TiNb wire is preferably a pre-alloyed wire, and the main components are Ti and Nb, where the mass fraction of the Nb element is 47.6% and the mass fraction of the Ti element is 52.4%; the TA15 titanium alloy wire is preferably a wire conforming to GB / T 13810-2017.

[0062] In the present invention, the diameters of the pure Ta wire, the pure Nb wire, the pure Zr wire, the TiNb wire, the TA0 pure Ti wire, and the TA15 titanium alloy wire are 1.4 mm to 1.8 mm, preferably 1.6 mm; the diameter of the pure Mo wire is 1.0 mm to 1.4 mm, preferably 1.2 mm. Different wire diameters directly correspond to different wire feeding speeds, and the corresponding relationship is in the following wire feeding speed calculation formula.

[0063] In the present invention, the titanium substrate is preferably a TC4 titanium alloy substrate with a thickness of 5 mm to 10 mm, more preferably 5 mm to 7 mm, and further preferably 5 mm. The thickness of the substrate mainly affects two factors, heat dissipation and residual stress, in additive manufacturing. If the substrate is too thin, the heat dissipation capacity is limited, resulting in too high a temperature of the molten pool or even melting through the substrate, and it is prone to warping and deformation, affecting the accuracy of the subsequent deposited layer and the stability of the overall structure. If the substrate is too thick, the heat dissipation capacity becomes stronger, the cooling rate of the molten pool increases, resulting in poor fluidity of the molten pool, which may lead to uneven mixing of the molten pool and composition segregation, and the residual stress increases, which may lead to the formation of cracks, especially during layer-by-layer deposition.

[0064] In the present invention, the arc additive deposition process is carried out in an atmosphere of protective gas. Preferably, the protective gas is argon. The main function of argon is to form an inert atmosphere to prevent the high-temperature molten pool and solidified metal from being contaminated by gases such as oxygen in the air. If the flow rate is too low, the protection effect will be insufficient, resulting in metal oxidation to form brittle oxides and reducing the interface bonding ability. If the flow rate is too high, turbulence will be formed, resulting in the molten pool metal being disturbed. In this application, the preferred argon flow rate is 18 L / min to 22 L / min.

[0065] In the present invention, the arc types of the welding torches of the TIG multi-wire additive manufacturing system are all DC pulsed arcs. The moving speed of the welding torch is mainly related to the total wire feeding speed. If the speed is too slow, the residence time of the molten pool will be too long, the heat input will be too large, resulting in too large a size of the molten pool, edge collapse, and even overheating and melting through of the substrate. If the speed is too fast, it may lead to too fast a cooling rate of the molten pool, insufficient fluidity of the liquid metal, resulting in uneven mixing of the molten pool and composition segregation, and even discontinuity of the weld bead, affecting the forming accuracy. In the present invention, the CNC machine tool controls the moving speed of the welding torch to be 80 mm / min to 120 mm / min, preferably 90 mm / min to 110 mm / min, and more preferably 100 mm / min.

[0066] The welding heat input parameters for preheating the TC4 titanium alloy substrate are as follows: the peak current is 280 A to 320 A, preferably 300 A; the peak duty cycle is 28% to 32%, preferably 30%; the pulse frequency is 1.0 Hz, and the base current is 90 A to 110 A, preferably 100 A. More preferably, the number of preheating passes for the titanium substrate is 2 passes. By limiting the preheating parameters of the TC4 titanium alloy substrate within the above range in the present invention, it can ensure that the TC4 substrate is fully preheated, and fish-scale patterns are formed on the processing path, increasing the wettability between the metal droplets and the substrate and forming a wider weld bead.

[0067] In the present invention, in the calculation method of the wire feeding speed of each wire of the TaMoNbZrTi high-entropy alloy in step (2), pure Ta wire, pure Zr wire, TiNb wire with a diameter of d 1 = 1.6 mm and pure Ta wire, pure Zr wire, TiNb wire with a diameter of d 2Pure Mo wire with a diameter of 1.2 mm, where the mass fraction of Nb element in the TiNb wire is 47.6%, and the mass fraction of Ti element is 52.4%. The relative atomic masses of each metal element are: Ar Ta = 180.948, Ar Mo = 95.94, Ar Nb = 92.906, Ar Zr = 91.224, Ar Ti = 47.867, and the densities of the corresponding pure metal substances are: ρ Ta = 16.65 g / cm3, ρ Mo = 10.22 g / cm3, ρ Nb = 8.57 g / cm3, ρ Zr = 6.49 g / cm3, ρ Ti = 4.506 g / cm3. Assuming that there is no volume change during the melting process, the density ρ of the TiNb wire TiNb ≈ 5.82 g / cm3. Therefore, the amount of substance of each element in the alloy per unit time t is:

[0068]

[0069] Therefore, the total amount of substance in the alloy per unit time t is:

[0070] n 总 = n Ta + n Mo + n Nb + n Zr + n Ti

[0071] In the example of the present invention, the atomic ratio of each element in the TaMoNbZrTi high-entropy alloy is 2:2:1:2:2. By substituting the atomic masses and densities of each element and solving the system of equations simultaneously, the wire feeding speeds of each wire can be obtained. After calculation, the preferred wire feeding speeds of the pure Ta wire and the TiNb wire are: 0.3 m / min to 0.5 m / min, and the preferred wire feeding speeds of the pure Mo wire and the pure Zr wire are: 0.4 m / min to 0.6 m / min. More preferably, the pure Ta wire and the TiNb wire are 0.4 m / min, and the pure Mo wire and the pure Zr wire are 0.5 m / min.

[0072] In the present invention, for the calculation method of the wire feeding speed of each wire in the NbZrTi medium-entropy alloy in the step (3), pure Nb wire with a diameter d = 1.6 mm, pure Zr wire, and TA0 pure Ti wire are used. The relative atomic masses of each metal element are: Ar Nb = 92.906, Ar Zr = 91.224, Ar Ti = 47.867, and the densities of the corresponding pure metal substances are: ρNb = 8.57 g / cm3, ρ Zr = 6.49 g / cm3, ρ Ti = 4.506 g / cm3. The amount of substance of each element in the alloy per unit time t is as follows:

[0073]

[0074] Therefore, the total amount of substance in the alloy per unit time t is:

[0075] n 总 = n Nb + n Zr + n Ti

[0076] In the examples of the present invention, the atomic ratio of each element in the NbZrTi medium-entropy alloy is 1:1:1. Substituting the atomic masses and densities of each element and solving the system of equations simultaneously can obtain the wire feeding speeds of each wire. After calculation, the preferred wire feeding speeds of pure Nb wire and TA0 pure Ti wire are: 0.3 m / min to 0.5 m / min, and the preferred wire feeding speed of pure Zr wire is: 0.4 m / min to 0.6 m / min. More preferably, the wire feeding speed of pure Nb wire and TA0 pure Ti wire is 0.4 m / min, and the wire feeding speed of pure Zr wire is 0.5 m / min.

[0077] In the present invention, the preferred wire feeding speed of the TA15 titanium alloy wire in step (4) is:

[0078] 1.6 m / min to 2.0 m / min, more preferably 1.8 m / min.

[0079] In the present invention, all the wire materials are preferably suspended on their respective wire spool fixing devices in the form of wire spools and guided into the wire feeding mechanism through their respective wire feeding tubes. The wire feeding wheels in the wire feeding mechanism rotate at a constant speed set by the control system, and the wire materials clamped between the wire feeding wheels are transported to the nozzle through different wire feeding channels, and the angle between the wire material nozzle and the welding torch is ensured to be 40 to 50 degrees, and it is ensured that the intersection of the four wire materials (or the extension lines of the wire materials) and the extension line of the welding torch are located on the same vertical line. By limiting the wire feeding speeds and diameters of pure Ta wire, pure Mo wire, pure Zr wire and TiNb wire within the above ranges in the present invention, a TaMoNbZrTi high-entropy alloy deposition layer with the corresponding alloy composition can be ensured to be obtained; by limiting the wire feeding speeds and diameters of pure Nb wire, pure Zr wire and TA0 pure Ti wire within the above ranges, a NbZrTi medium-entropy alloy deposition layer with the corresponding alloy composition can be ensured to be obtained; by limiting the wire feeding speed and diameter of the TA15 titanium alloy wire within the above ranges, a TA15 titanium alloy deposition layer can be ensured to be obtained.

[0080] In the present invention, the pure Ta wire, pure Mo wire, pure Nb wire, pure Zr wire, TA0 pure Ti wire, and TA15 titanium alloy wire are preheated by an auxiliary heating device in the wire feeding mechanism, and the auxiliary heating device is preferably a hot wire power supply. The hot wire current for preheating the pure Ta wire and pure Mo wire is a DC power supply of 300 A to 400 A, more preferably a DC power supply of 350 A to 400 A; the hot wire current for preheating the pure Nb wire and pure Zr wire is a DC power supply of 150 A to 250 A, more preferably a DC power supply of 180 A to 220 A. These single-element wire materials such as pure Ta wire, pure Mo wire, pure Nb wire, pure Zr wire, and TA0 pure Ti wire have relatively high melting points and are difficult to soften during the wire feeding process. Moreover, the resistivity of single-element metals is relatively low, and higher heating efficiency is required. Therefore, a DC hot wire power supply is used, which has higher thermal efficiency. The resistivity of the TA15 titanium alloy wire is relatively high and the melting point is relatively low. Therefore, in the present invention, an AC hot wire power supply can make the heat input more uniform and reduce the risk of local overheating and local melting. The hot wire current for preheating the TA15 titanium alloy wire is 100 A to 140 A, and the AC power supply has a frequency of 200 Hz. Using 200 Hz makes use of the skin effect of alternating current. A higher AC frequency can make the skin effect more obvious, and the current is more concentrated on the surface of the wire, preventing local overheating and improving the stability during the manufacturing process. The TiNb wire is preferably preheated without an auxiliary heating device. In the present invention, the hot wire current is limited within the above range, which can ensure that the pure Ta wire, pure Mo wire, pure Nb wire, pure Zr wire, TA0 pure Ti wire, TiNb wire, and TA15 titanium alloy wire can be melted to form molten droplets under the subsequent defined heat input of the welding machine.

[0081] In the present invention, the welding machine heat input parameters of the TaMoNbZrTi high-entropy alloy deposition layer in step (2) are: peak current is 280 A to 300 A; peak duty cycle is 30% to 36%; pulse frequency is 0.8 Hz to 1.2 Hz; base current is 90 A to 110 A. The welding machine heat input parameters of the NbZrTi medium-entropy alloy deposition layer in step (3) are: peak current is 265 A to 295 A; peak duty cycle is 33% to 37%, pulse frequency is 0.8 Hz to 1.2 Hz; base current is 40 A to 60 A. The welding machine heat input parameters of the TA15 titanium alloy deposition layer in step (4) are: peak current is 270 A to 290 A; peak duty cycle is 43% to 47%; pulse frequency is 1.6 Hz to 2.0 Hz; base current is 20 A to 40 A. In the present invention, the parameters of the welding machine heat input mainly depend on the melting point of the wire material and the wire feeding speed. The higher the melting point of the wire material and the faster the wire feeding speed, the higher the heat input required. In the present invention, limiting the welding machine heat input within the above range can ensure that the wire material is fully melted and a stable molten droplet transfer mode is formed, thereby improving the quality of the deposition layer, which has both a good appearance and a uniform composition.

[0082] In the present invention, the layer-by-layer deposition of arc additive manufacturing is carried out from bottom to top. In the examples of the present invention, after the CNC machine tool completes one scan of the machining path, it lifts upward by the height of one deposition layer along the deposition direction, returns to the starting point of the previous machining path, and continues the scan of the next machining path. The layer height mainly affects the forming quality of the sample. Too low layer height will lead to slow deposition efficiency. And the heat accumulation becomes high. As the number of layers increases, the overall heat input increases, resulting in grain growth and reduced performance. And it will lead to excessive remelting and an increase in the melt width, making the melt depth of the upper layer insufficient and affecting the connection between layers. When the layer height is too high, it will cause the intersection points of the wire materials and the deposition layer not to be on the same plane, resulting in interference between the wire materials, uneven spreading of the molten pool, affecting deposition stability, resulting in a rough surface, and possibly forming unfused defects. The optimal layer height of a single layer is obtained by observing with a dedicated high-definition arc tracking camera device and combining experiments. Among them, the layer height of a single layer of the TaMoNbZrTi high-entropy alloy deposition layer is 1.8 mm to 2.2 mm, preferably 2.0 mm; the layer height of a single layer of the NbZrTi medium-entropy alloy deposition layer is 1.5 mm to 1.9 mm, preferably 1.7 mm; the layer height of a single layer of the TA15 titanium alloy deposition layer is 1.9 mm to 2.1 mm, preferably 2.0 mm.

[0083] Example 1

[0084] The object of the present invention is to provide a method for preparing a high-entropy alloy titanium alloy gradient structure, using NbZrTi medium-entropy alloy as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure, and using a TIG multi-wire additive manufacturing system and a CNC machine tool. The method steps are as follows:

[0085] (1) Establish a three-dimensional model of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure to be manufactured. The three-dimensional model is a single-pass thin-walled part with a length of 120 mm, a width of 20 mm, and a height of 100 mm. Compile a machining path program according to the three-dimensional model and import the machining path program into the CNC machine tool control system. The detailed G code of the machining path program is as follows:

[0086] G92 X0 Y0 Z0

[0087] G91

[0088] M14

[0089] M36

[0090] M38

[0091] M40

[0092] M42

[0093] G01 X120 F100

[0094] M37

[0095] M39

[0096] M41

[0097] M43

[0098] M15

[0099] G01 Z2.0

[0100] G01 X-120 F2000

[0101] M02

[0102] (2) According to the target components Ta 3 Mo 3 NbZr 4 Ti 2 , pure Ta wire with a diameter of 1.6 mm, pure Zr wire, and TiNb wire, and pure Mo wire with a diameter of 1.2 mm are transported to the lower part of the welding torch through different wire feeding mechanisms. A TC4 titanium substrate with a length of 300 mm, a width of 300 mm, and a thickness of 5 mm is fixed in a CNC machine tool and preheated. In a closed environment, protective gas argon with a flow rate of 20 L / min is introduced. Through the wire feeding mechanism, the four wire materials are melted under the action of an electric arc at different or the same wire feeding speeds. Through the CNC machine tool, the nozzle moves with the welding torch along the machining path described in step (1) at a moving speed of 100 mm / min, and the four wire materials are simultaneously stacked layer by layer 25 layers on the preheated titanium substrate to obtain a TaMoNbZrTi high-entropy alloy deposition layer;

[0103] (3) Replace the four wire materials in step (2) with pure Nb wire with a diameter of 1.6 mm, pure Zr wire, TA0 pure Ti wire, and TA15 titanium alloy wire, and transport them to the lower part of the welding torch through different wire feeding mechanisms. Close the wire feeding mechanism of the TA15 titanium alloy wire, and the three wire materials of pure Nb wire, pure Zr wire, and TA0 pure Ti wire are melted under the action of an electric arc at different or the same wire feeding speeds under the control of the wire feeding mechanism. Through the CNC machine tool, the nozzle moves with the welding torch along the machining path described in step (1) at a moving speed of 100 mm / min, and the three wire materials are simultaneously stacked layer by layer 5 layers on the TaMoNbZrTi high-entropy alloy deposition layer to obtain a NbZrTi medium-entropy alloy deposition layer on the TaMoNbZrTi high-entropy alloy deposition layer;

[0104] (4) Turn off the wire feeding mechanisms for pure Nb wire, pure Zr wire, and TA0 pure Ti wire, and turn on the wire feeding mechanism for TA15 titanium alloy wire. The TA15 titanium alloy wire melts under the action of an electric arc at a certain wire feeding speed under the control of the wire feeding mechanism. Through the CNC machine tool, the nozzle moves with the welding torch along the machining path described in step (1) at a moving speed of 100 mm / min. Stack 21 layers of TA15 titanium alloy wire on the NbZrTi medium-entropy alloy deposition layer to obtain a TA15 titanium alloy deposition layer on the NbZrTi medium-entropy alloy deposition layer, and finally obtain a "de-entropy transition" thin-walled part with the NbZrTi medium-entropy alloy as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure.

[0105] In the examples of the present invention, the purity of the pure Ta wire and the pure Mo wire is not less than 99.95%; the purity of the pure Nb wire, the pure Zr wire, and the TA0 pure Ti wire is not less than 99.99%; the TiNb wire is a pre-alloyed wire, and its main components are Ti and Nb, where the mass fraction of the Nb element is 47.6% and the mass fraction of the Ti element is 52.4%; the TA15 titanium alloy wire is a wire that complies with the national standard GB / T13810-2017.

[0106] In the examples of the present invention, the arc types adopted by the welding torches of the TIG multi-wire additive manufacturing system are all DC pulsed arcs.

[0107] In the examples of the present invention, the welding machine heat input parameters for preheating the TC4 titanium alloy substrate in step (2) are: peak current 300 A; peak duty cycle 30%; pulse frequency 1.0 Hz, base current 100 A. Preheat for 2 passes.

[0108] In the examples of the present invention, the wire feeding speeds of each wire in step (2) are: pure Ta wire and TiNb wire 0.4 m / min, pure Mo wire and pure Zr wire 0.5 m / min; the wire feeding speeds of each wire in step (3) are: pure Nb wire and TA0 pure Ti wire 0.4 m / min, pure Zr wire 0.5 m / min; in the present invention, the wire feeding speed of the TA15 titanium alloy wire in step (4) is 1.8 m / min.

[0109] In the examples of the present invention, all the wires are suspended on their respective wire spool fixing devices in the form of wire spools and are guided into the wire feeding mechanism through their respective wire feeding tubes. The wire feeding wheels in the wire feeding mechanism rotate at a constant speed at the above-set wire feeding speeds, and the wires clamped between the wire feeding wheels are transported to the nozzle through different wire feeding channels, ensuring that the angle between the wire nozzle and the welding torch is 45°, and ensuring that the intersection point of the four wires (or the extension lines of the wires) and the extension line of the welding torch are on the same vertical line.

[0110] In the example of the present invention, the pure Ta wire, pure Mo wire, pure Nb wire, pure Zr wire, TA0 pure Ti wire, and TA15 titanium alloy wire are preheated by a hot wire power supply auxiliary heating device in the wire feeding mechanism. A 400A DC power supply for the hot wire current to preheat the pure Ta wire and pure Mo wire; a 200A DC power supply for the hot wire current to preheat the pure Nb wire and pure Zr wire. A 120A, 200Hz AC power supply for preheating the TA15 titanium alloy wire.

[0111] In the example of the present invention, the welding heat input parameters of the TaMoNbZrTi high-entropy alloy deposition layer in step (2) are: peak current 290A; peak duty cycle 33%; pulse frequency 1.0Hz; base current 100A. The welding heat input parameters of the NbZrTi medium-entropy alloy deposition layer in step (3) are: peak current 280A; peak duty cycle 35%, pulse frequency 1.0Hz; base current 50A. The welding heat input parameters of the TA15 titanium alloy deposition layer in step (4) are: peak current 280A; peak duty cycle 45%; pulse frequency 1.8Hz; base current 30A.

[0112] In the example of the present invention, the layer height of a single layer of the TaMoNbZrTi high-entropy alloy deposition layer is 2.0mm; the layer height of a single layer of the NbZrTi medium-entropy alloy deposition layer is 1.7mm; the layer height of a single layer of the TA15 titanium alloy deposition layer is 2.0mm.

[0113] The macroscopic morphology diagram of the "entropy reduction transition" thin-walled part prepared through this example is as Figure 1 shown. The prepared thin-walled part is 125mm long, 16mm wide in fusion width, and 100mm high (where the TaMoNbZrTi high-entropy alloy deposition layer is 50mm; the TiNbZr medium-entropy alloy deposition layer is 8mm; the TA15 titanium alloy deposition layer is 42mm). In this embodiment, a "entropy reduction transition" thin-walled part with a NbZrTi medium-entropy alloy as the intermediate layer of the TaMoNbZrTi high-entropy alloy / TA15 titanium alloy gradient structure is prepared by the TIG double-wire arc additive manufacturing method, which has a dense layer deposition morphology, good structural formability, and no obvious welding defects such as cracks and pores.

[0114] The Instron 5985 universal testing machine was used to conduct room-temperature quasi-static compression mechanical property tests on the "entropy reduction transition" thin-walled parts prepared in this example. It was found that at room temperature, the average compressive strength of the "entropy reduction transition" thin-walled parts was 1164 MPa. The Gleeble 3500 thermal simulation testing machine was used to conduct high-temperature quasi-static compression mechanical property tests on the "entropy reduction transition" thin-walled parts prepared in the example at 800 °C. It was found that at a high temperature of 800 °C, the maximum compressive strength of the "entropy reduction transition" thin-walled parts could reach 232 MPa, exceeding 165 MPa of TA15 at the same temperature.

[0115] The Thermo Fisher Apreo scanning electron microscope was used to observe the microscopic morphology of the interface between the high-entropy alloy and the medium-entropy alloy of the thin-walled parts prepared in this example, as Figure 2 shown. It can be seen that there are no microscopic cracks at the interface between the high-entropy alloy and the medium-entropy alloy, and no obvious unmelted particles or macroscopic segregation are found in the high-entropy alloy part and the medium-entropy alloy part, indicating that the compositions of the high-entropy alloy and the medium-entropy alloy are uniform. The high-entropy alloy part shows an obvious dendritic morphology. The Bruker XFlash 6130 energy spectrometer was used to perform area scanning on the dendritic structure of the high-entropy alloy, and the results are as Figure 3 shown in. (a) is the micrograph of the dendritic structure of the high-entropy alloy; (b) is the distribution map of Ta element in the high-entropy alloy; (c) is the distribution map of Mo element in the high-entropy alloy; (d) is the distribution map of Nb element in the high-entropy alloy; (e) is the distribution map of Zr element in the high-entropy alloy; (f) is the distribution map of Ti element in the high-entropy alloy. It can be seen that the dendrite trunks in the high-entropy alloy part are mainly enriched with Ta and Mo elements, Nb and Zr elements are enriched between the dendrites, and there is no obvious microscopic segregation behavior of Ti element.

[0116] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features, but these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high entropy alloy titanium alloy gradient structure, characterized in that: A TIG multi-wire additive manufacturing system is used to first deposit pure Ta wire, pure Mo wire, pure Zr wire and TiNb wire layer by layer on a preheated titanium substrate to obtain a TaMoNbZrTi high entropy alloy deposition layer; then pure Nb wire, pure Zr wire and TA0 pure Ti wire are deposited layer by layer on the upper surface of the TaMoNbZrTi high entropy alloy deposition layer to obtain a NbZrTi medium entropy alloy deposition layer; then TA15 titanium alloy wire is deposited layer by layer on the upper surface of the NbZrTi medium entropy alloy deposition layer to obtain a TA15 titanium alloy deposition layer, and a high entropy alloy titanium alloy gradient structure with NbZrTi medium entropy alloy as the intermediate layer of the TaMoNbZrTi high entropy alloy / TA15 titanium alloy gradient structure is obtained.

2. The method for preparing a high entropy alloy titanium alloy gradient structure according to claim 1, characterized in that: The diameters of the pure Ta wire, pure Nb wire, pure Zr wire, TA0 pure Ti wire, and TA15 titanium alloy wire are 1.4 mm to 1.8 mm, and the diameter of the pure Mo wire is 1.0 mm to 1.4 mm.

3. The method for preparing a high entropy alloy titanium alloy gradient structure according to claim 2, characterized in that: The process was carried out using a TIG multi-filament additive manufacturing system and a CNC machine, and included the following steps: S1. Establish a three-dimensional model of the TaMoNbZrTi high entropy alloy / TA15 titanium alloy gradient structure to be manufactured, and compile a processing path program according to the three-dimensional model; S2, conveying pure Ta wire, pure Mo wire, pure Zr wire and TiNb wire to the bottom of the welding gun through different wire feeding mechanisms, and melting the four wire materials under the action of the electric arc through the wire feeding mechanism; using a CNC machine tool, the nozzle moves along with the welding gun according to the processing path described in step S1, and the four wire materials are deposited layer by layer on the preheated titanium substrate to obtain a TaMoNbZrTi high entropy alloy deposition layer; S3: replacing the four wire materials in step S2 with pure Nb wire, pure Zr wire, TA0 pure Ti wire and TA15 titanium alloy wire, and delivering them to the bottom of the welding gun through different wire feeding mechanisms; closing the wire feeding mechanism of the TA15 titanium alloy wire, and melting the three wire materials, namely, pure Nb wire, pure Zr wire and TA0 pure Ti wire, under the control of the wire feeding mechanism and under the action of the electric arc; using a CNC machine tool, the nozzle moves along with the welding gun according to the processing path described in step S1, and the three wire materials are deposited layer by layer on the TaMoNbZrTi high entropy alloy deposition layer at the same time, so as to obtain a NbZrTi medium entropy alloy deposition layer on the TaMoNbZrTi high entropy alloy deposition layer; S4. Turn off the wire feeding mechanisms of the three types of wires, namely, pure Nb wire, pure Zr wire and TA0 pure Ti wire, and turn on the wire feeding mechanism of the TA15 titanium alloy wire. The TA15 titanium alloy wire melts under the control of the wire feeding mechanism and the action of the electric arc. Through the CNC machine tool, the nozzle moves along with the welding gun according to the processing path described in step S1, and the TA15 titanium alloy wire is deposited layer by layer on the NbZrTi medium entropy alloy deposition layer, and a TA15 titanium alloy deposition layer is obtained on the NbZrTi medium entropy alloy deposition layer, and finally a high entropy alloy titanium alloy gradient structure with the NbZrTi medium entropy alloy as the intermediate layer of the TaMoNbZrTi high entropy alloy / TA15 titanium alloy gradient structure is obtained.

4. The method for preparing a high entropy alloy titanium alloy gradient structure according to claim 3, characterized in that: The CNC machine tool controls the moving speed of the welding gun to be 80 mm / min to 120 mm / min, and the arc type used by the welding gun is a DC pulse arc.

5. The method for preparing a high entropy alloy titanium alloy gradient structure according to claim 3, characterized in that: The arc additive deposition processes of steps S2, S3 and S4 are all carried out under a protective gas atmosphere, the protective gas is argon, and the argon flow rate is 18L / min to 22L / min.

6. The method for preparing a high entropy titanium alloy gradient structure according to claim 3, characterized in that: The welding machine heat input parameters of the TaMoNbZrTi high entropy alloy deposition layer in step S2 are: peak current of 280A to 300A; peak duty cycle of 30% to 36%; pulse frequency of 0.8Hz to 1.2Hz; base current of 90A to 110A; wire feeding speeds of pure Ta wire and TiNb wire are: 0.3m / min~0.5m / min, the wire feeding speed of pure Mo wire and pure Zr wire is: 0.4m / min~0.6m / min; The heat input parameters of the welding machine for the NbZrTi medium entropy alloy deposition layer in step S3 are: peak current of 265A to 295A; peak duty cycle of 33% to 37%; pulse frequency of 0.8Hz to 1.2Hz; base current of 40A to 60A; The wire feeding speed of pure Nb wire and TA0 pure Ti wire is: 0.3m / min~0.5m / min, the wire feeding speed of pure Zr wire is: 0.4m / min~0.6m / min; The welding machine heat input parameters of the TA15 titanium alloy deposition layer in step S4 are: peak current of 270A to 290A; peak duty cycle of 43% to 47%; pulse frequency of 1.6Hz to 2.0Hz; base current of 20A to 40A; and wire feeding speed of TA15 titanium alloy wire of 1.6m / min to 2.0m / min.

7. The method for preparing a high entropy alloy titanium alloy gradient structure according to claim 3, characterized in that: A hot wire power supply auxiliary heating device is used in the wire feeding mechanism. The hot wire current for preheating the pure Ta wire and pure Mo wire is a 300A-400A DC power supply; the hot wire current for preheating the pure Nb wire and pure Zr wire is a 150A-250A DC power supply; the hot wire current for preheating the TA15 titanium alloy wire is 100A-140A, and the frequency is 200Hz AC power supply.

8. The method for preparing a high entropy alloy titanium alloy gradient structure according to claim 3, characterized in that: In step S2, the titanium substrate adopts a TC4 titanium alloy substrate with a thickness of 5mm to 10mm. The heat input parameters of the welding machine for preheating the titanium substrate are: peak current of 280A to 320A; peak duty cycle of 28% to 32%; pulse frequency of 1.0Hz; base current of 90A to 110A, and the number of preheating passes of the titanium substrate is 2 times.

9. The method for preparing a high entropy titanium alloy gradient structure according to claim 1, characterized in that: The layer height of a single layer of the TaMoNbZrTi high entropy alloy deposition layer is 1.8 mm to 2.2 mm; the layer height of a single layer of the NbZrTi medium entropy alloy deposition layer is 1.5 mm to 1.9 mm; and the layer height of a single layer of the TA15 titanium alloy deposition layer is 1.9 mm to 2.1 mm.

10. A high entropy alloy titanium alloy gradient structure, characterized in that: The method is prepared by any one of claims 1 to 9.

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