Cu-cr-nb-ti alloy and method for manufacturing the same

Abstract

The application designs a Cu-Cr-Nb-Ti alloy for the first time, and develops a 3D printing process and a heat treatment process matched with the alloy.The alloy comprises the following components in mass percentage: Cr 1.6-1.7wt.%, Nb 1.3-2.2wt.%, Ti 0.1-0.2wt.%, and the balance being copper; the product comprises a 3D printing state and a heat treatment state; wherein the relative density of the 3D printing state product is higher than 99%; the microhardness, the tensile strength and the electrical conductivity of the heat treatment state product are 1.05-2 times, 1.05-1.75 times and 3.5-5 times of those of the 3D printing state product respectively.The component design of the application is reasonable, the 3D printing process window is wide, the preparation process is simple, the performance of the obtained product is excellent, and the product is convenient for large-scale industrial application.

Description

TECHNICAL FIELD

[0001] The present application relates to a Cu-Cr-Nb-Ti alloy and a preparation method thereof, and belongs to the technical development field of Cu-Cr-Nb alloys. BACKGROUND

[0002] The Cu-Cr-Nb alloy has excellent mechanical properties, electrical conductivity and high-temperature stability, and has a broad application prospect in the fields of aerospace engines, nuclear energy and power systems. Since the United States NASA carried out research in this regard, the Cu-Cr-Nb alloy has attracted widespread attention.

[0003] The solubility of Cr and Nb atoms in the copper matrix of Cu-Cr-Nb alloys is small, which is easy to form Cr2Nb phase. The melting point of Cr2Nb phase is high, and the elastic modulus and hardness are high, which is difficult to effectively control by subsequent processing, and seriously affects the comprehensive performance of the alloy. At present, the preparation methods of Cu-Cr-Nb alloy mainly include melt spinning, casting-deformation processing, powder metallurgy, etc. The strip-shaped Cu-2Cr-0.5Nb (at.%) alloy prepared by melt spinning has fine grains and uniform composition [Ellis D, et al. Formation of Cr and Cr2Nb precipitates in rapidly solidified Cu-Cr-Nb ribbon[J]. Ultramicroscopy, 1989, 30(1): 210-216.]. The mechanical properties of Cu-Cr-Nb alloy prepared by casting-deformation processing are excellent, in which the tensile strength of Cu-0.47Cr-0.16Nb (wt.%) alloy at room temperature reaches 453 MPa [Guo X, et al. Microstructure and properties of Cu-Cr-Nb alloy with high strength, high electrical conductivity and good softening resistance performance at elevated temperature[J]. Materials Science and Engineering: A, 2019, 749: 281-290.], and the microhardness of Cu-2Cr-1.35Nb-0.15Zr alloy can reach 126 HV [Yang Y, et al. Development of novel Cu-Cr-Nb-Zr alloys with the aid of computational thermodynamics[J]. Materials & Design, 2018, 156: 370-380.]. However, the copper alloy material prepared by deformation processing will recrystallize at high temperature, which leads to the softening of the alloy and reduces the high-temperature service performance of the alloy. At present, the powder metallurgy processes used for the preparation of Cu-Cr-Nb alloy mainly include hot-pressing sintering and spark plasma sintering (SPS).Cu-8Cr-4Nb (at.%) alloy with high density can be prepared by hot-pressing sintering [Shukla A, et al. Densification behavior and mechanical properties of Cu-Cr-Nb alloy powders [J]. Materials Science and Engineering: A, 2012, 551: 241-248.], but the sintering temperature is high, reaching 1000°C, and the Cr2Nb phase grows. The tensile strength of Cu-2Cr-1Nb (at.%) alloy prepared by SPS can reach 332 MPa [Lv X, et al. Effect of heat treatment on Cr2Nb phase and properties of spark plasma sintered Cu-2Cr-1Nb alloy [J]. Materials, 2020, 13(12): 2860.]; the microhardness of Cu-2Cr-1.35Nb-0.15Zr (wt.%) alloy reaches 133 HV, and the electrical conductivity is 74.6% IACS [Cheng B, et al. Tailoring microstructure in sintered Cu-Cr-Nb-Zr alloys for fusion components [J]. Journal of Nuclear Materials, 2021, 551: 152956.]. The size of the alloy prepared by SPS process is small, which is difficult to meet the demand of large-size components. Therefore, it is urgent to develop a preparation process of large-size high-performance Cu-Cr-Nb alloy.

[0004] The cooling rate of additive manufacturing is fast, which can effectively refine the grain and improve the comprehensive performance of the alloy. The additive manufacturing technology can be used to integrally prepare complex-shaped parts. However, copper alloy has high laser reflectivity, and the porosity of the Cu-Cr-Nb alloy formed by laser additive manufacturing is high, which seriously affects the performance of the alloy. The hot isostatic pressing treatment of the formed part can effectively eliminate small size pores, but the tensile strength is significantly reduced. Ren Yake [Ren Yake, et al. Process parameter optimization of selective laser melting of Cu-Cr-Nb alloy [J]. Powder Metallurgy Materials Science and Engineering, 2022, 27(1): 66-76.] used the optimal SLM process parameters to prepare Cu-1.93Cr-0.74Nb(at.%) alloy, and the relative density was 99.3%. Seltzman [Seltzman A, et al. Fracture characteristics and heat treatment of laser powderbed fusion additively manufactured GRCop-84 copper [J]. Materials Science and Engineering: A, 2021: 141690.] used SLM to prepare Cu-8Cr-4Nb(at.%) alloy, and the tensile strength reached 740MPa, and the elongation was 20%. Ai Yongkang [Ai Yongkang, et al. High temperature stability of microstructure and properties of Cu-Cr-Nb-Ce alloy prepared by selective laser melting [J]. Powder Metallurgy Materials Science and Engineering, 2022, 27(5): 1-9.] found that the grain morphology did not change significantly, and the second phase grew significantly after 1000℃ high temperature heat treatment. After 10, 50 and 100h, the microhardness of the alloy decreased from 126HV to 84, 79 and 75HV, and the electrical conductivity was 54.6%IACS after 10h heat treatment.

[0005] It is found that so far there is little report on the technology of using 3D printing to prepare Cu-Cr-Nb-Ti alloy and increasing the mechanical and electrical properties of the material by appropriate low temperature heat treatment. SUMMARY

[0006] The present application first designs a Cu-Cr-Nb-Ti alloy, and develops a 3D printing process and a heat treatment process matched therewith.

[0007] The Cu-Cr-Nb-Ti alloy according to the present application comprises the following components in mass percentage:

[0008] Cr 1.6-1.7wt.%, Nb 1.3-2.2wt.%, Ti 0.1-0.2wt.%, the balance being copper; the product includes a 3D printing state and a heat treated state; wherein the relative density of the 3D printing state product is higher than 99%; the microhardness of the heat treated state product is 1.05-2 times the microhardness of the 3D printing state product, the microhardness of the heat treated state product is greater than 145HV; the tensile strength is 1.05-1.75 times the tensile strength of the 3D printing state product; the electrical conductivity is 3.5-5 times the electrical conductivity of the 3D printing state product.

[0009] The application discloses a preparation method of a Cu-Cr-Nb-Ti alloy, which comprises the following steps:

[0010] Step one

[0011] The Cu-Cr-Nb-Ti alloy powder with a designed composition is used as raw material powder, and a 3D printing state product is prepared by adopting an SLM process; during 3D printing, the power is controlled to be 300-350 W, preferably 300-330 W; and the scanning speed is controlled to be 600-900 mm / s, preferably 650-800 mm / s.

[0012] Step two

[0013] The 3D printing state product obtained in step one is taken as a processing object, and is directly aged at 450-600 DEG C, preferably 450-550 DEG C for 5-360 min, preferably 10-60 min, and more preferably 20-30 min.

[0014] The application discloses a preparation method of a Cu-Cr-Nb-Ti alloy, wherein the particle size of the raw material powder is less than 100 microns, and is preferably 4-98 microns.

[0015] The raw material powder is prepared as follows:

[0016] The melting point of pure Cu is 1083 DEG C, the melting point of pure Cr is 1907 DEG C, the melting point of pure Nb is 2468 DEG C, and the melting point of pure Ti is 1668 DEG C; a Cr-Nb intermediate alloy with a melting point of 1640-1660 DEG C is selected as a raw material. The Cr-Nb intermediate alloy is prepared by vacuum arc melting, and the vacuum degree is kept to be higher than 0.1 Pa; in order to ensure the uniformity of the ingot composition and the complete melting of Cr and Nb, the stirring is carried out for 2-5 min after the complete melting of Cr and Nb, and then the cooling and solidification are carried out, and then the above steps are repeated more than three times.

[0017] Cr-Nb alloy prepared by arc melting, electrolytic copper (> 99.99%), Cu-Cr intermediate alloy and sponge titanium (> 99.7%) as raw materials for gas atomization powder preparation, alloy powder is prepared by the tight coupling argon gas atomization system produced by British PSI company, graphite crucible is used as the crucible, the melting temperature is 1600-1680 DEG C, the holding time is 10-40 min, the furnace pressure is 0.22-0.23 bar, and the gas pressure is 3.5-4.5 MPa. Because Ti is active, it is added 3-5 min before spraying. The Cu-Cr-Nb-Ti alloy powder with suitable particle size is screened by using a vibrating screening device.

[0018] The application discloses a preparation method of a Cu-Cr-Nb-Ti alloy; during 3D printing, the layer thickness is controlled to be 25-50 mu m, preferably greater than or equal to the average particle size of the powder, such as 30-40 mu m; the lap spacing is 0.08-0.12 mm, preferably 0.08-0.1 mm; and the interlayer rotation angle is 67 degrees, and a snake-shaped scanning strategy is adopted during 3D printing.

[0019] The powder particle size is normally distributed, and the average particle size is 34-35 mu m.

[0020] The application discloses a preparation method of a Cu-Cr-Nb-Ti alloy; during 3D printing, the layer thickness is controlled to be 25-50 mu m, preferably greater than or equal to the average particle size of the powder, such as 30-40 mu m; the lap spacing is 0.08-0.12 mm, preferably 0.08-0.1 mm; and the interlayer rotation angle is 67 degrees, and a snake-shaped scanning strategy is adopted during 3D printing.

[0021] The application discloses a preparation method of a Cu-Cr-Nb-Ti alloy; when the scanning rate is 800 mm / s and the laser power is 300 W, the surface roughness of the Cu-Cr-Nb-Ti alloy is 15.6 mu m.

[0022] The application discloses a preparation method of a Cu-Cr-Nb-Ti alloy; after 360 min of heat treatment, the Cu-Cr-Nb-Ti alloy prepared in a heat-treated state has double-scale second phases with a size of 25-50 nm and less than 10 nm, and the second phases are dispersedly distributed in the alloy matrix. By comparing the second phases of alloys with different aging temperatures, it is found that with the increase of the aging temperature, the number of the second phases in the alloy increases, especially the number of the second phases with a small size. In addition, with the increase of the aging temperature, the morphology of the second phases changes obviously. The second phases in the alloy aged at 450 DEG C-550 DEG C are in a granular shape. The second phases in the alloy aged at 600 DEG C have rod-like and granular morphologies, and the second phases obviously agglomerate.

[0023] The application discloses a preparation method of a Cu-Cr-Nb-Ti alloy, and the 3D printing process parameters are as follows: the power is 325 W, and the scanning speed is 800 mm / s when the composition of raw materials used for the 3D printing part is as follows: Cr is 1.65 wt.%, Nb is 1.35 wt.%, Ti is 0.12 wt.%, and the balance is copper.

[0024] When the aging temperature is 450 DEG C, the peak hardness of the alloy is reached after aging for 120 min, and is 262 HV 0.2 .

[0025] When the aging temperature is 500 DEG C, the peak hardness of the alloy is reached after aging for 30 min, and is 260 HV 0.2 .

[0026] When the aging temperature is 550 DEG C and 600 DEG C, the peak hardness of the alloy is reached after aging for 10 min, and is 243 HV 0.2 and 219 HV 0.2 .

[0027] With the increase of the temperature, the time for the Cu-Cr-Nb-Ti alloy to reach the peak hardness is shortened, and the peak hardness is obviously reduced.

[0028] The application discloses a preparation method of a Cu-Cr-Nb-Ti alloy, and the 3D printing process parameters are as follows: the power is 325 W, and the scanning speed is 800 mm / s when the composition of raw materials used for the 3D printing part is as follows: Cr is 1.65 wt.%, Nb is 1.35 wt.%, Ti is 0.12 wt.%, and the balance is copper.

[0029] When the direct aging process is 450 DEG C / 120 min, the microhardness of the Cu-Cr-Nb-Ti alloy is 262 HV 0.2 . When the direct aging process is 600 DEG C / 360 min, the alloy is most seriously softened, and the microhardness is only 148 HV 0.2 , which is close to the microhardness (139 HV 0.2 ) of the SLM forming part.

[0030] It is also found in the technical development process that the electrical conductivity of the alloy is continuously increased with the increase of the aging time under different temperatures; the higher the aging temperature is, the higher the electrical conductivity of the alloy is. When the direct aging process is 600 DEG C / 360 min, the electrical conductivity of the Cu-Cr-Nb-Ti alloy is 77.1 %IACS. When the aging process is 450 DEG C / 360 min, 500 DEG C / 360 min and 550 DEG C / 360 min, the electrical conductivities of the alloy are 60.9 %IACS, 66.8 %IACS and 70.1 %IACS respectively.

[0031] Combined with microhardness and electrical conductivity analysis, the optimized SLM prepared Cu-Cr-Nb-Ti alloy is aged at 500℃ for 30min, and the product with microhardness of 260HV, tensile strength of 728MPa and electrical conductivity of 59.4%IACS can be obtained. 0.2 , the tensile strength is 728MPa, and the electrical conductivity is 59.4%IACS.

[0032] The present application discloses a preparation method of Cu-Cr-Nb-Ti alloy, when the composition of the raw material for the 3D printed part is: Cr1.65wt.%, Nb1.35wt.%, Ti0.12wt.%, and the balance is copper, the 3D printing process parameters are: power 325W, scanning speed 800mm / s, and the printed Cu-Cr-Nb-Ti alloy is prepared.

[0033] When the aging temperature is 500℃, the yield strength of the product obtained by aging for 10-360min is 490-622MPa, and the ultimate tensile strength is 616-728MPa.

[0034] The components and printing process designed by the present application can improve the yield strength of the product to 611-622MPa and the ultimate tensile strength to 695-728MPa within 10-30min by aging at 500℃.

[0035] The present application discloses a preparation method of Cu-Cr-Nb-Ti alloy, when the composition of the raw material for the 3D printed part is: Cr1.65wt.%, Nb1.35wt.%, Ti0.12wt.%, and the balance is copper, the 3D printing process parameters are: power 325W, scanning speed 800mm / s, and the printed Cu-Cr-Nb-Ti alloy is prepared.

[0036] When the alloy is aged at 450℃, 550℃ and 600℃ for 360min, the yield strength is 626MPa, 384MPa and 271MPa respectively, and the ultimate tensile strength is 708MPa, 526MPa and 428MPa respectively.

[0037] Principle and advantage

[0038] 1、The present application first designs a Cu-Cr-Nb-Ti alloy, and the SLM process window of the designed Cu-Cr-Nb-Ti alloy is obviously wider than that of Cu-Cr-Nb alloy, which is beneficial to the preparation of high relative density Cu-Cr-Nb-Ti formed parts.

[0039] 2、Based on the first designed Cu-Cr-Nb-Ti alloy, the present application develops a 3D printing process and a heat treatment process matched therewith;

[0040] 3. The Cu-Cr-Nb-Ti alloy direct aging process is designed for the first time, and a low-temperature short-time aging process for rapidly improving mechanical properties and electrical properties (especially electrical conductivity) is explored;

[0041] 4. The Cu-Cr-Nb-Ti alloy prepared by appropriate parameters has a print state XY plane organization composed of fine crystals in the center of the molten pool channel and coarse crystals on both sides, an XZ plane organization composed of water drop-shaped grains, long columnar crystals and equiaxed crystals, and a multi-scale coordinated grain organization;

[0042] 5. The Cu-Cr-Nb-Ti alloy prepared by appropriate parameters has a print state organization with fine and dispersed second phases with a size of 28-50nm; the size of the second phase in the fine crystal is smaller than that in the coarse crystal;

[0043] 6. The print state Cu-Cr-Nb-Ti alloy is subjected to appropriate heat treatment, and a uniformly distributed double-scale nanometer second phase with a size of 25-50nm and less than 10nm is formed in the matrix, and the strength and electrical conductivity are simultaneously improved. BRIEF DESCRIPTION OF DRAWINGS

[0044] APPENDIX Figure 1 The particle size distribution diagram of the raw material powder used for the examples;

[0045] APPENDIX Figure 2 The morphology characterization diagram of the raw material powder used for the examples;

[0046] APPENDIX Figure 3 The characterization diagram of the influence of different 3D printing process parameters on the relative density of the Cu-Cr-Nb-Ti alloy forming piece;

[0047] APPENDIX Figure 4 The characterization diagram of the surface roughness of the Cu-Cr-Nb-Ti alloy forming piece obtained by different 3D printing process parameters;

[0048] Figure 5 The microstructure characterization diagram of the Cu-Cr-Nb-Ti alloy prepared by different process parameters;

[0049] Figure 6 The influence diagram of direct aging on the microhardness and electrical conductivity of the Cu-Cr-Nb-Ti alloy;

[0050] Figure 7 The XRD pattern of the Cu-Cr-Nb-Ti alloy aged at 500 DEG C for different times;

[0051] Figure 8 The microstructure characterization diagram of the XY plane of the Cu-Cr-Nb-Ti alloy aged at 500 DEG C for different times;

[0052] Figure 9 Tensile property diagram of Cu-Cr-Nb-Ti alloy aged at 500℃ for different time.

[0053] Figure 10 Tensile property diagram of Cu-Cr-Nb-Ti alloy aged at 450, 550 and 600℃. DETAILED DESCRIPTION

[0054] 1. Raw material preparation

[0055] The melting point of pure Cu is 1083℃, the melting point of pure Cr is 1907℃, the melting point of pure Nb is 2468℃, and the melting point of pure Ti is 1668℃. If pure metals are vacuum melted, the melting points of each raw material differ greatly, which will cause serious burning loss of raw materials. Therefore, the experiment selects Cr-Nb intermediate alloy with a melting point of 1650℃ as the raw material. The Cr-Nb intermediate alloy is prepared by vacuum arc melting, and the vacuum degree is maintained above 0.1 Pa. To ensure the uniformity of the ingot composition, after Cr and Nb are fully melted, stirring for 2 min, cooling and solidification, then repeat the above steps for 3 times.

[0056] The Cr-Nb alloy prepared by arc melting is used as the raw material for gas atomization powder preparation together with electrolytic copper (>99.99%), Cu-Cr intermediate alloy and titanium sponge (>99.7%). The alloy powder is prepared by a tight-coupling argon gas atomization system produced by the British PSI company, the crucible is graphite crucible, the melting temperature is 1600-1680℃, the holding time is 30 min, the furnace pressure is 0.22-0.23 bar, and the gas pressure is 3.5-4.5 MPa. Ti is added 5 min before spraying due to its high activity. The Cu-Cr-Nb-Ti alloy powder with a particle size of 15-61 μm is screened out by using a vibrating screening device as the raw material powder. The specific composition is shown in Table 1.

[0057] Table 1 Chemical composition table of raw material powder

[0058]

[0059] The particle size of the raw material powder ranges from 4.6 to 98.1 μm, the average particle size is 34.8 μm, and Dv(10), Dv(50) and Dv(90) are 12.5 μm, 32.6 μm and 68.9 μm respectively. The powder particle size shows a logarithmic normal distribution, which is relatively concentrated (as shown in Figure 1 The scanning electron microscope image of the raw material powder morphology is shown in Figure 2 ; Figure 2 Composed of four figures (a), (b), (c), (d), wherein Figure 2 (a) is the overall morphology of the powder, Figure 2 (b) is the morphology of the large particle powder, Figure 2(c) small particle powder morphology, Figure 2 (d) is Figure 2 (c) local morphology of the corresponding powder. It can be seen from the figure that most of the Cu-Cr-Nb-Ti alloy powder has good sphericity, and only a few powders are irregularly shaped, and some powders are satellite powders with small size powder particles adhering to the surface.

[0060] Table 2 SLM laser power, scanning rate and part number

[0061]

[0062] Table 2 SLM laser power, scanning rate and part number. The layer thickness used in the specific embodiments of the present application is 30 μm, the overlap distance is 0.1 mm, the interlayer rotation angle is 67°, and the serpentine scanning strategy is used.

[0063] The 3D printing series experiments were carried out according to the above Table 2, and the performance of the products was detected, as shown in Figures 3-5 .

[0064] Figure 3 consisting of four figures (a), (b), (c) and (d), Figure 3 (a) is the curve of relative density with laser power at different scanning rates, Figure 3 (b) is the curve of relative density with scanning rate at different laser powers, Figure 3 (c) is the relationship between bulk energy density and relative density (the same color symbol represents the same laser power part, and the dashed line box represents the same scanning rate part), Figure 3 (d) is the forming process window of Cu-Cr-Nb-Ti alloy (the dashed line box represents the preparation parameters of the parts with relative density greater than 99%), Figure 3 (a) It is found that there is a nonlinear relationship between relative density and laser power. From Figure 3 (b) it can be seen that there is also a nonlinear relationship between relative density and scanning rate. From the results of Figure 3 (a) and (b), the relative density of the Cu-Cr-Nb-Ti alloy part prepared by using laser power of 325 W and scanning rate of 800 mm / s is the highest, reaching 99.26%. From Figure 3 (c) it can be seen that there is a large difference in the relative density of the Cu-Cr-Nb-Ti alloy parts prepared at similar bulk energy densities. The influence of bulk energy density on relative density is constrained by scanning rate and laser power. The relative density of samples prepared by using the same scanning rate but different laser powers has little difference. At the same time, the relative density of samples prepared by using the same laser power but different scanning rates has large difference. From Figure 3(d)It can be seen that the process parameter combination corresponding to the relative density greater than 99.0% is regarded as the best process window (in the dashed line box). The SLM process window of the Cu-Cr-Nb-Ti alloy is obviously wider than that of the Cu-Cr-Nb alloy, which is conducive to the preparation of high relative density Cu-Cr-Nb-Ti formed parts.

[0065] From Figure 4 It can be seen that the minimum surface roughness of the alloy is 15.6 μm, and the maximum surface roughness is 24.1 μm. By comparing the surface roughness of the formed parts prepared by different process parameters, it can be found that at the same laser power, the surface roughness decreases first and then increases with the increase of the scanning speed; and at the same scanning speed, the change trend of the surface roughness has no obvious connection with the laser power. This shows that the influence of the scanning speed on the surface roughness of the Cu-Cr-Nb-Ti alloy formed part is greater than that of the laser power.

[0066] Figure 5 The metallographic structure photos of the XZ plane of the formed parts (the porosity in the lower left corner, the relative density higher than 99% is marked with a red frame, the formed part with irregularly shaped pores is marked with a blue frame, and the formed part with circular pores is marked with a green frame), the defects of the Cu-Cr-Nb-Ti formed part are mainly pores, and no cracks are observed. By counting the porosity of the formed part, it is found that the porosity of the formed part with a relative density higher than 99% (the five samples in the red dashed line box) is lower than 0.5%. At the same laser power, the minimum porosity appears in the formed part with a scanning speed of 800 mm / s, which is consistent with the Figure 3 (b) shown in the relative density change of the formed part.

[0067] The 3D printed products (formed parts prepared at a laser power of 325 W and a scanning speed of 800 mm / s) are heat treated according to the process parameters in Table 3 below; during heat treatment, the heating rate is 10 ℃ / min;

[0068] Table 3 Heat treatment process parameters

[0069]

[0070] The properties of each product after heat treatment are shown in Figures 6-9 .

[0071] Figure 6 Composed of (a) and (b), wherein Figure 6 (a) is a curve graph of the influence of aging process on the microhardness of the product; Figure 6 (b) is a curve graph of the influence of aging process on the electrical conductivity of the product. Figure 6(a) shows the effect of direct aging on the microhardness of Cu-Cr-Nb-Ti alloy. It can be seen that at different temperatures, the microhardness of the alloy increases first and then decreases with the increase of aging time, but the aging time to reach the peak hardness is different. With the increase of temperature, the time to reach the peak hardness of Cu-Cr-Nb-Ti alloy is shortened, and the peak hardness is obviously reduced. When the direct aging process is 450℃ / 120min, the microhardness of Cu-Cr-Nb-Ti alloy is the highest. Figure 6 (b) shows the effect of direct aging on the electrical conductivity of Cu-Cr-Nb-Ti alloy. It can be found that at different temperatures, the electrical conductivity of the alloy increases with the increase of aging time; the higher the aging temperature, the higher the electrical conductivity of the alloy. When the direct aging process is 600℃ / 360min, the electrical conductivity of Cu-Cr-Nb-Ti alloy is the best, which is 77.1%IACS. Combined with the analysis of microhardness and electrical conductivity, the best aging process of Cu-Cr-Nb-Ti alloy prepared by SLM is 500℃ / 30min, the microhardness is 260HV 0.2 , and the electrical conductivity is 59.4%IACS.

[0072] Figure 7 consisting of (a), (b), wherein Figure 7 (a) is the XRD pattern of XY plane, Figure 7 (b) is the XRD pattern of XZ plane. It can be seen from Figure 7 that all the formed parts have the same diffraction peaks, i.e. Cu(111), (200) and (220) crystal face peaks, and no related diffraction peaks of Cr, Nb, Ti, etc. are present. From Figure 7 (a), it can be found that the Cu(220) peak is the strongest, and the Cu(200) peak is the weakest; the intensity of Cu(220) diffraction peak decreases with the increase of aging time, while the intensity of Cu(111) and Cu(200) peaks increases. From Figure 7 (b), it can be seen that the Cu(111) peak of XZ plane is the strongest, and the Cu(220) peak is the weakest; the intensity of Cu(111) peak decreases with the extension of aging time. It can be known that the extension of aging time will lead to the weakening of the preferred orientation degree of the alloy grains.

[0073] Figure 8 consisting of (a), (b), (c), (d), (e), (f). Among them, Figure 8 (a), (c), (e) are respectively the characterization diagrams of the second phase in the large-size grains of the alloy aged at 500℃ for 10min, 30min and 360min; Figure 8 (b), (d), (f) are respectively the characterization diagrams of the second phase in the small-size grains of the alloy aged at 500℃ for 10min, 30min and 360min. From Figure 8It can be seen that: after aging treatment, the Cu-Cr-Nb-Ti alloy has double-scale second phases, 25-50 nm and less than 10 nm, which are fine and dispersed in the alloy grains. Extending the aging time, the number of near-spherical second phases decreases, and the number of cubic second phases increases.

[0074] Figure 9 consisting of (a), (b), wherein Figure 9 (a) is a stress-strain curve diagram after heat treatment, Figure 9 (b) is a yield strength, ultimate tensile strength and elongation diagram of the product after heat treatment. It can be seen that: Figure 9 The yield strength of the alloys aged at 500℃ for 10min, 30min and 360min is 611MPa, 622MPa and 490MPa respectively, the ultimate tensile strength is 695MPa, 728MPa and 616MPa respectively, and the elongation is 11.5%, 16.3% and 13.7% respectively. At the same temperature, with the extension of aging time, the mechanical properties of Cu-Cr-Nb-Ti alloy first increase and then decrease. Among them, the mechanical properties of the alloy aged for 30min are the best, and the strength is significantly better than that of Cu-Cr-Nb-Ti in the printing state (the yield strength of the printing state is 293MPa, and the ultimate tensile strength is 416MPa), but the elongation decreases (the elongation of the printing state is 27.8%). After aging for 360min, the mechanical properties of the alloy decrease, and obvious softening occurs. This shows that 500℃ / 30min is the best direct aging process for SLM prepared Cu-Cr-Nb-Ti alloy. Figure 10 consisting of (a), (b), wherein Figure 10 (a) is a stress-strain curve diagram after heat treatment, Figure 10 (b) is a yield strength, ultimate tensile strength and elongation diagram of the product. The yield strength of the alloys aged at 450℃, 550℃ and 600℃ for 360min is 626MPa, 384MPa and 271MPa respectively, the ultimate tensile strength is 708MPa, 526MPa and 428MPa respectively, and the elongation is 11%, 16.7% and 17.9% respectively. All are lower than the mechanical properties of Cu-Cr-Nb-Ti alloy aged at 500℃ / 30min.

Claims

1. A Cu-Cr-Nb-Ti alloy, characterized by: comprises the following components in mass percentage: Cr 1.6-1.7 wt.%, Nb 1.3-2.2 wt.%, Ti 0.1-0.2 wt.%, and the balance being copper; the product comprises a 3D printing state and a heat treated state; wherein the relative density of the 3D printing state product is higher than 99%; the microhardness of the heat treated state product is greater than 145 HV; the tensile strength is 1.05-1.75 times that of the 3D printing state product; the electrical conductivity is 3.5-5 times that of the 3D printing state product; The Cu-Cr-Nb-Ti alloy is prepared by the following steps: Step one The Cu-Cr-Nb-Ti alloy powder with the designed composition is used as the raw material powder, and a 3D printing state product is prepared by using a selective laser melting process; during 3D printing, the power is controlled to be 325 W, and the scanning speed is controlled to be 800 mm / s; Step two The 3D printing state product obtained in step one is used as the processing object, and is directly aged at 450-550 ℃ for 10-60 min; the second phase in the alloy aged at 450 ℃-550 ℃ is in a granular shape; The raw material powder is prepared by the following method: The melting point of pure Cu is 1083 ℃, the melting point of pure Cr is 1907 ℃, the melting point of pure Nb is 2468 ℃, and the melting point of pure Ti is 1668 ℃; if the pure metals are vacuum melted, a Cr-Nb intermediate alloy with a melting point of 1640-1660 ℃ is selected as the raw material; the Cr-Nb intermediate alloy is prepared by vacuum arc melting, and the vacuum degree is kept to be higher than 0.1 Pa; in order to ensure that the composition of the Cr-Nb intermediate alloy ingot is uniform and Cr and Nb are fully melted, the Cr-Nb intermediate alloy is stirred for 1-5 min after being fully melted, and then is cooled and solidified; the above steps are repeated more than 3 times; The Cr-Nb alloy prepared by arc melting is used as the raw material for gas atomization powder preparation together with electrolytic copper, a Cu-Cr intermediate alloy and titanium sponge, and an alloy powder is prepared by a tight coupling argon gas atomization system; a graphite crucible is used as the crucible, the melting temperature is 1600-1680 ℃, the holding time is 10-40 min, the furnace pressure is 0.22-0.23 bar, and the gas pressure is 3.5-4.5 MPa; Ti is added 3-5 min before spraying due to its high activity; a vibrating screening device is used to screen the Cu-Cr-Nb-Ti alloy powder with a suitable particle size.

2. The Cu-Cr-Nb-Ti alloy according to claim 1, characterized in that: The particle size of the raw material powder used is less than 100 μm.

3. The Cu-Cr-Nb-Ti alloy according to claim 1, characterized in that: During 3D printing, the layer thickness is controlled to be 25-50 μm, the overlapping distance is 0.08-0.12 mm, and the interlayer rotation angle is 67°; a snake-shaped scanning strategy is used during 3D printing.

4. The Cu-Cr-Nb-Ti alloy according to claim 1, characterized by: The Cu-Cr-Nb-Ti alloy prepared in the heat treated state has double-scale second phases with a size of 25-50 nm and less than 10 nm, which are dispersedly distributed in the alloy grains.

5. The Cu-Cr-Nb-Ti alloy according to claim 1, characterized by: When the composition of the raw material used for 3D printing is: Cr 1.65 wt.%, Nb 1.35 wt.%, Ti 0.12 wt.%, and the balance being copper, the 3D printing process parameters used are: power 325 W, scanning speed 800 mm / s, to prepare a printing state Cu-Cr-Nb-Ti alloy; The peak hardness of 262 HV was reached after aging the alloy for 120 min at 450 °C 0.2 ; The peak hardness of 260 HV was reached after aging the alloy for 30 min at 500 °C 0.2 ; The aging temperature is 550 ℃, and the alloy can reach the peak hardness after aging for 10 min, and the peak hardness is 243 HV 0.2 ; The electric conductivity of the alloy is 60.9% IACS, 66.8% IACS and 70.1% IACS respectively at 450℃, 500℃ and 550℃; When the aging temperature is 500℃, the yield strength of the product aged for 10-360min is 490-622MPa, and the ultimate tensile strength is 616-728MPa.

6. The Cu-Cr-Nb-Ti alloy according to claim 1, characterized in that: In combination with the aging temperature of 500℃, the yield strength of the product is increased to 610-622MPa within 10-30min, and the ultimate tensile strength is 695-728MPa.

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