Layered regulation and control method for microstructure of additive manufacturing titanium-aluminum alloy

Abstract

The invention provides an additive manufacturing titanium-aluminum alloy microstructure layering regulation and control method which comprises the following steps: (1) preheating a bottom plate in electron beam selective melting equipment, and then laying titanium-aluminum alloy powder on the bottom plate; (2) setting a printing model and parameters for printing the titanium-aluminum alloy, starting an electron beam to sequentially carry out powder bed preheating and filling scanning printing on the titanium-aluminum alloy powder in the step (1), and cooling to obtain the titanium-aluminum alloy of which the microscopic structure is not layered or the microscopic structure is layered into one level; the powder bed preheating comprises first preheating and second preheating which are carried out in sequence; the first preheated beam is smaller than the second preheated beam. The titanium-aluminum alloy powder laid on the preheated bottom plate is sequentially subjected to powder bed preheating and filling scanning printing, the powder bed preheating mode is optimized, and the titanium-aluminum alloy with the ideal structure morphology and the excellent comprehensive performance is obtained on the premise that the time cost and auxiliary equipment are not additionally increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing of titanium aluminide alloys, and relates to a method for hierarchical regulation of the microstructure of additive manufactured titanium aluminide alloys. Background Art

[0002] At present, the processing methods of TiAl alloys mainly include casting, ingot metallurgy and powder metallurgy technologies. The casting method is relatively mature. Through investment casting (including gravity casting and centrifugal casting) and permanent die casting technologies, TiAl alloy components such as compressor blades and turbine blades can be manufactured. However, due to the high solidification shrinkage rate of TiAl alloys and poor castability, it will lead to insufficient casting, and shrinkage cavities and inclusion defects often occur. In addition, in order to avoid the reaction between the highly reactive TiAl alloy and the ceramic crucible under melting, a cold crucible is used in the casting process, resulting in a decrease in superheat capacity. Therefore, the mold needs to be preheated, and the preheating operation may cause the grains of the formed part to be coarse and large lamellar structures to appear, seriously affecting the performance of the formed part.

[0003] Existing additive manufacturing is a potential technical means to replace precision casting for preparing titanium aluminide alloys. By finely adjusting the production process, additive manufacturing can control the growth of the microstructure, reduce the addition of surplus, and reduce the dependence of products on post-treatment. Electron beam selective melting (EBM) technology is a very promising additive manufacturing process. It uses metal powder as raw material and obtains formed specimens by selectively melting and layer-by-layer scanning with a focused electron beam under high vacuum. Since EBM can quickly near-net shape complex three-dimensional components, avoid oxidation to generate impurities, and does not waste materials with good economic benefits, it is a very promising TiAl alloy forming process and has attracted wide attention at home and abroad. However, the EBM forming of titanium aluminide alloys is very prone to tissue stratification phenomenon, as Figure 1 shown, resulting in a decrease in the comprehensive performance of the material.

[0004] In summary, there is an urgent need to provide a method for hierarchical regulation of the microstructure of additive manufactured titanium aluminide alloys to obtain titanium aluminide alloy component products with both ideal tissue morphology and excellent comprehensive performance. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for hierarchical regulation of the microstructure of additive manufactured titanium aluminide alloys. By optimizing the powder bed preheating method and combining the regulation of relevant parameter ranges in the bottom plate preheating, powder bed preheating and filling and scanning printing, without additional increasing the time cost and auxiliary equipment, effectively control the loss of Al element during the printing process, and then obtain titanium aluminide alloy components with high density and excellent tissue morphology.

[0006] To achieve the purpose of the present invention, the following technical solutions are adopted:

[0007] The present invention provides a method for hierarchical regulation of the microstructure of additive manufactured titanium aluminide alloys. The method comprises the following steps:

[0008] (1) Preheat the bottom plate in an electron beam selective melting equipment, and then lay titanium aluminide alloy powder on the bottom plate;

[0009] (2) Set the printing model and parameters for titanium aluminide alloy printing, and turn on the electron beam to sequentially perform powder bed preheating and filling scanning printing on the titanium aluminide alloy powder described in step (1). After cooling, a titanium aluminide alloy with no microstructure stratification or with microstructure stratification at the first level is obtained;

[0010] The powder bed preheating includes a first preheating and a second preheating performed sequentially; the beam current of the first preheating is less than the beam current of the second preheating.

[0011] In the present invention, before preheating the bottom plate, the titanium aluminide alloy powder is placed in an EBM powder bin, the bottom plate is placed in the forming chamber, and the bottom plate is in the central position.

[0012] The method provided by the present invention, by sequentially performing powder bed preheating and filling scanning printing on the titanium aluminide alloy powder laid on the preheated bottom plate, and combining with optimizing the powder bed preheating method, obtains a titanium aluminide alloy with both ideal tissue morphology and excellent comprehensive performance without additional time cost and auxiliary equipment.

[0013] It should be noted that by performing secondary preheating on the powder bed to increase the forming temperature, the overall energy fluctuation becomes smaller, thereby reducing the loss of aluminum element during the forming of titanium aluminide alloy. On the premise of ensuring the density, the tendency of microstructure stratification of titanium aluminide alloy is reduced.

[0014] As a preferred technical solution of the present invention, the beam current for preheating the bottom plate in step (1) is 40 - 80 mA, and the scanning speed is 15 - 35 m / s.

[0015] The preheating time of the bottom plate in step (1) > 40 min.

[0016] After preheating the bottom plate in step (1), the temperature of the bottom plate is 1050 - 1250 °C.

[0017] As a preferred technical solution of the present invention, by mass percentage, the titanium aluminide alloy powder in step (1) comprises the following elements: Al 29.8 wt% - 35.0 wt%, Mn 3.0 wt% - 6.0 wt%, Nb 2.0 wt% - 6.0 wt%, Cr 1.0 wt% - 4.0 wt%, B 0.1 wt% - 1.0 wt%, and the balance is Ti and unavoidable inclusions.

[0018] The atomic content of aluminum element in the titanium-aluminum alloy powder described in step (1) is 44.0 at% to 47.0 at%.

[0019] The particle size distribution of the titanium-aluminum alloy powder described in step (1) is 45 - 150 μm.

[0020] After laying in step (1), vacuum pumping treatment and filling with protective gas are successively carried out.

[0021] As a preferred technical solution of the present invention, the width of the powder bed preheating described in step (2) is 100 - 240 mm 2 ;

[0022] The scanning speed of the first preheating described in step (2) is 15 - 35 m / s.

[0023] The scanning speed of the second preheating described in step (2) is 15 - 40 m / s.

[0024] As a preferred technical solution of the present invention, the number of repetitions of the first preheating and the second preheating described in step (2) are each independently 1 - 80 times.

[0025] The beam current of the first preheating described in step (2) is 10 - 70 mA.

[0026] The beam current of the second preheating described in step (2) is 40 - 100 mA.

[0027] As a preferred technical solution of the present invention, the defocus value of the first preheating described in step (2) is less than the defocus value of the second preheating.

[0028] The defocus value of the first preheating described in step (2) is 10 - 200 mA.

[0029] The defocus value of the second preheating described in step (2) is 30 - 200 mA.

[0030] As a preferred technical solution of the present invention, the beam current of the filling scanning and printing described in step (2) is 3 - 30 mA, the scanning speed is 0.3 - 5 m / s, and the filling spacing is 0.03 - 0.3 mm.

[0031] The defocus value of the filling scanning and printing described in step (2) is -15 - -4 mA or 5 - 15 mA.

[0032] As a preferred technical solution of the present invention, during the cooling in step (2), the electron beam and the vacuum are turned off, and after filling with protective gas, cooling is carried out.

[0033] As a preferred technical solution of the present invention, after cooling in step (2), the microstructure of the titanium-aluminum alloy is observed, classified according to the microstructure characteristics, and then the grade of the obtained titanium-aluminum alloy is determined.

[0034] The grading includes being divided into 5 grades according to the microstructural morphology of the titanium aluminide alloy, specifically: grade zero means no lamination in the microstructure; grade one means there are contrast differences in the microstructure and γ bands with similar sizes, and the difference between the widths of each γ band is <1 times; grade two means there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is <50 μm; grade three means there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is ≥50 μm; grade four means the microstructures of each layer are different.

[0035] As a preferred technical solution of the present invention, the aluminum element loss of the titanium aluminide alloy in step (2) is ≤2.0 at%.

[0036] The density of the titanium aluminide alloy in step (2) is >99.5%.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The method provided by the present invention, by sequentially performing powder bed preheating and filling and scanning printing on the titanium aluminide alloy powder laid on the preheated bottom plate, combined with optimizing the powder bed preheating method, obtains a titanium aluminide alloy with both ideal microstructural morphology and excellent comprehensive performance without additional time cost and auxiliary equipment.

[0039] (2) The method provided by the present invention, by regulating the relevant parameter ranges in the bottom plate preheating, powder bed preheating and filling and scanning printing, can effectively control the loss of Al element during the printing process, and further reduce the tendency of microstructure lamination on the premise of ensuring the density of the titanium aluminide alloy; among them, the aluminum element loss of the prepared titanium aluminide alloy is ≤1.1 at%, the density is >99.5%, and there is no lamination in the microstructure or the microstructure lamination is grade one. Description of the Drawings

[0040] Figure 1 It is a microstructural diagram of a conventional electron beam selective melting formed titanium aluminide alloy provided by the present invention.

[0041] Figure 2 It is a microstructural diagram of the titanium aluminide alloy obtained by the method provided in Example 1 of the present invention.

[0042] Figure 3 It is a microstructural diagram of the titanium aluminide alloy obtained by the method provided in Example 2 of the present invention.

[0043] Figure 4 It is a microstructural diagram of the titanium aluminide alloy obtained by the method provided in Example 2 of the present invention after heat treatment.

[0044] Figure 5 It is a microstructural diagram of the titanium aluminide alloy obtained by the method provided in Example 3 of the present invention.

[0045] Figure 6 It is the microstructure diagram of the titanium-aluminum alloy obtained by the method provided in Comparative Example 2 of the present invention.

[0046] Figure 7 It is the microstructure diagram of the titanium-aluminum alloy obtained by the method provided in Comparative Example 2 of the present invention after heat treatment. Specific Embodiments

[0047] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0048] The specific embodiments of the present invention provide a method for hierarchical regulation of the microstructure of additively manufactured titanium-aluminum alloy, and the method includes the following steps:

[0049] (1) Preheat the bottom plate in the electron beam selective melting equipment, and then lay the titanium-aluminum alloy powder on the bottom plate;

[0050] (2) Set the printing model and parameters for printing the titanium-aluminum alloy, and turn on the electron beam to sequentially perform powder bed preheating and filling and scanning printing on the titanium-aluminum alloy powder in step (1), and after cooling, obtain a titanium-aluminum alloy with no microstructure stratification or the microstructure stratification being at the first level;

[0051] The powder bed preheating includes the first preheating and the second preheating performed in sequence; the beam current of the first preheating is less than the beam current of the second preheating.

[0052] In the present invention, the powder bed is first preheated with a smaller beam current, and then the powder bed is preheated with a larger beam current to sequentially complete the preheating of the powder bed.

[0053] In some embodiments of the present invention, the beam current for preheating the bottom plate in step (1) is 40-80 mA, for example, it can be 45 mA, 50 mA, 55 mA, 60 mA, 65 mA, 70 mA or 75 mA, etc., and the scanning speed is 15-35 m / s, for example, it can be 16 m / s, 18 m / s, 20 m / s, 22 m / s, 25 m / s, 26 m / s, 28 m / s, 30 m / s, 32 m / s or 34 m / s, etc., but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0054] In some embodiments of the present invention, the preheating time of the bottom plate in step (1) > 40 min, for example, it can be 42 min, 45 min, 46 min, 48 min, 20 min, 55 min or 60 min, etc., but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0055] In some embodiments of the present invention, after preheating the bottom plate in step (1), the temperature of the bottom plate is 1050-1250 °C, for example, it can be 1060 °C, 1080 °C, 1100 °C, 1120 °C, 1150 °C, 1160 °C, 1180 °C, 1200 °C, 1220 °C or 1240 °C, etc., but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0056] It should be noted that by optimizing the relevant parameter range of the bottom plate preheating, the stability of the printing initial environment can be ensured when forming titanium aluminide by EBM, and the phenomenon of powder blowing does not occur during the initial process of powder bed preheating.

[0057] In some embodiments of the present invention, in terms of mass percentage, the titanium aluminide powder in step (1) includes the following elements: Al 29.8wt% - 35.0wt%, Mn 3.0wt% - 6.0wt%, Nb 2.0wt% - 6.0wt%, Cr 1.0wt% - 4.0wt%, B 0.1wt% - 1.0wt%, and the balance is Ti and inevitable inclusions.

[0058] In the present invention, the mass content of Al in the titanium aluminide powder is 29.8wt% - 35.0wt%, for example, it can be 30.0wt%, 30.5wt%, 31.0wt%, 31.5wt%, 32.0wt%, 32.5wt%, 33.0wt%, 33.5wt%, 34.0wt% or 34.5wt%, etc., the mass content of Mn in the titanium aluminide powder is 3.0wt% - 6.0wt%, for example, it can be 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt% or 5.5wt%, etc., the mass content of Nb in the titanium aluminide powder is 2.0wt% - 6.0wt%, for example, it can be 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt% or 5.5wt%, etc., the mass content of Cr in the titanium aluminide powder is 1.0wt% - 4.0wt%, for example, it can be 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt% or 3.5wt%, etc., the mass content of B in the titanium aluminide powder is 0.1wt% - 1.0wt%, for example, it can be 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt% or 0.9wt%, etc., but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0059] In some embodiments of the present invention, the atomic content of aluminum element in the titanium-aluminum alloy powder in step (1) is 44.0 at% to 47.0 at%. For example, it can be 44.2 at%, 44.5 at%, 44.8 at%, 45.0 at%, 45.2 at%, 45.5 at%, 45.8 at%, 46.0 at%, 46.2 at%, 46.5 at% or 46.8 at% etc., but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0060] It should be noted that by optimizing the composition design of the titanium-aluminum alloy, reasonably regulating the content of alloying elements, and further controlling the range of Al atom content in the titanium-aluminum alloy, the tendency of microstructure delamination in the forming process of the titanium-aluminum alloy can be effectively reduced.

[0061] In some embodiments of the present invention, the particle size distribution of the titanium-aluminum alloy powder in step (1) is 45 - 150 μm.

[0062] In the present invention, the particle size distribution of the titanium-aluminum alloy powder only needs to meet the requirements of the EBM process, and those skilled in the art can determine it according to actual needs.

[0063] In some embodiments of the present invention, after laying in step (1), vacuum pumping treatment and filling with protective gas are successively carried out.

[0064] In the present invention, the vacuum pumping treatment is carried out until the pressure in the EBM equipment meets the requirements. For example, the vacuum pressure in the forming chamber should be ≤ 0.3 Pa, and the protective gas includes helium.

[0065] In some embodiments of the present invention, the width of the powder bed preheating in step (2) is 100 - 240 mm 2 , for example, it can be 100 mm 2 , 140 mm 2 , 160 mm 2 , 170 mm 2 , 180 mm 2 , 190 mm 2 , 200 mm 2 , 220 mm 2 or 230 mm 2 etc., but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0066] In some embodiments of the present invention, the scanning speed of the first preheating in step (2) is 15-35 m / s. For example, it can be 16 m / s, 18 m / s, 20 m / s, 22 m / s, 25 m / s, 26 m / s, 28 m / s, 30 m / s, 32 m / s or 34 m / s, etc., but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0067] In some embodiments of the present invention, the scanning speed of the second preheating in step (2) is 15-40 m / s. For example, it can be 16 m / s, 18 m / s, 20 m / s, 22 m / s, 25 m / s, 26 m / s, 28 m / s, 30 m / s, 32 m / s, 35 m / s, 36 m / s or 38 m / s, etc., but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0068] In some embodiments of the present invention, the number of repetitions of the first preheating and the second preheating in step (2) are each independently 1-80 times. For example, it can be 5 times, 10 times, 20 times, 30 times, 40 times, 50 times, 60 times or 70 times, etc., but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0069] In some embodiments of the present invention, the beam current of the first preheating in step (2) is 10-70 mA. For example, it can be 15 mA, 20 mA, 25 mA, 30 mA, 35 mA, 40 mA, 45 mA, 50 mA, 55 mA, 60 mA or 65 mA, etc., but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0070] In some embodiments of the present invention, the beam current of the second preheating in step (2) is 40-100 mA. For example, it can be 45 mA, 50 mA, 55 mA, 60 mA, 65 mA, 70 mA, 75 mA, 80 mA, 85 mA, 90 mA or 95 mA, etc., but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0071] In some embodiments of the present invention, the defocus value of the first preheating in step (2) is less than the defocus value of the second preheating.

[0072] In some embodiments of the present invention, the defocus value of the first preheating in step (2) is 10-200 mA. For example, it can be 20 mA, 30 mA, 50 mA, 80 mA, 100 mA, 120 mA, 130 mA, 150 mA, 160 mA or 180 mA, etc., but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0073] In some embodiments of the present invention, the defocus value of the second preheating in step (2) is 30 - 200 mA. For example, it can be 40 mA, 50 mA, 80 mA, 100 mA, 120 mA, 130 mA, 150 mA, 160 mA or 180 mA, etc., but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0074] It should be noted that by optimizing the relevant parameter range of the powder bed preheating, increasing the defocus during the powder bed preheating and reducing the scanning time of the powder bed preheating, the average energy input during each layer melting can be reduced. Further, the powder bed sintering state can be reduced, and then the aluminum element loss during the EBM forming of titanium aluminum alloy can be reduced, thereby reducing the tendency of microstructural delamination, and then obtaining a titanium aluminum alloy with no microstructural delamination or a microstructural delamination of grade one.

[0075] In some embodiments of the present invention, the beam current of the filling scan printing in step (2) is 3 - 30 mA. For example, it can be 5 mA, 8 mA, 10 mA, 12 mA, 15 mA, 18 mA, 20 mA, 22 mA, 25 mA or 28 mA, etc., the scanning speed is 0.3 - 5 m / s. For example, it can be 0.5 m / s, 1 m / s, 1.5 m / s, 2 m / s, 2.5 m / s, 3 m / s, 3.5 m / s, 4 m / s or 4.5 m / s, etc., and the filling spacing is 0.03 - 0.3 mm. For example, it can be 0.05 mm, 0.08 mm, 0.1 mm, 0.12 mm, 0.15 mm, 0.18 mm, 0.2 mm, 0.22 mm, 0.25 mm or 0.28 mm, etc., but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0076] In some embodiments of the present invention, the defocus value of the filling scan printing in step (2) is -15 - -4 mA or 5 - 15 mA. For example, it can be -12 mA, -10 mA, -8 mA, -6 mA, 6 mA, 8 mA, 10 mA, 12 mA or 14 mA, etc., but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0077] It should be noted that by optimizing the relevant parameter range of the filling scan printing, it can ensure that the aluminum element loss caused by the overall energy input fluctuation during the EBM forming of titanium aluminum alloy ≤ 2.0 at%, thereby reducing the tendency of microstructural delamination, and then obtaining a titanium aluminum alloy with no microstructural delamination or a microstructural delamination of grade one. In addition, by controlling the defocus value range of the filling scan printing, the focusing state of the filling beam current can be adjusted, so that the beam spot size deviates from the optimal focusing state. When the beam spot size is 300 - 400 μm, on the premise of ensuring the density of the titanium aluminum alloy, the microstructural delamination state can be weakened.

[0078] In some embodiments of the present invention, during the cooling process in step (2), the electron beam and vacuum are turned off, and a protective gas is filled before cooling.

[0079] In some embodiments of the present invention, after the cooling in step (2), the titanium-aluminum alloy is also subjected to a microstructure analysis, and graded according to the morphological characteristics of the microstructure, and then the grade of the obtained titanium-aluminum alloy is determined;

[0080] The grading includes dividing into 5 grades according to the morphological appearance of the microstructure of the titanium-aluminum alloy, specifically: grade zero means no stratification in the microstructure; grade one means there are contrast differences in the microstructure and γ bands with similar sizes, and the difference between the widths of each γ band is < 1 times; grade two means there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is < 50 μm; grade three means there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is ≥ 50 μm; grade four means the microstructures of each layer are different.

[0081] It should be noted that when the microstructure stratification of the titanium-aluminum alloy is grade zero or grade one, the material properties are basically not affected by the stratification state; and when the microstructure stratification of the titanium-aluminum alloy is grade one, the stratification phenomenon can be eliminated by subsequent heat treatment.

[0082] In some embodiments of the present invention, the aluminum element loss of the titanium-aluminum alloy in step (2) is ≤ 2.0 at%, for example, it can be 1.0 at%, 0.8 at%, 0.6 at%, 0.5 at%, 0.2 at% or 0 at%, etc., but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0083] In some embodiments of the present invention, the density of the titanium-aluminum alloy in step (2) is > 99.5%, for example, it can be 99.6%, 99.7%, 99.8% or 99.9%, etc., but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0084] In the present invention, the obtained titanium-aluminum alloy has both an ideal morphological appearance and excellent comprehensive properties.

[0085] In some embodiments of the present invention, the method includes the following steps:

[0086] (1) Preheat the bottom plate in the electron beam selective melting equipment to a temperature of 1050 - 1250 °C, then lay the titanium-aluminum alloy powder on the bottom plate, and then perform vacuum pumping and filling with a protective gas in sequence;

[0087] The beam current for preheating the bottom plate is 40 - 80 mA, the scanning speed is 15 - 35 m / s; the preheating time of the bottom plate > 40 min;

[0088] In terms of mass percentage, the titanium-aluminum alloy powder described in step (1) includes the following elements: Al 29.8 wt% - 35.0 wt%, Mn 3.0 wt% - 6.0 wt%, Nb 2.0 wt% - 6.0 wt%, Cr 1.0 wt% - 4.0 wt%, B 0.1 wt% - 1.0 wt%, and the balance is Ti and unavoidable inclusions;

[0089] (2) Set the printing model and parameters for titanium-aluminum alloy printing, turn on the electron beam, and sequentially perform powder bed preheating and filling scanning printing on the titanium-aluminum alloy powder described in step (1). After cooling, a titanium-aluminum alloy with an aluminum element loss ≤ 2.0 at%, a relative density > 99.5%, and a microstructure without stratification or a microstructure stratification of grade one is obtained;

[0090] The width of the powder bed preheating is 100 - 240 mm 2 ; The powder bed preheating includes first preheating and second preheating carried out in sequence; the number of repetitions of the first preheating and the second preheating are each independently 1 - 80 times; the beam current of the first preheating is less than that of the second preheating; the defocus value of the first preheating is less than that of the second preheating; the scanning speed of the first preheating is 15 - 35 m / s, the beam current is 10 - 70 mA, and the defocus value is 10 - 200 mA; the scanning speed of the second preheating is 15 - 40 m / s, the beam current is 40 - 100 mA, and the defocus value is 30 - 200 mA;

[0091] The beam current of the filling scanning printing is 3 - 30 mA, the scanning speed is 0.3 - 5 m / s, and the filling pitch is 0.03 - 0.3 mm; the defocus value of the filling scanning printing is -15 - -4 mA or 5 - 15 mA;

[0092] During the cooling process, turn off the electron beam and vacuum, and then cool after filling with a protective gas;

[0093] After cooling, microstructure analysis is also carried out on the titanium-aluminum alloy, and grading is performed according to the morphological characteristics of the microstructure, and then the grade of the obtained titanium-aluminum alloy is determined;

[0094] The grading includes classifying into 5 grades according to the microstructure morphology of the titanium-aluminum alloy, specifically: grade zero means no stratification in the microstructure; grade one means there are contrast differences in the microstructure and γ bands with similar sizes, and the difference in the width of each γ band is < 1 times; grade two means there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is < 50 μm; grade three means there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band ≥ 50 μm; grade four means the microstructures of each layer of the microstructure are different.

[0095] Unless otherwise defined, the technical terms used in the following examples and comparative examples have the same meanings as commonly understood by those skilled in the art to which the present invention pertains.

[0096] Example 1

[0097] This example provides a method for hierarchical regulation of the microstructure of additive manufactured titanium aluminide alloy. The method includes the following steps:

[0098] (1) Preheat the bottom plate in the electron beam selective melting equipment to a temperature of 1150 °C, then lay titanium aluminide alloy powder with a particle size distribution of 50 - 105 μm on the bottom plate. Subsequently, evacuate the forming chamber to a vacuum pressure of 0.05 Pa, and finally fill the forming chamber with helium;

[0099] The beam current for preheating the bottom plate is 75 mA, and the scanning speed is 25 m / s; the preheating time of the bottom plate is 50 min;

[0100] By mass percentage, the titanium aluminide alloy powder in step (1) includes the following elements: Al 31.0 wt%, Mn 4.8 wt%, Nb 5.1 wt%, Cr 1.0 wt%, B 0.8 wt%, and the balance is Ti and inevitable inclusions;

[0101] (2) Set the printing model and parameters for titanium aluminide alloy printing, and turn on the electron beam to sequentially perform powder bed preheating and filling and scanning printing on the titanium aluminide alloy powder in step (1). After cooling, titanium aluminide alloy is obtained;

[0102] The width of the powder bed preheating is 200 mm 2 ; the powder bed preheating includes the first preheating and the second preheating performed in sequence; the number of repetitions of the first preheating is 7 times, and the number of repetitions of the second preheating is 45 times; the beam current for the first preheating is 23 mA, the scanning speed is 18 m / s, and the defocus value is 30 mA; the beam current for the second preheating is 90 mA, the scanning speed is 37 m / s, and the defocus value is 100 mA;

[0103] The beam current for the filling and scanning printing is 12 mA, the defocus value is 9 mA, the scanning speed is 2.3 m / s, and the filling pitch is 0.11 mm;

[0104] During the cooling process, turn off the electron beam and vacuum, and backfill helium into the forming chamber for cooling.

[0105] Example 2

[0106] This example provides a method for hierarchical regulation of the microstructure of additive manufactured titanium aluminide alloy. The method includes the following steps:

[0107] (1)Preheat the bottom plate in the electron beam selective melting equipment to a temperature of 1050 °C, then lay titanium-aluminum alloy powder with a particle size distribution of 50 - 105 μm on the bottom plate. Subsequently, evacuate the forming chamber to a vacuum pressure of 0.05 Pa, and finally fill the forming chamber with helium gas;

[0108] The beam current for preheating the bottom plate is 40 mA and the scanning speed is 23 m / s; the preheating time of the bottom plate is 55 min;

[0109] By mass percentage, the titanium-aluminum alloy powder in step (1) includes the following elements: Al 34.89 wt%, Mn 3.2 wt%, Nb 3.92 wt%, Cr 1.2 wt%, B 0.4 wt%, and the balance is Ti and unavoidable inclusions;

[0110] (2)Set the printing model and parameters for titanium-aluminum alloy printing, and turn on the electron beam to sequentially perform powder bed preheating and filling and scanning printing on the titanium-aluminum alloy powder in step (1). After cooling, titanium-aluminum alloy is obtained;

[0111] The width of the powder bed preheating is 150 mm 2 ; The powder bed preheating includes the first preheating and the second preheating carried out in sequence; the number of repetitions of the first preheating is 8 times, and the number of repetitions of the second preheating is 52 times; the beam current of the first preheating is 25 mA, the scanning speed is 15 m / s, and the defocus value is 35 mA; the beam current of the second preheating is 55 mA, the scanning speed is 25 m / s, and the defocus value is 80 mA;

[0112] The beam current for the filling and scanning printing is 5 mA, the defocus value is -4 mA, the scanning speed is 1.3 m / s, and the filling pitch is 0.1 mm;

[0113] During the cooling process, turn off the electron beam and the vacuum, and backfill helium gas into the forming chamber for cooling.

[0114] Example 3

[0115] This example provides a method for hierarchical control of the microstructure of additive manufactured titanium-aluminum alloy, and the method includes the following steps:

[0116] (1)Preheat the bottom plate in the electron beam selective melting equipment to a temperature of 1250 °C, then lay titanium-aluminum alloy powder with a particle size distribution of 50 - 105 μm on the bottom plate. Subsequently, evacuate the forming chamber to a vacuum pressure of 0.05 Pa, and finally fill the forming chamber with helium gas;

[0117] The beam current for preheating the bottom plate is 80 mA and the scanning speed is 30 m / s; the preheating time of the bottom plate is 45 min;

[0118] In terms of mass percentage, the titanium-aluminum alloy powder described in step (1) includes the following elements: Al 32.3 wt%, Mn 5.4 wt%, Nb 3.8 wt%, Cr 2.5 wt%, B 0.3 wt%, and the balance is Ti and inevitable inclusions;

[0119] (2) Set the printing model and parameters for titanium-aluminum alloy printing, turn on the electron beam, and sequentially perform powder bed preheating and filling scanning printing on the titanium-aluminum alloy powder described in step (1), and obtain a titanium-aluminum alloy after cooling;

[0120] The width of the powder bed preheating is 240 mm 2 ; The powder bed preheating includes the first preheating and the second preheating carried out in sequence; the number of repetitions of the first preheating and the second preheating are each independently 30 times; the beam current of the first preheating is 50 mA, the scanning speed is 35 m / s, and the defocus value is 100 mA; the beam current of the second preheating is 100 mA, the scanning speed is 40 m / s, and the defocus value is 180 mA;

[0121] The beam current of the filling scanning printing is 15 mA, the defocus value is 8 mA, the scanning speed is 3 m / s, and the filling spacing is 0.1 mm;

[0122] During the cooling process, turn off the electron beam and the vacuum, and backfill helium gas into the forming chamber for cooling.

[0123] Example 4

[0124] This example provides a method for hierarchical control of the microstructure of additively manufactured titanium-aluminum alloy. Except that the bottom plate is preheated to a temperature of 900 °C in step (1), other conditions are the same as those in Example 1.

[0125] Example 5

[0126] This example provides a method for hierarchical control of the microstructure of additively manufactured titanium-aluminum alloy. Except that the bottom plate is preheated to a temperature of 1350 °C in step (1), other conditions are the same as those in Example 1.

[0127] Example 6

[0128] This example provides a method for hierarchical control of the microstructure of additively manufactured titanium-aluminum alloy. Except that the width of the powder bed preheating described in step (2) is 100 mm 2 other than that, other conditions are the same as those in Example 1.

[0129] Example 7

[0130] This example provides a method for hierarchical control of the microstructure of additively manufactured titanium-aluminum alloy. Except that the width of the powder bed preheating described in step (2) is 300 mm 2 other than that, other conditions are the same as those in Example 1.

[0131] Example 8

[0132] This example provides a method for layer-by-layer regulation of the microstructure of additively manufactured titanium aluminide alloy. Except that the beam current for the first preheating in step (2) is 80 mA and the beam current for the second preheating is 95 mA, other conditions are the same as those in Example 1.

[0133] Example 9

[0134] This example provides a method for layer-by-layer regulation of the microstructure of additively manufactured titanium aluminide alloy. Except that the beam current for the first preheating in step (2) is 50 mA and the beam current for the second preheating is 100 mA, other conditions are the same as those in Example 1.

[0135] Example 10

[0136] This example provides a method for layer-by-layer regulation of the microstructure of additively manufactured titanium aluminide alloy. Except that the defocus values for both the first preheating and the second preheating in step (2) are 50 mA, other conditions are the same as those in Example 1.

[0137] Example 11

[0138] This example provides a method for layer-by-layer regulation of the microstructure of additively manufactured titanium aluminide alloy. Except that the defocus value for the fill scan printing in step (2) is 0 mA, other conditions are the same as those in Example 1.

[0139] Example 12

[0140] This example provides a method for layer-by-layer regulation of the microstructure of additively manufactured titanium aluminide alloy. Except that the defocus value for the fill scan printing in step (2) is 20 mA, other conditions are the same as those in Example 1.

[0141] Comparative Example 1

[0142] This comparative example provides a method for layer-by-layer regulation of the microstructure of additively manufactured titanium aluminide alloy. Except that only 60 passes of the first preheating are performed during the powder bed preheating in step (2), that is, the second preheating is not carried out, other conditions are the same as those in Example 1.

[0143] Comparative Example 2

[0144] This comparative example provides a method for layer-by-layer regulation of the microstructure of additively manufactured titanium aluminide alloy. Except that only 60 passes of the second preheating are performed during the powder bed preheating in step (2), that is, the first preheating is not carried out, other conditions are the same as those in Example 1.

[0145] Comparative Example 3

[0146] This comparative example provides a method for hierarchical control of the microstructure of additive manufactured titanium aluminide alloys. Except that the powder bed is not preheated in step (2), other conditions are the same as those in Example 1.

[0147] The titanium aluminide alloys obtained in the above examples and comparative examples were subjected to microstructure analysis, and classified according to the morphological characteristics of the microstructure, and then the grades of the obtained titanium aluminide alloys were determined. The results are as Figure 2-6 shown in Table 1. Among them, the classification standard is divided into 5 grades according to the microstructure morphology of the titanium aluminide alloy, specifically: grade zero means no stratification in the microstructure; grade one means there are contrast differences in the microstructure and γ bands with similar sizes, and the difference between the widths of each γ band is < 1 times; grade two means there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is < 50 μm; grade three means there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is ≥ 50 μm; grade four means that the microstructures of each layer of the microstructure are different.

[0148] Figure 2-3 Figs. 4 and 5 are the microstructure diagrams of the titanium aluminide alloys obtained by the methods provided in Examples 1-3. It can be seen that the titanium aluminide alloys with no stratification or grade one stratification in the microstructure can be obtained by using the method provided by the present invention; Figure 4 Fig. 6 is the microstructure diagram of the titanium aluminide alloy obtained by the method provided in Example 2 after heat treatment. When the microstructure stratification of the titanium aluminide alloy is grade one, the stratification phenomenon can be eliminated by subsequent heat treatment.

[0149] Figure 6 Figs. 7 and 8 are the microstructure diagrams of the titanium aluminide alloys obtained by the method provided in Comparative Example 2. It can be seen that the stratification phenomenon is serious, which is grade three; Figure 7 Fig. 9 is the microstructure diagram of the titanium aluminide alloy obtained by the method provided in Comparative Example 2 after heat treatment. When the microstructure stratification of the titanium aluminide alloy is grade three, the stratification phenomenon cannot be eliminated by subsequent heat treatment.

[0150] The titanium aluminide alloys obtained in the above examples and comparative examples were tested for aluminum element loss and density. The results are shown in Table 1. Among them, the aluminum element loss was tested by inductively coupled plasma atomic emission spectrometry, and the density was tested by metallographic method.

[0151] Table 1

[0152]

[0153] As can be seen from Table 1:

[0154] (1) The method provided in Examples 1-3 of the present invention can effectively control the loss of Al element during the printing process by optimizing the powder bed preheating method and combining the control of the relevant parameter ranges in the base plate preheating, powder bed preheating and filling scanning printing, thereby obtaining a titanium-aluminum alloy component with high density and excellent microstructure morphology; wherein the aluminum element loss of the obtained titanium-aluminum alloy is ≤1.1at%, the density is >99.5%, and the microstructure has no stratification or the microstructure stratification is level one;

[0155] (2) By comparing Example 1 with Examples 4-5, it can be seen that when the preheating temperature of the base plate is too low, the ambient temperature in the equipment is too low, which will cause powder blowing in the early stage of titanium-aluminum alloy forming, resulting in printing failure; when the preheating temperature of the base plate is too high, although it does not affect the microstructure of the titanium-aluminum alloy component, due to the presence of a certain thickness of powder under the base plate, part of the titanium-aluminum powder will be overburned, reducing the powder recovery rate and the yield rate;

[0156] (3) It can be seen from the comparison between Example 1 and Examples 6-7 that when the preheating width of the powder bed is too low, the equipment utilization rate will be reduced and the density will be reduced; when the preheating width of the powder bed is too high, due to the limited power of the equipment, the preheating width is large and the required temperature is high, the titanium aluminum alloy will be formed at a temperature lower than the target temperature, resulting in printing failure;

[0157] (4) By comparing Example 1 with Examples 8-10, it can be seen that when the beam current of the first preheating process is too high during the powder bed preheating, the probability of powder blowing caused by the charge effect is greatly increased, resulting in printing failure; when the beam current of the second preheating process is too high during the powder bed preheating process, the false sintering phenomenon caused by the excessive beam current is prominent, resulting in increased aluminum loss of the titanium aluminum alloy, too hard powder bed, poor microstructure, and reduced powder recovery rate; when the defocus values ​​of the first preheating and the second preheating process are the same, due to the difference in beam current, the optimal focusing states applicable to the two are inconsistent, and powder blowing, overburning and other phenomena will occur, resulting in printing failure; by comparing Example 1 with Comparative Examples 1-2, it can be seen that when the powder bed preheating only performs the first preheating, the first preheating beam current is small, resulting in too low a powder bed temperature, and the titanium aluminum alloy cannot be formed; when the powder bed preheating only performs the second preheating, the second preheating beam current is large, resulting in too high a powder bed energy, too hard titanium aluminum alloy powder bed, and poor microstructure of the alloy component;

[0158] (5) By comparing Example 1 with Examples 11-12, it can be seen that when the defocus value of the fill scan printing is 0, the electron beam spot is over-focused and the energy is high, resulting in an increase in the aluminum loss of the titanium aluminum alloy; when the defocus value of the fill scan printing is too high, the electron beam spot is too dispersed, resulting in a serious decrease in the density of the titanium aluminum alloy;

[0159] (6) By comparing Example 1 with Comparative Example 3, it can be seen that if the powder bed is not preheated, the titanium aluminum alloy printing fails due to the lack of powder bed heat.

[0160] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for additive manufacturing of titanium aluminum alloy microstructure layering control, characterized in that: The method comprises the following steps: (1) Preheating the bottom plate in the electron beam selective melting equipment, and then laying titanium aluminum alloy powder on the bottom plate; (2) setting a printing model and parameters for titanium-aluminum alloy printing, turning on the electron beam to sequentially perform powder bed preheating and filling scanning printing on the titanium-aluminum alloy powder in step (1), and obtaining a titanium-aluminum alloy with no microstructure stratification or a first-level microstructure stratification after cooling; The powder bed preheating includes a first preheating and a second preheating performed sequentially; the beam current of the first preheating is smaller than the beam current of the second preheating.

2. The method according to claim 1, characterized in that In step (1), the base plate preheating beam current is 40-80 mA and the scanning speed is 15-35 m / s; The bottom plate preheating time in step (1) is greater than 40 minutes; After preheating the bottom plate in step (1), the temperature of the bottom plate is 1050-1250°C.

3. The method according to claim 1, characterized in that In terms of mass percentage, the titanium aluminum alloy powder in step (1) comprises the following elements: Al 29.8wt%~35.0wt%, Mn 3.0wt%~6.0wt%, Nb 2.0wt%~6.0wt%, Cr 1.0wt%~4.0wt%, B 0.1wt%~1.0wt%, and the balance is Ti and unavoidable inclusions; The atomic content of aluminum in the titanium aluminum alloy powder in step (1) is 44.0 at% to 47.0 at%; The particle size distribution of the titanium aluminum alloy powder in step (1) is 45-150 μm; After the laying in step (1), vacuum treatment and protective gas filling are carried out in sequence.

4. The method according to claim 1, characterized in that The width of the powder bed preheating in step (2) is 100~240mm 2 ; Step (2) The scanning speed of the first preheating is 15-35 m / s; Step (2) The scanning speed of the second preheating is 15-40 m / s.

5. The method according to claim 1, characterized in that Step (2) the first preheating and the second preheating are repeated 1 to 80 times independently; Step (2) The first preheating beam current is 10-70 mA; Step (2) The second preheating beam current is 40-100 mA.

6. The method according to claim 1, characterized in that Step (2) the defocus value of the first preheating is smaller than the defocus value of the second preheating; Step (2) The defocus value of the first preheating is 10-200 mA; The defocus value of the second preheating in step (2) is 30-200 mA.

7. The method according to claim 1, characterized in that In step (2), the beam current of the filling scanning printing is 3-30 mA, the scanning speed is 0.3-5 m / s, and the filling spacing is 0.03-0.3 mm; The defocus value of the fill scan printing in step (2) is -15~-4mA or 5~15mA.

8. The method according to claim 1, characterized in that During the cooling process in step (2), the electron beam and vacuum are turned off, and the protective gas is filled in before cooling.

9. The method according to claim 1, characterized in that: After the cooling in step (2), the titanium aluminum alloy is subjected to microstructural analysis and is graded according to the microstructural morphology characteristics, and then the grade of the obtained titanium aluminum alloy is determined; The grading includes 5 levels according to the microstructure morphology of the titanium aluminum alloy, specifically: level 0 means that the microstructure has no stratification; level 1 means that the microstructure has contrast differences, and there are γ bands of similar size, and the difference between the widths of each γ band is less than 1 times; level 2 means that the microstructure has γ bands with obvious size differences or segregation, and the width of the γ band is less than 50μm; level 3 means that the microstructure has γ bands with obvious size differences or segregation, and the width of the γ band is ≥50μm; level 4 means that the microstructures of each layer are different.

10. The method according to claim 1, characterized in that The aluminum element loss of the titanium aluminum alloy in step (2) is ≤2.0at%; The density of the titanium aluminum alloy in step (2) is greater than 99.5%.

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