A method for controlling the microstructure of titanium-aluminum alloys in additive manufacturing

Abstract

The present invention provides a method for controlling the microstructure stratification of titanium-aluminum alloys in additive manufacturing, the method comprising: (1) preheating a base plate in an electron beam selective melting device, and then laying titanium-aluminum alloy powder on the base plate; (2) setting a printing model and parameters for titanium-aluminum alloy printing, turning on an electron beam, and sequentially performing powder bed preheating and filling scanning printing on the titanium-aluminum alloy powder in step (1), to obtain a titanium-aluminum alloy having no microstructure or a first-level microstructure after cooling; the powder bed preheating comprises 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. By sequentially performing powder bed preheating and filling scanning printing on the titanium-aluminum alloy powder laid on the preheated base plate, combined with optimizing the powder bed preheating method, a titanium-aluminum alloy having both ideal microstructure morphology and excellent comprehensive performance is obtained without adding additional time cost and auxiliary equipment.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing of titanium-aluminum alloys, and relates to a method for controlling the microstructure of titanium-aluminum alloys by layering. Background Art

[0002] Currently, TiAl alloy processing methods primarily include casting, ingot metallurgy, and powder metallurgy. Casting methods are relatively mature, and TiAl alloy components such as compressor blades and turbine blades can be manufactured through investment casting (including gravity casting and centrifugal casting) and permanent die casting. However, due to the high solidification shrinkage of TiAl alloys and their poor castability, they can lead to under-casting and often produce shrinkage cavities and inclusion defects. Furthermore, to prevent the highly active TiAl alloy from reacting with the ceramic crucible when molten, the casting process uses a cold crucible, which reduces the overheating capacity and necessitates mold preheating. This preheating process can result in coarse grains and large lamellar structures in the formed part, seriously affecting the performance of the formed part.

[0003] Existing additive manufacturing is a technical means with the potential to replace precision casting for the preparation of titanium aluminum alloys. Through fine-tuning of the production process, additive manufacturing can control the growth of microstructures, reduce excess addition, and reduce the product's dependence on post-processing. Electron beam selective melting (EBM) technology is a highly promising additive manufacturing process, which uses metal powder as raw material and uses a focused electron beam under high vacuum to obtain formed specimens through selective melting and layer-by-layer scanning. Because EBM can quickly and nearly net-form three-dimensional components of complex shapes, while avoiding oxidation to generate impurities and having good economic benefits without wasting materials, it is a highly promising TiAl alloy forming process that has attracted widespread attention at home and abroad. However, EBM forming titanium aluminum alloys is very prone to organizational stratification, such as Figure 1 As shown, the overall performance of the material is reduced.

[0004] In summary, there is an urgent need to provide a method for hierarchical control of the microstructure of titanium-aluminum alloys in additive manufacturing, so as to obtain titanium-aluminum alloy component products with both ideal microstructure and excellent comprehensive performance. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method for the layered regulation of the microstructure of titanium-aluminum alloy in additive manufacturing. By optimizing the powder bed preheating method and combining the regulation of the relevant parameter ranges in the base plate preheating, powder bed preheating and filling scanning printing, the loss of Al element in the printing process is effectively controlled without adding additional time costs and auxiliary equipment, thereby obtaining titanium-aluminum alloy components with high density and excellent microstructure.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for controlling the microstructure of titanium-aluminum alloy by additive manufacturing, the method comprising the following steps:

[0008] (1) Preheating the bottom plate in the electron beam selective melting equipment, and then laying titanium aluminum alloy powder on the bottom plate;

[0009] (2) setting the 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 or a microstructure with a first-level stratification after cooling;

[0010] 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.

[0011] In the present invention, before preheating the base plate, titanium aluminum alloy powder is placed in the EBM powder bin, and the base plate is placed in the forming chamber and is placed in the center.

[0012] The method provided by the present invention sequentially performs powder bed preheating and filling scanning printing on the titanium aluminum alloy powder laid on the preheated base plate, and combines the optimization of the powder bed preheating method to obtain a titanium aluminum alloy with ideal microstructure and excellent comprehensive performance without adding additional time cost and auxiliary equipment.

[0013] It should be noted that by performing secondary preheating of the powder bed and increasing the forming temperature, the overall energy fluctuation is reduced, thereby reducing the loss of aluminum elements during the forming of titanium-aluminum alloy, and reducing the microstructural stratification tendency of titanium-aluminum alloy while ensuring density.

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

[0015] The time for preheating the bottom plate in step (1) is greater than 40 minutes.

[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, the titanium aluminum alloy powder in step (1) includes the following elements, in terms of mass percentage: 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.

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

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

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

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

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

[0023] The scanning speed of the second preheating 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 in step (2) is independently 1-80 times.

[0025] In step (2), the first preheating beam current is 10-70 mA.

[0026] In step (2), the second preheating beam current is 40-100 mA.

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

[0028] In step (2), the defocus value of the first preheating is 10-200 mA.

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

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

[0031] The defocus value of the fill scan printing in step (2) is -15~-4mA or 5~15mA.

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

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

[0034] The grading includes 5 levels based on 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.

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

[0036] The density of the titanium-aluminum alloy in step (2) is greater than 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 sequentially performs powder bed preheating and filling scanning printing on the titanium aluminum alloy powder laid on the preheated base plate, and combines the optimization of the powder bed preheating method to obtain a titanium aluminum alloy with both ideal microstructure and excellent comprehensive performance without adding additional time cost and auxiliary equipment;

[0039] (2) The method provided by the present invention can effectively control the loss of Al element during the printing process by regulating the relevant parameter ranges in base plate preheating, powder bed preheating and filling scanning printing, thereby reducing the tendency of microstructure stratification while ensuring the density of titanium aluminum alloy; wherein the aluminum element loss of the prepared titanium aluminum alloy is ≤1.1at%, the density is >99.5%, and the microstructure has no stratification or the microstructure stratification is level one. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a microstructure diagram of titanium-aluminum alloy formed by conventional electron beam selective melting provided by the present invention.

[0041] Figure 2 This is a microstructure diagram of the titanium aluminum alloy obtained by the method provided in Example 1 of the present invention.

[0042] Figure 3 This is a microstructure diagram of the titanium aluminum alloy obtained by the method provided in Example 2 of the present invention.

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

[0044] Figure 5 This is a microstructure diagram of the titanium aluminum alloy obtained by the method provided in Example 3 of the present invention.

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

[0046] Figure 7 This is a microstructure diagram of the titanium aluminum alloy obtained by the method provided in Comparative Example 2 of the present invention after heat treatment. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0048] A specific embodiment of the present invention provides a method for controlling the microstructure of a titanium-aluminum alloy by additive manufacturing, the method comprising the following steps:

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

[0050] (2) setting the 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 or a microstructure with a first-level stratification after cooling;

[0051] 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.

[0052] In the present invention, a smaller beam flow is first used to perform a first preheating on the powder bed, and then a larger beam flow is used to perform a second preheating on the powder bed, thereby completing the preheating of the powder bed in sequence.

[0053] In some embodiments of the present invention, the beam current for preheating the base plate in step (1) is 40-80 mA, for example, 45 mA, 50 mA, 55 mA, 60 mA, 65 mA, 70 mA, or 75 mA, and the scanning speed is 15-35 m / s, for example, 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, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0054] In some embodiments of the present invention, the time for preheating the bottom plate in step (1) is greater than 40 minutes, for example, it can be 42 minutes, 45 minutes, 46 minutes, 48 minutes, 20 minutes, 55 minutes or 60 minutes, etc., but is not limited to the listed values, and other values not listed within the numerical range are also 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, 1060°C, 1080°C, 1100°C, 1120°C, 1150°C, 1160°C, 1180°C, 1200°C, 1220°C or 1240°C, etc., but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0056] It should be noted that by optimizing the relevant parameter range of the base plate preheating, the initial printing environment can be guaranteed to be stable during EBM forming of titanium-aluminum alloy, and powder blowing can be prevented from occurring during the initial preheating process of the powder bed.

[0057] In some embodiments of the present invention, the titanium aluminum alloy powder in step (1) includes the following elements, in percentage by mass: 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.

[0058] In the present invention, the mass content of Al in the titanium-aluminum alloy 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-aluminum alloy 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-aluminum alloy 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-aluminum alloy 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-aluminum alloy 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 is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0059] In some embodiments of the present invention, the atomic content of aluminum 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 is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0060] It should be noted that by optimizing the composition design of titanium-aluminum alloy, rationally regulating the content of alloying elements, and further controlling the range of Al atomic content in titanium-aluminum alloy, the tendency of microstructural stratification of titanium-aluminum alloy during the forming process 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 further determine it according to actual needs.

[0063] In some embodiments of the present invention, after the laying in step (1), vacuuming and filling with protective gas are performed in sequence.

[0064] In the present invention, the vacuum treatment is performed until the pressure inside the EBM equipment meets the requirements, for example, the vacuum pressure of 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 100~240mm 2 , for example, it can be 100mm 2 , 140mm 2 , 160mm 2 , 170mm 2 , 180mm 2 , 190mm 2 , 200mm 2 , 220mm 2 or 230mm 2 The present invention is not limited to the listed values, and other values not listed in the numerical range are also 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, and other values not listed within the numerical range are also 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, and other values not listed within the numerical range are also applicable.

[0068] In some embodiments of the present invention, the number of repetitions of the first preheating and the second preheating in step (2) is independently 1-80 times, for example, 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, and other values not listed within the numerical range are also 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, and other values not listed within the numerical range are also applicable.

[0070] In some embodiments of the present invention, the second preheating beam current in step (2) is 40-100 mA, for example, 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, and other values not listed within the numerical range are also applicable.

[0071] In some embodiments of the present invention, the defocus value of the first preheating in step (2) is smaller 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 10~200mA, for example, it can be 20mA, 30mA, 50mA, 80mA, 100mA, 120mA, 130mA, 150mA, 160mA or 180mA, etc., but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

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

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

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

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

[0077] It should be noted that by optimizing the relevant parameter range of the fill scan printing, the aluminum element loss caused by the overall energy input fluctuation during EBM forming of titanium-aluminum alloy can be guaranteed to be ≤2.0at%, thereby reducing the tendency of microstructural stratification and obtaining titanium-aluminum alloy with no microstructural stratification or microstructural stratification of the first level. In addition, by controlling the defocus value range of the fill scan printing, the focus state of the fill beam can be adjusted, causing the beam spot size to deviate from the optimal focus state. When the beam spot size is between 300 and 400μm, the microstructural stratification state is weakened while ensuring the density of the titanium-aluminum alloy.

[0078] In some embodiments of the present invention, during the cooling process of step (2), the electron beam and vacuum are turned off, and cooling is performed after filling with protective gas.

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

[0080] The grading includes 5 levels based on 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.

[0081] It should be noted that when the microstructural stratification of the titanium-aluminum alloy is at level zero or level one, the material properties are basically not affected by the stratification state; and when the microstructural stratification of the titanium-aluminum alloy is at level 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 ≤2.0at%, for example, it can be 1.0at%, 0.8at%, 0.6at%, 0.5at%, 0.2at% or 0at%, etc., but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

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

[0084] In the present invention, the obtained titanium aluminum alloy has both ideal organizational morphology and excellent comprehensive performance.

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

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

[0087] The beam current of the base plate preheating is 40-80 mA, and the scanning speed is 15-35 m / s; the base plate preheating time is greater than 40 minutes;

[0088] 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;

[0089] (2) Setting the printing model and parameters for titanium-aluminum alloy printing, turning on the electron beam to perform powder bed preheating and filling scanning printing on the titanium-aluminum alloy powder in step (1) in sequence, and obtaining a titanium-aluminum alloy having an aluminum element loss of ≤2.0at%, a density of >99.5%, and a microstructure with no stratification or a microstructure with a first-level stratification after cooling;

[0090] The width of the powder bed preheating is 100~240mm 2 The powder bed preheating includes a first preheating and a second preheating performed sequentially; the number of repetitions of the first preheating and the second preheating is independently 1-80 times; the beam current of the first preheating is smaller than the beam current of the second preheating; the defocus value of the first preheating is smaller than the defocus value 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 fill scan printing is 3~30mA, the scanning speed is 0.3~5m / s, and the filling spacing is 0.03~0.3mm; the defocus value of the fill scan printing is -15~-4mA or 5~15mA;

[0092] During the cooling process, the electron beam and vacuum are turned off, and cooling is performed after filling with protective gas;

[0093] After the cooling, the titanium-aluminum alloy is subjected to microstructural analysis and is graded according to microstructural morphology characteristics, and then the grade of the obtained titanium-aluminum alloy is determined;

[0094] The grading includes 5 levels based on the microstructure morphology of the titanium aluminum alloy, specifically: level 0 means no stratification of the microstructure; level 1 means there is a contrast difference in the microstructure, 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 there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is less than 50μm; level 3 means there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is ≥50μm; level 4 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 belongs.

[0096] Example 1

[0097] This embodiment provides a method for controlling the microstructure of a titanium-aluminum alloy by additive manufacturing, the method comprising the following steps:

[0098] (1) The base plate in the electron beam selective melting equipment is preheated to a temperature of 1150°C, and then titanium aluminum alloy powder with a particle size distribution of 50-105 μm is laid on the base plate. The forming chamber is then vacuumed to a vacuum pressure of 0.05 Pa, and finally helium is filled into the forming chamber;

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

[0100] In terms of mass percentage, the titanium aluminum alloy powder in step (1) comprises the following elements: Al 31.0wt%, Mn 4.8wt%, Nb 5.1wt%, Cr 1.0wt%, B 0.8wt%, and the balance is Ti and unavoidable inclusions;

[0101] (2) setting the printing model and parameters for titanium aluminum alloy printing, turning on the electron beam to perform powder bed preheating and filling scanning printing on the titanium aluminum alloy powder in step (1) in sequence, and obtaining the titanium aluminum alloy after cooling;

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

[0103] The fill scan printing has a beam current of 12 mA, a defocus value of 9 mA, a scan speed of 2.3 m / s, and a fill spacing of 0.11 mm;

[0104] During the cooling process, the electron beam and vacuum are turned off, and helium is backfilled into the forming chamber for cooling.

[0105] Example 2

[0106] This embodiment provides a method for controlling the microstructure of a titanium-aluminum alloy by additive manufacturing, the method comprising the following steps:

[0107] (1) The base plate in the electron beam selective melting equipment is preheated to a temperature of 1050°C, and then titanium aluminum alloy powder with a particle size distribution of 50-105 μm is laid on the base plate. The forming chamber is then vacuumed to a vacuum pressure of 0.05 Pa, and finally helium is filled into the forming chamber;

[0108] The beam current of the base plate preheating is 40 mA, the scanning speed is 23 m / s, and the base plate preheating time is 55 minutes;

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

[0110] (2) setting the printing model and parameters for titanium aluminum alloy printing, turning on the electron beam to perform powder bed preheating and filling scanning printing on the titanium aluminum alloy powder in step (1) in sequence, and obtaining the titanium aluminum alloy after cooling;

[0111] The width of the powder bed preheating is 150mm 2 The powder bed preheating includes a first preheating and a second preheating performed sequentially; the first preheating is repeated 8 times, and the second preheating is repeated 52 times; the beam current of the first preheating is 25mA, the scanning speed is 15m / s, and the defocus value is 35mA; the beam current of the second preheating is 55mA, the scanning speed is 25m / s, and the defocus value is 80mA;

[0112] The beam current of the fill scan printing is 5 mA, the defocus value is -4 mA, the scanning speed is 1.3 m / s, and the fill spacing is 0.1 mm;

[0113] During the cooling process, the electron beam and vacuum are turned off, and helium is backfilled into the forming chamber for cooling.

[0114] Example 3

[0115] This embodiment provides a method for controlling the microstructure of a titanium-aluminum alloy by additive manufacturing, the method comprising the following steps:

[0116] (1) The base plate in the electron beam selective melting equipment is preheated to a temperature of 1250°C, and then titanium aluminum alloy powder with a particle size distribution of 50-105 μm is laid on the base plate. The forming chamber is then vacuumed to a vacuum pressure of 0.05 Pa, and finally helium is filled into the forming chamber;

[0117] The beam current of the base plate preheating is 80 mA, the scanning speed is 30 m / s, and the base plate preheating time is 45 minutes;

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

[0119] (2) setting the printing model and parameters for titanium aluminum alloy printing, turning on the electron beam to perform powder bed preheating and filling scanning printing on the titanium aluminum alloy powder in step (1) in sequence, and obtaining the titanium aluminum alloy after cooling;

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

[0121] The fill scan printing has a beam current of 15 mA, a defocus value of 8 mA, a scan speed of 3 m / s, and a fill spacing of 0.1 mm;

[0122] During the cooling process, the electron beam and vacuum are turned off, and helium is backfilled into the forming chamber for cooling.

[0123] Example 4

[0124] This embodiment provides a method for controlling the microstructure layering of titanium-aluminum alloy during additive manufacturing. Except for step (1) preheating the base plate to a temperature of 900° C., other conditions are the same as those in Example 1.

[0125] Example 5

[0126] This embodiment provides a method for controlling the microstructure layering of titanium-aluminum alloys during additive manufacturing. Except for step (1) preheating the base plate to a temperature of 1350° C., other conditions are the same as those in Example 1.

[0127] Example 6

[0128] This embodiment provides a method for controlling the microstructure of titanium-aluminum alloy by additive manufacturing, except that the width of the powder bed preheating in step (2) is 100 mm. 2 Except for this, other conditions are the same as those in Example 1.

[0129] Example 7

[0130] This embodiment provides a method for controlling the microstructure of titanium-aluminum alloy by additive manufacturing, except that the width of the powder bed preheating in step (2) is 300mm. 2 Except for this, other conditions are the same as those in Example 1.

[0131] Example 8

[0132] This embodiment provides a method for controlling the microstructure layering of titanium-aluminum alloys in additive manufacturing. Except that in step (2), the first preheating beam current is 80 mA and the second preheating beam current is 95 mA, other conditions are the same as those in Example 1.

[0133] Example 9

[0134] This embodiment provides a method for controlling the microstructure layering of titanium-aluminum alloy during additive manufacturing. Except that in step (2), the first preheating beam current is 50 mA and the second preheating beam current is 100 mA, other conditions are the same as those in Example 1.

[0135] Example 10

[0136] This embodiment provides a method for controlling the microstructure layering of titanium-aluminum alloy during additive manufacturing. Except that the defocusing values of the first preheating and the second preheating in step (2) are both 50 mA, other conditions are the same as those in Example 1.

[0137] Example 11

[0138] This embodiment provides a method for controlling the microstructure layering of titanium-aluminum alloys during additive manufacturing. Except for the defocus value of the fill scan printing in step (2) being 0 mA, other conditions are the same as those in embodiment 1.

[0139] Example 12

[0140] This embodiment provides a method for controlling the microstructure layering of titanium-aluminum alloys in additive manufacturing. Except that the defocus value of 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 controlling the microstructure layering of titanium-aluminum alloy in additive manufacturing. Except that only 60 first preheating cycles are performed in the powder bed preheating step (2), i.e., no second preheating is performed, other conditions are the same as those in Example 1.

[0143] Comparative Example 2

[0144] This comparative example provides a method for controlling the microstructure layering of titanium-aluminum alloy in additive manufacturing. Except that only 60 second preheatings are performed in the powder bed preheating step (2), i.e., no first preheating is performed, other conditions are the same as those in Example 1.

[0145] Comparative Example 3

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

[0147] The titanium aluminum alloys obtained in the above examples and comparative examples were subjected to microstructural analysis and were graded according to their microstructural morphology. The grades of the obtained titanium aluminum alloys were then determined. Figure 2-6 As shown in Table 1. The grading standard is divided into 5 levels based on the microstructure morphology of the titanium aluminum alloy, specifically: level 0 means no stratification of the microstructure; level 1 means there is a contrast difference in the microstructure, 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 there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is less than 50 μm; level 3 means there are γ bands with obvious size differences or segregation in the microstructure, and the width of the γ band is ≥50 μm; level 4 means the microstructures of each layer of the microstructure are different.

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

[0149] Figure 6 They are respectively the microstructure diagrams of the titanium aluminum alloy obtained by the method provided in Comparative Example 2, and it can be seen that the delamination phenomenon is serious, which is level three; Figure 7 This is a microstructure diagram of the titanium-aluminum alloy obtained by the method provided in Example 2 after heat treatment. When the microstructure of the titanium-aluminum alloy is stratified into three levels, the stratification phenomenon cannot be eliminated by subsequent heat treatment.

[0150] The aluminum loss and density of the titanium aluminum alloys obtained in the above examples and comparative examples were tested, and the results are shown in Table 1. The aluminum loss was tested by inductively coupled plasma atomic emission spectrometry, and the density was tested by metallography.

[0151] Table 1

[0152]

[0153] From Table 1 we can see that:

[0154] (1) The methods 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 fill scanning printing, thereby obtaining a titanium-aluminum alloy component with high density and excellent microstructure; 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) From the comparison between Example 1 and 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) From the comparison between Example 1 and Examples 6-7, it can be seen 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 below the target temperature, resulting in printing failure;

[0157] (4) From the comparison between Example 1 and 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, 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; from the comparison between Example 1 and 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 alloy components;

[0158] (5) From the comparison between Example 1 and 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 increased aluminum loss in 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) From the comparison between Example 1 and 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 is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for controlling the microstructure of titanium-aluminum alloy by additive manufacturing, 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 the 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 or a microstructure with a first-level 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; the beam current of the first preheating is 10-70 mA; the beam current of the second preheating is 40-100 mA; the defocus value of the first preheating is smaller than the defocus value of the second preheating; the defocus value of the first preheating is 10-200 mA; the defocus value of the second preheating is 30-200 mA; The defocus value of the fill scan printing is -15~-4mA or 5~15mA.

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 filling with protective gas are carried out in sequence.

4. The method according to claim 1, wherein 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; The scanning speed of the second preheating in step (2) is 15-40 m / s.

5. The method according to claim 1, wherein In step (2), the first preheating and the second preheating are repeated 1 to 80 times independently.

6. The method according to claim 1, characterized in that The beam current of the filling scanning printing in step (2) is 3~30mA, the scanning speed is 0.3~5m / s, and the filling spacing is 0.03~0.3mm.

7. The method according to claim 1, characterized in that During the cooling process of step (2), the electron beam and vacuum are turned off, and cooling is carried out after filling with protective gas.

8. The method according to claim 1, characterized in that After the cooling in step (2), the titanium-aluminum alloy is subjected to a 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 based on 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.

9. 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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