An additive manufacturing method for TiAl alloy

Abstract

The present invention relates to an additive manufacturing method for a TiAl alloy, comprising: selecting TiAl alloy powder; establishing a three-dimensional model; planning a scanning path: when the width of the part cross-section is less than a preset partition width, scanning is performed using a standard scanning line length; otherwise, the part cross-section is divided into regions, and scanning is performed using a partition scanning line length; the standard scanning line length is greater than the partition scanning line length; loading the TiAl alloy powder into the powder bin of an electron beam additive manufacturing device, and performing scanning and melting. By controlling the content of the Al element in the TiAl alloy powder, the present invention ensures that the alloy solidification process proceeds along the β solidification path, which helps to form fine equiaxed crystals; by controlling the content of the B element, borides with a dispersed distribution are formed, which play a role in refining the microstructure; by setting the preset partition width, partition overlap width, and partition offset width, the differences in microstructure and properties caused by remelting at the partition scanning overlap are solved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of additive manufacturing, and in particular, to an additive manufacturing method for TiAl alloy. Background Art

[0002] TiAl alloy has high specific strength, high specific modulus and good high-temperature performance. Its density is only half of that of nickel-based superalloys. It is a very promising lightweight high-temperature alloy, with great advantages in reducing the weight of aircraft engines. It is considered as a new generation of high-temperature resistant lightweight structural material in the service temperature range of 650-900°C.

[0003] The powder bed electron beam additive manufacturing technology is suitable for the integral forming of TiAl alloy components due to its advantages of near-net shaping, high preheating temperature (up to 1100°C), small residual stress and high production efficiency, and has become the preferred forming method for preparing TiAl alloy blades. In addition, the electron beam has a high energy density. During the solidification process, due to the rapid solidification of the tiny molten pool, the formed alloy structure is very fine, and the performance is often higher than that of traditional cast alloys. Therefore, the TiAl alloy prepared by the powder bed electron beam additive manufacturing technology is expected to promote the application and development of large-size TiAl alloy blades in the new generation of high-performance aero-engines.

[0004] In the related technology, by adjusting the composition of TiAl alloy (such as adding Ta, W, etc.), the mechanical properties of the alloy are significantly improved, and the service temperature is increased. However, the addition of Ta and W elements will bring problems such as solidification segregation, high alloy density and high cost; it is difficult to meet the forming of large-size and complex TiAl alloy components only by adjusting the scanning current and scanning speed parameters of the electron beam selective melting forming process.

[0005] Therefore, it is necessary to improve one or more problems existing in the above-mentioned related technical solutions.

[0006] It should be noted that this part is intended to provide background or context for the technical solution of the present invention stated in the claims. The description herein is not admitted to be prior art merely because it is included in this part. Summary of the Invention

[0007] The purpose of the present invention is to provide an additive manufacturing method for TiAl alloy, so as to solve at least to some extent one or more problems caused by the limitations and defects of the related technology.

[0008] The present invention provides an additive manufacturing method for TiAl alloy, including:

[0009] Select TiAl alloy powder with a particle size range of 45 - 150 μm. The atomic percentage of Al, Mn, Nb, and B in the TiAl alloy powder is 43 - 46%, 2.2 - 2.4%, 2 - 2.1%, and 0.5 - 1% respectively, and the balance is Ti;

[0010] Establish a three-dimensional model of the part;

[0011] Plan the scanning path: When the cross-sectional width of the part is less than the preset partition width, scan with a standard scan line length; when the cross-sectional width of the part is greater than or equal to the preset partition width, divide the cross-section of the part into regions and scan with a partition scan line length. Among them, the value range of the preset partition width is 10 mm - 45 mm, the standard scan line length is greater than the partition scan line length, the partition overlap width is 0.05 mm - 0.1 mm, and the partition offset width ≥ 3 mm;

[0012] Preheat the substrate: Load the TiAl alloy powder into the powder bin of the electron beam additive manufacturing equipment and perform scanning preheating. Among them, the electron beam scanning speed in the substrate preheating stage is 10 - 20 m / s, the electron beam scanning current is 20 - 90 mA, and the substrate is preheated to 1050 - 1100 °C;

[0013] Solid melting: The electron beam scanning speed in the solid melting stage is 3 - 5 m / s, and the electron beam scanning current is 15.5 - 17.5 mA.

[0014] In the present invention, the powder particle size D 50 = 70 - 80 μm, D 90 = 120 - 130 μm, and the powder fluidity is 25 - 35 s / 50 g.

[0015] In the present invention, the partition scan line length is 10 mm - 30 mm.

[0016] In the present invention, the value range of the preset partition width is 10 mm - 30 mm.

[0017] In the present invention, for the cross-section of the part that needs to be divided into regions, divide the cross-section of the part into multiple partitions. When the sum of the widths of some partitions among the multiple partitions is less than the partition scan line length, perform combined melting scanning on this part of the partitions.

[0018] In the present invention, the slice layer thickness of the three-dimensional model is 50 - 100 μm, the scanning method is serpentine scanning, and the adjacent scan line spacing is 0.05 - 0.15 mm.

[0019] In the present invention, the energy input in the solid melting stage is 26.67 - 36.67 J / mm 3, the electron beam scanning current is 16 - 16.5 mA, and the electron beam scanning speed is 3 - 4 m / s.

[0020] In the present invention, the method further includes: performing microstructure analysis on the formed part.

[0021] The technical solution provided by the present invention may include the following beneficial effects:

[0022] In the present invention, by controlling the content of Al element in the TiAl alloy powder, it can ensure that the solidification process of the TiAl alloy proceeds along the β solidification path, which is helpful for the formation of fine equiaxed grains; by controlling the content of B element, dispersed borides can be formed. The borides, as nucleation sites, play a role in refining the microstructure by hindering grain growth; by setting the preset partition width, partition overlap width, and partition offset width, when electron beam selective melting forming large-sized TiAl alloy complex components, the problems of excessive difference in scan line length and remelting at the partition scan overlap causing differences in microstructure and performance are solved. The microstructure of the TiAl alloy parts prepared in this application is a uniform and fine duplex structure, with more excellent mechanical properties. Description of the Drawings

[0023] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments consistent with the present disclosure, and are used together with the specification to explain the principles of the present disclosure. Obviously, the drawings in the following description are only some embodiments of the present disclosure. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 A schematic flow chart showing the additive manufacturing method of TiAl alloy in an exemplary embodiment of the present invention;

[0025] Figure 2 Showing the microstructure of the overlap zone and non-overlap zone when the partition offset width is 1 mm;

[0026] Figure 3 Showing the microstructure of the overlap zone and non-overlap zone when the partition offset width is 3 mm;

[0027] Figure 4 Showing a schematic diagram of partition settings during partition melting in an exemplary embodiment of the present invention;

[0028] Figure 5 Showing a schematic diagram of partition settings during partition melting in another exemplary embodiment of the present invention;

[0029] Figure 6 Showing the alloy electron micrograph (5 μm) in an exemplary embodiment of the present invention;

[0030] Figure 7 Show the electron microscope image of the alloy (50μm) in the exemplary embodiment of the present invention;

[0031] Figure 8 Show the alloy solidification path diagram in the exemplary embodiment of the present invention. Detailed implementation manners

[0032] The exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, the exemplary embodiments can be implemented in various forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this invention will be more complete and comprehensive, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0033] In addition, the drawings are only schematic illustrations of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and thus their repeated description will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0034] In this exemplary embodiment, a method for additive manufacturing of a TiAl alloy is provided. Referring Figure 1 as shown, the method includes steps S101 to S105, which are specifically as follows:

[0035] Step S101: Select TiAl alloy powder with a particle size range of 45 to 150 μm. The atomic percentage of Al, Mn, Nb, and B in the TiAl alloy powder is 43 to 46%, 2.2 to 2.4%, 2 to 2.1%, and 0.5 to 1% respectively, and the balance is Ti. Preferably, the powder particle size D 50 = 70 to 80 μm, D 90 = 120 to 130 μm, and the powder fluidity is 25 to 35 s / 50 g.

[0036] Step S102: Establish a three-dimensional model of the part. The slice layer thickness of the three-dimensional model is 50 to 100 μm, for example, it can be 60 μm, 70 μm, 80 μm, etc., but is not limited thereto.

[0037] Step S103: Plan the scanning path: When the width of the part cross-section is less than the preset partition width, scan with the standard scanning line length; when the width of the part cross-section is greater than or equal to the preset partition width, divide the part cross-section into regions and scan with the partition scanning line length; wherein, the value range of the preset partition width is 10 mm to 45 mm, the standard scanning line length is greater than the partition scanning line length, the partition overlap width is 0.05 mm to 0.1 mm, and the partition offset width ≥ 3 mm.

[0038] In some embodiments, when the width of the part cross-section of the odd layers of the part is less than the preset partition width, no region division is required; when the width of the part cross-section of the even layers is greater than or equal to the preset partition width, the part cross-section is divided into regions and scanned with the partition scanning line length. For example, when scanning the 1st, 3rd, 5th... layers of the part cross-section, no region division is performed, and direct scanning such as serpentine scanning can be used. After dividing the 2nd, 4th, 6th... layers of the part cross-section into regions, then scan.

[0039] For another example, please refer to Figure 4 , when performing the region division operation on the nth layer, divide the 30 mm width into partition 1 and partition 2. At this time, the width D1 of partition 1 and the width D2 of partition 2 are both 15 mm; for the layers spaced after the nth layer, the n + 2, n + 4, n + 6, n + 8, n + 10 layers are all divided into 3 partitions, and the corresponding widths of each layer change as Figure 4 shown. When the n + 2nd layer melts, it is divided into 3 partitions (D1, D2, and D3) for melting. At this time, the widths of the three partitions are 12 mm, 15 mm, and 3 mm respectively, and the D1 and D3 regions can be merged for melting, so as to ensure that the scanning line length is still 15 mm; similarly, when the n + 4th layer melts, the widths of the three partitions (D1, D2, and D3) are 9 mm, 15 mm, and 6 mm respectively, and the D1 and D3 regions are merged for melting; until the n + 10th layer, similar to the nth layer, it is divided into 2 regions (D1 and D2) for melting, and the partition widths are both 15 mm.

[0040] Step S104: Substrate preheating: Load the TiAl alloy powder into the powder bin of the electron beam additive manufacturing equipment and perform scanning preheating. Among them, the electron beam scanning speed in the substrate preheating stage is 10 to 20 m / s, the electron beam scanning current is 20 to 90 mA, and the substrate is preheated to 1050 to 1100 °C.

[0041] Step S105: Solid melting: The electron beam scanning speed in the solid melting stage is 3 to 5 m / s, and the electron beam scanning current is 15.5 to 17.5 mA.

[0042] In the pre-preheating stage of powder bed preheating, the starting preheating current of the electron beam is 20 - 40 mA, increasing in a stepped manner in 2 - 4 levels successively, so that the final current reaches 75 - 90 mA, and the preheating time is 20 - 25 s. In the post-preheating stage of the powder bed, the scanning current of the electron beam remains at 75 - 90 mA, and the preheating time is 15 - 20 s.

[0043] In this embodiment, by controlling the content of Al element in the TiAl alloy powder, it can ensure that the alloy solidification process proceeds along the β solidification path, which is helpful for the formation of fine equiaxed grains; by controlling the content of B element, dispersed borides can be formed. As nucleation sites, the borides play a role in refining the microstructure by hindering grain growth; by setting the preset partition width, partition lap width, and partition offset width, when electron beam selective melting is used to form large-sized TiAl alloy complex components, the problem of excessive difference in scanning line length and the re-melting at the partition scanning lap resulting in differences in microstructure and properties is solved. The microstructure of the TiAl alloy parts prepared by this application is a uniform and fine duplex structure, having more excellent mechanical properties.

[0044] Among them, for the setting of the partition offset width, as Figure 2 shown, when the partition offset width is 1 mm, the structure in the lap zone is severely damaged due to re-melting, and there are obvious differences from the structure in the non-lap zone. As Figure 3 shown, when the partition offset width is 3 mm, there are no obvious differences between the structure in the lap zone and the non-lap zone, and the forming quality is good. Therefore, the partition offset width d ≥ 3 mm.

[0045] On the basis of the above embodiments, the additive manufacturing method of TiAl alloy further includes: performing microstructure analysis on the formed part to analyze whether the quality of the formed part meets the requirements, so as to verify whether the additive manufacturing method is reasonable.

[0046] The following uses a specific test example to illustrate the additive manufacturing process of this application.

[0047] Step 1: Use the plasma rotating electrode atomization method to make TiAl alloy rods into TiAl alloy powder with a particle size of 45 - 150 μm. The composition of the powder (atomic percentage) is Ti - 46Al - 2.2Mn - 2Nb - 0.8B. The D 50 of the powder particle size is 78 μm, D 90 is 123 μm, and the powder fluidity is 27 s / 50 g.

[0048] Step 2: Establish a three-dimensional model of the part and perform path planning. As Figure 5As shown, the size of the three-dimensional model is 20mm×80mm×20mm, the scanning line spacing is 0.1mm, a serpentine scanning strategy is adopted, and the slice layer thickness is 90μm. During path planning, area division processing is carried out. The preset partition width D = 20mm, the partition lap width is 0.05mm, and the partition offset width d = 3mm. At the (n + 1)-th layer, it is divided into 4 regions (D1, D2, D3, and D4), each with a width of 20mm; at the (n + 3)-th layer, partition offset is performed, and it is divided into 5 regions (D1, D2, D3, D4, and D5), with widths of 17mm, 20mm, 20mm, 20mm, and 3mm respectively. Among them, regions D1 and D5 can be merged and melted so that the scanning line length remains 20mm. And so on, layer-by-layer partition stacking is completed.

[0049] Step 3: Load the TiAl alloy powder into the powder bin of the electron beam additive manufacturing equipment, evacuate the forming chamber of the equipment, and layer by layer perform powder spreading - preheating before the powder bed - selective melting forming - preheating after the powder bed - powder spreading process until the solid stacking of each layer is completed.

[0050] Among them, printing starts when the substrate is preheated to 1050~1100°C. The energy input for melting the solid part is 26.67~36.67 J / mm 3 , corresponding to an electron beam scanning current of 16~16.5 mA and an electron beam scanning speed of 3~4 m / s. In the preheating stage before the powder bed, the initial preheating current of the electron beam is 40 mA, increasing in 2~4 step levels successively so that the final current reaches 85 mA, and the preheating time is 20~25 s. In the preheating stage after the powder bed, the electron beam scanning current remains 85 mA, and the preheating time is 15~20 s.

[0051] Step 4: Conduct microstructure analysis on the formed part, as Figure 6 shown, the microstructure of the formed part consists of uniformly fine lamellar crystal clusters (α2 / γ) and equiaxed γ grains, with an average grain size of 0.95μm. After testing, the room-temperature tensile strength of the formed part can reach 954 MPa, and the elongation is 1.9%.

[0052] Perform heat treatment (1390°C / 2h) on the samples of the as-deposited formed part, as Figure 7 shown, the microstructure is uniformly fine fully lamellar structure, and the size of the lamellar crystal clusters is 50~60μm. After testing, the room-temperature tensile strength of the sample in the heat-treated state is 662 MPa, and the elongation is 1.81%. The room-temperature mechanical properties of the TiAl alloy parts prepared in this application in different states are shown in Table 1.

[0053] Table 1 Room-temperature mechanical properties of TiAl alloy parts prepared in this application in different states

[0054]

[0055] Compared with the Ti-48Al-2Cr-2Nb alloy, the Ti-46Al-2.2Mn-2Nb-0.8B alloy has a significantly increased tensile strength while maintaining the same plastic level. As Figure 8 shown, the solidification process of the Ti-46Al-2.2Mn-2Nb-0.8B alloy follows the β solidification path: L→L+β→β→β+α→α→α2+γ. During the β→α phase transformation, the β and α phases satisfy the Burgers orientation relationship. Similarly, during the precipitation of the γ phase from the α phase, the γ and α phases satisfy the Burgers (a Dutch crystallographer's name) orientation relationship. The addition of boride has an impact on a series of phase transformation processes of the matrix L→β, β→α, and α→α2+γ. On the one hand, boride can act as heterogeneous nucleation sites to help the β grains nucleate during the L→β transformation, and act as heterogeneous nucleation sites for α and γ respectively during the β→α and α→α2+γ phase transformations, forming daughter phases that do not have an orientation relationship with the parent phase, thereby significantly refining the grains. On the other hand, the presence of boride can hinder the growth of daughter phase grains. During the electron beam additive manufacturing process, the tiny molten pool solidifies at an extremely fast cooling rate, and a large degree of supercooling is conducive to the formation of crystal nuclei, promoting grain refinement. Therefore, the Ti-46Al-2.2Mn-2Nb-0.8B alloy prepared by electron beam additive manufacturing technology effectively improves the mechanical properties of the material through multiple grain refinement mechanisms.

[0056] It should be understood that the orientation or positional relationships indicated by terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. in the above description are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the embodiments of the present invention.

[0057] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0058] In the embodiments of the present invention, unless otherwise clearly defined or limited, terms such as "install", "connect", "couple", "fix", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0059] In the embodiments of the present invention, unless otherwise clearly defined or limited, the first feature being "above" or "below" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely means that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "below" and "beneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely means that the horizontal height of the first feature is lower than that of the second feature.

[0060] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example" or "some examples", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0061] Those skilled in the art will readily conceive of other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention, which follow the general principles of the present invention and include the common general knowledge or conventional technical means in the technical field not disclosed in the present invention. The specification and examples are only regarded as exemplary, and the true scope and spirit of the present invention are pointed out by the appended claims.

Claims

1. An additive manufacturing method for TiAl alloy, characterized in that, Including: Select TiAl alloy powder with a particle size range of 45 - 150 μm. The atomic percentage of Al, Mn, Nb, and B in the TiAl alloy powder is respectively: 43 - 46%, 2.2 - 2.4%, 2 - 2.1%, 0.5 - 1%, and the balance is Ti; Establish a three-dimensional model of the part; Plan the scanning path: When the cross-sectional width of the part is less than the preset partition width, scan with the standard scan line length; when the cross-sectional width of the part is greater than or equal to the preset partition width, divide the cross-section of the part into regions and scan with the partition scan line length. Among them, the value range of the preset partition width is 10 mm - 45 mm, the standard scan line length is greater than the partition scan line length, the partition overlap width is 0.05 mm - 0.1 mm, and the partition offset width ≥ 3 mm; the partition scan line length is 10 mm - 30 mm; Substrate preheating: Load the TiAl alloy powder into the powder bin of the electron beam additive manufacturing equipment for scanning preheating. Among them, the electron beam scanning speed in the substrate preheating stage is 10 - 20 m / s, the electron beam scanning current is 20 - 90 mA, and the substrate is preheated to 1050 - 1100 °C; Solid melting: The electron beam scanning speed in the solid melting stage is 3 - 5 m / s, and the electron beam scanning current is 15.5 - 17.5 mA.

2. The additive manufacturing method of the TiAl alloy according to claim 1, wherein The powder particle size D of the TiAl alloy powder 50 = 70~80 μm, D 90 = 120~130 μm, and the powder fluidity is 25~35 s / 50 g.

3. The additive manufacturing method of the TiAl alloy according to claim 1, characterized in that, The value range of the preset partition width is 10 mm - 30 mm.

4. The additive manufacturing method of the TiAl alloy according to claim 3, characterized in that For the cross-section of the part that needs to be divided into regions, divide the cross-section of the part into multiple partitions. When the sum of the widths of some partitions in the multiple partitions is less than the partition scan line length, perform combined melting scanning on this part of the partitions.

5. The additive manufacturing method of the TiAl alloy according to claim 1, characterized in that, The slice layer thickness of the three-dimensional model is 50 - 100 μm, the scanning method is serpentine scanning, and the adjacent scan line spacing is 0.05 - 0.15 mm.

6. The additive manufacturing method of the TiAl alloy according to claim 1, wherein The energy input during the solid melting stage is 26.67 - 36.67 J / mm 3 , the electron beam scanning current is 16 - 16.5 mA, and the electron beam scanning speed is 3 - 4 m / s.

7. The additive manufacturing method of the TiAl alloy according to claim 1, characterized in that, The method further includes: performing microstructure analysis on the formed part.

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