Additive manufacturing method of TiAl alloy

Abstract

The invention relates to a TiAl alloy additive manufacturing method. The TiAl alloy additive manufacturing method comprises the steps that TiAl alloy powder is selected; establishing a three-dimensional model; a scanning path is planned; when the section width of the part is smaller than the preset partition width, a standard scanning line length is adopted for scanning; on the contrary, the section of the part is subjected to region division, and the partition scanning line length is adopted for scanning; the standard scanning line is longer than the partition scanning line; and the TiAl alloy powder is loaded into a powder bin of electron beam additive manufacturing equipment, and scanning melting is carried out. According to the method, the content of the Al element in the TiAl alloy powder is controlled, so that the alloy solidification process is carried out according to a beta solidification path, and formation of fine isometric crystals is facilitated; by controlling the content of the B element, borides which are distributed in a dispersed mode are formed, and the effect of refining the microscopic structure is achieved; by setting the preset partition width, the partition lap joint width and the partition offset width, the structure and performance difference caused by remelting at the partition scanning lap joint is solved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of additive manufacturing technology, and in particular to an additive manufacturing method of 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 high-temperature alloy. It is a very promising lightweight high-temperature alloy with great advantages in reducing the weight of aircraft engines. It is considered to be a new generation of high-temperature resistant lightweight structural material with a service temperature range of 650~900℃.

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

[0004] In the related art, by adjusting the composition of TiAl alloy (such as adding Ta, W, etc.), the mechanical properties of the alloy are significantly improved, and the use temperature is increased. However, the addition of Ta and W elements will bring about problems such as solidification segregation, high alloy density, and high cost; it is difficult to meet the forming requirements of large-scale complex TiAl alloy components by only 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 section is intended to provide background or context for the technical solutions of the present invention stated in the claims. The description herein is not admitted to be prior art by inclusion in this section. Summary of the invention

[0007] The object of the present invention is to provide a method for additive manufacturing of TiAl alloy, thereby solving one or more problems caused by limitations and defects of the related art at least to a certain extent.

[0008] The present invention provides a TiAl alloy additive manufacturing method, comprising: A TiAl alloy powder with a particle size range of 45-150 μm is selected, wherein the atomic percentages of Al, Mn, Nb and B in the TiAl alloy powder are 43-46%, 2.2-2.4%, 2-2.1% and 0.5-1%, respectively, and the balance is Ti; Build a 3D model of the part; Plan the scanning path: when the width of the part section is less than the preset partition width, the standard scanning line length is used for scanning; when the width of the part section is greater than or equal to the preset partition width, the part section is divided into regions and the partition scanning line length is used for scanning; wherein the preset partition width ranges from 10mm to 45mm, the standard scanning line length is greater than the partition scanning line length, the partition overlap width is 0.05mm to 0.1mm, and the partition offset width is ≥3mm; Substrate preheating: the TiAl alloy powder is loaded into the powder bin of the electron beam additive manufacturing equipment for scanning preheating, wherein 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 3~5m / s, and the electron beam scanning current is 15.5~17.5mA.

[0009] In the present invention, the powder particle size D of the TiAl alloy powder is 50 =70~80μm, D 90 =120~130μm, powder fluidity is 25~35s / 50g.

[0010] In the present invention, the partition scanning line length is 10mm~30mm.

[0011] In the present invention, the preset partition width ranges from 10 mm to 30 mm.

[0012] In the present invention, for a part cross section that needs to be divided into regions, the part cross section is divided into multiple partitions, and when the sum of the widths of some of the multiple partitions is less than the partition scanning line length, the partial partitions are merged and melt scanned.

[0013] 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 spacing between adjacent scanning lines is 0.05-0.15 mm.

[0014] In the present invention, the energy input in the solid melting stage is 26.67~36.67J / mm 3 , the electron beam scanning current is 16~16.5mA, and the electron beam scanning speed is 3~4m / s.

[0015] In the present invention, the method further comprises: performing a tissue analysis on the formed part.

[0016] The technical solution provided by the present invention may include the following beneficial effects: In the present invention, by controlling the Al element content in the TiAl alloy powder, it is possible to ensure that the solidification process of the TiAl alloy is carried out according to the β solidification path, which is conducive to the formation of fine equiaxed crystals; by controlling the B element content, a dispersed boride can be formed, and the boride acts as a nucleation particle, which refines the microstructure by hindering the growth of grains; by setting a preset partition width, a partition overlap width, and a partition offset width, the problem of excessive difference in scanning line length and remelting of the partition scanning overlap when forming large-sized TiAl alloy complex components by electron beam selective melting is solved. The microstructure of the TiAl alloy parts prepared by the present application is a uniform and fine dual-state structure with more excellent mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0018] Figure 1 A schematic flow chart showing a method for additive manufacturing of a TiAl alloy in an exemplary embodiment of the present invention; Figure 2 It shows the organization of the overlap area and the non-overlap area when the partition offset width is 1mm; Figure 3 It shows the organization of the overlap area and the non-overlap area when the partition offset width is 3mm; Figure 4 A schematic diagram showing a partition arrangement during partition melting in an exemplary embodiment of the present invention; Figure 5 A schematic diagram showing a partition setting during partition melting in another exemplary embodiment of the present invention; Figure 6 An electron microscope image (5 μm) of an alloy in an exemplary embodiment of the present invention is shown; Figure 7 An electron microscope image (50 μm) of an alloy in an exemplary embodiment of the present invention is shown; Figure 8 A diagram showing the solidification path of an alloy in an exemplary embodiment of the present invention is shown. DETAILED DESCRIPTION

[0019] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the present invention will be more comprehensive and complete and fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0020] In addition, the accompanying drawings are only schematic illustrations of embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings represent the same or similar parts, and their repeated descriptions will be omitted. Some of the block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0021] This example embodiment provides a TiAl alloy additive manufacturing method, referring to Figure 1 As shown, the method includes steps S101 to S105, which are specifically as follows: Step S101: Select a TiAl alloy powder with a particle size range of 45-150 μm, wherein the atomic percentages of Al, Mn, Nb and B in the TiAl alloy powder are 43-46%, 2.2-2.4%, 2-2.1% and 0.5-1%, respectively, and the remainder is Ti. Preferably, the powder particle size D of the TiAl alloy powder is 50 =70~80μm, D 90 =120~130μm, powder fluidity is 25~35s / 50g.

[0022] Step S102: Establishing a three-dimensional model of the part, wherein the slice layer thickness of the three-dimensional model is 50-100 μm, for example, 60 μm, 70 μm, 80 μm, etc., but not limited thereto.

[0023] Step S103: Plan the scanning path: when the part section width is less than the preset partition width, use the standard scanning line length for scanning; when the part section width is greater than or equal to the preset partition width, divide the part section into regions and use the partition scanning line length for scanning; wherein the preset partition width has a value range of 10mm~45mm, the standard scanning line length is greater than the partition scanning line length, the partition overlap width is 0.05mm~0.1mm, and the partition offset width is ≥3mm.

[0024] In some embodiments, when the width of the part section of the odd-numbered layers of the part is less than the preset partition width, no area division is required; when the width of the part section of the even-numbered layers is greater than or equal to the preset partition width, the part section is divided into regions and scanned using the partition scanning line length. For example, when scanning the 1st, 3rd, 5th... layers of the part section, no area division is performed, and the serpentine scanning method or the like is directly used for scanning. The 2nd, 4th, 6th... layers of the part section are divided into regions before scanning.

[0025] For another example, see Figure 4 , when performing the area division operation on the nth layer, the 30mm width is divided into partition 1 and partition 2. At this time, the width D1 of partition 1 and the width D2 of partition 2 are both 15mm; for the layers behind the nth layer, the n+2, n+4, n+6, n+8, and n+10 layers are all divided into 3 partitions, and the width of each layer is as follows Figure 4 When the n+2th layer is melted, it is divided into three partitions (D1, D2 and D3) for melting. At this time, the widths of the three partitions are 12mm, 15mm and 3mm respectively, and the D1 and D3 areas can be melted together to ensure that the scanning line length is still 15mm; similarly, when the n+4th layer is melted, the widths of the three partitions (D1, D2 and D3) are 9mm, 15mm and 6mm respectively, and the areas D1 and D3 are melted together; until the n+10th layer, it is the same as the nth layer, divided into two areas (D1 and D2) for melting, and the width of the partitions is 15mm.

[0026] Step S104: preheating the substrate: the TiAl alloy powder is loaded into the powder bin of the electron beam additive manufacturing equipment for scanning preheating, wherein the electron beam scanning speed of 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.

[0027] Step S105: entity melting: the electron beam scanning speed in the entity melting stage is 3-5 m / s, and the electron beam scanning current is 15.5-17.5 mA.

[0028] In the preheating stage of the powder bed, the electron beam initial preheating current is 20~40mA, which is increased in 2~4 steps, so that the final current reaches 75~90mA, and the preheating time is 20~25s. In the post-preheating stage of the powder bed, the electron beam scanning current is maintained at 75~90mA, and the preheating time is 15~20s.

[0029] In this embodiment, by controlling the Al element content in the TiAl alloy powder, it is possible to ensure that the alloy solidification process follows the β solidification path, which is conducive to the formation of fine equiaxed crystals; by controlling the B element content, a dispersed boride can be formed, and the boride acts as a nucleation particle, which refines the microstructure by hindering the growth of grains; by setting the preset partition width, partition overlap width and partition bias width, the problem of excessive difference in scanning line length and remelting of the partition scanning overlap when the electron beam selective melting forms large-sized TiAl alloy complex components is solved. The microstructure of the TiAl alloy parts prepared by this application is a uniform and fine dual-state structure with more excellent mechanical properties.

[0030] Among them, for the setting of partition offset width, such as Figure 2 As shown in the figure, when the partition offset width is 1 mm, the overlap area has serious tissue burns due to remelting, and there is a significant difference in the tissue structure with the non-overlap area. Figure 3 As shown in the figure, when the partition offset width is 3mm, there is no obvious difference in the structure between the overlapping area and the non-overlapping area, and the forming quality is good, so the partition offset width d≥3mm.

[0031] On the basis of the above embodiments, the additive manufacturing method of TiAl alloy further includes: performing a microstructure analysis on the formed parts to analyze whether the quality of the formed parts meets the requirements, thereby verifying whether the additive manufacturing method is reasonable.

[0032] The additive manufacturing process of the present application is described below through a specific test example.

[0033] Step 1: Use plasma rotating electrode atomization method to make TiAl alloy rod into TiAl alloy powder with a particle size of 45~150μm, and the composition (atomic percentage) of the powder is Ti-46Al-2.2Mn-2Nb-0.8B. 50 =78μm, D 90 =123μm, powder fluidity is 27s / 50g.

[0034] Step 2: Create a 3D model of the part and perform path planning. Figure 5As shown in the figure, the size of the 3D model is 20mm×80mm×20mm, the scanning line spacing is 0.1mm, the serpentine scanning strategy is adopted, and the slice thickness is 90μm. During path planning, the area division processing is performed, and the preset partition width D=20mm, the partition overlap width is 0.05mm, and the partition offset width d=3mm. At the n+1 layer, it is divided into 4 areas (D1, D2, D3 and D4), all with a width of 20mm; at the n+3 layer, the partition offset is performed and divided into 5 areas (D1, D2, D3, D4 and D5), with widths of 17mm, 20mm, 20mm, 20mm and 3mm respectively, of which the D1 and D5 areas can be merged and melted so that the scanning line length is still 20mm. And so on, the layer-by-layer partition stacking is completed.

[0035] 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 after reaching the vacuum degree, carry out the powder spreading - preheating before the powder bed - selective melting and forming - preheating after the powder bed - powder spreading process layer by layer until the solid accumulation and forming of each layer is completed.

[0036] The printing process starts when the substrate is preheated to 1050~1100℃. The energy input for melting the solid parts is 26.67~36.67J / mm 3 , the corresponding electron beam scanning current is 16~16.5mA, and the electron beam scanning speed is 3~4m / s. In the preheating stage before the powder bed, the electron beam initial preheating current is 40mA, which is increased in 2~4 steps, so that the final current reaches 85mA, and the preheating time is 20~25s. In the post-preheating stage of the powder bed, the electron beam scanning current is maintained at 85mA, and the preheating time is 15~20s.

[0037] Step 4: Analyze the structure of the formed parts, such as Figure 6 As shown in the figure, the microstructure of the formed part is composed of uniform and fine lamellar crystals (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 954MPa and the elongation is 1.9%.

[0038] The samples of the deposited parts were heat treated (1390℃ / 2h), as shown in Figure 7 As shown, the microstructure is a uniform and fine full-lamellar structure, the lamellar crystal cluster size is 50~60μm, and the room temperature tensile strength of the sample in the heat-treated state is 662MPa and the elongation is 1.81%. The room temperature mechanical properties of the TiAl alloy parts prepared in this application under different conditions are shown in Table 1.

[0039] Table 1 Room temperature mechanical properties of TiAl alloy parts prepared in this application under different conditions Compared with Ti-48Al-2Cr-2Nb alloy, Ti-46Al-2.2Mn-2Nb-0.8B alloy has a significantly improved tensile strength while maintaining the same plasticity level. Figure 8 As shown in the figure, the solidification process of 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 orientation relationship. The addition of borides affects the matrix L→β, β→α, and α→α2+γ phase transformations. On the one hand, borides can act as heterogeneous nucleation points to help the nucleation of β grains during the L→β transformation, and act as heterogeneous nucleation points of α and γ during the β→α and α→α2+γ phase transformations, respectively, to form sub-phases that have no orientation relationship with the parent phase, thereby significantly refining the grains; on the other hand, the presence of borides can hinder the growth of sub-phase grains. During the electron beam additive manufacturing process, the tiny molten pool solidifies at an extremely fast cooling rate, and the large undercooling is conducive to the formation of crystal nuclei and promotes 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.

[0040] It should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like that may appear in the above description indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the embodiments of the present invention.

[0041] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0042] In the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, or a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] In the embodiments of the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0044] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction 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 may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0045] Those skilled in the art will readily appreciate 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 common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present invention are indicated by the appended claims.

Claims

1. A method for additive manufacturing of TiAl alloy, characterized in that: include: A TiAl alloy powder with a particle size range of 45-150 μm is selected, wherein the atomic percentages of Al, Mn, Nb and B in the TiAl alloy powder are 43-46%, 2.2-2.4%, 2-2.1% and 0.5-1%, respectively, and the balance is Ti; Build a 3D model of the part; Plan the scanning path: when the width of the part section is less than the preset partition width, the standard scanning line length is used for scanning; when the width of the part section is greater than or equal to the preset partition width, the part section is divided into regions and the partition scanning line length is used for scanning; wherein the preset partition width ranges from 10mm to 45mm, the standard scanning line length is greater than the partition scanning line length, the partition overlap width is 0.05mm to 0.1mm, and the partition offset width is ≥3mm; Substrate preheating: the TiAl alloy powder is loaded into the powder bin of the electron beam additive manufacturing equipment for scanning preheating, wherein 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 3~5m / s, and the electron beam scanning current is 15.5~17.5mA.

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

3. The additive manufacturing method of TiAl alloy according to claim 1, characterized in that: The partition scanning line length is 10mm~30mm.

4. The additive manufacturing method of TiAl alloy according to claim 3, characterized in that: The preset partition width ranges from 10 mm to 30 mm.

5. The additive manufacturing method of TiAl alloy according to claim 4, characterized in that: For a part cross section that needs to be divided into regions, the part cross section is divided into multiple partitions. When the sum of the widths of some of the multiple partitions is less than the partition scanning line length, a merged melting scan is performed on the partial partitions.

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

7. The additive manufacturing method of TiAl alloy according to claim 1, characterized in that: The energy input in the solid melting stage is 26.67~36.67J / mm 3 , the electron beam scanning current is 16~16.5mA, and the electron beam scanning speed is 3~4m / s.

8. The additive manufacturing method of TiAl alloy according to claim 1, characterized in that: The method further comprises: performing a structural analysis on the formed part.

Images