A method for eliminating anisotropy of microstructure and performance of additive manufactured ti-al alloy

Abstract

The application discloses a method for eliminating anisotropy of a microstructure and performance of additive manufacturing TiAl alloy, and relates to the field of additive manufacturing.The method comprises the following steps: step 1, depositing Ti48Al alloy by adopting an electric arc additive manufacturing technology to obtain a Ti48Al alloy deposition layer; step 2, performing in-situ heat treatment on the deposition layer, that is, performing re-scanning treatment on the deposition layer without adding deposition materials; and step 3, after the re-scanning treatment, continuously repeating steps 1 and 2 to deposit Ti48Al alloy, so that Ti48Al alloy with uniform full lamellar crystal group microstructure is obtained.The method can not only eliminate the non-uniformity and anisotropy of the microstructure of the additive manufacturing TiAl alloy, but also obtain the Ti48Al alloy with fine full lamellar crystal group microstructure and improve the mechanical performance of the material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of additive manufacturing, in particular to a method for eliminating the anisotropy of microstructure and performance of additive manufacturing TiAl alloy. BACKGROUND

[0002] With the continuous development of the aviation industry, the requirement for engine specific thrust is getting higher and higher. TiAl-based alloy has the advantages of low density, high specific strength, excellent high-temperature oxidation resistance and creep resistance, etc., so it can effectively reduce the mass of the engine while meeting the service requirements of the engine turbine blade, thereby improving the specific thrust of the engine, and is expected to become a substitute material for nickel-based high-temperature alloy, and has a bright application prospect in the field of aerospace engines. However, the room temperature ductility of TiAl alloy is low, and it is difficult to process and form complex-shaped workpieces by traditional preparation technology, the production cost is high, which restricts the development and application of TiAl alloy. Therefore, it is of great significance to develop a near-net-shape TiAl alloy processing and preparation technology.

[0003] Additive manufacturing is based on the principle of layer-by-layer deposition to prepare alloy parts, which can realize the near-net-shape forming of alloy parts. Compared with traditional process technology, additive manufacturing technology has the advantages of high forming efficiency, short cycle, good flexibility, low cost, etc., and has great advantages in preparing parts with complex structure and difficult to process and form. Therefore, in the preparation of TiAl alloy, additive manufacturing technology has great advantages, which has attracted great interest of domestic and foreign researchers, and extensive research has been carried out, and a large amount of research results have been achieved.

[0004] In the process of additive manufacturing, when the next layer is deposited, the deposited layer undergoes partial remelting and multiple heat treatment, forming a non-uniform non-equilibrium state microstructure, which has an adverse effect on the mechanical properties. The deposited TiAl-based alloy along the deposition direction forms an alternating layer band microstructure composed of complex microstructure and coarse lamellar crystal group organization, as well as anisotropic mechanical properties. No matter what additive manufacturing technology is used, the deposited TiAl alloy along the deposition direction forms an alternating layer band microstructure composed of dendritic crystals and full lamellar crystal groups, which leads to anisotropic mechanical properties, which has an adverse effect on the further development and application of additive manufacturing TiAl alloy technology.

[0005] So far, there is still a lack of methods that can effectively eliminate the non-uniformity of the microstructure of additive manufacturing TiAl-based alloy and improve the mechanical properties of the alloy, as well as methods for eliminating anisotropy.

[0006] Therefore, the person skilled in the art is committed to developing a method for eliminating the anisotropy of the microstructure and performance of additive manufacturing TiAl alloy, which can not only eliminate the unevenness and anisotropy of the microstructure of additive manufacturing TiAl-based alloy, but also obtain a fine full lamellar colony microstructure and improve the mechanical properties of the material. SUMMARY

[0007] In view of the above defects of the prior art, the technical problem to be solved by the present application is how to eliminate the anisotropy of the microstructure and performance of additive manufacturing TiAl alloy and improve its mechanical properties.

[0008] To achieve the above-mentioned purpose, the present application provides a method for eliminating the anisotropy of the microstructure and performance of additive manufacturing TiAl alloy, which comprises the following steps:

[0009] Step 1: depositing Ti48Al alloy to obtain a Ti48Al alloy deposition layer by using arc additive manufacturing technology;

[0010] Step 2: in-situ heat treatment of the deposition layer, i.e. without adding deposition material, re-scanning treatment of the deposition layer;

[0011] Step 3: after re-scanning treatment, continue to repeat steps 1 and 2 to deposit Ti48Al alloy to obtain Ti48Al alloy with uniform full lamellar colony microstructure.

[0012] Further, the arc additive manufacturing technology in step 1 is double-wire plasma arc additive manufacturing technology, and the specific process parameters are as follows: deposition current 90-115 A, substrate temperature 400-620℃, scanning speed 1-2 mm / s, and atmosphere argon.

[0013] Further, the microstructure of the Ti48Al alloy deposition layer in step 1 is uneven zonal characteristics along the deposition direction, which presents alternating distribution of dendritic structure zone and full lamellar colony microstructure zone.

[0014] Further, the lamellar spacing of the full lamellar colony microstructure in the deposition layer in step 1 is 0.45-0.7 μm.

[0015] Further, the size of the full lamellar colony microstructure in the deposition layer in step 1 is 200-350 μm.

[0016] Further, the in-situ heat treatment in step 2 is as follows: stop wire feeding, re-scan the Ti48Al alloy deposition layer obtained in step 1 at a re-scan speed of 1.5-3 mm / s, and the scanning direction of the re-scan treatment is the same as the scanning direction of the deposition process in step 1.

[0017] Further, the lamellar spacing of the full lamellar colony microstructure of the Ti48Al alloy obtained in step 3 is 0.12-0.54 μm.

[0018] Further, the size of the full lamellar colony microstructure of the Ti48Al alloy obtained in step 3 is 148-183 μm.

[0019] Further, the Ti48Al alloy deposition layers in steps 1-3 are accumulated layer by layer to form a Ti48Al deposition wall, the deposition direction of the Ti48Al deposition wall is the Z direction, the scanning direction is the Y direction, and the width direction is the X direction.

[0020] Further, the orientation distribution and room temperature tensile properties of the Ti48Al alloy microstructure obtained in step 3 are isotropic.

[0021] In a preferred embodiment of the present application, before in-situ heat treatment, the cooling mode of the deposition layer is natural cooling in an argon atmosphere.

[0022] Compared with the prior art, the present application has the following beneficial technical effects:

[0023] 1. The present application proposes a method of layer-by-layer rescan in the additive manufacturing process to achieve the purpose of in-situ heat treatment, eliminate the layer banding microstructure, and obtain a uniform full lamellar colony microstructure. In the process of layer-by-layer rescan, the number of thermal cycles of the deposited layer in the alpha phase region above the alpha phase transition temperature is increased, which promotes the transformation of dendritic crystal microstructure to full lamellar colony microstructure. Thus, the layer banding microstructure characteristics of the as-deposited TiAl alloy are eliminated, and a uniform full lamellar colony microstructure is obtained, eliminating the anisotropy of mechanical properties.

[0024] 2. The present application can simultaneously control the microstructure of the material during manufacturing, avoiding the adverse effects of subsequent heat treatment on the mechanical properties due to the growth of the colony size. By adjusting the process parameters of rescan, controlling the thermal cycle parameters, and then controlling the heat input size of rescan, the colony size and lamellar spacing of the full lamellar colony microstructure can be controlled, which can not only eliminate the uneven layer banding characteristics of the as-deposited TiAl alloy, but also reduce the size of the alloy colony microstructure and lamellar spacing, and improve the mechanical properties of the alloy.

[0025] 3. In the rescan process, the deposited layer is subjected to multiple heat treatments by layer-by-layer rescan, which promotes the transformation of the dendritic crystal microstructure of the as-deposited TiAl alloy to full lamellar colony microstructure, and from non-equilibrium state to equilibrium state, thereby improving the mechanical properties of the alloy.

[0026] The concept, specific structure and technical effects of the present application will be further described below with reference to the accompanying drawings to fully understand the purpose, features and effects of the present application. Attached Figure Description

[0027] Figure 1 These are three-dimensional metallographic images of TiAl alloy samples manufactured by dual-wire plasma arc additive manufacturing, representing comparative and preferred embodiments of the present invention.

[0028] Figure 2 These are the electron backscattering diffraction analysis results of the TiAl alloy samples manufactured by dual-wire plasma arc additive manufacturing in the comparative and preferred embodiments of the present invention.

[0029] Figure 3 These are three-dimensional images of the microhardness distribution of TiAl alloy samples manufactured by dual-wire plasma arc additive manufacturing in comparative and preferred embodiments of the present invention.

[0030] Figure 4 The comparative and preferred embodiments of the present invention show the room temperature mechanical tensile properties of TiAl alloys manufactured by dual-wire plasma arc additive manufacturing in the 0° and 90° directions. Detailed Implementation

[0031] The following description, with reference to the accompanying drawings, illustrates several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0032] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, the thickness of some components has been appropriately exaggerated in the drawings.

[0033] Comparative Example

[0034] Ti48Al alloy was prepared using dual-wire plasma arc additive manufacturing technology. Specific process parameters were as follows: deposition current 115 A, substrate temperature 560 °C, scanning speed 1.5 mm / s, argon atmosphere, and tailing argon protection. The Ti48Al alloy was deposited layer by layer using the same parameters to obtain the deposited Ti48Al alloy. The Ti48Al alloy deposits accumulated layer by layer to form a deposition wall. The deposition direction of the deposition wall was the Z-direction, the scanning direction was the Y-direction, and the width direction was the X-direction. The deposited Ti48Al alloy exhibited an uneven, banded characteristic along the Z-direction of the deposition direction, consisting of alternating dendritic and lamellar cluster regions. The size of the lamellar clusters was 208 μm, and the interlamellar spacing was 0.48 μm.

[0035] Example 1

[0036] Ti48Al alloy was prepared by double wire plasma arc additive manufacturing technology, and the specific process parameters were as follows: deposition current 115 A, substrate temperature 560 ℃, scanning speed 1.5 mm / s, and argon atmosphere with trailing argon protection. The as-deposited Ti48Al alloy showed uneven layer band characteristics along the deposition direction, which alternately distributed dendritic structure zone and full lamellar colony structure zone. In-situ heat treatment was carried out on the as-deposited Ti48Al alloy. During the process of layer-by-layer deposition of Ti48Al alloy by double wire plasma arc additive manufacturing, for each deposition layer, a re-scan speed of 1.5 mm / s was adopted, the wire feeding was stopped, and re-scan treatment was carried out, and Ti48Al alloy was prepared layer by layer, which was recorded as in-situ heat treatment 1.5-1.5. The deposition layers of Ti48Al alloy were accumulated layer by layer to form a deposition wall, the deposition direction of the deposition wall was Z direction, the scanning direction was Y direction, and the width direction was X direction. The scanning direction of re-scan treatment was the same as that of the deposition process. The full lamellar colony structure size of the in-situ heat treatment 1.5-1.5 sample was 183 μm, and the lamellar spacing of the full lamellar colony structure was 0.54 μm.

[0037] Example 2

[0038] Ti48Al alloy was prepared by double wire plasma arc additive manufacturing technology, and the specific process parameters were as follows: deposition current 115 A, substrate temperature 560 ℃, scanning speed 1.5 mm / s, and argon atmosphere with trailing argon protection. The as-deposited Ti48Al alloy showed uneven layer band characteristics along the deposition direction, which alternately distributed dendritic structure zone and full lamellar colony structure zone. In-situ heat treatment was carried out on the as-deposited Ti48Al alloy. During the process of layer-by-layer deposition of Ti48Al alloy by double wire plasma arc additive manufacturing, for each deposition layer, a re-scan speed of 1.5 mm / s was adopted, the wire feeding was stopped, and re-scan treatment was carried out, and Ti48Al alloy was prepared layer by layer, which was recorded as in-situ heat treatment 1.5-1.5. The deposition layers of Ti48Al alloy were accumulated layer by layer to form a deposition wall, the deposition direction of the deposition wall was Z direction, the scanning direction was Y direction, and the width direction was X direction. The scanning direction of re-scan treatment was the same as that of the deposition process. The full lamellar colony structure size of the in-situ heat treatment 1.5-1.5 sample was 183 μm, and the lamellar spacing of the full lamellar colony structure was 0.54 μm.

[0039] Example 3

[0040] Ti48Al alloy was prepared by double wire plasma arc additive manufacturing technology, and the specific process parameters were as follows: deposition current 90 A, substrate temperature 620 ℃, scanning speed 1 mm / s, and argon atmosphere, and trailing argon protection. The as-deposited Ti48Al alloy along the deposition direction presents uneven layer band characteristics alternatingly distributed by dendritic crystal organization area and full lamellar crystal organization area. The as-deposited Ti48Al alloy was in-situ heat treated. During the process of layer-by-layer deposition of Ti48Al alloy by double wire plasma arc additive manufacturing, for each deposition layer, a re-scan speed of 3 mm / s was adopted, the wire feeding was stopped, and re-scan treatment was carried out, and Ti48Al alloy was prepared layer by layer. The deposition layers of Ti48Al alloy are accumulated layer by layer to form a deposition wall, the deposition direction of the deposition wall is Z direction, the scanning direction is Y direction, and the width direction is X direction. The scanning direction of re-scan treatment is the same as that of the deposition process. After in-situ heat treatment, the full lamellar crystal organization size of the sample is 148 μm, and the lamellar spacing of the full lamellar crystal organization is 0.54 μm.

[0041] Example 4

[0042] Ti48Al alloy was prepared by double wire plasma arc additive manufacturing technology, and the specific process parameters were as follows: deposition current 90 A, substrate temperature 400 ℃, scanning speed 2 mm / s, and argon atmosphere, and trailing argon protection. The as-deposited Ti48Al alloy along the deposition direction presents uneven layer band characteristics alternatingly distributed by dendritic crystal organization area and full lamellar crystal organization area. The as-deposited Ti48Al alloy was in-situ heat treated. During the process of layer-by-layer deposition of Ti48Al alloy by double wire plasma arc additive manufacturing, for each deposition layer, a re-scan speed of 3 mm / s was adopted, the wire feeding was stopped, and re-scan treatment was carried out, and Ti48Al alloy was prepared layer by layer. The deposition layers of Ti48Al alloy are accumulated layer by layer to form a deposition wall, the deposition direction of the deposition wall is Z direction, the scanning direction is Y direction, and the width direction is X direction. The scanning direction of re-scan treatment is the same as that of the deposition process. After in-situ heat treatment, the full lamellar crystal organization size of the sample is 148 μm, and the lamellar spacing of the full lamellar crystal organization is 0.54 μm.

[0043] Figure 1 is a three-dimensional metallographic structure diagram of the double wire plasma arc additive manufacturing TiAl alloy sample of the comparative example and preferred examples 1 and 2 of the present application. The as-deposited Ti48Al alloy prepared in the comparative example is shown in Figure 1 (a), which presents obvious layer band distribution along the Z direction. The in-situ heat treated Ti48Al alloy prepared in examples 1 and 2 has the organization as shown in Figure 1 (b) and (c), which both present uniform full lamellar crystal organization, and the layer distribution characteristics have disappeared, indicating that the anisotropy of the organization disappears.

[0044] Figure 2 These are the electron backscattering diffraction analysis results of the TiAl alloy samples manufactured by dual-wire plasma arc additive manufacturing in comparative examples and preferred embodiments 1 and 2 of this invention. In-situ heat treatment 1.5-1.5 ( Figure 2 (b) and 1.5-3 samples ( Figure 2 (c) shows no significant difference in the orientation distribution diagram and pole figure of the full lamellar cluster structure in each direction of the texture intensity, and is similar to that of the deposited Ti48Al alloy. Figure 2 Compared to (a), the anisotropy of crystal orientation in each plane of the microstructure of the in-situ heat-treated sample is significantly reduced.

[0045] Figure 3 These are three-dimensional images of the microhardness distribution of TiAl alloy samples manufactured by dual-wire plasma arc additive manufacturing, representing the comparative examples and preferred embodiments 1 and 2 of this invention. It can be seen that the uniformity of the microhardness distribution in both groups of samples after in-situ heat treatment is significantly improved compared to the deposited state, and anisotropy disappears.

[0046] Figure 4 This describes the room-temperature mechanical tensile properties of TiAl alloy samples manufactured by dual-wire plasma arc additive manufacturing in the 0° and 90° directions, as shown in the comparative example and preferred embodiment 2 of this invention. Compared with deposited Ti48Al alloy (… Figure 4 (a) Compared to in-situ heat-treated sample 1.5-3, Figure 4 (b) shows significantly improved room temperature tensile properties and a significantly reduced degree of anisotropy.

[0047] The above embodiments, through the use of the heat treatment design concept of this invention, eliminate the non-uniform layered structure of Ti48Al alloy in plasma arc dual-wire additive manufacturing, and obtain a fine and uniform full-lamellar cluster structure. This invention, by controlling the process parameters of rescanning, achieves the goals of eliminating the non-uniform layered characteristics of the deposited TiAl alloy, reducing the size of the alloy cluster structure and the interlamellar spacing, and improving the mechanical properties of the alloy.

[0048] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method of eliminating anisotropy of microstructure and properties of an additively manufactured TiAl alloy, characterized in that, The method comprises the following steps: Step 1: depositing a Ti48Al alloy layer by using an electric arc additive manufacturing technology, wherein the specific process parameters are as follows: a deposition current of 90-115 A, a substrate temperature of 400-620 DEG C, a scanning speed of 1-2 mm / s, and an argon atmosphere; the microstructure of the Ti48Al alloy layer in step 1 presents an uneven zonal feature along the deposition direction, which is alternately distributed by dendritic crystal organization and full lamellar crystal organization; the lamellar spacing of the full lamellar crystal organization in the deposition layer in step 1 is 0.45-0.7 μm, and the size of the full lamellar crystal organization in the deposition layer in step 1 is 200-350 μm; Step 2: in-situ heat treatment of the deposition layer, i.e. without adding deposition materials, the deposition layer is subjected to a re-scan treatment; the in-situ heat treatment is as follows: stopping the wire feeding, and re-scanning the Ti48Al alloy deposition layer obtained in step 1 at a re-scan speed of 1.5-3 mm / s, wherein the scanning direction of the re-scan treatment is the same as that of the deposition process in step 1; Step 3: after the re-scan treatment, steps 1 and 2 are repeated to deposit Ti48Al alloy, so as to obtain Ti48Al alloy with uniform full lamellar crystal organization, wherein the lamellar distribution feature disappears, and the anisotropy of the microstructure disappears; the lamellar spacing of the full lamellar crystal organization in the obtained Ti48Al alloy is 0.12-0.54 μm, the size of the full lamellar crystal organization is 148-183 μm, and the orientation distribution and room temperature tensile properties of the microstructure of the obtained Ti48Al alloy are not anisotropic.

2. The method of claim 1, wherein, The Ti48Al alloy deposition layers in steps 1-3 are accumulated layer by layer to form a deposition wall, wherein the deposition direction of the deposition wall is the Z direction, the scanning direction is the Y direction, and the width direction is the X direction.

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