A method for ultra-high temperature plastic forming of TiAl alloy blades

Abstract

The present invention provides a method for ultra-high temperature plastic forming of TiAl alloy blades, which relates to the field of ultra-high temperature forming engine blades, and includes the following steps: preparing a TiAl alloy blade blank; spraying a lubricating coating on the periphery of the blade blank, and spraying a mold release agent on the mold; placing the blade blank in a vacuum isothermal forming device, heating it to an ultra-high temperature for ultra-high temperature die forging, and obtaining a forged blank after cooling; and performing subsequent processing on the forged blank to obtain a TiAl alloy blade. The present invention uses a vacuum isothermal deformation device to ultra-high temperature to prepare TiAl alloy blades, which greatly reduces the deformation resistance of the alloy, avoids cracking of the mold and the material, and improves the yield rate and equipment utilization rate; makes full use of the β to α transformation in the solid phase transformation process to form a variety of variants, and can obtain a near-lamellar or full-lamellar structure with uniform organization and smaller size; a single deformation can obtain a product that meets the service organization.

Description

Technical Field

[0001] The invention relates to the field of ultra-high temperature forming engine blades, and in particular to an ultra-high temperature plastic forming method for TiAl alloy blades. Background Art

[0002] The characteristics of TiAl alloy are: light weight and high strength, excellent high temperature mechanical properties, and superior oxidation resistance. It is the best iterative material for increasing thrust-to-weight ratio, improving fuel efficiency, and achieving lightweight in aerospace and vehicle engines. The density of TiAl alloy is about 4.1-4.3g / cm 3 , which is half of that of nickel-based high-temperature alloys. TiAl alloys can maintain good high-temperature tensile properties and creep properties in the high-temperature range of 600-900°C. Deformed TiAl alloys have the advantages of uniform and fine structure and excellent performance, and have broad application prospects in aerospace and vehicle engines.

[0003] However, at present, deformed TiAl alloys are usually melted into billets, forged, and prepared by conventional forging or isothermal die forging. The blade forging blanks are then combined with subsequent complicated heat treatment processes to control the organization, and finally machined into parts of specific shapes. Affected by the thermal strength of the metal mold, the die forging is generally carried out in the α+γ dual-phase region of about 1200°C, and the forging is a dual-state organization. In order to improve the service performance of TiAl alloys, heat treatment at a higher temperature is required after forging to increase the content of lamellar clusters. Since the organization is coarse and uneven after full lamellar treatment, the heat treatment is difficult and the effect is not ideal. In addition, the required vacuum isothermal deformation equipment is complex and expensive. These problems hinder the application of deformed TiAl alloys. Therefore, the vacuum isothermal forging process that shortens the process flow and accurately controls the organization needs to be explored urgently.

[0004] In the prior art, a method for forming blade blanks by using isothermal forging and superplasticity of materials under high temperature and low strain has been proposed. This process has strict requirements on equipment and experimental conditions, and requires subsequent heat treatment, which has high time and equipment costs. Another person skilled in the art has proposed "an ultra-high temperature vacuum isothermal forging device and a sheath-free isothermal forging method for intermetallic compounds", and proposed to use vacuum isothermal forging equipment to deform intermetallic compounds, reducing problems such as oxidation, and the required organization needs to be regulated by subsequent heat treatment. Lin Junpin et al. proposed "a full-lamellar deformed TiAl alloy and its preparation method", which uses high-temperature forging equipment to deform in the single-phase α zone and precisely control cooling to obtain a fine full-lamellar organization. The single-phase α phase zone deformation method is conducive to obtaining a fine full-lamellar organization, but it requires the alloy to have a good processing window and has strict temperature control requirements.

[0005] At present, there are still many problems in the process and equipment of high-temperature forming TiAl alloys, such as insufficient temperature tolerance of the equipment, short service life of the die due to the large deformation resistance of intermetallic compounds during die forging, high equipment maintenance costs, and coarse alloy structure due to long-term heat preservation. In addition, due to the complex process flow, it is difficult to efficiently obtain blades with service structure, and subsequent heat treatment is required, so the cost is also high. Summary of the invention

[0006] The present invention provides a TiAl alloy blade ultra-high temperature plastic forming method to solve the technical problems in the prior art that during the TiAl alloy forming process, the alloy has high deformation resistance, the mold is easy to be damaged, the alloy structure is coarse, and it is difficult to efficiently obtain blades with service structure.

[0007] In order to achieve the above-mentioned invention object, the technical solution provided by the present invention is as follows:

[0008] A TiAl alloy blade ultra-high temperature plastic forming method comprises the following steps:

[0009] S1. A TiAl alloy blade blank having a certain grain size is prepared by deformation means or casting technology, and processed into a blank shape required for die forging;

[0010] S2, spraying lubricating paint on the outer periphery of the blade blank and spraying a release agent on the mold;

[0011] S3, placing the blade blank sprayed with lubricating coating into a vacuum isothermal forming device, heating it to an ultra-high temperature for ultra-high temperature die forging, wherein the ultra-high temperature die forging temperature is in the α+β dual-phase region or the β single-phase region, and the specific temperature is slightly different according to the alloy composition, and then taking it out after controlled cooling to obtain a forging blank;

[0012] S4. The forging blank is subsequently processed to obtain a TiAl alloy blade having a structure that meets service requirements.

[0013] Preferably, the grain size of the blade blank in S1 is less than 500 μm.

[0014] Preferably, the composition of the TiAl alloy is Ti-(43-47)Al-(4-8)Nb-(0-0.5)Mo-aX-bZ, wherein the X element may be composed of one or more metal elements selected from Cr, V, Ta, W, Mn and rare earth elements, and the Z element may be composed of one or more non-metal elements selected from C, B, Si and N, a and b are both less than 1, the total atomic content of the X element does not exceed 2%, the total atomic content of the Z element does not exceed 2%, and the rest are impurity elements. The main function of adding the X and Z elements here is to refine the structure.

[0015] Preferably, the lubricating coating and the release agent in S2 are both high temperature resistant boron nitride powder or emulsion.

[0016] Preferably, the mold in S2 is a high-purity hard graphite mold.

[0017] Preferably, the ultra-high temperature die forging rate in S3 is ≤0.1s -1 , cooling rate ≤100℃ / min. After the ultra-high temperature die forging is completed, the solid phase transformation process of the alloy structure during the cooling process is β+α→α→γ+α→γ+α2 or β→β+α→α→γ+α→γ+α2.

[0018] Preferably, the temperature of the ultra-high temperature die forging in S3 is 1360-1450°C.

[0019] Preferably, the heating process of ultra-high temperature die forging in S3 includes three stages: in the first stage, the temperature is increased to 800°C at a rate of 30-100°C / min, and the average temperature is 0-60min; in the second stage, the temperature is increased to 1250°C at a rate of 20-50°C / min, and the average temperature is 0-60min; in the third stage, the temperature is increased to the ultra-high temperature die forging temperature at a heating rate of ≤20°C / min, and the average temperature is 0-60min.

[0020] Preferably, the subsequent processing in S4 includes wire cutting, milling, grinding and / or surface treatment.

[0021] Preferably, the structure of the TiAl alloy blade in S4 is a near-lamellar or full-lamellar structure with a size of 50-130 μm.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] The present invention prepares TiAl alloy blades at ultra-high temperature through vacuum isothermal deformation equipment, and through deformation in the α+β two-phase region or the β single-phase region, the deformation resistance of the alloy is greatly reduced, the cracking of the mold and the material is avoided, and the yield rate of alloy deformation and the equipment utilization rate are improved; the ultra-high temperature deformation method provides a sufficient deformation window for the alloy, and deformation in the α+β two-phase region and the β single-phase region produces tissue refinement. At the same time, it fully utilizes the transformation from β to α in the solid-state phase change process to form a variety of variants, which is beneficial to the precise regulation of the organization during the controlled cooling process, and can form α2 / γ lamellar clusters with completely different orientations in the β grains, thereby obtaining a near-lamellar or full-lamellar organization with uniform organization and smaller size; the ultra-high temperature plastic forming method can achieve a single deformation to obtain a product that meets the service organization, the deformation is fully automated, the process is simple, stable, efficient, and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1The organizational structure diagram of a TiAl alloy blade prepared by an ultra-high temperature plastic forming method of a TiAl alloy blade provided in Example 1;

[0025] Figure 2 The organizational structure diagram of a TiAl alloy blade prepared by an ultra-high temperature plastic forming method of a TiAl alloy blade provided in Example 2;

[0026] Figure 3 The organizational structure diagram of a TiAl alloy blade prepared by an ultra-high temperature plastic forming method of a TiAl alloy blade provided in Example 3;

[0027] Figure 4 The organizational structure diagram of a TiAl alloy blade prepared by an ultra-high temperature plastic forming method of a TiAl alloy blade provided in Example 4;

[0028] Figure 5 This is a diagram of the organizational structure of a TiAl alloy blade prepared by the ultra-high temperature plastic forming method of a TiAl alloy blade provided in Comparative Example 1. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment provides a TiA1 alloy blade ultra-high temperature plastic forming method, comprising the following steps:

[0032] S1. Prepare a blade blank of TiAl alloy, wherein the grain size of the blade blank is 150 μm, and process it into a blank shape required for die forging, wherein the composition of the TiAl alloy is: Ti-43Al-4Nb-0.5Mo-0.1B;

[0033] S2. Use a high-pressure spray gun to evenly spray boron nitride (BN) emulsion on the rough blade and the working surface of the high-purity hard graphite mold, and dry them for later use;

[0034] S3. Place the blade blank sprayed with lubricating coating into vacuum isothermal forming equipment, heat it to ultra-high temperature for ultra-high temperature die forging, and the heating process of ultra-high temperature die forging: heat it to 800℃ at a heating rate of 30℃ / min, keep it warm for 0min, then heat it to 1250℃ at a heating rate of 50℃ / min, keep it warm for 60min, then heat it to 1450℃ (β phase region) at a heating rate of 15℃ / min, keep it warm for 5min, and then heat it to 150℃ (β phase region) at a strain rate of 0.05s -1 After forging, the forging blank is taken out after controlled cooling. The cooling rate is 50℃ / min. During the cooling process, the solid phase transformation process of the alloy structure is β→β+α→α→γ+α→γ+α2;

[0035] S4. The forging blank is subjected to wire cutting to remove the flash of the forging blank, and is subjected to appropriate machining to obtain a TiAl alloy blade having a structure that meets service requirements.

[0036] Figure 1 This is the organizational structure diagram of the TiAl alloy blade prepared in this embodiment. The organization is a full-layer of 130μm, the organization is equiaxed, there is no obvious deformation texture, and the organization uniformity is good.

[0037] Example 2

[0038] This embodiment provides a TiAl alloy blade ultra-high temperature plastic forming method, comprising the following steps:

[0039] S1. Prepare a blade blank of TiAl alloy, wherein the grain size of the blade blank is 115 μm, and process the blank into a blank shape required for die forging, wherein the composition of the TiAl alloy is: Ti-44.5Al-4Nb-0.5Mo-0.1B;

[0040] S2. Use a high-pressure spray gun to evenly spray boron nitride (BN) emulsion on the rough blade and the working surface of the high-purity hard graphite mold, and dry them for later use;

[0041] S3, placing the blade blank sprayed with lubricating coating into vacuum isothermal forming equipment, heating to ultra-high temperature for ultra-high temperature die forging, ultra-high temperature die forging heating process: heating to 800°C at a heating rate of 100°C / min, keeping warm for 60min, then heating to 1250°C at a heating rate of 20°C / min, keeping warm for 0min, then heating to 1400°C (α+β phase region) at a heating rate of 15°C / min, keeping warm for 5min, and then heating at a strain rate of 0.03s -1 After forging, the forging blank is taken out after controlled cooling. The cooling rate is 50℃ / min. During the cooling process, the solid phase transformation process of the alloy structure is β+α→α→γ+α→γ+α2;

[0042] S4. The forging blank is subjected to wire cutting to remove the flash of the forging blank, and is subjected to appropriate machining to obtain a TiAl alloy blade having a structure that meets service requirements.

[0043] Figure 2 This is the organizational structure diagram of the TiAl alloy blade prepared in this embodiment. The organization is a full lamellar organization with a size of 100 μm. The organization is spindle-shaped, with a certain amount of fine γ grains remaining around the lamellar cluster boundary, and there is a relatively obvious deformation texture.

[0044] Example 3

[0045] This embodiment provides a TiAl alloy blade ultra-high temperature plastic forming method, comprising the following steps:

[0046] S1. Prepare a blade blank of TiAl alloy, the grain size of which is 90 μm, and process it into a blank shape required for die forging. The composition of the TiAl alloy is Ti-47Al-8Nb-0.2W-0.1B-0.05Y.

[0047] S2. Use a high-pressure spray gun to evenly spray boron nitride (BN) emulsion on the rough blade and the working surface of the high-purity hard graphite mold, and dry them for later use;

[0048] S3. Place the blade blank sprayed with lubricating coating into vacuum isothermal forming equipment, heat it to ultra-high temperature for ultra-high temperature die forging, and the heating process of ultra-high temperature die forging: heat it to 800℃ at a heating rate of 65℃ / min, keep it warm for 30min, then heat it to 1250℃ at a heating rate of 40℃ / min, keep it warm for 30min, then heat it to 1360℃ (α+β phase region) at a heating rate of 13℃ / min, keep it warm for 5min, and then heat it to 1360℃ (α+β phase region) at a heating rate of 13℃ / min. -1 After forging, the forging blank is taken out after controlled cooling, and the cooling rate is 50℃ / min;

[0049] S4. The forging blank is subjected to wire cutting to remove the flash of the forging blank, and is subjected to appropriate machining to obtain a TiAl alloy blade having a structure that meets service requirements.

[0050] Figure 3 This is the organizational structure diagram of the TiAl alloy blade prepared in this embodiment. The organization is a near-lamellar organization with a size of 50 μm. The organization is equiaxed, with residual γ grain strips left due to deformation, and there is a relatively obvious deformation texture.

[0051] Example 4

[0052] This embodiment is similar to Embodiment 1, except that in this embodiment, the composition of the TiAl alloy in S1 is Ti-43Al-4Nb-0.5Mo.

[0053] Figure 4 This is the organizational structure diagram of the TiAl alloy blade prepared in this embodiment. After forging, controlled cooling is performed to obtain a full lamellar organization with an average lamellar cluster size of 200μm. The organization is equiaxed, there is no obvious deformation texture, and the organization has good uniformity.

[0054] contrast Figure 1 and Figure 4 It can be seen that adding X and Z elements can promote tissue refinement and improve the mechanical strength of the leaves.

[0055] Comparative Example 1

[0056] This comparative example is similar to Example 1, except that the temperature of the ultra-high temperature die forging in this example is 1270° C. (α+γ phase region).

[0057] Figure 5 This is the organizational structure diagram of the TiAl alloy blade prepared in this comparative example. Its organization is a twisted lamellar organization and γ grains. The organization is uneven and the performance is poor. Further regulation is required before it can be used.

[0058] The blades in Examples 1-4 and Comparative Example 1 were taken to measure the mechanical strength and mold service life. The measured data are shown in Table 1;

[0059] Table 1 Blade performance test data

[0060]

[0061] Note: Mould replacement cycle / service life: refers to the service life of the mould during the processing, that is, the maximum number of parts that can be processed without changing the mould, unit (piece).

[0062] When W and Y (yttrium) in Example 3 are replaced by Mn, Cr, V, and Ta, and B is replaced by C, Si, and N, the microstructure and mechanical properties of the obtained TiAl alloy blade are similar to those in Example 3.

[0063] from Figures 1 to 5 It can be seen that the blade prepared by the preparation method of the present invention has a distinct lamellar structure and good tissue uniformity. According to the data in Table 1, it can be found that the blades prepared by the preparation methods in Examples 1, 2, and 3 have excellent mechanical strength and the mold has a long service life during the preparation process.

[0064] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A TiAl alloy blade ultra-high temperature plastic forming method, characterized in that: The following steps are involved: S1. Preparing a blade blank of TiAl alloy; the composition of the TiAl alloy is: Ti-(43-47)Al-(4-8)Nb-(0-0.5)Mo-aX-bZ, wherein the X element is composed of one or more metal elements selected from Cr, V, Ta, W, Mn and rare earth elements, the Z element is composed of one or more non-metal elements selected from C, B, Si and N, and both a and b are less than 1; S2, spraying lubricating paint on the outer periphery of the blade blank and spraying a release agent on the mold; S3, placing the blade blank sprayed with lubricating coating into a vacuum isothermal forming device, heating it to an ultra-high temperature for ultra-high temperature die forging, wherein the temperature of the ultra-high temperature die forging is in the α+β dual-phase region or the β single-phase region, and the temperature of the ultra-high temperature die forging is 1360-1450°C, and then taking it out after controlled cooling to obtain a forging blank; the ultra-high temperature die forging rate is ≤0.1s -1 , cooling rate ≤ 100℃ / min; the ultra-high temperature die forging heating process includes 3 stages, the first stage, heating to 800℃ at a rate of 30-100℃ / min, average temperature 0-60min; the second stage, heating to 1250℃ at a rate of 20-50℃ / min, average temperature 0-60min; The third stage is to heat up to the ultra-high temperature die forging temperature at a heating rate of ≤20°C / min, and the temperature is averaged for 0-60min; S4. The forging blank is subsequently processed to obtain the TiAl alloy blade, wherein the structure of the TiAl alloy blade is a near-lamellar or full-lamellar structure with a size of 50-130 μm.

2. The ultra-high temperature plastic forming method of a TiAl alloy blade according to claim 1, characterized in that: The grain size of the blade blank in S1 is less than 500 μm.

3. The ultra-high temperature plastic forming method of a TiAl alloy blade according to claim 1, characterized in that: The lubricating coating and the release agent described in S2 are both high temperature resistant boron nitride powder or emulsion.

4. The ultra-high temperature plastic forming method of a TiAl alloy blade according to claim 1, characterized in that: The mold is a high-purity hard graphite mold.

5. The ultra-high temperature plastic forming method of a TiAl alloy blade according to claim 1, characterized in that: The subsequent processing described in S4 includes wire cutting, milling, grinding and / or surface treatment.

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