CN118291899A - Manufacturing method of 0-degree lamellar preferred orientation ultrahigh plasticity high niobium TiAl alloy - Google Patents

Abstract

The present invention belongs to the technical field of lightweight and high-temperature resistant TiAl intermetallic compounds, and discloses a method for manufacturing a high-niobium TiAl alloy with ultra-high plasticity and 0° lamellar preferential orientation. S1, first step hot extrusion in the α single-phase region; S2, intermediate annealing in the α+γ two-phase region; S3, second step hot extrusion in the α single-phase region; S4, post-annealing treatment. The present invention prepares a high-niobium TiAl alloy with fine-grained nearly full lamellar organizational characteristics by designing process systems such as two-step hot extrusion in the α single-phase region, intermediate annealing in the α+γ two-phase region, and post-annealing treatment, and simultaneously realizes precise control of the 0° lamellar preferential orientation. The present invention specifically solves the common problems of intrinsic brittleness and strength-plasticity mismatch of high-niobium TiAl alloys, and realizes a substantial simultaneous improvement in room temperature plasticity and wide temperature range strength; room temperature plasticity and strength within 850°C are at the highest level of current polycrystalline TiAl alloys, second only to PST-TiAl single crystals.

Description

A method for manufacturing a 0° lamellar preferred orientation ultra-high plasticity high niobium TiAl alloy

Technical Field

The invention relates to the technical field of lightweight, high-temperature-resistant TiAl intermetallic compounds, and in particular to a method for manufacturing a 0° lamellar preferentially oriented ultra-high plasticity high-niobium TiAl alloy.

Background technique

γ-TiAl-based intermetallic compounds (TiAl alloys for short) have outstanding advantages such as low density (4.0g/cm ³ ), excellent specific strength, specific modulus, oxidation resistance and creep resistance within 900℃, and are very likely to replace nickel-based high-temperature alloys in the fields of aerospace engines and thermal protection structures. Precision cast and die-forged TiAl alloy turbine blades, turbocharger impellers and valves have been used in new aircraft engines and automobile engines, achieving significant weight reduction and energy saving and emission reduction effects. However, metallic bonds and covalent bonds coexist in TiAl alloys, and the L1 ₀ structured γ-TiAl and DO ₁₉ structured α ₂ -Ti ₃ Al ordered phases have few movable slip systems, making dislocation movement difficult, resulting in the common problems of intrinsic brittleness at room temperature and strength-plasticity mismatch.

In terms of improving the room temperature plasticity, high temperature mechanical properties and service organization stability of TiAl alloys, the academic community has done a lot of research work in alloying, grain refinement, organization isomerization and lamellar orientation control. However, the room temperature plasticity of polycrystalline TiAl alloys has always been difficult to break through 2.5%; especially for hot-deformed TNM alloys co-alloyed with Nb and Mo, even if organization isomerization is achieved, the room temperature elongation is often less than 1.0%. Moreover, the improvement of the room temperature plasticity of current TiAl alloys often comes at the expense of high temperature strength, creep resistance and organization stability, and it is difficult to break the strength-plasticity inversion relationship. High niobium TiAl alloys (5% to 9% Nb, atomic percentage) have a significant solid solution strengthening effect, achieving excellent high temperature, high strength, creep resistance and oxidation resistance within 850°C, and are regarded as a model for the development of TiAl alloys. However, the room temperature brittleness of (polycrystalline) high niobium TiAl alloys is more prominent. They also face the problems of poor thermal stability of the α ₂ /γ lamellar structure, easy instability decomposition and precipitation of brittle β _o and ω (ω _o ) phases, which hinder the development and application of this type of alloy.

The latest research in the academic community shows that the control of lamellar preferential orientation will be a potential important measure to solve the room temperature brittleness and wide temperature range strength-plasticity inversion relationship of TiAl alloy. The most representative achievement is the polysynthetically twinned (PST) high niobium TiAl single crystal prepared by the team of Academician Chen Guang of Nanjing University of Science and Technology using the seed crystal method optical suspension directional solidification technology, which has achieved a leapfrog improvement in comprehensive properties such as room temperature plasticity, wide temperature range strength, creep resistance and thermal stability (Nature Mater.15(8)(2016)876-881; CN201410529844.5). This PST high niobium TiAl single crystal with a single 0° lamellar orientation (lamellar interface is parallel to the tensile direction) has a room temperature elongation of up to 6.9%, a yield strength of 708MPa, a tensile strength of 978MPa, and a yield strength of 637MPa at 900℃. However, directional solidification technology is limited by the TiAl alloy system and complex phase transformation process, with complex process, high equipment requirements and low production efficiency. In addition, the anisotropy of single crystal TiAl alloy is prominent, and the plasticity and fracture toughness perpendicular to the layer interface are very poor, which makes mechanical processing and assembly difficult, and also affects the use in specific high temperature and complex stress environments.

Hot-casing extrusion is a key method for TiAl alloy parent materials for aircraft engine blades. At present, the research results on hot extrusion of TiAl alloys at home and abroad have preliminarily proved that hot extrusion is conducive to achieving lamellar preferred orientation, and lamellar preferred orientation helps to improve room temperature plasticity and improve work hardening ability. Based on publicly published literature, in recent years, the Institute of Metal Research, Chinese Academy of Sciences, Beijing University of Science and Technology, and Northwest University of Technology have explored hot-casing extrusion technology for Ti4822, high niobium TiAl and TNM alloys, respectively, and have made certain progress in lamellar orientation control. However, the room temperature elongation of Ti4822, high niobium TiAl and TNM alloys with full lamellar or nearly full lamellar structures prepared by hot extrusion is difficult to exceed 2.5%, and the room temperature plasticity of TNM alloy is still less than 1.0%. This shows that the room temperature plasticity and high temperature strength of TiAl alloys by hot extrusion are affected by the coupling of multiple factors such as the degree of lamellar preferred orientation, lamellar structure characteristics and alloying effect. In order to achieve a simultaneous substantial improvement in both room temperature plasticity and wide temperature range strength of high niobium TiAl alloys, comprehensive improvements are needed in the hot extrusion process, heat treatment system and alloy composition.

Summary of the invention

Based on the above analysis, the purpose of the present invention is to provide a method for manufacturing a high-niobium TiAl alloy with ultra-high plasticity and 0° lamellar preferential orientation, which can solve the difficult problems of insufficient room temperature plasticity and inverted strength-plasticity relationship of high-niobium TiAl alloy by means of precise control of 0° lamellar preferential orientation and microstructural fine structure.

In order to achieve the above object, the technical solution adopted by the present invention is as follows: A method for manufacturing a 0° lamellar preferred orientation ultra-high plasticity high niobium TiAl alloy comprises the following steps:

S1, the first step of hot extrusion in the α single-phase region;

S2, intermediate annealing in the α+γ dual phase region;

S3, the second step of hot extrusion in the α single-phase region;

S4, post-annealing treatment.

The high niobium TiAl alloy has an α single phase region, the temperature span of the α single phase region is not less than 60°C, and below the γ phase/α phase transformation temperature _Tα , there is only an α+γ dual phase region, that is, there is no _βo and ω ( _ωo ) phase. The manufacturing method of the high niobium TiAl alloy initial billet is not required, but the oxygen content should be less than 0.10wt%, and the total extrusion ratio of the two-step hot extrusion of step S1+step S3 in the single α phase region is not less than 25:1.

The atomic percentage of Nb in the high niobium TiAl alloy is 5% to 6.5%. In step S1, the first step of hot extrusion in the α single phase region is to select a temperature of T _α + (0 to 40)°C in the single α phase region, keep the sheathed high niobium TiAl alloy billet warm for 0.5 to 4 hours, and then take it out of the furnace for hot extrusion.

In step S1, the α single-phase region is first hot extruded, the extrusion ratio is controlled between 4:1 and 9:1, and the extrusion speed is between 8 mm/s and 15 mm/s.

Experimental studies have shown that the first step of hot extrusion in the α single-phase region can generate a streamlined nearly full lamellar structure, with the lamellar interfaces of most lamellar crystal clusters parallel to the extrusion direction; the recrystallization and refinement of high-temperature α grains and the partial decomposition of the lamellar structure (L(α/γ)→γ+α) are simultaneously achieved. For high-niobium TiAl alloy billets produced by the melt-casting method, after the first step of hot extrusion in the α single-phase region in step S1, the lamellar crystal cluster size is generally less than 150μm, and a γ+α ₂ fine grain band with a ratio of 5% to 20% is generated.

In step S2, the intermediate annealing in the α+γ dual phase region is to place the hot extruded billet obtained in step S1 into a high temperature electric furnace or an atmosphere protection furnace, and perform annealing treatment in the α+γ dual phase region. Specifically, the billet is kept at a temperature between T _α -20°C and T _α -60°C for 1 to 8 hours, and after the annealing is completed, the billet is furnace cooled or air cooled to room temperature to obtain the alloy bar in the first step hot extrusion and intermediate annealing state.

Experimental studies have shown that after the first hot extrusion of the α single-phase region in step S1 and the intermediate annealing of the α+γ dual-phase region in step S2, the high-temperature _α grains will undergo dynamic recrystallization and refinement, and the α→γ phase transformation and partial decomposition of the lamellar structure (L(α/γ)→γ+α) will occur below the T α temperature, thus forming a streamlined fine-grained dual-state structure. The interface of most α ₂ /γ lamellar crystal clusters maintains an angle of ±15° with the extrusion direction, that is, the 0° lamellar preferred orientation is initially achieved; the lamellar crystal cluster size is generally less than 60μm, and there is a γ+α ₂ fine grain band with an area ratio of 20% to 50% around the lamellar crystal cluster.

In step S3, the second step of hot extrusion in the α single phase region is to re-sheath the rod-shaped billet obtained in step S2, and then select T _α + (30-90)° C. temperature in the single α phase region to complete the second step of hot extrusion.

In step S3, the second step of hot extrusion in the α single-phase region is to place the rod-shaped billet in a high-temperature electric furnace or an atmosphere-protected resistance furnace, keep it at T _α + (30-90)°C for 1-4 hours, and then take it out of the furnace for hot extrusion. The extrusion ratio is controlled at 6:1 to 16:1, and the extrusion speed is 10-18 mm/s.

According to a large number of experimental results, it is proved that the second step hot extrusion in the α single-phase region can further increase the lamellar cluster content to 90%, and the size of the lamellar cluster is basically less than 40μm; at the same time, a higher 0° lamellar preferred orientation strength is obtained, ensuring that 70% of the lamellar clusters have 0° lamellar preferred orientation.

In step S4, the post-annealing treatment is to perform annealing treatment in the α+γ dual-phase range on the extruded billet obtained in step S3, with the annealing temperature controlled between T _α and T _α -60°C for 1 to 6 hours.

In step S4, the annealing post-treatment, the heat treatment equipment used can be any one of a conventional high-temperature muffle furnace, a high-temperature atmosphere protection heat treatment furnace and a vacuum annealing furnace, and the cooling method can be furnace cooling and air cooling. Wherein, when the annealing temperature is between T _α and T _α -20°C, a fine-grained nearly full-lamellar structure with a preferred orientation of 0° lamellar will be formed, the size of the lamellar crystal cluster is generally less than 40μm, and the proportion of the lamellar crystal cluster is not less than 85%, that is, the higher the temperature, the higher the proportion of the lamellar crystal cluster. When the annealing temperature is between T _α -20°C and T _α -60°C, a fine-grained dual-state structure with a preferred orientation of 0° lamellar will be formed, the size of the lamellar crystal cluster is basically less than 30μm, and the proportion of the lamellar crystal cluster is 50% to 80%. The lower the annealing temperature, the lower the proportion of the lamellar crystal cluster.

According to a large number of experimental results, it has been proved that strictly implementing steps S1 to S4 can ensure that the lamellar interface of more than 70% of the lamellar crystal clusters, that is, the (0001) crystal plane of the α ₂ lamella, presents an angle of ±15° with the extrusion direction, that is, forming the so-called 0° lamellar preferred orientation. And the obtained 0° lamellar preferred orientation near full lamellar structure high niobium TiAl alloy has a crystal cluster size generally less than 40μm, a room temperature elongation of 4.5% to 6.5%, a yield strength of not less than 750MPa, a tensile strength of 920 to 1050MPa, and a tensile strength of 850℃ is still higher than 600MPa.

The basic design concept of the present invention is to ensure that the high-niobium TiAl alloy has a wide temperature range of α single-phase region, because the high-temperature disordered hcp structure α phase preferentially undergoes cylindrical slip during the unidirectional hot extrusion process, that is, the {1-100}<11-20> slip system is activated, and the basal plane {0001} of the high-temperature α grains after extrusion deformation will tend to be parallel to the extrusion direction. In this way, the two-step α phase region hot extrusion will promote the recrystallization and refinement of the α grains, and simultaneously form a wire texture with the {0001} α basal plane parallel to the extrusion direction. During the cooling to below the T _α temperature after hot extrusion and the annealing treatment in the dual-phase region, the γ lamellae are rapidly precipitated from the parent phase α grains to form an α/γ lamella structure. The precipitation of γ lamellae from α grains follows a strict Blackburn orientation relationship, i.e., {1-10}γ//{0001}α, <111>γ//<11-20>α, so that the lamellae interface of the high-temperature α/γ lamellae cluster inherits the preferred orientation of the {0001} basal plane of the parent phase α grain. When further cooled to below the eutectoid transformation temperature T _eu , the high-temperature α is ordered, and the α/γ lamellae structure is transformed into an α ₂ /γ lamellae structure, and the preferred orientation of the lamellae interface is always inherited, that is, the 0° lamellae preferred orientation is maintained. The two-step α phase hot extrusion, α+γ dual phase intermediate annealing and post-annealing treatment below T _α temperature are combined to achieve the 0° lamellae preferred orientation while ensuring the formation of fine α ₂ /γ lamellae clusters, achieving a cluster size of less than 40 microns and free of β _o and ω (ω _o ) brittle phases.

The beneficial effects of the present invention are as follows: the manufacturing method of a 0° lamellar preferentially oriented ultra-high plasticity high niobium TiAl alloy provided by the present invention is achieved by regulating the two-step hot extrusion in the α single-phase region, and assisting the intermediate annealing and post-annealing treatment in the α+γ dual-phase region. The method proposed by the present invention is faster, more efficient and more cost-effective than the seed crystal method for oriented solidification, and is second only to the PST TiAl single crystal in terms of mechanical properties. Compared with the previous hot extrusion and solution treatment schemes of TiAl alloys, the method of the present invention realizes the simultaneous and precise control of the lamellar crystal grain size and the 0° lamellar preferential orientation. Compared with the traditional hot extruded high niobium TiAl alloy, the 0° lamellar preferentially oriented high niobium TiAl alloy prepared by the present invention does not contain brittle β _o and ω (ω _o ) phases, and has higher room temperature plasticity and service thermal stability.

The present invention organically combines alloy design, 0° lamellar preferred orientation control and lamellar grain refinement, and successfully achieves a significant improvement in the room temperature plasticity and wide temperature range strength of high niobium TiAl alloy. The room temperature plasticity of conventional hot-extruded high niobium TiAl alloys reported so far is less than 2%, the room temperature plasticity of hot-extruded 4822 alloy is less than 2.5%, and the room temperature plasticity of hot-extruded TNM alloy is even less than 1.0%.

The present invention manufactures a 0° lamellar preferred orientation high niobium TiAl alloy Ti-45Al-6Nb (atomic ratio) with nearly full lamellar structure, the average cluster size is only 35 microns, and more than 70% of the lamellar clusters show 0° lamellar orientation characteristics. The room temperature elongation is up to 6.0%, the yield strength and tensile strength are as high as 750 and 970MPa respectively, and the tensile strength at 850℃ is still 640MPa. In terms of room temperature plasticity and tensile strength within 850℃, the 0° lamellar preferred orientation high niobium TiAl alloy manufactured by the present invention is at the highest level of current polycrystalline TiAl alloys, second only to PST TiAl single crystals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of the manufacturing process of 0° lamellar preferred orientation ultra-high plasticity high niobium TiAl alloy.

Figure 2 shows the microstructural characteristics of the single-phase α-phase primary hot extrusion observed by scanning electron microscopy;

FIG3 is the microstructural characteristics of the intermediate annealing sample observed by scanning electron microscope;

FIG4 is the microstructural characteristics of the 0° lamellar preferred orientation high niobium TiAl alloy observed by scanning electron microscope;

FIG5 is a room temperature tensile curve of a 0° lamellar preferred orientation high niobium TiAl alloy.

Detailed ways

The present invention provides a method for manufacturing an ultra-high plasticity high niobium TiAl alloy with 0° lamellar preferred orientation, as shown in FIG1 , which comprises the following steps: S1, first step hot extrusion in the α single-phase region; S2, intermediate annealing in the α+γ dual-phase region; S3, second step hot extrusion in the α single-phase region; S4, post-annealing treatment. The innovation of the present invention lies in: organically combining the two-step hot extrusion in the α single-phase region and the two-step annealing treatment in the α+γ dual-phase region, scientifically exerting the dynamic recrystallization and phase transformation decomposition effects, and realizing the rapid refinement of the lamellar crystal clusters; with the help of the secondary hot extrusion at a higher temperature in the α single-phase region, the texturing of the α grain {0001} basal plane and the high-strength 0° lamellar preferred orientation are realized. Compared with the traditional hot extrusion and solution treatment scheme, the high niobium TiAl alloy lamellar crystal clusters prepared by the present invention are fine, the crystal cluster size is generally less than 40μm, and more than 70% of the lamellar crystal clusters have 0° lamellar preferred orientation. Compared with the preparation of 0° lamellar oriented PST TiAl single crystal by seed crystal method, the manufacturing method of the present invention is faster, more efficient and cost-effective. The fine-grained high-niobium TiAl alloy with 0° lamellar preferred orientation has mechanical properties second only to the strength and plasticity of PST TiAl single crystal. Compared with the traditional hot extruded high-niobium TiAl alloy, the 0° lamellar preferred orientation high-niobium TiAl alloy manufactured by the present invention does not contain brittle β _o and ω (ω _o ) phases, and for the first time achieves a simultaneous leap-forward improvement in room temperature plasticity and wide temperature range strength.

In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

Example 1

This embodiment provides a method for manufacturing a 0° lamellar preferred orientation ultra-high plasticity high niobium TiAl alloy Ti-45Al-6Nb (atomic ratio). According to the phase diagram calculation results, the _Tα phase transition point of the alloy is 1290°C, the temperature span of the single α phase interval is 100°C, and there is an α+γ dual phase interval below _Tα , and no _βo and ω phases exist.

First, the first step of hot extrusion in the α single phase region of step S1 is performed. The Ti-45Al-6Nb ingot is subjected to conventional sheathing treatment, and then kept at 1290°C in the single α phase region for 2 hours. After being taken out of the furnace, glass lubricant is rolled on it, and it is sent into the extrusion barrel to complete hot sheathing extrusion to obtain the first hot extruded rod. Among them, the extrusion ratio is controlled at 5:1, and the extrusion speed is 15mm/s. Figure 2 shows the internal structure characteristics of the first step of hot extrusion rod. The lamellar structure basically presents streamlined characteristics, the lamellar interface is parallel to the extrusion direction (horizontal direction), and there are a large number of γ and _α2 fine grain bands around the lamellar structure.

Next, the intermediate annealing in the α+γ dual phase region of process step S2 is started. The extruded rod obtained in step S1 is removed from the jacket, placed in a high-temperature electric furnace, and annealed at 1240°C in the α+γ dual phase region for 4 hours. After furnace cooling, the annealed rod is obtained. Figure 3 shows the microstructural characteristics after intermediate annealing in the α+γ dual phase region. It is found that the intermediate annealing in the dual phase region produces equiaxed dual-state structural characteristics, and the lamellar crystal clusters undergo obvious recrystallization refinement and equiaxation. The crystal cluster size is generally less than 40μm, and the lamellar interface still maintains a 0° preferred orientation.

Then, the second step of hot extrusion in the α single phase region of process step S3 is carried out. The annealed bar in step S2 is re-wrapped, and then kept at 1340°C in the single α phase region for 1 hour, and then taken out of the furnace for hot-wrapped extrusion. The total extrusion ratio of the two-step extrusion is controlled at 36:1, and the extrusion speed is 10 mm/s.

Finally, the annealing post-treatment of step S4 is performed. The secondary hot extruded rod in step 3 is kept at 1275°C, which is lower than the temperature of T _α, for 2 hours and then furnace cooled. In this way, after completing the operations of steps S1-S4 in sequence, the manufacture of the 0° lamellar preferred orientation high niobium TiAl alloy Ti-45Al-6Nb is completed. Figure 4 shows the morphological characteristics of the microstructure of the 0° lamellar preferred orientation high niobium TiAl alloy observed under a scanning electron microscope. It can be seen that this embodiment generates a fine-grained nearly full lamellar structure with 0° lamellar preferred orientation. The lamellar interface of the lamellar crystal group is almost parallel to the extrusion direction (vertical direction), and the size of the lamellar crystal group is generally less than 35μm. Through mechanical property testing, the room temperature elongation of the 0° lamellar preferred orientation high niobium TiAl alloy Ti-45Al-6Nb manufactured by this implementation scheme is as high as 5.5%, the tensile strength is as high as 970MPa, and the tensile strength at 850°C still reaches 640MPa. Figure 5 shows the room temperature tensile performance curve of the high niobium TiAl alloy in this embodiment.

Example 2

This embodiment provides a method for manufacturing a 0° lamellar preferred orientation ultra-high plasticity high niobium TiAl alloy Ti-45Al-6Nb-0.1B-0.1Y (atomic ratio). According to the phase diagram, the _Tα phase transition point of the alloy is calculated to be 1290°C, the temperature span of the single α phase interval is 100°C, and there is an α+γ dual phase interval with a temperature span of 200°C below _Tα , and no _βo and ω phases exist.

The difference between this embodiment and the specific embodiment 1 is that trace Y and B elements are added to the high niobium TiAl alloy, which helps to refine the size of the lamellar crystal clusters of the initial ingot, inhibit the coarsening of high-temperature α grains during hot extrusion and heat treatment in the α single-phase region, and promote the formation of fine lamellar crystal clusters. At the same time, the trace rare earth Y element can absorb oxygen atoms in the γ and α ₂ phase lattices in the process of generating Y ₂ O ₃ through in-situ oxidation reaction, thereby improving the purity of the alloy.

The difference between this embodiment and the specific embodiment 1 is that the post-annealing treatment in step S4 is completed by heat preservation at T _α -30°C (about 1260°C) for 2 hours and then furnace cooling. The purpose is to increase the content of γ equiaxed grains and form a fine-grained dual-state structure with 0° lamellar preferred orientation, so as to further improve the room temperature plasticity.

The advantages of this embodiment are: the generated 0° lamellar preferred orientation high niobium TiAl alloy has fine-grained dual-state structure characteristics, the size of the crystal group is generally less than 25μm, but the content of the lamellar crystal group is reduced to 65%, and the abnormally coarse streamlined lamellar structure disappears completely. The addition of trace rare earth Y reduces the oxygen atom content of the γ and _α2 ordered phase lattices and improves the dislocation slip ability. Through mechanical property testing, it is found that the room temperature elongation of the 0° lamellar preferred orientation high niobium TiAl alloy Ti-45Al-6Nb-0.1Y-0.1B manufactured by this implementation scheme is as high as 6.0%, the tensile strength is as high as 940MPa, and the tensile strength at 850℃ reaches 580MPa.

Comparative Example 1

This embodiment provides a method for manufacturing a random lamellar oriented high niobium TiAl alloy Ti-45Al-6Nb (atomic ratio). The difference between this comparative embodiment and specific embodiment 1 is that process step S3 is to complete the second step of hot extrusion of the once extruded billet obtained in step S2 in the α+γ dual phase region. The extrusion temperature is selected at T _α -20°C (about 1270°C), and the extrusion ratio is still maintained at 9:1, and the extrusion speed is 10mm/s. This is the two-step hot extrusion process route commonly used for TiAl alloys.

After completing steps S1-S4, this comparative example generates conventional fine-grained nearly full lamellar structure characteristics, the 0° lamellar preferred orientation characteristics disappear, and the lamellar interface of the lamellar crystal cluster presents a random orientation. Through mechanical property testing, it is found that the room temperature elongation of this conventional fine-grained nearly full lamellar structure high niobium TiAl alloy is only 1.5%, the tensile strength reaches 920MPa, and the tensile strength at 850℃ is 600MPa.

Comparative Example 2

This comparative example provides a method for manufacturing a 0° lamellar preferred orientation coarse-grained full lamellar structure high niobium TiAl alloy Ti-45Al-6Nb (atomic ratio). The difference between this comparative example and specific example 1 is that process step S4 is to subject the α single-phase region two-step hot extrusion billet obtained in step S3 to a solid solution treatment at a temperature above T _α , that is, the annealing treatment is completed in a single α phase interval. The specific solid solution temperature is selected at T _α +40°C (about 1330°C), and the furnace is cooled after keeping warm for 1 hour.

After completing steps S1-S4, this comparative example generates a coarse-grained full-lamellar structure characteristic with a 0° lamellar preferred orientation. Although the 0° lamellar preferred orientation is maintained, the lamellar crystal group content is 100%. However, the lamellar crystal group is coarse, and the crystal group size is generally 100-150μm. Through tensile performance testing, it is found that the room temperature elongation of this 0° lamellar preferred orientation coarse-grained full-lamellar high-niobium TiAl alloy is only 1.2%, the tensile strength reaches 880MPa, and the tensile strength at 850℃ is 680MPa.

Comparative Example 3

This embodiment provides a method for manufacturing a 0° lamellar preferred orientation high plasticity high niobium TiAl alloy Ti-45Al-8Nb-0.1B-0.1Y (atomic ratio). According to the phase diagram, the _Tα phase transition point of the alloy is 1275°C, the temperature span of the single α phase interval is 80°C, there is an α+γ+ _βo three-phase interval below _Tα , and brittle _βo and ω ( _ωo ) phases exist below 900°C.

The difference between this embodiment and specific embodiment 2 is that the Nb content of the high niobium TiAl alloy is increased to 8%, which is the component system of the conventional high niobium TiAl alloy, and has the highest solid solution strengthening effect, but it is easy to precipitate brittle β _o and ω (ω _o ) phases. After completing process steps S1 to S4, a fine-grained dual-state structure with 0° lamellar preferential orientation is still generated, but β _o grains and nano ω _o precipitation phases are present in the microstructure. Through mechanical property testing, it is found that the room temperature elongation of the 0° lamellar preferentially oriented high niobium TiAl alloy Ti-45Al-8Nb-0.1Y-0.1B manufactured by this implementation scheme is reduced to 3.5%, the tensile strength is as high as 980MPa, and the tensile strength at 850℃ reaches 670MPa.

In summary, the method for manufacturing a 0° lamellar preferentially oriented ultra-high plasticity high niobium TiAl alloy proposed in the present invention has high feasibility, simple process and good economy, and completely solves the common problems of low room temperature plasticity, strength-plasticity mismatch and poor thermal stability existing in current polycrystalline high niobium TiAl alloys.

The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any person skilled in the art can use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims (10)

1. The manufacturing method of the 0-degree lamellar preferred orientation ultrahigh plasticity high niobium TiAl alloy is characterized by comprising the following steps of:

S1, performing first-step hot extrusion in an alpha single-phase area;

S2, intermediate annealing of an alpha+gamma biphase region;

S3, performing hot extrusion in the alpha single-phase region in the second step;

s4, annealing post-treatment.

2. The method for producing a 0 ° lamellar preferred orientation ultrahigh plasticity high niobium TiAl alloy according to claim 1, characterized in that the high niobium TiAl alloy has a single alpha single phase region having a temperature span of not less than 60 ℃ and having only an alpha+gamma dual phase region below the gamma/alpha transition temperature T _α, and no beta _o phase and no omega (omega _o) phase; the total extrusion ratio of the two-step hot extrusion of the step S1 and the step S3 in the single alpha single-phase region is not lower than 25:1.

3. The method for manufacturing the 0-degree lamellar preferred orientation ultrahigh plasticity high niobium TiAl alloy according to claim 2, wherein the atomic percentage content of Nb in the high niobium TiAl alloy is 5% -6.5%.

4. The method for manufacturing the 0-degree sheet preferred orientation ultrahigh-plasticity high-niobium TiAl alloy according to claim 2 or 3, wherein the first-step hot extrusion of the alpha single-phase region is specifically carried out by selecting a temperature of T _α + (0-40) DEG C in a single alpha-phase region, preserving the temperature of the high-niobium TiAl alloy blank subjected to the sheath treatment for 0.5-4 hours, and discharging the blank to carry out hot extrusion.

5. The method for manufacturing the 0-degree sheet preferred orientation ultrahigh-plasticity high-niobium TiAl alloy according to claim 4, wherein the alpha+gamma dual-phase region intermediate annealing is specifically that the blank obtained after the hot extrusion in the step S1 is subjected to alpha+gamma dual-phase region annealing treatment, and the temperature is kept between T _α -20 ℃ and T _α -60 ℃ for 1-8 hours.

6. The method for manufacturing the 0-degree sheet preferred orientation ultrahigh-plasticity high-niobium TiAl alloy according to claim 5, wherein the second step of hot extrusion in the alpha single-phase region is specifically to re-sheath the blank obtained in the step S2, and hot extrusion is performed in a single alpha phase region, wherein the hot extrusion temperature is T _α + (30-90).

7. The method for manufacturing the 0-degree sheet preferred orientation ultrahigh-plasticity high-niobium TiAl alloy according to claim 6, wherein the annealing post-treatment is specifically that the blank obtained in the step S3 is removed from a sheath, and is subjected to an alpha+gamma dual-phase zone annealing treatment, wherein the annealing temperature is between T _α and T _α -60 ℃, and the heat preservation is carried out for 1-6 hours.

8. The method for manufacturing the 0-degree lamellar preferred orientation ultrahigh plasticity high niobium TiAl alloy according to claim 7, wherein the annealing temperature is between T _α and T _α -20 ℃ to generate the 0-degree lamellar preferred orientation fine-grain near-full lamellar tissue high niobium TiAl alloy; the size of the lamellar crystal clusters is less than 40 mu m, and the occupied area ratio is not less than 85 percent.

9. The method for manufacturing the 0-degree sheet preferred orientation ultrahigh-plasticity high-niobium TiAl alloy according to claim 8, wherein a sheet interface of more than 70% of sheet crystal groups, namely (0001) crystal faces of alpha ₂ sheets, forms an included angle with a hot extrusion direction within a range of +/-15 degrees.

10. The method for manufacturing the 0-degree lamellar preferred orientation ultrahigh plasticity high niobium TiAl alloy according to any one of claims 1 to 9, wherein the obtained 0-degree lamellar preferred orientation fine-grain near-full lamellar tissue high niobium TiAl alloy has a room temperature elongation of 4.5 to 6.5 percent, a yield strength of not lower than 750MPa and a tensile strength of 920 to 1050MPa; the tensile strength at 850 ℃ is not lower than 600MPa.