A high-thermal-strength Ti2AlNb alloy and its thermomechanical treatment method

Abstract

This invention belongs to the field of high-temperature titanium alloy technology, and relates to a high-thermal-strength Ti2AlNb alloy and its thermomechanical treatment method. The alloy composition has the following atomic percentages: 18%–25% Al, 18%–26% Nb, 0.3%–2.5% Sn, 1%–4.0% Zr, 0.6%–1.2% Si, 0%–2.0% Mo, 0%–2.0% W, 0%–2.0% Ta, 0%–5.0% B, with the balance being Ti and unavoidable impurities. The thermomechanical treatment method for this alloy includes: Step 1, crushing and refining the as-cast microstructure; Step 2, deformation to prepare a metastable microstructure with high distortion energy and high supersaturation; Step 3, heat treatment to obtain a high-thermal-strength microstructure. This alloy and its thermomechanical treatment method further improve the thermal strength of the Ti2AlNb alloy with O+B2 as the main phase, increasing the target service temperature of the alloy from the current 650℃–700℃ to 700℃–750℃.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature titanium alloy technology, and relates to a high thermal strength Ti2AlNb alloy and its thermomechanical treatment method. Background Technology

[0002] Ti2AlNb alloy is a lightweight, high-temperature resistant structural material with excellent comprehensive performance. It has high specific strength, high specific stiffness, good thermal strength, and resistance to oxidation and ignition. It also has good processing performance. It is a potential candidate material for large key components such as aero-engine casings, discs, and aircraft skins, and is expected to replace Ni-based superalloys to achieve significant weight reduction benefits.

[0003] To further improve the overall performance of Ti2AlNb alloys, various alloying schemes have emerged. Examples include quaternary alloys: Ti-Al-Nb-Ta, Ti-Al-Nb-Er, Ti-Al-Nb-Mo, Ti-Al-Nb-Si, Ti-Al-Nb-Y, Ti-Al-Nb-W, and Ti-Al-Nb-B; pentagonal alloys: Ti-Al-Nb-Mo-Fe, Ti-Al-Nb-Mo-Zr, Ti-Al-Nb-Mo-Si, Ti-Al-Nb-WB, and Ti-Al-Nb-WV; and more complex alloying element combinations: Ti-Al-Nb-V-(Y-Si) (application number: CN201410685690.9), Ti-Al-Nb-V-Mo-Zr-Si (application number: CN201611207559.7), and Ti-Al-Nb-V-Mo-Zr-Hf-Si (application number: CN201510652682.9).

[0004] Among the aforementioned alloying elements, Mo, W, V, Fe, Ta, and the main element Nb are all β / B2 stabilizing elements, which can lower the B2→B2+α2 phase transformation point and improve the solid solution strengthening effect of the B2 phase. Zr is a neutral element with little effect on the phase transformation point, but it can simultaneously improve the solid solution strengthening effect of both the B2 and α2 phases. Si and B can form hard ceramic particles, producing a second-phase strengthening effect. Er and Y are rare earth elements, which have the effect of refining grains. The selective matching application of the above alloying elements can, to a certain extent, regulate the processing and service performance of the alloy. Compared with the multi-component composite strengthening effect of the β / B2 phase, the existing alloying schemes lack a richer and more diverse strengthening effect on the precipitated α2 / O phase. Apart from the main element Al, only the neutral element Zr makes a certain contribution. This limits the high-temperature thermal strength performance of the alloy, making it difficult to achieve a wider range of improvement and failing to meet the application requirements of future advanced aero-engines for higher-performance lightweight structural materials. Summary of the Invention

[0005] The purpose of this invention is to provide a high-thermal-strength Ti2AlNb alloy and its thermomechanical treatment method, which solves the problems of insufficient strengthening of the α2 / O phase and insufficient overall thermal strength of existing alloys. By simultaneously improving the composite strengthening effect of the B2 phase and the α2 / O phase, as well as the pinning effect of the grain / phase boundaries, and by controlling the thermomechanical treatment process to obtain a high-density woven basket structure, the thermal strength of the Ti2AlNb alloy composed mainly of O+B2 phases is further improved, and the target service temperature of the alloy is increased from the current 650℃~700℃ to 700℃~750℃.

[0006] To solve this technical problem, the technical solution of the present invention is as follows:

[0007] On the one hand, a high thermal strength Ti2AlNb alloy is provided, wherein the atomic percentages of the alloy composition are 18%–25% Al, 18%–26% Nb, 0.3%–2.5% Sn, 1.0%–4.0% Zr, 0.6%–1.2% Si, 0%–2.0% Mo, 0%–2.0% W, 0%–2.0% Ta, 0%–5.0% B, and the balance is Ti and unavoidable impurities.

[0008] Preferably, the alloy has an atomic percentage of 18%–25% Al, 22%–26% Nb, 0.3%–1.5% Sn, 2.0%–4.0% Zr, 0.6%–1.0% Si, with the balance being Ti and unavoidable impurities.

[0009] Preferably, the alloy has an atomic percentage of 18%–25% Al, 18%–26% Nb, 1.5%–2.5% Sn, 1.0%–2.0% Zr, 0.6%–1.0% Si, with the balance being Ti and unavoidable impurities.

[0010] Furthermore, the alloy has the following atomic percentages: 18%–25% Al, 18%–26% Nb, 1.0%–2.0% Sn, 2.0%–3.0% Zr, 0.8%–1.2% Si, 0.5%–1.5% Mo, with the balance being Ti and unavoidable impurities.

[0011] Furthermore, the alloy has an atomic percentage of 18%–25% Al, 18%–26% Nb, 0.5%–1.5% Sn, 0.5%–1.5% Zr, 0.6%–1.0% Si, 1%–5% B, with the balance being Ti and unavoidable impurities.

[0012] Furthermore, the alloy has the following atomic percentages: 18%–25% Al, 18%–26% Nb, 1.0%–2.0% Sn, 2.0%–3.0% Zr, 0.8%–1.2% Si, 0.5%–2% (W, Mo, Ta), with the balance being Ti and unavoidable impurities, wherein (Mo, W, Ta) indicates the presence of at least two of the three elements Mo, W, and Ta.

[0013] On the other hand, a thermomechanical treatment method for improving the thermal strength properties of the Ti2AlNb alloy is provided, the method comprising the following steps:

[0014] Step 1: Refining the as-cast microstructure:

[0015] The Ti2AlNb alloy ingot is subjected to 3 to 5 hot deformations at 30°C to 150°C above the β / B2 phase transformation point, with each hot deformation amounting to 30% to 50%.

[0016] This step utilizes the principle of deformation recrystallization to focus on the β / B2 phase. Through multiple deformation cycles, the coarse β / B2 phase in the as-cast state is broken down and refined.

[0017] Step 2: Deformation preparation of metastable tissues with high distortion energy and high supersaturation:

[0018] The billet obtained in step one is in T P Hot deformation is carried out at +(10~30)℃, with a deformation amount of 15%~30%. After deformation, the billet is cooled, where T p The solution temperature of Ti5Si3 is 1.

[0019] Through deformation and rapid cooling, the β / B2 phase was cooled to room temperature in a state of distorted grain boundaries, high intragranular distortion energy, and high supersaturation, preparing for subsequent heat treatment to regulate the precipitation morphology of the O phase. Simultaneously, at T... p The above temperature deformation avoids the precipitation of Ti5Si3 during the heating process before deformation. On the one hand, it eliminates the participation of Ti5Si3 in deformation, reduces deformation resistance, and improves process plasticity; on the other hand, it avoids the growth of Ti5Si3 during the heating process, laying the foundation for controlling a finer and more uniform dispersion of Ti5Si3.

[0020] Step 3: Heat treatment to obtain a microstructure with high thermal strength:

[0021] The billet obtained in step two undergoes two heat treatments: the first heat treatment is performed at T... O - After holding at (30~50)℃ for 1~3 hours, remove from the furnace and cool; the second heat treatment involves holding at 780℃~830℃ for 6~24 hours, then removing from the furnace and air cooling, where T O This is the upper limit temperature of the B2+O two-phase region.

[0022] Through the first heat treatment, the B2 phase precipitates a high-density woven basket-like O phase under the synergistic effect of high distortion energy and high supersaturation. This O phase is a high-thermal-strength O phase after alloying modification with elements such as Sn and Zr. At the same time, fine and dispersed Ti5Si3 phase precipitates at the grain boundaries of the O phase.

[0023] Through a second heat treatment, fine O phases are further precipitated on the B2 matrix, completing the stabilization treatment of the B2 phase.

[0024] Preferably, the billet cooling method in step two is air cooling or oil cooling.

[0025] Preferably, the billet cooling method in step three is air cooling or oil cooling.

[0026] The final microstructure formed through the two heat treatments in step three features: a fine B2 phase matrix with twisted grain boundaries, on which a basket-like O phase containing elements such as Sn and Zr is distributed, exhibiting high thermal strength; and the O phase grain boundaries are pinned by fine and dispersed Ti5Si3 phases. Alloys with this composition and microstructure exhibit significantly improved thermal strength.

[0027] The beneficial effects of this invention are:

[0028] By introducing Sn and Zr, two neutral elements from high-temperature Ti alloys, and Si, which provides dispersion strengthening, into Ti2AlNb alloys, synergistic composite strengthening and toughening of the α2 / O and B2 phases and their grain / phase boundaries are achieved without increasing the risks associated with segregation, inclusions, and other compositional uniformity control. This is combined with thermomechanical treatment to regulate the high-density braided basket microstructure, further enhancing the alloy's high-temperature strength. The synergistic strengthening effect of the neutral elements Sn and Zr on α2 / O is far superior to that of Sn or Zr alone. Si forms a fine, dispersed ceramic phase, Ti5Si3, which pins grain / phase boundaries, increasing grain boundary strength under high-temperature conditions, hindering grain boundary sliding, and improving high-temperature strength. Nb alloying is the main strengthening factor for the B2 phase matrix; supplemented by the multi-element composite solid solution strengthening effect of high-melting-point elements such as Mo, W, and Ta, the performance of the B2 phase can be further improved. Boron refines the B2 grains and also provides dispersion strengthening. By controlling the precipitation of a high-density woven basket-like O phase in the B2 matrix through deformation heat treatment, and suppressing the coarsening of Ti5Si3, a finely dispersed Ti5Si3 phase is obtained, thereby enhancing the pinning effect on the O phase grain boundaries and improving thermal strength. Therefore, in Ti2AlNb alloys with O+B2 as the main phase, the above alloying scheme can achieve synergistic composite strengthening and toughening of the matrix B2 phase, the reinforcing α2 / O phase, and the grain / phase boundaries. Simultaneously, the above thermomechanical treatment scheme can obtain a high-density woven basket structure and ensure the finely dispersed distribution of the Ti5Si3 phase, significantly improving the alloy's high-temperature strength, creep resistance, and other thermal strength properties. Attached Figure Description

[0029] Figure 1 This is a diagram of the high-density woven basket structure obtained in Example 1;

[0030] Figure 2 This is a diagram of the high-density woven basket structure obtained in Example 2;

[0031] Figure 3 This is a diagram of the high-density woven basket structure obtained in Example 3;

[0032] Figure 4 This is a diagram of the high-density woven basket structure obtained in Example 4;

[0033] Figure 5 This is a diagram of the high-density woven basket structure obtained in Example 5;

[0034] Figure 6 The grain boundary morphology of Ti5Si3 pinned O phase. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The features of various aspects of the embodiments of the present invention will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can also be practiced without these specific details. The following description of the embodiments is merely intended to provide a better understanding of the invention by illustrating examples. The invention is not limited to any specific setups and methods provided below, but covers all improvements, substitutions, etc., to product structures and methods without departing from the spirit of the invention.

[0037] In the various accompanying drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the invention.

[0038] The high thermal strength Ti2AlNb alloy of the present invention has the following atomic percentages: 18%–25% Al, 18%–26% Nb, 0.3%–2.5% Sn, 1.0%–4.0% Zr, 0.6%–1.2% Si, 0%–2.0% Mo, 0%–2.0% W, 0%–2.0% Ta, 0%–5.0% B, with the balance being Ti and unavoidable impurities.

[0039] The nominal composition of the high thermal strength Ti2AlNb alloys in the examples is shown in Table 1. The specific implementation methods for preparing the high thermal strength Ti2AlNb alloys numbered 2-6 in Table 1 are as follows.

[0040] Example 2:

[0041] Preparation of a high-thermal-strength Ti-23Al-22Nb-0.8Sn-3.5Zr-0.8Si alloy, alloy T β =1050℃, Tp=1000℃, T O =930℃.

[0042] Alloy ingots were prepared by three-stage vacuum arc remelting. The ingots were then subjected to four hot deformations at 1180℃, 1150℃, 1130℃, and 1100℃, with deformation amounts of 50%, 35%, 35%, and 30%, respectively. Subsequently, a 25% hot deformation was performed at 1020℃. After deformation, the ingots were air-cooled. The ingots were then held at 900℃ for 1.5 hours, air-cooled, and held at 790℃ for 12 hours before being air-cooled again to obtain a high-thermal-strength material.

[0043] Example 3:

[0044] A high-thermal-strength Ti-21Al-24Nb-2Sn-1.5Zr-0.8Si alloy was prepared. β =1030℃, Tp=1040℃, T O =910℃.

[0045] Alloy ingots were prepared by three-stage vacuum arc remelting. The alloy ingots were subjected to four hot deformations at 1180℃, 1150℃, 1100℃, and 1060℃, with deformation amounts of 40%, 30%, 30%, and 30% respectively. Then, a hot deformation of 30% was performed at 1050℃. After deformation, the ingots were air-cooled. Subsequently, the ingots were held at 880℃ for 2 hours, air-cooled, held at 780℃ for 24 hours, and air-cooled to obtain high thermal strength material.

[0046] Example 4:

[0047] Preparation of a high-thermal-strength Ti-20Al-24Nb-2.5Sn-1.5Zr-1Si-1Mo alloy, alloy T β =1070℃, Tp=1020℃, T O =950℃.

[0048] Alloy ingots were prepared by three-stage vacuum arc remelting. The alloy ingots were then subjected to three hot deformations at 1180℃, 1150℃, and 1120℃, with deformation amounts of 40%, 30%, and 30% respectively. Subsequently, a hot deformation of 25% was performed at 1050℃. After deformation, the ingots were air-cooled. Then, the ingots were heat-treated by holding at 920℃ for 1.5 hours, air-cooling, holding at 800℃ for 24 hours, and air-cooling to obtain high thermal strength material.

[0049] Example 5:

[0050] Preparation of a high-thermal-strength Ti-22Al-25Nb-1Sn-1Zr-0.8Si-2B alloy, alloy T β =1070℃, Tp=1050℃, T O =940℃.

[0051] Alloy ingots were prepared by three-stage vacuum arc remelting. The alloy ingots were then subjected to three hot deformations at 1180℃, 1150℃, and 1100℃, with deformation amounts of 40%, 35%, and 35% respectively. Subsequently, a hot deformation of 30% was performed at 1080℃. After deformation, the ingots were air-cooled. Then, the ingots were heat-treated by holding at 900℃ for 1.5 hours, air-cooling, holding at 810℃ for 15 hours, and air-cooling to obtain high thermal strength material.

[0052] Example 6:

[0053] A high-thermal-strength Ti-22Al-23Nb-1.5Sn-2.5Zr-1Si-0.5W-0.5Ta alloy was prepared. β =1090℃, Tp=1030℃, T O =960℃.

[0054] Alloy ingots were prepared by three-stage vacuum arc remelting. The ingots were then subjected to four hot deformations at 1200℃, 1180℃, 1150℃, and 1120℃, with deformation amounts of 45%, 40%, 35%, and 30%, respectively. Subsequently, a 25% hot deformation was performed at 1040℃. After deformation, the ingots were air-cooled. The ingots were then heat-treated by holding at 930℃ for 1.5 hours, air-cooled, and then holding at 830℃ for 8 hours before air-cooling to obtain a high-thermal-strength material.

[0055] Table 1 Alloy composition and mechanical properties

[0056]

[0057] The results show that by using three key elements (Sn, Zr, and Si) supplemented with multi-element alloying of Mo, W, Ta, and B, and combined with the aforementioned thermomechanical treatment method, the high-temperature strength and creep rupture properties of the alloy are significantly improved, while the room-temperature plasticity of the alloy does not decrease significantly, remaining above 6%. The tensile strength at 650℃ increases from 860 MPa to over 900 MPa, the tensile strength at 700℃ increases from 770 MPa to over 850 MPa, and the tensile strength at 750℃ exceeds 800 MPa. The creep rupture time at 700℃ / 260 MPa is increased to over 100 hours.

[0058] While maintaining good room temperature strength and ductility, the alloy has achieved significant improvements in high temperature strength and creep resistance.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A high thermal strength Ti2AlNb alloy, characterized in that: The alloy composition has an atomic percentage of 18%–25% Al, 22%–26% Nb, 0.3%–2.5% Sn, 2.5%–4.0% Zr, 0.8%–1.2% Si, 1%–5.0% B, and 0.5%–2% (W, Mo, Ta), with the balance being Ti and unavoidable impurities, wherein (Mo, W, Ta) indicates the presence of at least two of the three elements Mo, W, and Ta.

2. The Ti2AlNb alloy according to claim 1, characterized in that: The alloy contains 0.3%–1.5% Sn and 0.8%–1.0% Si.

3. The Ti2AlNb alloy according to claim 1, characterized in that: The alloy contains 1.0%–2.0% Sn, 2.5%–3.0% Zr, 0.8%–1.2% Si, and 0.5%–1.5% Mo.

4. A thermomechanical treatment method for improving the thermal strength properties of the Ti2AlNb alloy according to claim 1, characterized in that, The method steps are as follows: Step 1: Refining the as-cast microstructure: The Ti2AlNb alloy ingot is subjected to 3 to 5 hot deformations at 30℃ to 150℃ above the β / B2 phase transformation point, with each hot deformation accounting for 30% to 50%; Step 2: Deformation preparation of metastable microstructure with high distortion energy and high supersaturation: The billet obtained in Step 1 is subjected to T... P The billet is hot-deformed at 10~30℃, with a deformation amount of 15%~30%. After deformation, the billet is air-cooled or oil-cooled, where T p This is the dissolution temperature of Ti5Si3; Step 3: Heat treatment to obtain a high-thermal-strength microstructure: The billet obtained in Step 2 undergoes two heat treatments: the first heat treatment is carried out at T... O - After holding at (30~50)℃ for 1~3 hours, remove from the furnace and air-cool or oil-cool; the second heat treatment involves holding at 780℃~830℃ for 6~24 hours, then removing from the furnace and air-cooling, where T O This is the upper limit temperature of the B2+O two-phase region.

5. The method according to claim 4, characterized in that: In step one, the deformation amount is 30% to 50% per firing.

6. The method according to claim 4, characterized in that: In step two, the billet is cooled by either air cooling or oil cooling.

7. The method according to claim 4, characterized in that: In step three, the billet is cooled by either air cooling or oil cooling.

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