A multi-step heat treatment method for improving the strength and toughness of a ti al / ti2alnbn laminated composite

Abstract

The application provides a multi-step heat treatment method for improving the strength and toughness of a TiAl / Ti2AlNb layered composite material, comprising: performing one solid solution treatment on the rolled TiAl / Ti2AlNb layered composite material, and then rapidly air cooling to room temperature; performing one aging treatment on the TiAl / Ti2AlNb layered composite material after the solid solution treatment, and then furnace cooling to room temperature; performing two solid solution treatments on the TiAl / Ti2AlNb layered composite material after the one aging treatment, and then immediately water cooling to room temperature; performing two aging treatments on the TiAl / Ti2AlNb layered composite material after the two solid solution treatments, and then furnace cooling to room temperature; and through the multi-step heat treatment, the TiAl / Ti2AlNb layered composite material obtained after rolling is regulated to obtain the best organizational state of the TiAl and Ti2AlNb alloys, and meanwhile, the formation of brittle phases at the diffusion interface of the composite material is avoided, and the strength and toughness of the TiAl / Ti2AlNb layered composite material are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal materials, and particularly relates to a multi-step heat treatment method for improving the strength and toughness of a TiAl / Ti2AlNb laminated composite material. BACKGROUND

[0002] As an important high-temperature structural material in the field of aerospace, TiAl alloy has always been favored by researchers. However, despite the advantages of low density, high specific strength and excellent oxidation resistance, the application of TiAl alloy is still limited by the intrinsic brittleness of intermetallic compounds. In recent years, it has been found that the nacre layer of shell-like organisms has the characteristics of low density, high strength and toughness. The nacre layer is formed by the alternating stacking of soft and hard layers, and based on this inspiration, various metal laminated composites have been designed, which also confirms that this special brick and mortar structure can effectively improve the performance of the alloy and achieve the goal of improving the strength and toughness together, which brings hope to TiAl alloy. Among them, the TiAl / Ti2AlNb laminated composite system has great application prospect. Because the service temperature of Ti2AlNb alloy is between Ti and TiAl alloy, it can better play the high-temperature performance advantage of TiAl alloy. At the same time, it has excellent fracture toughness, impact toughness and fatigue resistance, and is the most potential toughening material.

[0003] At present, the methods for preparing TiAl / Ti2AlNb laminated composites mainly include foil hot pressing method, diffusion welding method and pack rolling method. The pack rolling method can realize the preparation of large-size TiAl / Ti2AlNb laminated composites at a lower cost; however, due to the narrow hot working window of TiAl alloy (1150-1250℃), which is much higher than that of Ti2AlNb alloy (850-1100℃), in order to meet the hot deformation requirements of TiAl alloy, the deformation temperature selected during the preparation of the laminated composite is relatively high. At the same time, due to the wide interfacial diffusion layer (100-200μm) of the rolled TiAl / Ti2AlNb laminated composite, attention should be paid to avoid the formation of interfacial brittle phases during the multi-step heat treatment process. Therefore, there is an urgent need for a heat treatment process that can improve the strength and toughness of TiAl / Ti2AlNb laminated composite. SUMMARY

[0004] The purpose of the present application is to provide a multi-step heat treatment method for improving the strength and toughness of a TiAl / Ti2AlNb laminated composite material. By multi-step heat treatment, the TiAl / Ti2AlNb laminated composite material obtained after rolling is adjusted to obtain the best organizational state of TiAl and Ti2AlNb alloys, while ensuring that the diffusion interface of the composite does not form brittle phases, thereby ultimately improving the strength and toughness of the TiAl / Ti2AlNb laminated composite material.

[0005] To achieve the above purpose, the present application provides the following technical solutions:

[0006] The application provides a multi-step heat treatment method for improving the strength and toughness of a TiAl / Ti2AlNb layered composite, comprising the following steps:

[0007] S1: performing one solid solution treatment on the rolled TiAl / Ti2AlNb layered composite, and then rapidly air cooling to room temperature;

[0008] S2: performing one aging treatment on the TiAl / Ti2AlNb layered composite after the solid solution treatment in S1, and furnace cooling to room temperature, and the one aging treatment temperature is 900-950 ℃;

[0009] S3: performing two solid solution treatments on the TiAl / Ti2AlNb layered composite after the one aging treatment in S2, and then immediately water cooling to room temperature, the two solid solution temperature is 1080-1100 ℃, and the two solid solution time is 0.1-0.25 h;

[0010] S4: performing two aging treatments on the TiAl / Ti2AlNb layered composite after the two solid solution treatments in S3, and furnace cooling to room temperature, and the two aging treatment temperature is 750-850 ℃.

[0011] Preferably, after the multi-step heat treatment method, a layered composite with a combination of a TiAl alloy with pearlite and lamella and a Ti2AlNb alloy with coarse O lath is finally obtained.

[0012] Preferably, the one solid solution treatment in S1 is performed in a box furnace, and the one solid solution treatment temperature is 1280-1300 ℃, and the holding time is 0.5-1 h.

[0013] Preferably, the one aging treatment in S2 has a holding time of 3-12 h.

[0014] Preferably, the two aging treatment in S4 has a holding time of 2-24 h.

[0015] Preferably, the TiAl / Ti2AlNb layered composite has a thickness of 1-10 mm, the TiAl alloy has a component of Ti-43Al-4Nb-Mo-0.1B in atomic percentage, and the Ti2AlNb alloy has a component of Ti-22Al-25Nb in atomic percentage.

[0016] Compared with the prior art, the application has the following beneficial technical effects:

[0017] The present application adopts a two-step solid solution aging heat treatment method to regulate the microstructure of a TiAl / Ti2AlNb laminated composite, successfully obtains the best microstructure state of TiAl and Ti2AlNb alloys under the premise of avoiding the precipitation of interface brittle phase, and can simultaneously improve the strength and toughness of the TiAl / Ti2AlNb laminated composite; through the two-step solid solution aging treatment, a laminated composite with a dual structure (pearlite + lamella) of TiAl alloy and a coarse O lath of Ti2AlNb alloy is finally obtained, the advantages of the two alloys are fully utilized, and the strength and toughness of the TiAl / Ti2AlNb laminated composite are further improved. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments will be briefly described below, and it should be known that the drawings described below only relate to some embodiments of the present disclosure, rather than limit the present disclosure, wherein:

[0019] Figure 1 is a multi-step heat treatment step and microstructure schematic diagram of the TiAl / Ti2AlNb laminated composite in the present application embodiment 1-4, wherein (a) is the corresponding microstructure schematic diagram of the two-step solid solution aging heat treatment for regulating the TiAl alloy layer and the Ti2AlNb alloy layer respectively, (b) is the microstructure schematic diagram of the TiAl / Ti2AlNb laminated composite before heat treatment, and (c) is the microstructure schematic diagram of the TiAl / Ti2AlNb laminated composite after heat treatment.

[0020] Figure 2 is the microstructure of the TiAl alloy layer in the present application embodiment 1-4, (a) is the extremely fine nanoscale lamella structure formed after one-step solid solution treatment, (b) is the dual structure formed after the TiAl alloy layer in the embodiment 1 is subjected to one-step aging treatment, (c) is the dual structure formed after the TiAl alloy layer in the embodiment 2 is subjected to one-step aging treatment, and (d) is the dual structure formed after the TiAl alloy layer in the embodiment 4 is subjected to one-step aging treatment.

[0021] Figure 3 is the microstructure of the Ti2AlNb alloy layer in the present application embodiment 1-4, (a) is the B2 single-phase structure formed after two-step solid solution treatment, (b) is the fine needle-like O lath structure formed after the Ti2AlNb alloy layer in the embodiment 1 is subjected to two-step aging treatment, and (c) is the coarse O lath structure formed after the Ti2AlNb alloy layer in the embodiment 3 is subjected to two-step aging treatment.

[0022] Figure 4 is the microstructure of the TiAl / Ti2AlNb laminated composite before and after heat treatment in the present application embodiment 1-4, (a) is the microstructure before heat treatment, and (b) is the microstructure of the TiAl / Ti2AlNb laminated composite after two-step solid solution aging in the embodiment 4.

[0023] Figure 5 Figure 5 is a three-point bending stress-strain curve of the TiAl / Ti2AlNb laminated composite before and after heat treatment according to the present application, and the corresponding fracture toughness (K IC ) value, wherein the thick solid line is the bending stress-strain curve of the TiAl / Ti2AlNb laminated composite after heat treatment according to Example 3. DETAILED DESCRIPTION

[0024] In order to make the purposes, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by a person of ordinary skill in the art without creative effort also belong to the scope of protection of the present disclosure.

[0025] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this present subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0026] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all directed to the same embodiment, or to a single alternative embodiment. It is explicitly contemplated that embodiments described herein can be combined.

[0027] The present application provides a multi-step heat treatment method for improving the strength and toughness of a TiAl / Ti2AlNb laminated composite, comprising the following steps:

[0028] S1: performing a first solution treatment on the rolled TiAl / Ti2AlNb laminated composite, and then rapidly air cooling to room temperature;

[0029] S2: performing a first aging treatment on the TiAl / Ti2AlNb laminated composite after the solution treatment in S1, and cooling to room temperature in the furnace, the first aging treatment temperature being 900-950°C;

[0030] S3: the TiAl / Ti2AlNb laminated composite material after the first aging treatment in S2 is subjected to a second solid solution treatment, and then immediately water-cooled to room temperature, the second solid solution temperature is 1080-1100℃, and the second solid solution time is 0.1-0.25h;

[0031] S4: the TiAl / Ti2AlNb laminated composite material after the second solid solution treatment in S3 is subjected to a second aging treatment, and then furnace-cooled to room temperature, the second aging treatment temperature is 750-850℃.

[0032] In the present application, the first solid solution treatment in S1 is carried out in a box furnace, and the first solid solution treatment temperature is preferably 1280-1300℃, for example, it can be 1280℃, 1290℃, 1300℃, and the holding time is preferably 0.5-1h, for example, it can be 0.5h, 0.7h, 0.8h, 1h.

[0033] In the present application, the TiAl alloy is preferably a third-generation β-γ type TiAl alloy with strong deformation ability, and the specific composition is Ti-43Al-4Nb-Mo-0.1B (at.%), and the Ti2AlNb alloy composition is Ti-22Al-25Nb (at.%). The thickness of the TiAl / Ti2AlNb laminated composite material obtained after rolling is preferably 1-10mm. After the first solid solution treatment of the TiAl / Ti2AlNb laminated composite material after rolling, the TiAl alloy layer obtains extremely fine nanoscale lamellas.

[0034] In the present application, the first aging treatment temperature in S2 is preferably 900-950℃, for example, it can be 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, and the first aging treatment holding time is preferably 3-12h, for example, it can be 3h, 6h, 9h, 12h, and more preferably 6-12h.

[0035] In the present application, the first aging treatment in S2 is used to trigger the cellular reaction of the TiAl alloy layer, so that part of the extremely fine nanoscale lamellas obtained in S1 is transformed into a kind of pearlite-like structure. The pearlite-like structure content is 30%-80%, forming a kind of dual-state structure of lamellar groups and pearlite-like mixed, which improves the strength and toughness of the TiAl alloy layer. Among them, the content of the pearlite-like structure is in direct proportion to the first aging temperature and the first aging time. In addition, the first aging temperature does not exceed 950℃, although 950-1100℃ is a common cellular reaction temperature range, but long time aging in this temperature range will cause a large amount of Al(Ti,Nb)2 brittle phase to precipitate at the interface of the TiAl / Ti2AlNb laminated composite material, which will deteriorate the performance of the composite material.

[0036] In the present application, the secondary solid solution temperature is preferably 1080-1100℃, for example, it can be 1080℃, 1090℃, 1100℃, and the secondary solid solution time is preferably 0.1-0.25h, for example, it can be 0.1h, 0.12h, 0.15h, 0.2h, 0.25h.

[0037] In the present application, during the secondary solid solution, the TiAl / Ti2AlNb laminated composite is placed in the furnace after the furnace temperature rises to the solid solution temperature, and the secondary solid solution time is determined according to the size of the composite, but it should not be less than 6 minutes or more than 15 minutes. If the time is too short, the needle-shaped O lath in the Ti2AlNb alloy layer cannot be fully solid-solved in the B2 matrix; if the time is too long, the bimodal structure obtained in the S1-S2 steps will change significantly, and at the same time, long-term holding will accelerate the diffusion of interface elements, thereby causing the formation of interface brittle Al(Ti, Nb)2 phase.

[0038] In the present application, the secondary aging treatment temperature is preferably 750-850℃, for example, it can be 750℃, 800℃, 850℃, etc., and the secondary aging treatment holding time is preferably 2-24h, for example, it can be 2h, 6h, 10h, 12h, 16h, 19h, 24h, etc., and more preferably 12-24h.

[0039] In the present application, the secondary aging temperature and time control the size and content of the O lath in the Ti2AlNb layer. The higher the aging temperature, the larger the O lath, and the longer the aging time, the more the O lath. Fine O lath can improve the strength of the alloy, and large O lath can improve the toughness of the alloy.

[0040] The technical solutions in the present application will be described clearly and completely in combination with the embodiments in the present application as follows: Embodiment 1

[0041] This embodiment takes a 3-layer TiAl / Ti2AlNb laminated composite as an example for multi-step heat treatment, which is carried out according to the following steps:

[0042] S1: A wire cutting is used to cut several 5×10mm samples from the TiAl / Ti2AlNb laminated composite obtained by canning rolling, and then the samples are subjected to a first solid solution treatment at 1280℃, and after holding for 1h, they are taken out and air-cooled to room temperature;

[0043] S2: The samples after the first solid solution treatment in the S1 step are subjected to a first aging treatment at 900℃, and after holding for 6h, they are furnace-cooled to room temperature;

[0044] S3: The samples after the first solid solution and aging in S1 and S2 are subjected to a secondary solid solution treatment at 1080℃, and after holding for 10min, they are taken out and water-cooled to room temperature;

[0045] S4: The sample after the secondary solid solution treatment in S3 is subjected to secondary aging treatment at 750°C, and after 12h of heat preservation, it is cooled to room temperature in the furnace. Example 2

[0046] This embodiment takes a 3-layer TiAl / Ti2AlNb laminated composite as an example to perform multi-step heat treatment, which is performed according to the following steps:

[0047] S1: A wire cutting is used to cut several 5x10mm samples from the TiAl / Ti2AlNb laminated composite obtained by canning rolling, and the samples are subjected to primary solid solution treatment at 1280°C, and after 1h of heat preservation, they are immediately taken out and air-cooled to room temperature;

[0048] S2: The sample after the primary solid solution treatment in S1 is subjected to primary aging treatment at 930°C, and after 12h of heat preservation, it is cooled to room temperature in the furnace;

[0049] S3: The sample after the primary solid solution and aging treatment in S1 and S2 is subjected to secondary solid solution treatment at 1080°C, and after 10min of heat preservation, it is immediately water-cooled to room temperature;

[0050] S4: The sample after the secondary solid solution treatment in S3 is subjected to secondary aging treatment at 750°C, and after 12h of heat preservation, it is cooled to room temperature in the furnace. Example 3

[0051] This embodiment takes a 3-layer TiAl / Ti2AlNb laminated composite as an example to perform multi-step heat treatment, which is performed according to the following steps:

[0052] S1: A wire cutting is used to cut several 5x10mm samples from the TiAl / Ti2AlNb laminated composite obtained by canning rolling, and the samples are subjected to primary solid solution treatment at 1280°C, and after 1h of heat preservation, they are immediately taken out and air-cooled to room temperature;

[0053] S2: The sample after the primary solid solution treatment in S1 is subjected to primary aging treatment at 930°C, and after 12h of heat preservation, it is cooled to room temperature in the furnace;

[0054] S3: The sample after the primary solid solution and aging treatment in S1 and S2 is subjected to secondary solid solution treatment at 1080°C, and after 10min of heat preservation, it is immediately water-cooled to room temperature;

[0055] S4: The sample after the secondary solid solution treatment in S3 is subjected to secondary aging treatment at 850°C, and after 12h of heat preservation, it is cooled to room temperature in the furnace. Example 4

[0056] The present embodiment takes a 3-layer TiAl / Ti2AlNb laminated composite as an example to perform multi-step heat treatment, specifically in the following steps:

[0057] S1: adopt wire cutting to cut several 5x10mm samples from the TiAl / Ti2AlNb laminated composite obtained by canning rolling, and perform one solid solution treatment at 1280°C, take out immediately after 1h of heat preservation, and air cool to room temperature;

[0058] S2: perform one aging treatment on the sample after one solid solution treatment in step S1 at 950°C, and cool to room temperature in the furnace after 24h of heat preservation;

[0059] S3: perform two solid solution treatment on the sample after one solid solution and aging in S1 and S2 at 1080°C, and water cool to room temperature after 10min of heat preservation;

[0060] S4: perform two aging treatment on the sample after two solid solution treatment in S3 at 850°C, and cool to room temperature in the furnace after 12h of heat preservation.

[0061] Figure 1 is the multi-step heat treatment steps and microstructure schematic diagram of the TiAl / Ti2AlNb laminated composite in examples 1-4, wherein (a) is the microstructure schematic diagram corresponding to the regulation of the TiAl alloy layer and the Ti2AlNb alloy layer respectively by two-step solid solution and aging heat treatment, (b) is the microstructure schematic diagram of the TiAl / Ti2AlNb laminated composite before heat treatment, and (c) is the microstructure schematic diagram of the TiAl / Ti2AlNb laminated composite after heat treatment.

[0062] Figure 2 is the microstructure of the TiAl alloy layer in examples 1-4, (a) is the extremely fine nanoscale lamellar structure formed after one solid solution treatment, (b) is the dual-state structure (containing 30% pearlite) formed after one aging treatment of the TiAl alloy layer in example 1, (c) is the dual-state structure (containing 50% pearlite) formed after one aging treatment of the TiAl alloy layer in example 2, and (d) is the dual-state structure (containing 80% pearlite) formed after one aging treatment of the TiAl alloy layer in example 4.

[0063] Figure 3 is the microstructure of the Ti2AlNb alloy layer in examples 1-4, (a) is the B2 single-phase structure formed after two solid solution treatment, (b) is the fine acicular O lath structure formed after two aging treatment of the Ti2AlNb alloy layer in example 1, and (c) is the coarse O lath structure formed after two aging treatment of the Ti2AlNb alloy layer in example 3.

[0064] Figure 4are microstructures of TiAl / Ti2AlNb laminated composites before and after heat treatment in Examples 1-4, (a) is the microstructure before heat treatment, the TiAl alloy is near lamellar, the Ti2AlNb alloy is fine acicular O lath, and the diffusion interface is about 150-200 μm, (b) is the microstructure of the TiAl / Ti2AlNb laminated composite in Example 4 after two-step solution and aging, the TiAl alloy is a duplex structure (containing 80% pearlite), the Ti2AlNb alloy is coarse O lath, and the diffusion interface is about 350-380 μm.

[0065] Figure 5 are three-point bending stress-strain curves of samples of TiAl / Ti2AlNb laminated composites before and after heat treatment and the corresponding fracture toughness (K IC ) values, wherein the thick solid line is the bending stress-strain curve of the TiAl / Ti2AlNb laminated composite after heat treatment according to Example 3, and it can be seen that the strength and toughness of the composite after two-step solution and aging heat treatment are significantly improved.

[0066] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A multi-step heat treatment method for improving the strength and toughness of TiAl / Ti2AlNb layered composites, characterized in that, The method includes the following steps: S1: The rolled TiAl / Ti2AlNb layered composite material is subjected to a first solution treatment, followed by rapid air cooling to room temperature; the first solution treatment temperature is 1280-1300℃, and the holding time is 0.5-1h; S2: The TiAl / Ti2AlNb layered composite material after solution treatment in S1 is subjected to a first aging treatment, and then cooled to room temperature in the furnace. The first aging treatment temperature is 900-950℃; the first aging treatment holding time is 3-12h. S3: The TiAl / Ti2AlNb layered composite material that has undergone one aging treatment in S2 is subjected to a second solution treatment, and then immediately cooled to room temperature with water. The second solution temperature is 1080-1100℃ and the second solution time is 0.1-0.25h. S4: The TiAl / Ti2AlNb layered composite material after the second solution treatment in S3 is subjected to a second aging treatment, and then cooled to room temperature in the furnace. The second aging treatment temperature is 750-850℃; the second aging treatment holding time is 2-24h.

2. The multi-step heat treatment method for improving the strength and toughness of TiAl / Ti2AlNb layered composites according to claim 1, characterized in that, After the multi-step heat treatment method, a layered composite material combining a TiAl alloy with pearlite and lamellae and a Ti2AlNb alloy with coarse O-lamellae is finally obtained.

3. The multi-step heat treatment method for improving the strength and toughness of TiAl / Ti2AlNb layered composites according to claim 1, characterized in that, The solution treatment described in S1 is carried out in a box furnace.

4. The multi-step heat treatment method for improving the strength and toughness of TiAl / Ti2AlNb layered composites according to any one of claims 1-3, characterized in that, The thickness of the TiAl / Ti2AlNb layered composite is 1-10 mm, the atomic percentage of the TiAl alloy composition is Ti-43Al-4Nb-Mo-0.1B, and the atomic percentage of the Ti2AlNb alloy composition is Ti-22Al-25Nb.

Images