CN117604313A - A high Nb content TiAl intermetallic compound porous material and its preparation method - Google Patents

Abstract

The invention discloses a TiAl intermetallic compound porous material with high Nb content and a preparation method thereof, and belongs to the field of intermetallic compound porous material preparation. In the present invention, coarse TiAl alloy powder with low oxygen content and ultra-fine Nb powder with high oxygen content are mixed, put into a stainless steel jacket, vibrated, evacuated, sealed, and then sequentially subjected to the first stage hot isostatic pressing sintering at 850 to 950°C. And the second stage hot isostatic pressing sintering at 1000~1150℃ is obtained. This invention is based on the physical accumulation of coarse-grained powder into pores, and utilizes the easy diffusion characteristics between Nb and TiAl to achieve TiAl sintering at a lower sintering temperature. By adjusting the hot isostatic pressing temperature and pressure, the porosity is 40 ~50%. The process of the invention is simple, the production cost is low, and it is suitable for industrial production.

Description

A high Nb content TiAl intermetallic compound porous material and its preparation method

Technical field

The invention relates to a TiAl intermetallic compound porous material and a preparation method thereof, in particular to a high Nb content TiAl intermetallic compound porous material and a preparation method thereof, and belongs to the field of preparation of intermetallic compound porous materials.

Background technique

Porous materials have the advantages of low relative density, high specific strength, large specific surface area, and good permeability. They are widely used in aerospace, petrochemical, metallurgical environment and other fields, especially in the fields of sound insulation, heat insulation, separation, filtration, and vibration reduction. , adsorption, catalysis and other functional requirements. At present, porous materials for industrial application include polymer porous materials, ceramic porous materials, metal porous materials and intermetallic compound porous materials. Due to the existence of ionic bonds and covalent bonds, TiAl intermetallic compound porous materials have the advantages of porous ceramics and porous metals, and are considered to be one of the most promising high-temperature filtration materials at present.

At present, TiAl intermetallic compound porous materials are mainly prepared by powder metallurgy methods. The formation of pores comes from three aspects: (1) Based on the biased diffusion effect caused by the large differences in the intrinsic diffusion coefficients of different elements, Kirkendall is formed in the material. Pores, such pores are usually small-sized pores; (2) pores are formed by the physical accumulation of raw material powders, and these pores are affected by the particle size and distribution of the powder; (3) pores are formed by adding pore-forming agents. Based on these pore-forming principles, elemental powder is often used as raw material in the preparation of porous materials to maximize the Kirkendall effect; pressureless sintering or micro-pressure sintering is often used in the sintering process to ensure physical pore formation, but the process needs to be strictly controlled to ensure Dimensional accuracy.

In the field of TiAl intermetallic compound additive manufacturing, due to the strict requirements on powder particle size during the manufacturing process, there is a widespread phenomenon of excess coarse-grained TiAl alloy powder. For example, the electron beam selective melting forming technology (EBSM) requires the size of TiAl intermetallic compound powder to be 40 to 100 μm, while the size of TiAl intermetallic compound powder prepared by the plasma rotating electrode method (PREP) is usually 45 to 250 μm, of which the size is less than 100 μm. The powder is about 60 to 70%, which means that at least 30% of the coarse powder cannot be used for EBSM additive manufacturing. Although this type of coarse powder has the advantage of low oxygen content, there is currently no suitable application field, and due to the difficulty in separating various elements in the powder, the value of this type of coarse powder is extremely low (the sales price is about the price of sponge titanium 60-70%), which also indirectly leads to the high cost of additive manufacturing of TiAl parts and the waste of resources.

In addition, the use temperature of TiAl intermetallic compound porous materials is usually below 800°C. Above this temperature, the alloy is easily oxidized to generate Ti ₂ O and Al ₂ O ₃ , which in turn blocks the pores and seriously affects its filtration effect. To continue to increase the use temperature, it is usually necessary to increase the Nb element content and prepare high Nb content porous materials.

At present, a method has not yet been found to use waste coarse powder in the field of TiAl intermetallic compound additive manufacturing to manufacture high Nb content TiAl porous materials, so that it can not only meet the needs of high-temperature filtration, but also recycle existing industrial waste powder.

Contents of the invention

In view of the lack of existing technology, the first purpose of the present invention is to provide a high Nb content TiAl intermetallic compound porous material, which has good porosity and can also achieve good filtration effects at higher temperatures.

The second object of the present invention is to provide a method for preparing porous materials of TiAl intermetallic compounds with high Nb content. This method is based on the physical accumulation of coarse-grained powders to form pores, and utilizes the easy diffusion characteristics between Nb and TiAl to produce a lower TiAl sintering is achieved at the sintering temperature, and the metallurgical connection of all powders is ensured by controlling the two-stage hot isostatic pressing temperature. This method has the advantages of simple process flow and low production cost, and is suitable for industrial production.

In order to achieve the above technical objectives, the present invention provides a method for preparing high Nb content TiAl intermetallic compound porous materials. In this method, low oxygen content TiAl alloy coarse powder and high oxygen content ultrafine Nb powder are mixed and then packed into a stainless steel bag. The sleeve is vibrated, evacuated, sealed, and then sequentially undergoes the first-stage hot isostatic pressing sintering at 850-950°C and the second-stage hot isostatic pressing sintering at 1000-1150°C to obtain; the low oxygen content TiAl The particle size of the alloy coarse powder is greater than 150 μm (+100 mesh), and the oxygen content is less than 400 ppm; the particle size of the high oxygen content ultrafine Nb powder is less than 25 μm (-500 mesh), and the oxygen content is greater than 2000 ppm.

In the technical solution of the present invention, by mixing TiAl alloy coarse powder with low oxygen content and ultrafine Nb powder with high oxygen content, on the one hand, the oxygen content in the final product can be maintained in the range of 800 to 1200 ppm, while reducing the cost of the process. difficulty while ensuring the plasticity of the product; on the other hand, the significant particle size difference between the two is used to form pores based on the physical accumulation of coarse particle size. At the same time, the easy diffusion characteristics between Nb and TiAl are used to realize it at a lower sintering temperature. TiAl is sintered, and finally a high Nb content TiAl intermetallic compound porous material is obtained.

The key to the present invention is to control the temperature of hot isostatic pressing after mixing TiAl alloy coarse powder and ultrafine Nb powder with significantly different particle sizes. The hot isostatic pressing sintering of the present invention is divided into two stages. The principle of the first stage sintering is to utilize the diffusion between Nb powder and TiAl to achieve metallurgical bonding between the powders. The temperature is selected according to the relationship between Nb and TiAl. Diffusion dynamics. Through the diffusion between Nb and TiAl, the Nb content in the TiAl alloy raw material is significantly increased by 6 to 8 at.%, and the prepared porous material is a high Nb content TiAl porous material. However, due to the low proportion of Nb powder in the original mixed powder, it is difficult to ensure that all TiAl powders are metallurgically connected after the first-stage hot isostatic pressing sintering, so the second-stage sintering needs to be performed at a higher temperature. In addition, the present invention achieves primary metallurgical bonding between powders through low-temperature sintering in the first stage, thereby reducing the sintering temperature and time in the second stage to a certain extent, improving production efficiency and reducing production costs.

As a preferred solution, the weight of the Nb powder is 12% to 16% of the weight of the TiAl alloy coarse powder. The weight of the Nb powder used in the present invention converted into an atomic percentage of the Nb element in the porous material is 8 to 10 at.%, which belongs to the composition range of titanium-aluminum alloys with high niobium content. Theoretically, the maximum porosity of pure coarse powder after sintering is 60%. When the weight of Nb powder is 12 to 16% of the weight of TiAl coarse powder, the maximum theoretical porosity of sintering after mixing is 57%. Therefore, the porosity during actual sintering Less than 57%.

As a preferred solution, the TiAl alloy coarse powder is low-cost Ti-48Al-2Nb-2Cr coarse powder discarded in the field of additive manufacturing. The type of powder used in the present invention is not only extremely low in price, but also has an oxygen content lower than that of fine powder.

As a preferred solution, the TiAl alloy powder is screened plasma rotating electrode atomized coarse powder; the Nb powder is obtained by ball milling. The -500 mesh ball-milled ultra-fine Nb powder used in the present invention is usually difficult to utilize due to the high oxygen content in the powder, so the price is relatively low. Therefore, the present invention selects Ti-48Al-2Nb-2Cr coarse powder and ultrafine Nb powder discarded in the field of additive manufacturing as raw materials, which can significantly reduce costs while ensuring the performance of the final product.

As a preferred solution, the wall thickness of the stainless steel jacket is 1.2 to 1.5 mm, and the hexagonal boron nitride powder is wiped on the inner wall of the jacket before loading. The inventor found that in order to match the smaller hot isostatic pressing pressure in the subsequent process, it is necessary to use a thinner wall thickness envelope; and the purpose of wiping the hexagonal boron nitride powder on the inner wall is to prevent the envelope from collapsing with the powder under the action of temperature and pressure. Diffusion, and facilitates smooth peeling of the cover after hot isostatic pressing.

As a preferred solution, the pressures of the first stage hot isostatic pressing sintering and the second stage hot isostatic pressing sintering are both 60 to 80 MPa. Since the sintering process of TiAl porous materials provided by the existing technology mostly adopts pressureless sintering or micro-pressure sintering, the sintering process is inevitably accompanied by volume expansion. In the present invention, the conditions for densification sintering of TiAl intermetallic compounds are set lower than 60 to 80 MPa. The purpose of lower sintering is to reduce volume expansion, which is more conducive to shape control after sintering, thereby simplifying the subsequent processing of the product.

As a preferred solution, the first-stage hot isostatic pressing sintering process is as follows: the temperature is 900-950°C, the heating rate is 10-15°C/min, and the holding time is 2-3 hours; the second-stage The process of hot isostatic pressing sintering is as follows: the temperature is 1000~1050℃, the heating rate is 5~10℃/min, the holding time is 1~2h, and the furnace is cooled after sintering is completed. The purpose of the first stage sintering in the present invention is to cause the diffusion of Nb and TiAl. Therefore, when selecting the temperature, it is necessary to consider the diffusion behavior between Nb and TiAl. When the first stage sintering temperature is lower than 900°C, the diffusion behavior between Nb and TiAl The slow diffusion between them will cause the sintering time to be significantly prolonged; when the sintering temperature is higher than 950°C, the diffusion rate is too fast, making it difficult to control the preparation process. The purpose of the second stage of sintering is to combine the TiAl powder that has not undergone metallurgical bonding. Therefore, when selecting the temperature, it is necessary to consider the diffusion behavior between TiAl and TiAl. When the sintering temperature in the second stage is lower than 1000°C, TiAl and TiAl The slow diffusion between TiAl will cause the sintering time to be significantly prolonged; when the sintering temperature is higher than 1050°C, the diffusion rate will also be too fast, which will increase the difficulty of control in actual production. On the one hand, the selection of heating rate must consider production efficiency. It is not advisable to use a too low heating rate to prolong the production cycle. On the other hand, it is not advisable to use an excessively high heating rate to prevent the sintering temperature from exceeding the set range due to the temperature rise, thereby not causing the sintering temperature to exceed the set range. Conducive to temperature control.

As a preferred solution, the mixing time is 20 to 24 hours.

The invention also provides a TiAl intermetallic compound porous material with high Nb content, which is obtained by the above preparation method.

As a preferred solution, the atomic percentage of Nb element in the porous material is 8 to 10%, the porosity is 40 to 50%, and the original Nb powder in the porous material is fully diffused. The TiAl intermetallic compound porous material of the present invention has a higher Nb content, which increases the service temperature of the porous material. At the same time, the porous material of the present invention has high porosity, which can ensure that the porous material has excellent filtration performance.

Principles and effects

Compared with the existing technology that uses element powders and utilizes the Kirkendall effect to prepare TiAl intermetallic compound porous materials, the present invention uses powders discarded in industrial production as raw materials, and its price is lower than that of pure metal element powders. It has a cost advantage and at the same time achieves the Efficient use of resources. The principle of pore formation in the present invention is to use the physical accumulation of coarse-grained powder to form large-sized gaps. Therefore, there is no need to add a pore-forming agent during the sintering process, and the pollution caused by the pore-forming agent is avoided.

The present invention utilizes the excellent diffusion ability between Nb element and TiAl matrix to realize the preparation of high Nb content porous materials with low Nb content alloy powder, which not only increases the use temperature of TiAl intermetallic compound porous materials, but also reduces the cost of raw materials; in addition, The low-temperature sintering process of Nb and TiAl in the first stage achieves a metallurgical bond between the powders, reduces the sintering temperature and time in the second stage, improves production efficiency, and reduces production costs.

Description of drawings

Figure 1 shows the micromorphology of the TiAl intermetallic compound porous material prepared by the present invention.

Detailed ways

The following are preferred embodiments of the present invention, not all embodiments. Without departing from the innovative principle of this process, any equivalent process transformation made using the contents of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be deemed to be within the scope of patent protection of the present invention.

Example 1

The +100 mesh Ti-48Al-2Nb-2Cr coarse powder obtained by the plasma rotating electrode atomization method and the -500 mesh high oxygen content ultrafine Nb powder obtained by the ball milling method are used as raw materials. Weigh 10 kilograms of TiAl powder and 1.2 kilograms of pure Nb powder, place them in a V-shaped mixer and mix them thoroughly for 20 hours; after the mixing is completed, put the mixed powder into a stainless steel bag with a wall thickness of 1.2mm, and vacuum it to 10 ^-4 Pa after sealing, wipe the hexagonal boron nitride powder on the inner wall of the bag before loading the powder; the sealed bag containing the mixed powder is sintered in a hot isostatic pressing furnace, set the pressure to 60MPa, and the heating rate to 10°C/min , when the temperature reaches 900°C, keep it for 3 hours, then keep the pressure unchanged, raise the temperature to 1050°C at a rate of 5°C/min and continue sintering for 1 hour, and then cool with the furnace; remove the jacket and obtain a porosity of 50%. A TiAl intermetallic compound porous material with an Nb content of 8at.% has a thermal conductivity of 2.0W·m ^-1 ·K ^-1 .

Example 2

The +100 mesh Ti-48Al-2Nb-2Cr coarse powder obtained by the plasma rotating electrode atomization method and the -500 mesh high oxygen content ultrafine Nb powder obtained by the ball milling method are used as raw materials. Weigh 10 kilograms of Ti-48Al-2Nb-2Cr coarse powder and 1.6 kilograms of pure Nb powder, place them in a V-shaped mixer and mix them thoroughly for 24 hours; after the mixing is completed, put the mixed powder into a stainless steel bag with a wall thickness of 1.5mm. into the bag, and evacuate to 10 ^-4 Pa and then seal it. Wipe the hexagonal boron nitride powder on the inner wall of the bag before loading the powder; the sealed bag containing the mixed powder is sintered in a hot isostatic pressing furnace, and the pressure is set to 80MPa. The heating rate is 15°C/min. When the temperature reaches 950°C, keep the temperature for 3 hours, then keep the pressure unchanged, raise the temperature to 1050°C at a rate of 10°C/min and continue sintering for 2 hours, and then cool with the furnace; remove the jacket. A TiAl intermetallic compound porous material with a porosity of 40% and an Nb content of 10at.% was obtained. The thermal conductivity of the porous material was 3.0W·m ^-1 ·K ^-1

Example 3

The +100 mesh Ti-48Al-2Nb-2Cr coarse powder obtained by the plasma rotating electrode atomization method and the -500 mesh high oxygen content ultrafine Nb powder obtained by the ball milling method are used as raw materials. Weigh 10 kilograms of Ti-48Al-2Nb-2Cr coarse powder and 1.5 kilograms of pure Nb powder, place them in a V-shaped mixer and mix them thoroughly for 22 hours; after the mixing is completed, put the mixed powder into a stainless steel bag with a wall thickness of 1.5mm. into the bag and evacuated to 10 ^-4 Pa and then sealed. Before loading the powder, wipe the hexagonal boron nitride powder on the inner wall of the bag; the sealed bag containing the mixed powder is sintered in a hot isostatic pressing furnace, and the pressure is set to 70MPa. The heating rate is 10°C/min. When the temperature reaches 930°C, keep the temperature for 2 hours, then keep the pressure unchanged, raise the temperature to 1000°C at a rate of 10°C/min and continue sintering for 2 hours, and then cool with the furnace; remove the jacket. A TiAl intermetallic compound porous material with a porosity of 44% and an Nb content of 9.5at.% was obtained. The thermal conductivity of the porous material was 2.8W·m ^-1 ·K ^-1 .

Example 4

The +100 mesh Ti-48Al-2Nb-2Cr coarse powder obtained by the plasma rotating electrode atomization method and the -500 mesh high oxygen content ultrafine Nb powder obtained by the ball milling method are used as raw materials. Weigh 10 kilograms of Ti-48Al-2Nb-2Cr coarse powder and 1.3 kilograms of pure Nb powder, place them in a V-shaped mixer and mix them thoroughly for 24 hours; after the mixing is completed, put the mixed powder into a stainless steel bag with a wall thickness of 1.2mm into the bag, and evacuate to 10 ^-4 Pa and then seal it. Wipe the hexagonal boron nitride powder on the inner wall of the bag before loading the powder; the sealed bag containing the mixed powder is sintered in a hot isostatic pressing furnace, and the pressure is set to 80MPa. The heating rate is 15°C/min. When the temperature reaches 920°C, keep the temperature for 3 hours, then keep the pressure unchanged, raise the temperature to 1050°C at a rate of 5°C/min and continue sintering for 1 hour, and then cool with the furnace; remove the jacket. A TiAl intermetallic compound porous material with a porosity of 47% and an Nb content of 8.5at.% was obtained. The thermal conductivity of the porous material was 2.4W·m ^-1 ·K ^-1 .

Comparative example 1

Other process parameters are the same as those in Embodiment 1, except that the first stage of sintering is abandoned during sintering and the second stage of sintering is performed directly. Since the sintering temperature in the second stage is higher than that of the first stage, the diffusion between Nb and TiAl can still be satisfied. However, due to The diffusion between Nb and TiAl is faster than the diffusion between TiAl and TiAl. Sintering between Nb and TiAl occurs preferentially, resulting in unsintered TiAl powder remaining in the final sintered ingot, and the composition of the prepared porous material is not stable. Meets the scope.

Comparative example 2

Other process parameters are the same as Example 1, except that the sintering pressure in both stages is increased to 100MPa. Due to the excessive sintering pressure, the porosity of the prepared porous material is only 20%, and the thermal conductivity reaches 6.2W·m ^-1 ·K ^-1 , the high-temperature filtration efficiency of the material becomes worse.

Comparative example 3

Other process parameters are the same as in Example 1, except that the sintering temperature in the first stage is increased to 1050°C, and the sintering temperature in the second stage is increased to 1250°C. Due to the increase in sintering temperature, it is beneficial to the densification of alloy sintering and the final sintered green body. The density reaches 92% and the porosity is only 8%, which does not meet the range of porous material porosity.

Comparative example 4

Other process parameters are the same as in Example 1. Only the weight of Nb powder in the raw material is increased to 25% of the weight of the TiAl alloy coarse powder. The content of fine-grained Nb powder is increased, resulting in the gap between the TiAl coarse powder being filled with more fine-grained Nb. Powder filling reduces the theoretical porosity, and the porosity after sintering is only 38%, which is not conducive to the filtration performance of porous materials.

Claims (10)

1. A method for preparing high Nb content TiAl intermetallic compound porous materials, which is characterized in that: low oxygen content TiAl alloy coarse powder and high oxygen content ultrafine Nb powder are mixed and then put into a stainless steel jacket for vibration and pumping. After vacuuming and sealing, the first stage hot isostatic pressing sintering at 850~950℃ and the second stage hot isostatic pressing sintering at 1000~1150℃ are obtained; The particle size of the low oxygen content TiAl alloy coarse powder is greater than 150 μm, and the oxygen content is less than 400 ppm; The particle size of the high oxygen content ultrafine Nb powder is less than 25 μm, and the oxygen content is greater than 2000 ppm. 2. A method for preparing a high Nb content TiAl intermetallic compound porous material according to claim 1, characterized in that the weight of the Nb powder is 12 to 16% of the weight of the TiAl alloy coarse powder. 3. A method for preparing a high Nb content TiAl intermetallic compound porous material according to claim 1 or 2, characterized in that: the TiAl alloy coarse powder is low-cost Ti-48Al-2Nb discarded in the field of additive manufacturing -2Cr coarse powder. 4. A method for preparing a high Nb content TiAl intermetallic compound porous material according to claim 3, characterized in that: The TiAl alloy coarse powder is screened plasma rotating electrode atomized powder; The Nb powder is obtained by ball milling. 5. A method for preparing a high Nb content TiAl intermetallic compound porous material according to claim 1, characterized in that: the wall thickness of the stainless steel cladding is 1.2~1.5mm, and the inner wall of the cladding is wiped in six directions before loading the powder. Boron nitride powder. 6. A method for preparing a high Nb content TiAl intermetallic compound porous material according to claim 1, characterized in that: the pressures of the first stage hot isostatic pressing sintering and the second stage hot isostatic pressing sintering are uniform. is 60~80MPa. 7. A method for preparing a high Nb content TiAl intermetallic compound porous material according to claim 6, characterized in that: The process of hot isostatic pressing sintering in the first stage is as follows: the temperature is 900-950°C, the heating rate is 10-15°C/min, and the heat preservation time is 2-3 hours; The second stage hot isostatic pressing sintering process is as follows: the temperature is 1000-1050°C, the temperature rise rate is 5-10°C/min, the holding time is 1-2h, and the furnace is cooled after the sintering is completed. 8. The method for preparing a high Nb content TiAl intermetallic compound porous material according to any one of claims 4 to 7, characterized in that: the powder mixing time is 20 to 24 hours. 9. A TiAl intermetallic compound porous material with high Nb content, characterized in that it is obtained by the preparation method according to any one of claims 1 to 8. 10. A TiAl intermetallic compound porous material with high Nb content according to claim 9, characterized in that: the atomic percentage of Nb element in the porous material is 8 to 10%, and the porosity is 40 to 50%.