High-nb-content ti-al intermetallic compound porous material and preparation method thereof

Abstract

The application discloses a kind of high Nb content TiAl intermetallic compound porous materials and preparation method thereof, belong to intermetallic compound porous material preparation field.The application mixes low oxygen content TiAl alloy coarse powder and high oxygen content superfine Nb powder after powder, and then is loaded into stainless steel jacket, is vibrated, is vacuumized, is sealed, and then is sequentially subjected to 850~950 DEG C first stage hot isostatic pressing sintering and 1000~1150 DEG C second stage hot isostatic pressing sintering, and is obtained immediately.The application is based on the physical accumulation of coarse particle size powder into pore, utilizes the easy diffusion characteristics between Nb and TiAl, realizes TiAl sintering at lower sintering temperature, and realizes porosity of 40~50% by adjusting temperature and pressure of hot isostatic pressing.The application has simple technological process, low production cost, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to a TiAl intermetallic compound porous material and its preparation method, particularly to a high Nb content TiAl intermetallic compound porous material and its preparation method, belonging to the field of intermetallic compound porous material preparation. Background Technology

[0002] Porous materials possess advantages such as low relative density, high specific strength, large specific surface area, and good permeability, and are widely used in aerospace, petrochemical, metallurgical, and environmental fields, particularly in areas requiring functional applications such as sound insulation, heat insulation, separation, filtration, vibration damping, adsorption, and catalysis. Currently, industrially applied porous materials include polymer porous materials, ceramic porous materials, metal porous materials, and intermetallic compound porous materials. TiAl intermetallic compound porous materials, due to the presence of both ionic and covalent bonds, combine the advantages of porous ceramics and porous metals, and are considered one of the most promising high-temperature filtration materials.

[0003] Currently, TiAl intermetallic porous materials are mainly prepared using powder metallurgy. The formation of pores originates from three aspects: (1) the partial diffusion effect caused by the large difference in the intrinsic diffusion coefficients of different elements, which leads to the formation of Kirkendall pores in the material. These pores are usually small in size; (2) pores are formed by the physical stacking of raw material powders. 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 powders are often used as raw materials 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.

[0004] In the field of TiAl intermetallic compound additive manufacturing, due to the strict requirements on powder particle size in the manufacturing process, there is a general surplus of coarse-grained TiAl alloy powder. For example, electron beam selective melting (EBSM) requires TiAl intermetallic compound powder size of 40–100 μm, while TiAl intermetallic compound powder prepared by plasma rotating electrode process (PREP) typically has a size of 45–250 μm, of which about 60–70% is smaller than 100 μm. This 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 are currently no suitable applications. Moreover, due to the difficulty in separating the various elements in the powder, the value of this type of coarse powder is extremely low (the selling price is about 60–70% of the price of sponge titanium), which indirectly leads to the high cost and resource waste in the additive manufacturing of TiAl parts.

[0005] Furthermore, the operating temperature of TiAl intermetallic compound porous materials is typically below 800℃. Above this temperature, the alloy is easily oxidized, generating Ti2O and Al2O3, which clog the pores and severely affect its filtration efficiency. To further increase the operating temperature, it is usually necessary to increase the Nb content and prepare porous materials with high Nb content.

[0006] Currently, there is no known method for manufacturing high-Nb-content TiAl porous materials using waste coarse powder from the TiAl intermetallic compound additive manufacturing field, which can both meet the requirements of high-temperature filtration and make resource utilization of existing industrial waste powder. Summary of the Invention

[0007] In view of the lack of existing technology, the first objective of this invention is to provide a high Nb content TiAl intermetallic compound porous material that has good porosity and can achieve good filtration effect at higher temperatures.

[0008] The second objective of this invention is to provide a method for preparing a high-Nb-content TiAl intermetallic porous material. This method is based on the physical stacking of coarse-grained powders to form pores. Utilizing the easy diffusion between Nb and TiAl, TiAl sintering is achieved at a relatively low sintering temperature. Furthermore, the metallurgical bonding of all powder particles is ensured by controlling the two-stage hot isostatic pressing temperature. This method has the advantages of simple process flow and low production cost, making it suitable for industrial production.

[0009] To achieve the above-mentioned technical objectives, this invention provides a method for preparing a high-Nb-content TiAl intermetallic compound porous material. The method involves mixing low-oxygen-content TiAl alloy coarse powder and high-oxygen-content ultrafine Nb powder, then packing the mixture into a stainless steel casing, vibrating it, evacuating it, and sealing it. The mixture is then subjected to a first-stage hot isostatic pressing sintering at 850–950°C and a second-stage hot isostatic pressing sintering at 1000–1150°C to obtain the final product. The low-oxygen-content TiAl alloy coarse powder has a particle size greater than 150 μm (+100 mesh) and an oxygen content less than 400 ppm; the high-oxygen-content ultrafine Nb powder has a particle size less than 25 μm (-500 mesh) and an oxygen content greater than 2000 ppm.

[0010] In the technical solution of this invention, by mixing low-oxygen-content TiAl alloy coarse powder and high-oxygen-content ultrafine Nb powder, on the one hand, the oxygen content in the final product can be maintained in the range of 800-1200ppm, which reduces the difficulty of the process while ensuring the plasticity of the product; on the other hand, by utilizing the significant particle size difference between the two, pores are formed based on the physical stacking of coarse particles, and by utilizing the easy diffusion characteristics between Nb and TiAl, TiAl sintering is achieved at a lower sintering temperature, ultimately obtaining a high-Nb-content TiAl intermetallic compound porous material.

[0011] The key to this invention lies in controlling the temperature of hot isostatic pressing (HIP) after mixing coarse TiAl alloy powder with significant particle size differences and ultrafine Nb powder. The HIP sintering of this invention is divided into two stages. The principle of the first stage sintering is to achieve metallurgical bonding between the powders through diffusion between Nb powder and TiAl, with the temperature selected based on the diffusion kinetics between Nb and TiAl. Through diffusion between Nb and TiAl, the Nb content in the TiAl alloy raw material is significantly increased by 6-8 at.%, resulting in 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 achieve metallurgical bonding after the first stage of HIP sintering. Therefore, a second stage of sintering at a higher temperature is required. Furthermore, this invention achieves primary metallurgical bonding between the powders through low-temperature sintering in the first stage, thus reducing the sintering temperature and time of the second stage to a certain extent, improving production efficiency, and reducing production costs.

[0012] As a preferred embodiment, the Nb powder weight is 12-16% of the TiAl alloy coarse powder weight. The Nb powder weight used in this invention, converted to an atomic percentage of Nb in the porous material, is 8-10 at.%, falling within the composition range of high-niobium-content titanium-aluminum alloys. Theoretically, the maximum porosity after sintering pure coarse powder is 60%. When the Nb powder weight is 12-16% of the TiAl coarse powder weight, the maximum theoretical porosity after mixing and sintering is 57%. Therefore, the actual porosity during sintering is less than 57%.

[0013] As a preferred embodiment, the TiAl alloy coarse powder is a low-cost Ti-48Al-2Nb-2Cr coarse powder discarded in the additive manufacturing field. This type of powder used in the present invention is not only extremely inexpensive but also has a lower oxygen content than fine powders.

[0014] As a preferred embodiment, the TiAl alloy powder is a coarse powder obtained by plasma rotating electrode atomization after sieving; the Nb powder is obtained by ball milling. The -500 mesh ball-milled ultrafine Nb powder used in this invention is usually difficult to utilize due to its high oxygen content, and therefore inexpensive. Therefore, this invention uses Ti-48Al-2Nb-2Cr coarse powder and ultrafine Nb powder, which are waste materials from the additive manufacturing field, as raw materials, which can significantly reduce costs while ensuring the performance of the final product.

[0015] As a preferred embodiment, the stainless steel sheath has a wall thickness of 1.2–1.5 mm, and hexagonal boron nitride powder is wiped onto the inner wall of the sheath before powder loading. The inventors discovered that a thinner sheath is necessary to match the relatively low hot isostatic pressing pressure in subsequent processes; and the purpose of wiping the inner wall with hexagonal boron nitride powder is to prevent diffusion between the sheath and the powder under temperature and pressure, and to facilitate smooth peeling of the sheath after hot isostatic pressing.

[0016] As a preferred embodiment, the pressures of both the first-stage hot isostatic pressing (HIP) sintering and the second-stage HIP sintering are 60–80 MPa. Since the sintering processes of TiAl porous materials provided by existing technologies mostly employ pressureless or low-pressure sintering, the sintering process inevitably involves volume expansion. This invention sets the sintering conditions to be lower than the densification sintering conditions of TiAl intermetallic compounds: 60–80 MPa. The purpose of this is to reduce volume expansion, which is more conducive to shape control after sintering, thereby simplifying subsequent product processing.

[0017] As a preferred embodiment, the first-stage hot isostatic pressing (HIP) sintering process is as follows: temperature 900–950℃, heating rate 10–15℃ / min, holding time 2–3 h; the second-stage HIP sintering process is as follows: temperature 1000–1050℃, heating rate 5–10℃ / min, holding time 1–2 h, followed by furnace cooling after sintering. The purpose of the first-stage sintering in this invention is to facilitate the diffusion of Nb and TiAl. Therefore, the diffusion behavior between Nb and TiAl needs to be considered when selecting the temperature. When the first-stage sintering temperature is below 900℃, the diffusion between Nb and TiAl is slow, leading to a significant extension of the sintering time; when the sintering temperature is above 950℃, the excessively rapid diffusion rate increases the difficulty of controlling the preparation process. The purpose of the second-stage sintering is to bond the TiAl powder that has not yet undergone metallurgical bonding. Therefore, when selecting the temperature, the diffusion behavior between TiAl particles needs to be considered. When the sintering temperature in the second stage is below 1000℃, the diffusion between TiAl particles is slow, which will lead to a significant increase in sintering time. When the sintering temperature is above 1050℃, the diffusion rate will be too fast, increasing the difficulty of control during actual production. The selection of the heating rate needs to consider both production efficiency and temperature control. On the one hand, a heating rate that is too low should not be used, as this would prolong the production cycle. On the other hand, a heating rate that is too high should not be used, as this would cause the sintering temperature to exceed the set range, which would be detrimental to temperature control.

[0018] As a preferred embodiment, the mixing time is 20 to 24 hours.

[0019] The present invention also provides a high Nb content TiAl intermetallic compound porous material, which is obtained by the above preparation method.

[0020] As a preferred embodiment, the porous material contains 8-10% Nb atomic percentage and has a porosity of 40-50%, ensuring sufficient diffusion of the original Nb powder. The TiAl intermetallic compound porous material of this invention has a high Nb content, which increases the operating temperature of the porous material. Simultaneously, the high porosity of the porous material ensures excellent filtration performance.

[0021] Principles and effects

[0022] Compared to existing technologies that use elemental powders and the Kirkendall effect to prepare TiAl intermetallic porous materials, this invention uses waste powders from industrial production as raw materials. These powders are cheaper than pure metal elemental powders, offering a cost advantage while achieving efficient resource utilization. The pore formation principle of this invention utilizes the physical accumulation of coarse-grained powders to create large-sized gaps. Therefore, no pore-forming agent needs to be added during sintering, avoiding contamination caused by pore-forming agents.

[0023] This invention utilizes the excellent diffusion ability between Nb and TiAl matrix to prepare high-Nb-content porous materials from low-Nb-content alloy powder. This not only increases the service temperature of TiAl intermetallic compound porous materials and reduces raw material costs, but also achieves a primary metallurgical bond between Nb and TiAl in the first-stage low-temperature sintering process, reducing the sintering temperature and time in the second stage, thereby improving production efficiency and reducing production costs. Attached Figure Description

[0024] Figure 1 The microstructure of the TiAl intermetallic porous material prepared in this invention is shown. Detailed Implementation

[0025] The following are preferred embodiments of the present invention, but not all embodiments. Without departing from the innovative principles of this process, any equivalent process modifications made based on the content of this specification, or direct or indirect applications in other related technical fields, shall be considered within the scope of patent protection of this invention.

[0026] Example 1

[0027] +100 mesh Ti-48Al-2Nb-2Cr coarse powder obtained by plasma rotating electrode atomization and -500 mesh high oxygen content ultrafine Nb powder obtained by ball milling were used as raw materials. 10 kg of TiAl powder and 1.2 kg of pure Nb powder were weighed and thoroughly mixed in a V-type mixer for 20 hours. After mixing, the mixed powder was placed into a 1.2 mm thick stainless steel sleeve and evacuated to 100°C. -4After sealing with Pa, hexagonal boron nitride powder was wiped onto the inner wall of the casing before filling with powder. The sealed casing containing the mixed powder was sintered in a hot isostatic pressing furnace with a pressure of 60 MPa and a heating rate of 10 °C / min. When the temperature reached 900 °C, it was held for 3 hours, and then the pressure was kept constant while the temperature was increased to 1050 °C at a rate of 5 °C / min for another hour of sintering. Subsequently, it was cooled with the furnace. After removing the casing, a TiAl intermetallic porous material with a porosity of 50% and an Nb content of 8 at.% was obtained. The thermal conductivity of this porous material was 2.0 W·m. -1 ·K -1 .

[0028] Example 2

[0029] +100 mesh Ti-48Al-2Nb-2Cr coarse powder obtained by plasma rotating electrode atomization and -500 mesh high-oxygen-content ultrafine Nb powder obtained by ball milling were used as raw materials. 10 kg of Ti-48Al-2Nb-2Cr coarse powder and 1.6 kg of pure Nb powder were weighed and placed in a V-type mixer for 24 hours to mix thoroughly. After mixing, the mixed powder was placed into a 1.5 mm thick stainless steel sleeve and vacuumed to 100°C. -4 After sealing with Pa, hexagonal boron nitride powder was wiped onto the inner wall of the casing before filling with powder. The sealed casing containing the mixed powder was sintered in a hot isostatic pressing furnace with a pressure of 80 MPa and a heating rate of 15 °C / min. When the temperature reached 950 °C, it was held for 3 hours, and then the pressure was kept constant while the temperature was increased to 1050 °C at a rate of 10 °C / min for another 2 hours of sintering. The casing was then cooled with the furnace. After removing the casing, a TiAl intermetallic porous material with a porosity of 40% and an Nb content of 10 at.% was obtained. The thermal conductivity of this porous material was 3.0 W·m. -1 ·K -1

[0030] Example 3

[0031] +100 mesh Ti-48Al-2Nb-2Cr coarse powder obtained by plasma rotating electrode atomization and -500 mesh high-oxygen-content ultrafine Nb powder obtained by ball milling were used as raw materials. 10 kg of Ti-48Al-2Nb-2Cr coarse powder and 1.5 kg of pure Nb powder were weighed and placed in a V-type mixer for 22 hours of thorough mixing. After mixing, the mixed powder was placed into a 1.5 mm thick stainless steel sleeve and evacuated to 100°C. -4After sealing with Pa, hexagonal boron nitride powder was wiped onto the inner wall of the casing before filling with powder. The sealed casing containing the mixed powder was sintered in a hot isostatic pressing furnace with a pressure of 70 MPa and a heating rate of 10 °C / min. When the temperature reached 930 °C, it was held for 2 hours. Then, while maintaining the pressure, the temperature was increased to 1000 °C at a rate of 10 °C / min and sintered for another 2 hours, followed by furnace cooling. The casing was removed to obtain a TiAl intermetallic porous material with a porosity of 44% and an Nb content of 9.5 at.%. The thermal conductivity of this porous material was 2.8 W·m. -1 ·K -1 .

[0032] Example 4

[0033] +100 mesh Ti-48Al-2Nb-2Cr coarse powder obtained by plasma rotating electrode atomization and -500 mesh high-oxygen-content ultrafine Nb powder obtained by ball milling were used as raw materials. 10 kg of Ti-48Al-2Nb-2Cr coarse powder and 1.3 kg of pure Nb powder were weighed and thoroughly mixed in a V-type mixer for 24 hours. After mixing, the mixed powder was placed into a 1.2 mm thick stainless steel sleeve and evacuated to 100°C. -4 After sealing with Pa, hexagonal boron nitride powder was wiped onto the inner wall of the casing before filling with powder. The sealed casing containing the mixed powder was sintered in a hot isostatic pressing furnace with a pressure of 80 MPa and a heating rate of 15 °C / min. When the temperature reached 920 °C, it was held for 3 hours, and then the pressure was kept constant while the temperature was increased to 1050 °C at a rate of 5 °C / min for another hour of sintering. Subsequently, it was cooled with the furnace. After removing the casing, a TiAl intermetallic porous material with a porosity of 47% and an Nb content of 8.5 at.% was obtained. The thermal conductivity of this porous material was 2.4 W·m. -1 ·K -1 .

[0034] Comparative Example 1

[0035] Other process parameters are the same as in Example 1, except that the first stage of sintering is abandoned and the second stage of sintering is carried out directly. Since the sintering temperature of the second stage is higher than that of the first stage, the diffusion between Nb and TiAl can still be satisfied. However, since the diffusion between Nb and TiAl is faster than the diffusion between TiAl and TiAl, the sintering between Nb and TiAl occurs preferentially, resulting in the presence of unsintered TiAl powder in the final sintered ingot. The composition of the prepared porous material does not meet the range.

[0036] Comparative Example 2

[0037] Other process parameters were the same as in Example 1, except that the sintering pressure in both stages was increased to 100 MPa. Due to the excessive sintering pressure, the porosity of the prepared porous material was only 20%, and the thermal conductivity reached 6.2 W·m. -1 ·K -1 The high-temperature filtration efficiency of the material deteriorates.

[0038] Comparative Example 3

[0039] Other process parameters are the same as in Example 1, except that the sintering temperature of the first stage is increased to 1050°C and the sintering temperature of the second stage is increased to 1250°C. Due to the increased sintering temperature, it is beneficial to densify the alloy during sintering. The density of the final sintered blank reaches 92%, and the porosity is only 8%, which does not meet the range of porosity for porous materials.

[0040] Comparative Example 4

[0041] Other process parameters are the same as in Example 1, except that the weight of Nb powder in the raw materials is increased to 25% of the weight of TiAl alloy coarse powder. The increased content of fine-particle-size Nb powder leads to more fine-particle-size Nb powder filling the gaps between TiAl coarse powders, resulting in a decrease in theoretical porosity. After sintering, the porosity is only 38%, which is not conducive to the filtration performance of porous materials.

Claims

1. A method for preparing a high-Nb-content TiAl intermetallic porous material, characterized in that: The low-oxygen-content TiAl alloy coarse powder and high-oxygen-content ultrafine Nb powder are mixed and then placed in a stainless steel sleeve, vibrated, vacuumed, and sealed. The mixture is then subjected to a first-stage hot isostatic pressing sintering at 850~950℃ and a second-stage hot isostatic pressing sintering at 1000~1150℃ to obtain the final product. The low-oxygen-content TiAl alloy coarse powder has a particle size greater than 150 μm and an oxygen content less than 400 ppm. The high oxygen content ultrafine Nb powder has a particle size of less than 25 μm and an oxygen content of more than 2000 ppm. The TiAl alloy coarse powder is a low-cost Ti-48Al-2Nb-2Cr coarse powder discarded in the additive manufacturing field; The pressure of the first stage hot isostatic pressing sintering and the second stage hot isostatic pressing sintering is 60~80MPa. The weight of the Nb powder is 12-16% of the weight of the TiAl alloy coarse powder.

2. The method for preparing a high-Nb-content TiAl intermetallic porous material according to claim 1, characterized in that: The TiAl alloy coarse powder is a plasma rotating electrode atomized powder after sieving. The Nb powder was obtained by ball milling.

3. The method for preparing a high-Nb-content TiAl intermetallic porous material according to claim 1, characterized in that: The stainless steel sheath has a wall thickness of 1.2~1.5mm, and hexagonal boron nitride powder is wiped on the inner wall of the sheath before filling with powder.

4. The method for preparing a high-Nb-content TiAl intermetallic porous material according to claim 3, characterized in that: The first stage of hot isostatic pressing sintering process is as follows: the temperature is 900~950℃, the heating rate is 10~15℃ / min, and the holding time is 2~3h; The second stage 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.

5. A method for preparing a high-Nb-content TiAl intermetallic porous material according to any one of claims 2 to 4, characterized in that: The mixing time is 20-24 hours.

6. A high-Nb-content TiAl intermetallic compound porous material, characterized in that: It is obtained by the preparation method according to any one of claims 1 to 5.

7. A high-Nb-content TiAl intermetallic porous material according to claim 6, characterized in that: The porous material contains 8-10% Nb atomic percentage and has a porosity of 40-50%.

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