WO2021031231A1 - Hot isostatic pressing process for ti2alnb alloy powder - Google Patents

Abstract

A hot isostatic pressing process for Ti₂AlNb alloy powder, which belongs to the field of powder metallurgy titanium alloys. The process comprises: firstly placing a bag sleeve containing Ti₂AlNb powder into a hot isostatic pressing device to undergo a first stage of treatment under low temperature and constant pressure, to densify the material; then continuing to heat to allow the bag sleeve to rise in temperature along with the oven to a hot isostatic pressing temperature T2 and holding the temperature for a period of time to so that the organization of the materials is uniform; and stopping heating and cooling along with the oven to room temperature so as to obtain a Ti₂AlNb alloy component.

Description

A Ti Hot isostatic pressing process of 2AlNb alloy powder Technical field

The invention relates to the technical field of powder metallurgy titanium alloys, in particular to a hot isostatic pressing process of _{Ti 2 AlNb alloy powder.}

Background technique

Ti ₂ AlNb alloy is a Ti-Al intermetallic compound alloy with orthogonal structure O phase as the main phase. It has excellent strength, fracture toughness and creep resistance at 650～750℃, and has low density and Good oxidation resistance, so Ti ₂ AlNb alloy has a strong application potential in the hot end parts of aeroengines. Ti ₂ AlNb alloy complex components currently mainly use precision casting or split forging + welding forming process. Precision casting has casting defects such as shrinkage, porosity, and composition segregation that are difficult to completely solve, resulting in high rejection rate and widespread use of over-tolerance; forging The combined welding method has low material utilization and the risk of cracking in the welded joint, which is difficult to meet the requirements of high reliability and weight reduction of modern aeroengines.

In recent years, with the development of powder milling technology and powder near-net forming technology, the use of hot isostatic pressing near-net forming technology can solve the problems of macroscopic composition segregation and microstructure inhomogeneity of the _{cast and deformed Ti 2 AlNb alloy.} The limitations of the ingot size and thermal deformation equipment limit the _{shape and size of the deformed Ti 2} AlNb alloy, which can form large-sized complex components with uniform material composition, microstructure and good performance consistency. Through Micro-CT analysis, it is found that Ti ₂ AlNb is easy to cause alloying elements such as Al and Nb to segregate along the forging streamline, while powder metallurgy alloys have no obvious component segregation.

However, the powdered Ti ₂ AlNb alloy prepared by powder metallurgy technology also has its own shortcomings, such as uneven density when preparing large-scale and complex components, the durability of powder alloys is lower than that of forged alloys, and the body performance of large-scale complex components The performance of the test bar is uneven. For the high-temperature durability of powder Ti ₂ AlNb alloy, domestic and foreign researchers have developed a series of methods, which mainly include: after powder hot isostatic pressing and consolidation, the use of extrusion, isothermal forging, ring rolling and other processes The powder blank undergoes a large amount of deformation to improve the phase distribution and uniformity of the powder alloy; there is no doubt that these methods have limited the application fields of the material.

Summary of the invention

The purpose of the present invention is to provide a _{hot isostatic pressing process for Ti 2} AlNb alloy powder, which can directly obtain powder Ti ₂ AlNb alloy blanks with excellent durability through hot isostatic pressing.

In order to achieve the above objectives, the technical solutions adopted by the present invention are as follows:

A _{hot isostatic pressing process for Ti 2} AlNb alloy powder, the process including the following steps:

(1) Prepare Ti ₂ AlNb clean pre-alloyed powder, sieving the powder to obtain powder with a size less than or equal to 250 microns, and put the sieved powder into a carbon steel or stainless steel sheath, degas at high temperature and seal welding ；

(2) Low-temperature pressure-keeping treatment: Put the powder-filled envelope obtained in step (1) into a hot isostatic pressing device, and reach the predetermined temperature T1 and pressure F1 by simultaneously raising the temperature and increasing the pressure or first raising the pressure and then increasing the pressure. Afterwards, carry out low-temperature and pressure-keeping treatment to ensure the densification of the material structure;

(3) Hot isostatic pressing treatment: After step (2) low-temperature holding pressure treatment, continue heating, so that the sheath is heated to the hot isostatic pressing temperature T2 with the furnace and kept for a period of time to ensure uniform material structure;

(4) Stop heating and cool down to room temperature with the furnace to obtain Ti-Al alloy components.

In the above step (1), the Ti ₂ AlNb clean pre-alloyed powder adopts crucible-free induction melting ultrasonic gas atomization method (electrode induction melting gas atomization, EIGA) or plasma rotating electrode process (plasma rotating electrode process, PREP) preparation.

In the above step (2), the value range of the predetermined temperature T1 is

Between; where:

Is the O+B2+α ₂ →B2+α ₂ phase transition point of Ti _{2 AlNb alloy,}

Pressure F1≥100MPa.

In the above step (2), the time of the low-temperature holding pressure treatment is 30min-2h.

In the above step (3), the range of the hot isostatic pressing temperature T2 is between ( _TB2 -25℃)～( _TB2 -5℃), where: T _B2 is the α ₂ + of Ti _{2 AlNb alloy} B2→B2 phase transition point, T _B2 = 1055°C.

In the above step (3), the holding time is 2h-5h.

In the above step (3), the pressure in the heat preservation process should be greater than or equal to 100 MPa.

The process of the present invention is suitable for hot isostatic pressing and consolidation forming and uniform densification of _{Ti 2 AlNb alloy powder. The process improves the density of each part of the Ti 2} AlNb alloy component, thereby increasing the endurance life _{of the Ti 2 AlNb alloy.}

The advantages and beneficial effects of the present invention are:

1. The process of the present invention is divided into two steps. The temperature T1 range of the first step is:

Between, the gas pressure F1 should be greater than or equal to 100MPa, and the holding time is 30min～2h. The first step is to continue heating after the completion of low-temperature holding pressure to make the material rise to the hot isostatic pressure temperature T2 and keep it warm. The range of T2 is between ( _TB2 -25℃)～( _TB2 -5℃). The gas pressure should be greater than or equal to 100MPa, and the holding time should be 2h-5h to make the material continue to be densified and ensure the uniformity of the material structure. This process is the second step. After the completion of the heat preservation process, the alloy is kept under pressure and cooled to room temperature. The invention is used for hot isostatic pressing and consolidation forming of the rapidly solidified Ti-Al alloy powder, eliminates macroscopic pore defects, improves the density of each part of a complex component, and improves the comprehensive mechanical properties of the alloy, especially the endurance life.

2. The process of the present invention can be realized on a traditional hot isostatic pressing machine, and the applicable scope of the process is the hot isostatic pressing consolidation molding _{of Ti-Al alloy (Ti 2} AlNb, Ti _{3 Al and TiAl) powders.}

3. The invention is simple and practical, and can improve the overall metallurgical quality of the powder alloy and increase the durability of the powder alloy, thereby reducing its manufacturing cost.

4. The process of the present invention is suitable for preparing powder metallurgy titanium alloy components formed by direct hot isostatic pressing.

Description of the drawings

Figure 1 is the hot isostatic pressing process curve; among them: (a) Process system B, (b) Process system C.

detailed description

_{The invention is a Ti 2} AlNb alloy powder hot isostatic pressing process that can improve the overall metallurgical quality of the powder alloy and the endurance life of the powder alloy, and the details are as follows:

1. Use crucible-free induction melting ultrasonic gas atomization method (electrode induction melting gas atomization, EIGA) or plasma rotating electrode atomization method (plasma rotating electrode process, PREP) to prepare Ti ₂ AlNb clean pre-alloy powder, and obtain the size by sieving For powder less than or equal to 250 microns, put the powder into a low-carbon steel or stainless steel sheath, and then seal and weld after high temperature degassing. The use of powder with a size less than or equal to 250 microns is to reduce the amount of hollow powder; the use of carbon steel or stainless steel sheathing is because in the temperature range used in the present invention, the sheathing material is completely solid and has a certain strength; high temperature degassing is In order to maximize the removal of the gas adsorbed on the powder surface, the high temperature degassing temperature range is 150-350℃, and the degassing time is 8 hours to 16 hours.

2. Put the powder sheath prepared in the first step into the hot isostatic pressing equipment, and reach the process conditions of the first stage by increasing the pressure with the furnace or first heating and then increasing the pressure, and start the low temperature holding treatment. The low temperature holding temperature of the first step should be selected at

Between, the gas pressure should be greater than or equal to 100MPa, and the time should be greater than or equal to 30 minutes and less than or equal to 2 hours.

The temperature of the first stage process low temperature holding treatment is selected in

The difference is based on the following reasons. First, the hot isostatic pressing temperature of traditional powder titanium alloys (such as Ti-6Al-4V alloy and Ti-5Al-2.5Sn alloy) is 920℃～960℃, Ti ₂ AlNb intermetallic compound Compared with traditional titanium alloys, it has higher strength and greater resistance to thermal deformation, so the hot isostatic pressing temperature is higher. Second, the _{chemical activity of Ti 2} AlNb intermetallic compounds is stronger than that of traditional titanium alloys. It reacts with almost all ceramic crucible and nozzle materials and is easily Contaminated by impurities such as oxygen, the specific surface area of the powder will increase and it will be more easily contaminated. Therefore, the hot isostatic pressing temperature is higher than that of traditional titanium alloys to break the original particle boundaries of the powder and eliminate macroscopic pore defects.

The holding time of the first step is greater than or equal to 30 minutes and less than or equal to 2 hours due to the following reasons: First, within the temperature range of the first step selected in the present invention, the complete compaction of the powder compact requires at least 30 minutes ; Second, too long holding time will cause the alloy to undergo phase transformation and affect the mechanical properties.

3. After the first step is completed, continue heating, and heat the powder jacket with the furnace to between (T _B2 -25℃)～(T _B2 -5℃) and keep it for a period of time. This process is the second step of heat Isostatic processing stage; the holding time of the second step should be greater than or equal to 2 hours and less than or equal to 5 hours to ensure uniform material structure, and the pressure is greater than or equal to 100MPa. After the second step is completed, the heating is stopped and the furnace is cooled to Room temperature. The design of the second step process is based on the following reasons: First, relying on the creep diffusion mechanism to control the slow densification to improve the uniformity and consistency of the density of various parts of the powder alloy complex components, so as to ensure the mechanical properties of the complex components Consistency and stability; Second, increasing the hot isostatic pressing temperature is equivalent to doing a high temperature solution heat treatment, which can promote the _{complete transformation of α 2} and O phase to B2 phase, stabilize the alloy microstructure, and further improve the comprehensive mechanical properties of the material.

The present invention will be further described in detail below in conjunction with the drawings, comparative examples and embodiments.

The compositions of the following comparative examples and example alloys are shown in Table 1:

Table 1. Ti ₂ AlNb alloy composition (wt.%)

Main phase transformation points of powder Ti _{2 AlNb alloy:}

α ₂ +B2→B2, alloy transformation point T _B2 =1055℃;

O+B2+α ₂ →B2+α ₂ , alloy phase transformation point

Comparative example 1

In Comparative Example 1, argon gas atomization was used to prepare the alloy powder, and the powder with a size of 250 microns or less was packed into a carbon steel jacket, and then subjected to hot isostatic pressing after vacuum degassing. The following process system (A) is selected for this alloy:

The temperature is increased with the furnace to the hot isostatic pressure condition: 1030℃/100MPa/3 hours, and the furnace is cooled after completion.

Comparative example 2

The difference from Comparative Example 1 is that the hot isostatic pressure is 140 MPa.

In Comparative Example 2, argon gas atomization was used to prepare the alloy powder, and the powder with a size of less than 250 microns was packed into a carbon steel sheath, and then subjected to hot isostatic pressing after vacuum degassing. The following process system (B) is selected for this alloy. The curve of process system (B) is shown in Figure 1(a). The specific conditions are as follows:

Heating and pressure increase with the furnace to hot isostatic pressure conditions: 1030℃/140MPa/3 hours, cooling with the furnace after completion;

_{Table 2 shows the comprehensive mechanical properties of the powder Ti 2} AlNb alloy prepared by the process system (A) and the process system (B) _{. It can be seen that the powder Ti 2} AlNb alloy prepared by the process system (A) and the process system (B) There is no difference in tensile properties and durability. This is because the temperature effect is the most significant among the HIP parameters (time, temperature, pressure), and the pressure effect is small.

Table 2. Mechanical properties _{of powder metallurgy Ti 2} AlNb alloy prepared by process A and process B

Example 1

The difference from Comparative Example 2 is that a low temperature holding stage is added before the hot isostatic pressing treatment.

In Example 1, argon atomization was used to prepare the alloy powder, and the powder with a size below 250 microns was packed into a carbon steel ladle, and after vacuum degassing, a low-temperature pressure holding treatment was performed, and then a hot isostatic pressing treatment was performed. The following process system (C) is selected for this alloy. The curve of process system (C) is shown in Figure 1(b). The specific process conditions are as follows:

The first stage of low-temperature pressure holding process: increase the pressure with the furnace, 1010℃/140MPa/1 hour, and cool with the furnace after completion;

The second stage hot isostatic pressing process: 1030℃/140MPa/3 hours, cooling to room temperature with the furnace.

The holding temperature in the first stage of the system is

The holding temperature in the second stage of the system is ( _TB2 -25℃).

_{Table 3 shows the comprehensive mechanical properties of powder Ti 2} AlNb alloy prepared by process system (B) and process system (C). It can be seen that the room temperature strength and plasticity _{of powder Ti 2} AlNb alloy prepared by process system (C) are slightly reduced However, the strength and plasticity at 650°C have been significantly improved, and the endurance life under 650°C/360MPa conditions has been significantly improved. Since the main task of powder densification is in the heating and pressurization stage of hot isostatic pressing, a large number of pores inside the powder compact are eliminated at this stage. The hot isostatic pressing temperature is the driving force for the phase change, and the hot isostatic pressing time determines the degree of phase change. For the actual powder Ti ₂ AlNb alloy complex components, it is necessary to set a heat preservation step at the key stage of densification, such as 1010 ℃, so that the densification process of each part of the powder component can be uniformly performed, thereby improving the comprehensive mechanical properties of the material, especially the high temperature durability life.

Table 3. Mechanical properties _{of powder metallurgy Ti 2} AlNb alloy prepared by process B and process C

The results of the examples show that the process of the present invention can increase _{the density of various parts of the powder Ti 2} AlNb alloy complex components, solve the problem of the mechanical properties of large-size complex components and the performance of the test bar, and is suitable for preparing direct hot isostatic pressing Powder metallurgy titanium alloy components. In the first step of the present invention, the temperature of the first step is to set a step in the low temperature stage to increase the density of each part of the powder alloy and promote the densification of the powder alloy. The results of the examples also fully confirm this. The heat preservation stage of the second step of the hot isostatic pressing of the present invention can stabilize the tissue and promote the complete phase transition. Therefore, the process of the present invention can be directly applied to the hot isostatic pressing of _{Ti 2 AlNb alloy powder.}

Claims (8)

1. A _{hot isostatic pressing process of Ti 2} AlNb alloy powder, characterized in that: the process includes the following steps:

   (1) Prepare Ti ₂ AlNb pre-alloy powder, sieving the powder to obtain powder with a size less than or equal to 250 microns, and put the sieved powder into a carbon steel or stainless steel sheath, degas at high temperature and seal welding;

   (2) Low-temperature pressure-keeping treatment: Put the powder-filled envelope obtained in step (1) into a hot isostatic pressing device, and reach the predetermined temperature T1 and pressure F1 by simultaneously raising the temperature and increasing the pressure or first raising the pressure and then increasing the pressure. Afterwards, carry out low-temperature and pressure-keeping treatment to ensure the densification of the material structure;

   (3) Hot isostatic pressing treatment: After step (2) low-temperature holding pressure treatment, continue heating, so that the sheath is heated to the hot isostatic pressing temperature T2 with the furnace and kept for a period of time to ensure uniform material structure;

   (4) Stop heating and cool down to room temperature with the furnace to obtain Ti ₂ AlNb alloy components.
2. _{The hot isostatic pressing process of Ti 2} AlNb alloy powder according to claim 1, characterized in that: in step (1), the Ti ₂ AlNb pre-alloy powder adopts a crucible-free induction melting ultrasonic gas atomization method or plasma rotation Prepared by electrode atomization method.
3. _{The hot isostatic pressing process of Ti 2} AlNb alloy powder according to claim 1, characterized in that: in step (2), the predetermined temperature T1 has a value range of

   

   Between, where:

   

   Is the O+B2+α ₂ →B2+α ₂ phase transition point of Ti _{2 AlNb alloy,}

   

   Pressure F1≥100MPa.
4. _{The hot isostatic pressing process of Ti 2} AlNb alloy powder according to claim 1 or 3, characterized in that: in step (2), the time for the low-temperature holding pressure treatment is 30 min-2h.
5. _{The hot isostatic pressing process of Ti 2} AlNb alloy powder according to claim 1, characterized in that: in step (3), the range of the hot isostatic pressing temperature T2 is (T _B2 -25°C) ~ (T _B2 -5°C), where: T _B2 is the α ₂ +B2→B2 phase transition point of Ti _{2 AlNb alloy, and T B2} =1055°C.
6. _{The hot isostatic pressing process of Ti 2} AlNb alloy powder according to claim 1 or 5, characterized in that: in step (3), the holding time is 2h-5h.
7. _{The hot isostatic pressing process of Ti 2} AlNb alloy powder according to claim 1 or 5, characterized in that: in step (3), the pressure in the heat preservation process should be greater than or equal to 100 MPa.
8. _{The hot isostatic pressing process of Ti 2} AlNb alloy powder according to claim 1, characterized in that: the process is suitable for hot isostatic pressing consolidation forming and uniform densification of _{Ti 2 AlNb alloy powder, and the process improves Ti 2} The density of each part of the AlNb alloy component, thereby improving the durability of the _{Ti 2 AlNb alloy.}

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