CN103551573B - Previous particle boundary precipitation preventable high-temperature alloy powder hot isostatic pressing process - Google Patents

Abstract

The invention belongs to the field of powder metallurgy superalloys, and specifically relates to a hot isostatic pressing process for superalloy powders that can avoid the precipitation of carbides and other precipitates along the boundaries of powder primary particles, and is suitable for preparing direct hot isostatic pressing powder metallurgy superalloy components . The hot isostatic pressing temperature of the first step should be higher than the initial melting temperature of the low melting point phase of the alloy powder and lower than 15 degrees Celsius above the solidus line of the completely homogenized alloy, the gas pressure should be greater than or equal to 90MPa, and the time should be greater than or equal to 20 Minutes and less than or equal to 1 hour. After the first step is completed, stop heating and let the material cool down with the furnace to below the initial melting temperature of the low melting point phase of the alloy. The time should be greater than or equal to 2 hours to ensure that the low melting point phase formed during the cooling process after the first step is completely dissolved. After the first step is completed, the alloy is cooled to room temperature with the furnace under pressure. The process of the invention can avoid precipitation of carbides and other precipitates along the boundaries of the primary powder particles, thereby obtaining an alloy with a dense microstructure of equiaxed crystals.

Description

Hot isostatic pressing process of superalloy powders that can avoid the precipitation of primary particle boundary phases

technical field

The invention belongs to the field of powder metallurgy superalloys, and specifically relates to a hot isostatic pressing process for superalloy powders that can avoid the precipitation of carbides and other precipitates along the boundaries of powder primary particles, and is suitable for preparing direct hot isostatic pressing powder metallurgy superalloy components .

Background technique

Superalloys are the most widely used materials in aero-engines. The mechanical properties and temperature-bearing capacity of superalloys greatly depend on the amount of strengthening elements added to the alloy. Too much addition of strengthening elements will increase the macro and micro segregation of the alloy, deteriorate the microstructure uniformity and hot workability, and even make it impossible to hot work. The preparation of alloy powder by rapid solidification technology can effectively inhibit the segregation of elements formed during the solidification process of the alloy, so that more strengthening elements can be added to the superalloy without reducing the uniformity of its structure. The superalloy compacted from rapidly solidified powder has uniform microstructure and excellent mechanical properties, and is widely used in hot-end parts such as aerospace engine turbine disks. However, superalloys prepared by powder metallurgy technology also have their own shortcomings, that is, when the powder is consolidated by hot isostatic pressing, precipitates such as carbides will precipitate along the powder surface. The preferential precipitation of these precipitates will make the plasticity of the alloy lower, and the grain boundary of the powder is also a potential source of cracks in the alloy, which affects the reliability of the powder superalloy consolidated by direct hot isostatic pressing.

In order to improve the precipitation of the precipitated phase along the boundaries of the original powder particles to improve the reliability of the powder at high temperature, researchers at home and abroad have developed a series of methods, which mainly include:

1. After the hot isostatic pressing of the powder, use extrusion, billet forging, isothermal forging and other processes to deform the powder billet with a large amount of deformation to change the shape of the original particle boundary of the powder and change the distribution of precipitates on it;

2. The powder alloy billet consolidated by hot isostatic pressing is subjected to a long-term high-temperature solution heat treatment to partially dissolve the precipitated phase;

3. By adding other elements, such as: Hf, to improve the phase precipitation of the original particle boundary.

Undoubtedly, these methods have increased the manufacturing cost of powder superalloy.

Contents of the invention

The purpose of the present invention is to provide a superalloy powder hot isostatic pressing process that can avoid precipitation of carbides and other precipitates along the powder primary particle boundaries, and can directly obtain powder superalloy blanks with excellent microstructure and properties through hot isostatic pressing.

Technical scheme of the present invention is:

A hot isostatic pressing process for superalloy powder that can avoid the precipitation of carbides and other precipitates along the boundary phase of the original powder particles. The specific process steps are as follows:

(1). Prepare superalloy powder by gas atomization or other methods, sieve the powder to obtain a powder with a size less than or equal to 155 microns, put the sieved powder into a carbon steel or stainless steel sheath, and degas at high temperature And seal welding;

(2). Put the powder package prepared in the first step into the hot isostatic pressing equipment, and start hot isostatic pressing after reaching the predetermined conditions by simultaneously raising the temperature and increasing the pressure or first raising the temperature and then increasing the pressure;

The process conditions of the first step of hot isostatic pressing are that the temperature of hot isostatic pressing is higher than the initial melting temperature of the low melting point phase of the alloy powder, lower than 15 degrees Celsius above the solidus line of the completely homogenized alloy, and the pressure is greater than or equal to 90MPa , the holding time after reaching the temperature in the furnace body is greater than or equal to 20 minutes, and less than or equal to 1 hour;

(3). After the first step is completed, the heating is stopped, and the powder sheath is cooled with the furnace until it is kept below the initial melting temperature of the low melting point phase of the alloy powder, and the heat preservation process is the second step;

The holding time of the second step is greater than or equal to 2 hours to ensure that the low melting point phase formed during the cooling process after the first step can be completely dissolved during the heat preservation process, and the pressure is greater than or equal to 90MPa. After the second step is completed, stop heating and cool in the furnace to room temperature.

The hot isostatic pressing process of superalloy powders that can avoid the precipitation of carbides and other precipitates along the boundary phases of the original particles of the powder is suitable for hot isostatic pressing of nickel-iron-based superalloy powders or nickel-based superalloy powders. .

In the hot isostatic pressing process of superalloy powder that can avoid the precipitation of carbides and other precipitates along the boundary phases of the primary powder particles, in step (1), the size obtained by sieving is preferably less than or equal to 105 microns.

In the hot isostatic pressing process of superalloy powder that can avoid the precipitation of carbides and other precipitates along the boundary phases of the original powder particles, in step (1), the size obtained by sieving is preferably less than or equal to 55 microns.

In the hot isostatic pressing process of superalloy powder that can avoid the precipitation of carbides and other precipitates along the boundary phases of the original powder particles, for GH4169 and its derivative alloy powders, the initial melting temperature of the low melting point phase is the Laves phase of GH4169 and its derivative alloys Melting temperature; for other γ′ phase-strengthened nickel-based superalloy powders, the initial melting temperature of the low melting point phase is the γ/γ′ eutectic temperature.

In the hot isostatic pressing process of superalloy powder that can avoid the precipitation of precipitated phases such as carbides along the boundary phases of powder primary particles, in step (2), the pressure of hot isostatic pressing preferably ranges from 120 to 150 MPa.

In the hot isostatic pressing process of superalloy powder that can avoid the precipitation of precipitated phases such as carbides along the boundary phases of the primary powder particles, in step (3), the pressure during the heat preservation process preferably ranges from 120 to 150 MPa.

Advantage of the present invention and beneficial effect are:

1. The process of the present invention is divided into two steps. The hot isostatic pressing temperature range of the first step is: higher than the initial melting temperature of the low melting point phase of the alloy powder and lower than 15 degrees Celsius above the solidus line of the fully homogenized alloy, the gas pressure It should be greater than or equal to 90MPa, and the holding time should be greater than or equal to 20 minutes and less than or equal to 1 hour. After the first step is completed, stop heating and let the material cool down with the furnace until it is below the initial melting temperature of the low melting point phase of the alloy and keep it warm. The heat preservation process is the second step. The holding time of the second step should be greater than or equal to 2 hours to ensure that the low-melting point phase formed during the cooling process after the first step is completely dissolved. After the second step is completed, the alloy is cooled to room temperature with the furnace under pressure. The invention is used for hot isostatic pressing consolidation molding of rapidly solidified high-temperature alloy powder, combined with near-net forming technology, can prepare powder high-temperature alloy components with complex shapes, thereby improving the utilization rate of alloy materials.

2. The present invention can be realized on a traditional hot isostatic press, and the scope of application of this process is the hot isostatic consolidation molding of nickel-iron-based superalloy powder and nickel-based superalloy powder.

3. The invention is simple and practical, and can shorten the manufacturing process of the powder superalloy component, thereby reducing its manufacturing cost.

Description of drawings

Fig. 1 (a)-Fig. 1 (b) is the microstructure (metallographic photograph) of the powder metallurgy GH4169G alloy that utilizes system A of the present invention to prepare; Wherein, Fig. 1 (a) magnification is * 100, Fig. 1 (b ) magnification is ×200.

Fig. 2 (a)-Fig. 2 (b) is the room temperature and 650 ℃ tensile fracture (scanning electron microscope photo) of the powder metallurgy GH4169G alloy prepared by utilizing system A of the present invention and heat-treated; Wherein, Fig. 2 (a) is room temperature , Figure 2(b) is 650°C.

Fig. 3 (a)-Fig. 3 (b) is the microstructure (metallographic photograph) of the powder metallurgy GH4169G alloy that utilizes system B of the present invention to prepare; Wherein, Fig. 3 (a) magnification is * 100, and Fig. 3 (b ) magnification is ×200.

Fig. 4 (a)-Fig. 4 (b) is the room temperature and 650 ℃ tensile fracture (scanning electron micrograph) of the powder metallurgy GH4169G alloy prepared by utilizing system B of the present invention and heat-treated; wherein, Fig. 4 (a) is room temperature , Figure 4(b) is 650°C.

Detailed ways

The present invention is a hot isostatic pressing process of superalloy powder that can avoid precipitation of carbides and other precipitates along the boundary phase of the original powder particles, specifically as follows:

1. Prepare superalloy powder by gas atomization and other methods, obtain powder with a size less than or equal to 155 microns (preferably less than or equal to 105 microns, preferably less than or equal to 55 microns) by sieving, and pack the powder into Low carbon steel or stainless steel sheath, sealed and welded after high temperature degassing. The use of fine powder is to reduce the amount of ceramic inclusions in the powder and reduce the amount of hollow powder; the use of carbon steel or stainless steel sheath is because in the temperature range used in the present invention, the sheath material is completely solid, has a certain strength and will not Reaction with powder; high-temperature degassing is to remove the gas adsorbed on the powder surface to the greatest extent, so as to reduce the tendency of the alloy to form heat-induced pores during subsequent heat treatment. The temperature range of high-temperature degassing is 180 degrees Celsius to 500 degrees Celsius.

2. Put the powder package prepared in the first step into the hot isostatic pressing equipment, and reach the process conditions of the first stage by increasing the temperature and pressure of the furnace or first raising the temperature and then increasing the pressure, and start the hot isostatic pressing. The process condition of the first stage of hot isostatic pressing is that the temperature is higher than the initial melting temperature of the low melting point phase of the alloy powder (such as: the melting temperature of the Laves phase of the GH4169 series alloy, the γ/ γ′ eutectic temperature), lower than 15 degrees Celsius above the solidus line of the completely homogenized alloy, and the pressure is greater than or equal to 90MPa. After the furnace body reaches the temperature, the holding time is greater than or equal to 20 minutes and less than or equal to 1 hour. There are two reasons for the temperature selection of the first stage of process conditions in the temperature range where an appropriate amount of liquid phase is formed. The first is that the solubility of carbon and other elements in the alloy matrix increases at high temperatures, and carbides and other phases are not easy to precipitate on the powder surface. The second is that the partial melting of part of the powder surface makes the nucleation of carbides and other phases lose their attachment positions. The holding time of the first step is greater than or equal to 20 minutes, and less than or equal to 1 hour is based on the following reasons: first, in the temperature range of the first step selected by the present invention, the complete compaction of the powder compact needs at least 20 minutes ; Second, if the holding time is too long, the grain size of the alloy compact will be too large, which will affect the mechanical properties.

3. After the first step of hot isostatic pressing is completed, the heating is stopped, and the powder sheath is cooled with the furnace until it is kept below the initial melting temperature of the low melting point phase of the alloy powder, and the heat preservation process is the second step. The holding time of the second step should be greater than or equal to 2 hours to ensure that the segregated phase formed during the cooling process after the first step can be completely dissolved during the heat preservation process, and the pressure should be greater than or equal to 90MPa. After the second step is completed, stop heating and follow the furnace Cool to room temperature. The reason why there must be a second step process is that part of the liquid phase will be generated inside the jacket during the first step of hot isostatic pressing, and these liquid phases will form the Laves phase during the cooling process after the first step (GH4169 and its derivatives Alloy) and γ/γ′ eutectic (γ′-strengthened nickel-based superalloy), Laves phase and γ/γ′ eutectic are inherently brittle, which are potential sources of cracks during alloy application and must be eliminated. The way to eliminate Laves phase and γ/γ′ eutectic is to keep the alloy below the melting temperature of Laves phase or γ/γ′ eutectic for a long time. The second step must be completed in the presence of external pressure, rather than in a pressureless high-temperature furnace after the hot isostatic pressing of the alloy is completed, because the existence of external pressure can avoid thermally induced pores in the alloy blank.

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

Example 1

The composition of the alloy is shown in Table 1:

Table 1. Alloy composition of GH4169G

Cr Mo Al Ti Nb C B P Ni Fe 19.3 2.98 0.5 1.04 4.94 0.031 0.008 0.023 53.5 margin

In this embodiment, argon gas atomization is used to prepare the powder of the alloy, and the powder with a size below 105 microns is packed into a stainless steel sheath, and hot isostatic pressing is performed after vacuum degassing. The following process system (A) was selected for this alloy:

In the first stage, the temperature and pressure are increased with the furnace, 1245 ° C / 150 MPa / 0.5 hours, and cooled with the furnace after completion;

The second stage heat preservation process, 1110°C/150MPa/4 hours, cool to room temperature with the furnace.

The hot isostatic pressing temperature of the first stage of the system is higher than the Laves phase melting temperature (1210°C) but lower than the alloy solidus temperature (1260°C)

The microstructure of the alloy prepared by this process is shown in Fig. 1(a) and Fig. 1(b). It can be seen that the microstructure of the alloy prepared by this process is uniform and fine, the distribution of precipitates is uniform, and almost no to the morphology of the original powder.

The alloy prepared by this process was subjected to direct aging treatment to test its tensile properties at room temperature and 650°C and durability at 650°C/760MPa. The results are shown in Table 2 (Process A). It can be seen from the table that the tensile properties of the alloy at room temperature and 650°C have met the standard of GH4169 alloy and are much higher than that of K4169 alloy. The durability of the alloy is excellent, especially the durability of 650℃/690MPa exceeds 700 hours, which is comparable to that of the deformed GH4169G alloy.

The tensile fracture morphology of the alloy after heat treatment at room temperature and 650 °C is shown in Figure 2(a) and Figure 2(b). It can be seen that the fracture mode is dominated by plastic dimples, which shows that the hot isostatic pressing process The powder is well bound.

Example 2

The difference from Example 1 is that the temperature in the first stage of this embodiment is above the solidus line of the alloy, and more liquid phases will be formed during the hot isostatic pressing process, so the temperature in the second stage increases accordingly, so that Ensure that the Laves phase formed after cooling in the first stage can be fully eliminated.

In this embodiment, argon gas atomization is used to prepare the powder of the alloy, and the powder with a size below 105 microns is packed into a stainless steel sheath, and hot isostatic pressing is performed after vacuum degassing. The following process system (B) was selected for this alloy:

In the first stage, the temperature and pressure are increased with the furnace, 1265 ° C / 150 MPa / 0.5 hours, and cooled with the furnace after completion;

The second stage of heat preservation process, 1140 ° C / 150 MPa / 4 hours, cooled to room temperature with the furnace.

The hot isostatic pressing temperature in the first stage of this system is higher than the Laves phase melting temperature (1210℃) and alloy solidus temperature (1260℃).

The microstructure of the alloy prepared by this process is shown in Figure 3(a) and Figure 3(b). It can be seen that this process has obtained a completely equiaxed microstructure, and the precipitation of carbide phases at the boundaries of the original powder particles has been completed. Avoid it altogether.

The alloy prepared by this process was subjected to direct aging treatment to test its tensile properties at room temperature and 650°C and durability at 650°C/760MPa. The results are shown in Table 2 (Process B). It can be seen from the table that the tensile properties of the alloy at room temperature and 650°C have met the standard of GH4169 alloy and are much higher than that of K4169 alloy. However, because the grain size is slightly larger than that prepared by process A, the strength level is lower than that of process A, and the durability of the alloy is also very good.

The tensile fracture morphology of the alloy at room temperature and 650°C after heat treatment is shown in Fig. 4(a) and Fig. 4(b). It can be seen that the tensile fracture modes of the alloy at room temperature and 650°C are complete plastic dimple fractures. Surface alloy powders are well bonded.

Table 2. Mechanical properties of the powder metallurgy GH4169G alloy prepared by the present invention after heat treatment

The results of the examples show that the process of the present invention can avoid the precipitation of carbides and other precipitates along the boundaries of the original powder particles, thereby obtaining a compact and equiaxed microstructure, fractured with plastic dimples during tensile deformation, and the mechanical properties can be compared with those of the same composition The performance of the wrought alloy is comparable to that of the alloy, and the process can shorten the manufacturing process of the powder metallurgy superalloy component and thereby reduce its manufacturing cost. Except for GH4169G alloy, other nickel-iron-based superalloy powders and nickel-based superalloy powders are all suitable for using the hot isostatic pressing process of superalloy powders of the present invention to avoid the precipitation of the original grain boundary phase, because carbon is the structure of all Polycrystalline superalloys must add grain boundary strengthening elements. So as long as these alloys are prepared by powder metallurgy process, they will have the problem of precipitation of carbide and other precipitates along the powder boundary, which has been reported in a large number of literatures. The temperature of the first step of the present invention is that a small amount of liquid phase appears in the powder, and the appearance of the liquid phase will cause the precipitation of carbides to lose attachment, and the solubility of the alloy to carbon is also greatly improved at high temperatures, which also reduces the possibility of carbide precipitation. At the same time, the partial melting of the alloy will also cause the powder to lose its original shape. And the result of embodiment has also verified these completely.

It's just that the low-melting point structure formed when the γ'-strengthened nickel-based superalloy solidifies is the γ/γ' eutectic, while the low-melting point phase formed when the nickel-iron-based superalloy solidifies is the Laves phase. Therefore, the process of the present invention can be directly applied to hot isostatic pressing of nickel-iron-based superalloy powder. For γ′-strengthened nickel-based superalloys, it is only necessary to adjust the characteristic temperature slightly. The first step should also be at the temperature where a small amount of liquid phase is formed, and the second step should be at the temperature of the γ/γ′ eutectic Below the initial melting temperature.

Claims (7)

1. the superalloy powder heat and other static pressuring processes that primary granule border can be avoided to separate out mutually, is characterized in that, concrete technology step is as follows:

(1). prepare superalloy powder with gas atomization or additive method, powder is carried out sieve to obtain the powder that size is less than or equal to 155 microns, the powder that sieves out is loaded carbon steel or stainless steel jacket, high-temperature degassing soldering and sealing;

(2). powder jacket prepared by step (1) is put into hot isostatic apparatus, with while increasing temperature and pressure or first the heat up mode of boosting afterwards reach predetermined condition after start high temperature insostatic pressing (HIP);

The process conditions of first step high temperature insostatic pressing (HIP) are, the temperature of high temperature insostatic pressing (HIP) is higher than the initial melting temperature of the low melting point phase of alloy powder, than more than the solidus of complete homogenize such alloys 15 degrees Celsius low, pressure is more than or equal to 90 MPa, be more than or equal to 20 minutes to the rear temperature retention time of temperature in body of heater, be less than or equal to 1 hour;

(3). after the first step completes, stop heating, be incubated below initial melting temperature powder jacket being cooled to the furnace the low melting point phase of alloy powder, insulating process is second step;

The temperature retention time of second step is more than or equal to 2 hours, and can melt completely in insulating process mutually with the low melting point formed in cooling procedure after ensureing the first step, pressure is more than or equal to 90 MPa, and after second step completes, stopping heating cooling to room temperature with the furnace.

2. according to the superalloy powder heat and other static pressuring processes avoiding primary granule border to separate out mutually according to claim 1, it is characterized in that, the high temperature insostatic pressing (HIP) consolidation that this technique is applicable to ferronickel based high-temperature alloy powder or Ni-base Superalloy Powder is shaping.

3. according to the superalloy powder heat and other static pressuring processes avoiding primary granule border to separate out mutually according to claim 1, it is characterized in that, in step (1), being less than or equal to 105 microns by sieving to obtain being preferably dimensioned to be.

4. according to the superalloy powder heat and other static pressuring processes avoiding primary granule border to separate out mutually according to claim 1, it is characterized in that, in step (1), obtain size by screening and be preferably and be less than or equal to 55 microns.

5. according to the superalloy powder heat and other static pressuring processes avoiding primary granule border to separate out mutually according to claim 1, it is characterized in that, for GH4169 and derivative alloy powder thereof, the initial melting temperature of low melting point phase is the Laves phase fusion temperature of GH4169 and derivative alloy thereof; For the Ni-base Superalloy Powder that other γ ' strengthen mutually, the initial melting temperature of low melting point phase is γ/γ ' eutectic temperature.

6. according to the superalloy powder heat and other static pressuring processes avoiding primary granule border to separate out mutually according to claim 1, it is characterized in that, in step (2), the pressure preferable range of high temperature insostatic pressing (HIP) is 120 ~ 150 MPa.

7. according to the superalloy powder heat and other static pressuring processes avoiding primary granule border to separate out mutually according to claim 1, it is characterized in that, in step (3), the pressure preferable range of insulating process is 120 ~ 150 MPa.