A large-size ETA phase-strengthened superalloy and its preparation method

Abstract

The present invention discloses a large-sized ETA-phase strengthened superalloy and a preparation method thereof, aiming to improve the high-temperature resistance of the alloy. To this end, on the one hand, the large-sized ETA-phase strengthened superalloy provided by an embodiment of the present invention, in terms of phase composition, the superalloy includes a matrix, γ' phase and η phase; wherein, the grain size of the matrix is 10-30 μm, the γ' phase is dispersedly distributed in the matrix, the η phase is uniformly distributed in the matrix, the distribution form of the η phase is divided into needle-shaped and sheet-shaped, the average length of the η phase is 30-50 μm, and the size of the γ' phase is 30-200 nm.

Description

Technical Field

[0001] The present invention belongs to the technical field of superalloy preparation, and particularly relates to a large-sized ETA-phase strengthened superalloy and a preparation method thereof. Background Art

[0002] Nickel-based superalloys have excellent tensile strength, creep resistance, fatigue resistance, and oxidation resistance in the temperature range of 540°C - 1000°C, and are the essential materials for key high-temperature components in core components such as aeroengines and gas turbines. In terms of composition, the high-temperature strength of nickel-based superalloys is mainly enhanced by solid solution strengthening and precipitation phase precipitation, among which the effect of precipitation strengthening is the most significant.

[0003] However, to improve the efficiency of aeroengines and gas turbines, increasing the gas temperature before the turbine is the most effective means, which poses more stringent requirements for the high-temperature service performance of superalloy materials. For example, as an important rotating component on the engine, the working temperature of the rim of the turbine disk will be increased from 750°C to above 800°C. However, the long-term use temperature of existing nickel-based turbine disks is limited to the range of 600 - 750°C. Therefore, there is an urgent need to develop a superalloy material with high yield strength and excellent high-temperature creep properties. Summary of the Invention

[0004] The main purpose of the present invention is to provide a large-sized ETA-phase strengthened superalloy and a preparation method thereof, aiming to improve the high-temperature resistance of the alloy.

[0005] To this end, on the one hand, the large-sized ETA-phase strengthened superalloy provided by an embodiment of the present invention, in terms of phase composition, the superalloy includes a matrix, γ' phase, and η phase; wherein,

[0006] The grain size of the matrix is 10 - 30 μm, the γ' phase is dispersedly distributed in the matrix, the η phase is uniformly distributed in the matrix, the average length of the η phase is 30 - 50 μm, the size of the γ' phase is 30 - 200 nm, and the distribution morphology of the η phase is divided into needle-like and sheet-like.

[0007] Specifically, the volume fraction of the γ' phase is 40% - 50%, and the volume fraction of the η phase is 8 - 12%.

[0008] Specifically, in terms of composition, the weight percentages of each element in the superalloy are as follows:

[0009] Al 2.5% - 4%, Ti 3.8% - 5%, Cr 10% - 14%, Co 13% - 18%, Nb 0% - 3.3%, Mo 2.8% - 3.3%, Ta 2.8% - 7.5%, W 2.5% - 3.2%, C 0.01% - 0.05%, B 0% - 0.01%, 0% - 0.1% rare earth elements, and the balance Ni.

[0010] Specifically, the mass fraction ratio of Ti / Al is in the range of 1.4 - 2.0;

[0011] The mass fraction of Al + Ti + Nb + Ta is in the range of 11.8% - 16%;

[0012] (Ti + Nb + Ta) / Al mass fraction ratio is in the range of 2.5 - 4.5;

[0013] The mass fraction of Mo + W is in the range of 5.5% - 6.3%.

[0014] Specifically, it includes loading the pre-alloyed powder into a hot extrusion jacket, vacuum-sealing and heating it, then placing it in an extrusion die for hot extrusion, and finally air-cooling it to room temperature to obtain a hot-extruded bar; removing the jacket from the hot-extruded bar and performing heat treatment to obtain a superalloy product; among which,

[0015] The heat treatment process is: keeping the hot-extruded bar at 1180 °C - 1200 °C for 1.5 - 2.5 hours and then air-cooling it to 720 °C - 760 °C, and then keeping it at 720 °C - 760 °C for 22 - 24 hours and then furnace-cooling it.

[0016] Specifically, the extrusion temperature of the hot-extruded bar is 1120 °C - 1140 °C, and the extrusion ratio is 15:1 - 17:1.

[0017] Specifically, load the pre-alloyed powder into a stainless steel jacket with a diameter of 96 mm and a height of 230 mm, and evacuate and seal-weld it at 400 °C.

[0018] Specifically, the diameter of the hot-extruded bar is about 24 mm.

[0019] Specifically, the pre-alloyed powder is an air-atomized powder with a particle size of 15 - 53 microns.

[0020] Principle and advantages

[0021] For the superalloy provided in this application, the length dimension of the η phase is significantly larger than that of the γ' phase, realizing large-size coupling strengthening from nano to micron scale. Such a design makes it so that although the fine γ' phase will dissolve back into the matrix at high temperatures and thus lose the precipitation strengthening effect, the large-size η phase is difficult to dissolve back and will continue to hinder the movement of grain boundaries and dislocations, playing a role in precipitation strengthening.

[0022] In addition, the distribution patterns of the η-phase can be divided into two types: flaky and needle-like. Some needle-like η-phases (with a length greater than the grain size of the matrix phase and a width much smaller than the grain size of the matrix phase) can penetrate across grains and connect two or more grains, significantly pinning the grain boundaries. It is difficult for the grain boundaries to slip and deform under external stress, achieving the effects of particle strengthening and grain boundary pinning. Therefore, the alloy has excellent high-temperature resistance.

[0023] In the preparation method provided by the present invention, the inventors rationally adjusted the contents of elements such as Ti and Ta, and combined with a suitable heat treatment system, so that when the η-phase was precipitated, harmful TCP phases such as σ-phase and μ-phase were not precipitated, and the η-phase and γ'-phase achieved large-scale coupling strengthening from the nano-scale to the micro-scale.

[0024] Specifically, in terms of composition design: considering the influence of alloy composition on the microstructure and properties, by increasing the Ti / Al ratio, the precipitation of the η-phase (Ni 3 Ti) was promoted. At the same time, the total amount of Ti+Al+Nb+Ta was controlled to ensure that the content of the γ'-phase was above 40%, maintaining the level of precipitation strengthening. In addition, the contents of solid solution strengthening elements such as W and Mo were reasonably adjusted to strengthen the matrix phase without precipitating brittle and harmful phases. The content of the antioxidant element Cr was controlled at an effective level, and the effects of grain boundary strengthening and grain boundary purification were achieved through the addition of trace elements such as C, B, and Zr. By means of the coupling strengthening of the η-phase and γ'-phase, a high-temperature alloy material that can work at higher temperatures and stress levels was developed.

[0025] In terms of the heat treatment system: in this application, the hot-extruded bar was held at 1180°C - 1200°C for 1.5 - 2.5 hours and then air-cooled to 720°C - 760°C to ensure the precipitation of large-sized η-phase, promote the dissolution of the initial large-sized γ'-phase and the reprecipitation of small-sized γ'-phase. Then, it was held at 720°C - 760°C for 22 - 24 hours and then furnace-cooled to enable the full precipitation of fine tertiary γ'-phase. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 is the microstructure of the high-temperature alloy prepared in Example 1 Figure 1 ;

[0028] Figure 2 is the microstructure of the high-temperature alloy prepared in Example 1 Figure 2 ;

[0029] Figure 3 The microstructure of the high temperature alloy prepared in Example 1 is Figure 1 ;

[0030] Figure 4 The microstructure of the high temperature alloy prepared in Example 2 Figure 2 ;

[0031] in: Figure 1 The image size is 100μm×100μm. Figure 2 The image size is 10μm×10μm. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] From the composition point of view, the high temperature strength of nickel-based superalloys is mainly enhanced by solid solution strengthening and precipitation phase precipitation, among which precipitation strengthening has the most significant effect. At present, the strengthening phases of nickel-based superalloys are mainly γ′ and γ′′ phases, which are usually small squares or spherical forms, while the lamellar η phase with a hexagonal structure is larger in size and is often accompanied by the appearance of some topological dense phases. While consuming strengthening elements such as Al, Ti, and Ta, it provides more crack sources for the failure of superalloys. Therefore, the η phase is often considered to be detrimental to the organizational stability of the material, and the precipitation of the η phase is avoided as much as possible in the previous composition design process.

[0034] However, the inventors have found that if, when precipitating the η phase, harmful TCP phases such as the σ phase and the μ phase can be controlled not to precipitate, and the η phase and the γ′ phase can be coupled on a large scale from nanometers to micrometers, and the length of the η phase is designed to be significantly larger than the matrix phase, the introduced η phase will not only not reduce the performance of the alloy, but also improve the high temperature resistance of the alloy. This is because at high temperatures, although the fine γ′ phase will dissolve back into the matrix and then lose the effect of precipitation strengthening, the large-sized η phase is difficult to dissolve back and will continue to hinder the movement of grain boundaries and dislocations, thereby playing a role of precipitation strengthening.

[0035] In addition, the η phase is divided into two forms: lamellar and needle-shaped. The slender needle-shaped η phase will penetrate across the grains and string together two or more grains, with a significant pinning effect on the grain boundaries. The grain boundaries are difficult to slip and deform under external stress, achieving the effects of particle strengthening and pinning grain boundaries. Therefore, the alloy has excellent high temperature resistance.

[0036] A large-sized ETA phase-strengthened superalloy. In terms of phase composition, the superalloy includes a matrix, γ' phase, and η phase; wherein, the grain size of the matrix is 10 - 30 μm, the γ' phase is dispersedly distributed in the matrix, the η phase is uniformly distributed in the matrix in the form of flakes or needles, the length of the η phase is 30 - 50 μm, and the size of the γ' phase is 30 - 200 nm.

[0037] In terms of phase composition, for the superalloy provided in this application, the η phase and γ' phase achieve large-sized coupling from the nanoscale to the microscale. Moreover, when the length dimension of the needle-shaped η phase is larger than that of the matrix phase, and the width dimension is significantly smaller than that of the matrix phase, such η phases will penetrate through the matrix and string together two or more matrix grains. Through the above analysis, it can be seen that the superalloy provided in this application has excellent high-temperature resistance.

[0038] Specifically, the volume fraction of the γ' phase is 40% - 50%, and the volume fraction of the η phase is 8 - 12%.

[0039] To obtain the superalloy with the above phase composition, in terms of chemical composition, the weight percentages of each element in the superalloy are as follows: Al 2.5% - 4%, Ti 3.8% - 5%, Cr 10% - 14%, Co 13% - 18%, Nb 0% - 3.3%, Mo 2.8% - 3.3%, Ta 2.8% - 7.5%, W 2.5% - 3.2%, C 0.01% - 0.05%, B 0% - 0.01%, 0% - 0.1% rare earth elements, and the balance is Ni; moreover,

[0040] The mass fraction ratio of Ti / Al is in the range of 1.4 - 2.0, the mass fraction of Al + Ti + Nb + Ta is in the range of 11.8% - 16%, the mass fraction ratio of (Ti + Nb + Ta) / Al is in the range of 2.5 - 4.5, and the mass fraction of Mo + W is in the range of 5.5% - 6.3%.

[0041] In this application, by increasing the Ti / Al ratio to between 1.4 and 2.0, and the mass fraction ratio of (Ti + Nb + Ta) / Al being in the range of 2.5 - 4.5, the precipitation of the η phase (Ni 3 Ti) is promoted. At the same time, controlling the total amount of Ti + Al + Nb + Ta ensures that the content of the γ' phase is above 40% to maintain the level of precipitation strengthening. In addition, reasonably adjusting the content of solid solution strengthening elements such as W and Mo strengthens the matrix phase without precipitating brittle harmful phases, and controlling the content of the antioxidant element Cr at an effective level, and achieving the effects of grain boundary strengthening and grain boundary purification through the addition of trace elements such as C, B, and Zr.

[0042] A preparation method of a large-size ETA phase-strengthened superalloy. Using the superalloy pre-alloyed powder with the above-mentioned ratio, the preparation process is as follows: The pre-alloyed powder is loaded into a hot extrusion sleeve, vacuum-sealed and heated, then placed in an extrusion die for hot extrusion, and then air-cooled to room temperature to obtain a hot-extruded bar; The hot-extruded bar is removed from the sleeve and heat-treated to obtain a superalloy product.

[0043] Among them, to obtain an ideal alloy structure, the heat treatment process is: The hot-extruded bar is held at 1180 °C - 1200 °C for 1.5 - 2.5 hours and then air-cooled to 720 °C - 760 °C, and then held at 720 °C - 760 °C for 22 - 24 hours and then furnace-cooled.

[0044] In this embodiment, by controlling the solution treatment temperature at 1180 °C - 1200 °C and adding an appropriate holding time, the precipitation of large-size η phase is ensured, promoting the re-solution of the initial large-size γ' phase and the re-precipitation of small-size γ' phase. When the temperature exceeds this temperature, the grains will grow abnormally, and when it is lower than this temperature, it is not conducive to the precipitation of large-size η phase, and it is difficult for the γ' phase to re-solve and re-precipitate into fine secondary γ' phase and subsequent tertiary γ' phase. By controlling the aging treatment temperature at 720 °C - 760 °C and adding an appropriate holding time, the full precipitation of fine tertiary γ' phase can be achieved. When the temperature exceeds this temperature, it will cause the growth of γ' phase and the precipitation of other harmful phases, and when it is lower than this temperature, it will cause the difficulty of full precipitation of fine tertiary γ' phase.

[0045] The following will elaborate on the solution of this application in combination with specific embodiments. Example 1

[0046] A preparation method of a large-size ETA phase-strengthened superalloy. The pre-alloyed powder with a particle size of 15 - 53 microns is loaded into a hot extrusion sleeve with a diameter of 96 mm and a height of about 230 mm, vacuum-pumped, sealed and welded, then placed in an extrusion die with an extrusion temperature of 1120 °C - 1140 °C and an extrusion ratio of 15:1 - 17: for hot extrusion, and then air-cooled to room temperature to obtain a hot-extruded bar with a diameter of about 24 mm. After removing the sleeve from the hot-extruded bar, it is held at 1180 °C for 2 hours and then air-cooled to 750 °C, and then held at 750 °C for 24 hours and then furnace-cooled to obtain a superalloy; Among them, the weight percentages of each element in the pre-alloyed powder are:

[0047] Al 2.7%, Ti 4.1%, Cr 12.5%, Co 13.3%, Nb 3.3%, Mo 3.0%, Ta 3.1%, W 3.2%, C 0.05%, B 0.01%, Sc 0.01%, and the balance Ni.

[0048] The obtained material structure is as shown in the appendix Figure 1 and Figure 2As shown, the matrix phase grain size is 14 μm. In the figure, the white is the η phase, with an average size of 45 μm in the length direction and a volume fraction of 12% for the entire η phase. The average size of the γ′ phase is 185 nm and the volume fraction is 45%.

[0049] In addition, from Figure 1 it can be seen that the η phase is divided into two morphologies: flake and needle-like. Some relatively large needle-like η phases (with a length greater than the matrix phase grain size and a width much smaller than the matrix phase grain size, such as a needle-like η phase with a length of 35 μm and a width of 1 μm) will penetrate across two or more grains, significantly pinning the grain boundaries. It is difficult for the grain boundaries to slip and deform under external stress, achieving the effects of particle strengthening and grain boundary pinning. Therefore, the alloy has excellent high-temperature resistance. Example 2

[0050] Different from Example 1, in this example, the composition of the pre-alloyed powder is: Al 3.3%, Ti 4.8%, Cr 10.6%, Co 18.0%, Nb 3.0%, Mo 2.9%, Ta 4.6%, W 3.0%, C 0.04%, B 0.01%, Sc 0.01%, and the balance Ni.

[0051] In the obtained material microstructure, the matrix phase grain size is 15 μm. The η phase is also divided into two morphologies: flake and needle-like. The average size of the entire η phase in the length direction is about 40 μm, the volume fraction is about 10%, the size of the γ′ phase is 185 nm, and the volume fraction is 43%. Example 3

[0052] Different from Example 1, in this example, the composition of the pre-alloyed powder is: Al 2.6%, Ti 5%, Cr 11.8%, Co 13.1%, Nb 3.2%, Mo 2.8%, Ta 3.3%, W 2.9%, C 0.03%, B 0.01%, Hf 0.01%, and the balance Ni.

[0053] In the obtained material microstructure, the matrix phase grain size is 16 μm. In the material microstructure, the η phase is divided into two morphologies: flake and needle-like. The average size of the η phase in the length direction is 40 μm, the volume fraction is about 13%, the size of the γ′ phase is 152 nm, and the volume fraction is 41%. Example 4

[0054] Different from Example 1, in this example, after removing the cladding from the hot-extruded bar, it is held at 1200 °C for 2.5 hours and then air-cooled to 730 °C, and then held at 730 °C for 22 hours and then furnace-cooled.

[0055] In the obtained material structure, the grain size of the matrix phase is 25 μm. In the material structure, the η phase has two morphologies: flaky and acicular. The average size in the length direction of the η phase is 48 μm, the volume fraction is about 12%, the size of the γ′ phase is 180 nm, and the volume fraction is 45%.

[0056] Comparative Example 1

[0057] Different from Example 1, the composition of the pre-alloyed powder in this comparative example is: Al 2.5%, Ti 6%, Cr 16%, Co 15%, Nb 0%, Mo 3.0%, Ta 0%, W 1.3%, C 0.05%, B 0.01%, Sc 0.01%, and the balance Ni.

[0058] As Figure 3 In the obtained material structure, the grain size of the matrix phase is 27 μm. Since (Ti + Nb + Ta) / Al < 2.5, no η phase precipitates in the structure, and the γ′ phase is the only strengthening phase, with an average size of 220 nm and a volume fraction of ~50%.

[0059] Comparative Example 2

[0060] Different from Example 1, the composition of the pre-alloyed powder in this comparative example is: Al 3.5%, Ti 2.5%, Cr 13%, Co 8%, Nb 3.5%, Mo 3.5%, Ta 0%, W 3.5%, C 0.06%, B 0.01%, Sc 0.01%, and the balance Ni. As Figure 4 Harmful white TCP phases such as σ phase and μ phase appear in the obtained material structure because the content of refractory elements such as W and Mo is too high. When the mass fraction of Mo + W is greater than 6.3 wt%, harmful phases are likely to precipitate and the tissue stability decreases.

[0061] Comparative Example 3

[0062] Different from Example 1, after removing the cladding from the hot-extruded bar in this comparative example, it is held at 1150 °C for 2 hours and then air-cooled to 650 °C, and then held at 650 °C for 22 hours and then furnace-cooled. In the obtained material structure, the grain size of the matrix phase is 20 μm, and the size of the flaky or acicular phase in the length direction of the η phase is only about 4 μm. This is because the treatment temperature is relatively low, and the η phase cannot precipitate and grow, with a volume fraction of about 7%, the size of the γ′ phase is 130 nm, and the volume fraction is 40%.

[0063] In terms of mechanical properties analysis, the alloys of the examples have better tensile properties at room temperature and high temperature than the alloys of the comparative examples, as shown in Table 1 and Table 2. This is because conventional superalloys are strengthened only by the γ' phase and it is difficult to achieve the effect of cross-scale coupling strengthening. Moreover, the size of the γ' phase is below micrometers, and the fine γ' phase will dissolve back into the matrix at high temperature, and then lose the precipitation strengthening effect. The large-size η phase that is difficult to dissolve back will continue to hinder the movement of grain boundaries and dislocations, achieving the effect of particle strengthening and pinning grain boundaries. Therefore, the performance advantage of the alloys of the examples at high temperature will be more obvious.

[0064] Table 1 Room temperature tensile properties of the alloys of the examples and comparative alloys prepared by powder metallurgy process

[0065] Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) Example 1 1376 1638 15 Example 2 1316 1592 16 Example 3 1318 1598 16.5 Example 4 1331 1604 15 Comparative example 1 1204 1542 15 Comparative example 2 1125 1535 17 Comparative example 3 950 1445 21

[0066] Table 2 650°C tensile properties of the alloys of the examples and comparative alloys prepared by powder metallurgy process

[0067] Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) Example 1 1235 1516 9.5 Example 2 1178 1512 13.5 Example 3 1180 1520 14 Example 4 1215 1523 11 Comparative example 1 1149 1491 9.3 Comparative example 2 1047 1391 14 Comparative example 3 830 1170 18

[0068] The above examples are merely illustrations clearly showing the present invention and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the examples here. The obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A large-sized ETA phase-strengthened superalloy, characterized in that: In terms of phase composition, the superalloy includes a matrix, γ′ phase and η phase; among them, the grain size of the matrix is 10~30 μm, the γ′ phase is dispersedly distributed in the matrix, and the size of the γ′ phase is 30~200 nm; the η phase is uniformly distributed in the matrix, the average length of the η phase is 30~50 μm, and the distribution form of the η phase is divided into needle-like and flake-like; The weight percentages of each element in the superalloy are: Al 2.5%-4%, Ti 3.8%-5%, Cr 10%-14%, Co 13%-18%, Nb 0%-3.3%, Mo 2.8%-3.3%, Ta 2.8%-7.5%, W 2.5%-3.2%, C 0.01%-0.05%, B 0%-0.01%, 0%-0.1% rare earth elements, and the balance is Ni.

2. The large-sized ETA phase-strengthened superalloy according to claim 1, characterized in that: the volume fraction of the γ′ phase is 40%~50%, and the volume fraction of the η phase is 8-12%.

3. The large-sized ETA phase-strengthened superalloy according to claim 2, characterized in that: the ratio of the mass fraction of Ti / Al is in the range of 1.4~2.0; the mass fraction of Al+Ti+Nb+Ta is in the range of 11.8%~16%; (Ti+Nb+Ta) / Al the ratio of the mass fraction is in the range of 2.5~4.5; the mass fraction of Mo+W is in the range of 5.5%~6.3%.

4. The preparation method of the large-sized ETA phase-strengthened superalloy according to any one of claims 1-3, characterized in that, including loading the pre-alloyed powder into a hot extrusion sleeve, vacuum-sealing and heating it, then placing it in an extrusion die for hot extrusion, and then air-cooling it to room temperature to obtain a hot-extruded bar; removing the sleeve from the hot-extruded bar and performing heat treatment to obtain a superalloy product; among them, the heat treatment process is: keeping the hot-extruded bar at 1180 °C - 1200 °C for 1.5 - 2.5 hours and then air-cooling it to 720 °C - 760 °C, and then keeping it at 720 °C - 760 °C for 22 - 24 hours and then furnace-cooling.

5. The preparation method according to claim 4, characterized in that: the extrusion temperature of the hot-extruded bar is 1120 °C - 1140 °C, and the extrusion ratio is 15:1 - 17:

1.

6. The preparation method according to claim 4, characterized in that: loading the pre-alloyed powder into a stainless steel sleeve with a diameter of 96 mm and a height of 230 mm, and evacuating and sealing at 400 °C.

7. The preparation method according to claim 5, characterized in that: the diameter of the hot-extruded bar is about 24 mm.

8. The preparation method according to claim 4, characterized in that: the pre-alloyed powder uses gas atomized powder with a particle size of 15~53 microns.

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