CN111440967B

CN111440967B - High-thermal-stability high-strength Re-free nickel-based single crystal superalloy and preparation process thereof

Info

Publication number: CN111440967B
Application number: CN202010381269.4A
Authority: CN
Inventors: 李金国; 刘纪德; 刘金来; 梁静静; 赵乃仁; 王志辉; 侯桂臣; 王新广; 周亦胄; 孙晓峰
Original assignee: Institute of Metal Research of CAS
Current assignee: Institute of Metal Research of CAS
Priority date: 2020-05-08
Filing date: 2020-05-08
Publication date: 2021-12-31
Anticipated expiration: 2040-05-08
Also published as: CN111440967A

Abstract

The invention provides a high-thermal stability high-strength Re-free nickel-based single crystal superalloy and a preparation process thereof, belonging to the field of nickel-based single crystal superalloys. The alloy comprises the following chemical components in percentage by weight: 7.1-11% of Cr, 7.5-14% of Co, 0.5-3% of Mo, 7-10% of W, 4.5-7% of Al, 5-9% of Ta, 0.5-3% of Ti and the balance of Ni. The alloy has excellent thermal stability, high-temperature strength, oxidation resistance and cold and hot fatigue performance, the mechanical property of the alloy is still maintained at a higher level after the alloy is subjected to long-time thermal exposure at high temperature, a noble metal element Re is not contained, the durability of the alloy is equivalent to that of a typical Rene N5 alloy containing 3% of Re, and the cost is reduced by more than 50%. The method is particularly suitable for manufacturing hot-end high-temperature components with long service life and high reliability in the fields of aviation, aerospace, energy sources and the like.

Description

High-thermal-stability high-strength Re-free nickel-based single crystal superalloy and preparation process thereof

Technical Field

The invention relates to the technical field of nickel-based single crystal superalloy, in particular to a high-thermal-stability high-strength Re-free nickel-based single crystal superalloy and a preparation process thereof.

Background

With the development of the industrial fields of aviation, aerospace, energy and the like, the requirement on the temperature bearing capacity of high-temperature alloy materials is continuously improved. In order to meet the requirements of advanced equipment power propulsion systems, the high-temperature alloy undergoes several development processes from isometric crystal to directional columnar crystal and single crystal, and the temperature bearing capacity of the high-temperature alloy is remarkably improved. Since the advent of nickel-based single crystal alloys, nickel-based single crystal alloys have become the preferred material for hot end components of advanced aircraft engines and industrial gas turbines due to their high temperature-bearing capacity, superior creep resistance, and good oxidation and corrosion resistance. So far, single crystal alloys have been developed for many generations, and with the increasing generations of single crystal high temperature alloys, the total amount of refractory elements such as W, Mo and Cr is gradually increased, and the high temperature strength is gradually improved. However, with the increase of the total amount of the refractory elements, the tendency of separating out the TCP harmful phase in the alloy is obviously enhanced, the TCP harmful phase can become a crack initiation position, and meanwhile, the strengthening effect of the refractory elements is also reduced, so that the mechanical property of the alloy is obviously reduced, and the long-term service life of parts is damaged. Therefore, it is a future development trend to obtain high-thermal stability and high-strength nickel-based single crystal superalloy. In addition, from the second generation of single crystal superalloys, the refractory element rhenium (Re) is almost added to strengthen the alloy, but rhenium is a rare element and has very little reserve in the crust. In addition, rhenium is expensive, and the addition of rhenium to the single crystal alloy not only greatly increases the cost of the alloy, but also tends to cause the precipitation of a TCP phase, which is detrimental to the thermal stability of the alloy. With the urgent need of high strength, low cost and high reliability alloy in the industrial field, especially in the aviation industry field, it is necessary to develop a second generation high temperature single crystal Ni-based alloy with high thermal stability and high strength without adding rare noble metal element Re.

Disclosure of Invention

In order to solve the problems of poor high-temperature structure stability, low strength, high cost and the like of the nickel-based single crystal superalloy in the prior art, the invention aims to provide a high-heat-stability high-strength Re-free nickel-based single crystal superalloy and a preparation process thereof, wherein the alloy has excellent medium-temperature and high-temperature strength, high structure heat stability, strong oxidation resistance, no precious metal element Re, equivalent durability to the performance of a typical Rene N5 alloy containing 3 wt.% of Re, and the cost is reduced by more than 50%. Is particularly suitable for manufacturing hot-end high-temperature components in the fields of aviation, aerospace, energy sources and the like.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a high-thermal-stability high-strength Re-free second-generation nickel-based single crystal superalloy (DD98m) comprises the following chemical components in percentage by weight:

7.1-11% of Cr, 7.5-14% of Co, 0.5-3% of Mo, 7-10% of W, 4.5-7% of Al, 5-9% of Ta, 0.5-3% of Tis and the balance of Ni.

The alloy comprises the following preferred chemical components in percentage by weight:

7.5-9.5% of Cr, 7.8-11% of Co, 1.8-3% of Mo, 7.5-9.5% of W, 4.5-6.5% of Al, 5-9% of Ta, 1.0-2.5% of Ti, and the balance of Ni.

In the chemical components of the nickel-based single crystal superalloy, the weight ratio of Ti to Al is controlled to be 0.25-0.4.

In the nickel-based single crystal superalloy, impurity elements meet the following requirements:

O≤0.003wt.％，N≤0.002wt.％，S≤0.003wt.％，P≤0.002wt.％，Si≤0.2wt.％，Pb≤0.0003wt.％，Bi≤0.00005wt.％。

the alloy chemical composition design of the invention is mainly based on the following:

the excellent high-temperature strength of the nickel-based single crystal superalloy comes from the solid solution strengthening effect of alloy elements and the precipitation strengthening effect of a precipitation phase. In order to obtain excellent high-temperature endurance/creep performance, a large amount of alloy elements are generally required to be added for improving the strength of the whole system, for example, elements such as Re, Ru, W and Mo are added for improving the solid solution strengthening effect of a matrix, and elements such as Al, Ti and Ta are added for improving the volume fraction of a precipitation phase and improving the particle strengthening effect of the precipitation phase. However, while the strength of the alloy is considered sufficiently, problems such as structural deterioration caused by excessive alloying and difficulty in forming parts must be considered, and these problems tend to increase the tendency of harmful phases to appear in the single crystal alloy or the tendency of the parts to have mixed crystals, resulting in deterioration of alloy properties or poor engineering applicability. In addition, effective control of the alloy manufacturing cost is one of the factors that must be considered in order to achieve sustainable development in important industrial fields such as aircraft engines. Based on the design concept, the influence of various factors is fully considered in the alloy of the invention at the beginning of design. More W, Mo, Cr and other elements are added into the alloy, so that the solid solution strengthening effect of an alloy matrix is improved, the elements such as Re, Ru and the like are effectively replaced, the alloy strength is improved, and the manufacturing cost is reduced; on the other hand, in order to avoid the problem of increasing the tendency of harmful phase precipitation caused by the increase of solid solution strengthening elements, more Co element is added into the alloy, so that the stability of an alloy system is improved similarly to Ru element, and the stability of a high-temperature structure of the alloy is improved. Meanwhile, in order to obtain a better precipitation strengthening effect, a large amount of Al, Ti, Ta and other precipitation phase forming elements need to be added into the alloy, but the durability of the alloy tends to increase firstly and then decrease along with the increase of the Al, Ti and Ta, and researches show that the atomic percentages of the precipitation phase forming elements and the solid solution strengthening elements are more suitable between 15 and 16 percent, and the ratio of Ti to Al is more suitable between 0.25 and 0.4; therefore, the contents of Al, Ti and Ta should be controlled to be 4.7-6.7% of Al, 5-9% of Ta and 0.5-3% of Ti, respectively.

Firstly, weighing alloy raw materials (pure metal simple substances of elements such as Ni, Co, Cr, W, Mo, Ta, Al, Ti and the like are used as raw materials) according to required alloy components, smelting in a vacuum induction smelting furnace, and then casting into a master alloy; remelting a mother alloy by adopting directional solidification equipment, and directionally solidifying and casting the mother alloy into a single crystal rod by adopting a spiral crystal selection method or a seed crystal method; the single crystal rod needs to be heat treated before use. The single crystal rod is subjected to heat treatment by adopting a vacuum or common muffle furnace, and the heat treatment system is carried out according to the following steps:

(1) high-temperature solution treatment: the temperature is gradually increased from 1240 ℃ to 1300 ℃ by adopting a staged temperature increasing method, and the specific process flow is as follows: heating from room temperature to 1240 ℃ and preserving heat for 1h, then heating to 1270 ℃ and preserving heat for 1h, then heating to 1280 ℃ and preserving heat for 1h, then heating to 1290 ℃ and preserving heat for 2h, then heating to 1300 ℃ and preserving heat for 4h, and then taking out and cooling to room temperature in the air.

(2) High-temperature aging treatment: keeping the temperature at 1050-.

(3) And (3) low-temperature aging treatment: keeping the temperature at 850-900 ℃ for 20-28 hours, and taking out the product to be cooled to room temperature in the air.

The invention has the following beneficial effects:

(1) the invention develops a high-thermal-stability and high-strength Re-free nickel-based single crystal superalloy based on a synergistic coupling action mechanism of strengthening elements between high-temperature structural stability and high-temperature strength, and the superalloy has excellent durability and high-temperature oxidation resistance, wherein the durability of the superalloy reaches 190h at 1093 ℃/137MPa, the durability of the superalloy reaches 280h at 1038 ℃/172MPa, the durability of the superalloy reaches 108h at 1010 ℃/235MPa, and the durability of the superalloy reaches 281h at 800 ℃/750 MPa.

(2) The alloy of the invention has complete oxidation resistance at 1010 ℃ and good hot corrosion resistance at 900 DEG C

(3) The alloy of the invention has the endurance life equivalent to the performance of a typical second generation single crystal superalloy Rene N5 containing 3% Re, but the cost is more than 50% lower than that of the Rene N5 alloy because of no element Re.

(4) After the alloy of the invention is subjected to heat exposure experiments for 1000 hours at 950 ℃ and 1050 ℃, the alloy still has high-temperature strength and good structural stability.

(5) The alloy of the invention has a density of 8.57g/cm³And the density is lower than that of the foreign mature alloy Rene N5.

Drawings

FIG. 1 is an as-cast structure of an alloy of example 1 of the present invention;

FIG. 2 is the as-cast structure of the alloy of example 2 of the present invention;

FIG. 3 is a heat treated structure of the alloy of example 3 of the present invention;

FIG. 4 is a heat treated structure of the alloy of example 4 of the present invention;

FIG. 5 is a creep deformation curve for the alloy of example 6;

FIG. 6 is a graph of isothermal oxidation kinetics for the alloy of example 6;

FIG. 7 is the structure of the alloy of example 6 after 500h of heat exposure;

FIG. 8 is the structure of the alloy of example 6 after 1000h of thermal exposure;

FIG. 9 is the structure of example 6 alloy after 2000h of heat exposure;

FIG. 10 is a comparison of the cold-hot cycle fatigue crack length test for the alloy of example 6 of the present invention.

Detailed Description

The following examples further illustrate the invention and are not intended to limit the invention thereto.

The following specific preparation method requirements for each example and comparative alloy: the method comprises the steps of smelting raw materials by using a vacuum induction smelting furnace, casting the raw materials into a master alloy with chemical components meeting requirements, preparing a single crystal rod by using a directional solidification furnace, and carrying out heat treatment before use.

Preparing single crystal alloy on an industrial directional solidification furnace, wherein the temperature gradient range of the directional solidification furnace is 40-80 ℃/cm, the pouring temperature is 1480-1550 ℃, the temperature of a mold shell is consistent with the pouring temperature, and a single crystal test bar is prepared within the growth rate of 3-8 mm/min.

The heat treatment system of the single crystal alloy of the invention is as follows:

(1) high-temperature solution treatment, keeping the temperature at 1240-1300 ℃ for 4-10 hours, and air cooling to room temperature, wherein the specific process comprises the following steps: firstly heating to 1240 ℃ and preserving heat for 1h, then heating to 1270 ℃ and preserving heat for 1h, then heating to 1280 ℃ and preserving heat for 1h, then heating to 1290 ℃ and preserving heat for 2h, finally heating to 1300 ℃ and preserving heat for 4h, and air cooling to room temperature.

(2) High-temperature aging treatment, namely preserving the heat for 4 to 6 hours at 1050-;

(3) and (4) low-temperature aging treatment, keeping the temperature at 850-900 ℃ for 20-28 hours, and air cooling to room temperature.

Examples 1 to 6:

the chemical compositions of the nickel-based single crystal superalloys of inventive examples 1-6 are shown in table 1.

Table 1 list of chemical composition (wt.%) of the alloys of the invention (examples 1-6)

Alloy (I)	Cr	Co	W	Al	Ti	Ta	Mo	Re	Ni
										Example 1	7.8	8.0	8.0	5.2	1.56	5.5	1.8	0	Surplus
Example 2	7.8	8.5	8.0	6.5	2.0	8.5	1.8	0	Surplus
										Example 3	9.1	10.0	9.2	5.5	1.45	5.5	2.5	0	Surplus
Example 4	9.2	10.2	9.0	6.3	2.3	8.5	2.5	0	Surplus
										Example 5	8	10.5	8.5	6	2.0	8.5	2.2	0	Surplus
Example 6	8.5	11	8.5	5	1.5	8.0	2	0	Surplus
										Rene N5	7.0	7.5	5.0	6.2	0	6.5	1.5	3	Surplus

The alloy in the above example was subjected to performance testing, with the following results:

1. the density measurement of the alloy of example 6 was 8.57g/cm³。

2. The alloy of example 5 was subjected to a durability test after heat treatment and machining, and the results are shown in table 2.

TABLE 2 example 5 alloy durability

Temperature/degree	stress/MPa	Long life/h	Elongation/percent
				1093	137	190	7
1038	172	280	13
				1010	235	108	21
1100	190	153	14
				980	250	210	14
800	750	281	15

3. The durability data for the alloy of example 6 of the invention and the comparative alloy Rene N5 under several test conditions are shown in Table 3.

TABLE 3 permanence of the alloy of example 6 and the comparative alloy Rene N5

4. The as-cast structure of the alloy of example 1 of the present invention is shown in FIG. 1.

5. The as-cast structure of the alloy of example 2 of the present invention is shown in FIG. 2.

6. The structure of the alloy of example 3 of the present invention after heat treatment is shown in FIG. 3.

7. The structure of the alloy of example 4 of the present invention after heat treatment is shown in FIG. 4.

8. The strain-time creep curve of the alloy of example 6 of the present invention is shown in FIG. 5. It can be seen that the creep life of the alloy decreases significantly with increasing stress. Under the three stress conditions, the initial stage of creep is not obvious, and the creep acceleration stage is obvious. The time for steady state creep gradually decreases with increasing stress. This indicates that the stress has a significant effect on the change in creep rate under high temperature conditions.

9. The constant temperature oxidation kinetics curve of the alloy of example 6 of the present invention at 1010 ℃ is shown in FIG. 6. It can be seen that the weight of the sample tends to increase with the oxidation time, the weight gain increasing rapidly in the initial phase and then decreasing in magnitude. The average oxidation rate of the alloy at 1010 ℃ for 50h-100h is 0.035g/m²·h^-1The alloy is determined according to HB5258-2000 "test method for measuring oxidation resistance of Steel and high temperature alloyThe temperature of 1010 ℃ is the complete oxidation resistance level.

10. The microstructure of the alloy of the embodiment 6 of the invention after long-term aging for 1000h, 500h, 1000h and 2000h is shown in figures 7-9, and no harmful TCP phase is precipitated. This indicates that the structure of the alloy of the present invention has excellent thermal stability.

11. The room temperature and high temperature tensile properties of the alloy of example 6 of the invention after 100h of thermal exposure at 950 ℃ and 1050 ℃ are shown in table 4. It can be seen that the strength of the alloy is reduced, but the high temperature strength is maintained at a high level.

TABLE 4 tensile Properties at 100h ageing at two temperatures

12. The room temperature and high temperature tensile properties of the alloy of example 6 of the invention after 500h of thermal exposure at 950 ℃ and 1050 ℃ are shown in table 5. It can be seen that the strength of the alloy is reduced, but the high temperature strength is maintained at a high level.

TABLE 5 tensile Properties at two temperatures over 500h

13. The room temperature and high temperature tensile properties of the alloy of example 6 of the invention after 1000h of thermal exposure at 950 ℃ and 1050 ℃ are shown in table 6. It can be seen that the strength of the alloy is reduced, but the high temperature strength is maintained at a high level.

TABLE 6 tensile Properties at 1000h ageing at two temperatures

14. The high temperature durability of the alloy of example 6 of the present invention after different time thermal exposures at 950 ℃ and 1050 ℃ is shown in Table 7. It can be seen that the endurance life is gradually reduced with the extension of the heat exposure time and the increase of the temperature, but the alloy still has higher endurance performance after 1000h of heat exposure.

TABLE 7 permanence of the alloys after long term aging at 1010 ℃/235MPa

15. The comparison of the fatigue crack length test results of the alloy of example 6 of the present invention and other alloys under the cold and hot cycle at room temperature to 1000 ℃ is shown in FIG. 10, which shows that the alloy of the present invention (DD98m) has excellent thermal crack resistance.

Claims

1. A high-thermal stability high-strength Re-free nickel-based single crystal superalloy is characterized in that: the alloy comprises the following chemical components in percentage by weight:

7.1-11% of Cr, 10.2-14% of Co, 0.5-3% of Mo, 7-10% of W, 4.5-7% of Al, 8.0-9% of Ta, 0.5-3% of Ti and the balance of Ni; the weight ratio of Ti to Al is controlled to be 0.25-0.4;

the preparation process of the high-thermal stability high-strength Re-free nickel-based single crystal superalloy comprises the steps of firstly weighing alloy raw materials according to required alloy components, and casting a master alloy after smelting in a vacuum induction smelting furnace; remelting a mother alloy by adopting directional solidification equipment, and directionally solidifying into a single crystal rod by adopting a spiral crystal selection method or a seed crystal method; carrying out heat treatment on the single crystal rod before use; the single crystal rod is subjected to heat treatment by adopting a vacuum or common muffle furnace, and the heat treatment system is carried out according to the following steps:

(1) high-temperature solution treatment: adopting a staged heating method, and gradually heating the temperature from 1240 ℃ to 1300 ℃;

(2) high-temperature aging treatment: preserving the heat for 4-6 hours at 1050-;

(3) and (3) low-temperature aging treatment: keeping the temperature at 850-900 ℃ for 20-28 hours, and cooling to room temperature in air.

2. A high thermal stability high strength Re-free nickel based single crystal superalloy as in claim 1, wherein: the alloy comprises the following chemical components in percentage by weight:

7.5-9.5% of Cr, 10.2-11% of Co, 1.8-3% of Mo, 7.5-9.5% of W, 4.5-6.5% of Al, 8.9-9% of Ta, 1.0-2.5% of Ti and the balance of Ni.

3. A high thermal stability high strength Re-free nickel based single crystal superalloy according to claim 1 or 2, wherein: in the nickel-based single crystal superalloy, the components of impurities meet the following requirements:

O≤0.003wt.%，N≤0.002wt.%，S≤0.003wt.%，P≤0.002wt.%，Si≤0.2wt.%，Pb≤0.0003wt.%，Bi ≤0.00005wt.%。

4. a high thermal stability high strength Re-free nickel based single crystal superalloy as in claim 1, wherein: the specific process of the high-temperature solid solution treatment comprises the following steps: heating to 1240 ℃ and preserving heat for 1h, then heating to 1270 ℃ and preserving heat for 1h, then heating to 1280 ℃ and preserving heat for 1h, then heating to 1290 ℃ and preserving heat for 2h, finally heating to 1300 ℃ and preserving heat for 4h, and air cooling to room temperature.