阅读说明：本技术 一种低密度且抗热腐蚀性能优良的单晶高温合金及其制备工艺 (Single crystal high temperature alloy with low density and excellent hot corrosion resistance and preparation process thereof ) 是由 刘金来 赵乃仁 王新广 周亦胄 孙晓峰 于 2020-12-01 设计创作，主要内容包括：本发明公开了一种低密度且抗热腐蚀性能优良的单晶高温合金,属于抗热腐蚀单晶高温合金及其制备和热处理领域。合金化学成分：Cr 15.5～16.5％,Co 8.0～9.0％,W 5.6～6.4％,Al 3.6～4.2％,Ti 3.6～4.2％,Ta 0.7～1.2％,其余为Ni。采用单晶生长工艺制备,单晶生长炉温度梯度40K/cm～80K/cm,浇注温度1500～1550℃,经热处理后使用。本发明合金在1000℃/137MPa持久条件下寿命≥300h,其承温能力比DZ438G合金提高约20℃；高温抗氧化性能和抗热腐蚀性能均优于抗热腐蚀合金K438G和DZ438G。热处理窗口宽,固溶处理易于控制。(The invention discloses a single crystal high-temperature alloy with low density and excellent hot corrosion resistance, belonging to the field of hot corrosion resistance single crystal high-temperature alloys and preparation and heat treatment thereof. The alloy comprises the following chemical components: 15.5-16.5% of Cr, 8.0-9.0% of Co, 5.6-6.4% of W, 3.6-4.2% of Al, 3.6-4.2% of Ti, 0.7-1.2% of Ta and the balance of Ni. The preparation method is characterized by adopting a single crystal growth process, wherein the temperature gradient of a single crystal growth furnace is 40-80K/cm, the pouring temperature is 1500-1550 ℃, and the single crystal growth furnace is used after heat treatment. The service life of the alloy is more than or equal to 300h under the lasting condition of 1000 ℃/137MPa, and the temperature bearing capacity of the alloy is improved by about 20 ℃ compared with that of the DZ438G alloy; the high-temperature oxidation resistance and the hot corrosion resistance are both superior to hot corrosion resistance alloys K438G and DZ 438G. The heat treatment window is wide, and the solution treatment is easy to control.)

1. A single crystal superalloy with low density and excellent hot corrosion resistance, comprising: the single crystal superalloy comprises the following chemical components in percentage by weight: 15-17% of Cr, 7-10% of Co, 5-7% of W, 3.5-4.5% of Al, 3.5-4.5% of Ti, 0.5-1.5% of Ta and the balance of Ni.

2. A single crystal superalloy with low density and excellent hot corrosion resistance as in claim 1, wherein: the single crystal superalloy comprises the following chemical components in percentage by weight: 15.5-16.5% of Cr, 8.0-9.0% of Co, 5.6-6.4% of W, 3.6-4.2% of Al, 3.6-4.2% of Ti, 0.7-1.2% of Ta and the balance of Ni.

3. A single crystal superalloy with low density and excellent hot corrosion resistance as in claim 1, wherein: the single crystal alloy comprises the following chemical components in percentage by weight:

16% of Cr, 8.5% of Co, 6% of W, 3.9% of Al, 3.8% of Ti, 1% of Ta and the balance of Ni.

4. A single crystal superalloy with low density and excellent hot corrosion resistance as in claim 1, wherein: the sum of the Al and Ti contents in percentage by weight in the alloy is more than 7.5%, and the weight ratio of the Al to the Ti is between 0.78 and 119.

5. The method for preparing a single crystal superalloy having a low density and excellent hot corrosion resistance as set forth in any of claims 1 to 4, wherein: preparing materials according to chemical components of the single crystal high-temperature alloy, preparing a master alloy by adopting a vacuum induction furnace smelting process, and then preparing the single crystal high-temperature alloy by adopting a directional solidification furnace and according to a single crystal growth process; in the single crystal growth process, the temperature gradient range of the single crystal growth furnace is 40-80K/cm, the pouring temperature is 1500-1550 ℃, the temperature of the mold shell is consistent with the pouring temperature, and the growth rate is 3-8 mm/min.

6. A method of producing a single crystal superalloy with low density and excellent hot corrosion resistance as claimed in claim 5, wherein: the heat treatment system of the single crystal superalloy comprises the following steps:

(1) solution treatment: preserving heat for 6-10 hours at 1090-1110 ℃, then raising the temperature to 1230-1250 ℃, preserving heat for 3-6 hours, and then air cooling to room temperature;

(2) high-temperature aging treatment: preserving the heat for 2-5 hours at 1080-1100 ℃, and then air-cooling to room temperature;

(3) and (3) low-temperature aging treatment: preserving the temperature for 20-26 hours at 830-870 ℃, and then cooling to room temperature in air.

7. A method of producing a single crystal superalloy having a low density and excellent hot corrosion resistance as set forth in claim 6, wherein: the heat treatment system of the single crystal superalloy comprises the following steps:

(1) solution treatment: keeping the temperature at 1100 ℃ for 8 hours, then heating to 1240 ℃ and keeping the temperature for 4 hours, and then cooling to room temperature in air;

(2) high-temperature aging treatment: preserving the heat at 1090 ℃ for 2 hours, and then cooling the mixture to room temperature in air;

(3) and (3) low-temperature aging treatment: the temperature was maintained at 850 ℃ for 24 hours, followed by air cooling to room temperature.

Technical Field

The invention relates to a hot corrosion resistant single crystal high temperature alloy and the preparation and heat treatment field thereof, in particular to a low density single crystal high temperature alloy with excellent hot corrosion resistance and the preparation process thereof, which is mainly suitable for the blade material of a turbine engine used below 1000 ℃.

Background

The nickel-based single crystal superalloy is the material of choice for critical components that are subjected to the highest temperatures and the highest stress loads in advanced turbine engines at present and for a considerable period of time in the future due to its superior overall properties.

The development of single crystal superalloys can be divided into three types: (1) alloying method is to add considerable Al element to ensure the quantity of gamma' strengthening phase; meanwhile, a large amount of W, Mo, Ta, Re and other refractory metal elements are added to further improve the strength, but the alloy density is also increased to 8.5-9.0g/cm³. The addition of Re greatly increases the price of the alloy. Meanwhile, in order to maintain good structural stability and avoid the precipitation of harmful phases such as sigma, mu and the like, the content of Cr has to be reduced, which inevitably damages the oxidation resistance and the hot corrosion resistance. Representative of such alloys are PWA1480, CMSX-4, Ren N6, and the like. (2) The alloying method is to add appropriate amount of refractory metals such as Al, W, Ta, etc. to ensure high Cr content and obtain good hot corrosion resistance, but high mechanical property is difficult to obtain. Typical single crystal alloys are those such as AF56, SC-16, and the like. (3) From the perspective of engine design, particularly for moving blades, the use of high-density alloy can generate large centrifugal stress, so that the blades and a turbine disc generate large load, and the failure probability of the engine is increased. Therefore, low-density single crystal alloys have also received considerable attention, and various low-density single crystal alloys have been developed internationally, such as CMSX-6, RR2000, and the like. Because different types of alloys have different alloying characteristics, alloys with the two performance characteristics are hardly reported.

Disclosure of Invention

The invention aims to provide a single crystal superalloy with low density and excellent hot corrosion resistance and a preparation process thereof, which are used for solving the problems of high cost, high density, difficulty in considering hot corrosion resistance and the like in the prior art, wherein the use temperature can reach 1000 ℃, and the single crystal superalloy is mainly suitable for blade materials of turbine engines used at the temperature of more than 900 ℃ and below 1000 ℃.

The technical scheme of the invention is as follows:

a single crystal high temperature alloy with low density and excellent hot corrosion resistance comprises the following specific chemical components (wt%):

15-17% of Cr, 7-10% of Co, 5-7% of W, 3.5-4.5% of Al, 3.5-4.5% of Ti, 0.5-1.5% of Ta and the balance of Ni.

The preferred chemical composition (wt%) of the hot corrosion resistant single crystal superalloy is as follows:

15.5-16.5% of Cr, 8.0-9.0% of Co, 5.6-6.4% of W, 3.6-4.2% of Al, 3.6-4.2% of Ti, 0.7-1.2% of Ta and the balance of Ni.

The optimal chemical composition (wt%) of the hot corrosion resistant single crystal superalloy is as follows:

16% of Cr, 8.5% of Co, 6% of W, 3.9% of Al, 3.8% of Ti, 1% of Ta and the balance of Ni.

The preparation method of the hot corrosion resistant single crystal alloy comprises the following steps: preparing materials according to chemical components of the single crystal high-temperature alloy, preparing a master alloy by adopting a vacuum induction furnace smelting process, and then preparing the single crystal high-temperature alloy by adopting a directional solidification furnace and according to a single crystal growth process; in the single crystal growth process, the temperature gradient range of the single crystal growth furnace is 40-80K/cm, the pouring temperature is 1500-1550 ℃, the temperature of the mold shell is consistent with the pouring temperature, and the growth rate is 3-8 mm/min. The alloy can be used for preparing single crystal blades or test bars.

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

(1) solution treatment: preserving heat for 6-10 hours at 1090-1110 ℃, then raising the temperature to 1230-1250 ℃, preserving heat for 3-6 hours, and then air cooling to room temperature;

(2) high-temperature aging treatment: preserving the heat for 2-5 hours at 1080-1100 ℃, and then air-cooling to room temperature;

(3) and (3) low-temperature aging treatment: preserving the temperature for 20-26 hours at 830-870 ℃, and then cooling to room temperature in air.

The preferred heat treatment system of the hot corrosion resistant single crystal alloy of the invention is as follows:

(1) solution treatment: keeping the temperature at 1100 ℃ for 8 hours, then heating to 1240 ℃ and keeping the temperature for 4 hours, and then cooling to room temperature in air;

(2) high-temperature aging treatment: preserving the heat at 1090 ℃ for 2 hours, and then cooling the mixture to room temperature in air;

(3) and (3) low-temperature aging treatment: the temperature was maintained at 850 ℃ for 24 hours, followed by air cooling to room temperature.

The design mechanism of the alloy of the invention is as follows:

the component design of the alloy adopts higher Cr content to ensure the hot corrosion resistance of the alloy, although lower Ta content is selected, more Ti element is added to realize the strengthening level of gamma 'and reduce the density of the alloy, and the solid solution strengthening and the precipitation strengthening of the gamma' of the alloy elements are exerted as much as possible by fully solid dissolving and changing the aging temperature and time; meanwhile, the alloy has enough hot corrosion resistance and has the mechanical property level of the first generation of single crystal by utilizing the interaction of alloy elements.

The chemical composition is designed mainly based on the following reasons:

cr can improve the corrosion resistance of the alloy and can generate a certain solid solution strengthening effect, so that the content of Cr must be large enough; meanwhile, the content of Cr is not too high, so that a TCP phase is precipitated in the alloy to damage the structural stability of the alloy. The content of Cr in the invention is selected to be 15-17 wt%, and the preferable content range is 15.5-16.5%. According to the object of the present invention, the content of Ta is reduced by appropriately increasing the content of Ti while taking into consideration the effects of the respective alloying elements.

The effect of Co on phase precipitation is controversial, and Co improves alloy structure stability but reduces fracture strength and oxidation resistance. Erickson limited Co content to 3 wt% in CMSX-10, which is said to reduce the tendency of TCP phase formation; walston recommended high Co levels in Rene N6 (up to 12.5 wt%), for phase stability; earlier work of the invention shows that Co reduces the precipitation temperature of the gamma 'phase, so that eutectic and cast coarse gamma' phases are easy to dissolve back into a matrix, and the Co is beneficial to eliminating dendritic crystal segregation of alloy elements during solution treatment, thereby improving the structure stability of the alloy. But when the content is too high, the growth of gamma' is inhibited, so that the size of the alloy is reduced, and the high-temperature strength of the alloy is further reduced. Therefore, the content of the selected Co is 7-10 wt%, and the preferable content range is 8-9%.

W is distributed in the matrix and gamma' phase in a balanced manner and is a strong solid solution strengthening element. However, the excessive addition of W can cause the instability of a microstructure, so that a gamma phase is supersaturated, and a TCP brittle phase such as a sigma phase, a mu phase and P and even an alpha-W phase are easily formed, thereby damaging the mechanical property of the alloy; and excessive addition of W causes freckles consisting of chain-like equiaxed grains to appear in the alloy. The reason for this is that heavy elements such as W are unevenly distributed to the dendrite trunk, so that the liquid density of the mushy zone is lower than that of the upper bulk liquid phase, and convection instability is caused, thereby causing secondary dendrite breakage. In the alloy of the invention, the content of W is 5-7 wt%, preferably 5.6-6.4 wt%.

Mo is a solid solution strengthening element, can increase the mismatching degree of gamma/gamma', enable a mismatching dislocation network to be dense, effectively block dislocation movement and improve performance; however, Mo has a bad influence on the hot corrosion performance of the alloy, so that Mo element is not added into the alloy.

The amount of the gamma ' phase is determined by Al, Ti, Ta and other elements, Al is used as a main element for forming gamma ', the oxidation resistance of the alloy can be obviously improved, but when the content is too high, the precipitation amount of gamma ' is too much, and the endurance strength of the alloy is reduced, so that the Al content is 3.5-4.5%, and the preferable range is 3.6-4.2%. Ti not only has an influence on the total amount of gamma ', but also obviously influences the strengthening level of the gamma', and is beneficial to the corrosion resistance of the alloy, but also has negative influence on the oxidation resistance, so that more Ti is added into the alloy, and the content of the Ti is between 3.5 and 4.5 percent, and the preferable range is 3.6 to 4.2 percent. Ta improves the strength of the alloy by solid solution strengthening and improving the strength of gamma 'particles, Ta is not a forming element of a TCP phase, Ta can improve the solid solubility curve of the gamma' phase and can effectively promote the oxidation resistance, hot corrosion resistance and durability of an aluminum coating of the alloy, but Ta has high density and cost. The content of Ta in the present invention is 0.5 to 1.5 wt%, preferably 0.7 to 1.2%.

In order to ensure the excellent hot corrosion resistance of the alloy, the content of Cr is not less than 15 percent. In order to ensure good strength of the alloy, a sufficient volume fraction and a sufficiently strengthened gamma' phase must be precipitated in the alloy, so that the sum of the weight percentages of Al and Ti in the alloy is more than 7.5%, and the weight ratio of Al to Ti is approximately equal to 1 (between 0.78 and 119). To ensure the low cost characteristics of the alloy, the content of Ta does not exceed 1.5%.

The invention adopts a vacuum induction furnace for smelting, firstly casts the master alloy, and then carries out heat treatment according to the single crystal growth process and the heat treatment system.

The invention has the beneficial effects that:

1. the invention adopts directional solidification to prepare single crystal alloy, and the alloy has excellent hot corrosion resistance and good high-temperature strength through solid solution homogenization treatment, high-temperature aging treatment and low-temperature aging treatment.

2. Compared with the prior art, the invention has excellent hot corrosion resistance and good mechanical property.

(1) Resistance to hot corrosion

About 3.5mg/cm of surface coating²Na of (2)₂SO₄+25 wt.% NaCl mixed salt, weight loss not higher than 2mg/cm hot-etched at 950 ℃ for 50h²。

(2) Instantaneous tensile Property

800℃：σ_0.2≥800MPa；1000℃：σ_0.2≥380MPa；

(3) Durability performance

The lasting life is more than or equal to 300h at 1000 ℃/150 MPa; the temperature bearing capacity is improved by about 20 ℃ compared with the typical hot corrosion resistant oriented alloy DZ 438G.

3. The alloy of the invention has low content of noble element Ta, thus having low cost and density.

4. The invention has wide heat treatment window and easy control of solution treatment.

Drawings

FIG. 1 is a microstructure of the alloy of example 1 after a full heat treatment.

FIG. 2 is a comparison of the Larson-Miller curves for the alloy of example 1 and a typical hot corrosion resistant oriented alloy DZ 438G.

FIG. 3 is a comparison of the constant temperature oxidation weight gain curves at 900 ℃ for the alloy of example 1 and typical hot corrosion resistant alloys K438G and DZ 438G.

FIG. 4 is a graph of the alloy of example 1 surface coated with about 3.5mg/cm at 900 deg.C with typical hot corrosion resistant alloys K438G and DZ438G²Na of (2)₂SO₄+25 wt.% NaCl mixed salt hot corrosion weight gain curves comparison.

FIG. 5 is a graph of the alloy of example 1 surface coated with about 3.5mg/cm at 950 deg.C with typical hot corrosion resistant alloys K438G and DZ438G²Na of (2)₂SO₄+25 wt.% NaCl mixed salt hot corrosion weight gain curves comparison.

FIG. 6 is a graph showing the relationship between the stress amplitude of low cycle fatigue and the cycle number of fracture at 760 ℃ for the alloy of example 1.

FIG. 7 is a graph showing the relationship between the stress amplitude of high cycle fatigue and the cycle number of fracture of the alloy of example 1 at 800 ℃.

Detailed Description

Example 1

The specific compositions of the alloys of this example are shown in table 1, and for comparison, the chemical compositions of K438G and DZ438G are also shown in table 1.

TABLE 1 chemical composition (wt%) of inventive example 1 and comparative alloys K438G and DZ438G

After the materials are proportioned and vacuum induction smelted according to the alloy components, a master alloy ingot with the size of phi 80 multiplied by 500mm is cast, then the master alloy ingot is polished to remove oxide skin, and the master alloy ingot is cut into proper blocks for preparing single crystal rods.

The single crystal rod is prepared on the directional solidification furnace by adopting a spiral crystal selection method. The temperature gradient of the single crystal growth furnace is 60K/cm, the pouring temperature is 1550 ℃, and the temperature of the mold shell is consistent with the pouring temperature; and standing for 5 minutes, and pulling with a preset single crystal growth rate of 6mm/min to prepare the single crystal rod.

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

(1) solution treatment: keeping the temperature at 1100 ℃ for 8 hours, then heating to 1240 ℃ and keeping the temperature for 4 hours, and then cooling to room temperature in air;

(2) high-temperature aging treatment: preserving the heat at 1090 ℃ for 2 hours, and then cooling the mixture to room temperature in air;

(3) and (3) low-temperature aging treatment: the temperature was maintained at 850 ℃ for 24 hours, followed by air cooling to room temperature.

By adopting the heat treatment system, more than 99% of eutectic and cast gamma 'can be dissolved, and fine (0.4-0.5 mu m) cubic gamma' phases which are uniformly distributed and regularly arranged are precipitated, so that the alloy components are ideally and uniformly distributed, and the stability of the alloy structure is favorably realized. The microstructure of the alloy after complete heat treatment is shown in FIG. 1.

The instantaneous tensile properties of the alloy at various temperatures are shown in table 2, along with the properties of the DZ438G alloy for comparison.

TABLE 2 instantaneous tensile Properties of the alloy of example 1 and tensile Properties of the DZ438G alloy

From table 2, it can be seen that the yield strength and tensile strength of the alloy show some increase with increasing temperature from room temperature to 760 ℃, and in particular the increase in tensile strength is more pronounced, reaching a peak strength at 760 ℃, and rapidly decreasing beyond 760 ℃, but still exceeding the DZ438G alloy at 850 ℃. The yield strength at 950 ℃ is slightly lower than that of the DZ438G alloy, but the tensile strength is still obviously higher than that of the DZ438G alloy, and the alloy has higher middle and high temperature strength levels.

The performance data of the alloy in example 1 under different endurance conditions are shown in table 3, and it can be seen that the alloy has higher endurance life and endurance plasticity, and has the possibility that the maximum service temperature can reach 1000 ℃.

TABLE 3 permanence of the alloy of example 1

Persistent conditions	Long service life (h)	Elongation (%)
			1000℃/167MPa	130	18.8
1000℃/137MPa	374	14.4
			950℃/245MPa	84	17.4
950℃/235MPa	137	18.0
			950℃/196MPa	346	10.4
900℃/363MPa	141	18.4
			900℃/333MPa	211	22.8
900℃/294MPa	334	18.0
			850℃/519MPa	79	18.8
850℃/470MPa	158	-
			850℃/441MPa	210	12.4
800℃/647MPa	116	16.4
			800℃/588MPa	398	20.0
800℃/529MPa	424	16.0
			750℃/774MPa	173	14.0
750℃/755MPa	211	17.6
			750℃/725MPa	443	14.4

The Larson-Miller curve of the alloy of example 1 and the typical hot corrosion resistant oriented alloy DZ438G is shown in fig. 2, and it can be seen that the alloy of the invention has significant performance advantages compared with the alloy of DZ438G in a wide range of temperature and stress, while the alloy of the invention has significant advantages of low density and low cost, which shows that the alloy of the invention has wide popularization and application prospects.

The constant temperature oxidation weight gain curve of the alloy of example 1 at 900 ℃ is shown in fig. 3, and it can be seen that the weight gain rate of the alloy of the present application is significantly lower than that of the K438G and DZ438G alloys, indicating that the alloy of the present application has excellent oxidation resistance.

FIGS. 4 and 5 show hot corrosion of the alloy of example 1 at 900 deg.C and 950 deg.C, both with a salt coating of about 3.5mg/cm²Na of (2)₂SO₄+25 wt.% NaCl mixed salt. It can be seen that the weight gain rate of the alloy of the present application is significantly lower than that of the typical hot corrosion resistant alloys K438G and DZ438G, indicating that the alloy of the present application has superior hot corrosion resistance.

The relationship between the cycle of fracture and the stress amplitude of the alloy of example 1 at 760 ℃ in low cycle fatigue is shown in fig. 6, where the sample is a smooth sample, the stress ratio is-1, and the waveform is a triangular wave. It can be seen that the fatigue strength of the alloy is 540MPa, indicating that the alloy has good low cycle fatigue resistance.

The relationship between the cycle of fracture and the stress amplitude of the alloy of example 1 at 800 ℃ in high cycle fatigue is shown in fig. 7, where the sample is a smooth sample, the stress ratio is R0.1, and the waveform is a triangular wave. It can be seen that the fatigue limit of the alloy is 538MPa, indicating that the alloy has good high cycle fatigue resistance.

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.