A method of surface strengthening of a nickel-based single crystal superalloy blade

Abstract

The present application relates to heavy gas turbine turbine blade manufacturing technical field, especially to a kind of surface strengthening method of nickel-based single crystal high-temperature alloy blade.The surface strengthening method provided by the present application comprises the following steps: nickel-based single crystal high-temperature alloy blade is sequentially subjected to segmented solid solution treatment, air cooling, aging treatment, sand blasting treatment and electrolytic polishing treatment;The segmented solid solution treatment includes sequentially carried out first solid solution treatment and second solid solution treatment;The first solid solution treatment is carried out in non-oxygen-containing atmosphere, and the second solid solution treatment is carried out in oxygen-containing atmosphere.The surface strengthening method can improve the surface strength of nickel-based single crystal high-temperature alloy blade, so as to inhibit the generation of turbine blade surface crack source.

Description

Technical Field

[0001] This invention relates to the field of heavy-duty gas turbine blade manufacturing technology, and in particular to a surface strengthening method for nickel-based single-crystal high-temperature alloy blades. Background Technology

[0002] Turbine blades are among the most critical components of heavy-duty gas turbines, typically operating under conditions of high temperature, high pressure, and alternating stress and temperature fields. Nickel-based single-crystal superalloys, which primarily hinder dislocation movement by precipitating a uniformly dispersed γ' phase and virtually eliminating all grain boundaries, are widely used in gas turbine blades due to their excellent high-temperature mechanical properties.

[0003] In practical applications, turbine blades are assembled into a turbine disk by connecting the blade tenon and the disk groove. Therefore, the tenon typically experiences start-stop cycles, high-frequency vibrations, resonance, centrifugal forces at high temperatures, and cyclic thermal stress, resulting in various types of fatigue damage. Fatigue damage primarily originates from localized contact between the mating surfaces (tenon and groove), manifesting as fretting fatigue or high-cycle fatigue. Once fatigue cracks begin and propagate on the tenon surface, they pose a serious threat to industrial applications.

[0004] To suppress the formation of surface cracks in turbine blades, surface strengthening treatment is necessary to improve fatigue resistance. Current surface strengthening methods mainly fall into two categories: one is shot peening or laser shock peening, which induces plastic deformation on the turbine blade surface, refining the target material's surface microstructure and obtaining a certain depth of compressive stress, thereby improving the material's surface strength. However, this process introduces a large amount of residual stress into the turbine blade surface, which can induce recrystallization during high-temperature service, accelerating the oxidation process. Simultaneously, the surface roughness increases after processing, making it difficult to meet precision requirements. The other type of surface strengthening method is thermochemical treatment, which forms a hardening coating through carburizing, nitriding, etc. However, this coating performs poorly under high loads and has poor adhesion to the substrate. Summary of the Invention

[0005] The purpose of this invention is to provide a surface strengthening method for nickel-based single-crystal superalloy blades, which can improve the surface strength of nickel-based single-crystal superalloy blades, thereby suppressing the generation of surface crack sources on turbine blades.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a surface strengthening method for nickel-based single-crystal superalloy blades, comprising the following steps:

[0008] The nickel-based single-crystal superalloy blades were subjected to segmented solution treatment, air cooling, aging treatment, sandblasting treatment, and electrolytic polishing treatment in sequence.

[0009] The segmented solution treatment includes a first solution treatment and a second solution treatment performed sequentially.

[0010] The first solution treatment is carried out in an oxygen-free atmosphere, while the second solution treatment is carried out in an oxygen-containing atmosphere.

[0011] Preferably, the time ratio of the first solution treatment to the second solution treatment is (3-5):1.

[0012] Preferably, the first solution treatment is performed in a vacuum or protective atmosphere;

[0013] The temperature of the first solution treatment is 1240-1280℃, the holding time is 1-2.5h, and the heating rate is 10-15℃ / min.

[0014] Preferably, the second solution treatment is carried out in an air atmosphere;

[0015] The temperature of the second solution treatment is 1150–1250℃, and the holding time is 0.2–1h.

[0016] Preferably, the initial sandblasting pressure is 0.6-0.8 MPa, the distance between the spray gun and the workpiece is 80-100 mm, and the quartz sand particle size is 0.18-0.25 mm.

[0017] Preferably, the anode for the electrolytic polishing process is a nickel-based single-crystal superalloy blade that has undergone sandblasting, and the cathode is lead;

[0018] The area of ​​the cathode is 2 to 3 times the area of ​​the anode.

[0019] Preferably, the electrolyte used in the electropolishing process includes a 30% (w / w) aqueous solution of phosphoric acid.

[0020] Preferably, the current density of the electropolishing treatment is 20–30 mA / dm². 3 The time is 3 to 5 minutes.

[0021] This invention provides a surface strengthening method for nickel-based single-crystal superalloy turbine blades, comprising the following steps: sequentially performing segmented solution treatment, air cooling, aging treatment, sandblasting treatment, and electrolytic polishing treatment on the nickel-based single-crystal superalloy blades; the segmented solution treatment includes a first solution treatment and a second solution treatment performed sequentially; the first solution treatment is performed in an oxygen-free atmosphere, and the second solution treatment is performed in an oxygen-containing atmosphere. The core of this surface strengthening method lies in the segmented solution treatment, which is first performed in an oxygen-free atmosphere, followed by surface pre-oxidation in an oxygen-containing atmosphere, and then air cooling to precipitate a secondary γ' phase on the alloy surface to strengthen the turbine blade; furthermore, the purpose of subsequent electrolytic polishing is to resolve the residual stress introduced during the removal of the surface oxide film, and to avoid recrystallization during the subsequent service of the turbine blade. This scheme effectively avoids the influence of induced recrystallization defects caused by surface strengthening with residual stress, and also eliminates concerns such as easy peeling and low strength of chemical coatings. By refining the microstructure of the strengthening phase on the surface of nickel-based single-crystal superalloy, the surface strength of the turbine blades can be improved. At the same time, there is no introduction of residual stress, making it more suitable for casting single-crystal turbine blades. On the other hand, by simply adjusting the oxygen environment conditions in the heat treatment process, without adding other substances to the surface, it is easier to process the subsequent thermal expansion coating, which greatly saves time, labor and economic costs.

[0022] Compared with existing technologies, the surface strengthening method of the present invention has the following superior effects:

[0023] 1) In the segmented solution treatment process, the solute gradient on the alloy surface is changed by introducing air, and the fine γ' phase precipitated on the turbine blade surface can improve its surface strength. Unlike traditional surface strengthening processes that introduce a large amount of plastic deformation, leading to surface recrystallization that affects subsequent service processes, this process does not require a coating, avoiding the problems of poor coating performance under high loads and poor adhesion to the substrate. It also eliminates the need for additional process equipment, greatly saving time, labor, and economic costs.

[0024] 2) This invention removes the oxide film on the surface through sandblasting and improves the surface roughness of the turbine blades by electropolishing, thus avoiding the recrystallization effect caused by the introduced residual stress.

[0025] 3) This invention refines the surface microstructure of the first-generation nickel-based single-crystal high-temperature alloy turbine blades, achieving surface reinforcement without affecting subsequent processing. It provides a good foundation for supplementing the coating layer for composite reinforcement or spraying thermal barrier coating. Attached Figure Description

[0026] Figure 1 This is a schematic flowchart of the surface strengthening method described in this invention;

[0027] Figure 2The image shows the microstructure of the first-generation nickel-based single-crystal superalloy turbine blade after the surface strengthening treatment described in Example 1.

[0028] Figure 3 A size comparison diagram of the γ' phase of the first-generation nickel-based single-crystal superalloy turbine blades before and after the surface strengthening treatment described in Example 1;

[0029] Figure 4 A comparison of the mechanical strength of the first-generation nickel-based single-crystal superalloy turbine blades after surface strengthening treatment as described in Example 1 and Comparative Example 1;

[0030] Figure 5 The image shows the microstructure of the first-generation nickel-based single-crystal superalloy turbine blade after the surface strengthening treatment described in Comparative Example 1. Detailed Implementation

[0031] like Figure 1 As shown, the present invention provides a surface strengthening method for nickel-based single-crystal superalloy blades, comprising the following steps:

[0032] The nickel-based single-crystal superalloy blades were subjected to segmented solution treatment, air cooling, aging treatment, sandblasting treatment, and electrolytic polishing treatment in sequence.

[0033] The segmented solution treatment includes a first solution treatment and a second solution treatment performed sequentially.

[0034] The first solution treatment is carried out in an oxygen-free atmosphere, while the second solution treatment is carried out in an oxygen-containing atmosphere.

[0035] The present invention does not impose any special limitations on the composition of the nickel-based single crystal high-temperature alloy blades; any composition well known to those skilled in the art can be used.

[0036] In this invention, the time ratio of the first solution treatment to the second solution treatment is preferably (3-5):1, more preferably (3-4):1, and most preferably 3:1.

[0037] In this invention, the first solution treatment is carried out in a vacuum or protective atmosphere; the protective atmosphere is preferably an argon atmosphere or a nitrogen atmosphere; the temperature of the first solution treatment is preferably 1240-1280℃, more preferably 1240-1250℃, and most preferably 1250℃; the holding time is preferably 1-2.5h, more preferably 1-2h, and most preferably 1h; the heating rate is preferably 10-15℃ / min, more preferably 10-12℃ / min, and most preferably 10℃ / min.

[0038] In this invention, the second solution treatment is preferably carried out in an air atmosphere; the temperature of the second solution treatment is preferably 1150–1250°C, more preferably 1150–1180°C, and most preferably 1150°C; the holding time is preferably 0.2–1 h, more preferably 0.25–0.33 h, and most preferably 0.33 h. After the second solution treatment is completed, this invention also preferably includes air cooling. This invention does not have any special limitations on the air cooling process, and any process well known to those skilled in the art can be used.

[0039] In this invention, the preferred method for the segmented solution treatment process is to place the nickel-based single-crystal high-temperature alloy blade in a vacuum heat treatment furnace, first perform solution treatment under vacuum or protective atmosphere conditions, and then introduce flowing air for further solution treatment.

[0040] In this invention, the introduction of flowing air during the second solution treatment is to provide an oxidation environment for the nickel-based single-crystal superalloy, forming a solute gradient on the alloy surface, which will precipitate fine γ' strengthening phases during subsequent solution aging, thereby achieving surface strengthening.

[0041] In this invention, the air cooling after the first and second solution treatments is preferably replaced by gas quenching or oil quenching.

[0042] The present invention does not impose any special limitations on the aging process, and any aging process well known to those skilled in the art can be used. In an embodiment of the present invention, the aging process specifically involves: heating from room temperature to 1080°C under vacuum conditions at a heating rate of 10°C / min, holding at that temperature for 4 hours, and then air cooling; then heating from room temperature to 845°C under vacuum conditions at a heating rate of 10°C / min, holding at that temperature for 24 hours, and then air cooling; or heating from room temperature to 1080°C under vacuum conditions at a heating rate of 10°C / min, holding at that temperature for 4 hours, and then air cooling.

[0043] In this invention, the aging treatment promotes the formation and growth of precipitates in the alloy. This process helps to enhance the high-temperature mechanical properties of the high-temperature alloy and improve its creep resistance and oxidation resistance.

[0044] After the aging process is completed, the present invention preferably includes air cooling. The present invention does not have any special limitations on the air cooling process, and any process known to those skilled in the art can be used.

[0045] In this invention, the initial sandblasting pressure is preferably 0.6-0.8 MPa, more preferably 0.6-0.7 MPa, and most preferably 0.6 MPa; the distance between the spray gun and the workpiece is preferably 80-100 mm, more preferably 90-100 mm, and most preferably 100 mm; the quartz sand particle size is preferably 0.18-0.25 mm, more preferably 0.18-0.20 mm, and most preferably 0.18 mm (80 mesh).

[0046] In this invention, the purpose of the sandblasting treatment is to remove the oxide film that appears during the segmented solution treatment stage. To prevent the plastic deformation introduced during the sandblasting process from causing nucleation and recrystallization during the service of the turbine blade, electrolytic polishing technology is used to remove the applied stress.

[0047] After the sandblasting process is completed, the present invention preferably includes ultrasonic cleaning; the cleaning agent used for ultrasonic cleaning is preferably a water-based metal cleaning agent; the temperature of ultrasonic cleaning is preferably room temperature, the time is preferably 30-60 min, more preferably 35-55 min, and most preferably 40-50 min.

[0048] In this invention, the anode for the electrolytic polishing treatment is preferably a nickel-based single-crystal high-temperature alloy blade subjected to sandblasting, and the cathode is preferably lead; the area of ​​the cathode is preferably 2 to 3 times the area of ​​the anode, more preferably 2 to 2.5 times, and most preferably 2 times. The electrolyte used in the electrolytic polishing treatment preferably includes a 30% (w / w) aqueous solution of phosphoric acid; the current density of the electrolytic polishing treatment is preferably 20 to 30 mA / dm³. 3 More preferably 20-25 mA / dm 3 The optimal value is 20mA / dm. 3 The preferred time is 3 to 5 minutes, more preferably 3.5 to 4.5 minutes, and most preferably 3.8 to 4.2 minutes.

[0049] The surface strengthening method for nickel-based single-crystal high-temperature alloy blades provided by the present invention will be described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0050] Comparative Example 1

[0051] The first-generation nickel-based single-crystal superalloy turbine blades (IN792LC turbine blades) were subjected to solution treatment in a vacuum heat treatment furnace. The solution treatment conditions were as follows: first, under vacuum conditions, the temperature was increased from room temperature to 1250°C at a heating rate of 10°C / min, and the solution was maintained for 2.0 hours, followed by air cooling; then, an aging treatment was performed. The aging treatment process involved heating from room temperature to 1080°C under vacuum conditions at a heating rate of 10°C / min, holding at that temperature for 4 hours, and air cooling; then, under vacuum conditions, the temperature was increased from room temperature to 845°C at a heating rate of 10°C / min. The turbine blades were annealed at ℃ for 24 hours and then air-cooled. After aging, the turbine blades were sandblasted to remove the surface oxide film. The initial sandblasting pressure was 0.8 MPa, the distance between the blasting gun and the workpiece was 80 mm, and the quartz sand particle size was 0.18 mm. After ultrasonic cleaning, the sandblasted turbine blades were used as the anode, and lead was used as the cathode. The electrode area of ​​the cathode was 2.5 times that of the anode. The electrolyte was a 20% phosphoric acid aqueous solution, and the current density for electrolytic polishing was 30 mA / dm³. 3 The time is 3 minutes;

[0052] Figure 5 The image shows the microstructure of the first-generation nickel-based single-crystal superalloy turbine blade after the above treatment. Figure 5 It can be seen that after the above treatment, all the outer edge surfaces of the first-generation nickel-based single crystal high-temperature alloy turbine blades show γ' phase loss zones, exhibiting hardness degradation.

[0053] Example 1

[0054] The first-generation nickel-based single-crystal superalloy turbine blades (IN792LC turbine blades) were subjected to segmented solution treatment in a vacuum heat treatment furnace. First, under vacuum conditions, the temperature was increased from room temperature to 1250°C at a heating rate of 10°C / min, and solution was maintained for 1.5 hours. Then, under flowing air conditions, the solution was maintained for another 0.5 hours, followed by air cooling. Afterward, an aging treatment was performed. The aging treatment process involved heating from room temperature to 1080°C under vacuum conditions at a heating rate of 10°C / min, holding at that temperature for 4 hours, and then air cooling. Finally, under vacuum conditions, the temperature was increased from room temperature to 1080°C at a heating rate of 10°C / min, and solution was maintained for another 4 hours. The turbine blades were heated to 845℃ and held for 24 hours, then air-cooled. After aging, the turbine blades were sandblasted to remove the surface oxide film. The initial sandblasting pressure was 0.6 MPa, the distance between the spray gun and the workpiece was 100 mm, and the quartz sand particle size was 0.18 mm. After ultrasonic cleaning, the sandblasted turbine blades were used as the anode, and lead was used as the cathode. The electrode area of ​​the cathode was twice that of the anode. The electrolyte was a 30% phosphoric acid aqueous solution, and the current density for electrolytic polishing was 20 mA / dm². 3 The time is 5 minutes;

[0055] Fifty sets of the above-mentioned turbine blades were selected and subjected to the above-mentioned surface strengthening treatment simultaneously.

[0056] Figure 2 The image shows the microstructure of the first-generation nickel-based single-crystal superalloy turbine blade after the aforementioned surface strengthening treatment. Figure 2 It can be seen that after the surface strengthening treatment, fine γ' phases appear on the outer edge surface of all turbine blades;

[0057] Figure 3 This is a size comparison diagram of the γ' phase after surface strengthening treatment of the aforementioned first-generation nickel-based single-crystal superalloy turbine blades. Figure 3 It can be seen that after surface strengthening treatment, the γ' phase size on the surface of the first-generation nickel-based single-crystal high-temperature alloy turbine blade is reduced by 52.53% compared with the internal structure.

[0058] Figure 4 The table below shows a comparison of the mechanical strength of the first-generation nickel-based single-crystal superalloy turbine blade after the surface strengthening treatment described above and the first-generation nickel-based single-crystal superalloy turbine blade after the treatment in Comparative Example 1 (the upper figure shows the turbine blade after the treatment in Example 1, and the lower figure shows the turbine blade after the treatment in Comparative Example 1). Specific values ​​are shown in Table 1. Figure 4 It can be seen that the strength of the first-generation nickel-based single-crystal high-temperature alloy turbine blade after the surface strengthening treatment described in this invention is increased by 37.3% compared with Comparative Example 1, and it has excellent surface strengthening effect.

[0059] Table 1. Comparison of mechanical strength data of turbine blades after treatment in Example 1 and Comparative Example 1.

[0060]

[0061] Example 2

[0062] The first-generation nickel-based single-crystal superalloy turbine blade (IN792LC turbine blade) was subjected to segmented solution treatment in a vacuum heat treatment furnace. First, it was heated from room temperature to 1250℃ at a heating rate of 10℃ / min under vacuum conditions for 1 hour, followed by another hour of solution treatment under flowing air. After air cooling, it underwent aging treatment, which involved heating from room temperature to 1080℃ at a heating rate of 10℃ / min under vacuum conditions, holding at that temperature for 4 hours, and then air cooling. The aged turbine blade was then subjected to sandblasting to remove the surface oxide film. The initial sandblasting pressure was 0.8 MPa, the distance between the blasting gun and the workpiece was 80 mm, and the quartz sand particle size was 0.18 mm. After ultrasonic cleaning, the sandblasted turbine blade was used as the anode, and lead was used as the cathode. The electrode area of ​​the cathode was 2.5 times that of the anode. The electrolyte was a 20% phosphoric acid aqueous solution, and the current density for electrolytic polishing was 30 mA / dm². 3 The time is 3.5 minutes;

[0063] After the above surface strengthening treatment, fine γ' phases appeared on the outer edge surface of all turbine blades, and statistical comparison of the γ' phase size showed obvious refinement.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the original invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for surface strengthening of nickel-based single-crystal superalloy blades, characterized in that, Includes the following steps: The nickel-based single-crystal superalloy blades were subjected to segmented solution treatment, air cooling, aging treatment, sandblasting treatment, and electrolytic polishing treatment in sequence. The segmented solution treatment includes a first solution treatment and a second solution treatment performed sequentially. The first solution treatment is carried out in an oxygen-free atmosphere, and the second solution treatment is carried out in an oxygen-containing atmosphere; The time ratio of the first solution treatment to the second solution treatment is (3~5):1; The first solution treatment is performed in a vacuum or protective atmosphere; The temperature of the first solution treatment is 1240~1280℃, the holding time is 1~2.5h, and the heating rate is 10~15℃ / min; The second solution treatment is carried out in an air atmosphere; The temperature of the second solution treatment is 1150~1250℃, and the holding time is 0.2~1h.

2. The surface strengthening method as described in claim 1, characterized in that, The initial sandblasting pressure for the sandblasting process is 0.6~0.8MPa, the distance between the spray gun and the workpiece is 80~100mm, and the particle size of the quartz sand is 0.18~0.25mm.

3. The surface strengthening method as described in claim 1, characterized in that, The anode for the electrolytic polishing process is a nickel-based single-crystal high-temperature alloy blade that has undergone sandblasting, and the cathode is lead. The area of ​​the cathode is 2 to 3 times the area of ​​the anode.

4. The surface strengthening method as described in claim 1 or 3, characterized in that, The electrolyte used in the electropolishing process includes a 30% (w / w) aqueous solution of phosphoric acid.

5. The surface strengthening method as described in claim 4, characterized in that, The current density for the electropolishing process is 20~30 mA / dm. 3 The time is 3 to 5 minutes.

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