Method for improving high-temperature-resistant fatigue damage of high-temperature alloy by coupling grain boundary engineering and laser shock

Abstract

The invention discloses a method for improving high-temperature-resistant fatigue damage of a high-temperature alloy by coupling grain boundary engineering and laser shock, which comprises the following steps of: performing circulating cold rolling and annealing treatment by taking a GH5188 cobalt-based high-temperature alloy plate as an object based on the idea of grain boundary engineering to remarkably improve the proportion and connectivity of a high-coincidence lattice grain boundary (namely a special grain boundary); the capability of inhibiting generation and expansion of internal cracks of the alloy is improved; performing plastic deformation on the surface of the material through laser shock, refining surface grains, forming a high residual compressive stress layer on the surface of the material, and inhibiting fatigue cracks from invading or extruding from the surface of the material; and grain boundary engineering is combined with laser shock, a grain boundary-surface cross-scale collaborative optimization system is established, and the along-grain fatigue fracture resistance and the surface fatigue damage resistance of an internal structure are synergistically improved.

Description

Technical Field

[0001] The invention discloses a method for improving high-temperature fatigue damage resistance of a high-temperature alloy by coupling grain boundary engineering and laser shock, and belongs to the technical field of metal material deformation and heat treatment and laser processing. Background Art

[0002] As a high-performance material, GH5188 cobalt-based superalloy is widely used in aero-engine hot-end components due to its excellent high-temperature strength, creep resistance, oxidation resistance, and fatigue resistance. However, due to the complex temperatures and cyclic loads to which superalloys are subjected during use, they are prone to fatigue damage and failure, seriously impacting the safety and reliability of aero-engines.

[0003] At present, researchers have proposed methods to improve the fatigue properties of materials, mainly including grain refinement, grain boundary engineering, surface strengthening, additive manufacturing and nano-precipitation strengthening. Although these methods can achieve remarkable results in other materials, they still have obvious shortcomings in solving the fatigue failure problem of the current GH5188 high-temperature alloy in service environment. Grain refinement, as a classic method to improve the mechanical properties of metal materials, will greatly increase the proportion of grain boundaries inside the material, effectively enhance the hindering effect on fatigue crack propagation, and at the same time complicate and segregate the crack propagation path to delay crack propagation. However, under high temperature conditions, fine-grained structures (especially ultrafine-grained and nano-crystalline structures) have low thermal stability and are prone to coarsening and grain boundary migration, which reduces the strength and fatigue properties of the material. Therefore, the large-scale grain refinement of the overall organization has insufficient structural stability in high-temperature environments, and the strengthening effect may degrade, so it is not suitable for improving the fatigue properties of GH5188 alloy in complex high-temperature environments.

[0004] In summary, although existing methods have made considerable progress in improving the fatigue performance of metal materials, a single method is difficult to simultaneously address the problems of high-temperature weakening of internal grain boundaries and surface fatigue cracks, and cannot fundamentally improve the fatigue performance of the GH5188 hot end components.

[0005] Therefore, developing a simple, efficient, low-cost process method that can significantly improve the fatigue life of GH5188 cobalt-based high-temperature alloy not only has important theoretical research value, but also has important practical significance for improving the performance level of my country's high-temperature alloy materials and meeting the needs of high-end industrial applications. Summary of the Invention

[0006] Aiming at the fatigue failure problem of GH5188 hot end components caused by high-temperature intergranular fracture and surface fatigue cracks under service conditions, based on a detailed investigation of the current research status at home and abroad and the latest developments in GH5188 alloy fatigue research, the present invention proposes a method for improving the high-temperature fatigue damage resistance of high-temperature alloys by coupling grain boundary engineering and laser shock, which solves the limitation of a single strategy with separate action domains (grain boundary engineering to optimize the internal grain boundary network vs. laser shock to optimize surface properties) that is difficult to comprehensively improve the high-temperature fatigue performance.

[0007] The present invention adopts a "both internal and external strengthening" approach, that is, through grain boundary engineering, a GH5188 plate with optimized grain boundary characteristic distribution is obtained, and then the surface of the plate with optimized grain boundary characteristic distribution is strengthened by laser shock peening technology to prepare a gradient structure GH5188 plate with optimized grain boundary characteristic distribution, coarse grains inside, fine grains on the surface, and high residual compressive stress; this method can improve the mechanical properties and fatigue life of high-temperature alloys, and is simple to operate, low-cost, green and pollution-free. To achieve the above purpose, the present invention adopts the following technical solution: a method for improving the high-temperature fatigue damage resistance of high-temperature alloys by coupling grain boundary engineering and laser shock peening, comprising the following steps:

[0008] (1) Grain boundary engineering treatment: The shape of the high-temperature alloy is adjusted to be flat, and rolling, annealing heat treatment, and water cooling are performed in sequence, and then the rolling, annealing heat treatment, and water cooling are repeated twice to obtain the high-temperature alloy after grain boundary engineering treatment;

[0009] (2) Laser shock treatment: clean the surface of the high-temperature alloy obtained in step (1), coat the absorption layer on the cleaned material surface, place the sample coated with the absorption layer material into the initial position of the laser shock path, turn on the laser, position the laser spot at the initial position of the shock path, turn on the water robot, adjust the water outlet position so that the water sprayed can just form a uniform constraint layer on the sample surface; set the laser parameters, ensure that the links between the various robots are unobstructed, import the simulation path, and perform laser shock strengthening on the sample surface.

[0010] Preferably, the high temperature alloy described in the present invention is GH5188 cobalt-based high temperature alloy

[0011] Preferably, the rolling conditions in step (1) of the present invention are: a rotation speed of 1 to 5 rpm, a frequency of 1 to 5 Hz, and a rolling deformation of 5% to 15%.

[0012] Preferably, the heat treatment conditions in step (1) of the present invention are: keeping warm at 1050°C-1150°C for 30min-60min.

[0013] Preferably, the absorption layer in step (2) of the present invention is aluminum foil. During the experiment, it was found that when black tape is used as the absorption layer material, it often breaks, seriously affecting the quality of material processing, while when aluminum foil is used, the occurrence of breakage can be greatly reduced. Therefore, 120 μm thick aluminum foil produced by 3M Company is selected as the absorption layer material. When coating the absorption layer, gaps and bubbles should be avoided as much as possible to prevent the absorption layer from breaking during the impact process.

[0014] Preferably, the water outlet of the mechanical arm of the waterway robot of the present invention has an inclination angle of 30-60°, so that the deionized water forms a uniform water film with a thickness of 1-2 mm on the surface of the sample.

[0015] Preferably, the laser parameters in step (2) of the present invention are: pulse energy of 1-8 J, pulse width of 18-20 ns, circular spot diameter of 2-5 mm, spot overlap rate of 30-50%, frequency of 1-5 Hz, and number of impacts of 1-5 times.

[0016] The CSL grain boundary described in the present invention is: when two adjacent grains rotate around a certain rotation axis at a specific angle, there will be some overlap of atomic positions in their crystal lattices. These overlapping points constitute a super-periodic lattice, called the coincident position lattice (CSL). Σ is a key parameter for characterizing the CSL grain boundary, which is defined as the ratio of the unit cell volume of the coincident lattice to the unit cell volume of a single grain; mathematically expressed as: Σ = unit cell volume of the coincident lattice / unit cell volume of a single grain / unit cell volume of a single grain. The smaller the value of Σ, the higher the proportion of overlapping positions and the more ordered the grain boundary structure.

[0017] The low Σ3 grain boundary described in the present invention is a twin boundary, which is commonly found in the twin boundaries of face-centered cubic (FCC) metals and corresponds to a 60° rotation around the

[111] axis.

[0018] The laser shock coupled grain boundary engineering of the present invention is proposed to address the fatigue failure problem of GH5188 hot end components caused by high-temperature intergranular fracture and surface fatigue cracks under service conditions. It is based on a detailed investigation of the current research status at home and abroad and the grasp of the latest developments in GH5188 alloy fatigue research. Combining grain boundary engineering with laser shock can establish a "grain boundary-surface" cross-scale collaborative optimization system, synergistically improve the ability of internal organizations to resist intergranular fatigue fracture and surface fatigue damage, and achieve "internal and external improvement" of material fatigue performance.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The method of the present invention can increase the proportion of low-ΣCSL grain boundaries in the material without changing the alloy composition, thereby obtaining a plate with optimized grain boundary feature distribution; it can not only improve the corrosion resistance and fatigue resistance of the material, but also reduce the defect density at the grain boundaries, further enhancing the high-temperature strength of the high-temperature alloy.

[0021] (2) The method of the present invention not only increases the proportion of low ΣCSL grain boundaries in the alloy, but also increases the proportion of low Σ3 grain boundaries.

[0022] (3) The present invention ensures the uniformity of the grain boundary engineering layer through uniform rolling deformation and precise annealing control; this uniform grain boundary structure not only improves the overall performance of the material, but also reduces the heterogeneity of local performance, further improving the reliability and service life of the material.

[0023] (4) The present invention proposes a "both internal and external" strengthening method, that is, a plate with optimized grain boundary characteristic distribution is obtained through grain boundary engineering, and then laser shock is performed on the surface of the plate with optimized grain boundary characteristic distribution to obtain a gradient structure plate with coarse grains inside, fine grains on the surface and high residual compressive stress; this method can effectively improve the mechanical properties and fatigue life of the alloy.

[0024] (5) By using the grain boundary engineering coupled laser shock strengthening method of the present invention, the proportion of low ΣCSL grain boundaries inside the high-temperature alloy specimen can be increased to more than 70%, the surface microhardness can be increased by more than 60%, the room temperature tensile strength can be increased by more than 29%, the yield strength can be increased by more than 78%, and the fatigue life can be increased by more than 46%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 (a), (b), (c), and (d) are the special grain boundary distribution maps of the initial, GBE-1, GBE-2, and GBE-3, respectively.

[0026] Figure 2 This is a diagram of the special grain boundary ratio before and after grain boundary engineering treatment.

[0027] Figure 3 Microhardness diagram before and after laser shock coupled grain boundary engineering.

[0028] Figure 4 The stress-strain curves before and after laser shock coupled grain boundary engineering.

[0029] Figure 5 Summary of strength and elongation before and after laser shock coupled grain boundary engineering.

[0030] Figure 6 Fatigue life diagram before and after grain boundary engineering.

[0031] Figure 7、 Figure 8 Fatigue life diagram before and after laser shock coupled grain boundary engineering. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0033] The embodiment of the present invention is described by taking the GH5188 plate as an example.

[0034] Example 1

[0035] (1) GH5188 alloy was selected and processed into a size (length × width × thickness) of 40 mm × 100 mm × 3.2 mm by wire cutting. The shape of the GH5188 alloy was trimmed. The upper and lower surfaces of the plate needed to be trimmed flat and symmetrical to ensure uniform deformation of the material during rolling.

[0036] (2) The sample after the treatment in step (1) is subjected to a 5% cold working deformation treatment at room temperature using a rolling mill, with the rolling mill operating at a frequency of 5 Hz and a speed of 5 rpm.

[0037] (3) The GH5188 alloy deformed in step (2) is subjected to annealing heat treatment again, kept at 1100° C. for 45 minutes, and then water-cooled.

[0038] (4) Then repeat steps (2) and (3) twice to obtain the grain boundary characteristic distribution GBE-1 of the GH5188 alloy after grain boundary engineering treatment.

[0039] (6) Apply an absorbent layer of aluminum foil to the surface of the cleaned material. During the coating process, try to avoid creating gaps and bubbles on the surface to prevent the absorbent layer from breaking during the impact process.

[0040] (7) The sample coated with the absorption layer material is clamped on the manipulator, and the manipulator is remotely controlled to move the sample into the initial position of the laser impact path.

[0041] (8) Turn on the laser and position the laser spot at the initial position of the impact path.

[0042] (9) Turn on the waterway robot, adjust the water outlet angle of the waterway robot arm to 50°, and adjust the position of the water outlet so that the water sprayed can just form a uniform constraint layer on the surface of the sample; so that the deionized water forms a uniform water film with a thickness of 1-2 mm on the surface of the sample.

[0043] (10) Enter the laser shock peening program at the operating end, set the laser parameters, set the laser energy to 8J, the pulse width to 20ns, the circular spot diameter to 2mm×2mm, the spot overlap rate to 50%, and the frequency to 5Hz. Ensure that the links between the various robots are unobstructed, import the simulation path, and perform laser shock peening on the surface of the sample with three shock times; the sample is named GBE-1+LSP-3.

[0044] (11) After the impact, remove the absorption layer and clean it with ethanol.

[0045] (12) Polishing is used to remove the appropriate thickness of the surface damage layer after laser shock strengthening; after laser shock strengthening, the surface of the strengthened area is polished or ground to remove at least 20 μm of the strengthening layer depth, thereby ensuring the surface smoothness while reducing the damage to the pressure layer to a certain extent.

[0046] The grain boundary characteristics of the sample were measured by EBSD (electron backscatter diffraction) method. Figure 1 (b) shows that the proportion of low ΣCSL grain boundaries increases to 85.09%, and the proportion of low Σ3 grain boundaries increases to 77.3%. Figure 2 As shown in the figure, the surface hardness measured by microhardness tester is significantly improved, from 257.67HV before strengthening to 376.96HV, and the hardness is increased by 46.30%. Figure 3 As shown in the figure, the room temperature yield strength of GH5188 alloy measured by a universal tensile testing machine increased from 441.71MPa to 788.79MPa, an increase of 78.58%, and the tensile strength increased from 858.66MPa to 1108.06MPa, an increase of 29.05%. Figure 4 As shown in the figure, the fatigue life of GBE-1+LSP-3 was increased from the initial 9401 cycles to 14477 cycles, an increase of 53.99%, and an increase of 43.45% compared to the 10092 cycles of GBE-1. The fatigue life of GBE-1+LSP-5 was increased from the initial 9401 cycles to 10809 cycles, an increase of 14.98%, and an increase of 7.10% compared to the 10092 cycles of GBE-1. Figure 6 、 Figure 7 shown.

[0047] Example 2

[0048] (1) GH5188 alloy was selected and processed into a size (length × width × thickness) of 40 mm × 100 mm × 3.2 mm by wire cutting. The shape of the GH5188 alloy was trimmed. The upper and lower surfaces of the plate needed to be trimmed flat and symmetrical to ensure uniform deformation of the material during rolling.

[0049] (2) The sample after the treatment in step (1) is subjected to a 10% cold working deformation treatment at room temperature using a rolling mill, with the rolling mill operating at a frequency of 5 Hz and a speed of 5 rpm.

[0050] (3) The GH5188 alloy deformed in step (2) is subjected to annealing heat treatment again, kept at 1100° C. for 60 minutes, and then water-cooled.

[0051] (4) Then repeat steps (2) and (3) twice to obtain the grain boundary characteristic distribution GBE-2 of the GH5188 alloy after grain boundary engineering treatment.

[0052] (6) Apply an absorbent layer of aluminum foil to the surface of the cleaned material. During the coating process, try to avoid creating gaps and bubbles on the surface to prevent the absorbent layer from breaking during the impact process.

[0053] (7) The sample coated with the absorption layer material is clamped on the manipulator, and the manipulator is remotely controlled to move the sample into the initial position of the laser impact path.

[0054] (8) Turn on the laser and position the laser spot at the initial position of the impact path.

[0055] (9) Turn on the water channel robot and adjust the water outlet angle of the water channel robot arm to 60° so that the deionized water forms a uniform water film with a thickness of 1-2 mm on the surface of the sample.

[0056] (10) Enter the laser shock peening program at the operating end, set the laser parameters, set the laser energy to 8J, the pulse width to 20ns, the circular spot diameter to 2mm×2mm, the spot overlap rate to 50%, and the frequency to 5Hz. Ensure that the links between the various robots are unobstructed, import the simulation path, and perform laser shock peening on the surface of the sample with three shock times; the sample is named GBE-2+LSP-3.

[0057] (11) After the impact, remove the absorption layer and clean it with ethanol.

[0058] (12) Polishing is used to remove the appropriate thickness of the surface damage layer after laser shock peening. After laser shock peening, the surface of the strengthened area is polished or ground to remove at least 20 μm of the strengthening layer depth, which can ensure the surface smoothness while reducing the damage to the pressure layer to a certain extent.

[0059] The grain boundary characteristics of the sample were measured by EBSD (electron backscatter diffraction) method. Figure 1 (c) shows that the proportion of low ΣCSL grain boundaries increases to 74.28%, and the proportion of low Σ3 grain boundaries increases to 62.50%. Figure 2As shown in the figure, the surface hardness measured by microhardness tester is significantly improved, from 257.67HV before strengthening to 396.27HV, and the hardness is increased by 53.79%. Figure 3 As shown in Figure 2, the room temperature yield strength of GH5188 alloy measured by a universal tensile testing machine increased from 441.71MPa to 813.33MPa, an increase of 84.13%, and the tensile strength increased from 858.66MPa to 1135.03MPa, an increase of 32.19%. Figure 4 As shown in the figure, the fatigue life of GBE-2 was measured by SANS CMT4104 electronic tensile testing machine and increased from the initial 9401 cycles to 9628 cycles, an increase of 2.41%. Figure 6 shown.

[0060] Example 3

[0061] (1) GH5188 alloy was selected and processed into a size (length × width × thickness) of 40 mm × 100 mm × 3.2 mm by wire cutting. The shape of the GH5188 alloy was trimmed. The upper and lower surfaces of the plate needed to be trimmed flat and symmetrical to ensure uniform deformation of the material during rolling.

[0062] (2) The sample after the treatment in step (1) is subjected to a 15% cold working deformation treatment at room temperature using a rolling mill, with the rolling mill operating at a frequency of 5 Hz and a speed of 5 rpm.

[0063] (3) The GH5188 alloy deformed in step (2) is subjected to annealing heat treatment again, kept at 1100° C. for 30 minutes, and then water-cooled.

[0064] (4) Then repeat steps (2) and (3) twice to obtain the grain boundary characteristic distribution GBE-3 of the GH5188 alloy after grain boundary engineering treatment.

[0065] (6) Apply an absorbent layer of aluminum foil to the surface of the cleaned material. During the coating process, try to avoid creating gaps and bubbles on the surface to prevent the absorbent layer from breaking during the impact process.

[0066] (7) The sample coated with the absorption layer material is clamped on the manipulator, and the manipulator is remotely controlled to move the sample into the initial position of the laser impact path.

[0067] (8) Turn on the laser and position the laser spot at the initial position of the impact path.

[0068] (9) Turn on the water channel robot and adjust the water outlet angle of the water channel robot arm to 30° so that the deionized water forms a uniform water film with a thickness of 1-2 mm on the surface of the sample.

[0069] (10) Enter the laser shock peening program at the operating end, set the laser parameters, set the laser energy to 8J, the pulse width to 20ns, the circular spot diameter to 2mm×2mm, the spot overlap rate to 50%, and the frequency to 5Hz. Ensure that the links between the various robots are unobstructed, import the simulation path, and perform laser shock peening on the surface of the sample with three shock times; the sample is named GBE-3+LSP-3.

[0070] (11) After the impact, remove the absorption layer and clean it with ethanol.

[0071] (12) Polishing is used to remove the appropriate thickness of the surface damage layer after laser shock strengthening; after laser shock strengthening, the surface of the strengthened area is polished or ground to remove at least 20 μm of the strengthening layer depth, thereby ensuring the surface smoothness while reducing the damage to the pressure layer to a certain extent.

[0072] The grain boundary characteristics of the sample were measured by EBSD (electron backscatter diffraction) method. Figure 1 As shown in (d), the proportion of low ΣCSL grain boundaries increases to 70.31%, and the proportion of low Σ3 grain boundaries increases to 60.00%. Figure 2 As shown in the figure, the surface hardness measured by microhardness tester is significantly improved, from 257.67HV before strengthening to 430.32HV, and the hardness is increased by 67.00%. Figure 3 As shown in the figure, the room temperature yield strength of GH5188 alloy was measured by a universal tensile testing machine to be 848.27 MPa, which was 92.04% higher than the initial 441.71 MPa. The tensile strength increased from 858.66 to 1146.31 MPa, an increase of 33.50%, and the elongation decreased to 41.68%. Figure 4 As shown in the figure, the fatigue life of the steel sheet was increased from the initial 9401 cycles to 13758 cycles using a SANS CMT4104 electronic tensile testing machine, an increase of 46.35%. Figure 5 shown.

[0073] The fatigue life of GBE-3+LSP-3 was measured by SANS CMT4104 electronic tensile testing machine and increased from the initial 9401 cycles to 13758 cycles, an increase of 46.35%, which was 22.36% higher than the 11244 cycles of GBE-3. However, the fatigue life of GBE-3+LSP-5 decreased from the initial 9401 cycles to 9086 cycles, a decrease of 3.35%, which was 19.19% lower than the 11244 cycles of GBE-3. Figure 6 、 Figure 8 shown.

[0074] The above examples show that grain boundary engineering can improve the high-temperature fatigue performance of GH5188, but the improvement effect is limited. When laser shock is applied to it, its fatigue performance is further improved, and its high-temperature fatigue performance can be improved by up to 53.99%. In the present invention, when the inventors want to apply more laser shocks to further improve the high-temperature fatigue performance of GH5188, they find that its high-temperature fatigue performance actually decreases, and is even lower than the initial fatigue performance. It can be seen that when the number of shocks increases, the residual compressive stress on the surface of the material tends to be saturated, the surface roughness will deteriorate, and surface microcracks will be induced, which will become the source of fatigue cracks, thereby reducing fatigue performance.

[0075] The contents illustrated in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, rather than to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention made by those skilled in the art shall fall within the scope defined by the claims attached to the present application.

Claims

1. A method for improving high temperature fatigue damage resistance of high temperature alloys by coupling grain boundary engineering and laser shock, characterized in that: The steps include: (1) Grain boundary engineering treatment: Adjust the shape of the high-temperature alloy to be flat, and then perform rolling, annealing heat treatment, water cooling in sequence, and then repeat rolling, annealing heat treatment, and water cooling twice to obtain the high-temperature alloy after grain boundary engineering treatment; (2) Laser shock treatment: clean the surface of the high-temperature alloy obtained in step (1), coat the absorption layer on the cleaned material surface, place the sample coated with the absorption layer material into the initial position of the laser shock path, turn on the laser, position the laser spot at the initial position of the shock path, turn on the water robot, adjust the water outlet position so that the water sprayed can just form a uniform constraint layer on the sample surface; set the laser parameters, ensure that the links between the various robots are unobstructed, import the simulation path, and perform laser shock strengthening on the sample surface.

2. The method for improving high-temperature fatigue damage resistance of high-temperature alloys by coupling grain boundary engineering and laser shock according to claim 1, characterized in that: The high-temperature alloy is GH5188 cobalt-based high-temperature alloy.

3. The method for improving high-temperature fatigue damage resistance of high-temperature alloys by coupling grain boundary engineering and laser shock according to claim 1, characterized in that: The rolling conditions in step (1) are: a rotation speed of 1 to 5 rpm, a frequency of 1 to 5 Hz, and a rolling deformation of 5% to 15%.

4. The method of improving high-temperature fatigue damage resistance of high-temperature alloys by coupling grain boundary engineering and laser shock according to claim 1, characterized in that: The heat treatment conditions in step (1) are: keeping warm at 1050°C-1150°C for 30min-60min.

5. The method of improving high temperature fatigue damage resistance of high temperature alloys by coupling grain boundary engineering and laser shock according to claim 1, characterized in that: The absorption layer in step (2) is aluminum foil.

6. The method of improving high temperature fatigue damage resistance of high temperature alloys by coupling grain boundary engineering and laser shock according to claim 1, characterized in that: The water outlet of the water robot's mechanical arm is tilted at an angle of 30-60°, so that the deionized water forms a uniform water film with a thickness of 1-2 mm on the surface of the sample.

7. The method of improving high temperature fatigue damage resistance of high temperature alloys by coupling grain boundary engineering and laser shock according to claim 1, characterized in that: The laser parameters in step (2) are: pulse energy of 1-8 J, pulse width of 18-20 ns, circular spot diameter of 2-5 mm, spot overlap rate of 1-50%, frequency of 1-5 Hz, and number of impacts of 1-5 times.

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