A method of improving the fatigue performance of a metal blade and a blade processed by the method

Abstract

This invention provides a method for improving the fatigue performance of metal blades and blades processed by this method. It addresses the technical problems inherent in traditional surface strengthening techniques for improving the fatigue performance of metal blades, such as the gradual attenuation of residual compressive stress under high-temperature conditions, the balance between uniformity and consistency of strengthening, and the negative effects of the strengthening process itself. The method for improving the fatigue performance of metal blades provided by this invention employs physical vapor deposition (PVD) or chemical vapor deposition (CVD) to directly deposit a ceramic coating on the surface of the metal blade substrate. This deposition method, combined with the constraint conditions of the ceramic coating, not only further reduces the stress amplitude borne by the blade, but also significantly delays or even prevents the initiation of fatigue cracks and effectively inhibits the crack propagation rate in the initial stage, thereby improving the fatigue resistance of the blade. Simultaneously, it effectively increases the blade's stiffness and reduces its plastic deformation.

Description

Technical Field

[0001] This invention relates to metal blades and methods for improving the fatigue performance of metal blades, specifically to a method for improving the fatigue performance of metal blades by introducing a ceramic coating and blades processed by the method. Background Technology

[0002] In power plants such as aero engines and gas turbines, metal blades (such as turbine blades and compressor blades) are core rotating components. They operate in extremely harsh environments for extended periods, enduring complex alternating stresses caused by high temperatures, high centrifugal forces, and high-cycle cyclic loads induced by unsteady airflow disturbances. Although these alternating stresses are below the material's yield strength, they can easily lead to the initiation and propagation of cracks at minute defects on the metal blade surface under long-term action, ultimately resulting in high-cycle fatigue failure. This has become a key bottleneck restricting the lifespan of metal blades and the overall reliability of the system.

[0003] Currently, traditional methods for improving the fatigue performance of metal blades mainly include optimizing aerodynamic design and surface strengthening techniques. Among these, surface strengthening is the most direct and widely used process for improving the fatigue performance of metal blades. Its core concept is not to reduce the external load on the metal blade, but to significantly enhance its "intrinsic ability" to resist fatigue damage by actively intervening in the physical and mechanical state of the blade surface. Surface strengthening techniques mainly include shot peening, laser shock peening, and surface nanostructuring. The core mechanism of shot peening and laser shock peening in improving the fatigue performance of metal blades is to introduce a high-amplitude residual compressive stress field into the surface layer of the metal blade (typically tens of micrometers to several millimeters deep). This introduced residual compressive stress field can delay the initiation of fatigue cracks and effectively suppress the crack propagation rate in the initial stage. Surface nanofiberization refines the grain size of a material's surface layer to the nanoscale through intense plastic deformation (such as surface mechanical grinding, ultrasonic shot peening, and high-energy shot peening). Its strengthening mechanism is complex: on one hand, the ultrafine grain size follows the Hall-Page relationship, significantly improving the surface strength and hardness; on the other hand, the intense plastic deformation process also introduces deep and strong residual compressive stress. The synergistic effect of these two factors allows the nanofiberized surface layer to more effectively suppress crack initiation and hinder early crack propagation. Compared to shot peening, surface nanofiberization can achieve a qualitative change in surface microstructure and properties while obtaining a deeper residual compressive stress field, especially impacting components operating at moderate temperatures. Despite the significant effects and mature technology of surface strengthening, it still faces several objective and severe challenges:

[0004] (a) The residual compressive stress will gradually decrease under high temperature conditions.

[0005] Under the long-term high-temperature service environment of the engine, the material will undergo creep and stress release, causing the carefully introduced residual compressive stress to gradually decay, and the durability of the strengthening effect will be tested.

[0006] (ii) The challenge of balancing uniformity and consistency.

[0007] Metal blades have complex geometries, including concave surfaces, edges, and transition areas that are difficult to reach. At the same time, even slight fluctuations in process parameters can directly affect the strengthening effect, leading to performance differences between batches.

[0008] (iii) Strengthening the process itself can bring negative effects.

[0009] For example, excessive shot peening may worsen surface roughness or cause microstructural damage, thus becoming a new source of cracks; the high pressure of laser shock may also cause microscopic deformation in thin-walled areas. Summary of the Invention

[0010] The purpose of this invention is to address the technical problems of traditional methods for improving the fatigue performance of metal blades based on surface strengthening technology, such as the gradual decay of residual compressive stress under high temperature conditions, the difficulty in balancing the uniformity and consistency of strengthening, and the negative effects brought about by the strengthening process itself. The invention provides a method for improving the fatigue performance of metal blades and blades processed by this method.

[0011] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0012] A method for improving the fatigue performance of metal blades, characterized by comprising the following steps:

[0013] A ceramic coating with a thickness of 5μm to 20μm is directly deposited on the surface of a metal blade substrate using chemical vapor deposition or physical vapor deposition techniques.

[0014] The ceramic coating must meet the following constraints during its preparation:

[0015] The surface roughness difference between the ceramic coating and the metal blade substrate is less than or equal to 10% of the surface roughness of the metal blade substrate;

[0016] The elastic modulus of the ceramic coating is 2 to 5 times that of the metal blade matrix;

[0017] The surface defect rate of the ceramic coating is less than 10%.

[0018] Furthermore, the ceramic coating is a nitride ceramic coating, an oxide ceramic coating, or a diamond ceramic coating.

[0019] Furthermore, the thickness of the ceramic coating is 10μm~20μm.

[0020] Furthermore, the thickness of the ceramic coating is 15 μm.

[0021] In addition, the present invention also provides a blade processed by the above-described method for improving the fatigue performance of metal blades, which is characterized in that it includes a metal blade substrate and a ceramic coating disposed on the surface of the metal blade substrate.

[0022] The surface roughness difference between the ceramic coating and the metal blade substrate is less than or equal to 10% of the surface roughness of the metal blade substrate;

[0023] The elastic modulus of the ceramic coating is 2 to 5 times that of the metal blade matrix;

[0024] The surface defect rate of the ceramic coating is less than 10%.

[0025] Furthermore, the ceramic coating is a nitride ceramic coating, an oxide ceramic coating, or a diamond ceramic coating.

[0026] Furthermore, the thickness of the ceramic coating is 10μm~20μm.

[0027] Furthermore, the thickness of the ceramic coating is 15 μm.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] 1. This invention provides a method for improving the fatigue performance of metal blades. Based on the metal fatigue damage mechanism, a ceramic coating is directly deposited on the surface of the metal blade substrate using physical vapor deposition (PVD) or chemical vapor deposition (CVD). The ceramic filtration technology in this deposition process, combined with direct deposition on the metal blade substrate, not only reduces the number of manufacturing steps but also effectively controls the surface defect rate of the ceramic coating, allowing the residual compressive stress introduced by the ceramic coating to reach the GPa level. This invention introduces a ceramic coating with high elastic modulus, high residual compressive stress, and a thickness of 5μm~20μm onto the surface of the metal blade substrate, and makes the surface roughness of the ceramic coating close to that of the metal blade substrate. Compared with existing technologies, this further reduces the stress amplitude borne by the blade, significantly delays or even prevents the initiation of fatigue cracks, and effectively inhibits the crack propagation rate in the initial stage, thereby improving the fatigue resistance of the blade. Simultaneously, it effectively increases the blade stiffness and reduces the plastic deformation of the blade.

[0030] 2. The blade processed by the above-mentioned method for improving the fatigue performance of metal blades includes a metal blade substrate and a ceramic coating disposed on the surface of the metal blade substrate. It is particularly suitable for blade surfaces with thin thickness, and can improve the fatigue resistance of the blade without deforming it. At the same time, it can also be used for blades with complex geometric surfaces and areas that are difficult to reach by laser or shot peening, such as concave surfaces, edges, and transition areas. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a blade manufactured according to an embodiment of the present invention, which improves the fatigue performance of metal blades.

[0032] The annotations in the attached figures are explained as follows:

[0033] 1-Metal blade substrate, 2-Ceramic coating. Detailed Implementation

[0034] To make the objectives, advantages, and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0035] Example 1

[0036] A method for improving the fatigue performance of metal blades includes the following steps:

[0037] A titanium nitride ceramic coating 2 with a thickness of 15 μm was directly deposited on the surface of a metal blade substrate 1 made of TC4 titanium alloy using physical vapor deposition technology.

[0038] When preparing the ceramic coating 2 on the surface of the metal blade substrate 1, the following three constraints apply to the ceramic coating 2:

[0039] (i) The surface roughness difference between the ceramic coating 2 and the metal blade substrate 1 is less than or equal to 10% of the surface roughness of the metal blade substrate 1, in order to avoid the introduction of new crack sources after the introduction of the ceramic coating 2. In this embodiment, the surface roughness of the metal blade substrate 1 is Ra0.65, and the surface roughness of the prepared ceramic coating 2 is Ra0.70.

[0040] (ii) The elastic modulus of the ceramic coating 2 is 2 to 5 times that of the metal blade substrate 1, and is used to improve the overall bending stiffness of the metal blade substrate 1 after the introduction of the ceramic coating 2. In this embodiment, the elastic modulus of the metal blade substrate 1 is 120 GPa, and the elastic modulus of the ceramic coating 2 is 384.54 GPa, which is approximately 3.2 times that of the metal blade substrate 1.

[0041] (iii) The surface defect rate of ceramic coating 2 is less than 10%, which makes it basically free of unmelted metal particles.

[0042] Blades processed using the methods described above for improving the fatigue performance of metal blades, such as... Figure 1 As shown, it includes a metal blade substrate 1 and a ceramic coating 2 disposed on the surface of the metal blade substrate 1.

[0043] Example 2

[0044] The only difference between this embodiment and Embodiment 1 is that in this embodiment, chemical vapor deposition is used to prepare the ceramic coating 2 on the surface of the metal blade substrate 1.

[0045] Traditional methods such as shot peening, laser shock peening, and surface nano-sizing, which involve first performing shot peening / laser shock peening / nano-sizing on the surface of the metal blade substrate before depositing a coating using pulsed magnetron sputtering, result in a high surface defect rate in the coating. Furthermore, the deposited coating can become a new source of fatigue. In contrast, this invention uses physical vapor deposition (PVD) or chemical vapor deposition (CVD) to directly deposit a ceramic coating 2 onto the surface of the metal blade substrate 1. The ceramic filtration technology in this deposition process, combined with direct deposition on the metal blade substrate 1, not only reduces the number of steps in the blade fabrication process but also effectively controls the surface defect rate of the ceramic coating 2, allowing the residual compressive stress introduced by the ceramic coating 2 to reach the GPa level (the residual compressive stress of the ceramic coating 2 in Example 1 is approximately -3 GPa). Therefore, when the ceramic coating 2 prepared by this invention meets the above three constraints, the GPa-level residual compressive stress introduced by the ceramic coating 2, compared to existing technologies, not only further reduces the stress amplitude borne by the blade but also significantly delays or even prevents the initiation of fatigue cracks and effectively inhibits the crack propagation rate in the initial stage, thereby improving the fatigue resistance of the blade. Simultaneously, it effectively increases the blade's stiffness and reduces its plastic deformation.

[0046] In other embodiments of the present invention, the thickness of the ceramic coating 2 can be selected between 5μm and 20μm, preferably 10μm to 20μm, depending on the usage environment and design requirements, and is not specifically limited here.

[0047] Meanwhile, the ceramic coating 2 can also be an oxide ceramic coating, a diamond ceramic coating, or other nitride ceramic coatings, which can be selected according to the material of the metal blade substrate 1 and the above-mentioned constraints.

[0048] The technical effects of the present invention will be further illustrated by the following specific tests.

[0049] According to HB5277, TC4 titanium alloy was processed into two plate-shaped structures. One of them was used as a traditional metal blade sample. On the other plate-shaped structure, a ceramic coating 2 with a thickness of 15 μm and meeting the above-mentioned constraints was prepared by physical vapor deposition technology, thus forming a metal blade sample with ceramic coating 2.

[0050] Comparison of bending stiffness:

[0051] The bending stiffness of the metal blade specimen with ceramic coating 2 is calculated using the following formula:

[0052]

[0053] Where E represents the elastic modulus of the metal blade sample with ceramic coating 2 introduced; I total Moment of inertia of the metal blade specimen with ceramic coating 2 introduced; E s I represents the elastic modulus of the metal blade matrix 1; s - Moment of inertia of the metal blade substrate 1; E c - Elastic modulus of ceramic coating 2; I s - Moment of inertia of ceramic coating 2.

[0054] Although the thickness of the metal blade substrate 1 in this embodiment is 3 mm, while the thickness of the ceramic coating 2 is only 15 μm, the ceramic coating 2 is located on the material surface, far from the neutral axis of the metal blade substrate 1. Furthermore, the elastic modulus of the ceramic coating 2 in this embodiment is approximately 3.2 times that of the metal blade substrate 1. Substituting these data into the above formula, we find that the bending stiffness of the metal blade sample with the ceramic coating 2 is approximately 1.1 times that of the conventional metal blade sample. Therefore, it can be seen that the contribution of the ceramic coating 2 to the overall bending stiffness of the metal blade is not negligible.

[0055] Vibration fatigue performance comparison:

[0056] Before the vibration fatigue test, the conventional metal blade sample and the metal blade sample with ceramic coating 2 introduced in this invention were measured using an ES-10D-240 vibration fatigue testing machine. The results showed that the first-order vibration frequency of the conventional metal blade sample was 287.72 Hz, while the first-order vibration frequency of the metal blade sample with ceramic coating 2 introduced in this invention was 307.2 Hz. Then, the vibration fatigue test was carried out using the ES-10D-240 vibration fatigue testing machine under the following conditions:

[0057] 1) Test frequency: First-order bending natural frequency of TC4 blade;

[0058] 2) Control method: Vibration control is performed when the TC4 blade is 10mm away from the blade tip.

[0059] 3) Strain monitoring: using resistance strain gauges;

[0060] 4) Displacement monitoring: A laser displacement sensor is used;

[0061] 5) Test conditions: 1×10 7 Number of cycles, median fatigue strength (90% confidence level, 5% error limit);

[0062] 6) During the test, if the vibration frequency of the tested blade decreases by 1% within the specified number of cycles, the test shall be stopped, the test object (blade) shall be subjected to a dye penetrant test, and the results shall be recorded. If the blade develops cracks, the time of test stoppage shall be recorded; if the test is stopped due to damage to the tooling, the time of test stoppage shall be recorded, a new tooling shall be replaced, and the test shall continue.

[0063] 7) Sample installation method: When conducting vibration fatigue tests on the blade, the blade is fixed on a special fixture, and then the special fixture is rigidly fixed on the vibration table. The moving parts of the vibration table drive the fixture and the blade to vibrate together. The vibration table outputs a sinusoidal excitation signal of a fixed frequency, and the excited blade vibrates sinusoidally at the same frequency.

[0064] Vibration fatigue test results show that the median fatigue limit of the metal blade sample with ceramic coating 2 introduced in this invention is 372.5 MPa after 10 million cycles, while the median fatigue limit of the conventional metal blade sample is 277.5 MPa after 10 million cycles. Compared with the conventional metal blade sample, the fatigue limit of the metal blade sample of this invention increased by 34% after the introduction of ceramic coating 2.

[0065] Comparison of geometrically necessary dislocation densities:

[0066] Electron backscatter diffraction was used to analyze the geometrically necessary dislocation (GND) density at the working section of the metal blade sample with ceramic coating 2 introduced in this invention and the conventional metal blade sample after undergoing 10 million cycles at 300 MPa. The results showed that the average GND of the conventional metal blade sample at 300 MPa was approximately 2.03 × 10⁻⁶. 14 / m 2 The GND of the metal blade sample with ceramic coating 2 introduced in this invention is approximately 1.75 × 10⁻⁶. 14 / m 2 This indicates that the resistance to plastic deformation of the metal blade sample with ceramic coating 2 introduced in this invention has been effectively increased.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A method for improving the fatigue performance of metal blades, characterized in that, Includes the following steps: A ceramic coating (2) with a thickness of 5 μm to 20 μm was directly deposited on the surface of a metal blade substrate (1) using chemical vapor deposition or physical vapor deposition techniques. The ceramic coating must meet the following constraints during its preparation: The surface roughness difference between the ceramic coating (2) and the metal blade substrate (1) is less than or equal to 10% of the surface roughness of the metal blade substrate (1); The elastic modulus of the ceramic coating (2) is 2 to 5 times that of the metal blade substrate (1); The surface defect rate of the ceramic coating (2) is less than 10%.

2. The method for improving the fatigue performance of metal blades according to claim 1, characterized in that: The ceramic coating (2) is a nitride ceramic coating, an oxide ceramic coating, or a diamond ceramic coating.

3. The method for improving the fatigue performance of metal blades according to claim 2, characterized in that: The thickness of the ceramic coating (2) is 10μm~20μm.

4. The method for improving the fatigue performance of metal blades according to claim 3, characterized in that: The thickness of the ceramic coating (2) is 15 μm.

5. A blade manufactured by the method for improving the fatigue performance of metal blades according to any one of claims 1-4, characterized in that: It includes a metal blade substrate (1) and a ceramic coating (2) disposed on the surface of the metal blade substrate (1); The surface roughness difference between the ceramic coating (2) and the metal blade substrate (1) is less than or equal to 10% of the surface roughness of the metal blade substrate (1); The elastic modulus of the ceramic coating (2) is 2 to 5 times that of the metal blade substrate (1); The surface defect rate of the ceramic coating (2) is less than 10%.

6. The blade according to claim 5, characterized in that: The ceramic coating (2) is a nitride ceramic coating, an oxide ceramic coating, or a diamond ceramic coating.

7. The blade according to claim 6, characterized in that: The thickness of the ceramic coating (2) is 10μm~20μm.

8. The blade according to claim 7, characterized in that: The thickness of the ceramic coating (2) is 15 μm.

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