Method for measuring ductile-brittle transition temperature of metal bottom layer of thermal barrier coating of gas turbine based on high-temperature tensile test

Abstract

The invention provides a method for measuring ductile-brittle transition temperature of a metal bottom layer of a thermal barrier coating of a gas turbine based on a high-temperature tensile test, which comprises the following steps of: S1, casting and processing a turbine blade base material into a standard high-temperature tensile test bar, and coating the surface of the test bar with the metal bottom layer of the thermal barrier coating according to an actual thermal process of the blade; s2, respectively breaking one test bar at n temperature points Tmin,..., Tmax DEG C; s3, checking the fracture morphology of the tensile test bar after the test; and S4, adding a test bar at each temperature point, repeating fracture morphology inspection work, if fracture conditions are consistent, obtaining that the ductile-brittle transition temperature of the test bar coating is between (T-100) DEG C and T DEG C, and if the fracture of the test bar at the same temperature point generates opposite characteristics, adding the test bar. The measuring method has the advantages that the number of samples is reduced, the technical state of the coating meets the requirements of a real blade spraying process, the measuring result fits the actual application condition, and the accuracy is higher.

Description

Technical Field

[0001] The present invention belongs to the field of gas turbine temperature measurement, and particularly relates to a method for measuring the ductile-brittle transition temperature of the metal substrate of a thermal barrier coating for a gas turbine based on a high-temperature tensile test. Background Technique

[0002] A gas turbine is a complex and precise high-tech product that operates in a harsh environment of high temperature, high pressure, high rotational speed, and high salt spray corrosion. Among them, the turbine is one of the main components of the gas turbine, which converts the energy of high-temperature and high-pressure gas into kinetic energy and mechanical energy to drive the compressor, propeller, and accessory drive system. To improve the ability of turbine component materials to resist high-temperature oxidation and high-temperature corrosion, spraying a thermal barrier coating on the surface of turbine blades has become one of the key technologies to increase the pre-turbine temperature and extend the service life of turbine blades. Due to the characteristics of the metal substrate material of the thermal barrier coating being brittle at low temperatures and ductile at high temperatures, under the actual working conditions of turbine blades, there is a problem that the metal substrate cracks before the blade matrix, and then the matrix is also involved in cracking. Therefore, the ductile-brittle transition temperature of the metal substrate of the thermal barrier coating becomes an important index determining the service life of turbine blades.

[0003] Currently, the measurement method of the ductile-brittle transition temperature mostly adopts the small punch test method. This method requires special fixtures and testers, and the specimens need to be specially prepared into thin coating materials. The specimen production is difficult, the yield is low, the cost is high, and the thickness of the coating specimen is often much thicker than the actual application environment, increasing the internal defects of the coating, resulting in a deviation between the measured value of the ductile-brittle transition temperature and the value under actual application conditions.

[0004] In summary, the existing methods for measuring the ductile-brittle transition temperature of the metal substrate of the thermal barrier coating have disadvantages such as high cost, great difficulty, and a certain deviation between the measurement results and the values under actual application conditions. Summary of the Invention

[0005] The purpose of the present invention is to solve the disadvantages of the existing methods for measuring the ductile-brittle transition temperature of the thermal barrier coating, such as high cost, great difficulty, and a certain deviation between the measurement results and the values under actual application conditions, and further provide a method for measuring the ductile-brittle transition temperature of the metal substrate of the thermal barrier coating for a gas turbine based on a high-temperature tensile test, with standardized specimens, standardized test equipment, the technical state of coating preparation conforming to actual application conditions, and the measurement results being more guiding for actual applications.

[0006] A method for measuring the ductile-brittle transition temperature of the metal substrate of the thermal barrier coating for a gas turbine based on a high-temperature tensile test includes the following steps:

[0007] S1, casting and machining a standard high-temperature tensile test bar from the turbine blade matrix material, and coating the metal substrate of the thermal barrier coating on the surface of the test bar according to the actual thermal process of the blade;

[0008] S2. At a total of n temperature points from Tmin to Tmax °C, break one test bar at each temperature point;

[0009] Among them, Tmin is the integer value of the average temperature during the slow roll operation of the blade, and Tmax is the integer value of the highest working temperature of the blade;

[0010] S3. After the test, check the fracture morphology of the broken test bar;

[0011] S4. Add one test bar at each temperature point and repeat the fracture morphology inspection work. If the fracture conditions are the same, it can be concluded that the ductile-brittle transition temperature of the test bar coating is between (T - 100) °C and T °C. If the fracture surfaces of the test bars at the same temperature point show opposite characteristics, add more test bars.

[0012] Furthermore, the metal bottom layer includes M(Co, CoNi, NiCo, Ni)CrAlY, CoAl, (Ni, Pt)Al, PtAl 2 , NiAl, Al.

[0013] Furthermore, there shall be no coating on the threaded ends on both sides of the test bar in S1.

[0014] Furthermore, in S1, the coating thickness range meets the requirements of the nominal thickness of the blade coating, and the coating performance meets the requirements of the bending test and thermal shock test indicators.

[0015] Furthermore, the number of test pieces in S1 is not less than 16.

[0016] Furthermore, during the S2 test process, first load to reach 0.2% strain, stabilize for 1 minute, then start loading, and control the strain rate of the applied tensile stress at 4×10-4 s-1 until the test bar is completely broken.

[0017] Furthermore, during the S2 test process, the temperature fluctuation in the furnace is less than ±4 °C.

[0018] Furthermore, the fracture morphology of the broken test bar in S3 is specifically as follows: at a certain temperature and above, the fracture surface shows slip characteristics or dimples, showing certain ductile fracture characteristics. The degree of surface crack cracking near the fracture is small, the crack width is narrow, and mainly small cracks; after the test at (T - 100) °C and below, the fracture surface shows brittle cleavage characteristics, fracture mode characteristics such as transgranular and intergranular failures, there are a large number of surface cracks near the fracture, the degree of cracking is large, the crack width is wide, and the cracks are flush with the fracture surface, indicating that the ductile-brittle transition temperature of the test bar coating is between (T - 100) °C and T °C.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. Compared with the small punch test method, the method for measuring the ductile-brittle transition temperature of the metal substrate of the thermal barrier coating of the present invention can improve the yield rate of test pieces and save time and economic costs.

[0021] 2. The method for measuring the ductile-brittle transition temperature of the metal substrate of the thermal barrier coating of the present invention provides a standardized specimen and standardized test equipment, which is more convenient for designers to carry out research and application.

[0022] 3. The coating preparation technical state of the test piece of the method for measuring the ductile-brittle transition temperature of the metal substrate of the thermal barrier coating of the present invention conforms to the actual application conditions. Therefore, the measurement results are more instructive for actual application and more meaningful for engineering application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a dimensional drawing of the high-temperature tensile test bar of the present invention;

[0024] Figure 2 (a) is a comparison diagram A of the fracture morphology of the test bar of the present invention;

[0025] Figure 2 (b) is a comparison diagram B of the fracture morphology of the test bar of the present invention;

[0026] Figure 3 (a) is a comparison diagram A of the surface cracks near the fracture of the test bar of the present invention;

[0027] Figure 3 (b) is a comparison diagram B of the surface cracks near the fracture of the test bar of the present invention;

[0028] Figure 3 (c) is a comparison diagram C of the surface cracks near the fracture of the test bar of the present invention;

[0029] Figure 3 (d) is a comparison diagram D of the surface cracks near the fracture of the test bar of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be further described below with reference to the accompanying drawings.

[0031] As Figures 1-3 shown, a method for measuring the ductile-brittle transition temperature of the metal substrate of the thermal barrier coating of a gas turbine based on a high-temperature tensile test includes the following steps:

[0032] S1. Coating process, phase distribution, chemical composition, heat treatment regime, microstructure, substrate material, and coating thickness all have a certain influence on the determined ductile-brittle transition temperature. Therefore, a standard high-temperature tensile test bar is cast and machined from the substrate material of the turbine blade. The surface of the test bar is coated with a metallic bond coat of the thermal barrier coating according to the actual thermal process of the blade. The following metal bond coats are all applicable to the present invention: M(Co, CoNi, NiCo, Ni)CrAlY, CoAl, (Ni, Pt)Al, PtAl 2 , NiAl, Al, etc. Such coatings have the characteristic of ductile-brittle transition during the operation of the unit under different working conditions. There shall be no coating at both threaded ends. The coating thickness range shall meet the requirements of the nominal thickness of the blade coating, and the coating performance shall meet the requirements of the bending test and thermal shock test indicators. The number of test pieces is not less than 16;

[0033] S2. At n temperature points from Tmin (the integer of the average temperature during the slow-speed operation of the blade, e.g., 400 °C), ……, Tmax °C (the integer of the highest working temperature of the blade, e.g., 900 °C) (one temperature point is set every 100 °C), one test bar is pulled to break at each temperature point. During the test, first load to reach 0.2% strain and stabilize for 1 minute, and then start loading. The strain rate of the applied tensile stress is controlled according to 4×10 -4 s -1 until the test bar is completely pulled to break. During the test, the temperature fluctuation in the furnace shall not be greater than ±4 °C;

[0034] S3. After the test, check the fracture morphology of the pulled test bar. At a certain temperature (such as T °C) and above, the fracture shows slip characteristics, and even dimples appear, showing certain characteristics of ductile fracture. The degree of surface crack cracking near the fracture is small, the crack width is narrow, and mainly small cracks; while at (T - 100) °C and below, the fracture after the test shows brittle cleavage characteristics, fracture modes such as transgranular and intergranular failures, there are a large number of surface cracks near the fracture, the degree of cracking is large, the crack width is wide, and the cracks are flush with the fracture. It shows that the ductile-brittle transition temperature of the test bar coating is between (T - 100) °C and T °C;

[0035] S4. Add one test bar at each temperature point and repeat the work of checking the fracture morphology. If the fracture conditions are the same, it can be concluded that the ductile-brittle transition temperature of the test bar coating is between (T - 100) °C and T °C. If the fractures of the test bars at the same temperature point show opposite characteristics, add one test bar, and it is also acceptable if the fracture conditions of the added test bar are the same.

[0036] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for measuring the ductile-brittle transition temperature of the metal bottom layer of a gas turbine thermal barrier coating based on a high temperature tensile test, characterized in that: The following steps are involved: S1, using turbine blade substrate material to cast and process into a standard high-temperature tensile test bar, the surface of the test bar is coated with a thermal barrier coating metal base layer according to the actual thermal process of the blade; S2, break a test rod at each of the n temperature points Tmin, ..., Tmax℃; Among them, Tmin is the average temperature of the blade during slow operation, and Tmax is the maximum operating temperature of the blade. S3, check the fracture morphology of the tensile test bar after the test; S4, add a test rod at each temperature point and repeat the fracture morphology inspection. If the fracture conditions are consistent, it can be concluded that the ductile-brittle transition temperature of the test rod coating is between (T-100)℃ and T℃. If the fracture of the test rod at the same temperature point produces opposite characteristics, add a test rod.

2. The method for measuring the ductile-brittle transition temperature of the metal bottom layer of a gas turbine thermal barrier coating based on a high temperature tensile test according to claim 1, characterized in that: The metal bottom layer includes M(Co, CoNi, NiCo, Ni)CrAlY, CoAl, (Ni, Pt)Al, PtAl2, NiAl, Al.

3. The method for measuring the ductile-brittle transition temperature of the metal bottom layer of a gas turbine thermal barrier coating based on a high temperature tensile test according to claim 1, characterized in that: No coating is allowed on the threaded ends on both sides of the S1 test rod.

4. The method for measuring the ductile-brittle transition temperature of the metal bottom layer of a gas turbine thermal barrier coating based on a high temperature tensile test according to claim 1, characterized in that: The coating thickness range in S1 is in accordance with the nominal thickness requirements of the blade coating, and the coating performance meets the requirements of the bending test and thermal shock test indicators.

5. The method for measuring the ductile-brittle transition temperature of the metal bottom layer of a gas turbine thermal barrier coating based on a high temperature tensile test according to claim 1, characterized in that: The number of test pieces in S1 is ≮16.

6. The method for measuring the ductile-brittle transition temperature of the metal bottom layer of a gas turbine thermal barrier coating based on a high temperature tensile test according to claim 1, characterized in that: During the S2 test, the load was first applied to reach a strain of 0.2%, stabilized for 1 minute, and then loading began. The strain rate of the tensile stress was controlled at 4×10-4s-1 until the test rod was completely broken.

7. A method for measuring the ductile-brittle transition temperature of a metal bottom layer of a thermal barrier coating of a gas turbine based on a high temperature tensile test according to claim 6, characterized in that: During the test in S2, the temperature fluctuation in the furnace is less than ±4°C.

8. The method for measuring the ductile-brittle transition temperature of the metal bottom layer of a gas turbine thermal barrier coating based on a high temperature tensile test according to claim 1, characterized in that: The fracture morphology of the tensile test rod in S3 is specifically as follows: at a certain temperature or above, the fracture shows slip characteristics, or dimples appear, showing certain ductile fracture characteristics, the cracking degree of surface cracks near the fracture is small, the crack width is narrow, and small cracks are dominant; after the test at a temperature of (T-100)℃ or below, the fracture shows fracture mode characteristics such as brittle cleavage characteristics, transgranular and intergranular failure, there are a large number of surface cracks near the fracture, the cracking degree is large, the crack width is wide, and the cracks are flush with the fracture, indicating that the ductile-brittle transition temperature of the test rod coating is between (T-100)℃ and T℃.

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