Method for preparing a coating with longitudinal cracks on the surface of a gas turbine blade by laser preheating

Abstract

The present invention discloses a method for preparing a coating with longitudinal cracks on the surface of a gas turbine blade by laser preheating, which includes: 1. Building a device for laser preheating of the blade and coating preparation; 2. Obtaining the internal and external temperature correction coefficients of the gas turbine blade specimen at a set preheating temperature; 3. Obtaining the temperature drop correction coefficient of the gas turbine blade specimen at a set preheating temperature; 4. Laser preheating and spraying of the gas turbine blade to be sprayed. The method of the present invention has simple steps. A laser heating device is used to preheat the rotating gas turbine blade to improve the uniformity of the surface temperature distribution of the gas turbine blade, so that the coating with longitudinal cracks can have a long service life while maintaining good performance.

Description

Technical Field

[0001] The invention belongs to the technical field of gas turbine blade coatings, and particularly relates to a method for preparing a coating with longitudinal cracks on the surface of a gas turbine blade by laser preheating. Background Technique

[0002] Gas turbines are one of the core power equipment in clean and efficient thermal power energy systems. The working environment of gas turbine blades is harsh. Thermal barrier coatings are mainly applied to gas turbine blades, which not only have a thermal barrier effect but also can prevent damage to the blades caused by oxidation, corrosion, foreign object erosion, etc. In order to improve the long-term service of thermal barrier coating materials, thermal barrier coatings with longitudinal crack structures have emerged. The presence of longitudinal cracks can increase the interfacial fracture resistance of the thermal barrier coating. The introduction of longitudinal cracks improves the strain tolerance of the thermal barrier coating, reduces the thermal stress accumulated in the coating caused by the difference in thermal expansion coefficients between the ceramic layer and the bonding layer, and thus extends its service life.

[0003] However, at present, the preheating treatment of the gas turbine blade substrate is achieved through a plasma spray gun. The thermal impulse that the plasma spray gun can provide in a short time is limited, which may lead to uneven temperature distribution on the blade. At the same time, using a plasma spray gun for preheating will cause the local temperature of the bonding layer to be too high, which will further cause oxidation of the bonding layer on the substrate. This oxidation reaction will change the physical and chemical properties of the bonding layer and may lead to early failure of the coating.

[0004] Therefore, a method for preparing a coating with longitudinal cracks on the surface of a gas turbine blade by laser preheating with a reasonable design is needed. A laser heating device is used to preheat the rotating gas turbine blade to improve the uniformity of the surface temperature distribution of the gas turbine blade, so that the coating with longitudinal cracks can have a long service life while maintaining good performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a coating with longitudinal cracks on the surface of a gas turbine blade by laser preheating in view of the above-mentioned deficiencies in the prior art. The method steps are simple and reasonably designed. A laser heating device is used to preheat the rotating gas turbine blade to improve the uniformity of the surface temperature distribution of the gas turbine blade, so that the coating with longitudinal cracks can have a long service life while maintaining good performance.

[0006] To solve the above technical problem, the technical solution adopted by the present invention is: A method for preparing a coating with longitudinal cracks on the surface of a gas turbine blade by laser preheating, the method comprising the following steps:

[0007] Step 1: Set up a blade laser preheating and coating preparation device:

[0008] Step 101: Set up a rotary workbench in the spraying chamber and a laser heating device outside the spraying chamber. The laser heating device is located on the left side of the rotary workbench.

[0009] Step 102: Set up an atmospheric plasma spraying device in the spraying chamber. The atmospheric plasma spraying device is located on the right side of the rotary workbench.

[0010] Step Two: Obtain the internal and external temperature correction coefficients of the gas turbine blade specimen at the set preheating temperature:

[0011] Install the gas turbine blade specimen on the rotary workbench, heat the gas turbine blade specimen using the laser heating device, calibrate the internal temperature and external temperature of the gas turbine blade specimen, and obtain the internal and external temperature correction coefficients of the gas turbine blade specimen at the set preheating temperature.

[0012] Step Three: Obtain the temperature drop correction coefficient of the gas turbine blade specimen at the set preheating temperature:

[0013] After heating the gas turbine blade specimen to meet the set preheating temperature, let it stand still in the spraying environment, and calibrate the average external temperature before standing still and the average external temperature after standing still of the gas turbine blade specimen to obtain the temperature drop correction coefficient of the gas turbine blade specimen at the set preheating temperature.

[0014] Step Four: Laser preheating and spraying of the gas turbine blade to be sprayed:

[0015] Step 401: Use the laser heating device to heat the gas turbine blade to be sprayed, and correct the internal temperature of the gas turbine blade to be sprayed based on the calibrated internal and external temperature correction coefficients and temperature drop correction coefficient until the surface temperature of the gas turbine blade to be sprayed meets the set preheating temperature.

[0016] Step 402: After the gas turbine blade to be sprayed is preheated, spray the surface of the gas turbine blade to be sprayed through the atmospheric plasma spraying device to form a coating with longitudinal cracks.

[0017] In the above method for laser preheating of a gas turbine blade to prepare a surface coating with longitudinal cracks, further, the rotary workbench includes a workbench, a turntable embedded in the workbench, and a rotary motor disposed at the bottom of the turntable and drivingly connected to the turntable. A heat-resistant steel fixture is provided at the center position of the turntable.

[0018] The laser heating device includes a fiber laser, a support frame disposed outside the spraying chamber, and a fiber laser head disposed on the support frame and connected to the fiber laser. A laser shaper passing through the spraying chamber is provided at the end of the fiber laser head. The laser emitted by the fiber laser head is projected onto the gas turbine blade through the laser shaper to heat the gas turbine blade.

[0019] The atmospheric plasma spraying equipment includes a base disposed in the spraying chamber, a six-axis robotic arm disposed on the base, and a plasma spray gun disposed at the end of the six-axis robotic arm. In step 402, the plasma spray gun is operated by the six-axis robotic arm to spray the surface of the gas turbine blade to be sprayed, forming a coating with longitudinal cracks.

[0020] For the method of preparing a surface with longitudinal cracks on a gas turbine blade by laser preheating as described above, further, step two is as follows:

[0021] Step 201: Insert the first thermocouple through the bottom channel of the root of the gas turbine blade specimen into the middle of the leading edge cavity of the gas turbine blade specimen, insert the second thermocouple through the bottom channel of the root of the gas turbine blade specimen into the middle of the trailing edge cavity of the gas turbine blade specimen, and insert the third thermocouple into the bottom channel of the root of the gas turbine blade specimen. Denote the inserted first thermocouple, second thermocouple, and third thermocouple as internal thermocouples.

[0022] Attach thermocouples to both the upper and lower parts of the leading edge surface, the blade body surface, and the trailing edge surface of the gas turbine blade specimen. Denote the attached thermocouples as external thermocouples.

[0023] Step 202: Install the root of the gas turbine blade specimen in a heat-resistant steel fixture, with the tip of the gas turbine blade specimen facing upward and the bottom surface of the root of the gas turbine blade specimen close to the surface of the turntable.

[0024] Step 203: Operate the rotating motor to rotate at a set speed and operate the fiber laser. The laser emitted by the fiber laser head and the laser shaper is projected onto the surface of the gas turbine blade specimen to heat the gas turbine blade specimen.

[0025] Step 204: During the process of the gas turbine blade specimen rotating and being heated, multiple internal thermocouples detect the temperature inside the gas turbine blade specimen and collect it according to the set sampling time, obtaining multiple internal temperature values at the i-th sampling time. At the same time, multiple external thermocouples detect the temperature on the surface of the gas turbine blade specimen and collect it according to the set sampling time, obtaining multiple external temperature values at the i-th sampling time. Where i is a positive integer.

[0026] Step 205: According to , obtain the standard deviation of the multiple external temperature values at the i-th sampling time relative to the set preheating temperature ; where represents the external temperature value collected by the j-th external thermocouple at the i-th sampling time, j and J are positive integers, and 1 ≤ j ≤ J, J represents the total number of external thermocouples; represents the set preheating temperature, The value range is 550°C to 750°C; and obtain the range of multiple external temperature values at the i-th sampling time and denote it as ;

[0027] Step 206, the standard deviation of multiple external temperature values at the i-th sampling time relative to the set preheating temperature and the range are judged. If is not greater than 10°C, is not greater than 25°C, it indicates that the heating of the gas turbine blade specimen meets the requirements of the set preheating temperature, and step 207 is executed; otherwise, continuously collect while rotating and heating the gas turbine blade specimen to obtain the standard deviation and range of multiple external temperature values at the (i + 1)-th sampling time relative to the set preheating temperature and judge until the heating of the gas turbine blade specimen meets the requirements of the set preheating temperature, and step 207 is executed;

[0028] Step 207, perform an averaging process on multiple external temperature values when the heating of the gas turbine blade specimen meets the requirements of the set preheating temperature to obtain the average external temperature of the gas turbine blade specimen; perform an averaging process on multiple internal temperature values when the heating of the gas turbine blade specimen meets the requirements of the set preheating temperature to obtain the average internal temperature of the gas turbine blade specimen;

[0029] Step 208, construct a correction relationship between the internal and external temperatures of the blade Tw = Tn + η×d; where, Tw is the external temperature quantity, Tn is the internal temperature quantity, the units of both Tw and Tn are °C, η is the correction coefficient of the internal and external temperatures, d is the average thickness of the gas turbine blade, and the unit of d is millimeters;

[0030] Step 209, assign the average internal temperature in step 207 to the internal temperature quantity, assign the average external temperature to the external temperature quantity, and input the correction relationship between the internal and external temperatures of the blade to obtain the correction coefficient of the internal and external temperatures of the gas turbine blade specimen at the set preheating temperature.

[0031] For the above method of laser preheating of gas turbine blades to prepare a longitudinally cracked coating on the surface, further, step three, the specific process is as follows:

[0032] Step 301, according to the method of steps 203 to 207, obtain the average external temperature when the heating of the gas turbine blade specimen meets the requirements of the set preheating temperature, and denote it as the average external temperature before standing of the gas turbine blade specimen;

[0033] Step 302, operate the rotating motor and the fiber laser to stop working, let the gas turbine blade specimen stand in the spraying environment for the spraying time of one layer of spraying of the gas turbine blade, and then obtain the average external temperature after standing;

[0034] Step 303: Compare the average external temperature before standing with the average external temperature after standing to obtain the temperature drop correction coefficient of the gas turbine blade specimen at the set preheating temperature.

[0035] For the above method of preparing a longitudinally cracked coating on the surface of a gas turbine blade by laser preheating, further, in step 401, the specific process is as follows:

[0036] Step 4011: Set internal thermocouples inside the gas turbine blade to be sprayed according to the method of step 201.

[0037] Step 4012: Heat the gas turbine blade to be sprayed according to the methods of steps 202 and 203.

[0038] Step 4013: During the process of heating the gas turbine blade to be sprayed while rotating, multiple internal thermocouples detect the temperature inside the gas turbine blade to be sprayed and collect it according to the set sampling time to obtain multiple internal temperature detection values at the e-th sampling time; where e is a positive integer.

[0039] Step 4014: Process the multiple internal temperature detection values at the e-th sampling time by taking the average to obtain the average internal temperature detection value at the e-th sampling time. ;

[0040] Step 4015: Denote the internal and external temperature correction coefficient at the set preheating temperature as and denote the temperature drop correction coefficient at the set preheating temperature as ;

[0041] Step 4016: According to , obtain the external temperature value at the e-th sampling time corrected based on the calibrated internal and external temperature correction coefficients and the temperature drop correction coefficient ;

[0042] Step 4017: Judge and . If , continuously heat the gas turbine blade to be sprayed and execute step 4018; if , then the surface heating of the gas turbine blade to be sprayed meets the set preheating temperature.

[0043] Step 4018: According to the methods of steps 4016 and 4017, obtain the external temperature value at the (e + 1)-th sampling time and judge until the surface heating of the gas turbine blade to be sprayed meets the set preheating temperature.

[0044] The above method for preparing a longitudinally cracked coating on the surface of a gas turbine blade by laser preheating is further described as follows after step four:

[0045] Step A: Repeat step four multiple times. For the coatings with longitudinal cracks prepared at different set preheating temperatures, obtain the longitudinal crack density of the coatings with longitudinal cracks through a scanning electron microscope.

[0046] Step B: Use the different set preheating temperatures as the abscissa and the corresponding longitudinal crack densities at different set preheating temperatures as the ordinate to obtain a scatter plot of the longitudinal crack density versus the preheating temperature.

[0047] Step C: Establish a relationship between the longitudinal crack density and the preheating temperature ; where N is the longitudinal crack density, in units of number of cracks / mm, a represents the first coefficient, b represents the second coefficient, T represents the set preheating temperature, T0 is the critical temperature when longitudinal cracks appear, and the units of T and T0 are °C.

[0048] Step D: Use the relationship between the longitudinal crack density and the preheating temperature in step C to fit the scatter plot of the longitudinal crack density versus the preheating temperature to obtain the fitted first and second coefficients; and input the fitted first and second coefficients into step C to obtain the relationship between the longitudinal crack density and the preheating temperature.

[0049] The present invention has the following advantages compared with the prior art:

[0050] 1. The method of the present invention has simple steps and reasonable design, and solves the problem of uneven preheating temperature distribution on the surface of the gas turbine blade before spraying.

[0051] 2. The gas turbine blade of the present invention is arranged on a rotating workbench and rotates with the rotating workbench. During the rotation of the gas turbine blade, it is heated by a laser heating device to improve the uniformity of the surface temperature distribution of the gas turbine blade.

[0052] 3. The present invention uses a laser heating device to heat the gas turbine blade to be sprayed, and corrects it based on the calibrated internal and external temperature correction coefficients and the temperature drop correction coefficient until the surface temperature of the gas turbine blade meets the set preheating temperature, avoiding the detection of thermocouples outside the gas turbine blade to be sprayed and reducing the impact on the plasma spray gun spraying in the subsequent process.

[0053] 4. Calibrate the internal temperature and external temperature of the gas turbine blade specimen, obtain the internal and external temperature correction coefficients of the gas turbine blade specimen at the set preheating temperature, and calibrate the average external temperature before standing and the average external temperature after standing of the gas turbine blade specimen to obtain the temperature drop correction coefficient of the gas turbine blade specimen at the set preheating temperature, so as to facilitate subsequent internal temperature correction based on the calibrated internal and external temperature correction coefficients and temperature drop correction coefficients, so that the surface temperature of the gas turbine blade meets the set preheating temperature.

[0054] 5. Preheat the gas turbine blade of the present invention. The preheating temperature can effectively reduce the energy consumption in the first stage of the YSZ molten powder, and reserve more energy for the initiation of longitudinal cracks in the second stage. Therefore, when preparing a coating with longitudinal cracks, it is necessary to preheat the gas turbine blade; then a plasma spray gun sprays the surface of the gas turbine blade to form a coating with longitudinal cracks, so that the coating with longitudinal cracks can have a long service life while maintaining good performance.

[0055] In summary, the method of the present invention has simple steps and reasonable design. A laser heating device is used to preheat the rotating gas turbine blade to improve the uniformity of the surface temperature distribution of the gas turbine blade, so that the coating with longitudinal cracks can have a long service life while maintaining good performance.

[0056] Next, through the drawings and embodiments, the technical solutions of the present invention will be further described in detail. Description of the Drawings

[0057] Figure 1 It is a structural schematic diagram of the present invention.

[0058] Figure 2 It is a method flow block diagram of the present invention.

[0059] 1 - Fiber laser; 2 - Support frame; 3 - Workbench;

[0060] 4 - Rotating motor; 5 - Six-axis robotic arm; 6 - Fiber laser head;

[0061] 7 - Gas turbine blade; 8 - Plasma spray gun; 9 - Heat-resistant steel fixture;

[0062] 10 - Laser shaper; 11 - Spraying chamber; 12 - Base; 13 - Turntable. Detailed Embodiments

[0063] As Figures 1 to 2 shown, the method for laser preheating of a gas turbine blade of the present invention to prepare a coating with longitudinal cracks on the surface includes the following steps:

[0064] Step 1. Build a blade laser preheating and coating preparation device:

[0065] Step 101: Build a rotating workbench inside the spraying chamber 11, and build a laser heating device outside the spraying chamber 11. The laser heating device is located on the left side of the rotating workbench;

[0066] Step 102: Build an atmospheric plasma spraying device inside the spraying chamber 11. The atmospheric plasma spraying device is located on the right side of the rotating workbench;

[0067] Step Two: Obtain the internal and external temperature correction coefficients of the gas turbine blade specimen at the set preheating temperature:

[0068] Install the gas turbine blade specimen on the rotating workbench, heat the gas turbine blade specimen using the laser heating device, calibrate the internal temperature and external temperature of the gas turbine blade specimen, and obtain the internal and external temperature correction coefficients of the gas turbine blade specimen at the set preheating temperature;

[0069] Step Three: Obtain the temperature drop correction coefficient of the gas turbine blade specimen at the set preheating temperature:

[0070] After heating the gas turbine blade specimen to meet the set preheating temperature, let it stand in the spraying environment, and calibrate the average external temperature before standing and the average external temperature after standing of the gas turbine blade specimen to obtain the temperature drop correction coefficient of the gas turbine blade specimen at the set preheating temperature;

[0071] Step Four: Laser preheating and spraying of the gas turbine blade to be sprayed:

[0072] Step 401: Use the laser heating device to heat the gas turbine blade 7 to be sprayed, and correct the internal temperature of the gas turbine blade 7 to be sprayed based on the calibrated internal and external temperature correction coefficients and the temperature drop correction coefficient until the surface temperature of the gas turbine blade 7 to be sprayed meets the set preheating temperature;

[0073] Step 402: After the gas turbine blade 7 to be sprayed is preheated, spray the surface of the gas turbine blade 7 to be sprayed through the atmospheric plasma spraying device to form a coating with longitudinal cracks.

[0074] In this embodiment, the rotating workbench includes a workbench 3, a turntable 13 embedded in the workbench 3, and a rotating motor 4 arranged at the bottom of the turntable 13 and drivingly connected to the turntable 13. A heat-resistant steel fixture 9 is arranged at the center position of the turntable 13;

[0075] The laser heating device includes a fiber laser 1, a support frame 2 disposed outside the spraying chamber 11, and a fiber laser head 6 disposed on the support frame 2 and connected to the fiber laser 1. A laser shaper 10 passing through the spraying chamber 11 is provided at the end of the fiber laser head 6. The laser emitted by the fiber laser head 6 is projected onto the gas turbine blade through the laser shaper 10 to heat the gas turbine blade.

[0076] The atmospheric plasma spraying device includes a base 12 disposed in the spraying chamber 11, a six-axis robotic arm 5 disposed on the base 12, and a plasma spray gun 8 disposed at the end of the six-axis robotic arm 5. In step 402, the plasma spray gun 8 is operated by the six-axis robotic arm 5 to spray the surface of the gas turbine blade 7 to be sprayed, forming a coating with longitudinal cracks.

[0077] In this embodiment, step two is specifically as follows:

[0078] Step 201: Insert the first thermocouple through the bottom channel of the root of the gas turbine blade specimen into the middle of the leading edge cavity of the gas turbine blade specimen, insert the second thermocouple through the bottom channel of the root of the gas turbine blade specimen into the middle of the trailing edge cavity of the gas turbine blade specimen, and insert the third thermocouple into the bottom channel of the root of the gas turbine blade specimen. The inserted first thermocouple, second thermocouple, and third thermocouple are denoted as internal thermocouples.

[0079] Thermocouples are mounted on both the upper and lower parts of the leading edge surface, the blade body surface, and the trailing edge surface of the gas turbine blade specimen. The mounted thermocouples are denoted as external thermocouples.

[0080] Step 202: Mount the root of the gas turbine blade specimen in the heat-resistant steel fixture 9 with the tip of the gas turbine blade specimen facing upward and the bottom surface of the root of the gas turbine blade specimen close to the surface of the turntable 13.

[0081] Step 203: Operate the rotating motor 4 to rotate at a set speed and operate the fiber laser 1. The laser emitted through the fiber laser head 6 and the laser shaper 10 is projected onto the surface of the gas turbine blade specimen to heat the gas turbine blade specimen.

[0082] Step 204: During the process of the gas turbine blade specimen rotating and being heated, multiple internal thermocouples detect the temperature inside the gas turbine blade specimen and collect it according to the set sampling time, obtaining multiple internal temperature values at the i-th sampling time. At the same time, multiple external thermocouples detect the temperature on the surface of the gas turbine blade specimen and collect it according to the set sampling time, obtaining multiple external temperature values at the i-th sampling time. Where i is a positive integer.

[0083] Step 205: According to , obtain the standard deviation of multiple external temperature values at the \(i\)-th sampling time relative to the set preheating temperature ; where represents the external temperature value collected by the \(j\)-th external thermocouple at the \(i\)-th sampling time, \(j\) and \(J\) are positive integers, and \(1\leq j\leq J\), \(J\) represents the total number of external thermocouples; represents the set preheating temperature, whose value range is \(550^{\circ}C\) to \(750^{\circ}C\); and obtain the range of multiple external temperature values at the \(i\)-th sampling time, denoted as ;

[0084] Step 206, for the standard deviation of multiple external temperature values at the \(i\)-th sampling time relative to the set preheating temperature and the range are judged. If is not greater than \(10^{\circ}C\),

[0085] is not greater than \(25^{\circ}C\), it indicates that the heating of the gas turbine blade specimen meets the set preheating temperature requirement, and step 207 is executed; otherwise, continuously rotate and heat the gas turbine blade specimen while collecting, obtain the standard deviation and range of multiple external temperature values at the \((i + 1)\)-th sampling time relative to the set preheating temperature and judge until the heating of the gas turbine blade specimen meets the set preheating temperature requirement, and step 207 is executed;

[0086] Step 207, perform an averaging process on multiple external temperature values when the heating of the gas turbine blade specimen meets the set preheating temperature requirement to obtain the external temperature mean value of the gas turbine blade specimen; perform an averaging process on multiple internal temperature values when the heating of the gas turbine blade specimen meets the set preheating temperature requirement to obtain the internal temperature mean value of the gas turbine blade specimen;

[0087] Step 208, construct a correction relationship formula for the internal and external temperatures of the blade \(T_w = T_n+\eta\times d\); where \(T_w\) is the external temperature quantity, \(T_n\) is the internal temperature quantity, the units of \(T_w\) and \(T_n\) are both \(^{\circ}C\), \(\eta\) is the internal and external temperature correction coefficient, and \(d\) is the average thickness of the gas turbine blade, and the unit of \(d\) is millimeters;

[0088] In this embodiment, step three is specifically as follows:

[0089] Step 301, according to the method of steps 203 to 207, obtain the external temperature mean value of the gas turbine blade specimen when the heating meets the set preheating temperature requirement, and denote it as the external temperature mean value before standing of the gas turbine blade specimen;

[0090] Step 302: Operate the rotary motor 4 and the fiber laser 1 to stop working, and let the gas turbine blade specimen stand still in the spraying environment for the spraying time of one layer of the gas turbine blade. After that, obtain the average external temperature after standing still.

[0091] Step 303: Compare the average external temperature before standing still with the average external temperature after standing still to obtain the temperature drop correction coefficient of the gas turbine blade specimen at the set preheating temperature.

[0092] In this embodiment, Step 401 is specifically as follows:

[0093] Step 4011: Set internal thermocouples inside the gas turbine blade 7 to be sprayed according to the method of Step 201.

[0094] Step 4012: Heat the gas turbine blade 7 to be sprayed according to the methods of Step 202 and Step 203.

[0095] Step 4013: During the process of rotating and heating the gas turbine blade 7 to be sprayed, multiple internal thermocouples detect the temperature inside the gas turbine blade 7 to be sprayed and collect it according to the set sampling time, and obtain multiple internal temperature detection values at the e-th sampling time; where e is a positive integer.

[0096] Step 4014: Process the multiple internal temperature detection values at the e-th sampling time by averaging to obtain the average internal temperature detection value at the e-th sampling time. ;

[0097] Step 4015: Denote the internal and external temperature correction coefficient at the set preheating temperature as , and denote the temperature drop correction coefficient at the set preheating temperature as ; ;

[0098] Step 4016: According to , obtain the external temperature value at the e-th sampling time corrected based on the calibrated internal and external temperature correction coefficient and the temperature drop correction coefficient. ;

[0099] Step 4017: Judge and . If , continue to heat the gas turbine blade 7 to be sprayed and execute Step 4018; if , then the surface heating of the gas turbine blade 7 to be sprayed meets the set preheating temperature.

[0100] Step 4018: Obtain and judge the external temperature value at the (e + 1)-th sampling time according to the methods of Step 4016 and Step 4017 until the surface heating of the gas turbine blade 7 to be sprayed meets the set preheating temperature.

[0101] In this embodiment, after Step Four, the specific process is as follows:

[0102] Step A: Repeat Step Four multiple times, and for the coatings with longitudinal cracks prepared at different set preheating temperatures, obtain the longitudinal crack density of the coatings with longitudinal cracks through a scanning electron microscope.

[0103] Step B: Use different set preheating temperatures as the abscissa and the corresponding longitudinal crack densities at different set preheating temperatures as the ordinate to obtain a scatter plot of the longitudinal crack density versus the preheating temperature.

[0104] Step C: Establish a relationship between the longitudinal crack density and the preheating temperature ; where N is the longitudinal crack density, in units of strips / mm, a represents the first coefficient, b represents the second coefficient, T represents the set preheating temperature, T0 is the critical temperature when longitudinal cracks appear, and the units of T and T0 are °C.

[0105] Step D: Use the relationship between the longitudinal crack density and the preheating temperature in Step C to fit the scatter plot of the longitudinal crack density versus the preheating temperature to obtain the fitted first coefficient and second coefficient; and input the fitted first coefficient and second coefficient into Step C to obtain the relationship between the longitudinal crack density and the preheating temperature.

[0106] In this embodiment, during actual use, the signal data lines of the internal thermocouple and the external thermocouple pass through the turntable 13 and can rotate with the turntable 13. A data collector is arranged at the bottom of the turntable 13, so that data acquisition is carried out synchronously with the rotation. In addition, it should be noted that the signal data lines of the internal thermocouple and the external thermocouple are sleeved with high-temperature resistant coating layers to meet the actual needs.

[0107] In this embodiment, during actual use, when the plasma spray gun 8 sprays the surface of the gas turbine blade 7 to be sprayed, the power is 38KW - 45KW, and the spraying distance is 60mm - 100mm. Other preparation process parameters can refer to those in the patent CN117072253B, Method for Designing, Manufacturing and Evaluating Thermal Barrier Coating for High-temperature Blade of Heavy-duty Gas Turbine.

[0108] In this embodiment, during actual use, the set rotation speed is 5RPM - 20RPM.

[0109] In this embodiment, during actual use, mullite stoppers are arranged on the workbench 3. The mullite stoppers are located on the side of the gas turbine blade away from the fiber laser head 6, and the laser that is not irradiated on the gas turbine blade is blocked by the mullite stoppers during the rotation process.

[0110] In this embodiment, the sampling time set in step 204 is 0.1 second to 1 second, and it can also be adaptively adjusted according to actual needs.

[0111] In this embodiment, the range is the maximum value minus the minimum value among multiple external temperature values at the i-th sampling time.

[0112] In this embodiment, during actual use, a tenon groove matching the root shape of the gas turbine blade is provided on the side of the heat-resistant steel fixture 9 close to the gas turbine blade, so as to stably clamp the gas turbine blade.

[0113] In this embodiment, during actual use, the gas turbine blade is a hollow blade.

[0114] In this embodiment, during actual use, the internal thermocouple of the gas turbine blade 7 to be sprayed can be taken out after the subsequent spraying is completed.

[0115] In this embodiment, during actual use, the longitudinal crack extends along the thickness direction of the coating on the surface of the gas turbine blade.

[0116] In this embodiment, it should be noted that the coating thickness on the surface of the gas turbine blade is 300 microns to 1000 microns, and the set preheating temperature value range is 550°C to 750°C to generate a crack density of 0.5 cracks / mm to 6 cracks / mm. If the crack density is too low, the thermal stress cannot be effectively released, increasing the risk of coating spalling. If the crack density is too high, the mechanical strength of the coating will be weakened and the thermal shock resistance will be reduced.

[0117] In this embodiment, during actual use, when spraying the blade, the rotation motor 4 can also be operated to drive the gas turbine blade to rotate to meet the spraying requirements, and conventional atmospheric plasma spraying means can be referred to.

[0118] In this embodiment, it should be noted that a thermocouple is provided inside the gas turbine blade 7 to be sprayed, and the internal temperature is corrected based on the calibrated internal and external temperature correction coefficients and the temperature drop correction coefficient subsequently, so that the surface temperature of the gas turbine blade meets the set preheating temperature, avoiding the interference of the external environment when using an infrared thermometer to detect the surface of the gas turbine blade 7 externally, and the laser radiation may enter the infrared thermometer to cause optical interference.

[0119] In summary, the method of the present invention has simple steps and reasonable design. The rotating gas turbine blade is preheated by a laser heating device to improve the uniformity of the surface temperature distribution of the gas turbine blade, so that the coating with longitudinal cracks can have a long service life while maintaining good performance.

[0120] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent structural changes made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a coating with longitudinal cracks on the surface of a gas turbine blade by laser preheating, characterized in that, The method includes the following steps: Step 1: Set up a device for laser preheating and coating preparation of blades: Step 101: Set up a rotating workbench inside the spraying chamber (11), and set up a laser heating device outside the spraying chamber (11). The laser heating device is located on the left side of the rotating workbench; Step 102: Set up an atmospheric plasma spraying device inside the spraying chamber (11). The atmospheric plasma spraying device is located on the right side of the rotating workbench; Step 2: Obtain the internal and external temperature correction coefficients of a gas turbine blade specimen at a set preheating temperature: Install the gas turbine blade specimen on the rotating workbench, heat the gas turbine blade specimen with the laser heating device, and calibrate the internal temperature and external temperature of the gas turbine blade specimen to obtain the internal and external temperature correction coefficients of the gas turbine blade specimen at the set preheating temperature; Step 3: Obtain the temperature drop correction coefficient of a gas turbine blade specimen at a set preheating temperature: After heating the gas turbine blade specimen to meet the set preheating temperature, let it stand in the spraying environment, and calibrate the average external temperature before standing and the average external temperature after standing of the gas turbine blade specimen to obtain the temperature drop correction coefficient of the gas turbine blade specimen at the set preheating temperature; Step 4: Laser preheating and spraying of the gas turbine blade to be sprayed: Step 401: Use the laser heating device to heat the gas turbine blade (7) to be sprayed, and correct the internal temperature of the gas turbine blade (7) to be sprayed based on the calibrated internal and external temperature correction coefficients and the temperature drop correction coefficient until the surface temperature of the gas turbine blade (7) to be sprayed meets the set preheating temperature; Step 402: After the gas turbine blade (7) to be sprayed is preheated, spray the surface of the gas turbine blade (7) to be sprayed through the atmospheric plasma spraying device to form a coating with longitudinal cracks; The rotating workbench includes a workbench (3), a turntable (13) embedded in the workbench (3), and a rotating motor (4) arranged at the bottom of the turntable (13) and drivingly connected to the turntable (13). A heat-resistant steel fixture (9) is arranged at the central position of the turntable (13); The laser heating device includes a fiber laser (1), a support frame (2) arranged outside the spraying chamber (11), and a fiber laser head (6) arranged on the support frame (2) and connected to the fiber laser (1). A laser shaper (10) passing through the spraying chamber (11) is arranged at the end of the fiber laser head (6); Step 2, the specific process is as follows: Step 201: Insert a first thermocouple through the bottom channel of the blade root of the gas turbine blade specimen into the middle of the leading edge cavity of the gas turbine blade specimen, insert a second thermocouple through the bottom channel of the blade root of the gas turbine blade specimen into the middle of the trailing edge cavity of the gas turbine blade specimen, insert a third thermocouple into the bottom channel of the blade root of the gas turbine blade specimen, and record the inserted first thermocouple, second thermocouple and third thermocouple as internal thermocouples; Thermocouples are mounted on the upper and lower parts of the leading edge surface, the blade body surface and the trailing edge surface of the gas turbine blade specimen, and the mounted thermocouples are recorded as external thermocouples; Step 202: Install the blade root of the gas turbine blade specimen in the heat-resistant steel fixture (9), with the blade tip of the gas turbine blade specimen facing upward and the bottom surface of the blade root of the gas turbine blade specimen close to the surface of the turntable (13). Step 203: Operate the rotary motor (4) to rotate at a set speed, and operate the fiber laser (1) to work. The laser emitted through the fiber laser head (6) and the laser shaper (10) is projected onto the surface of the gas turbine blade specimen to heat the gas turbine blade specimen. Step 204: During the process of heating the gas turbine blade specimen while it is rotating, multiple internal thermocouples detect the temperature inside the gas turbine blade specimen and collect it according to the set sampling time to obtain multiple internal temperature values at the i-th sampling time; meanwhile, multiple external thermocouples detect the temperature on the surface of the gas turbine blade specimen and collect it according to the set sampling time to obtain multiple external temperature values at the i-th sampling time; where i is a positive integer. Step 205: According to , obtain the standard deviation of multiple external temperature values relative to the set preheating temperature at the i-th sampling time ; where represents the external temperature value collected by the j-th external thermocouple at the i-th sampling time, j and J are positive integers, and 1 ≤ j ≤ J, and J represents the total number of external thermocouples; represents the set preheating temperature, with a value range of 550 °C to 750 °C; and obtain the range of multiple external temperature values at the i-th sampling time, denoted as ; Step 206: Calculate the standard deviation and range of multiple external temperature values at the i-th sampling time relative to the set preheating temperature and the range for judgment. If it is not greater than 10°C and the range is not greater than 25°C, it indicates that the heating of the gas turbine blade specimen meets the requirements of the set preheating temperature, and step 207 is executed; otherwise, continue to collect while rotating and heating the gas turbine blade specimen, obtain the standard deviation and range of multiple external temperature values at the (i + 1)-th sampling time relative to the set preheating temperature for judgment, until the heating of the gas turbine blade specimen meets the requirements of the set preheating temperature, and step 207 is executed; Step 207: Perform an averaging process on the multiple external temperature values when the heating of the gas turbine blade specimen meets the set preheating temperature requirement to obtain the average external temperature of the gas turbine blade specimen; perform an averaging process on the multiple internal temperature values when the heating of the gas turbine blade specimen meets the set preheating temperature requirement to obtain the average internal temperature of the gas turbine blade specimen. Step 208: Construct the blade internal and external temperature correction relationship Tw = Tn + η × d; where Tw is the external temperature quantity, Tn is the internal temperature quantity, the units of both Tw and Tn are °C, η is the internal and external temperature correction coefficient, d is the average thickness of the gas turbine blade, and the unit of d is millimeters. Step 209: Assign the average internal temperature in Step 207 to the internal temperature quantity, assign the average external temperature to the external temperature quantity, and input the blade internal and external temperature correction relationship to obtain the internal and external temperature correction coefficient of the gas turbine blade specimen at the set preheating temperature. Step three, the specific process is as follows: Step 301: According to the method in Steps 203 to 207, obtain the average external temperature of the gas turbine blade specimen when the heating meets the set preheating temperature requirement, and record it as the average external temperature before standing of the gas turbine blade specimen. Step 302: Operate the rotary motor (4) and the fiber laser (1) to stop working, and let the gas turbine blade specimen stand in the spraying environment for the spraying time of one layer of gas turbine blade spraying, and then obtain the average external temperature after standing. Step 303: Compare the average external temperature before standing with the average external temperature after standing to obtain the temperature drop correction coefficient of the gas turbine blade specimen at the set preheating temperature.

2. The method for preparing a coating with longitudinal cracks on the surface of a gas turbine blade by laser preheating according to claim 1, characterized in that: The laser emitted by the fiber laser head (6) is projected onto the gas turbine blade through the laser shaper (10) to heat the gas turbine blade. The atmospheric plasma spraying equipment includes a base (12) disposed in a spraying chamber (11), a six-axis robotic arm (5) disposed on the base (12), and a plasma spray gun (8) disposed at the end of the six-axis robotic arm (5). In step 402, the plasma spray gun (8) is operated by the six-axis robotic arm (5) to spray the surface of the gas turbine blade (7) to be sprayed, forming a coating with longitudinal cracks.

3. The method for preparing a coating with longitudinal cracks on the surface of a gas turbine blade by laser preheating according to claim 1, characterized in that: Step 401, the specific process is as follows: Step 4011: Set internal thermocouples inside the gas turbine blade (7) to be sprayed according to the method of step 201. Step 4012: Heat the gas turbine blade (7) to be sprayed according to the methods of step 202 and step 203. Step 4013: During the process of rotating and heating the gas turbine blade (7) to be sprayed, multiple internal thermocouples detect the temperature inside the gas turbine blade (7) to be sprayed and collect it according to the set sampling time, obtaining multiple internal temperature detection values at the e-th sampling time; where e is a positive integer. Step 4014, perform an averaging process on multiple internal temperature detection values at the e-th sampling time to obtain the average internal temperature detection value at the e-th sampling time ; Step 4015, record the internal and external temperature correction coefficients at the set preheating temperature as , and record the temperature drop correction coefficient at the set preheating temperature as ; Step 4016, according to , obtain the external temperature value at the e-th sampling time corrected based on the calibrated internal and external temperature correction coefficients and the temperature drop correction coefficient ; Step 4017: Determine and . If , continuously heat the gas turbine blade (7) to be sprayed, and execute Step 4018; if , the surface heating of the gas turbine blade (7) to be sprayed meets the set preheating temperature. Step 4018: Obtain and judge the external temperature value at the (e + 1)-th sampling time according to the methods of step 4016 and step 4017 until the surface heating of the gas turbine blade (7) to be sprayed meets the set preheating temperature.

4. The method for preparing a coating with longitudinal cracks on the surface of a gas turbine blade by laser preheating according to claim 1, characterized in that: After step four, the specific process is as follows: Step A: Repeat step four multiple times, and obtain the longitudinal crack density of the coating with longitudinal cracks prepared at different set preheating temperatures by a scanning electron microscope. Step B: Use different set preheating temperatures as the abscissa and the longitudinal crack density corresponding to different set preheating temperatures as the ordinate to obtain a scatter plot of longitudinal crack density versus preheating temperature. Step C: Establish the relationship between the longitudinal crack density and the preheating temperature ; where N is the longitudinal crack density, in units of cracks / mm, a represents the first coefficient, b represents the second coefficient, T represents the set preheating temperature, T0 is the critical temperature when longitudinal cracks occur, and the units of T and T0 are °C; Step D: Fit the scatter plot of longitudinal crack density versus preheating temperature using the longitudinal crack density and preheating temperature relationship formula in step C to obtain the first and second fitting coefficients; and input the first and second fitting coefficients obtained by fitting into step C to obtain the longitudinal crack density and preheating temperature relationship formula.

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