Preparation method of ceramic coating with longitudinal crack growth ability

Abstract

A method for preparing a ceramic coating with the ability to grow longitudinal cracks. It includes steps such as the preparation of MK resin solution; the preparation of the metal bonding layer; the preparation of the first layer of ceramic coating; the preparation and curing of the first layer of MK resin layer; the preparation of the second layer of ceramic coating; the preparation and curing of the second layer of MK resin layer, etc. The present invention has low cost and a relatively simple preparation process. Only a small amount of anhydrous ethanol and MK resin raw materials are needed. Inside and on the surface of the plasma-sprayed ceramic coating, a discontinuous MK resin layer is sprayed respectively using a reusable porous mask template, and a ceramic coating with the ability to grow longitudinal cracks can be prepared. On the basis of ensuring that the bonding strength of the ceramic coating does not decrease significantly, the longitudinal micro-cracking of the discontinuous MK resin layer during the thermal cycle can consume the thermal cycle energy, release the thermal cycle internal stress, and reduce the crack propagation driving force at the interface of part of the ceramic coating / bonding layer, thereby significantly improving the thermal cycle life of the ceramic coating.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic coating structure design and optimization, and in particular relates to a method for preparing a ceramic coating with longitudinal crack growth capability. Background Art

[0002] At present, ceramic coatings (thermal barrier coatings, high-temperature sealing coatings, etc.) prepared by plasma spraying (APS) technology have been widely used in the hot end components of aircraft engines. However, due to the harsh service environment, ceramic coatings are prone to peeling failure. There are two main mechanical inducements that cause conventional APS ceramic coatings to peel off easily. One of them is the growth stress formed by the volume growth of thermally grown oxides. The second inducement is the interface mismatch stress caused by the mismatch of thermal expansion coefficients between the high-temperature alloy substrate, bonding layer, ceramic coating and thermally grown oxide (TGO) layer. Therefore, one of the effective ways to improve the service life of ceramic coatings is to control the driving force of crack growth, that is, to release the growth stress of the TGO layer that continues to grow during the operation of the ceramic coating and the thermal mismatch stress at the ceramic coating / TGO interface.

[0003] Early researchers used electron beam physical vapor deposition (EB-PVD) to prepare ceramic coatings with a "columnar" structure. The internal stress can be effectively released through the micro-cracking of countless "columns", so the ceramic coatings prepared by the EB-PVD method have good performance, but the cost of EB-PVD is expensive and the coating deposition efficiency is very low. Later, plasma enhanced chemical vapor deposition technology (PE-CVD), laser chemical vapor deposition technology (L-CVD), plasma physical vapor deposition technology (PS-PVD) and low-pressure plasma spray thin coating technology (LPPS-TF) were developed successively, which can prepare "columnar" or "columnar"-like ceramic coatings, and improve the life of ceramic coatings to varying degrees. However, the above methods still face problems such as demanding raw material requirements, low deposition efficiency, expensive equipment or complex coating forming process.

[0004] Another way to release the internal stress in the ceramic coating is the microcrack technique. Initially, domestic and foreign scholars could prepare ceramic coatings with longitudinal cracks using suspension plasma spraying (SPS) and solution precursor plasma spraying (SPPS). These longitudinal cracks are similar to the gaps between columnar crystals in EB-PVD coatings and have the function of releasing internal stress, thereby improving the strain tolerance and lifespan of the ceramic coating. However, the process of forming coatings by SPS and SPPS is complex, and the volatilization of solvents in the suspension or solution precursor absorbs a large amount of heat. The spraying distance is greatly reduced compared to plasma spraying technology, resulting in reduced stability and controllability of the coating preparation process. In 2013 and 2014, Lisa Pin et al. and Lu Zhe et al. successively proposed methods of using sol-gel (Sol-Gel) + high-temperature heat treatment to generate reticulated cracks and surface concentrated heating to generate longitudinal cracks, which extended the service life of the ceramic coating to varying degrees. However, the crack morphology generated by using Sol-Gel + high-temperature treatment is irregular, and the density is uncontrollable. It is difficult for plasma spraying coatings to fill some cracking areas, making the lifespan of this structure of thermal barrier coatings have unstable factors. The method of using surface concentrated heating to generate longitudinal cracks has a low density and uneven distribution, and continuous growth of transverse cracks is likely to occur, with limited effect on improving the coating performance. In 2018, Zeng Jinyan et al. implanted microcracks in the ceramic coating by combining air plasma spraying (APS) with dry ice blasting technology. The vertical microcracks in the coating not only reduce the thermal stress but also improve the strain tolerance of the ceramic coating, thereby increasing the lifespan of the ceramic coating. However, this method cannot control the generation of transverse microcracks, and delamination failure caused by continuous growth of transverse cracks is likely to occur.

[0005] The above studies all optimized the microscopic morphology or microstructure of the ceramic coating using a certain technology or method. By releasing the continuously growing growth stress of the TGO layer and the thermal mismatch stress at the interface between the ceramic topcoat and the TGO layer during operation, the thermal cycle cracking resistance of the ceramic coating was improved. However, the above methods still face problems such as high preparation cost, low production efficiency, great technical difficulty, and poor effect. Summary of the Invention

[0006] In order to solve the above problems, the purpose of the present invention is to provide a method for preparing a ceramic coating with the ability to grow longitudinal cracks.

[0007] To achieve the above purpose, the method for preparing a ceramic coating with the ability to grow longitudinal cracks provided by the present invention includes the following steps carried out in sequence:

[0008] 1) Preparation of MK resin solution: Using a magnetic stirrer to stir anhydrous ethanol as the solvent and MK resin as the solute to prepare a resin solution;

[0009] 2) Preparation of the metal bonding layer: The CoCrAlY powder is sprayed onto the surface of the nickel-based alloy substrate by plasma spraying technology to prepare the metal bonding layer;

[0010] 3) Preparation of the first layer of ceramic coating: The YSZ powder (grade AI-1075) is sprayed onto the surface of the above metal bonding layer by plasma spraying technology to prepare the first layer of ceramic coating;

[0011] 4) Preparation of the first layer of MK resin layer: The MK resin solution prepared in step 1) is sprayed onto the surface of the first layer of ceramic coating by using a porous mask template and a spray gun to prepare the first layer of MK resin layer with the function of longitudinal crack growth;

[0012] 5) Curing of the first layer of MK resin layer: The nickel-based alloy substrate with the MK resin layer prepared in step 4) is placed in a high-temperature electric furnace for heating and curing;

[0013] 6) Preparation of the second layer of ceramic coating: Repeat step 3) to prepare the second layer of ceramic coating on the surface of the first layer of MK resin layer;

[0014] 7) Preparation of the second layer of MK resin layer: Repeat step 4) to prepare the second layer of MK resin layer on the surface of the second layer of ceramic coating;

[0015] 8) Curing of the second layer of MK resin layer: Repeat step 5) to fabricate the ceramic coating with the ability of longitudinal crack growth.

[0016] In step 1), the weight ratio of the absolute ethanol to the MK resin is 30 - 40∶5 - 7; the rotation speed of the magnetic stirrer is 700 - 800 r / min, the stirring time is 14 - 16 h, and the stirring temperature is room temperature.

[0017] In step 2), the voltage of the plasma spraying is 40 - 41 V, the current is 780 - 800 A, the powder feeding rate is 30 - 35 g / min, the spraying distance is 100 - 120 mm, and the thickness of the metal bonding layer is 100 - 150 μm.

[0018] In steps 3) and 6), the voltage of the plasma spraying is 40.5 - 41.5 V, the current is 790 - 810 A, the powder feeding rate is 35 - 40 g / min, the spraying distance is 100 - 120 mm, and the thickness of the first layer of ceramic coating is 200 - 250 μm.

[0019] In steps 4) and 7), the pressure of the spray gun is 0.5 - 0.6 MPa, the spraying distance is 150 - 200 mm, and the dosage of the sprayed MK resin solution is 8 - 10 ml / 506 mm 2 。

[0020] In steps 5) and 8), the heating and curing temperature of the high-temperature electric furnace is 600-800 °C, and the curing time is 25-35 min.

[0021] The method for preparing a ceramic coating with the ability to grow longitudinal cracks provided by the present invention has the following advantages:

[0022] (1) Low cost and relatively simple preparation process. Only a small amount of anhydrous ethanol and MK resin raw materials are needed. A discontinuous MK resin layer is respectively sprayed on the inside and surface of the plasma-sprayed ceramic coating by using a reusable porous mask template, and a ceramic coating with the ability to grow longitudinal cracks can be prepared.

[0023] (2) The discontinuous MK resin prepared based on the porous mask template can prevent the continuous growth of transverse cracks. On the basis of ensuring that the bonding strength of the ceramic coating does not decrease significantly, the longitudinal micro-cracking of the discontinuous MK resin layer during the thermal cycling process can consume the thermal cycling energy, release the thermal cycling internal stress, and reduce the crack propagation driving force at the interface of part of the ceramic coating / bonding layer, thereby significantly improving the thermal cycling life of the ceramic coating. Description of the Drawings

[0024] Figure 1 It is the microscopic morphology of the discontinuous MK resin layer prepared by using a spraying gun, where the magnification factors of (a) and (b) are 200 and 20 respectively.

[0025] Figure 2 It is the cross-sectional morphology of the ceramic coating with the ability to grow longitudinal cracks provided by the present invention before thermal cycling.

[0026] Figure 3 It is the cross-sectional morphology of the ceramic coating with the ability to grow longitudinal cracks provided by the present invention after 50 thermal cycles (one thermal cycle process is to keep the temperature at 1100 °C for 15 min and cool with compressed air for 15 min).

[0027] Figure 4 It is the cross-sectional morphology of the ceramic coating with the ability to grow longitudinal cracks provided by the present invention after 150 thermal cycles (one thermal cycle process is to keep the temperature at 1100 °C for 15 min and cool with compressed air for 15 min). Detailed Embodiments

[0028] The embodiments of the present invention are described in detail below. The embodiments are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0029] Example 1:

[0030] The method for preparing a ceramic coating with the ability to grow longitudinal cracks provided in this example includes the following steps carried out in sequence:

[0031] 1) Preparation of MK resin solution: Use a magnetic stirrer to stir anhydrous ethanol as the solvent and MK resin as the solute to prepare an MK resin solution. The weight ratio of anhydrous ethanol to MK resin is 30:5. The rotation speed of the magnetic stirrer is 700 r / min, the stirring time is 14 h, and the stirring temperature is room temperature;

[0032] 2) Preparation of metal bonding layer: Use plasma spraying technology to spray CoCrAlY powder (grade CO110) on the surface of a nickel-based alloy substrate to prepare a metal bonding layer. The voltage of plasma spraying is 40 V, the current is 780 A, the powder feeding rate is 30 g / min, the spraying distance is 100 mm, and the thickness of the metal bonding layer is 100 μm;

[0033] 3) Preparation of the first layer of ceramic coating: Use plasma spraying technology to spray YSZ powder (grade AI-1075) on the surface of the above metal bonding layer to prepare the first layer of ceramic coating. The voltage of plasma spraying is 40.5 V, the current is 790 A, the powder feeding rate is 35 g / min, the spraying distance is 100 mm, and the thickness of the first layer of ceramic coating is 200 μm;

[0034] 4) Preparation of the first layer of MK resin layer: Use a porous mask plate and a spray gun to spray the MK resin solution prepared in step 1) on the surface of the first layer of ceramic coating to prepare the first layer of MK resin layer with the function of longitudinal crack growth. The pressure of the spray gun is 0.5 MPa, the spraying distance is 150 mm, and the dosage of the sprayed MK resin solution is 8 ml / 506 mm 2 ;

[0035] 5) Curing of the first layer of MK resin layer: Place the nickel-based alloy substrate with the MK resin layer prepared in step 4) in a high-temperature electric furnace for heating and curing. The curing temperature is 600 °C, and the curing time is 25 min;

[0036] 6) Preparation of the second layer of ceramic coating: Repeat step 3) to prepare the second layer of ceramic coating on the surface of the first layer of MK resin. The voltage of plasma spraying is 40.5 V, the current is 790 A, the powder feeding rate is 35 g / min, the spraying distance is 100 mm, and the thickness of the second layer of ceramic coating is 200 μm;

[0037] 7) Preparation of the second layer of MK resin layer: Repeat step 4) to prepare the second layer of MK resin layer on the surface of the second layer of ceramic coating. The pressure of the spray gun is 0.5 MPa, the spraying distance is 150 mm, and the dosage of the sprayed MK resin solution is 8 ml / 506 mm 2 ;

[0038] 8) Curing of the second layer of MK resin layer: Repeat step 5), with a curing temperature of 600 °C and a curing time of 25 min, thereby fabricating the ceramic coating with the ability to grow longitudinal cracks.

[0039] Example 2:

[0040] The method for fabricating a ceramic coating with the ability to grow longitudinal cracks provided in this example includes the following steps carried out in sequence:

[0041] 1) Preparation of MK resin solution: Using a magnetic stirrer, stir anhydrous ethanol as the solvent and MK resin as the solute to prepare an MK resin solution. The weight ratio of anhydrous ethanol to MK resin is 35:6, the rotation speed of the magnetic stirrer is 750 r / min, the stirring time is 15 h, and the stirring temperature is room temperature;

[0042] 2) Preparation of the metal bonding layer: Using plasma spraying technology, spray CoCrAlY powder (grade CO110) on the surface of a nickel-based alloy substrate to prepare a metal bonding layer. The voltage of plasma spraying is 40.5 V, the current is 790 A, the powder feeding rate is 32 g / min, the spraying distance is 110 mm, and the thickness of the metal bonding layer is 120 μm.

[0043] 3) Preparation of the first layer of ceramic coating: Using plasma spraying technology, spray YSZ powder (grade AI-1075) on the surface of the above metal bonding layer to prepare the first layer of ceramic coating. The voltage of plasma spraying is 41 V, the current is 800 A, the powder feeding rate is 37 g / min, the spraying distance is 110 mm, and the thickness of the first layer of ceramic coating is 220 μm;

[0044] 4) Preparation of the first layer of MK resin layer: Using a porous mask template and a spray gun, spray the MK resin solution prepared in step 1) on the surface of the first layer of ceramic coating to prepare the first layer of MK resin layer with the function of growing longitudinal cracks. The pressure of the spray gun is 0.55 MPa, the spraying distance is 170 mm, and the dosage of the sprayed MK resin solution is 9 ml / 506 mm 2 ;

[0045] 5) Curing of the first layer of MK resin layer: Place the nickel-based alloy substrate with the first layer of MK resin layer prepared in step 4) in a high-temperature electric furnace for heating and curing. The curing temperature is 700 °C and the curing time is 30 min;

[0046] 6) Preparation of the second layer of ceramic coating: Repeat step 3) to prepare the second layer of ceramic coating on the surface of the first layer of MK resin layer. The voltage of plasma spraying is 41 V, the current is 800 A, the powder feeding rate is 37 g / min, the spraying distance is 110 mm, and the thickness of the second layer of ceramic coating is 220 μm;

[0047] 7) Preparation of the second layer of MK resin layer: Repeat step 4) to prepare the second layer of MK resin layer on the surface of the second layer of ceramic coating. The pressure of the spray gun is 0.55 MPa, the spray distance is 170 mm, and the dosage of the sprayed MK resin solution is 9 ml / 506 mm 2 ;

[0048] 8) Curing of the second layer of MK resin layer: Repeat step 5). The curing temperature is 700 °C and the curing time is 30 min, thus preparing the ceramic coating with the ability of longitudinal crack growth.

[0049] Example 3:

[0050] The method for preparing a ceramic coating with the ability of longitudinal crack growth provided in this example includes the following steps carried out in sequence:

[0051] 1) Preparation of MK resin solution: Use a magnetic stirrer to stir absolute ethanol as the solvent and MK resin as the solute to prepare an MK resin solution. The weight ratio of absolute ethanol to MK resin is 40:7, the rotation speed of the magnetic stirrer is 800 r / min, the stirring time is 16 h, and the stirring temperature is room temperature;

[0052] 2) Preparation of the metal bonding layer: Use plasma spraying technology to spray (CoCrAlY powder, grade CO110) on the surface of the nickel-based alloy substrate to prepare the metal bonding layer. The voltage of plasma spraying is 41 V, the current is 800 A, the powder feeding rate is 35 g / min, the spray distance is 120 mm, and the thickness of the metal bonding layer is 150 μm.;

[0053] 3) Preparation of the first layer of ceramic coating: Use plasma spraying technology to spray YSZ powder (grade AI-1075) on the surface of the above metal bonding layer to prepare the first layer of ceramic coating. The voltage of plasma spraying is 41.5 V, the current is 810 A, the powder feeding rate is 40 g / min, the spray distance is 120 mm, and the thickness of the first layer of ceramic coating is 250 μm;

[0054] 4) Preparation of the first layer of MK resin layer: Use a porous mask template and a spray gun to spray the MK resin solution prepared in step 1) on the surface of the first layer of ceramic coating to prepare the first layer of MK resin layer with the function of longitudinal crack growth. The pressure of the spray gun is 0.6 MPa, the spray distance is 200 mm, and the dosage of the sprayed MK resin solution is 10 ml / 506 mm 2 ;

[0055] 5) Curing of the first layer of MK resin layer: Place the nickel-based alloy substrate with the first layer of MK resin layer prepared in step 4) in a high-temperature electric furnace for heating and curing. The curing temperature is 800 °C and the curing time is 35 min;

[0056] 6) Preparation of the second-layer ceramic coating: Repeat step 3) to prepare the second-layer ceramic coating on the surface of the first-layer MK resin layer. The voltage of plasma spraying is 41.5 V, the current is 810 A, the powder feeding rate is 40 g / min, the spraying distance is 120 mm, and the thickness of the second-layer ceramic coating is 250 μm;

[0057] 7) Preparation of the second-layer MK resin layer: Repeat step 4) to prepare the second-layer MK resin layer on the surface of the second-layer ceramic coating. The pressure of the spraying gun is 0.6 MPa, the spraying distance is 200 mm, and the dosage of the sprayed MK resin solution is 10 ml / 506 mm 2 ;

[0058] 8) Curing of the second-layer MK resin layer: Repeat step 5). The curing temperature is 800 °C and the curing time is 35 min, thereby fabricating the ceramic coating with the ability of longitudinal crack growth.

[0059] Figure 1 is the microscopic morphology of the discontinuous MK resin layer prepared by using a spraying gun, where the magnification factors of (a) and (b) are 200 and 20 respectively. As can be seen from Figure 1 it, the MK resin layer prepared based on the shielding effect of the round-hole-shaped mask plate shows a discontinuous arrangement on the ceramic coating.

[0060] Figure 2 is the cross-sectional morphology of the ceramic coating with the ability of longitudinal crack growth provided by the present invention before thermal cycling. As can be seen from Figure 2 it, after adding two layers of discontinuous MK resin layers, there is no obvious interface in the cross-sectional morphology of the novel ceramic coating, the bonding between the ceramic coating and the discontinuous MK resin layer is good, and the novel ceramic coating has no cracking before thermal cycling.

[0061] Figure 3 and Figure 4 are respectively the cross-sectional morphologies of the ceramic coating with the ability of longitudinal crack growth provided by the present invention after 50 and 150 thermal cycles. As can be seen from Figure 3 it, after 50 thermal cycles of the novel ceramic coating, obvious longitudinal cracks appear in the ceramic coating, almost no obvious transverse cracks, and the bonding between the ceramic coating and the metal bonding layer is still good. As can be seen from Figure 4 it, with the continuous increase of the number of thermal cycles, after 150 thermal cycles of the novel ceramic coating, obvious sintering phenomenon occurs in the ceramic coating, but the longitudinal cracks are still dominant in the ceramic coating, only a small amount of transverse cracks, and only slight cracking appears at the interface between the ceramic coating and the metal bonding layer.

[0062] The reason why the ceramic coating with the ability to grow longitudinal cracks provided by the present invention has a good thermal cycle life is that, on the one hand, the discontinuous MK resin prepared based on the porous mask plate can prevent the continuous growth of transverse cracks, thereby ensuring that the bonding strength of the new ceramic coating does not decrease significantly; on the other hand, the longitudinal micro-cracking of the discontinuous MK resin layer during the thermal cycle process can consume the thermal cycle energy, release the thermal cycle internal stress, and reduce the crack propagation driving force at the interface of part of the ceramic coating / bonding layer, thereby significantly improving the thermal cycle life of the new ceramic coating.

Claims

1. A method for preparing a ceramic coating with the ability to grow longitudinal cracks, characterized in that: The ceramic coating preparation method includes the following steps carried out in sequence: 1) Preparation of MK resin solution: Using a magnetic stirrer to stir anhydrous ethanol as the solvent and MK resin as the solute to prepare a resin solution; 2) Preparation of metal bonding layer: Using plasma spraying technology to spray CoCrAlY powder on the surface of a nickel-based alloy substrate to prepare a metal bonding layer; 3) Preparation of the first layer of ceramic coating: Using plasma spraying technology to spray YSZ powder on the surface of the above metal bonding layer to prepare the first layer of ceramic coating; 4) Preparation of the first layer of MK resin layer: Using a porous mask template and a spray gun to spray the MK resin solution prepared in step 1) on the surface of the first layer of ceramic coating to prepare the first layer of MK resin layer with the function of longitudinal crack growth; 5) Curing of the first layer of MK resin layer: Placing the nickel-based alloy substrate with the MK resin layer prepared in step 4) in a high-temperature electric furnace for heating and curing; 6) Preparation of the second layer of ceramic coating: Repeating step 3) to prepare the second layer of ceramic coating on the surface of the first layer of MK resin layer; 7) Preparation of the second layer of MK resin layer: Repeating step 4) to prepare the second layer of MK resin layer on the surface of the second layer of ceramic coating; 8) Curing of the second layer of MK resin layer: Repeating step 5) to thus prepare the ceramic coating with the ability of longitudinal crack growth.

2. The method for preparing a ceramic coating with the ability to grow longitudinal cracks according to claim 1, characterized in that: In step 1), the weight ratio of the anhydrous ethanol to the MK resin is 30 - 40∶5 - 7; the rotation speed of the magnetic stirrer is 700 - 800 r / min, the stirring time is 14 - 16 h, and the stirring temperature is room temperature.

3. The method for preparing a ceramic coating with the ability to grow longitudinal cracks according to claim 1, characterized in that: In step 2), the voltage of the plasma spraying is 40 - 41 V, the current is 780 - 800 A, the powder feeding rate is 30 - 35 g / min, the spraying distance is 100 - 120 mm, and the thickness of the metal bonding layer is 100 - 150 μm.

4. The method for preparing a ceramic coating with the ability to grow longitudinal cracks according to claim 1, characterized in that: In steps 3) and 6), the voltage of the plasma spraying is 40.5 - 41.5 V, the current is 790 - 810 A, the powder feeding rate is 35 - 40 g / min, the spraying distance is 100 - 120 mm, and the thickness of the first layer of ceramic coating is 200 - 250 μm.

5. The method for preparing a ceramic coating with the ability to grow longitudinal cracks according to claim 1, characterized in that: In steps 4) and 7), the pressure of the spray gun is 0.5 - 0.6 MPa, the spraying distance is 150 - 200 mm, and the dosage of the sprayed MK resin solution is 8 - 10 ml / 506 mm 2 .

6. The method for preparing a ceramic coating with the ability to grow longitudinal cracks according to claim 1, characterized in that: In steps 5) and 8), the heating and curing temperature of the high-temperature electric furnace is 600 - 800 °C, and the curing time is 25 - 35 min.

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