Thermal barrier composite coating with gradient structure and method for producing same

Abstract

The application provides a thermal barrier composite coating with a gradient structure, comprising a substrate and a composite coating arranged on the substrate, wherein the composite coating comprises a bonding layer arranged on the substrate and an oxygen barrier layer arranged on the bonding layer; the bonding layer is made of a NiCrAlTiHfSi coating layer; the oxygen barrier layer has a continuous gradient structure; the oxygen barrier layer is made of a Si-HfO2 coating layer; the Si-HfO2 coating layer comprises 20%-80% of Si and 20%-80% of HfO2; and along the vertical direction of the Si-HfO2 coating layer close to the bonding layer, the content of HfO2 gradually decreases. The NiCrAlTiHfSi metal bonding layer and the Si-HfO2 oxygen barrier layer are prepared by a double-layer glow plasma surface metallurgy process, the working temperature is higher than 1250 DEG C, the prepared impregnation layer is dense and uniform, has a continuous gradient structure, and the atomic combination between the bonding layer and the oxygen barrier layer forms a gradient metallurgical interface, the prepared oxygen barrier layer has good bonding strength with the bonding layer, the stress concentration in the mechanical stress or the thermal cycle process is reduced, and the safety and service life are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coating preparation, and particularly relates to a thermal barrier composite coating with gradient structure and a preparation method thereof. BACKGROUND

[0002] With the continuous increase of the thrust-to-weight ratio of the aero-engine, the gas turbine inlet temperature is also increased, and the working temperature of the next generation of gas turbine blade thermal barrier coating will be above 1250 DEG C. At present, there is no suitable coating material. It is an urgent requirement for the rapid development of aero-engine to carry out research on new thermal barrier coatings with high temperature resistance, high thermal insulation and long service life.

[0003] The so-called thermal barrier coating is a coating system composed of a metal bonding layer and a ceramic surface coating. The metal bonding layer is one of the key components in the thermal barrier coating system, which can relieve the stress caused by the mismatch of the thermal expansion coefficients of the ceramic coating and the substrate and improve the oxidation resistance of the substrate alloy, and also serves as the substrate of the ceramic top layer to improve the physical compatibility of the coating and the substrate alloy. The ceramic coating as the oxygen barrier layer in the thermal barrier coating system has high heat resistance, corrosion resistance and low thermal conductivity, which can significantly improve the service life of the thermal barrier coating. The data shows that after the surface of the first stage turbine blade is coated with TBCs, the cooling air flow can be reduced by 50%, the specific fuel consumption can be reduced by 1% to 2%, and the service life of the blade can be increased by several times. In addition, TBCs also have wide application prospects in the thermal end components in the fields of ships, automobiles and energy.

[0004] The most important problem in the thermal barrier coating system is the bonding strength between the functional layers. In order to relieve the mismatch of the thermal expansion coefficients of the ceramic layer and the alloy substrate, and to improve the high temperature oxidation corrosion resistance of the substrate, a metal bonding layer is usually added between the alloy substrate and the ceramic layer. At high temperature, Al in the bonding layer diffuses outward and selectively oxidizes to form a dense alumina protective film, which prevents further oxidation of the bottom layer and thus protects the substrate. Since the composition of the bonding layer has a decisive effect on the growth rate, composition, integrity and bonding force with the substrate of the oxidation layer, which directly affects the service life of the thermal barrier coating, the optimization and selection of the composition of the bonding layer are very crucial to improve the service life of the thermal barrier coating.

[0005] The metal bonding layer material usually adopts MCrAlY (M is transition metal Fe, Ni, Co or Ni+Co). Since Fe2O3, CoO and the like are easy to chemically react with the monoclinic phase or cubic phase of ZrO2 at high temperature, the stability of the ZrO2 ceramic is reduced. Therefore, FeCrAlY and CoCrAlY are not suitable for the bonding bottom layer of the thermal barrier coating. Since the comprehensive performance of the oxidation resistance and the hot corrosion resistance of the NiCoCrAlY bonding layer is good, the bonding layer material used in the current aero-engine turbine blade mostly adopts this alloy system.

[0006] Generally, the content of Al in NiCoCrAlY alloy is controlled in the range of 8%~12% (mass fraction). The component Cr is mainly used to improve the oxidation resistance and sulfurization resistance of the bond coat. Under high temperature conditions, after the Al in the bond coat is oxidized completely, Cr will continue to form a Cr2O3 film between the alumina film and the bond coat, which plays a shielding role for the base alloy, and it can also promote the generation of Al2O3 film. However, an excessively thick oxidation film will reduce the interfacial adhesion, and when the thickness of the oxidation film between the MCrAlY layer and the ceramic layer reaches 3 μm~5 μm, the ceramic layer will be peeled off. Meanwhile, the addition of 0.3%~1% (mass fraction) of trace rare earth element Y can play the role of oxide pinning and grain refinement, thereby improving the adhesion of the Al2O3 film to the substrate under thermal cycling conditions and improving the thermal shock resistance of the coating. In addition, other alloying elements such as Si, Hf, Ta, Zr, etc. can be added to the coating to improve the mechanical properties and oxidation resistance of the coating. Trace elements play an important role in the metal bond coat system.

[0007] Of course, simply adjusting the composition of the metal bond coat is far from enough. The outermost oxygen barrier layer (ceramic layer) also needs to be structurally designed and compositionally optimized. 6%~8% Y2O3 stabilized ZrO2 (YSZ) is the ceramic layer material commonly used in the thermal barrier coating of aero-engine turbine blades. However, the working temperature of YSZ cannot exceed 1 200 ℃, and above this temperature, YSZ will expand due to phase transition; at the same time, due to sintering, the coating will be densified, which will lead to a decrease in the strain capacity of the coating and an increase in the thermal stress, accelerating the peeling failure of the coating. In addition, due to densification and reduction of porosity, the heat insulation capacity of the coating will also be significantly reduced. Therefore, Si-HfO2 composite coating has been proposed at home and abroad to improve the high-temperature service performance of the ceramic coating. The high melting point (2758 ℃) of HfO2 not only can increase the service temperature of the coating, but also Si will react with HfO2 to form HfSiO4, which has low oxygen diffusion rate and good phase stability, which can not only weaken the thermal stress accumulation caused by the phase transition of cristobalite, but also the dispersed HfSiO4 / HfO2 particles can effectively avoid the connection of internal cracks in the coating during growth. This ceramic coating has good high-temperature oxidation resistance and heat insulation capacity.

[0008] However, the insufficient bonding strength between the bond coat and the ceramic layer and the rapid growth of the TGO oxidation layer greatly limit the safety and service life of the thermal barrier coating.

[0009] Functional gradient material is proposed by Japanese scholar in 1987. The functional gradient material is a non-homogeneous material with continuously changing physical and chemical properties along a single dimension (horizontal, vertical or a certain angle) direction by special preparation method, so that the composition, organization, structure and porosity of the material continuously change along the single dimension direction. In practical application, the continuously changing functional gradient material can effectively reduce the interface mismatch problem, meet the use requirements of different environments and different parts, and greatly improve the applicability, reliability and service life of the part. SUMMARY

[0010] The present application aims to solve the problems of weak bonding strength between coating and substrate, insufficient service temperature of coating, and coating failure in high temperature and frequent vibration environment, and provides a thermal barrier coating with gradient structure, high bonding strength with substrate, good oxidation resistance and strong thermal cycle capacity, so as to improve the safety and service life of the thermal barrier coating.

[0011] The double-layer glow plasma surface metallurgy process has the functions of metal and non-metal single or multi-element composite plating, can prepare dense and uniform plating layer with continuous gradient structure, and generates atomic bonding between the bonding layer and the oxygen barrier layer to form a certain depth of gradient metallurgical interface, which makes the prepared bonding and oxygen barrier layer have good bonding strength between the bonding layer and the bonding layer, greatly reduces the stress concentration in the mechanical stress or thermal cycle process, and improves the safety and service life.

[0012] The technical scheme adopted by the present application is:

[0013] A thermal barrier composite coating with gradient structure, comprising a substrate and a composite coating arranged on the substrate, the composite coating comprising a bonding layer arranged on the substrate and an oxygen barrier layer arranged on the bonding layer, the bonding layer being a NiCrAlTiHfSi coating, the oxygen barrier layer having a continuous gradient structure, the oxygen barrier layer being a Si-HfO2 coating, the Si-HfO2 coating comprising 20% to 80% Si and 20% to 80% HfO2, and the HfO2 content gradually decreasing along the vertical direction of the Si-HfO2 coating close to the bonding layer.

[0014] Preferably, the thermal barrier composite coating with gradient structure, wherein the thickness of the bonding layer is 50 to 100 microns, and the thickness of the oxygen barrier layer is 20 to 40 microns.

[0015] Preferably, the thermal barrier composite coating with gradient structure, wherein the NiCrAlTiHfSi coating comprises 5% to 10% Hf, 10% to 15% Si, 20% Ni, 20% Cr, 20% Al and 20% Ti by mass percentage.

[0016] Preferably, the thermal barrier composite coating with gradient structure, wherein: the substrate comprises one of nickel-based alloy, titanium alloy and fiber reinforced composite material in terms of mass fraction.

[0017] A method for preparing a thermal barrier composite coating with gradient structure, comprising the following steps:

[0018] S1. polishing the substrate with sandpaper, and then ultrasonic cleaning for 10-15 min;

[0019] S2. preparing a bonding layer on the surface of the substrate by using double-layer glow plasma surface metallurgy to obtain a first sample;

[0020] S3. depositing an oxygen barrier layer on the surface of the bonding layer prepared in step S2 by using double-layer glow plasma surface metallurgy to obtain a second sample;

[0021] S4. placing the second sample prepared in step S3 into a vacuum diffusion annealing furnace for heat treatment to obtain a thermal barrier composite coating.

[0022] Preferably, the method for preparing a thermal barrier composite coating with gradient structure, wherein: in step S2, the double-layer glow plasma surface metallurgy comprises the following steps:

[0023] S21. placing the substrate into a double-layer glow plasma metallurgy furnace, vacuumizing to below 0.2 Pa, washing with protective gas for 2-3 times, and then maintaining the gas pressure at 20-40 Pa;

[0024] S22. pre-placing the substrate and NiCrAlTiHfSi alloy target material in the double-layer glow plasma surface metallurgy furnace, taking the substrate as the workpiece electrode and the NiCrAlTiHfSi alloy target material as the source electrode, keeping the glow in the furnace stable, increasing the temperature in the metallurgy furnace to 900-1300 ℃ for metallurgy treatment for 8-12 h to prepare a NiCrAlTiHfSi bonding layer on the surface of the substrate, and the distance between the source electrode and the workpiece electrode is 10-30 mm.

[0025] Preferably, the method for preparing a thermal barrier composite coating with gradient structure, wherein: in step S3, the double-layer glow plasma surface metallurgy comprises the following steps:

[0026] S31. placing the first sample into a double-layer glow plasma metallurgy furnace, vacuumizing to below 0.2 Pa, washing with protective gas for 2-3 times, and then maintaining the gas pressure at 20-40 Pa;

[0027] S32. Preposition the substrate, Si target and Hf target in the double-layer glow plasma surface metallurgy furnace, taking the substrate as the workpiece electrode, the Si target and Hf target as the source electrode, keeping the glow in the furnace stable, raising the temperature in the metallurgy furnace to 900-1300 DEG C for metallurgy treatment for 6-12 hours, preparing the Si-HfO2 coating on the surface of the first sample prepared in step S2, and the distance between the source electrode and the workpiece electrode is 10-30 mm.

[0028] Preferably, the preparation method of the thermal barrier composite coating with gradient structure, wherein the heat treatment temperature in step S4 is 600-1200 DEG C, and the heat treatment time is 15 hours.

[0029] Preferably, the preparation method of the thermal barrier composite coating with gradient structure, wherein the protective gas is one of argon or nitrogen.

[0030] Preferably, the preparation method of the thermal barrier composite coating with gradient structure, wherein the purity of the Si target and Hf target in step S32 is 99.99%.

[0031] The thermal barrier coating will receive continuous high temperature and vibration impact during service, and the conventional YSZ coating has good bonding strength and thermal shock resistance when the temperature is lower than 1200 DEG C. When the temperature is higher than 1200 DEG C, the volume of YSZ will expand due to phase transition, and the coating will be densified due to continuous high temperature, which will cause the strain capacity of the coating to decrease and the thermal stress to increase, accelerating the peeling failure of the coating. In order to improve the service temperature and service life of the thermal barrier coating, the Si-HfO2 coating with gradient structure is provided, the high melting point (2758 DEG C) of HfO2 can improve the service temperature of the coating, and the Si-O-Hf can form chemical combination and react into HfSiO4 with low oxygen diffusion rate and good phase stability, which can not only weaken the thermal stress accumulation caused by phase transition, but also effectively avoid the internal cracks of the coating from connecting with each other during the growth process of the dispersedly distributed HfSiO4 / HfO2 particles, so that the ceramic coating has good high-temperature oxidation resistance and thermal shock resistance.

[0032] For the common metal bond layer system MCrAlY, the excessive thickness of the oxidation film (TGO) will reduce the bonding force between the layers. The application adds a certain amount of active elements Ti, Hf and Si in the system, on the one hand, Hf can promote the selective oxidation of Al into pure Al2O3 and reduce the oxidation rate, and Ti can increase the compatibility of the bond layer alloy matrix, so that the bond layer has better bonding strength; on the other hand, the combination of Hf, O and Si can improve the bonding strength between the metal bond layer and the oxygen barrier layer.

[0033] The application has the following advantages:

[0034] (1) The present application prepares a NiCrAlTiHfSi metal bonding layer and a Si-HfO2 oxygen barrier layer by a double-layer glow plasma surface metallurgy process, and the working temperature exceeds 1250 DEG C. Compared with traditional processes (such as thermal spraying and cold spraying), the double-layer glow plasma surface metallurgy process has the functions of metal and non-metal single or multi-element composite plating, can prepare a dense and uniform plating layer with a continuous gradient structure, and generates an atomic bond between the bonding layer and the oxygen barrier layer to form a gradient metallurgical interface with a certain depth, which makes the prepared oxygen barrier layer and the bonding layer have good bonding strength, greatly reduces the stress concentration in the mechanical stress or thermal cycle process, and improves the safety and service life.

[0035] (2) The thermal barrier composite coating with a gradient structure of the present application adds a certain amount of active elements Ti, Hf and Si in the metal bonding layer NiCrAl. On the one hand, Hf can promote the selective oxidation of Al into pure Al2O3 and reduce the oxidation rate, and Ti can increase the compatibility of the bonding layer alloy matrix, so that the bonding layer has better bonding strength. On the other hand, the combination of Hf, O and Si can improve the bonding strength of the metal bonding layer and the oxygen barrier layer. The oxygen barrier layer is composed of Si and Hf products, which have excellent high-temperature oxidation resistance, can significantly improve the working temperature of the coating, inhibit phase transition, reduce stress concentration, and have a certain crack self-healing ability.

[0036] (3) The thermal barrier composite coating with a gradient structure of the present application has a special double-layer glow plasma surface metallurgy process, which can prepare a dense and uniform plating layer with a continuous gradient structure, greatly reduces the influence of the volume change of the phase caused by the thermal expansion coefficient, greatly improves the service environment and service life of the thermal barrier coating, and has a wide application prospect in the field of aerospace. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a structure schematic diagram of the thermal barrier composite coating with a gradient structure of the present application.

[0038] Figure 2 It is an interface morphology diagram of the thermal barrier composite coating bonding layer and the oxygen barrier layer of Example 3 of the present application (close to the middle layer).

[0039] Figure 3 It is an element content test result diagram of the thermal barrier composite coating of Example 3 of the present application (close to the middle layer).

[0040] Figure 4 It is an interface morphology diagram of the thermal barrier composite coating bonding layer and the oxygen barrier layer of Example 3 of the present application (close to the outer layer).

[0041] Figure 5 It is an element content test result diagram of the thermal barrier composite coating of Example 3 of the present application (close to the outer layer). Detailed Implementation

[0042] The present invention will be further described below with reference to specific accompanying drawings and embodiments.

[0043] A schematic diagram of the thermal barrier composite coating structure with gradient structure of the present invention is shown below. Figure 1 As shown, a metal adhesive layer is first sprayed onto the surface of the substrate, and then an oxygen barrier layer is prepared on the metal adhesive layer. The adhesive layer is used as a transition layer to improve the bonding strength between the oxygen barrier layer and the substrate, and to provide a certain degree of protection to the substrate.

[0044] The thermal barrier coating of the present invention comprises an adhesive layer and an oxygen barrier layer sequentially from the substrate surface. Preferably, the process parameters and thickness of the adhesive layer are fixed. The substrate for preparing the adhesive layer is selected as a titanium alloy. The process parameters for preparing the adhesive layer are: process temperature of 1000℃, electrode spacing of 15mm, working time of 10h, and target material for preparing the adhesive layer is a NiCrAlTiHfSi composite target with Si content of 10at% and Hf content of 10at%. The thickness of the prepared adhesive layer is 80μm. The tensile properties of the above-prepared coating are tested as follows: the bonding strength between the adhesive layer and the titanium alloy layer is 38.5MPa.

[0045] To facilitate understanding, the preparation of the fixed adhesive layer is illustrated through examples. The implementation process of the oxygen barrier layer with a gradient structure is explained below. However, the invention is not limited to the following examples.

[0046] Example 1

[0047] A method for preparing a thermal barrier composite coating with a gradient structure, comprising the following steps:

[0048] S1. Polish the substrate with 1000# sandpaper, then ultrasonically clean it for 10 minutes;

[0049] S2. Using a double-layer glow discharge plasma surface metallurgy method, an adhesive layer is prepared on the substrate surface to obtain the first sample;

[0050] S21. Place the substrate into a double-layer glow discharge plasma metallurgical furnace, evacuate to below 0.2 Pa, purge with protective gas 2-3 times, and maintain the gas pressure at 20 Pa.

[0051] S22. The substrate and NiCrAlTiHfSi alloy target are pre-placed in a double-layer glow discharge plasma surface metallurgy furnace, with the substrate as the workpiece electrode and the NiCrAlTiHfSi alloy target as the source electrode. The glow discharge in the furnace is kept stable. The temperature in the metallurgy furnace is raised to 1000℃ for metallurgical treatment for 10 hours. A NiCrAlTiHfSi coating is prepared on the surface of the substrate. The distance between the source electrode and the workpiece electrode is 15mm.

[0052] S3. Depositing an oxygen barrier layer on the bonding layer prepared in step S2 by using a double-layer glow plasma surface metallurgy method to obtain a second sample;

[0053] S31. Placing the first sample on a workpiece table in a double-layer glow plasma metallurgy furnace, vacuumizing to below 0.2 Pa, washing with a protective gas for 2-3 times, and then maintaining the gas pressure at 40 Pa;

[0054] S32. Pre-placing the substrate, Si target and Hf target in the double-layer glow plasma surface metallurgy furnace, the purity of the Si target and Hf target being 99.99%, taking the substrate as the workpiece electrode, the Si target and Hf target as the source electrode, keeping the glow in the furnace stable, increasing the temperature in the furnace to 900℃ for metallurgical treatment for 6 h, and preparing a Si-HfO2 coating on the bonding layer prepared in step S2, the distance between the source electrode and the workpiece electrode being 30 mm;

[0055] S4. Placing the composite coating prepared in step S3 in a vacuum diffusion annealing furnace for heat treatment, the heat treatment temperature being 600℃, and the heat treatment time being 15 h, to obtain a thermal barrier composite coating.

[0056] The thickness of the oxygen barrier layer prepared in Example 1 is 22 μm, the diffusion depth of the oxygen barrier layer and the bonding layer is about 6 μm after diffusion annealing heat treatment at 600℃, the cross-section microstructure is observed, the thermal shock resistance of the coating prepared above is detected: failure after 108 cycles at 1250℃, the high-temperature oxidation performance of the coating prepared above is detected: the oxidation weight gain rate of the coating is 3.5×10 -2 mg / (cm 2 ·h) after 100 h at 1250℃.

[0057] Example 2

[0058] A method for preparing a thermal barrier composite coating with a gradient structure, comprising the following steps:

[0059] S1. Polishing the substrate with 1000# sandpaper, and then ultrasonic cleaning for 10 min;

[0060] S2. Preparing a bonding layer on the substrate surface by using a double-layer glow plasma surface metallurgy method to obtain a first sample;

[0061] S21. Placing the substrate in a double-layer glow plasma metallurgy furnace, vacuumizing to below 0.2 Pa, washing with a protective gas for 2-3 times, and then maintaining the gas pressure at 20 Pa;

[0062] S22. The substrate and the NiCrAlTiHfSi alloy target are pre-placed in a double-layer glow plasma surface metallurgy furnace, the substrate is used as a workpiece electrode, the NiCrAlTiHfSi alloy target is used as a source electrode, the glow in the furnace is kept stable, the temperature in the metallurgy furnace is increased to 1000°C, and metallurgy treatment is performed for 10 hours to prepare a NiCrAlTiHfSi coating on the surface of the substrate, the distance between the source electrode and the workpiece electrode is 15 mm;

[0063] S3. An oxygen barrier layer is deposited on the surface of the bonding layer prepared in step S2 by using a double-layer glow plasma surface metallurgy method;

[0064] S31. The first sample is placed on a workpiece table in a layer glow plasma metallurgy furnace, vacuum is extracted to below 0.2 Pa, protective gas is washed in for 2-3 times, and then the gas pressure is maintained at 30 Pa;

[0065] S32. The substrate, the Si target and the Hf target are pre-placed in a double-layer glow plasma surface metallurgy furnace, the purity of the Si target and the Hf target is 99.99%, the substrate is used as a workpiece electrode, the Si target and the Hf target are used as source electrodes, the glow in the furnace is kept stable, the temperature in the metallurgy furnace is increased to 1000°C, and metallurgy treatment is performed for 7 hours to prepare a Si-HfO2 coating on the surface of the bonding layer prepared in step S2, the distance between the source electrode and the workpiece electrode is 20 mm;

[0066] S4. The composite coating prepared in step S3 is placed in a vacuum diffusion annealing furnace for heat treatment, the heat treatment temperature is 700°C, and the heat treatment time is 15 hours to obtain a thermal barrier composite coating.

[0067] The thickness of the oxygen barrier layer prepared in Example 2 is 28 μm, the diffusion depth of the oxygen barrier layer and the bonding layer is about 10 μm after diffusion annealing heat treatment at 700°C, cross-section microstructure observation, the thermal shock resistance of the coating prepared above is detected: 1250°C, 152 cycles of failure, the high-temperature oxidation performance of the coating prepared above is detected: 1250°C, 100h, the oxidation weight gain rate of the coating is 2.4×10 -2 mg / (cm 2 ·h).

[0068] Example 3

[0069] A preparation method of a thermal barrier composite coating with a gradient structure, comprising the following steps:

[0070] S1. The substrate is polished with 1000# sandpaper, and then ultrasonic cleaning is performed for 10 minutes;

[0071] S2. A bonding layer is prepared on the surface of the substrate by using a double-layer glow plasma surface metallurgy method to obtain a first sample;

[0072] S21. Put the substrate into the double-layer glow plasma metallurgy furnace, vacuumize to below 0.2 Pa, wash with protective gas for 2-3 times, and then maintain the gas pressure at 20 Pa;

[0073] S22. Put the substrate and the NiCrAlTiHfSi alloy target into the double-layer glow plasma surface metallurgy furnace, take the substrate as the workpiece electrode and the NiCrAlTiHfSi alloy target as the source electrode, keep the glow in the furnace stable, raise the temperature in the metallurgy furnace to 1000℃, and then perform metallurgy treatment for 10 h to prepare the NiCrAlTiHfSi coating on the surface of the substrate, and the distance between the source electrode and the workpiece electrode is 15 mm;

[0074] S3. Deposit the oxygen barrier layer on the surface of the bonding layer prepared in step S2 by using the double-layer glow plasma surface metallurgy method;

[0075] S31. Put the first sample into the workpiece table in the double-layer glow plasma metallurgy furnace, vacuumize to below 0.2 Pa, wash with protective gas for 2-3 times, and then maintain the gas pressure at 25 Pa;

[0076] S32. Put the substrate, the Si target and the Hf target into the double-layer glow plasma surface metallurgy furnace, the purity of the Si target and the Hf target is 99.99%, take the substrate as the workpiece electrode and the Si target and the Hf target as the source electrode, keep the glow in the furnace stable, raise the temperature in the metallurgy furnace to 1100℃, and then perform metallurgy treatment for 8 h to prepare the Si-HfO2 coating on the surface of the bonding layer prepared in step S2, and the distance between the source electrode and the workpiece electrode is 15 mm;

[0077] S4. Put the composite coating prepared in step S3 into the vacuum diffusion annealing furnace for heat treatment, the heat treatment temperature is 800℃, and the heat treatment time is 15 h to obtain the thermal barrier composite coating.

[0078] The thickness of the oxygen barrier layer prepared in Example 3 is 35 μm, the diffusion depth of the oxygen barrier layer and the bonding layer is about 16 μm after diffusion annealing heat treatment at 800℃, the cross-section microstructure is observed, the thermal shock resistance of the coating prepared above is detected: 1250℃, and the coating fails after 242 cycles; the high-temperature oxidation performance of the coating prepared above is detected: 1250℃, 100 h, and the oxidation weight gain rate of the coating is 1.1×10 -2 mg / (cm 2 ·h).

[0079] Example 4

[0080] A preparation method of a thermal barrier composite coating with gradient structure, comprising the following steps:

[0081] S1. Grind the substrate with 1000# sandpaper, and then ultrasonic clean for 10 min;

[0082] S2. Preparing a bonding layer on the surface of the substrate by using double-layer glow plasma surface metallurgy to obtain a first sample;

[0083] S21. Placing the substrate into the double-layer glow plasma metallurgy furnace, vacuumizing to below 0.2 Pa, washing with protective gas for 2-3 times, and then maintaining the gas pressure at 20 Pa;

[0084] S22. Pre-placing the substrate and the NiCrAlTiHfSi alloy target material in the double-layer glow plasma surface metallurgy furnace, taking the substrate as the workpiece electrode and the NiCrAlTiHfSi alloy target material as the source electrode, keeping the glow in the furnace stable, increasing the temperature in the metallurgy furnace to 1000℃, and performing metallurgy treatment for 10 h to prepare a NiCrAlTiHfSi bonding layer on the surface of the substrate, with the distance between the source electrode and the workpiece electrode being 15 mm;

[0085] S3. Depositing an oxygen barrier layer on the bonding layer prepared in step S2 by using double-layer glow plasma surface metallurgy;

[0086] S31. Placing the first sample on the workpiece table in the double-layer glow plasma metallurgy furnace, vacuumizing to below 0.2 Pa, washing with protective gas for 2-3 times, and then maintaining the gas pressure at 20 Pa;

[0087] S32. Pre-placing the substrate, the Si target material, and the Hf target material in the double-layer glow plasma surface metallurgy furnace, with the purity of the Si target material and the Hf target material both being 99.99%, taking the substrate as the workpiece electrode and the Si target material and the Hf target material as the source electrodes, keeping the glow in the furnace stable, increasing the temperature in the metallurgy furnace to 1200℃, and performing metallurgy treatment for 10 h to prepare a Si-HfO2 coating layer on the bonding layer prepared in step S2, with the distance between the source electrode and the workpiece electrode being 10 mm;

[0088] S4. Placing the composite coating layer prepared in step S3 into a vacuum diffusion annealing furnace for heat treatment, with the heat treatment temperature being 1000℃ and the heat treatment time being 15 h to obtain a thermal barrier composite coating layer.

[0089] The thickness of the oxygen barrier layer prepared in Example 4 is 38 μm, and the interdiffusion depth of the oxygen barrier layer and the bonding layer is about 11 μm after diffusion annealing heat treatment at 1000℃ and cross-section microstructure observation. The thermal shock resistance of the coating layer prepared above is detected: failure after 163 cycles at 1250℃. The high-temperature oxidation performance of the coating layer prepared above is detected: the oxidation weight gain rate of the coating layer is 2.1×10 -2 mg / (cm 2 ·h) after 100 h at 1250℃.

[0090] Comparative Example 1

[0091] The chamber of the double glow plasma surface metallurgy equipment furnace body is opened, the prepared ordinary sample is placed on the workpiece table, the inter-electrode distance is adjusted to 15 mm, the chamber is closed, the vacuum degree in the chamber is extracted to 25 Pa, then the chamber temperature is heated to 1100 ℃, after the temperature is stable, the working time is recorded, and the working time is 8 h; the prepared oxygen barrier layer has a thickness of 35 μm, 800 ℃ diffusion annealing heat treatment is carried out, the thermal shock resistance performance detection is carried out on the prepared coating: 1250 ℃, 62 cycles fail, and peeling is serious; the high-temperature oxidation performance detection is carried out on the prepared coating: 1250 ℃, 100 h, and the oxidation weight gain rate of the coating is 1.4×10 -2 mg / (cm 2 ·h).

[0092] Comparative example 2

[0093] The oxygen barrier layer is not deposited on the surface of the bonding layer, 800 ℃ diffusion annealing heat treatment is carried out, the thermal shock resistance performance detection is carried out on the prepared coating: 1250 ℃, 68 cycles fail; the high-temperature oxidation performance detection is carried out on the prepared coating: 1250 ℃, 100 h, and the oxidation weight gain rate of the coating is 12.6×10 -2 mg / (cm 2 ·h).

[0094] Table 1 lists the performance test results of examples 1-4 and comparative examples 1-2, the thermal cycle performance test is carried out on the sample with the coating by using a thermal shock furnace, the test temperature is 1250 ℃, the thermal cycle performance under different coatings is judged by the cycle number, the specific results are shown in Table 1, the weighed coating sample is placed in an alumina crucible, and is weighed after being oxidized in a muffle furnace at 1250 ℃ for 100 h, and the oxidation weight gain rate is calculated, the oxidation weight gain rate reflects the high-temperature oxidation resistance performance of the coating to a certain extent, and the specific results are shown in Table 1; it can be seen from the data results in Table 1 that, compared with the single-layer coating (without the oxygen barrier layer or without the bonding layer), the double-layer coating of the bonding layer and the oxygen barrier layer has better thermal cycle performance and high-temperature oxidation resistance performance; compared with different self-diffusion depths (continuous gradient structure), the higher the interdiffusion depth, the more significantly the thermal cycle performance is improved, which is attributed to the fact that the interdiffusion depth is in direct proportion to the bonding strength of the coating.

[0095] Table 1 performance comparison

[0096] Depth of interdiffusion (pm) Number of 1250°C cycles Oxidative weight gain rate (mg / (cm 2 ·h)) Example 1 6 108 3.5 Example 2 10 152 2.4 Example 3 16 242 1.1 Example 4 11 163 2.1 Comparative Example 1 0 (no bond coat) 62 1.4 Comparative Example 2 0 (no oxygen barrier) 68 12.6

[0097] Figure 1 It is a structural schematic diagram of the thermal barrier composite coating with a gradient structure of the application, the interdiffusion layer and the oxygen barrier layer are both continuous gradient structures, and it is worth noting that the composition gradient of the oxygen barrier layer is only schematic, and the specific composition is not limited thereto. Figures 2-5For the interface of the thermal barrier composite coating adhesive layer and the oxygen barrier layer of embodiment 3 of the present application, the morphology and element content at different positions are shown in the figure, obviously, the closer to the top layer of the coating in the vertical direction, the higher the Hf content and the lower the Si content, showing a composition gradient.

Claims

1. A thermal barrier composite coating having a gradient structure, characterized by: The composite coating comprises a substrate and a composite coating arranged on the substrate, the composite coating comprises a bonding layer arranged on the substrate and an oxygen barrier layer arranged on the bonding layer, the bonding layer is a NiCrAlTiHfSi coating, the oxygen barrier layer has a continuous gradient structure, the oxygen barrier layer is a Si-HfO2 coating, the Si-HfO2 coating comprises 20% to 80% of Si and 20% to 80% of HfO2, and the content of HfO2 gradually decreases along the vertical direction of the Si-HfO2 coating close to the bonding layer; and a mutual diffusion layer is arranged between the bonding layer and the oxygen barrier layer. The NiCrAlTiHfSi coating comprises 5% to 10% of Hf, 10% to 15% of Si, 20% of Ni, 20% of Cr, 20% of Al and 20% of Ti in terms of mass percentage. The preparation method of the thermal barrier composite coating with the gradient structure comprises the following steps: S1. polishing the substrate with sandpaper and then ultrasonic cleaning for 10 to 15 minutes; S2. preparing the bonding layer on the surface of the substrate by using a double-layer glow plasma surface metallurgy method to obtain a first sample; S3. depositing the oxygen barrier layer on the surface of the bonding layer prepared in step S2 by using the double-layer glow plasma surface metallurgy method to obtain a second sample; S4. placing the second sample prepared in step S3 into a vacuum diffusion annealing furnace for heat treatment to obtain the thermal barrier composite coating; The heat treatment temperature in step S4 is 600 to 1200 DEG C, and the heat treatment time is 15 hours.

2. The thermal barrier composite coating with a gradient structure according to claim 1, characterized in that: The thickness of the bonding layer is 50 to 100 microns, and the thickness of the oxygen barrier layer is 20 to 40 microns.

3. The thermal barrier composite coating with a gradient structure according to claim 1, wherein: The substrate comprises one of a nickel-based alloy, a titanium alloy and a fiber reinforced composite material in terms of mass fraction.

4. The thermal barrier composite coating with a gradient structure according to claim 1, wherein: In step S2, the double-layer glow plasma surface metallurgy method comprises the following steps: S21. placing the substrate into a double-layer glow plasma metallurgy furnace, vacuumizing to below 0.2 Pa, washing the gas for 2 to 3 times after introducing the protective gas, and maintaining the gas pressure at 20 to 40 Pa; S22. pre-placing the substrate and the NiCrAlTiHfSi alloy target material in the double-layer glow plasma surface metallurgy furnace, taking the substrate as the workpiece electrode, taking the NiCrAlTiHfSi alloy target material as the source electrode, keeping the glow in the furnace stable, raising the temperature in the metallurgy furnace to 900 to 1300 DEG C for metallurgical treatment for 8 to 12 hours to prepare the NiCrAlTiHfSi bonding layer on the surface of the substrate, and the distance between the source electrode and the workpiece electrode is 10 to 30 mm.

5. The thermal barrier composite coating with a gradient structure according to claim 1, wherein: In step S3, the double-layer glow plasma surface metallurgy method comprises the following steps: S31. placing the first sample into a double-layer glow plasma metallurgy furnace, vacuumizing to below 0.2 Pa, washing the gas for 2 to 3 times after introducing the protective gas, and maintaining the gas pressure at 20 to 40 Pa; S32. The substrate, Si target material, and Hf target material are pre-placed in a double-layer glow plasma surface metallurgy furnace, with the substrate as the workpiece electrode, the Si target material and Hf target material as the source electrode, the glow in the furnace is kept stable, the temperature in the metallurgy furnace is raised to 900-1300°C, and metallurgical treatment is performed for 6-12 hours to prepare a Si-HfO2 coating on the surface of the first sample prepared in step S2, and the distance between the source electrode and the workpiece electrode is 10-30 mm.

6. The thermal barrier composite coating with a gradient structure according to claim 4 or 5, characterized in that: The protective gas is one of argon or nitrogen.

7. The thermal barrier composite coating with a gradient structure according to claim 5, wherein: The purity of the Si target material and the Hf target material in step S32 is 99.99%.

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