Si-HfO2 environmental barrier bonding layer resistant to high-temperature thermal shock and preparation method of Si-HfO2 environmental barrier bonding layer

Abstract

The invention discloses a high-temperature thermal shock resistant Si-HfO2 environmental barrier bonding layer and a preparation method thereof.The preparation method comprises the steps that firstly, the surface of a SiC substrate is subjected to sand blasting pretreatment to increase the roughness, and after ultrasonic cleaning and drying are conducted, the surface of the substrate is subjected to ion bombardment cleaning in magnetron sputtering equipment; a polycrystalline pure Si target material and a polycrystalline pure HfO2 target material are placed on a direct-current power source and a radio-frequency power source of magnetron sputtering equipment respectively, and the Si-HfO2 bonding layer is evenly deposited on the surface of a base body in the argon inert protective atmosphere through the magnetron co-sputtering technology. The uniform and compact HfO2 modified Si bonding layer is prepared on the surface of the matrix material, the thermal shock resistance of the bonding layer is improved, meanwhile, the modified layer and the matrix have good bonding capacity, the coating is prevented from falling off in the service process, and therefore the effects of protecting the matrix and prolonging the working condition service life of the matrix are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of environmental barrier coatings for aeroengines, and particularly relates to a Si-HfO2 environmental barrier bonding layer with high temperature thermal shock resistance and a preparation method thereof. Background Art

[0002] SiC f / SiC ceramic matrix composites have become one of the key candidate materials to replace traditional nickel-based superalloys and achieve high thrust-to-weight ratio aeroengines due to their excellent comprehensive properties such as high specific strength and stable high-temperature performance. However, in a high-temperature turbine environment with the erosion of a flame flow containing high-temperature water vapor, oxygen, and molten corrosives, the surface stability of the ceramic matrix composites will drop sharply, resulting in the failure of the matrix and the loss of the serviceability of structural components.

[0003] Environmental barrier coatings (EBCs) have become the physical and chemical barrier between SiC f / SiC ceramic matrix composites and a harsh engine environment, as well as the key protection technology to improve the service life of hot-end components of engines, due to their excellent resistance to high-temperature water and oxygen corrosion, molten salt corrosion, and the ability to heal cracks and pores. Among them, the widely used pure Si bonding layer can improve the bonding force between the external coating and the matrix and reduce the degree of mismatch in physical and chemical properties. However, the thermally grown oxide (TGO) of it inevitably has a high-low temperature phase change accompanied by a certain volume expansion during thermal shock, and the thermal expansion behaviors before and after the phase change are quite different, resulting in the continuous accumulation of internal stress in the TGO layer and the non-TGO layer during the engine thermal cycle. In addition, the fracture toughness of Si is low. When the internal stress in the coating is too high, spalling will occur due to its low strength and high creep rate at high temperatures, resulting in phenomena such as cracks or spalling in the coating and ultimately failure, which becomes one of the limitations for the long-term service of environmental barrier coatings in a harsh engine environment. The HfO2 material itself has a high melting point, and the HfSiO4 formed by reacting with cristobalite at high temperatures meets the requirements of phase stability and physical property matching. Moreover, the increase in molar volume during the reaction can effectively close the microcracks generated by the accumulation of thermal stress in cristobalite. Previously, although the hafnium oxide-doped Si bonding layer prepared by traditional plasma spraying technology has the above advantages, the coating prepared by this method has a relatively high initial porosity, and its mechanical properties are difficult to meet the application requirements of high-speed and high-pressure service components of engines. In addition, the uniformity of the phase structure organization inside the coating is relatively low, and local failure is likely to occur prematurely during high-temperature thermal shock. The above situations limit the modification effect of hafnium oxide doping on the pure silicon bonding layer, thereby reducing the protection ability of the coating for the matrix material. Summary of the Invention

[0004] The present invention mainly solves the problem that the bonding layer of the environmental barrier coating is prone to delamination and spalling in the high and low temperature shock service environment. The main purpose is to provide an Si-HfO2 environmental barrier bonding layer with high temperature thermal shock resistance and its preparation method. A uniformly dense HfO2 modified Si bonding layer is prepared on the surface of the substrate material, which not only improves the thermal shock resistance of the bonding layer but also enables the modified layer to have good bonding ability with the substrate, avoiding the coating from falling off during service, thereby protecting the substrate and extending its service life under working conditions.

[0005] To solve the problems of the existing technology, the technical solution adopted by the present invention is as follows:

[0006] A preparation method of an Si-HfO2 environmental barrier bonding layer with high temperature thermal shock resistance, in which Si and HfO2 molecules are co-sputtered and deposited on the surface of SiC material by magnetron sputtering technology.

[0007] The above preparation method of an Si-HfO2 environmental barrier bonding layer with high temperature thermal shock resistance includes the following steps:

[0008] (1) Pretreatment of the surface of the substrate workpiece

[0009] After the surface of the SiC block is sandblasted to obtain roughness, it is placed in alcohol and ultrasonically cleaned, and then dried for later use;

[0010] (2) Cleaning and placing the workpiece

[0011] Before the sample is loaded into the furnace, the inner wall of the furnace and the surface of the target should be polished with fine sandpaper to remove the surface oxide film and impurities, and then wiped with a dust-free cloth dipped in anhydrous ethanol. The polysilicon target is used as the DC cathode, and the hafnium oxide target is used as the RF cathode. The distance between the substrate and the target is set to 50 mm, and it is installed on the rotatable substrate holder in the deposition chamber with a rotation speed of 10 r / min. Argon is used as the ionization gas;

[0012] (3) Vacuum pumping and pre-sputtering

[0013] The temperature of the heated substrate is 50 °C. The vacuum chamber of the magnetron sputtering equipment is closed. First, vacuum is pumped and argon is continuously introduced, and then ion cleaning is carried out. The specific process is as follows: The molecular pump is turned on to pump the gas in the vacuum furnace to the background vacuum of 8×10 -4 Pa, and then argon is introduced (flow rate: 25 sccm). The intake volume is controlled by the gate valve so that the working pressure in the chamber remains at 3 Pa; when starting to glow, the power on the polysilicon target is set to 120 W, the power on the hafnium oxide target is set to 150 W, and the pre-sputtering time on the substrate surface is 10 min;

[0014] (4) Co-sputtering

[0015] Keep the working air pressure in the control chamber at 0.65 Pa; reset the power on the polysilicon target to be constant at 180 W and the current to be 0.41 A; the power on the hafnium oxide target is constant at 180 W and the current is 0.92 A; the duty cycle is 80.6%, the frequency is 40.6 kHz, and the substrate bias voltage is -218 V; the deposition time is 8 h, and the film thickness is controlled to be 6.05 - 6.23 μm, thereby obtaining a Si-HfO2 environmental barrier bonding layer.

[0016] As an improvement, the surface roughness Ra described in step (1) is 0.8 - 1.2 μm.

[0017] As an improvement, the purity of the polysilicon target material described in step (2) is 99.999%, the diameter is 76.2 mm, the thickness is 4 mm, and a 1 mm copper backplane is bonded.

[0018] As an improvement, the purity of the hafnium oxide target material described in step (2) is 99.99%, the diameter is 76.2 mm, the thickness is 3 mm, and a 2 mm copper backplane is bonded.

[0019] The Si-HfO2 environmental barrier bonding layer prepared by the above preparation method, the thickness of the Si-HfO2 environmental barrier bonding layer is 6.05 - 6.23 μm; a typical dense columnar crystal structure; the internal phase structure is uniform after high-temperature thermal shock service at 1450 °C.

[0020] Beneficial effects:

[0021] Compared with the prior art, an anti-high-temperature thermal shock Si-HfO2 environmental barrier bonding layer and its preparation method of the present invention prepare a uniform and dense HfO2-modified Si bonding layer on the surface of the substrate material, while improving the thermal shock resistance of the bonding layer, the modified layer also has good bonding ability with the substrate, avoiding the coating from falling off during service, thereby protecting the substrate and extending its service life under working conditions. It has the following advantages:

[0022] (1) The melting point of the transition metal oxide HfO2 of the present invention is higher (HfO2: 2758 °C, Si: 1410 °C), which can ensure that the environmental barrier coating system is applicable to a higher service temperature environment; at the same time, compared with Si, HfO2 has more excellent oxidation resistance and fracture toughness (Si undergoes a ductile-brittle transition near 625 °C);

[0023] (2) The HfSiO4 dispersed particles formed by the Si-HfO2 bonding layer of the present invention during the thermal shock process can hinder or change the crack propagation path and improve the thermal shock service life of the coating;

[0024] (3) The DC / RF magnetron co-sputtering adopted by the present invention has the advantages of low sputtering temperature, small substrate deformation, and controllable coating composition;

[0025] (4) The coating of the present invention is prepared by magnetron sputtering technology, which has the characteristics of simple and controllable process, good repeatability, dense coating and good bonding force with the substrate. Description of the Drawings

[0026] Figure 1 are the microscopic morphologies and EDS-Mapping diagrams of Si-HfO2 coatings prepared under different processes, where (a) is Example 1, (b) is Comparative Example 1, and (c) is Comparative Example 2.

[0027] Figure 2 are the element contents of Si-HfO2 coatings prepared under different processes.

[0028] Figure 3 are the microscopic morphology diagrams of the Si-HfO2 coating prepared in Example 1 after thermal shock tests: (a) 50 times; (b) 100 times; (c) 150 times.

[0029] Figure 4 are the microscopic morphology diagrams of the Si-HfO2 coating prepared in Comparative Example 1 after thermal shock tests: (a) 50 times; (b) 100 times; (c) 150 times.

[0030] Figure 5 are the microscopic morphology diagrams of the Si-HfO2 coating prepared in Comparative Example 2 after thermal shock tests: (a) 50 times; (b) 100 times; (c) 150 times.

[0031] Figure 6 are the microscopic morphology diagrams of the pure Si bonding layer prepared in Comparative Example 3 after thermal shock experiments: (a) 50 times; (b) 100 times; (c) 150 times. Detailed Description of the Invention

[0032] Example 1

[0033] The present invention uses DC / RF co-sputtering technology to prepare an HfO2-doped Si environmental barrier bonding layer, and its preparation method includes the following process steps:

[0034] (1) Pretreatment of the substrate material

[0035] Prepare a SiC bulk material substrate, perform sandblasting on the surface to obtain a certain roughness (Ra: 1.0 μm), then place it in alcohol for ultrasonic cleaning, and then dry it with a hair dryer for standby.

[0036] (2) Cleaning and placing the workpiece

[0037] Before the sample is loaded into the furnace, the inner wall of the furnace body and the surface of the target should be polished with fine sandpaper to remove the surface oxide film and impurities, and then wiped with a lint-free cloth dipped in anhydrous ethanol. Use a polycrystalline silicon target (purity: 99.999%, size: diameter 76.2 mm, thickness 4 mm, bonded with 1 mm copper backplane) as the DC cathode, and a hafnium oxide target (purity: 99.99%, size: diameter 76.2 mm, thickness 3 mm, bonded with 2 mm copper backplane) as the RF cathode. Set the distance between the substrate and the target to 50 mm, install it on the rotatable substrate holder in the deposition chamber, and the rotation speed is 10 r / min. Argon is used as the main ionization gas.

[0038] (3) Vacuum pumping and pre-sputtering

[0039] Heat the substrate temperature to 40 °C, close the vacuum chamber of the magnetron sputtering equipment, first pump the vacuum and continuously introduce argon, and then perform ion cleaning. The specific process is as follows: Turn on the molecular pump to extract the gas in the vacuum furnace until the background vacuum is 8×10-4 Pa, and then introduce argon (flow rate: 25 sccm). Control the intake volume through the gate valve to keep the working pressure in the chamber at 3 Pa; when starting to glow, the power on the polycrystalline silicon target is set to 120 W, the power on the hafnium oxide target is set to 150 W, and the pre-sputtering time on the substrate surface is 10 min.

[0040] (4) Co-sputtering

[0041] Control the working pressure in the chamber to remain at 0.65 Pa; reset the power on the polycrystalline silicon target to be constant at 180 W, and the current is 0.41 A; the power on the hafnium oxide target is constant at 180 W, and the current is 0.92 A; the duty cycle is 80.6%, the frequency is 40.6 kHz, and the substrate bias voltage is -218 V; the deposition time is 8 h, so as to obtain a Si-HfO2 bonding layer with a thickness of 6.23 μm.

[0042] Comparative Example 1

[0043] In the co-sputtering stage, control the working pressure in the chamber to remain at 0.74 Pa; reset the power on the polycrystalline silicon target to be constant at 150 W, the current is 0.33 A, the power on the hafnium oxide target is constant at 210 W, and the current is 0.96 A. The rest is the same as in Example 1, and the thickness of the bonding layer is 6.07 μm.

[0044] Comparative Example 2

[0045] In the co-sputtering stage, control the working pressure in the chamber to remain at 0.81 Pa, reset the power on the polycrystalline silicon target to be constant at 130 W, the current is 0.29 A, the power on the hafnium oxide target is constant at 230 W, and the current is 0.95 A. The rest is the same as in Example 1, and the thickness of the bonding layer is 6.05 μm.

[0046] Comparative Example 3

[0047] The difference in the preparation steps of the bonding layer between Comparative Example 1 and Example 1 lies in that: during the co-sputtering stage, the working pressure in the chamber is controlled to be maintained at 0.55 Pa, the power on the polysilicon target is reset to be constant at 300 W, the current is 0.74 A, the power on the hafnium oxide target is constant at 0 W, and the current is 0 A. The rest is the same as in Example 1, and the thickness of the bonding layer is 4.93 μm.

[0048] Figure 2 Figure shows the microstructure of the Si-HfO2 composite bonding layers prepared for different examples. It can be seen from the figure that for the sample of Example 1, a Si-HfO2 bonding layer with uniform microstructure and good coating bonding can be prepared by DC / RF co-sputtering.

[0049] Figure 2 Figure shows the content of the Si-HfO2 composite bonding layers prepared for different examples. It can be seen from the figure that the Si / Hf atomic ratio contents of the composite bonding layers in Example 1, Comparative Example 1 and Comparative Example 2 are 19.25 / 71.55, 36.22 / 40.54 and 39.11 / 38.55 respectively.

[0050] The thermal shock resistance of the bonding layer is evaluated by the flowing air cooling method. The conditions are as follows: the sample is first placed in a lifting furnace at 1450 °C and kept warm for 1 h, and then taken out for air cooling and temperature reduction treatment for 15 min. This process is defined as one thermal shock cycle.

[0051] Figure 3 Figures show the microtopographies of the samples prepared in Example 1 after 50 thermal shocks ((a1)-(a2)), 100 thermal shocks ((b1)-(b2)) and 150 thermal shocks ((c1)-(c2)). It can be seen that: after 50 thermal shock experiments, the coating and the substrate do not peel off, and there are no obvious cracks on the coating surface. After EDS analysis, the dark gray matrix phase on the surface is cristobalite, and the light gray granular phase is HfSiO4; after 100 thermal shock experiments, the coating and the substrate still maintain good bonding, and the granular HfSiO4 phase on the coating surface increases, so that the microcracks in the matrix phase bypass the light gray granular phase, avoiding the connection of microcracks; after 150 thermal shock experiments, there are slight gaps between the coating and the substrate, but due to the increase in the content of the granular phase, the microcracks on the coating surface are closed. That is, the Si-HfO2 composite bonding layer obtained in this example maintains good high-temperature stability and thermal shock resistance at 1450 °C.

[0052] Figure 4Microscopic morphologies of the samples prepared in Comparative Example 2 after 50 thermal shocks ((a1)-(a2)), 100 thermal shocks ((b1)-(b2)), and 150 thermal shocks ((c1)-(c2)). Experimental results show that after 50 and 100 thermal shock tests, the composite coating of Comparative Example 1 remained intact and had good bonding with the substrate. After 150 thermal shock tests, a few cracks appeared on the coating surface, and there was a serious mismatch in the coefficient of thermal expansion between the excessive HfSiO4 in the coating and the substrate, resulting in interface peeling, indicating that this example could not withstand the thermal shock environment of 1450°C for 150 h.

[0053] Figure 5 Microscopic morphologies of the samples prepared in Comparative Example 2 after 50 thermal shocks ((a1)-(a2)), 100 thermal shocks ((b1)-(b2)), and 150 thermal shocks ((c1)-(c2)). Experimental results show that after 50 and 100 thermal shock tests, the composite coating of Comparative Example 2 still had good bonding ability with the substrate, and the surface was intact and dense. After 150 thermal shocks, peeling occurred between the coating and the substrate, and a few cracks appeared on the coating surface. This indicates that this example could not withstand the thermal shock environment of 1450°C for 150 h.

[0054] Figure 6 Microscopic morphologies of the samples prepared in Comparative Example 3 after 50 thermal shocks ((a1)-(a2)), 100 thermal shocks ((b1)-(b2)), and 150 thermal shocks ((c1)-(c2)). Experimental results show that after 50 thermal shock tests, the pure Si bonding layer of Comparative Example 1 had good bonding with the substrate, and a few cracks appeared on the surface. After 100 thermal shock tests, the mismatch in the coefficient of thermal expansion caused by the high-temperature and low-temperature phase transformation of cristobalite in the pure Si bonding layer promoted the accumulation of thermal stress during the thermal cycle, inducing through-cracks inside and surface cracking. After 150 thermal shock tests, the area of surface cracking increased, the number of through-cracks inside increased, and transverse cracking occurred along the coating / substrate interface.

[0055] It can be seen that the HfSiO4 phase generated by the Si-HfO2 composite bonding layer in Example 1 of the present invention during the thermal cycle can avoid the phase transformation of cristobalite, and the granular HfSiO4 phase improves the crack propagation path inside the coating, avoiding the phenomenon that the connection between cracks inside the coating develops to cracking, and significantly improving the thermal shock resistance of the bonding layer of the environmental barrier coating.

Claims

1. A preparation method of a Si-HfO2 environmental barrier bonding layer resistant to high-temperature thermal shock, characterized in that: The Si and HfO2 molecules are co-sputtered and deposited on the surface of the SiC material by magnetron sputtering technology.

2. The preparation method of a Si-HfO2 environmental barrier bonding layer resistant to high-temperature thermal shock according to claim 1, characterized in that, It includes the following steps: (1) Pretreatment of the surface of the substrate workpiece After sandblasting the surface of the SiC block to obtain roughness, it is placed in alcohol and ultrasonically cleaned, and then dried for standby; (2) Cleaning and placing the workpiece Before the sample is loaded into the furnace, the inner wall of the furnace and the surface of the target need to be polished with fine sandpaper to remove the surface oxide film and impurities, and then wiped with a dust-free cloth dipped in anhydrous ethanol. The polysilicon target is used as the DC cathode, and the hafnium oxide target is used as the RF cathode. The distance between the substrate and the target is set to 50 mm, and it is installed on the rotatable substrate holder in the deposition chamber with a rotation speed of 10 r / min. Argon is used as the ionization gas; (3) Vacuum pumping and pre-sputtering The temperature of the heated substrate is 50 °C. Close the vacuum chamber of the magnetron sputtering equipment. First, evacuate the air and continuously introduce argon gas, and then perform ion cleaning. The specific process is as follows: Turn on the molecular pump to extract the gas in the vacuum furnace until the background vacuum reaches 8×10 -4 Pa, and then introduce argon gas. Control the intake air volume through the gate valve to keep the working pressure in the chamber at 3 Pa. When starting to glow, the power on the polysilicon target is set to 120 W, the power on the hafnium oxide target is set to 150 W, and the pre-sputtering time on the substrate surface is 10 min; (4) Co-sputtering Control the working pressure in the chamber to be maintained at 0.65 Pa; reset the power on the polysilicon target to be constant at 180 W and the current to be 0.41 A; the power on the hafnium oxide target is constant at 180 W and the current is 0.92 A; the duty cycle is 80.6%, the frequency is 40.6 kHz, and the substrate bias voltage is -218 V; The deposition time is 8 h, and the film thickness is controlled to be 6.05 - 6.23 μm, so as to obtain the Si-HfO2 environmental barrier bonding layer.

3. The preparation method of a Si-HfO2 environmental barrier bonding layer with high temperature thermal shock resistance according to claim 2, characterized in that, The roughness Ra described in step (1) is 0.8 - 1.2 μm.

4. The preparation method of a Si-HfO2 environmental barrier bonding layer resistant to high-temperature thermal shock according to claim 2, characterized in that, The purity of the polysilicon target described in step (2) is 99.999%, the diameter is 76.2 mm, the thickness is 4 mm, and a 1 mm copper backplane is bonded.

5. The preparation method of a Si-HfO2 environmental barrier bonding layer resistant to high-temperature thermal shock according to claim 2, characterized in that, The purity of the hafnium oxide target described in step (2) is 99.99%, the diameter is 76.2 mm, the thickness is 3 mm, and a 2 mm copper backplane is bonded.

6. The Si-HfO2 environmental barrier bonding layer prepared by the preparation method according to any one of claims 1-5, characterized in that, The thickness of the Si-HfO2 environmental barrier bonding layer is 6.05 - 6.23 μm; it has a typical dense columnar crystal structure; the internal phase structure is uniform after high-temperature thermal shock service at 1450 °C.

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