A high-temperature corrosion protective metal-ceramic coating, its preparation method and its application

Abstract

This invention relates to the field of coating preparation technology, specifically to a high-temperature corrosion protective metal-ceramic coating, its preparation method, and its application. The coating raw materials are Ti2AlC powder, CeO2 powder, and metallic NiCrAlY powder. The proportion of Ti2AlC powder is 30%, the proportion of CeO2 powder is 0.75-1.25%, and the proportion of NiCrAlY powder is 68.75-69.25%. The composite coating is prepared on the surface of 12CrMoV boiler steel using high-velocity vapor deposition (HVOF) technology. The spraying process parameters are: kerosene flow rate 30 L / h, oxygen flow rate 53 m³ / h. 3 With a powder feeding rate of 30 g / min, a step distance of 3 mm, a spraying distance of 300 mm, and a spray gun moving speed of 800 mm / min, a composite chloride and sulfate corrosion test was conducted at 700℃ to investigate the application potential of the coating in the field of biomass power generation boilers, based on the service environment of biomass power generation boilers. Finally, a rare earth oxide CeO2-enhanced Ti2AlC-NiCrAlY high-temperature corrosion protective coating was prepared to extend the service life of biomass power generation boilers.

Description

Technical Field

[0001] This invention relates to the field of coating preparation technology, specifically to a high-temperature corrosion protective metal-ceramic coating, its preparation method, and its application. Background Technology

[0002] With the increasingly severe environmental problems caused by fossil fuel combustion, biomass fuels, represented by crop straw and solid waste, have become a key focus in the field of alternative energy. Biomass fuels have high alkali metal and chlorine content; the alkali metal chlorides formed after combustion easily accumulate on heated surfaces, corroding them at high temperatures and causing the oxide layer to thin or peel off. This is especially true in biomass co-firing power plants, where heated surface materials are exposed to complex deposits of various salts. The constantly changing chemical composition alters the corrosion mechanism, making the boiler environment more severe than with coal-fired power plants. This problem is particularly prominent in pressure components such as boiler tubes. Tube rupture accidents caused by thinning due to corrosion not only severely affect power generation efficiency but also endanger personnel and equipment safety. High-temperature corrosion continues to threaten the safe operation of the unit and limits the improvement of operating parameters.

[0003] Utilizing surface modification techniques to improve the high-temperature resistance of key components is a common method. As a mature surface engineering technology, thermal spraying holds an important position in the field of high-temperature protective coating preparation due to its wide process adaptability and high interfacial bonding strength. High-velocity vapor deposition (HVOF) technology produces coatings with dense structure, low porosity, and high bonding strength. Furthermore, the short residence time of powder in the flame allows for the formation of coatings with low oxide content, avoiding cracks and defects. This technology is also an economical and ideal means of preparing MAX phase materials such as Ti2Al, which are prone to phase decomposition. Therefore, HVOF is widely used in surface protection and repair in industrial production to improve the corrosion resistance of equipment and extend its service life. Although traditional NiCrAlY coatings possess excellent high-temperature oxidation resistance, their inherent hardness and thermal corrosion resistance are insufficient, severely limiting their long-term stable service in high-temperature corrosive environments.

[0004] In view of the above-mentioned defects, the inventors of this invention have finally obtained this invention after a long period of research and practice. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that traditional NiCrAlY coatings have excellent high-temperature oxidation resistance, but their inherent hardness and heat corrosion resistance are insufficient, which seriously restricts their long-term stable service in high-temperature corrosive environments. This invention provides a high-temperature corrosion protective metal-ceramic coating, its preparation method, and its application.

[0006] To achieve the above objectives, this invention discloses a method for preparing a high-temperature corrosion-resistant metal-ceramic coating, comprising the following steps:

[0007] S1, mix Ti2AlC, CeO2 powder, polyvinyl alcohol and 1-octanol, and then ball mill the mixture with deionized water to obtain a mixed slurry;

[0008] S2, the mixed slurry obtained in step S1 is subjected to spray granulation to obtain agglomerated powder, and the agglomerated powder is subjected to vacuum sintering and sieve classification to finally obtain CeO2-Ti2AlC powder.

[0009] S3, mix the CeO2-Ti2AlC powder obtained in step S2 with the NiCrAlY powder to obtain a mixed powder;

[0010] S4. High-temperature corrosion-resistant metal-ceramic coating is prepared on the roughened substrate using supersonic flame spraying technology to apply the mixed powder obtained in step S3.

[0011] In step S1, Ti2AlC is in the form of flake powder with a purity greater than 99.5%.

[0012] In step S1, the mass of polyvinyl alcohol accounts for 4% of the total mass of CeO2 and Ti2AlC, the mass of 1-octanol accounts for 0.4% of the total mass of CeO2 and Ti2AlC, and the mass ratio of the total mass of CeO2 and Ti2AlC to the mass of deionized water is 2:3.

[0013] In step S1, ball milling is carried out in an alumina ball mill jar for 4 hours at a rotation speed of 360 r / min.

[0014] In step S2, the temperature of vacuum sintering is 1200~1400 ℃.

[0015] In step S2, the CeO2-Ti2AlC powder obtained after sieving and grading has a particle size of 25~71 μm.

[0016] In step S3, the mass percentage of NiCrAlY powder in the mixed powder is 68.75%~69.25%, the mass percentage of Ti2AlC powder is 30%, and the mass percentage of CeO2 powder is 0.75~1.25%.

[0017] In step S5, the process parameters for supersonic flame spraying technology are: kerosene volume 30 L / h, oxygen flow rate 53 m³ / h. 3 / h, powder feed rate 30 g / min, step distance 3 mm, spraying distance 300 mm, spray gun moving speed 800 mm / min.

[0018] The present invention also discloses a high-temperature corrosion-resistant metal-ceramic coating prepared by the above preparation method and its application in a biomass power generation boiler.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses a CeO2-Ti2AlC phase to reinforce the NiCrAlY coating. Through optimization of processes such as granulation, mixing, and supersonic spraying, the prepared Ni-based composite coating is dense, tightly bonded to the substrate, and free of defects such as pores. During the coating preparation process, the Ti2AlC phase is well preserved, and no obvious decomposition is found. At the same time, the unique microcrack self-healing function of Ti2AlC forms oxides at high temperatures, which can fill the crack channels. CeO2 can inhibit the peeling of the oxide film and improve the coating's high-temperature corrosion resistance. Attached Figure Description

[0020] Figure 1 The morphology of CeO2-Ti2AlC powder prepared by the process in Comparative Example 2 and Examples 1, 2 and 3, wherein: (a) Comparative Example 2, (b) Example 1, (c) Example 2, (d) Example 3;

[0021] Figure 2 XRD patterns of the coatings in Comparative Examples 1 and 2 and Examples 1, 2 and 3;

[0022] Figure 3 The coating cross-sectional morphology of Comparative Examples 1 and 2 and Examples 1, 2 and 3 is shown, wherein: (a) Comparative Example 1, (b) Comparative Example 2, (c) Example 1, (d) Example 2, (e) Example 3;

[0023] Figure 4 Bar charts showing the microhardness of the coatings in Comparative Examples 1 and 2 and Examples 1, 2 and 3;

[0024] Figure 5 The weight gain curves of the coatings in Comparative Examples 1 and 2 and Examples 1, 2 and 3 after 100 h of hot corrosion are shown.

[0025] Figure 6 XRD patterns of the coatings in Comparative Examples 1 and 2 and Examples 1, 2 and 3 after 100 h of hot corrosion;

[0026] Figure 7 The surface morphology of the coatings of Comparative Examples 1 and 2 and Examples 1, 2 and 3 after 100 h of hot corrosion is shown in the following figures: (a) Comparative Example 1 (100 μm), (a1) Comparative Example 1 (20 μm), (b) Comparative Example 2 (100 μm), (b1) Comparative Example 2 (20 μm), (c) Example 2 (100 μm), (c1) Example 2 (20 μm). Detailed Implementation

[0027] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0028] Example 1

[0029] S1: Mix 4% polyvinyl alcohol and 0.4% 1-octanol with the CeO2 and Ti2AlC powders by weight. Add the mixture to an alumina ball mill jar at a CeO2-Ti2AlC to deionized water weight ratio of 2:3 and ball mill for 4 hours at a speed of 360 r / min to obtain a slurry.

[0030] S2: Spray granulation is performed on the slurry obtained in step S1 to obtain agglomerated powder, and then vacuum sintering is performed at a temperature of 1300 ℃. The agglomerated powder after vacuum sintering needs to be sieved and classified to obtain a particle size in the range of 25~71 μm.

[0031] S3: Mix the powder sieved in step S2 with NiCrAlY in the following proportions: 0.75% CeO2 powder, 30% Ti2AlC powder and 69.25% NiCrAlY powder, wherein the particle size of NiCrAlY powder is 15~45 μm.

[0032] S4: The substrate is roughened by sandblasting and then chamfered.

[0033] S5: A composite coating is prepared on the substrate using high-velocity oxygen flame (HVOF) spraying technology. The process parameters are: kerosene flow rate 30 L / h, oxygen flow rate 53 m³ / h. 3 / h, powder feed rate 30 g / min, step distance 3 mm, spraying distance 300 mm, spray gun moving speed 800 mm / min.

[0034] S6. A full-coverage spray coating was applied to the surface of the hot-corrosion sample, and a composite salt of KCl, NaCl, and Na2SO4 was selected to test the high-temperature corrosion performance of the sample at 700℃.

[0035] Example 2

[0036] S1: Mix 4% polyvinyl alcohol and 0.4% 1-octanol with the CeO2 and Ti2AlC powders by weight. Add the mixture to an alumina ball mill jar at a CeO2-Ti2AlC to deionized water weight ratio of 2:3 and ball mill for 4 hours at a speed of 360 r / min to obtain a slurry.

[0037] S2: Spray granulation is performed on the slurry obtained in step S1 to obtain agglomerated powder, and then vacuum sintering is performed at a temperature of 1300 ℃. The agglomerated powder after vacuum sintering needs to be sieved and classified to obtain a particle size in the range of 25~71 μm.

[0038] S3: Mix the sieved powder from step S2 with NiCrAlY in a ratio of 1% CeO2 powder, 30% Ti2AlC powder and 69% NiCrAlY powder, wherein the particle size of NiCrAlY powder is 15~45 μm.

[0039] S4: The substrate is roughened by sandblasting and then chamfered.

[0040] S5: A composite coating is prepared on the substrate using high-velocity oxygen flame (HVOF) spraying technology. The process parameters are: kerosene flow rate 30 L / h, oxygen flow rate 53 m³ / h. 3 / h, powder feed rate 30 g / min, step distance 3 mm, spraying distance 300 mm, spray gun moving speed 800 mm / min.

[0041] S6. A full-coverage spray coating was applied to the surface of the hot-corrosion sample, and a composite salt of KCl, NaCl, and Na2SO4 was selected to test the high-temperature corrosion performance of the sample at 700℃.

[0042] Example 3

[0043] S1: Mix 4% polyvinyl alcohol and 0.4% 1-octanol with the CeO2 and Ti2AlC powders by weight. Add the mixture to an alumina ball mill jar at a CeO2-Ti2AlC to deionized water weight ratio of 2:3 and ball mill for 4 hours at a speed of 360 r / min to obtain a slurry.

[0044] S2: Spray granulation is performed on the slurry obtained in step S1 to obtain agglomerated powder, and then vacuum sintering is performed at a temperature of 1300 ℃. The agglomerated powder after vacuum sintering needs to be sieved and classified to obtain a particle size in the range of 25~71 μm.

[0045] S3: Mix the powder sieved in step S2 with NiCrAlY in the following proportions: 1.25% CeO2 powder, 30% Ti2AlC powder and 68.75% NiCrAlY powder, wherein the particle size of NiCrAlY powder is 15~45 μm.

[0046] S4: The substrate is roughened by sandblasting and then chamfered.

[0047] S5: A composite coating is prepared on the substrate using high-velocity oxygen flame (HVOF) spraying technology. The process parameters are: kerosene flow rate 30 L / h, oxygen flow rate 53 m³ / h. 3 / h, powder feed rate 30 g / min, step distance 3 mm, spraying distance 300 mm, spray gun moving speed 800 mm / min.

[0048] S6. A full-coverage spray coating was applied to the surface of the hot-corrosion sample, and a composite salt of KCl, NaCl, and Na2SO4 was selected to test the high-temperature corrosion performance of the sample at 700℃.

[0049] Comparative Example 1

[0050] S1: The substrate is roughened by sandblasting and then chamfered.

[0051] S2: A NiCrAlY coating was prepared on the substrate using high-velocity oxygen flame (HVOF) spraying technology. The process parameters were: kerosene flow rate 30 L / h, oxygen flow rate 53 m³ / h. 3 The spray gun has a powder feed rate of 30 g / min, a step size of 3 mm, a spraying distance of 300 mm, and a spray gun moving speed of 800 mm / min. The NiCrAlY powder has a particle size of 15~45 μm.

[0052] S3: Apply a full-coverage spray to the surface of the hot-corrosion sample, selecting a composite salt of KCl, NaCl, and Na2SO4, and test the high-temperature corrosion performance of the sample at 700℃.

[0053] Comparative Example 2

[0054] S1: Mix 4% polyvinyl alcohol and 0.4% 1-octanol (by weight of Ti2AlC powder) with the mixture. Add the mixture to an alumina ball mill jar at a weight ratio of 2:3 (Ti2AlC to deionized water), and ball mill for 4 hours at a speed of 360 r / min to obtain a slurry.

[0055] S2: Spray granulation is performed on the slurry obtained in step S1 to obtain agglomerated powder, and then vacuum sintering is performed at a temperature of 1300 ℃. The agglomerated powder after vacuum sintering needs to be sieved and classified to obtain a particle size in the range of 25~71 μm.

[0056] S3: Mix the powder sieved in step S2 with NiCrAlY in a ratio of 30% Ti2AlC powder and 70% metallic NiCrAlY powder, wherein the particle size of NiCrAlY powder is 15~45 μm.

[0057] S4: The substrate is roughened by sandblasting and then chamfered.

[0058] S5: A composite coating is prepared on the substrate using high-velocity oxygen flame (HVOF) spraying technology. The process parameters are: kerosene flow rate 33 L / h, oxygen flow rate 53 m³ / h. 3 / h, powder feed rate 30 g / min, step distance 3 mm, spraying distance 300 mm, spray gun moving speed 800 mm / min.

[0059] S6. A full-coverage spray coating was applied to the surface of the hot-corrosion sample, and a composite salt of KCl, NaCl, and Na2SO4 was selected to test the high-temperature corrosion performance of the sample at 700℃.

[0060] The test method for the hot corrosion performance of coatings is as follows:

[0061] Hot corrosion experiments were conducted in a tube furnace, and the hot corrosion performance of the coating at 700 °C was tested using the salt coating method. KCl, NaCl, and Na₂SO₄ were mixed in a mass ratio of 1:1:1 and uniformly coated onto the surface of the fully coated sample, with a total salt concentration of 5–6 mg / cm³. 2 The error is controlled within ± 0.3 mg / cm². 2 Before the experiment, the crucible containing the salt-coated sample was weighed and the weight recorded using an electronic balance (domestic HZ-124 / 85S model) with a sensitivity of 0.01 mg. Every 20 h, the crucible was removed, cooled to room temperature, weighed, and the experiment continued. The cycle was repeated for a total of 100 h. The mass change during the hot corrosion process was calculated and the hot corrosion kinetic curve was plotted.

[0062] Figure 1 The morphology of CeO2-Ti2AlC powders prepared for the process described in Comparative Example 2 and Examples 1, 2, and 3 is shown. All powders exhibited spherical shapes after ball milling and vacuum sintering, meeting the requirements for spraying. Figures (b), (c), and (d) are SEM images with different CeO2 contents. By adjusting the ratio, the distribution of CeO2 on the Ti2AlC surface can be controlled, gradually transitioning from sporadic adhesion to uniform coating.

[0063] Figure 2 The XRD patterns of the coatings in Comparative Examples 1 and 2 and Examples 1, 2, and 3 are shown. The main phases of the coatings are Ni / Ni3Al, Ti2AlC, and TiC, with Ni / Ni3Al being the main phase of NiCrAlY. The TiC phase is obtained from the decomposition of the MAX phase and is present in very small amounts, indicating that the MAX phase powder is well preserved during the spraying preparation process. The intensity of the CeAlO3 diffraction peak increases with the increase of the CeO2 ratio.

[0064] Figure 3 SEM images of the cross-sections of the coatings in Comparative Examples 1 and 2, and Examples 1, 2, and 3 are shown. The coating in Comparative Example 1 exhibits obvious pores. Combined with the EDS results in Table 1, it can be seen that the grayish-white (region 1) Ni3Al / Ni phase is present in the coating. The remaining coatings have a dense structure, exhibiting obvious layered characteristics, without pores or other defects, and show good adhesion to the substrate. The light gray area represents the Ni / Ni3Al phase, the dark gray area represents the Ti2AlC and TiC phases, and the small amount of black phase is presumably a small amount of Al2O3 generated during the spraying process. Figure 3The cross-sectional morphology of the coating and the EDS energy dispersive spectroscopy analysis results in Table 1 show that a small amount of Ce element was detected in the coating. Its content was low in each region and it was mainly dispersed in the interior of the coating in the form of trace elements.

[0065] Figure 4 The bar chart shows the microhardness of the coatings in comparative examples and Examples 1, 2, and 3. The coating hardness was 599.8 HV after adding different amounts of CeO2 (0.75%, 1.0%, and 1.25%). 0.2 610.2 HV 0.2 and 620.5 HV 0.2 Compared with the control group without CeO2 (606 HV) 0.2 The hardness value fluctuated only within a small range and did not show a clear pattern of change, indicating that the amount of CeO2 added had no significant effect on the coating hardness.

[0066] Figure 5 The graph shows the weight gain curves of the coatings in Comparative Examples 1, 2, and 3 after 100 hours of hot corrosion. After 100 hours of hot corrosion testing, the coatings without CeO2 (Comparative Examples 1 and 2) showed a weight gain of 25.48 mg / cm³. 2 14.63 mg / cm 2 The weight gains of Examples 1, 2, and 3, which added 0.75%, 1.0%, and 1.25% CeO2, were 13.60 mg / cm³, respectively. 2 13.29 mg / cm 2 and 13.12 mg / cm 2 Because the NiCrAlY coating (Comparative Example 1) has many pores, it cannot prevent the penetration of corrosive media. The Ti2AlC-NiCrAlY coating (Comparative Example 2) provides a continuous elemental supply through the Ti2AlC phase to achieve the "self-healing" of the oxide layer and form a highly dense oxide layer mainly composed of Al2O3. When CeO2 is added (Examples 1, 2, and 3), it can promote the formation of a more continuous and dense oxide film, effectively preventing the penetration and diffusion of corrosive media. When the CeO2 addition is greater than 1.0% (Examples 2 and 3), the thermal corrosion weight gain of the coating remains basically unchanged. Further increasing the CeO2 content does not bring about a significant performance improvement. Therefore, from the perspective of experimental efficiency and cost, Example 2 can meet the research requirements.

[0067] Figure 6The XRD patterns of Comparative Examples 1 and 2 and Example 2 after 100 h of hot corrosion are shown. After 100 h of corrosion, the hot corrosion products of the NiCrAlY coating are mainly NiCr2O4, with a loose structure and no protective effect. With the addition of the Ti2AlC phase (Comparative Example 2), the complex corrosion products of the composite coating include different types of oxides (TiO2, Cr2O3, NiO, and Al2O3) and a small amount of spinel-structured NiCr2O4. When 1% CeO2 is added (Example 2), the hot corrosion products of the coating are mainly Cr2O3. This is because CeO2, as an active element, promotes the selective oxidation of Cr, lowers its nucleation barrier, and allows Cr to be preferentially oxidized at a lower temperature, ultimately leading to Cr2O3 becoming the dominant oxidation product.

[0068] Figure 7 SEM images of the surface morphology of Comparative Examples 1 and 2 and Example 2 after 100 h of hot corrosion. Figure 7 As shown in (a), the NiCrAlY coating surface is porous, and the corrosion products mainly consist of needle-like structures and gray Cr-rich spherical substances. The gray substances are primarily Cr2O3, while the needle-like structures are mainly NiCr2O4 spinel phase formed by oxidation. With the addition of the MAX phase (Comparative Example 2) and CeO2 (Example 2), the needle-like and clustered oxides on the corroded surface essentially disappear, resulting in a denser and smoother surface. The addition of CeO2 (Example 2) significantly improves the adhesion of the chromium oxide (Cr2O3) or aluminum oxide (Al2O3) film on the surface, inhibiting oxide film peeling. The fine cerium oxide particles can act as "pins" in the coating or oxide layer, sealing micro-cracks and preventing chloride and sulfate ions from penetrating into the substrate.

[0069] This invention significantly improves the high-temperature corrosion performance of Ti2AlC-NiCrAlY coating by adding CeO2, realizing the application of Ni-based alloy coatings in the field of high-temperature corrosion.

[0070] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-temperature corrosion-resistant metal-ceramic coating, characterized in that, Includes the following steps: S1, mix Ti2AlC, CeO2 powder, polyvinyl alcohol and 1-octanol, and then ball mill the mixture with deionized water to obtain a mixed slurry; S2, the mixed slurry obtained in step S1 is subjected to spray granulation to obtain agglomerated powder, and the agglomerated powder is subjected to vacuum sintering and sieve classification to finally obtain CeO2-Ti2AlC powder. S3, mix the CeO2-Ti2AlC powder obtained in step S2 with the NiCrAlY powder to obtain a mixed powder; S4. High-temperature corrosion-resistant metal-ceramic coating is prepared on the roughened substrate using supersonic flame spraying technology to apply the mixed powder obtained in step S3.

2. The method for preparing a high-temperature corrosion protective metal-ceramic coating as described in claim 1, characterized in that, In step S1, Ti2AlC is in the form of flake powder with a purity greater than 99.5%.

3. The method for preparing a high-temperature corrosion protective metal-ceramic coating as described in claim 1, characterized in that, In step S1, the mass of polyvinyl alcohol accounts for 4% of the total mass of CeO2 and Ti2AlC, the mass of 1-octanol accounts for 0.4% of the total mass of CeO2 and Ti2AlC, and the mass ratio of the total mass of CeO2 and Ti2AlC to the mass of deionized water is 2:

3.

4. The method for preparing a high-temperature corrosion protective metal-ceramic coating as described in claim 1, characterized in that, In step S1, ball milling is carried out in an alumina ball mill jar for 4 hours at a rotation speed of 360 r / min.

5. The method for preparing a high-temperature corrosion protective metal-ceramic coating as described in claim 1, characterized in that, In step S2, the temperature of vacuum sintering is 1200~1400 ℃.

6. The method for preparing a high-temperature corrosion protective metal-ceramic coating as described in claim 1, characterized in that, In step S2, the CeO2-Ti2AlC powder obtained after sieving and grading has a particle size of 25~71 μm.

7. The method for preparing a high-temperature corrosion protective metal-ceramic coating as described in claim 1, characterized in that, In step S3, the mass percentage of NiCrAlY powder in the mixed powder is 68.75%~69.25%, the mass percentage of Ti2AlC powder is 30%, and the mass percentage of CeO2 powder is 0.75~1.25%.

8. The method for preparing a high-temperature corrosion protective metal-ceramic coating as described in claim 1, characterized in that, The process parameters of the supersonic flame spraying technology in the step S5 are as follows: kerosene amount 30 L / h, oxygen flow rate 53 m 3 / h, powder feeding rate 30 g / min, step distance 3 mm, spraying distance 300 mm, and spraying gun moving speed 800 mm / min.

9. A high-temperature corrosion-resistant metal-ceramic coating prepared by the preparation method according to any one of claims 1 to 8.

10. The application of a high-temperature corrosion-resistant metal-ceramic coating as described in claim 9 in a biomass power generation boiler.

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