Plasma spraying high-temperature erosion resistant coating and coating preparation method

Abstract

The invention provides a plasma spraying high-temperature-erosion-resistant coating and a coating preparation method, and relates to the technical field of material surface treatment. Comprising the following components in parts by mass: 30-45 parts of tungsten carbide, 15-25 parts of chromium carbide-nickel-chromium alloy, 15-25 parts of yttria-stabilized zirconia, 5-10 parts of aluminum oxide-titanium dioxide composite ceramic, 10-20 parts of nickel-chromium-aluminum-yttrium alloy, 1-3 parts of nano aluminum oxide and 1-3 parts of lanthanum oxide. Multiphase collaborative design is adopted, tungsten carbide and chromium carbide-nickel-chromium alloy form double hard phases, the hardness is higher, aluminum oxide-titanium dioxide composite ceramic fills pores and improves compactness, rare earth and nanometer are adopted to cooperate, lanthanum oxide and nanometer aluminum oxide react to generate a LaAlO3 protective layer, oxidation weight gain is small, oxygen diffusion is inhibited, nanometer aluminum oxide refines grains, and the hardness is higher. In conclusion, the high-temperature oxidation resistance is high, and the erosion rate is low.

Description

Technical Field

[0001] The present invention relates to the technical field of material surface treatment, and particularly to a plasma-sprayed high-temperature erosion-resistant coating and a coating preparation method. Background Art

[0002] Erosion wear phenomena widely exist in many industrial sectors such as machinery, metallurgy, aerospace, energy, metallurgical mines, petrochemical industry, and construction, accounting for about 8% of the total number of various wear and tear damages. The harm it causes to industrial production is huge. For example, dust and sand particles in the air can reduce the service life of helicopter engines by 90%; the erosion of the elbows of the coal injection and slag discharge pipelines in thermal power plants and heat power plants is more than 50 times more serious than that of the straight-through parts, and the general overhaul and replacement period is 2 to 3 years; in the field of metallurgical mines, the pipelines for tail (single) ore transportation need to be repaired and replaced on average every 1 to 2 years due to long-term high-intensity erosion wear; in the flue gas power generation equipment of petrochemical enterprises, the broken catalyst solid particles entrained by high-temperature flue gas impact the turbine blades and related flow-through components at a high speed, causing serious erosion wear, shortening their service life severely, and requiring frequent furnace shutdowns for maintenance. Moreover, some shutdown failures are unpredictable, which not only seriously affects the safe operation of the equipment but also causes huge economic losses. Generally speaking, the erosion wear phenomenon first occurs on the material surface. Therefore, the surface of the material is the key to controlling erosion dynamics, and the surface quality determines the effect of erosion control. Thus, the role of the high-temperature erosion-resistant coating is crucial.

[0003] Existing commonly used high-temperature erosion-resistant coatings, such as pure WC-Co coatings, Al2O3-TiO2 coatings, and NiCrAlY coatings, have the following defects: For pure WC-Co coatings, oxidation is serious above 900°C, generating WO3 and resulting in a hardness drop of >30%; for Al2O3-TiO2 coatings, the erosion resistance is poor (erosion rate > 0.25mm 3 / g), and the thermal expansion coefficient does not match that of the metal matrix, making it easy to peel off; for NiCrAlY coatings, due to the lack of hard phases, the erosion resistance is weak (erosion rate 0.35mm 3 / g). In summary, the existing coatings cannot simultaneously meet the requirements of high-temperature oxidation resistance, erosion resistance, and strong interfacial bonding. Therefore, the present invention proposes a plasma-sprayed high-temperature erosion-resistant coating and a coating preparation method to solve the problems existing in the prior art. Summary of the Invention

[0004] In view of the above problems, the present invention proposes a plasma-sprayed high-temperature erosion-resistant coating and a coating preparation method. The plasma-sprayed high-temperature erosion-resistant coating has strong high-temperature oxidation resistance and a low erosion rate.

[0005] To achieve the object of the present invention, the present invention is realized through the following technical solutions: A plasma-sprayed high-temperature erosion-resistant coating, comprising the following components in mass ratio: tungsten carbide (WC) 30 - 45 parts, chromium carbide-nickel chromium alloy (Cr3C2-NiCr) 15 - 25 parts, yttria-stabilized zirconia (Y2O3-ZrO2) 15 - 25 parts, alumina-titania composite ceramic (Al2O3-TiO2) 5 - 10 parts, nickel-chromium-aluminum-yttrium alloy (NiCrAlY) 10 - 20 parts, nano-alumina (α-Al2O3) 1 - 3 parts, lanthanum oxide (La2O3) 1 - 3 parts.

[0006] Further improvement lies in: comprising the following components in mass ratio: tungsten carbide (WC) 40 parts, chromium carbide-nickel chromium alloy (Cr3C2-NiCr) 20 parts, yttria-stabilized zirconia (Y2O3-ZrO2) 20 parts, alumina-titania composite ceramic (Al2O3-TiO2) 8 parts, nickel-chromium-aluminum-yttrium alloy (NiCrAlY) 15 parts, nano-alumina (α-Al2O3) 2 parts, lanthanum oxide (La2O3) 2 parts.

[0007] Further improvement lies in: the molar content of Y2O3 in the yttria-stabilized zirconia is 8%, and the mass ratio of TiO2 in the alumina-titania composite ceramic is 13%.

[0008] Further improvement lies in: the particle size of the nano-alumina is 20 - 50 nm, and it is synthesized by the sol-gel method.

[0009] Further improvement lies in: the mass fraction of NiCr in the chromium carbide-nickel chromium alloy is 20%, and it is prepared by the self-propagating high-temperature synthesis method.

[0010] A preparation method of a plasma-sprayed high-temperature erosion-resistant coating, comprising the following steps:

[0011] S1: Ball-mill and mix tungsten carbide, chromium carbide-nickel chromium alloy, yttria-stabilized zirconia, alumina-titania composite ceramic, nickel-chromium-aluminum-yttrium alloy, nano-alumina, and lanthanum oxide powders;

[0012] S2: Sandblast and ultrasonically clean the surface of the substrate to be coated;

[0013] S3: Use an Ar-H2 mixed gas to plasma-spray the mixed powder materials onto the surface of the substrate to form a coating;

[0014] S4: Perform gradient heat treatment on the coating to cure the coating.

[0015] Further improvement lies in: in S1, ball-mill and mix for 8 - 12 h, the ball-to-material ratio is 5:1, and argon protection is used.

[0016] A further improvement lies in that: in S2, the surface of the substrate is subjected to sandblasting treatment until the roughness Ra≥6μm, and ultrasonic cleaning is carried out with acetone.

[0017] A further improvement lies in that: in S3, before plasma spraying, the mixed powder is preheated at 300°C for 2h to remove moisture, and the plasma spraying parameters are controlled: current 600 - 700A, voltage 70 - 80V, powder feeding rate 40 - 60g / min, spraying distance 80 - 150mm. After forming the coating, the coating thickness is controlled within 0.4 - 0.6mm.

[0018] A further improvement lies in that: in S4, the gradient heat treatment specifically includes:

[0019] Treat at 100°C for 2h;

[0020] Treat at 800°C for 1h;

[0021] Treat at 1200°C for 0.5h.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The present invention adopts a multi-phase collaborative design. Tungsten carbide and chromium carbide - nickel chromium alloy form a double hard phase with higher hardness. Alumina - titanium dioxide composite ceramics fill the pores to improve the density. The combination of rare earth and nano - technology is adopted. Lanthanum oxide reacts with nano - alumina to generate a LaAlO3 protective layer, with less oxidation weight gain, inhibiting oxygen diffusion. Nano - alumina refines the grains, further improving the density and toughness of the coating. In summary, the high - temperature oxidation resistance is strong and the erosion rate is low.

[0024] 2. The present invention adopts plasma spraying to form a gradient structure, with a bonding strength ≥75MPa. Through gradient heat treatment, a nano - crystalline oxide film is formed, breaking through the high - temperature limit of traditional coatings, making the coating micro - hardness higher and the thermal shock life longer. Description of the Drawings

[0025] Figure 1 It is a flow chart of the present invention. Detailed Embodiments

[0026] To deepen the understanding of the present invention, the following will further elaborate on the present invention in combination with embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation to the protection scope of the present invention.

[0027] Embodiment 1

[0028] According to Figure 1As shown, this embodiment proposes a plasma-sprayed high-temperature erosion-resistant coating, which includes the following components in mass ratio: 30 parts of tungsten carbide (WC), 15 parts of chromium carbide-nickel chromium alloy (Cr3C2-NiCr), 15 parts of yttria-stabilized zirconia (Y2O3-ZrO2), 5 parts of alumina-titania composite ceramic (Al2O3-TiO2), 10 parts of nickel-chromium-aluminum-yttrium alloy (NiCrAlY), 1 part of nano-alumina (α-Al2O3), and 1 part of lanthanum oxide (La2O3).

[0029] Tungsten carbide: provides high hardness and wear resistance; yttria-stabilized zirconia: resistant to high-temperature oxidation and thermal shock; chromium carbide-nickel chromium alloy: forms a dense antioxidant layer; nano-alumina: enhances hardness and interfacial bonding strength; alumina-titania composite ceramic: reduces the porosity of the coating; nickel-chromium-aluminum-yttrium alloy: acts as a bonding layer to improve wettability; lanthanum oxide: inhibits high-temperature oxidation and crack propagation

[0030] Multi-phase collaborative design: Tungsten carbide and chromium carbide-nickel chromium alloy form a double hard phase with a hardness of 1800 HV0.3; alumina-titania composite ceramic fills the pores (metallographic analysis shows a porosity of 1.2%), improving the density.

[0031] Rare earth and nano collaboration: Lanthanum oxide reacts with nano-alumina to form LaAlO3, inhibiting oxygen diffusion; nano-alumina refines the grains, improving the density and toughness of the coating.

[0032] The molar content of Y2O3 in the yttria-stabilized zirconia is 8%, and the mass fraction of TiO2 in the alumina-titania composite ceramic is 13%. The particle size of the nano-alumina is 20 - 50 nm and it is synthesized by the sol-gel method. The mass fraction of NiCr in the chromium carbide-nickel chromium alloy is 20% and it is prepared by the self-propagating high-temperature synthesis method.

[0033] A preparation method of a plasma-sprayed high-temperature erosion-resistant coating includes the following steps:

[0034] Ball-mill and mix tungsten carbide, chromium carbide-nickel chromium alloy, yttria-stabilized zirconia, alumina-titania composite ceramic, nickel-chromium-aluminum-yttrium alloy, nano-alumina, and lanthanum oxide powders; ball-mill and mix for 8 h, with a ball-to-material ratio of 5:1, and use argon protection;

[0035] Sandblast and ultrasonically clean the surface of the substrate to be coated; process until the roughness Ra ≥ 6 μm, and ultrasonically clean with acetone;

[0036] An Ar-H2 mixed gas is used to plasma spray the mixed powder onto the surface of the substrate to form a coating; before plasma spraying, the mixed powder is preheated at 300 °C for 2 h to remove moisture, and the plasma spraying parameters are controlled: current 600 A, voltage 70 V, powder feeding rate 40 g / min, spraying distance 80 - 150 mm. After forming the coating, the coating thickness is controlled at 0.4 mm; the particle size distribution of WC and Cr3C2-NiCr is 15 - 53 μm, and WC is angular crushed particles. For the prepared coating, its porosity ≤ 1.5%.

[0037] The coating is subjected to gradient heat treatment to cure the coating; the gradient heat treatment specifically includes: treating at 100 °C for 2 h; treating at 800 °C for 1 h; treating at 1200 °C for 0.5 h. The gradient heat treatment forms a nanocrystalline oxide film, breaking through the high-temperature limit of the traditional coating, making the microhardness of the coating reach 1300 HV0.3, and reducing the residual stress by 50% (measured by X-ray diffraction method).

[0038] Example 2

[0039] According to Figure 1 As shown, this example presents a plasma-sprayed high-temperature erosion-resistant coating, including the following components by mass ratio: tungsten carbide (WC) 40 parts, chromium carbide-nickel chromium alloy (Cr3C2-NiCr) 20 parts, yttria-stabilized zirconia (Y2O3-ZrO2) 20 parts, alumina-titania composite ceramic (Al2O3-TiO2) 8 parts, nickel-chromium-aluminum-yttrium alloy (NiCrAlY) 15 parts, nano-alumina (α-Al2O3) 2 parts, lanthanum oxide (La2O3) 2 parts.

[0040] Tungsten carbide: provides high hardness and wear resistance; yttria-stabilized zirconia: high-temperature oxidation and thermal shock resistance; chromium carbide-nickel chromium alloy: forms a dense antioxidant layer; nano-alumina: enhances hardness and interfacial bonding force; alumina-titania composite ceramic: reduces the coating porosity; nickel-chromium-aluminum-yttrium alloy: improves wettability as a bonding layer; lanthanum oxide: inhibits high-temperature oxidation and crack propagation

[0041] Multi-phase collaborative design: Tungsten carbide and chromium carbide-nickel chromium alloy form a double hard phase, with a hardness of 1800 HV0.3; the alumina-titania composite ceramic fills the pores (metallographic shows a porosity of 1.2%), improving the density.

[0042] Rare earth and nano synergy: Lanthanum oxide reacts with nano-alumina to generate LaAlO3, inhibiting oxygen diffusion; nano-alumina refines the grains, improving the density and toughness of the coating.

[0043] The molar content of Y2O3 in the yttria-stabilized zirconia is 8%, and the mass fraction of TiO2 in the alumina-titania composite ceramic is 13%. The particle size of the nano-alumina is 20 - 50 nm, and it is synthesized by the sol-gel method. The mass fraction of NiCr in the chromium carbide-nickel chromium alloy is 20%, and it is prepared by the self-propagating high-temperature synthesis method.

[0044] A preparation method of a plasma-sprayed high-temperature erosion-resistant coating includes the following steps:

[0045] Ball-mill and mix tungsten carbide, chromium carbide-nickel chromium alloy, yttria-stabilized zirconia, alumina-titania composite ceramic, nickel chromium aluminum yttrium alloy, nano-alumina, and lanthanum oxide powder; ball-mill and mix for 8 - 12 h, with a ball-to-powder ratio of 5:1, and use argon protection;

[0046] Sandblast and ultrasonically clean the surface of the substrate to be coated; process until the roughness Ra ≥ 6 μm, and ultrasonically clean with acetone;

[0047] Plasma-spray the mixed powder onto the substrate surface with an Ar-H2 mixed gas to form a coating; before plasma spraying, preheat the mixed powder at 300 °C for 2 h to remove moisture, control the plasma spraying parameters: current 650 A, voltage 75 V, powder feeding rate 50 g / min, spraying distance 80 - 150 mm. After forming the coating, control the coating thickness at 0.5 mm; the particle size distribution of WC and Cr3C2-NiCr is 15 - 53 μm, and WC is an angular broken particle. For the prepared coating, its porosity ≤ 1.5%;

[0048] Perform gradient heat treatment on the coating to cure the coating; the gradient heat treatment specifically includes: treating at 100 °C for 2 h; treating at 800 °C for 1 h; treating at 1200 °C for 0.5 h. The gradient heat treatment forms a nano-crystalline oxide film, breaking through the high-temperature limit of the traditional coating, making the microhardness of the coating reach 1300 HV0.3, and reducing the residual stress by 50% (measured by X-ray diffraction method).

[0049] Example Three

[0050] According to Figure 1 As shown, this example proposes a plasma-sprayed high-temperature erosion-resistant coating, including the following components by mass ratio: tungsten carbide (WC) 45 parts, chromium carbide-nickel chromium alloy (Cr3C2-NiCr) 25 parts, yttria-stabilized zirconia (Y2O3-ZrO2) 25 parts, alumina-titania composite ceramic (Al2O3-TiO2) 10 parts, nickel chromium aluminum yttrium alloy (NiCrAlY) 20 parts, nano-alumina (α-Al2O3) 3 parts, and lanthanum oxide (La2O3) 3 parts.

[0051] Tungsten carbide: provides high hardness and wear resistance; Yttria-stabilized zirconia: resistant to high-temperature oxidation and thermal shock; Chromium carbide-nickel chromium alloy: forms a dense anti-oxidation layer; Nano-aluminum oxide: enhances hardness and interfacial bonding strength; Alumina-titania composite ceramics: reduces the coating porosity; Nickel-chromium-aluminum-yttrium alloy: acts as a bonding layer to improve wettability; Lanthanum oxide: inhibits high-temperature oxidation and crack propagation

[0052] Multi-phase collaborative design: Tungsten carbide and chromium carbide-nickel chromium alloy form a dual hard phase with a hardness of 1800 HV0.3; Alumina-titania composite ceramics fill the pores (metallographic examination shows a porosity of 1.2%), improving the density.

[0053] Rare earth and nano synergy: Lanthanum oxide reacts with nano-aluminum oxide to form LaAlO3, inhibiting oxygen diffusion; Nano-aluminum oxide refines the grains, improving the density and toughness of the coating.

[0054] The molar content of Y2O3 in the yttria-stabilized zirconia is 8%, and the mass fraction of TiO2 in the alumina-titania composite ceramics is 13%. The particle size of the nano-aluminum oxide is 20 - 50 nm, synthesized by the sol-gel method. The mass fraction of NiCr in the chromium carbide-nickel chromium alloy is 20%, prepared by the self-propagating high-temperature synthesis method.

[0055] A preparation method of a plasma-sprayed high-temperature erosion-resistant coating, comprising the following steps:

[0056] Ball-mill and mix tungsten carbide, chromium carbide-nickel chromium alloy, yttria-stabilized zirconia, alumina-titania composite ceramics, nickel-chromium-aluminum-yttrium alloy, nano-aluminum oxide, and lanthanum oxide powders; Ball-mill and mix for 8 - 12 h, with a ball-to-powder ratio of 5:1, and use argon protection;

[0057] Perform sandblasting treatment and ultrasonic cleaning on the surface of the substrate to be coated; Treat to a roughness Ra≥6 μm, and perform ultrasonic cleaning with acetone;

[0058] Use an Ar-H2 mixed gas to plasma-spray the mixed powder onto the surface of the substrate to form a coating; Before plasma spraying, preheat the mixed powder at 300 °C for 2 h to remove moisture, control the plasma spraying parameters: current 700 A, voltage 80 V, powder feeding rate 60 g / min, spraying distance 80 - 150 mm. After forming the coating, control the coating thickness at 0.6 mm; The particle size distribution of WC and Cr3C2-NiCr is 15 - 53 μm, and WC is angular broken particles. For the prepared coating, its porosity ≤1.5%;

[0059] The coating is subjected to gradient heat treatment to cure the coating; the gradient heat treatment specifically includes: treating at 100 °C for 2 h; treating at 800 °C for 1 h; treating at 1200 °C for 0.5 h. The gradient heat treatment forms a nanocrystalline oxide film, breaking through the high-temperature resistance limit of the traditional coating, making the microhardness of the coating reach 1300 HV0.3, and reducing the residual stress by 50% (measured by X-ray diffraction method).

[0060] According to Example 1, Example 2 and Example 3, it can be concluded that the present invention has the following mass ratio components: 30-45 parts of tungsten carbide (WC), 15-25 parts of chromium carbide-nickel chromium alloy (Cr3C2-NiCr), 15-25 parts of yttria-stabilized zirconia (Y2O3-ZrO2), 5-10 parts of alumina-titania composite ceramic (Al2O3-TiO2), 10-20 parts of nickel-chromium-aluminum-yttrium alloy (NiCrAlY), 1-3 parts of nano-alumina (α-Al2O3), and 1-3 parts of lanthanum oxide (La2O3). The prepared coating has higher hardness, strong high-temperature oxidation resistance, low erosion rate and long thermal shock life.

[0061] Verification example:

[0062]

[0063] The present invention adopts multiphase collaborative design. Tungsten carbide and chromium carbide-nickel chromium alloy form a double hard phase with higher hardness. Alumina-titania composite ceramic fills the pores and improves the density. The rare earth and nano are synergistic. Lanthanum oxide and nano-alumina react to form a LaAlO3 protective layer with less oxidation weight gain, inhibiting oxygen diffusion. Nano-alumina refines the grains, further improving the density and toughness of the coating. In summary, it has strong high-temperature oxidation resistance and the erosion rate is as low as 0.07 mm 3 / g, which is 78% lower than that of the traditional Al2O3-TiO2 coating (0.32 mm 3 / g). At the same time, the present invention adopts plasma spraying to form a gradient structure with a bonding strength ≥ 75 MPa. Through gradient heat treatment, a nanocrystalline oxide film is formed, breaking through the high-temperature resistance limit of the traditional coating, making the microhardness of the coating higher and the thermal shock life longer.

[0064] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A plasma-sprayed high-temperature erosion-resistant coating, characterized in that, It includes the following components by mass ratio: 30 - 45 parts of tungsten carbide (WC), 15 - 25 parts of chromium carbide - nickel chromium alloy (Cr3C2 - NiCr), 15 - 25 parts of yttria - stabilized zirconia (Y2O3 - ZrO2), 5 - 10 parts of alumina - titania composite ceramic (Al2O3 - TiO2), 10 - 20 parts of nickel - chromium - aluminum - yttrium alloy (NiCrAlY), 1 - 3 parts of nano - alumina (α - Al2O3), and 1 - 3 parts of lanthanum oxide (La2O3).

2. The plasma sprayed high temperature erosion resistant coating according to claim 1, wherein: It includes the following components by mass ratio: 40 parts of tungsten carbide (WC), 20 parts of chromium carbide - nickel chromium alloy (Cr3C2 - NiCr), 20 parts of yttria - stabilized zirconia (Y2O3 - ZrO2), 8 parts of alumina - titania composite ceramic (Al2O3 - TiO2), 15 parts of nickel - chromium - aluminum - yttrium alloy (NiCrAlY), 2 parts of nano - alumina (α - Al2O3), and 2 parts of lanthanum oxide (La2O3).

3. The plasma-sprayed high-temperature erosion-resistant coating according to claim 1, wherein: In the yttria - stabilized zirconia, the molar content of Y2O3 is 8%, and in the alumina - titania composite ceramic, the mass proportion of TiO2 is 13%.

4. A plasma-sprayed high-temperature erosion-resistant coating according to claim 1, characterized in that: The particle size of the nano - alumina is 20 - 50 nm, and it is synthesized by the sol - gel method.

5. A plasma-sprayed high-temperature erosion-resistant coating according to claim 1, characterized in that: In the chromium carbide - nickel chromium alloy, the mass fraction of NiCr is 20%, and it is prepared by the self - propagating high - temperature synthesis method.

6. A method for preparing a plasma-sprayed high-temperature erosion-resistant coating, which is applied to the plasma-sprayed high-temperature erosion-resistant coating described in any one of the above claims 1-5, characterized in that, It includes the following steps: S1: Ball - mill and mix the powders of tungsten carbide, chromium carbide - nickel chromium alloy, yttria - stabilized zirconia, alumina - titania composite ceramic, nickel - chromium - aluminum - yttrium alloy, nano - alumina, and lanthanum oxide. S2: Sand - blast and ultrasonically clean the surface of the substrate to be coated. S3: Use an Ar - H2 mixed gas to plasma - spray the mixed powders onto the surface of the substrate to form a coating. S4: Perform gradient heat treatment on the coating to cure the coating.

7. The preparation method of a plasma-sprayed high-temperature erosion-resistant coating according to claim 6, characterized in that: In S1, ball - mill and mix for 8 - 12 h, the ball - to - powder ratio is 5:1, and argon protection is used.

8. The preparation method of a plasma-sprayed high-temperature erosion-resistant coating according to claim 6, characterized in that: In S2, sand - blast the surface of the substrate until the roughness Ra≥6 μm, and ultrasonically clean it with acetone.

9. The preparation method of a plasma-sprayed high-temperature erosion-resistant coating according to claim 6, wherein: In S3, before plasma - spraying, pre - heat the mixed powder at 300℃ for 2 h to remove moisture, control the plasma - spraying parameters: current 600 - 700 A, voltage 70 - 80 V, powder feeding rate 40 - 60 g / min, spraying distance 80 - 150 mm. After forming the coating, control the coating thickness to be 0.4 - 0.6 mm.

10. The preparation method of a plasma-sprayed high-temperature erosion-resistant coating according to claim 6, characterized in that: In S4, the gradient heat treatment specifically includes: Treat at 100℃ for 2 h; Treat at 800℃ for 1 h; Treat at 1200℃ for 0.5 h.

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