The following is the relevant knowledge of TBC coating preparation for reference:

1. TBC coating is used to prepare "aluminum duplex coating" for the maintenance of compressor components. This is a technology that has been disclosed. The spraying method is relatively simple, and the material purchase is not difficult.

2. TBC coating:

1) Thickness of coating: There will be corresponding coating thickness requirements on the drawing of each component requiring coating. The most accurate measurement method for coating thickness is metallographic measurement, but this is only applicable to the experimental stage. The most commonly used coating thickness measurement methods in production are: eddy current method and magnetic induction method. The error of direct measurement by such methods is generally large. Therefore, if necessary, it is necessary to manufacture a dedicated standard block for calibration before measurement. (Eddy current method for non-ferromagnetic materials; magnetic induction method for ferromagnetic materials)

2) Hardness of coating: not commonly used, HV (Vickers hardness) is generally used.

3) Judgment of coating quality:

(1) The bonding strength is one of the most important parameters, and the method specified in the ASTM C633 specification in the United States is often used for testing. The general requirements are: the metal layer is greater than 9000PSI, and the ceramic layer is greater than 4000PSI.

(2) Oxide: The metal layer oxide generally requires as little as possible.

(3) Empty: Generally, the less empty the metal layer is, the better. (APS TBC ceramics can be roughly divided into two categories: the main resolution factor is the spraying interval, generally the ceramic coating sprayed at a distance of 2 inches and below is fine with longitudinal cracks, and is often used for blade parts; generally 3 inches and above. The coatings sprayed at intervals are generally uniform and porous without obvious longitudinal cracks, and are often used for incinerator components. The boundary interval between the two types of coating structures is about 2.5 inches)

(4) Volcanoes: The less the better. (General requirements: less than one volcano per inch, less than one interface ash per inch)

(5) Cracks: Generally, longitudinal cracks are allowed in the TBC ceramic layer, but transverse cracks are not allowed. (General requirements: the viewpoint of transverse cracks must be less than 45 degrees, the length must be less than 75 microns, and the aspect ratio of longitudinal cracks must be greater than 25, and at least pass through half of the ceramic layer)

4) Preheating: Preheating has a very large impact on the quality of TBC. Generally speaking: it is not necessary to preheat before spraying the metal layer, and the temperature of the workpiece is required to be less than 204 degrees Celsius during the spraying process; it is necessary to preheat (preheat to 593 degrees Celsius) before spraying the ceramic layer, and the temperature of the workpiece should be maintained during the spraying process. Between 399 and 816 degrees Celsius.

5) Surface roughness Ra: the roughness Ra of the workpiece before metal coating is at least 2.5 microns; the roughness after metal coating is required to be between 7.6 and 11.43 microns (and preferably between 8.9 and 11.43 microns) . After spraying TBC, it is generally required to be polished, which is subject to the drawing requirements.

6) The point of view of spraying is an important factor affecting the quality of the coating. Try to keep it at 90 degrees (perpendicular to the surface of the workpiece spray). Generally, the smaller the viewing point, the worse the quality of the coating. When the spraying viewing point is less than 45 degrees, the sprayed coating is generally useless waste.

7) Selection of TBC materials: subject to the requirements of the workpiece drawings. Generally speaking: when the aluminum content in the metal layer material is high, the anti-oxidative corrosion of the coating is stronger, but when the aluminum content is greater than 12%, a brittle high aluminum phase will occur (the melting point of the high aluminum phase is extremely high, so the high Aluminium powder is also extremely difficult to prepare. For now, there is a technique for spraying with "composite powders" that can increase the aluminium content of the coating while preventing the brittleness of the coating. This technique is now proven and The effect is very good); the selection of ceramic layer materials is less, generally "yttrium oxide stable zirconia" is used, and the particle size of the powder depends on the type of parts. (Generally, blades with small particle size are used to generate higher fineness and longitudinal cracks, and incinerators are generally used with large particle size to generate porous structures)

8) The spraying interval has a great influence on the structure of the coating, especially the structure of the TBC ceramic layer.