1、 Characteristics of base material
Material type: The type of substrate material affects the applicability of high-temperature resistant coatings. For example, metal substrates (such as stainless steel, titanium alloys, etc.) have different characteristics such as thermal expansion coefficient, hardness, and surface roughness, while ceramic substrates (such as alumina ceramics, silicon nitride ceramics, etc.) have different chemical stability and high temperature resistance limits, requiring coatings to be well adapted to them. For example, high-temperature alloys are commonly used in aircraft engine components, and when coating their surfaces with high-temperature resistant coatings, the coating must consider factors such as the alloy's thermal deformation at high temperatures and its adhesion to the coating.
Surface condition: The roughness and cleanliness of the substrate surface are crucial. A rougher surface can provide a better adhesion foundation for the coating, but the roughness needs to be controlled within a reasonable range. Being too rough may lead to uneven coating thickness; A clean surface (free of impurities such as oil stains, oxide scales, dust, etc.) can ensure a tight bond between the coating and the substrate, preventing the coating from peeling off at high temperatures due to poor bonding. For example, before coating construction, it is often necessary to pre treat the substrate surface through processes such as sandblasting and acid washing to achieve the ideal surface state.
2、 The properties of the coating material itself
High temperature resistance: This is the most basic requirement, and the selected coating material should be able to withstand the target high temperature environment, with significant temperature differences in different application scenarios. For example, coatings used in ordinary industrial furnaces may only need to withstand temperatures of a few hundred degrees Celsius; When spacecraft re-enter the atmosphere, their surface coatings must be able to withstand temperatures of thousands of degrees Celsius, and anti-oxidation and high-temperature resistant coatings on carbon/carbon composite materials are designed to cope with such extreme high-temperature environments.
Chemical stability: Under high temperature conditions, coating materials need to have good chemical stability and not undergo chemical reactions with surrounding media such as oxygen, corrosive gases, molten metals, etc. For example, in the metallurgical industry, some high-temperature resistant coatings need to come into contact with high-temperature metal melts and corrosive gases such as sulfur. The chemical stability of the coating itself is necessary to ensure long-term use. The alumina coating in ceramic coatings is widely used in many such environments due to its excellent chemical stability.
Thermal expansion coefficient matching: The thermal expansion coefficients of the coating material and the substrate material should be matched as much as possible, so that during temperature changes, the coating and substrate can expand and contract synchronously, avoiding problems such as cracking and peeling of the coating due to excessive thermal stress. For example, when selecting a metal coating for high-temperature components of an engine, it is necessary to choose a coating material with a thermal expansion coefficient similar to that of the engine's metal components to ensure the integrity of the coating under high-temperature alternating heat cycles.
3、 Coating preparation equipment and process conditions
Preparation equipment:
Spraying equipment: such as plasma spraying equipment, it can generate high-temperature and high-speed plasma flame flow, heat and melt the coating material, and spray it onto the surface of the substrate to form a coating. It is suitable for the preparation of various ceramic, metal and other coating materials, and can meet the spraying requirements of different component shapes and sizes; The supersonic flame spraying equipment in thermal spraying can achieve higher speed and better bonding strength of coating materials, and is commonly used to prepare high-quality wear-resistant and high-temperature resistant coatings.
Sintering equipment: For some cases where coatings are formed through sintering processes, equipment such as high-temperature sintering furnaces are crucial. They need to be able to accurately control parameters such as temperature, heating rate, and holding time to ensure that the coating material is sintered densely on the substrate and obtains good high-temperature resistance. For example, when preparing thick film ceramic coatings, strict sintering processes are often required, which rely on high-performance sintering equipment.
Process parameters:
Temperature control: During the coating preparation process, both the flame flow temperature during spraying and the heating temperature during sintering must be precisely controlled. Excessive temperature may lead to coating material burning and structural deterioration; If the temperature is too low, it may cause the coating to bond poorly and have poor density. For example, when thermal spraying ceramic coatings, different ceramic materials have their suitable spraying temperature range, and once exceeded, it will affect the quality of the coating.
Thickness control: The coating thickness should be uniform and meet the design requirements. Overly thick coatings are prone to peeling, cracking, and other phenomena at high temperatures due to internal stress accumulation, while overly thin coatings may not achieve the expected protective effects such as high temperature resistance and wear resistance. For example, the thickness of high-temperature resistant coatings for some high-temperature pipelines needs to be controlled within a reasonable range of millimeters, achieved through precise spraying or coating processes.
4、 Quality inspection hardware facilities
Microstructure detection equipment: such as scanning electron microscope (SEM), can be used to observe the microstructure of the coating, examine the internal porosity, particle distribution, interface bonding and other microstructural characteristics of the coating, in order to determine whether the coating quality meets the high temperature resistance requirements. For example, SEM observation can clearly see whether there are defects such as cracks in the coating that affect its high temperature performance.
Composition analysis instruments, such as energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), etc., can analyze the elemental composition and phase structure of coatings to ensure accurate composition of coating materials. Deviations in composition may cause significant changes in the high-temperature resistance of coatings. For example, XRD can be used to analyze whether the proportion of various crystal phases in ceramic coatings is normal, in order to ensure their stability at high temperatures.
Performance testing equipment:
High temperature hardness testing equipment: It can detect the hardness changes of coatings at high temperatures. The degree of hardness retention indirectly reflects the deformation resistance and wear resistance of coatings at high temperatures. It is important for coating components that need to withstand friction, compression, and other working conditions at high temperatures.
Thermal cycle testing equipment: By simulating the actual temperature alternating cycle process, the integrity and performance stability of the coating under repeated thermal expansion and contraction are tested to see if there will be failure phenomena such as peeling and cracking, in order to evaluate whether the coating can adapt to long-term high-temperature use environment.

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High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.