The following are some factors that can affect the bonding strength between high-temperature resistant coatings and substrates:
1. Surface condition of the substrate
Roughness: Appropriate surface roughness helps to increase the mechanical interlocking effect between the coating and the substrate, and improve the bonding strength. For example, by using sandblasting and other processes to treat the surface of the substrate, a microscopic uneven structure can be formed. The coating can be embedded in these pits during the curing process. For example, after sandblasting on a metal substrate, a high-temperature resistant coating can be applied, which will make the bonding more firm. But if the roughness is too large, it may cause the coating to be difficult to cover evenly, resulting in local weak points, which in turn affects the bonding strength; However, if the surface is too smooth, the mechanical interlocking effect will be insufficient, and the bonding force will also be poor.
Cleanliness: If there are impurities such as oil stains, dust, rust, etc. on the surface of the substrate, they will form an isolation layer between the coating and the substrate, hindering the direct contact and chemical bonding between the coating and the substrate, and reducing the bonding strength. For example, before coating on a steel substrate, if the surface oil stains are not thoroughly removed, the coating is easily peeled off from the substrate after curing.
Oxidation layer situation: Some substrate materials will naturally form an oxidation layer on their surface, and some oxidation layers have a loose structure, which is not conducive to coating adhesion. For example, the natural oxidation layer on the surface of aluminum alloy is thin but relatively loose. If not properly treated, it will cause the coating to bond loosely with it; And some oxide layers can become intermediate transition layers that are conducive to bonding after treatment, enhancing the connection between the coating and the substrate.
2. Characteristics of the coating itself
Composition and structure: The chemical composition of the coating determines the type and degree of chemical bonding that may occur between it and the substrate. For example, certain coatings containing elements such as silicon and titanium can form chemical bonds through chemical reactions when in contact with a metal substrate, enhancing the bonding strength; If the molecular structure of the coating has more active functional groups, it is also conducive to interacting with the substrate and improving the bonding strength.
Flexibility: Coatings with good flexibility can better deform with the substrate when subjected to temperature changes, external forces, etc., reducing the risk of coating detachment from the substrate due to stress concentration and maintaining a good bonding state. For example, some organic modified ceramic coatings combine the high temperature resistance of ceramics with the flexibility of organic materials, and have relatively high bonding strength with the substrate.
3. Differences in thermal expansion coefficients
If the thermal expansion coefficients of the coating and the substrate material differ too much, the degree of expansion and contraction of the two will be inconsistent during temperature changes, resulting in significant thermal stress. When the thermal stress exceeds the bonding force between the coating and the substrate, it is easy for the coating to peel off or crack from the substrate, seriously affecting the bonding strength. For example, when ceramic coatings are combined with metal substrates, special transition layers and other measures are often required to alleviate thermal stress and ensure bonding strength due to significant differences in thermal expansion coefficients.
4. Pre treatment process
Surface activation treatment: Chemical plating, ion implantation, plasma treatment and other methods are used to activate the surface of the substrate, which can increase the active sites on the surface, promote the chemical reaction between the coating and the substrate, and enhance the bonding strength. For example, by depositing a thin metal film on the surface of a metal substrate through chemical plating, the subsequent coating can be more tightly bonded to it.
Pre coating primer treatment: Using primer, transition layer, etc. as a primer can improve the compatibility between the coating and the substrate, adjust the difference in thermal expansion coefficient between the two, play a bridging role, and enhance the overall bonding strength. For example, when coating a high-temperature resistant coating on a ceramic substrate, first applying an intermediate transition layer that has good affinity with both the ceramic and the coating can effectively improve the bonding effect between the final coating and the substrate.
5. Coating process
Coating method: Different coating methods such as spray coating, brush coating, dip coating, etc. have an impact on the bonding strength between the coating and the substrate. During spraying, the speed and angle at which coating particles collide with the substrate surface can affect their adhesion effect; The uniformity and intensity of brushing also affect the adhesion between the coating and the substrate; The viscosity and immersion time of the coating solution during the immersion process also affect the bonding strength.
Coating thickness: Unreasonable coating thickness can affect the bonding strength. If the coating is too thick, internal stress is prone to accumulate, which may cause the coating to separate from the substrate due to stress release during use; If the coating is too thin, it may not form a complete and effective coverage, and the bonding strength is also difficult to guarantee.
6. Curing process
Curing temperature: An appropriate curing temperature can fully crosslink and cure the coating, forming a stable structure and establishing a good bond with the substrate. Low temperature, incomplete coating curing, insufficient strength, and poor adhesion; If the temperature is too high, it may cause thermal stress and even cracking in the coating, which can damage the bonding state.
Curing time: If the curing time is too short, the coating cannot fully exert its properties and the bonding with the substrate is not strong enough; However, excessive curing time may also have adverse effects on the coating structure and bonding strength in some cases.

Room termperature curing polysilazane, pls check IOTA 9150, IOTA 9150K.       
High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.