Here are some testing methods that can be used to evaluate the bonding strength of antioxidant coatings:
Tensile testing method
Principle: By applying axial tensile force to the coated sample, the coating is separated from the substrate, and the maximum tensile force required for the coating to peel off from the substrate is measured to characterize the bonding strength between the coating and the substrate. For example, fix one end of the sample on the fixture of the tensile testing machine and the other end as well, then apply a uniform tensile force until the coating peels off, and record the corresponding maximum tensile force value.
Scope of application: Suitable for evaluating the bonding strength between various substrate materials (such as metals, ceramics, etc.) and different types of antioxidant coatings, especially for situations where the coating is firmly bonded to the substrate and expected to withstand certain tensile forces. However, for some coatings that are already thin and brittle, accurate measurements may be affected during the stretching process due to the coating breaking first.
Shear test method
Principle: Apply shear force to the interface between the coating and the substrate, causing the coating to detach from the substrate. Measure the corresponding shear failure load to determine the bonding strength. A common method is the planar butt shear test, which involves preparing a coated specimen into a butt joint and applying a shear force parallel to the interface at the joint surface; There is also a pin plate shear test, which uses a pin to pass through the coating and substrate, rotates the pin to separate the coating under shear action, and calculates the bonding strength value.
Scope of application: Widely used to evaluate the bonding performance between coatings and substrates under shear stress, it is very helpful for detecting the bonding strength of coatings under working conditions such as torsion and sliding friction. For example, this method can be used to detect surface coatings of some mechanical components when they face shear stress during operation.
scratch test 
Principle: Use a needle with high hardness to scratch the surface of the coating, while gradually increasing the load, and observe the critical load value when the coating experiences damage such as peeling and flaking. This critical load can to some extent reflect the bonding strength between the coating and the substrate. Generally speaking, the higher the critical load, the better the bonding strength. In practical operation, the scratching needle is usually installed on the scratch tester, which can accurately control parameters such as the movement speed and loading rate of the scratching needle.
Scope of application: This method is relatively easy to operate and suitable for various substrates and coating systems, especially for the rapid evaluation of the bonding strength of thin film antioxidant coatings. However, its results are a combination of qualitative and quantitative judgments, and more comparative analysis, with slightly lower accuracy compared to some direct tensile and shear tests.
Bending test method
Principle: Bend the coated sample to subject the bonding interface between the coating and the substrate to tensile and compressive stresses. Observe whether the coating peels off, cracks, and other phenomena occur during the bending process. Additionally, equipment with strain measurement devices can be used to further analyze the changes in the bonding state of the coating under different degrees of bending, in order to infer the bonding strength. For example, conducting three-point bending or four point bending tests on thin coated specimens.
Scope of application: It is commonly used to test the bonding strength between the coating and the substrate on samples with regular shapes and easy bending operations. For example, when some metal sheets are coated with anti-oxidation coatings, this method can be used to evaluate their bonding strength under possible bending deformation conditions.
Thermal shock test method
Principle: The coated sample is rapidly cycled between high and low temperature environments, utilizing the difference in thermal expansion coefficient between the coating and the substrate to generate stress during repeated thermal expansion and contraction processes. The adhesion strength is indirectly evaluated by observing whether the coating has peeled off, cracked, or other damage, as well as the integrity of the coating after a certain number of cycles. For example, first place the sample in a high-temperature furnace and heat it to a certain temperature for a certain period of time, then quickly remove it and place it in a low-temperature environment (such as liquid nitrogen) for cooling, and repeat this process multiple times.
Scope of application: Mainly used to test the bonding strength between coatings and substrates working in high-temperature alternating environments, such as surface anti-oxidation coatings on hot end components of aircraft engines and high-temperature furnace linings. These components will experience frequent temperature changes in actual use, and thermal shock tests can simulate this working condition well to examine the bonding strength.
Ultrasonic testing method
Principle: By utilizing the characteristics of reflection, refraction, and scattering of ultrasound at the interface between the coating and substrate, when ultrasound propagates to the interface, if the interface bonding is poor, significant acoustic signal changes will occur. By detecting these signal changes and using specialized ultrasound testing equipment and analysis software, the bonding status between the coating and substrate can be analyzed and judged, and the bonding strength can be qualitatively or quantitatively evaluated.
Scope of application: This method belongs to non-destructive testing and will not cause damage to the sample. It is suitable for testing coating components that have been installed on equipment or need to be sampled and tested in mass production. It can quickly screen for coatings that may have bonding problems. However, for accurate determination of bonding strength values, other methods need to be further determined.
Laser Induced Breakdown Spectroscopy (LIBS)
Principle: High energy density laser pulses are focused near the bonding interface between the coating and the substrate to generate plasma locally. By analyzing the spectral information emitted by the plasma, the distribution and changes of elements at the interface can be understood. When the coating and substrate are well bonded, the element distribution is relatively continuous and uniform, while when the bonding is poor, there may be abnormalities, which can be used to infer the bonding strength. At the same time, relevant algorithms can be used to quantitatively evaluate the bonding strength.
Scope of application: It can detect coatings and substrate systems of various materials, especially in analyzing the microstructure and element interactions at the interface between coatings and substrates. However, its equipment is relatively complex, and the operation and data analysis requirements are high. It is commonly used in professional research or quality inspection scenarios that require high coating bonding quality and in-depth analysis of interface conditions.

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