What is the definition of delamination in the context of coating failure?

Delamination in the context of coating failure specifically refers to the separation of layers within a coating system. This common issue often arises when there is surface contamination present before the application of the coating, such as oil, dust, or moisture, which prevents a proper bond between the layers. When subsequent layers are applied, they are unable to adhere correctly due to the contaminants, leading to the peeling away or separation that characterizes delamination.

By contrast, while temperature fluctuations, mechanical stress, and chemical exposure can certainly lead to other forms of coating failure, they do not specifically describe delamination. Temperature variations can cause coatings to expand and contract, potentially leading to cracks or other failures, but not specifically layer separation. Mechanical stress may also cause coatings to crack or break but is not tied directly to the failure of layers bonded to each other. Similarly, chemical exposure can degrade coatings or cause them to blister, but it does not directly correlate to the separation of layers as seen in delamination. Therefore, the definition clearly aligns with the scenario outlined in the correct answer.