Abstract
High‐performance adhesive bonds require clean, microscopically rough adherend surfaces that are compatible with the adhesive or primer. Such surface allow wetting by the polymer and a complete filling of the pores of ‘nooks and crannies’. The resulting mechanical bonds supplement or supplant the chemical bonds present. For durability in aggressive environments, aluminum bonds that are exposed to high humidity also require hydration‐resistant oxide surfaces. Such hydration resistance is inherent in some surfaces, e.g. phosphoric acid‐anodized surfaces, and can be high temperatures, such bonds require oxide‐free surfaces when exposed to temperatures above 300°C. These surfaces can be formed by plasma spraying a metallic powder coating onto the titanium alloy. Although preparation of high‐quality surfaces and bonds is achieved readily in the laboratory, occasional failures are observed in the manufacturing environment owing to, for example, contamination, pH or temperature variations. These processing problems can prevent wetting of the surface or can destroy the microrough morphology. A basic understanding of the mechanisms involved in the production of appropriate surfaces and their resulting adhesive bonds and in their degradation is critical to the evaluation of the failures and their remedy.