Polymer Microsphere-Enabled Composite Coating: Elastic Energy Storage–Release under Deep-Sea Alternating Loading

To address the failure of hard–soft interfaces in conventional inorganic–organic protective coatings under deep-sea alternating loading, a polymer microsphere-based composite coating was fabricated by a one-step process. The coating showed strong adhesion to the substrate (about 26.49 MPa). Based on the falling-ball impact process, a method was proposed to evaluate the elastic response of coating materials, from which the first flight time (FFT) was obtained and the elastic energy coefficient (EEC) was calculated. For a composite coating with a thickness of 80 μm and a microsphere content of 20 vol%, the FFT reached 418 ms, which was 138% of that of a pure PU coating. The elastic energy coefficient (EEC) reached 2.53. An elastic energy storage–release model was proposed to clarify the interfacial enhancement mechanism between microsphere-enabled energy storage and matrix-mediated energy release. After alternating loading from 0–20 MPa, the coating showed an EEC of 2.41, which was 6 times higher than that of an inorganic microsphere coating. The adhesion strength remained above 17 MPa. The coating also maintained stable elastic performance under marine engineering conditions (ultraviolet radiation, artificial seawater). This work provides a new perspective for the design of protective coatings for deep-sea alternating loading.