Influence of Dissipated Energy on the Bonding Strength of Cold-Sprayed Titanium Coatings on Selected Metallic Substrates.

Modern nanoindentation equipment allows for highly precise measurements of mechanical properties such as hardness and elastic modulus, generating detailed load-unload curves using advanced techniques and specialised software. In this study, titanium coatings were deposited on various metallic substrates using cold gas spraying. Before deposition, the spraying parameters (temperature, pressure, velocity, and distance) were statistically optimised using the Taguchi method, reducing the number of experiments required from 81 to 9. This approach allowed the identification of optimal spray conditions (T = 731.0 °C, p = 33.0 bar, V = 343.6 mm/s, d = 35.5 mm), which were then applied to substrates including brass, steel, titanium, Al7075, copper, magnesium, and Al2024. Mechanical characterisation included hardness (H), reduced modulus (E), coating adhesion, and dissipated energy, calculated from the area of the load-unload hysteresis loop. Each coating-substrate combination underwent 36 nanoindentation tests, and adhesion was evaluated by pull-off tests. The initial results showed a poor correlation between adhesion and conventional mechanical properties (χ of 17.1 for hardness and 16.2 for modulus, both with R < 0.24). In contrast, the dissipated energy showed an excellent correlation with adhesion (χ = 0.52, R = 0.92), suggesting that dynamic deformation mechanisms better describe bonding. This introduces a new perspective to predict and optimise cold-spray adhesion in industrial applications.