Indentation size effects in hardness of annealed NiB coatings

Nix–Gao’s factor (81/2) was replaced with (4.5C_t²) using variable constraint factor (C_t) for size-dependent analysis of crystalline coatings. Experimental investigations on annealed NiB coating (5 wt% boron) aimed at defense applications involved twelve Berkovich nanoindentation tests (displacements: 500, 1000, and 1500 nm; strain rates: 0.05, 0.1, 0.15, and 0.20 s⁻¹). SEM and XRD analyzed cauliflower-type surface morphology and crystallinity. NiB coatings exhibited Intrinsic hardness (H₀) of 9.65 ± 0.26 GPa, material characteristic length (h^*) of 194.8 ± 10 nm, and elastic modulus (E) of 264 ± 10 GPa. Indentation size effects of these coatings attributed to increased geometrically necessary dislocation density.