Influence of coating thickness on the impact damage mode in Fe-based amorphous coatings

Abstract The impact behavior of Fe-based amorphous coatings with various thicknesses fabricated by high-velocity-air-fuel thermal spraying was systematically investigated via 3D X-ray tomography. The results showed that the impact damage occurred principally by cracking in the coating, plastic deformation in the substrate, and delamination at the coating/substrate interface. It was found that the size of the interfacial delamination was a nonlinear function of the normalized coating thickness tc/a (i.e. the ratio of coating thickness (tc) to the contact radius (a)). Three thickness regions of distinctive damage modes were identified: thin coating region (tc/a ≤ 0.33), intermediate-thickness region (0.33   0.54). For tc/a ≤ 0.33, no delamination appeared in the coating/substrate interface. With an increase from tc/a = 0.33 to tc/a = 0.54, the extent of interfacial delamination increased quickly and reached a maximum. Finally, when tc/a > 0.54, the extent of delamination decreased when tc/a increased. In addition, it was indicated that the residual stress was found to decrease with the coating thickness, reflecting that the residual stress was excluded as a predominant factor of impact damage. Furthermore, a good agreement with the Hertz impact theory and finite element modeling was identified in the case of interfacial damage: significant delamination was observed in the 600 μm coating when the maximum shear stress occurred close to the coating/substrate interface. This finding can be used to assist the design of coated components in load-bearing applications.