Surface and Cross-Sectional Micro-scratch Characterization of Cold-Sprayed SS316L Coatings

Abstract

This study presents a scratch test-based framework for evaluating interfacial adhesion, inter-splat cohesion, and fracture toughness of cold-sprayed SS316L coatings on SS304 substrates, representing the first such application for this coating system. To systematically investigate the influence of process parameters on microstructure and mechanical performance, coatings were deposited at four traverse speeds (20, 100, 250, and 400 mm/s). Among these, the coating produced at 250 mm/s demonstrated the lowest porosity (0.14%) compared to porosities of 0.2, 2.04, and 2.04% at 20, 100, and 400 mm/s, respectively. Notably, this coating also achieved the highest fracture toughness (28 ± 4 MPa-m^0.5, as determined by Zhang’s model), closely approaching the bulk SS316L value (34 MPa-m^0.5). Superior inter-splat cohesion was evidenced by the smallest projected cone area (0.12 mm²) at the scratch indenter tip, with no splat debonding or cracks observed under progressive loading. Furthermore, exceptional interfacial adhesion was demonstrated, as coatings deposited at 250 and 400 mm/s exhibited no interface failure even at maximum applied loads (50 N). These findings establish scratch testing as a reliable quantitative tool for assessing fracture toughness in cold-sprayed coatings. Additionally, an intermediate traverse speed is identified as optimal for achieving the best combination of fracture toughness, inter-splat cohesion, and interfacial adhesion.