Insights into structural changes during scratch deformation of ductile coating systems: Plastic flow, microstructural transformations, and crack development

This study investigates the structural changes occurring during the scratch deformation of ductile materials, focusing on a composite aluminum (Al) coating on a steel substrate fabricated using a solid-state aluminizing technique. By analyzing the results of the scratch test with transmission electron microscopy (TEM) and focused ion beam (FIB) techniques, the research provides a detailed examination of plastic flow, microstructural transformations, and crack development. Results demonstrate that strong adhesion at the interface and similar mechanical properties between steel and Al layers facilitate co-deformation, crucial for maintaining the integrity of the composite structure. The study features the formation of a rolling-like laminated structure and significant grain refinement in both the steel and Al components, driven by plastic deformation. Observed atomic-scale intermixing and the formation of an amorphous interlayer highlight extensive material interactions during deformation. The visualization of crack progression using FIB allows for an in-depth understanding of the fracture process. Subsurface cracks initiate within the thin Al interlayer and propagate toward the surface, evolving through the coalescence of nanopores into microvoids and larger cavities, ultimately leading to crack propagation. Secondary internal cracks may arise due to stress fields generated by the primary crack, contributing to a complex network of internal cracks.