Effect of porosity on surface deformation and subsurface layer produced by scratch tests of sintered low-alloy steel

This study explores the effect of porosity on surface deformation and subsurface hardening in sintered Fe-Mo-C steel. Samples were sintered at temperatures of 850°C (high porosity) and 1000°C (low porosity) using spark plasma sintering (SPS). Scratch tests were conducted at normal loads of 5 N and 10 N, and surface profiles were analyzed using profilometry, while scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) provided insights into microstructural changes and deformation mechanisms at the subsurface. Results indicated that low-porosity samples exhibited less material removal and a shallower tribologically transformed layer, with higher plastic deformation, dislocation density, and stronger pile-up formation at the edges of the scratch. In contrast, high-porosity samples displayed more extensive material removal, thicker transformed layers, and heterogeneous deformation, with pores acting as stress concentrators that facilitated crack initiation and propagation. The friction coefficient increased with load, particularly for low-porosity samples, due to a higher accumulation of material resisting the indenter’s movement. These findings highlight the significant role of porosity in governing the tribological performance and mechanical behavior of sintered steels, providing valuable insights for both mechanical and biomedical engineering applications.