Fabrication and Characterization of Bulk Nanocrystalline Layer in Steel and Aluminum Alloys Formed by Shot Peening

The formation of bulk nanocrystalline (NC) layers in AISI 1075 pearlitic and martensitic steels and aluminum alloys 6061-T6 and 7075 using air blast shot peening was studied. The cross-sectional microstructure of the samples showed a gradual reduction of the grain size near the surface. The NC layers were characterized using optical and scanning electron microscopy and nanohardness measurements. 2D surface topography of the top surface was also carried out. The roughness of the peened surfaces depends on sample hardness. The hardened AISI 1075 martensitic steel had lower surface roughness value. NC layers of 5 to 15 μm thickness were observed in the steels whereas the aluminum alloys 6061 and 7075 yielded NC layers up to 20 to 25 μm thick. The measured nanohardness in the NC layers confirmed the higher hardness of the NC layer compared with the bulk material.