Study of the Effect of Surface Nanocrystalline Material on the Fracture Mechanism(Mechanical Behavior of Materials 1)

Surface Nanocrystallization by Surface Mechanical Attrition Treatment

“…Various surface plastic deformation processes have been developed to achieve a nanostructured surface layer in bulk coarse-grained materials [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Now we generally referred the techniques that achieve surface severe plastic deformation via mechanical attrition as to surface mechanical attrition treatment (SMAT) [11][12][13][14][15][16][17][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. These processes are based on surface dynamic plastic deformation induced by repeated impacts with high-velocity balls.…”

“…The research results on microstructures and properties of the surface layer treated by I-type SMAT can be found in [15-17, 29, 33-39]. When the vibrating chamber is driven by an ultrasonic generator, the SMAT process is named as II-type SMAT, for example ultrasonic shot peening (USSP) [12,14,[30][31][32][40][41][42][43][44][45]. For these processes, different devices were used to accelerate impacted balls and a wide range of kinetic energies was generated, which can induce different levels of surface plastic deformation on metallic materials.…”

“…5.1 Hardness and tensile strength. Mechanical property measurements of the SMAT samples showed a significant increment in hardness and tensile strength for the surface layer with nanostructures [36][37][38][42][43][44][45]. Figure 10 shows a variation of hardness along the depth from the treated surface as obtained from nanoindentation tests in the SMAT Fe sample [36].…”

“…The reason may be that the strain-induced nanostructured layer enhances the strength and rigidity of the surface so that the initiation and propagation of cracks and defects are prevented. In addition, the top surface layer with high rigidity and strength could block the movement of the dislocations out of the material surface during plastic deformation, which inhibits the formation of slip bands on materials surface [43].…”

Mechanical Properties of Metallic Materials Processed by Surface Severe Plastic Deformation

“…The nanostructured layer is able to impede dislocation movement and avoid the formation of surface slip bands, as highlighted by Altenberger et al 229) For a SMATed structure under tensile loading, Xing et al 230) revealed that the movement of dislocations in the transition zone, as presented in Section 2.1, is arrested by the nanostructured layer. This dislocation arrest prevents the formation of slip bands at the structure's surface due to the fact that the dislocation activities in the nanostructured layer are strongly restricted.…”