Abstract
A nanostructured surface layer (NSSL) was generated on a 316L stainless steel plate through surface nanocrystallization (SNC). The grains of the surface layer were refined to nanoscale after SNC treatment. Moreover, the microstructure and mechanical properties of NSSL were analyzed with a transmission electron microscope (TEM) and scanning electron microscope (SEM), through nanoindentation, and through reverse analysis of finite element method (FEM). TEM results showed that the grains in the NSSL measured 8 nm. In addition, these nanocrystalline grains took the form of random crystallographic orientation and were roughly equiaxed in shape. In situ SEM observations of the tensile process confirmed that the motions of the dislocations were determined from within the material and that the motions were blocked by the NSSL, thus improving overall yielding stress. Meanwhile, the nanohardness and the elastic modulus of the NSSL, as well as those of the matrix, were obtained with nanoindentation technology. The reverse analysis of FEM was conducted with MARC software, and the process of nanoindentation on the NSSL and the matrix was simulated. The plastic mechanical properties of NSSL can be derived from the simulation by comparing the results of the simulation and of actual nanoindentation.
Highlights
Nanocrystalline materials [1, 2] exhibit novel properties, unlike their coarse-grained polycrystalline counterparts
nanostructured surface layer (NSSL) was generated on a 316L stainless steel plate through Surface nanocrystallization (SNC) treatment
The microstructural and mechanical properties of the NSSL were analyzed through transmission electron microscope (TEM), scanning electron microscope (SEM), nanoindentation, and finite element method (FEM)
Summary
Nanocrystalline materials [1, 2] exhibit novel properties, unlike their coarse-grained polycrystalline counterparts. Most surface treatments can be used for SNC, including surface mechanical attrition treatment (SMAT) [4,5,6,7], high-energy shot peening [8], surface mechanical rolling treatment [9], and ultrasonic shot peening (USSP) [10,11,12]. Among these treatments, USSP is considered a promising process that can rapidly and effectively realize SNC.
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