Study Of The Mechanical Properties Of Surface Nanostructure By Nanoindentation

In engineering, most of failures of material begin from surface, so it is important to explore new surface-strengthening technologies in order to improve their durability. Surface nano-crystallization(SNC) has been regarded as one of the most prosperous surface technologies. SNC is a newly developed technique to form a nano-structured surface layer in bulk material. This technique will promote the global properties of materials through modifying the micro-structure and the property of the surface layer.This research studies the micro-structure, nano-hardness, and modulus, hardening index of 316L stainless steel after SNC treatment. The SNC treatment in 316L stainless steel can form nanostructure surface layers about 10μm thick. The microstructured of the surface layer of sample was characterized by means of X-ray diffraction. Experiment evidence shows that the microstructure of the surface layer of the sample was refined into nanoscale after SNC treatment. The grain sizes are about a few nanometers at the top surface layer, and gradually increase with the depth. Variations of the nanohardness and the modulus of 316L stainless steel after SNC with the distance to surface are studied by nanoindentation. The experimental shows that the nanohardness and the modulus decrease with increase of the distance to surface, then trend to a stabile value. And the hardening index of 316L stainless steel also decreases with increase of the distance to surface, then trend to the hardening index of matrix. Then this process of nanoindentation has been numerically simulated using the finite element software (MSC. Marc). The distribution of the deformation, the stress and strain, and the Mises equivalent stress for the nanostructur layer and the matrix were obtained under the same load.