Analytical Investigation Of Microstructure And Mechanical Properties On AISI 316L Stainless Steel After USPed

Surface nanocrystallization (SNC), including of surface self-nanocrystallization (SSNC) and hybrid surface nanocrystallization (HSNC), is a newly developed technique to form a nano-structure surface layer in bulk material. This technique will promote the global properties of materials through modifying the microstructure and property of the surface layer. And it will also significantly optimize the traditional surface treatment processes. Meanwhile, this technique will provide ideal specimen to systematically study the relationship between technique, structure and properties in nanometer size.In this paper, the research work is to characterize and measure the nano-mechanics properties of nano-materials in nanometer-scale range. A widely used AISI 316L stainless steel was selected to achieve SNC by means of ultrasonic shot peening(USP). The microstructure and composition of the surface layer treated by USPed was examined through using X-ray diffraction(XRD) and transmission electron microscopy(TEM).Experimental results showed that a layer of nanocrystal grains on sizes about 10 nm formed on the surface layer. The chemical composition of the layer was (8.03 Cr, 4.32 Ni, 3.86 Cu, 83.79 Fe)(Wt%). That was mainly composed of a kind of oxide nanocrystal particle in the surface layer, namely NiFe2O4 . And it was different to the composition of the matrix. At the same time, there was a little of martensite particles in the nanocrystal layer. It indicated that there was a phase transformation in the course of the ultrasonic shot peening. Nano-mechanics properties were measured to the USPed and unUSPed samples,including of tensile test , microhardness test and stess-strain test. The fracture morphology of the samples after tensioned was measured by means of scanning electron microscope(SEM). The fracture morphology had been analyzed for both the USPed sample and unUSPed sample. The microhardness was measured by a microhardness instrument for two kinds of samples. As a result, the microhardness of the USPed sample was higher than that of the unUSPed.