Surface Modification of Low Energy Helium Ion Implanted Austenitic Stainless Steel by Tensile Stress

Mechanical properties of low energy He irradiated 304SS have been investigated by means of tensile test and nano-identation hardness tests. Specimen size is 2.8×5.4×0.1mm in gauge and 12.4mm in total length. Specimens are irradiated with 8 keV helium ions at R.T.. 573K and 873K up to the fluence of 3×10^<21> He/m^2. Tensile tests are performed on unirradiated and irradiated specimens at a strain rate of 3.33×10^<-3>/s. In every irradiation condition, one specimen is tested to failure and the other two specimens are strained plastically to 10% and 20%. Formation of blisters with a diameter of about 500 nm is observed on the surface of tensile-tested specimens after R.T. irradiation. Some exfoliation of the blisters is also observed. When the irradiation temperature increases, a large number of cracks with a size of about several μm are formed on the surface together with exfoliation during the tensile test. The yield stress of specimens irradiated at R.T. and 573 K increases about 10% in comparison with that of the unirradiated specimen. The result of nano-indentation tests indicate that hardness near the surface increases depending on the irradiation temperature