In this paper, pure polycrystalline nickel with and without nitrgen (carbon) ion implantation has been fatigued. Surface layer microstructure of specimens with and without ion implantation, before and after fatigue, has been examined with AES, SEM and TEM. The reason why ion implantation influences fatigue life has been discussed. The experiment results show that the endurance limit of pure nickel with N~+ (C~+) implantation increases by 21% (25%). Compared with that of unimplanted specimens, the number of surface grains, in which slip bands could be found, decreases, slip bands become finer and specimen surface is still smooth after the implanted specimens were fatigued. Slip band cracking which is found in the unimplanted specimens is replaced by grain boundary cracking in N~+ implantation specimens, the two modes of crack initiation could be found in C~+ implantation specimens. It has been found that nickel surface layer is amorphized by carbon ion implantation, amorphous layer is crystallized in course of fatigue. Based on the analysis of experiment results, it is considered that the improvement in fatigue life by nitrogen ion implantation is attributed to the surface compressive stress, solid solution strengthen and lowering stacking fault energy; the increase of fatigue life of carbon-implanted specimens is because of forms of amorphous layer and fine grains.
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