50 keV B~+ ions was implanted to polycrvstalline with 50 keV B~+ to a dose o/ 3x 10~17 ions/cm~2 at room temperature.The specimens with and without B~+implantation were tested in micro-hardness and load or unload tensile fatigue under stress-controlled eondition. The surface layer structure was observed with IMA,SEM and TEM before and after implantation and/or fatigue.The B~+ implanted surface region consists of amorphous Ni-B phase,Ni_3B and Ni_4B_3 second phases,and damage structure.The corresponding measurements indicate that both surface micro-hardness and endurance limit of the specimens have increased after implantation.Compared with unimplanted specimens under the same fa- tigue condition,all implanted specimens show the smallest overall fatigue danage.The cyclic loading at room temperature can lead to migration of implanted B~+ out surface layer and reerystallization of amorphous Ni-B phase,Possible strengthening mechanisms.for these ex- perimental results were discussed.
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