Effect of Phosphorus Ion Implantation on the Fatigue Behaviour of Polycrystalline Nickel

Abstract

Polycrystalline nickel is implanted with 150 keV phosphorus ions to a dose of 5 × 1016 ions/cm2 at room temperature. The specimens with and without phosphorus implantation are tested in load‐unload tensile fatigue under stress‐controlled condition, and the implanted surface layer is investigated with AES, SEM, and TEM. It is found that the implanted surface region consists of an amorphous NiP phase and a Ni3P compound. Corresponding measurements of microhardness indicate that phosphorus implannation enhances the surface microhardness of nickel. A 19% increase in the endurance limit is found after phosphorus implantation. Compared with the unimplanted specimens under the same fatigue conditions, the number of surface grains in which slip bands could be found decreases, the slip bands become finer and homogeneous, and the surface is smooth. It is also found that the cyclic loading at room temperature can lead to migration of implanted phosphorus out of the surface layer and recrystallization of amorphous NiP phase. Possible strengthening mechanisms for these experimental results are discussed.

Fatigue of LIGA nickel

“…From these observations, crack initiation was associated with localized regions of deformation apparently produced by persistent slip bands (PSBs), as shown in Fig 3. Association between persistent slip bands and crack initiation in pure polycrystalline nickel has often been suggested (e.g. [5]), however, the apparent localization of the slip bands is unique and thought to be related to the strong texture [6] present in this electoplated alloy. There have been very few publications on the fatigue behavior of electroformed Nickel MEMS structures.…”