Low-Cycle Fatigue Behavior of Polycrystalline NiAl at Room Temperature

Abstract

The room temperature cyclic deformation of a cast and extruded NiAl alloy has been investigated. Low-cycle fatigue tests were performed under plastic strain control at strain ranges from 0.0002 to 0.0016. Cyclic hardening behavior has been analyzed and compared to the monotonic tensile and compressive behavior of the same material. Electroless nickel films applied to NiAl samples have little effect on monotonic deformation behavior, but do have a significant effect on cyclic deformation behavior, particularly cyclic stress asymmetry. Fractographic analysis has suggested that cycling at low plastic strain ranges may promote stable microcracking, while step testing indicates that cycling at lower plastic strain ranges can improve the cyclic life and/or stress levels achieved at the higher plastic strain ranges. Low plastic strain range cyclic prestrain can also significantly increase the monotonic tensile yield and ultimate strength of the material while most of the tensile ductility is retained.