Rolling contact fatigue deformation mechanisms of nickel-rich nickel-titanium-hafnium alloys

Abstract The deformation mechanisms that dictate the tribological performances of heat treated Ni55Ti45, Ni54Ti45Hf1 and Ni56Ti36Hf8 alloys are revealed through rolling contact fatigue (RCF) testing transmission electron microscopy (TEM) analyses. Analysis worn samples passed a 5×108 cycle RCF runout condition shows damage is primarily confined to bands propagate several hundred nanometers – microns beneath surface. These nucleate via localization dislocation slip within B2 austenite phase alloys. For Ni55Ti45 samples, further eventual spall failures occur by shearing dissolution strengthening Ni4Ti3 nanoprecipitates bands, followed nanocrystallization sometimes includes stress-induced nucleation B19? nanocrystals. Eventually, complete amorphization occurs prior fracture. relative 15 25% increase in stress performance alloy correlates with more limited depth damaged material wear surface; heavily failure sites only extends 1.5 µm into sample, compared > 6 for This superior resistance results from lower fraction matrix (? 13 %) highly both cubic Ni-rich NiTiHf H-phase nanoprecipitates. Specifically, this microstructure limits widths less than size nanoprecipitates, which turn inhibits precipitate processes precede amorphization.