Yttrium-doped nanocrystalline Ni₄Mo: Ultrahigh strength and high ductility combined with useful intermetallic properties

We show that bulk nanocrystalline Ni₄Mo can be synthesized by doping with small but critical concentrations of Y. Two alloys are included in the study with compositions of Ni₄Mo and Ni₄Mo + 0.01 wt% Y. Microstructural features derived from transmission electron microscopy observations are correlated with room-temperature tensile properties. Yttrium-doped Ni₄Mo is found to have room-temperature yield strength in excess of 800 MPa and tensile elongation to failure of about 40% while simultaneously retaining other useful physical and chemical properties of intermetallic compounds. Twinning rather than slip is found to be the predominant deformation mechanism, which is correlated with the superlattice structure of Ni₄Mo. Since deformation by twinning is polarized, this is expected to enhance the fatigue life.