Nanoindentation hardness and atomic force microscope imaging studies of pressure-quenched zirconium metal

We have carried out mechanical property measurements on zirconium metal compressed in a diamond anvil cell to 19 GPa at room temperature with subsequent quenching to room pressure. The irreversible transformation from the ambient hexagonal-close-packed phase to the simple hexagonal ω phase (AlB₂ structure) is confirmed by synchrotron energy dispersive x-ray diffraction followed by nanoindentation of the pressure-quenched sample. We document an 80% increase in hardness as a consequence of the pressure-induced transformation to the ω phase at room temperature. This is a large increase for a metallic phase transformation and can be attributed to the presence of sp²-hybrid bonds forming graphite-like nets in the (0001) plane of the AlB₂ structure. Atomic force microscopy of the indents shows that a plastic deformation of 2 μm in depth was achieved with a force of 200 mN. © 2000 American Institute of Physics.