Formation of face-centered-cubic zirconium by mechanical attrition

This study reports a hcp-->fcc polymorphic transformation in elemental zirconium induced by mechanical attrition in a planetary ball mill. The transformation is monitored and verified by x-ray and electron diffraction and high-resolution transmission electron microscopy. Grain size decreases and lattice parameter increases with continued milling. The phase change is gradual and is accompanied by about 9% increase in volume per atom. It is suggested that structural instability due to plastic strain, increasing lattice expansion, and negative (from core to boundary) hydrostatic pressure is responsible for this hcp-->fcc polymorphic transformation in zirconium. (C) 2002 American Institute of Physics.