Rules for crystallite size and dislocation density evolution in phases during pressure and plastic strain-induced α-ω transformation in Zr

The first in-situ XRD studies of the crystallite size and dislocation density evolution in phases during α-ω phase transformation (PT) in Zr under hydrostatic loading and plastic flow are performed. Rough diamond anvils (rough-DA) are introduced to intensify all occurring processes during plastic compression of Zr in a diamond anvil cell (DAC). The main rule is found that during α-ω PT, the crystallite size and dislocation density in ω-Zr depend solely on the volume fraction of ω-Zr and are independent of pressure, plastic strain tensor, its path, and initial nanostructure. Crystallite size in ω-Zr increases from 10 to 60 nm during the PT. Rough-DA produce a steady nanostructure in α-Zr before PT with smaller crystallite size and larger dislocation density than smooth-DA, leading to a reduction of the minimum PT pressure to a record value of 0.67 GPa, 9 times smaller than under hydrostatic loading. Under hydrostatic loading, the microstructure significantly varies before, during, and after PT, differently during loading and unloading. During the PT, microstructural parameters in ω-Zr are functions of the volume fraction of ω Zr only, independent of the plastic straining before transformation and pressure. The results may bring up economic strategies for producing nanocomposites and single-phase nanostructured materials with optimal properties.