Quantitative kinetic rules for plastic strain-induced α - ω phase transformation in Zr under high pressure

The systematic studies of various phenomena (strain-induced phase transformations (PTs), microstructure evolution, strength, and friction) in diamond-anvil cells are limited due to the unknown stress σ and plastic strain E^p tensor fields and PT kinetic equations. However, they could not be measured. We propose a deformational and kinetic model, a finite element method (FEM) approach, and combined FEM-experimental approaches to determine the spatial distributions of σ and E^p tensors in strongly plastically predeformed Zr, and kinetic equation for α-ω PT that are consistent with experimental data for the entire sample. Since the fields within the sample are highly heterogeneous, obtained data encompasses numerous complex 7D paths in the space defined by 3 components of E^p and 4 components of σ. Our advanced characterization shows that the governing kinetic equation depends on accumulated plastic strain (rather than time) and pressure, while remaining independent of E^p and deviatoric stress tensors. The experiments & FEM correspond well for all fields, including radial & azimuthal elastic strains averaged over the sample thickness, as well as the sample’s thickness profile. Our findings open new opportunities for advancing quantitative high-pressure/stress science, including mechanochemistry, synthesis of new nanostructured materials, geophysics, astrogeology, and tribology.