Interactions of lattice distortion fields in nano polycrystalline materials revealed by molecular dynamics and X-ray powder diffraction

Abstract

Interacting distortion fields from local and diffuse structural defects in metal nanomaterials were investigated via atomistic simulations supported by X-ray powder diffraction (XRPD) analysis. Numerical models of several large nano polycrystalline Pd microstructures embedding a wide range of defect types and densities were equilibrated via molecular dynamics (MD) to evaluate the interaction effects of various structural defects on the deformation-field components. Microstrain contributions from crystallite grain boundaries (GBs), line dislocations, and vacancies were determined from analysis of line broadening in Debye-simulated XRPD profiles. Dynamic disorder was investigated across the crystallites, revealing anisotropic vibrational components of atoms at the GBs. Although the estimated structural and microstructural properties agreed globally with the ideally expected parameters directly calculated from numerical models, widely dispersed values were observed among the assemblage of crystallites. Estimated dynamic and static Debye-Waller parameters used to account, respectively, for atomic thermal vibration and disorder across the GBs were in excellent agreement with experimental values observed by Inagaki et al. (J. Mater. Sci, 18 (1983) 1803) for Pd metal powders. However, the static component decreased with environmental temperature and increasing interaction between defects in different crystallites, approaching zero in the limit.