Nano-refinement of the face-centered cubic Zr(Fe,Cr)2 secondary phase particles in Zircaloy-4 alloy via localized-shearing/bending-driven fracture under high-temperature compression

Abstract

Nanoparticles are extensively introduced to improve the mechanical, physical, and chemical properties of alloys. In the present study, the underlying nano-refinement mechanisms of face-centered cubic Zr(Fe, Cr)2 secondary phase particles (SPPs) that precipitated in Zircaloy-4 alloy under high-temperature compression were investigated in detail by utilizing high-resolution transmission electron microscopy (HRTEM) and conventional TEM techniques. The frequently observed Zr(Fe, Cr)2 SPPs were incoherent with the matrix and exhibited brittle fracture behaviors without measurable plasticity. HRTEM observations revealed two mechanisms underlying the nano-refinement of incoherent micro-sized SPPs via localized shear fracture on {112¯}SPP and nanoprecipitate-assisted bending fracture, respectively. The latter was, for the first time, found to occur when the movements of large SPPs were blocked by nanometer-sized SPP during alloy deformation. Accordingly, two force models were proposed to visualize their potential nano-refinement processes. The knowledge attained from this study sheds new light on the deformation behaviors of Zr(Fe, Cr)2 SPPs and their associated size refinement mechanisms under high-temperature compression, and is expected to greatly benefit the process optimization of zirconium alloys to achieve precipitate nano-refinement.