Transition from micro-rod to nano-lamella eutectics and its hardening effect in niobium/silicide in-situ composites
(1. School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China;
2. Frontier Institute of Science and Technology Innovation, Beihang University, Beijing 100191, China;
3. Max-Planck-Institut für Eisenforschung, Max-Planck-Stra？e 1, Düsseldorf, 40237, Germany)
2. Frontier Institute of Science and Technology Innovation, Beihang University, Beijing 100191, China;
3. Max-Planck-Institut für Eisenforschung, Max-Planck-Stra？e 1, Düsseldorf, 40237, Germany)
Abstract: To improve the mechanical properties of niobium/silicide in-situ composites via rapid solidification, the evolution of eutectic geometry and the corresponding hardening effect in a prototype Nb-18Si (at.%) composite upon electron beam surface melting (EBSM), i.e., a rapid remelting and solidifying sequence, were studied. Results show that rod-like Nb solid solution (Nbss)/Nb3Si eutectics prevail in the arc-melted state, yet evolve into lamellar arrangements after EBSM. Atomic scale scanning transmission electron microscopy (STEM) and near-atomic scale atom probe tomography (APT) were employed to characterize the three-dimensional stacking of nano-laminated Nbss/Nb3Si eutectics and their compositions. Compared with the rod-like eutectics, the lamellar eutectics via EBSM demonstrate a prominent eutectic refinement (39.5 nm in spacing) and an increased volume fraction of Nbss (~41%). Nano-indentation testing reveals that with the microstructural transition from micro-rod to nano-lamella eutectics, a significant increment in hardness up to 13.9 GPa is achieved.
Key words: niobium/silicide composites; rapid solidi？cation; eutectic morphology; lamellar eutectics; rod-like eutectics