Transition of nc-SiC powder surface into grain boundaries during sintering by molecular dynamics simulation and neutron powder diffraction

Abstract

Abstract. We report a structural analysis of experimental nc-SiC ceramics with grain sizes ranging from 7 nm to 11 nm in diameter and computer generated samples of similar grain sizes. Pair Distribution Functions (PDFs) of real and virtual samples sintered under different pressures are compared. The standard size-strain methods are applied to the simulated mod-els and the results are discussed. Presented model is the first step toward atomistic under-standing of the processing-structure relations and atomic-level interpretation of diffraction patterns for nanoceramics. Introduction Silicon Carbide (SiC) based ceramics have many technological applications, which originate from their remarkable physical and chemical properties, e.g. high hardness, high melting temperature, light weight, and chemical stability. It is known that decreasing the grain size of polycrystalline ceramics to the nanometre regime can further improve their mechanical prop-erties [1-3]. For example, recent experiments on nanocrystalline (nc) SiC have demonstrated an increased hardness of this material [4]. Atomistic mechanisms underlying this so-called superhardness of nc-SiC have been revealed in recent computer simulations [5]. Despite of all the promising properties of nc-SiC, a detailed understanding of the processing – structure – property relations in this material is still lacking. X-ray and neutron diffractions are powerful and commonly used techniques for microstruc-ture characterization; however, analysis of diffraction patterns of nc materials presents addi-tional challenges. Due to an increased surface-to-volume ratio of nanoparticles, grain boundaries (GB) occupy a significant volume-fraction of the material and the coherently