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

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

摘要。我们对粒径在直径7纳米到11纳米范围内的实验性纳米碳化硅陶瓷以及类似粒径的计算机生成样本进行了结构分析。对在不同压力下烧结的实际样本和虚拟样本的对分布函数（PDFs）进行了比较。将标准的尺寸 - 应变方法应用于模拟模型，并对结果进行了讨论。所提出的模型是朝着从原子层面理解纳米陶瓷的加工 - 结构关系以及对衍射图案进行原子级解释迈出的第一步。 引言 碳化硅（SiC）基陶瓷有许多技术应用，这源于它们显著的物理和化学性质，例如高硬度、高熔点、重量轻以及化学稳定性。众所周知，将多晶陶瓷的晶粒尺寸减小到纳米范围可以进一步改善它们的机械性能[1 - 3]。例如，最近对纳米晶（nc）SiC的实验表明这种材料的硬度有所增加[4]。在最近的计算机模拟中已经揭示了纳米碳化硅这种所谓超硬现象背后的原子机制[5]。尽管纳米碳化硅具有所有这些有前景的性质，但对这种材料的加工 - 结构 - 性能关系仍缺乏详细的了解。 X射线和中子衍射是用于微观结构表征的强大且常用的技术；然而，对纳米材料衍射图案的分析带来了额外的挑战。由于纳米颗粒的表面积与体积之比增加，晶界（GB）占据了材料相当大的体积分数，并且相干地……