Clayton J D, Guziewski M, Ligda J P, Leavy R B, Knap J
DEVCOM Army Research Laboratory, Aberdeen Proving Ground, Adelphi, MD 21005, USA.
Materials (Basel). 2021 Mar 14;14(6):1408. doi: 10.3390/ma14061408.
Diamond-silicon carbide (SiC) polycrystalline composite blends are studied using a computational approach combining molecular dynamics (MD) simulations for obtaining grain boundary (GB) fracture properties and phase field mechanics for capturing polycrystalline deformation and failure. An authentic microstructure, reconstructed from experimental lattice diffraction data with locally refined discretization in GB regions, is used to probe effects of local heterogeneities on material response in phase field simulations. The nominal microstructure consists of larger diamond and SiC (cubic polytype) grains, a matrix of smaller diamond grains and nanocrystalline SiC, and GB layers encasing the larger grains. These layers may consist of nanocrystalline SiC, diamond, or graphite, where volume fractions of each phase are varied within physically reasonable limits in parametric studies. Distributions of fracture energies from MD tension simulations are used in the phase field energy functional for SiC-SiC and SiC-diamond interfaces, where grain boundary geometries are obtained from statistical analysis of lattice orientation data on the real microstructure. An elastic homogenization method is used to account for distributions of second-phase graphitic inclusions as well as initial voids too small to be resolved individually in the continuum field discretization. In phase field simulations, SiC single crystals may twin, and all phases may fracture. The results of MD calculations show mean strengths of diamond-SiC interfaces are much lower than those of SiC-SiC GBs. In phase field simulations, effects on peak aggregate stress and ductility from different GB fracture energy realizations with the same mean fracture energy and from different random microstructure orientations are modest. Results of phase field simulations show unconfined compressive strength is compromised by diamond-SiC GBs, graphitic layers, graphitic inclusions, and initial porosity. Explored ranges of porosity and graphite fraction are informed by physical observations and constrained by accuracy limits of elastic homogenization. Modest reductions in strength and energy absorption are witnessed for microstructures with 4% porosity or 4% graphite distributed uniformly among intergranular matrix regions. Further reductions are much more severe when porosity is increased to 8% relative to when graphite is increased to 8%.
采用一种计算方法对金刚石 - 碳化硅（SiC）多晶复合混合物进行研究，该方法结合了分子动力学（MD）模拟以获取晶界（GB）断裂特性，以及相场力学以捕捉多晶变形和失效。通过实验晶格衍射数据重建真实微观结构，并在晶界区域进行局部细化离散化，用于在相场模拟中探究局部不均匀性对材料响应的影响。名义微观结构由较大的金刚石和SiC（立方多型）晶粒、较小的金刚石晶粒和纳米晶SiC基体以及包裹较大晶粒的晶界层组成。这些层可能由纳米晶SiC、金刚石或石墨组成，在参数研究中，各相的体积分数在物理合理范围内变化。MD拉伸模拟得到的断裂能分布用于SiC - SiC和SiC - 金刚石界面的相场能量泛函中，其中晶界几何形状通过对真实微观结构上晶格取向数据的统计分析获得。采用弹性均匀化方法来考虑第二相石墨夹杂以及在连续场离散化中太小而无法单独分辨的初始孔隙的分布。在相场模拟中，SiC单晶可能孪生，所有相都可能断裂。MD计算结果表明，金刚石 - SiC界面的平均强度远低于SiC - SiC晶界的平均强度。在相场模拟中，具有相同平均断裂能的不同晶界断裂能实现以及不同随机微观结构取向对峰值总应力和延性的影响较小。相场模拟结果表明，无侧限抗压强度受到金刚石 - SiC晶界、石墨层、石墨夹杂和初始孔隙率的影响。孔隙率和石墨分数的探索范围基于物理观察，并受弹性均匀化精度限制的约束。对于在晶间基体区域均匀分布4%孔隙率或4%石墨的微观结构，强度和能量吸收有适度降低。当孔隙率增加到8%时，强度和能量吸收的进一步降低比石墨增加到8%时更为严重。
