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Processing and deformation mechanisms of boron carbide titanium diboride directionally solidified eutectics.

机译：碳化硼二硼化钛定向凝固共晶的加工和变形机理。

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摘要

Current military personnel armor solutions are generally monolithic ceramics including boron carbide (B4C), silicon carbide (SiC), titanium diboride (TiB2), and aluminum oxide (Al2O3). Recent work by the US Army Research Lab indicates that nanoscale ceramic composites are of interest for the next generation of armor ceramics. In this work, research on processing, properties, and deformation mechanisms of a micro/nano-scale composite of B4C and TiB2 is presented.;A high power laser (500-1000W) is used to melt an resolidify a psuedobinary eutectic mixture of 75 mol% B4C and 25 mol% TiB2. The resulting microstructure is of the lamellar-type eutectic: a matrix of B 4C with well-ordered TiB2 lamellae reinforcing phase throughout. The scale of the microstructure (the interlamellar spacing) is found to decrease with increasing laser scan rate, consistent with theories of eutectic growth. Use of the high power laser allows for eutectic growth rates up to 42 mm/s, which results in an interlamellar spacing of approximately 180 nm.;Residual stress distribution throughout the eutectic microstructure is calculated with finite element modeling. The boron carbide matrix is found to be in compression and the TiB2 phase in tension, as predicted by analytical calculations. Strain energy and principal stress concentrations are found at the tips of lamellae, corresponding to enhanced microcracking at lamellae tips during deformation.;Vickers indentation of eutectics results in hardness as high as ≈31 GPa at indenter loads of 10 N when the interlamellar spacing is 1 microm or smaller. Conversely, monolithic boron carbide (grain size 6 microm) was found to have a Vickers hardness of ≈27 GPa at 10 N indenter loads. Indentation fracture toughness is measured to be 1.66--2.80 MPa m in B4C-TiB2 eutectics, with no clear dependence on interlamellar spacing, and ≈1.95 MPa- m in B4C. Shear banding and fissuring is evident in deformed monolithic B4C and in some cases dislocations were observed in the TiB2 reinforcing phase of deformed eutectics. In some cases, the presence of the TiB2 reinforcing phase in the eutectic mitigates shear banding and fissuring found in monolithic B 4C, potentially leading to increased hardness.
机译：当前的军事人员装甲解决方案通常是整体陶瓷，包括碳化硼（B4C），碳化硅（SiC），二硼化钛（TiB2）和氧化铝（Al2O3）。美国陆军研究实验室的最新工作表明，纳米级陶瓷复合材料是下一代装甲陶瓷的关注点。在这项工作中，研究了B4C和TiB2的微米/纳米级复合材料的加工，性能和变形机理。;使用大功率激光（500-1000W）熔化并固化了75的伪二元共晶混合物摩尔％的B 4 C和25摩尔％的TiB 2。所得的微观结构是层状共晶的：B 4C的基质始终具有良好的TiB2片层增强相。发现微结构的尺度（层间间距）随着激光扫描速率的增加而减小，这与共晶生长理论一致。高功率激光的使用允许共晶生长速率高达42 mm / s，这导致层间间距约为180 nm。;通过有限元建模计算了整个共晶微结构的残余应力分布。如分析计算所预测，发现碳化硼基体处于压缩状态，而TiB2相处于拉伸状态。在片状尖端发现应变能和主应力集中，这对应于变形过程中片状尖端的微裂纹增强;当层间间距为10 N时，在10 N的压头载荷下，共晶的维氏压痕导致硬度高达＆ap; 31 GPa。 1微米或更小。相反，发现整体式碳化硼（粒度为6微米）在10 N压头载荷下的维氏硬度为＆ap; 27 GPa。在B4C-TiB2共晶中，压痕断裂韧性测得为1.66--2.80 MPa m，对层间距的依赖性不明显，在B4C中约为1.95 MPa-m。在变形的整体B4C中，剪切带和裂痕是明显的，在某些情况下，在变形的共晶体的TiB2增强相中观察到了位错。在某些情况下，共晶中TiB2增强相的存在减轻了整体B 4C中发现的剪切带和裂缝，可能导致硬度增加。

著录项

  • 作者

    White, Ryan M.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 224 p.
  • 总页数 224
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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