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Creep of silicon carbide hot-pressed with aluminum, boron, and carbon.

机译：蠕变的碳化硅与铝，硼和碳热压在一起。

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摘要

The creep of a high strength, high toughness SiC, sintered with Al, B, and C (ABC-SiC), was investigated. For elevated temperature applications, the time-dependent deformation, creep response, must be fully characterized for candidate materials. The mechanisms responsible for high temperature deformation in ABC-SiC were evaluated. The creep response was compared to materials that have glassy grain boundary phases but do not have interlocked grains.; The creep mechanisms were assessed by calculating the stress exponent and apparent activation energy. For creep tests conducted between 1200–1500°C, 50–200 MPa, the stress exponent, n, was ∼1. The activation energy for the same temperature and stress range was Ea ∼ 225 kJ/mol. This data was utilized in conjunction with microstructural features to determine the operative creep mechanisms. Characterization revealed isolated grains containing dislocations after creep. However, these dislocations were not the controlling creep mechanism, as evidenced by the low stress exponent and lack of dislocation slip and climb. Grain boundary analysis revealed that the boundaries changed upon exposure at creep temperatures. The initial amorphous grain boundaries exhibited crystalline features after the heat treatments.; The controlling creep mechanism was determined to be grain boundary sliding accommodated by diffusion along the grain boundary interlayer/SiC interface. Parallel mechanisms of solution-precipitation and cavitation were also operative in ABC-SiC. Additionally, the dislocations were likely introduced at regions of grain-to-grain contact where the local stresses were high.; The high temperature strength and long exposure oxidation resistance were assessed. The four-point bend strength of ABC-SiC decreased by a factor of 5, from ∼515 MPa to 100 MPa, as the temperature was increased from room temperature to 1300°C. However, long heat treatments in Ar improved the high temperature strength at 1300°C from ∼100 MPa to almost 400 MPa, while also improving the room temperature strength. Crystallization of the grain boundary phase during annealing limited softening of the grain boundary glass and thus minimized subcritical crack growth. Little degradation was observed for ABC-SiC after oxidation at 1200°C for ∼9.5 days.
机译：研究了烧结有Al，B和C（ABC-SiC）的高强度，高韧性SiC的蠕变。对于高温应用，必须针对候选材料充分表征随时间变化的变形，蠕变响应。评估了造成ABC-SiC高温变形的机理。将蠕变响应与具有玻璃状晶界相但没有互锁晶粒的材料进行了比较。通过计算应力指数和表观活化能评估蠕变机理。对于在1200–1500°C，50–200 MPa之间进行的蠕变测试，应力指数n约为1。在相同温度和应力范围内的活化能为E 〜225 kJ / mol。该数据与微结构特征一起用于确定有效的蠕变机理。表征表明，蠕变后分离出的晶粒含有位错。然而，这些位错不是控制蠕变的机制，这由低应力指数和缺乏位错滑移和爬升所证明。晶界分析表明，边界在蠕变温度下暴露后发生了变化。热处理后，最初的无定形晶界显示出晶体特征。确定控制蠕变机理为通过沿晶界中间层/ SiC界面扩散而容纳的晶界滑动。在ABC-SiC中，溶液-沉淀和空化的平行机制也起作用。另外，位错可能是在局部应力较高的晶粒与晶粒接触区域引入的。评估了高温强度和长时间暴露的抗氧化性。随着温度从室温升高到1300°C，ABC-SiC的四点弯曲强度降低了5倍，从约515 MPa降低到100 MPa。然而，在Ar中进行长时间的热处理将1300°C时的高温强度从〜100 MPa提高到几乎400 MPa，同时还提高了室温强度。退火过程中晶界相的结晶限制了晶界玻璃的软化，因此使亚临界裂纹的生长最小。在1200°C氧化约9.5天后，ABC-SiC几乎没有降解。

著录项

  • 作者

    Sixta, Mark Eldon.;

  • 作者单位

    University of California, Berkeley.;

  • 授予单位 University of California, Berkeley.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2000
  • 页码 179 p.
  • 总页数 179
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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