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首页> 外文学位 >Directional solidification, microstructures and mechanical properties of chromium-chromium silicide eutectic alloys.
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Directional solidification, microstructures and mechanical properties of chromium-chromium silicide eutectic alloys.

机译：铬-硅化铬共晶合金的定向凝固，显微组织和力学性能。

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摘要

Alloys based on intermetallics have been considered for high temperature structural applications. However, many of these alloys suffer from intrinsic brittleness and low fracture toughness at ambient temperature. Therefore, ductile phase toughened intermetallic composites are being investigated as a means to improve the fracture toughness. In this study, the Cr-Cr3 Si eutectic system is selected as a model system to investigate composites by directional solidification, where the strong, but brittle Cr3Si is combined with a more ductile Cr-rich solid solution.;A series of binary Cr-Si alloys with silicon concentrations ranging from 13 to 24 at.% were produced by arc melting and drop casting. The microstructural investigation suggests that the best composition for obtaining a fully lamellar structure is Cr-16.05 at.% Si, rather than the eutectic composition (Cr-15 at.% Si) indicated in the phase diagram. Uniform and well-aligned lamellar structures were obtained over a fairly wide range of solidification conditions, but not at very low or very high growth rates. The lamellar spacing was found to increase with decreasing solidification rate, in agreement with the Jackson-Hunt theory. In addition, for a fixed growth rate, the lamellar spacing was found to increase with increasing rotation rate. The growth directions in the lamellar eutectic were found to be 100> for the Cr3Si phase and 111> for the Cr solid solution phase. Eutectic microstructures (rod or lamellar) could also be produced at off-eutectic compositions, but only for a limited range of growth conditions.;The mechanical properties of the individual lamellae and the Cr-Cr 3Si composites were examined by nanoindentation, Vicker's hardness testing and three-point bend testing. It was found that the Vicker's hardness of Cr-Cr 3Si composites is about HV847, independent of the lamellar spacing. The Young's modulus of the Cr-Cr3Si eutectic composites measured by ultrasonic techniques is 312 GPa. The fracture toughness of single crystals of Cr3Si is very low (∼2.6 MPa□√m). Combination with a more ductile phase (Cr-rich solid solution) to make "ductile phase toughened" composites increases the fracture toughness to maximum 8.5 MPa√m.
机译：已经考虑将基于金属间化合物的合金用于高温结构应用。但是，许多这些合金在环境温度下都具有固有的脆性和低的断裂韧性。因此，正在研究韧性相增韧的金属间化合物作为改善断裂韧性的手段。在这项研究中，选择Cr-Cr3Si共晶体系作为模型体系，通过定向凝固研究复合材料，其中强而脆的Cr3Si与更易延展的富Cr固溶体结合。;一系列二元Cr-通过电弧熔化和滴铸生产出硅浓度为13至24 at。％的Si合金。显微组织研究表明，获得完全层状结构的最佳成分是Cr-16.05 at。％Si，而不是相图中所示的低共熔成分（Cr-15 at。％Si）。在相当宽的凝固条件下获得了均匀且排列整齐的层状结构，但不是以非常低或非常高的生长速率。与杰克逊-亨特理论一致，发现层间距随着凝固速率的降低而增加。另外，对于固定的生长速率，发现层间距随着旋转速率的增加而增加。发现层状共晶中的生长方向对于Cr 3 Si相为<100>，对于Cr固溶体相为<111>。共晶微观结构（棒状或层状）也可以在非共晶组成下产生，但仅在有限的生长条件下产生;通过纳米压痕，维氏硬度测试检查了单个薄片和Cr-Cr 3Si复合材料的机械性能和三点弯曲测试。发现Cr-Cr 3Si复合材料的维氏硬度约为HV847，与层状间距无关。通过超声技术测得的Cr-Cr3Si共晶复合材料的杨氏模量为312 GPa。 Cr3Si的单晶的断裂韧性非常低（〜2.6MPa·s·m）。与更具延展性的相（富铬固溶体）结合使用，可制成“韧性相韧化”复合材料，将断裂韧性提高到最大8.5MPa√m。

著录项

  • 作者

    Bei, Hongbin.;

  • 作者单位

    The University of Tennessee.;

  • 授予单位 The University of Tennessee.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2003
  • 页码 148 p.
  • 总页数 148
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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