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首页> 外文学位 >Shearing Mechanisms and Complex Particle Growth in Nickel Superalloy 718.
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Shearing Mechanisms and Complex Particle Growth in Nickel Superalloy 718.

机译：镍高温合金718的剪切机制和复杂颗粒的生长。

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摘要

Alloy 718 is a gamma"-strengthened Ni-base disk superalloy used in the aerospace industry, and it has been used prominently for decades. Though there has been extensive research into the processing/property relationships, there is very little known about the intermediate microstructure and mechanisms that are common in commercial 718 that dictate the yield strength. A variety of analytical techniques, including scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) were employed to investigate the microstructure of alloy 718 after various deformed conditions and heat treatment conditions.;The gamma" in alloy 718 following a commercial heat treatment was found to have both monolithic gamma" particles as well as composite particles in which gamma' and gamma" share a planar phase boundary. Isothermal heat treatments were applied to solutionized samples, and it was found that low heat treatment temperatures produced a large percentage of composite particles, but high temperatures led to the formation of a primarily monolithic structure. Additionally, these composite particles were shown to have a desirable stabilizing effect at high temperatures, and they were seen to grow much more slowly than their monolithic counterparts. STEM analysis was able easily show the morphology of any edge-on gamma" particles, and EDS was capable of determining the general morphology of in-plane particles. EDS was also useful in determining a rough volume fraction of each phase in tin foils, and it was found that the volume fraction of gamma' was slightly larger than that of gamma" after commercial heat treatments.;Deformation mechanisms were also characterized using STEM. Diffraction STEM was used on isolated dislocations and it was determined that isolated dislocations do not have contrast consistent with 1/2 dislocations, so some form of dislocation was thought to be operative. Atomic resolution STEM analysis uncovered a variety of mechanisms present in tensile samples. Deformation at 22°C was found to occur primarily through the isolated shearing of gamma" into an ISF configuration while the surrounding matrix is left without a fault by a partial loop forming at the gamma"/matrix interface. At 427°C, stacking faults were seen extending into the matrix, and isolate microtwins began to form in the gamma" phase. At 649°C, microtwins began to extend through the matrix and across large portions of the grain. The partials forming the microtwins are of multiple Burgers vector values, but they do not shear in a regular pattern. This indicates that the microtwin formation is likely assisted by localized reordering in the both the gamma' and gamma" phases. Even so, there was no evidence found for segregation of elements to faults or twins.;The understanding gained through this research has been used to inform precipitation and growth models. The precipitation and growth models will be combined with mechanistically-accurate yield strength models to improve predictions localized properties after a desired heat treatment.
机译：718合金是在航空航天工业中使用的伽玛增强型镍基圆盘高温合金，并且已在数十年中得到显着使用。尽管已经对加工/特性之间的关系进行了广泛研究，但对中间组织的了解却很少和商业718中决定屈服强度的常见机理，采用各种分析技术，包括扫描透射电子显微镜（STEM）和能量分散光谱（EDS），研究了在各种变形条件和加热条件下合金718的显微组织。处理条件；商业热处理后的合金718中的γ″被发现既具有整体的γ″颗粒，也具有其中γ′和γ″共享平面相界的复合颗粒。将等温热处理应用于固溶样品，发现低热处理温度会产生大量百分比的复合颗粒，但高温会导致形成整体结构。另外，这些复合颗粒显示出在高温下具有理想的稳定效果，并且发现它们的生长比其整体对应物慢得多。 STEM分析能够轻松显示出任何边缘gamma“颗粒的形貌，而EDS能够确定平面内颗粒的一般形貌。EDS还可用于确定锡箔中各相的粗略体积分数，并且经商业热处理后，发现γ'的体积分数略大于γ“的体积分数。衍射STEM用于孤立的脱位，并且确定孤立的脱位没有与1/2脱位一致的对比度，因此认为某种形式的脱位是可行的。原子分辨率STEM分析揭示了拉伸样品中存在的多种机制。发现在22°C时的变形主要是通过将gamma“隔离剪切成ISF构型而发生的，而周围的矩阵则由于在gamma” /矩阵界面处形成的局部环而没有缺陷。在427°C下，观察到堆垛层错延伸到基体中，并且在γ“相中开始形成分离的微孪晶。在649°C下，微孪晶开始延伸穿过基体并跨越晶粒的大部分。微双胞胎具有多个Burgers矢量值，但它们不会以规则的模式剪切，这表明微双胞胎的形成很可能是通过在γ'和γ“相中进行局部重排而得到帮助的。即便如此，也没有发现将元素分离到断层或孪生的证据。通过这项研究获得的理解已被用来为降水和生长模型提供信息。析出和生长模型将与机械精确的屈服强度模型结合，以改进所需热处理后的局部预测性能。

著录项

  • 作者

    McAllister, Donald Paul.;

  • 作者单位

    The Ohio State University.;

  • 授予单位 The Ohio State University.;
  • 学科 Materials science.;Aerospace engineering.
  • 学位 Ph.D.
  • 年度 2016
  • 页码 191 p.
  • 总页数 191
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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