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首页> 外文学位 >Correlation of short-term to long-term oxidation testing for alumina forming alloys and coatings.
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Correlation of short-term to long-term oxidation testing for alumina forming alloys and coatings.

机译：氧化铝形成合金和涂层的短期和长期氧化测试的相互关系。

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摘要

Engineering long cyclic oxidation life of high temperature materials requires success on two fronts. First a slow growing protective oxide scale must form during the elevated temperature exposure. To satisfy this aspect, alumina-forming alloys and coatings are widely accepted as leading materials for use in this environment and are the focus of this discussion. The second aspect is the formation of an adherent oxide that resists spallation during thermal cycling. The driving force for spallation is the stored elastic strain energy that develops from stresses in the oxide scale. Once this stored elastic strain energy exceeds the oxide-substrate interfacial toughness, cracking and subsequent spallation occurs followed by rapid oxidation of the substrate. With advances in alloy and coating development resulting in higher operating temperatures and increased service lives, researchers are faced with excessive laboratory time and cost required to perform a long-term cyclic oxidation test.;The challenge is to predict long-term oxidation behavior from short-term experiments. Since the rate limiting step to high temperature oxidation is a thermally activated process, previous investigations were performed at increased exposure temperatures for rapid degradation of the alloys and coatings to rank material performance. Others have mechanically induced oxide spallation to give insight on the adherence of oxide scales prior to spontaneous failure. In this investigation, short-term testing is employed to gain insight on long-term performance and to determine inputs into a cyclic oxidation model for life-time prediction.;This model operates in an iterative process where one iteration is a thermal cycle. The amount of oxide formed during the high temperature segment is calculated followed by the amount that is lost due to scale spallation during cooling. Retained oxide at the end of this cycle is used as the starting point for the following iteration. The two inputs into this model are the oxide scale growth and spallation behavior. Scale growth behavior corresponds to the isothermal growth kinetics that are experimentally determined by thermogravimetric analysis. Oxide scale spallation behavior is quantified by two short-term experiments of a novel acoustic emission experiment during a 24 hour exposure and the stress measurement of the scale after an exposure to the temperature of interest. Results from these short-term tests and modeled cyclic oxidation are compared to life-times from long-term cyclic oxidation tests.
机译：工程高温材料的长循环氧化寿命需要在两个方面取得成功。首先，在高温下必须形成缓慢生长的保护性氧化皮。为了满足这个方面，形成氧化铝的合金和涂层被广泛接受为在这种环境中使用的主要材料，并且是本讨论的重点。第二方面是在热循环过程中抵抗剥落的粘附氧化物的形成。剥落的驱动力是存储的弹性应变能，它是由氧化皮中的应力产生的。一旦该存储的弹性应变能超过氧化物-基底的界面韧性，就会发生破裂和随后的剥落，随后基底快速氧化。随着合金和涂层发展的进步导致更高的工作温度和更长的使用寿命，研究人员面临着进行长期循环氧化测试所需的大量实验室时间和成本。挑战在于从短时间内预测长期氧化行为学期实验。由于高温氧化的速率限制步骤是一个热活化过程，因此先前的研究是在升高的暴露温度下进行的，以快速降解合金和涂层，从而对材料性能进行排名。其他人则机械地诱发了氧化物剥落，从而洞察了自发失效之前氧化皮的附着情况。在这项研究中，采用短期测试来了解长期性能，并确定用于寿命预测的循环氧化模型的输入。该模型在迭代过程中运行，其中一个迭代是一个热循环。计算在高温段期间形成的氧化物的量，然后计算由于冷却期间的水垢剥落而损失的量。在该循环结束时保留的氧化物用作下一次迭代的起点。该模型的两个输入是氧化物垢的生长和剥落行为。鳞片的生长行为对应于通过热重分析通过实验确定的等温生长动力学。通过在一个24小时的暴露过程中进行的新型声发射实验的两个短期实验以及暴露在所关注温度下的氧化皮应力测量，可以量化氧化皮的剥落行为。将这些短期测试和建模的循环氧化的结果与长期循环氧化测试的寿命进行比较。

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  • 作者

    Stiger, Matthew J.;

  • 作者单位

    University of Pittsburgh.;

  • 授予单位 University of Pittsburgh.;
  • 学科 Engineering Metallurgy.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2004
  • 页码 194 p.
  • 总页数 194
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 冶金工业;工程材料学;
  • 关键词

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