Revealing the causes of the unusual mechanical behavior of B2 FeAl compounds

揭示 B2 FeAl 化合物异常机械行为的原因

• 批准号: 511095365
• 负责人: Dr. James Best
• 金额: --
• 依托单位: Institut für Angewandte Materialien - Werkstoffkunde (IAM-WK)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/511095365?language=en
• 关键词: Revealing; causes; unusual; mechanical; behavior

The project addresses the contribution of dislocation-mediated plastic deformation to the brittle-to-ductile transition (BDTT) of B2 FeAl intermetallic compounds, which show an unusual dependence of mechanical properties on composition. Even though being single-phase B2-ordered over a wide range of Al contents, FeAl alloys exhibit an abrupt, strong increase of both, yield strength/hardness and BDTT between approx. 40 to 45 at.% Al. To this day, a variety of interdependent, difficult-to-control materials parameters do not permit an unequivocal understanding of this phenomenon. Hence, a novel experimental approach applying micromechanical testing of diffusion couples and a single-specimen macroscopic tensile test procedure is proposed. The diffusion couples cover the entire composition range of the B2 FeAl phase within one sample. This allows studying the mechanical properties in dependence on composition by micro-mechanical testing to 800 °C of one and the same specimen with identical low contamination level and identical thermal history for all compositions. Testing of diffusion couples after heat treatments to adjust different levels of vacancy concentrations will provide quantitative and semi-quantitative information about the dependence of hardness/strength as a function of Al content and vacancy concentration, at temperatures covering BDTT. The diffusion couples are produced from the same alloys, which are also used for macroscopic tensile tests. Since conventionally applied mechanical tests to obtain BDTT require large numbers of specimens, a recently developed testing strategy only requiring a single specimen is applied in the present project. The test strategy relies on total strain-controlled cyclic tests with small total strain amplitudes at steps of increasing temperatures. Monitoring plastic strain amplitude allows for determination of BDTT indicated by a strong increase of plastic strain amplitude, additionally allowing for the strain rate dependence of BDTT to be addressed with a single sample. The dependence of BDTT on Al content and different vacancy concentration levels can be tracked in detail, and rationalized in conjunction with the micromechanical tests. The combined application of the two unique strategies to alloys fabricated from the same well-defined material allows the identification of the relationship of external conditions, such as temperature and strain rate, and intrinsic material parameters, such as Al content and vacancy concentration, on the onset stress of dislocation motion and the BDTT. This should lead to an improved understanding of the unusual mechanical behavior of B2-ordered FeAl alloys.

该项目解决了位错介导的塑性变形对B2 FeAl金属间化合物的脆韧性转变（BDTT）的贡献，B2 FeAl金属间化合物显示出机械性能对组合物的不寻常的依赖性。尽管在宽范围的Al含量上是单相B2有序的，但FeAl合金表现出屈服强度/硬度和BDTT在约1000 - 10000 μ m之间的突然的、强烈的增加。40至45原子%直到今天，各种相互依赖的，难以控制的材料参数不允许对这种现象有明确的理解。因此，提出了一种新的实验方法，应用扩散偶的微观力学测试和单试样宏观拉伸试验程序。扩散偶在一个样品内覆盖B2 FeAl相的整个组成范围。这允许通过对具有相同的低污染水平和所有组合物的相同热历史的同一个样品进行800 °C的微机械测试来研究取决于组合物的机械性能。热处理后的扩散偶的测试，以调整不同水平的空位浓度将提供定量和半定量的信息，硬度/强度的依赖性作为铝含量和空位浓度的函数，在温度覆盖BDTT。扩散偶由同样的合金制成，也用于宏观拉伸试验。由于传统应用的力学测试，以获得BDTT需要大量的标本，最近开发的测试策略，只需要一个单一的标本被应用在本项目。测试策略依赖于总应变控制循环测试，在温度升高的步骤中具有小的总应变幅。监测塑性应变幅度允许确定由塑性应变幅度的强烈增加指示的BDTT，另外允许用单个样品解决BDTT的应变速率依赖性。BDTT对Al含量和不同空位浓度水平的依赖性可以详细跟踪，并结合微观力学测试进行合理化。这两种独特的策略的组合应用，从相同的定义明确的材料制成的合金允许识别的外部条件，如温度和应变速率，和内在的材料参数，如铝含量和空位浓度，对位错运动的起始应力和BDTT的关系。这将导致更好地理解B2有序FeAl合金的不寻常的机械行为。