Effect of Grain Size on the Mechanical Properties of Multi-Phase Alloys

本研究的目的是了解第二相颗粒对选定金属和合金的力学行为的影响，因为它们的晶粒尺寸被缩小到最小的纳米尺度，可以通过生产大块、无人工制品的金属的加工方法来实现。科学的方法是：(1)在选定的fcc、bcc和hcp金属基体中引入控制尺寸、间距和体积分数的第二相颗粒；(2)通过适当的加工和热处理方法，将基体的晶粒尺寸减小到100 ~ 200 nm量级，并确定颗粒分布的参数；(3)利用电子显微镜、扫描探针显微镜、x射线衍射和热分析表征了晶粒尺寸分布和颗粒分布；(4)对比多相合金与基体金属的力学行为，揭示晶粒尺寸减小到纳米尺度时第二相对力学性能的影响；(5)制定适合现有样本量的测试方法，以优化力学测试工作。采用硬度、自动球压痕和小型化阀瓣弯曲测试来提供初始筛选。在选定的测试条件和微观结构参数范围内，将增加拉力和压缩测试。任务(6)涉及分析和建模，使用现象学和基于模型的分析，适合于识别潜在的变形机制。作为晶粒尺寸函数的应力-应变行为机制的微观力学模型应该有助于确定优化这类合金的性能和性能的策略。为了优化其机械性能和性能，用于工程应用的结构金属主要是多相合金而不是纯金属。人们期望多相合金以纳米晶的形式提供同样的好处。这类金属和合金的性能还没有被系统的力学测试记录下来，变形机制作为晶粒尺寸的函数也没有得到任何程度的理解。

The goal of this research is to understand the influence of second-phase particles on the mechanical behavior of selected metals and alloys as their grain sizes are reduced to the smallest nanosized scales that can be achieved with processing methods that produce bulk, artifact-free metals. The scientific approach is as follows: (1) introduce second-phase particles with controlled size, spacing and volume fraction into selected fcc, bcc and hcp metal matrices; (2) reduce the grain size of the matrix to the order of 100- 200 nm and the parameters that define the particle distributions by suitable processing and heat-treatment methods; (3) characterize the grain size distributions and particle distributions using electron microscopy, scanning-probe microscopy, x-ray diffraction and thermal analysis; (4) compare mechanical behavior of multi-phase alloys with matrix metals to reveal effects of second phases on the mechanical properties as the grain size is reduced to nanometer size scales; (5) develop test methods suited for the available sample sizes to optimize the mechanical testing effort. Hardness, automated ball-indentation and miniaturized disk-bend testing are employed to provide an initial screening. Tension and compression testing will be added for selected ranges of the test conditions and microstructural parameters. Task (6) involves analysis and modeling using phenomenological and model-based analyses appropriate for the identification of the underlying deformation mechanisms. A micro-mechanical model for stress-strain behavior mechanisms as a function of grain size should aid in defining strategies for optimizing the properties and performance of this class of alloys. To optimize their mechanical properties and performance, structural metals used for engineering applications are predominately multi-phase alloys rather than pure metals. It is expected that multi-phase alloys will provide these same benefits in nanocrystalline form. The properties of this class of metals and alloys have not been documented by systematic mechanical testing, and the deformation mechanisms as a function of grain size are not understood with any degree of confidence.