Investigation of the Roles of Strain Rate and Twinning in the High Ductility of B2 Intermetallic Compounds

该奖项由爱荷华州立大学材料研究部颁发，旨在测试两种理论，这些理论试图解释RM金属间化合物的高延展性，其中R是稀土金属，M是2,8 -13族的金属。金属间化合物的化学、物理、磁性和机械性能往往优于其他金属，但金属间化合物在改善工程性能方面的巨大潜力仍未得到充分利用，因为它们易碎，在室温下容易断裂。最近，在全有序、化学计量的B2金属间RM化合物中发现了室温下的高延展性和高断裂韧性，本研究项目探讨了两个可能解释RM金属间化合物高延展性的理论。一种理论将高延展性归因于晶界效应。迄今为止所研究的弧焊和热轧RM合金的平均晶粒尺寸约为0.2 mm。应变率敏感性将通过拉伸“跳跃试验”来测量，以确定晶界滑动等现象是否有助于延性。拉伸试验将在低温和高温下进行。第二种理论将高延展性归因于孪生效应。初步研究表明单晶RM金属间化合物有孪生的迹象。透射电子显微镜（TEM）变形的RM样品将用于寻找双胞胎。如果发现孪晶，透射电镜将确定孪晶平面和剪切方向。这些发现将支持或反驳这两种理论。通过建立基本的塑性机理，可以对新型RM金属间化合物的性能进行假设，指导今后合金的发展。由稀土金属R和2,8 -13族金属(M)制备的RM金属间化合物约有130种，其中一些金属间化合物在工程结构应用中具有潜在的用途。一些RM金属间化合物具有低密度或具有高抗氧化性，这表明在航空航天结构和涡轮机械中可能的应用。其他RM金属间化合物具有有趣的磁性和磁热行为。室温延展性和高断裂韧性将有助于这些合金的制造和提高性能。然而，研究RM化合物的最大价值可能在于促进对促进其可塑性的因素的理解。从这项研究中获得的见解将有助于指导未来努力提高其他金属间化合物的延展性。这项研究涉及研究生和本科生。

This award by the Division of Materials Research to Iowa State University is to test two theories that attempt to explain the high ductility of the RM intermetallics, where R is a rare earth metal and M is a metal from Groups 2, 8-13. The chemical, physical, magnetic, and mechanical properties of intermetallic compounds are often superior to those of other metals, but enormous potential of intermetallics to improve engineering performance remains underutilized because they are brittle and fracture easily at room temperature. Recently there has been the discovery of high ductility and high fracture toughness at room temperature in fully ordered, stoichiometric B2 intermetallic RM compounds, This research project explores two theories that might explain the high ductility of the RM intermetallic compounds. One theory attributes the high ductility to grain boundary effects. Arc-melted and hot rolled RM alloys studied to date form with average grain sizes of about 0.2 mm. Strain rate sensitivity will be measured by tensile "jump tests" to determine whether phenomena such as grain boundary sliding contribute to the ductility. Tensile tests will be performed at cryogenic and elevated temperatures. The second theory attributes the high ductility to twinning effects. Preliminary studies show indications of twinning in single crystal RM intermetallics. Transmission electron microscopy (TEM) of deformed RM specimens will be used to search for twins. If twins are found, TEM will determine twinning planes and shear directions. These findings will either support or refute each of the two theories. With the basic mechanism of ductility established, the performance of new RM intermetallics can then be hypothesized, guiding future alloy development.There are approximately 130 RM intermetallics prepared from a rare earth metal R and a metal (M) from Groups 2, 8-13, and some of these intermetallics have potential use in engineering structural applications. A few RM intermetallics have low densities or possess high oxidation resistance, suggesting possible applications in aerospace structures and turbomachinery. Other RM intermetallics have interesting magnetic and magnetocaloric behavior. Room temperature ductility and high fracture toughness would aid fabrication of these alloys and improve performance. However, the greatest value of studying the RM compounds could lie in advancing the understanding of the factors facilitating their plasticity. Insights gained from this study will be helpful in guiding future efforts to improve the ductility of other intermetallic compounds. The research involves both graduate and undergraduate students.