Karl A. Gschneidner - US grants

This project involves the development of a never-before-possible, next-generation lab for the teaching of x-ray diffraction (XRD). Although XRD is one of the most heavily used and depended upon of all analytical techniques in materials science and engineering, it has been extremely difficult to teach because of the time needed to run a typical x-ray scan. Hence, most of the class period is consumed by acquiring a scan, while any on-line, real-time analysis of the XRD data is impossible. Through this project, a new XRD system is developed for real-time analysis of crystallographic structures by using an x-ray generator with the high-speed acquisition capabilities of a position sensitive detector. The XRD hardware is linked to analysis software and databases by way of a local area network of PC-based engineering workstations to provide on-line, real-time analysis of XRD data and crystal structures. In this way, the major difficulty in teaching XRD, namely, the time needed to acquire a scan, is substantially diminished. This method revolutionizes the teaching of XRD because extended exposure to advanced studies involving XRD methodologies is available to undergrads for the first time.

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.