Woodruff School of Mechanical Engineering
Nuclear & Radiological Engineering and Medical Physics Programs
“Seeing Is Believing”:The Use of In-situ TEM to Investigate Metallic Systems under External Stimuli
Dr. Djamel Kaoumi
University of South Carolina
Friday, November 9, 2012 at 11:00:00 AM
Boggs Building, Room 3-47
One of the difficulties of studying processes occurring in a system under external stimulus such as irradiation and/or mechanical stress is the lack of kinetics information, since usually samples are examined ex-situ (i.e. after irradiation or after mechanical testing) so that only snapshots of the process are available. Given the dynamic nature of the phenomena of interest, direct in situ observation is often necessary to better understand the kinetics and driving forces of the processes involved. This can be done using in-situ Transmission Electron Microscopy (TEM). Indeed, the spatial resolution of the TEM makes it an invaluable tool in which one can continuously track the real-time response of a system to an external stimulus. This can help discover and quantify the fundamental rate-limiting microscopic processes and mechanisms governing the macroscopic properties.
In this presentation, diverse examples of on-going studies will be given which use in-situ TEM coupled with straining or ion irradiation. (i) In-situ straining in the TEM is used to investigate deformation mechanisms as it reveals the microstructure evolution under tensile strain as it proceeds in the material. The technique allows to follow crack propagation as well as elemental mechanisms such as slip band activation and dislocation pile-ups involved in the deformation propagation across the material. Such observations will be reported in the case of Ni-based alloys (Inconel 617 and Haynes 230) which are candidate materials for the heat exchanger in the Very High Temperature nuclear Reactor. (ii) In-situ Ion-irradiation in the TEM is used for studying the basic mechanisms of radiation damage formation and accumulation (defect density, defect interactions, precipitation or dissolution of second phases…). It allows for the direct determination of defect formation and the spatial correlation of the defect structures with the pre-existing microstructure (e.g. lath boundaries, network dislocations and precipitates) as a function of dose, dose rate, temperature and ion type. This type of studies is necessary to develop predictive models of in-reactor materials behavior. Examples covered in this talk include the defect formation and evolution in advanced Ferritic/Martensitic steels, the irradiation stability of precipitates in Oxide Dispersion Strengthened (ODS) steels, and irradiation-induced grain-growth in nanocrystalline metals.
Note: such in-situ investigations are usually coupled with bulk tests, however in this presentation the focus will be put on the in-situ technique.
Ph.D. Nuclear Engineering, The Pennsylvania State University, 2007.
M.Sc. Nuclear Engineering (minor in Materials Science and Engineering), University of Florida, 2001.
B. Sc. Physics, Institut National Polytechnique de Grenoble (INPG), Grenoble, France, 1999.
Dr Kaoumi is an assistant professor of Nuclear Engineering in the Mechanical Engineering Department of the University of South Carolina.
Dr Kaoumi’s research topics are in the field of development, characterization and testing of materials for nuclear applications, especially advanced alloys for structural and cladding applications in advanced nuclear systems (e.g. advanced F/M steels, nanostructured Oxide-Dispersion-Strengthened (ODS) steels, and high-temperature Ni-based alloys for heat exchangers).
Dr Kaoumi is particularly interested in developing an understanding of microstructure-property relationships in advanced alloys, with an emphasis on microstructure evolution under irradiation, high temperature and/or mechanical constraint and how it can impact macroscopic properties which