Nuclear reactors provide a promising alternative to fossil fuels in the quest for a magic bullet for the world’s increasing energy needs in the face of rising levels of greenhouse gases and consequent global temperature increase. However, in order to build the highly efficient reactors with low waste output needed for this purpose, materials with extremely high radiation tolerance and superior high-temperature properties are needed. One of the major detrimental effects of radiation due to high-energy neutrons that are prevalent in the reactor environment is the loss of ductility of the structural materials, making them brittle. This embrittlement is accompanied by a significant increase in strength, which depends on the dose of neutron irradiation.
In order to understand the effects of high doses of radiation on nuclear structural materials, ion irradiation is often used as a substitute for neutrons, since the former enables the achievement of high doses much faster (in days instead of years), and generally without activation of the samples. However, the ion irradiation method creates a very shallow damage layer (nm to ~20 μm) with a steep dose gradient. Therefore it becomes imperative to apply mechanical test methods which can allow testing of small volumes of material.
The Radiation Effects research group in the Nuclear Fuel Cycle division of ANSTO has developed and applied the techniques of micro-tensile testing for the specialised mechanical characterisation of ion irradiated materials. These methods provide an advantage over nanoindentation as they allow uniaxial testing, while the latter involves triaxial stress states. The group has also applied the conventional method of nanoindentation to this problem, and performed detailed analysis of the stress and strain fields when they interact with the radiated layers using finite element and analytical models. These studies, along with transmission electron microscopy, have brought new insight into the deformation behaviour of ion-irradiated materials. This talk will present some of this data and discuss the significance of these results in the context of radiation damage characterisation and testing.
Dhriti Bhattacharyya did his B.Tech. in Metallurgical Engineering from Indian Institute of Technology, Varanasi, India in 1995, and after a few years as Engineer in BHEL, India, went on to do his Ph.D. in Materials Science and Engineering from The Ohio State University, USA and graduated in 2004. His Ph.D. thesis was on the Development of Textures and Microstructures in Ti alloys. He then worked as a Post Doctoral researcher at OSU and at Los Alamos National Laboratory, USA till 2010.
There his work focused on the microstructure, deformation behaviour and radiation tolerance of nanoscale metallic multilayers and nanostructured steels. He has been working as a senior scientist investigating the effects of radiation damage on structural materials at ANSTO, Australia, since 2010, where he is leading the Radiation Effects project. The focus of his research here has been the various microstructural effects of ion and neutron irradiation on metallic alloys and multilayers, and their implications for the mechanical properties and strength of these materials at the microscopic scale.