MICROSTRUCTURAL ANALYSIS OF HELIUM DISTRIBUTION IN NICKEL AND INCONEL X750
Date
2016-07-21
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0001-8692-2054
Type
Thesis
Degree Level
Masters
Abstract
Nickel alloys have found ever increasing use in the nuclear sector in recent times. Inconel X750 and other nickel-based alloys are used in the construction of reactor fuel channels. Thermal neutrons cause transmutation of nickel, and the nuclear reactions that take place within some nuclear reactor components result in the production of helium. Helium accumulation causes the swelling, reduces material strength and finally leads to failure. This project addresses two impact areas, viz., i) improving safety of nuclear energy systems and, ii) advancing knowledge on nuclear materials used in CANDU (Canada Deuterium Uranium) reactors.
The project discusses the experiments carried out on helium irradiated pure Ni and Inconel X750 alloy in order to understand void formation due to helium. SEM (Scanning Electron Microscope) and TEM (Transmission Electron Microscopy) analyses were carried out to establish a relationship between helium void formation and temperature. In addition, EBSD (Electron Backscattered Diffractometry) analysis was carried out to analyse the concentration of helium voids at various grain boundaries.
The project explains in detail the use of SPECTER code to calculate the gas production levels and DPA (displacement per atom) and SRIM (Stopping and Range of Ions in Matter) software, which was used to carry out the various calculations necessary to perform helium ion implantation experiments. As it was difficult to work with irriadted materials from the reactor on account of safety concerns, and also cost associated with working with heavily irradiated materials, the method of helium ion implantation was adopted for this project.
Results showed that at higher temperatures both irradiated pure Ni and Inconel X750 alloy showed accumulation of voids towards the grain boundaries. TEM and EDS (Energy Dispersive Spectroscopy) analysis on irradiated pure Ni confirmed the presence of voids near the grain boundaries.
A statistical relationship was also established between the accumulation of voids and the grain boundary misorientation. It was found out that for both irradiated pure Ni and Inconel X750 alloy the concentration of voids increased with an increase in the grain boundary misorientation. This was due to more free volume available at higher angle grain boundaries.
Description
Keywords
Nickel alloys, CANDU reactor
Citation
Degree
Master of Science (M.Sc.)
Department
Mechanical Engineering
Program
Mechanical Engineering