Effects of Surface Oxidation on Vacancy Defects in Beta Nickel-Aluminum Alloys
Parthasarathi, Arvind
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/68643
Description
Title
Effects of Surface Oxidation on Vacancy Defects in Beta Nickel-Aluminum Alloys
Author(s)
Parthasarathi, Arvind
Issue Date
1980
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Language
eng
Abstract
Transmission Electron Microscopy and Auger Electron Spectroscopy has been used to make observations of the oxidation process in (beta)-NiAl alloys annealed under controlled conditions of temperature and oxygen partial pressure. Binary Ni-Al alloys, with nominally 47.5, 50.4 and 52.5 at .% Al, were examined. The Auger spectroscopy analysis showed that the predominant oxide formed on these alloys is Al(,2)O(,3), with a possible thin intermediate layer of spinel. Bulk oxidation experiments indicate that the oxide grows by outward diffusion of cations to the oxide/gas interface.
As a result of this diffusion, a counter-flow of vacancies occurs, and these vacancies are injected into the substrate. The vacancy injection results in formation and growth of interfacial voids and growth of existing vacancy dislocation loops and internal voids in thin foil samples. Vacancy loop growth rates increase with annealing time and also increase as the oxygen partial pressure is increased - in accordance with a vacancy injection model. This vacancy injection takes place in the alloys tested here, at temperatures above about 600(DEGREES) C, even in ultra high vacuum ( 850(DEGREES) C in UHV. In these samples the oxidation mechanism seems to change from cation diffusion to anion diffusion and as a result, vacancy defects shrink, rather than grow, in these samples.
In addition to vacancies injected by oxidation, vacancy defects are also formed from retained thermal vacancies. From quenching and ageing experiments, and using electron microscopy, an estimation of 1.45 (+OR-) 0.2 eV was made for the formation energy of a pair of vacancies, one on each sublattice. Large concentrations of thermal vacancies can be generated as a result of this low vacancy formation energy, and can be retained in the alloy even during slow cooling due to the impervious oxide formed.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
