Mechanical properties and influences of irradiation in dilute nanograined aluminum alloys

The aim of this dissertation is providing information to help develop alloys that are dimensionally stable in extreme environments. For example, nuclear reactors are exposed to high temperatures and high irradiation damage levels that can cause mechanical and microstructural instabilities such as creep, embrittlement, void swelling, and so on. If more knowledge regarding how materials behave in such extreme environments becomes available, the development of stable materials can be expedited. To achieve this goal, mechanical properties characterization of dilute nanocrystalline (nc-) aluminum alloys will be the primary focus of this work under various thermal treatments, along with additional characterization of these alloys under irradiation. These works include the thermal creep and irradiation induced creep responses of various Al alloy systems at elevated temperatures. For the hardness measurements, standard nanoindentation methods were employed. For creep measurements, a novel thin film bulge test technique was used due to many advantages. Microfabrication process was employed to make free standing thin films for creep tests, and DC sputtering was used to deposit a metal layer. The first part of this work concerns the strengthening mechanisms operating in nc-Al alloys which are promising materials for nuclear power plant application. Microstructure and mechanical characterizations under various annealing temperatures were performed. The results suggest that various mechanisms can strengthen nanocrystalline alloys, for example, solute doping of grain boundaries and solid solution strengthening. The second part presents the thermal creep response of various nc-Al alloys at various temperatures, and the results suggest Coble creep is a dominant mechanism over the range studied. For a creep test, a thin film bulge test method was employed. The work explores the effects different solute additions on creep rates and specifically, both in solid solution and in precipitates. Lastly, the effects of irradiation on nc-Al alloys are investigated. This irradiation study includes change of mechanical and microstructural properties under irradiation. Here, the importance of irradiation induced mixing on alloy hardness is demonstrated. The results of these studies are complementary to my work on the strengthening of these alloys during thermal annealing. Irradiation was also employed to examine self-organization in nc-Al-Sc and nc-Al-Sb alloys. The work provides strong evidence that these alloys do self-organize under irradiation and it raises interesting questions regarding the role of grain boundary diffusion in this process. Lastly, irradiation induced creep (IIC) measurements were performed using heavy ions to explore the role of alloys additions on creep response. These characterizations for Al alloys provide valuable information in the design of promising nanostructured materials for high temperature and nuclear applications.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2020

Author dc:creator

• Kim, Sung Eun

Contributors dc:contributor

• Averback, Robert S.
• Johnson, Harley T.
• Bellon, Pascal
• Maass, Robert E.

• nanocrystalline (nc-) Al Alloy, Self-Organization, Irradiation Effects, Strengthening mechanism of nc Alloys, in-situ Bulge Test, Thermal Creep, IIC,

Statement dc:rights

• Copyright 2019 Sung Eun Kim

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/106381

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/106381