Date of Award

5-2018

Degree Type

Thesis

Degree Name

Master of Science in Nuclear Engineering

Department

Nuclear Engineering

Committee Chair

Janelle P. Wharry

Committee Member 1

Gennady Miloshevsky

Committee Member 2

Robert Bean

Abstract

The objective of this study is to observe irradiation effects on the microstructure of nickelbased alloy after surface enhancements. Surface modifications as laser shock peening (LSP) and ultrasonic nanocrystal surface modification (UNSM) techniques were implemented on ATI 718 Plus alloy. These methods introduce compressive residual stresses to the surface of the material. It follows that the samples experienced a severe plastic deformation, and UNSM technique refines the grains. After irradiation was done by 2 MeV protons at 500ºC with damage dose 1 dpa, transmission electron microscopy (TEM) lamellae were made and bright field scanning TEM (BF STEM) images were taken to study the microstructure. TEM did not show any presence of voids and precipitates. Thus, the major contribution to irradiation damages came from dislocation loops. Dislocation loop analysis was made by measuring the sizes, calculating the number density and total line length of loops. Also, the relation between grains sizes, misorientations of the grains to the irradiation damages are discussed. Finally, nanoindentation tests were performed to evaluate mechanical properties of the samples after irradiation.

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