Doctoral Dissertations

Date of Award

12-2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Peter K. Liaw

Committee Members

Hahn Choo, Takeshi Egami, David C. Joy, John D. Landes

Abstract

This dissertation addresses two issues concerning the fundamental mechanical behavior of the nickel-based superalloys: (1) the deformation mechanisms and (2) the nano-precipitate-strengthening effect. The precipitates are known to fortify the mechanical behavior of the metallic alloys. These precipitates can interact with the matrix upon the applied load. While the precipitation strengthening has been facilitated for many purposes, this research puts forward the mechanistic understanding.

The dissertation considers the thesis that Deformation Mechanisms and Nanoprecipitate Strengthening and their effects on the microstructure are central to the mechanical behavior of nickel-based superalloys.

The experimental methods employed in this research are in-situ neutrondiffraction measurements, in-situ thermal characterization, ex-situ small-angle neutron-scattering, and electron microscopy experiments. The microscopic structural information obtained from the diffraction profiles is compared with the electronmicroscopy images to be complementary to each other. The microscopic features are connected with the macroscopic states, such as the applied stresses and temperature evolution to bridge the understanding of the bulk property.

This dissertation assumes that the macroscopic-material responses are the convolution of two contributions: the linear-elastic contribution and the plasticityinduced intra/inter-granular contribution. Within the context of this analysis, the mechanistic understanding of the deformation of the alloys is presented.

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