Date of Award

12-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Yanfei Gao

Committee Members

George M. Pharr, Peter K. Liaw, Zhili Zhang

Abstract

The material anisotropy is one of the most important material properties that cannot be disregarded in today’s world of materials designing and manufacturing. As new materials being developed and new material demands are introduced the inevitable focus on anisotropic materials has been brought under the spotlight. In this dissertation, several experimental and simulation project regarding material anisotropic effects on hexagonal close packed crystals such as Silicon Carbide as well and hierarchically structured solid solution ferritic based alloys. The general purpose was to demonstrate the improvement on various intended material properties using finite element method. Since indentation is a widely used experimental method nowadays to study different aspects of material properties, the use of theoretical modeling with computer aided programs to study the anisotropic behavior of multiple complex material structures is highly demanded. To this end, simulation was designed by using both conical and spherical indentation test to study the HCP single crystal responses. The result was compared and shown consistency with respect to the orientation dependence of HCP [hexagonal close packed] single crystals related to material hardness. In order to understand anisotropy on a microstructural level, structural alloys operating at high temperatures have attracted significant attention from industry due to the increasing demand for materials to be operated at high temperature conditions. Using finite element method to simulate the single phase alloy, alloy containing a L21 (Heusler phase precipitate type) precipitate also alloy containing both L21 precipitate and a B2 precipitate was done to study the strength improvement at high temperatures for these cases. The process of NiAl and Ni2TiAl (Nickel based intermetallic precipitate) precipitates embedded in Fe alloys tested at high temperature is an innovative approach to study the toughness improvement of these alloys. The material hardness improvement is carried out by combining experimental and finite element simulation to examine the lattice strain load transferring effect between alloy matrix and precipitates.

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