Date

2013

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Materials Science and Engineering

First Adviser

Vinci, Richard P.

Other advisers/committee members

Watanabe, Masashi; Jagota, Anand; Nied, Herman

Abstract

Grain boundary embrittlement in the Cu-Bi alloy system was investigated using small-scale fracture toughness tests that were based on commonly used bulk-scale tests. Tests were conducted on pure and Bi-doped <001> twist Cu bicrystals with misorientation angles of 6, 13, and 33 ̊ in order to determine the effect of misorientation angle on the degree of embrittlement. The results of these tests showed that the 6 ̊ grain boundary was nearly immune to embrittlement, showing little to no differences in fracture toughness values and failure mechanisms between the pure and doped specimens. However, the 33 ̊ boundary exhibited a significant amount of embrittlement, with a nearly 40% decrease in fracture toughness in the doped specimens compared to the pure and a distinct shift in the failure mechanism from transgranular shear to intergranular fracture. The 13 ̊ boundary exhibited an intermediate amount of embrittlement with a measurable drop in toughness, but not a clear shift in the failure mechanism. These results are consistent with previously published results from tests on bulk-scale bicrystals.Furthermore, a single-crystal plasticity model was incorporated into a commercial finite element software package (ABAQUS) in order to investigate the development of the plastic zone in front of the notches created in the test specimen. It was found that the size of this zone was likely constrained by the specimen dimensions, which had a significant impact on the measured fracture toughness values.

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