<p>Modern structural materials
utilize tailored microstructures to retain peak performance within the most
volatile operating conditions. Features such as grain size, grain boundary (GB)
character and morphology and secondary phases are just a few of the tunable
parameters. By tailoring these types of microstructural features, the
deformation behavior of the material is also altered. The localization of
plastic strain directly correlated to material failure. Thus, a systematic
approach was utilized to understand the effect of microstructural features on
the localization of plastic deformation utilizing digital image correlation
(DIC). First, at the macroscopic scale, strain accumulation is known to form
parallel to the plane of maximum shear stress. The local deviations in the
deformation pathways at the meso-scale are investigated relative to the plane
of maximum shear stress. The deviations in the deformation pathways are
observed to be a function of the accumulated local plastic strain magnitude and
the grain size. Next, strains
characterized via DIC were used to
calculate a value of incremental slip on the active slip systems and identify
cases of slip transmission. The incremental slip was
calculated based on a Taylor-Bishop-Hill algorithm, which determined a
qualitative assessment of deformation on a given slip system, by satisfying
compatibility and identifying the stress state by the principle of virtual
work. Inter-connected slip bands, between neighboring grains, were shown to
accumulate more incremental slip (and associated strain) relative to slip bands
confined to a single grain, where slip transmission did not occur. These
results rationalize the role of grain clusters which lead to intense strain
accumulation and thus serve as potential sites for fatigue crack initiation.
Lastly, at GB interfaces, the effect of GB morphology (planar or serrated) on
the cavitation behavior was studied during elevated temperature dwell-fatigue
at 700 °C. The resulting γ′ precipitate structures were characterized near GBs
and within grains. Along serrated GBs coarsened and elongated <a>γ′ </a>precipitates formed and consequently created adjacent
regions that were denuded of γ′ precipitates. Dwell-fatigue experiments were
performed at low and high stress amplitudes which varied the amount of imparted
strain on the specimens.<a> Additionally, the regions
denuded of the γ′ precipitates were observed to localize strain and to be
initial sites of cavitation.</a> <a>These results present a
quantitative strain analysis between two GB morphologies, which provided the
micromechanical rationale for the increased proclivity for serrated GBs to form
cavities.</a></p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/17144294 |
| Date | 20 December 2021 |
| Creators | John J Rotella (11811830) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY-ND 4.0 |
| Relation | https://figshare.com/articles/thesis/PREFERENTIAL_MICROSTRUCTURAL_PATHWAYS_OF_STRAIN_LOCALIZATION_WITHIN_NICKEL_AND_TITANIUM_ALLOYS/17144294 |
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