<div>
<div>
<div>
<p>The material responses and the deformation pattern of crystals are strongly influ-
enced by their microstructure, crystallographic texture and the presence of defects of
various types.
</p>
<p>In electronics, Sn coatings are widely used in circuits to protect conductors, reduce
oxidation and improve solderability. However, the spontaneous growth of whiskers
in Sn films causes severe system failures. Based on extensive experimental results,
whiskers are observed to grow from surface grains with shallow grain boundaries. The
underlying mechanism for these surface grains formation is crucial to predict potential
whisker sites. A phase field model is coupled with a single crystal plasticity model and
applied to simulate the grain boundary migration as well as the grain rotation process
in Sn thin film, which are two possible mechanisms for surface grain formation. The
grain boundary migration of three columnar grains is modeled and no surface grain is
formed due to large plastic dissipation. In polycrystal Sn thin film, the nucleation of
subgrains with shallow grain boundaries is observed for certain grain orientations on
the film surface and the location of which corresponds to the regions with high strain
energy density. From these simulations, it can be concluded that the grain rotation is
the mechanism for whisker grain formation and the nucleated subgrains may be the
potential whisker sites.
</p>
<p>Sn-based solders are also widely used in electronics packaging. The reliability and
the performance of SAC (Sn-Ag-Cu) solders are of key importance for the miniaturiza-
tion of electronics. The interfacial reaction between Cu substrates and Sn-based sol-
ders forms two types of brittle intermetallic compounds (IMCs), Cu6Sn5 and Cu3Sn.
</p>
</div>
</div>
<div>
<div>
<p>During the operation, the interconnecting solders usually experience thermal loading
and electric currents. These environmental conditions result in the nucleation of voids
in Cu3Sn layer and the growth of the IMCs. A phase field damage model is applied
to model the fracture behavior in Cu/Sn system with different initial void densities
and different Cu3Sn thickness. The simulation results show the fracture location is
dependent on the Cu3Sn thickness and the critical stress for fracture can be increased
by lowering the void density and Cu3Sn thickness.<br></p></div></div></div><div><div><div>
<p>In alloys, the stacking fault energy varies with the local chemical composition.
The effects of the stacking fault energy fluctuation on the strengthening of alloys
are studied using phase field dislocation method (PFDM) simulations that model the
evolution of partial dislocations in materials at zero temperature. Some examples are
shown to study the dependency of the yield stress on the stacking fault energy, the
decorrelation of partial dislocations in the presence of impenetrable and penetrable
particles. Simulations of the evolution of partial dislocations in a stacking fault energy
landscape with local fluctuations are presented to model the responses of high entropy
alloys. A strong size dependency is observed with a maximum strength when the mean
region size approaches the average equilibrium stacking fault width. The strength of
high entropy alloys could be improved by controlling the disorder in the chemical
misfit.
</p>
</div>
</div>
</div>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12888479 |
| Date | 28 August 2020 |
| Creators | Xiaorong Cai (9312344) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Relation | https://figshare.com/articles/thesis/PHASE_FIELD_MODELING_OF_MICROSTRUCTURE_EVOLUTION_IN_CRYSTALLINE_MATERIALS/12888479 |
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