<p>Ni-based superalloys have been
widely used for high temperature applications such as turbine blades for jet
propulsion and power plants due to their excellent creep, fatigue, and
corrosion resistance. But as the demand for higher temperature capability and
strength increases, there remains a need to better understand high temperature
deformation mechanisms and improve and strengthen superalloys at these elevated
temperatures. Recently, a correlation has been observed between solute
segregation at planar defects (stacking faults, antiphase boundaries, etc) and
enhanced high temperature creep properties – known colloquially as phase
transformation strengthening. Experimentally, regardless of alloy composition,
strong Co segregation at planar defects along with Cr has been observed. In
addition, it has been suggested by density functional theory work that Co would
promote Cr concentration at stacking faults by forming strong Cr-Co bonds.
Based on these findings, it was hypothesized the presence of Co provides a significant
thermodynamic driving force for segregation to planar defects. </p><p>In order to further investigate
the correlation between solute segregation and deformation mechanisms the
fabrication of a planar front single crystal Ni-based superalloy and its microstructure,
alloy composition, and microhardness properties of the as-zone melted and
solution heat treated states were investigated and compared to the
directionally-solidified state to study the effect of microsegregation on these
alloy characteristics. Next, new Co-containing, Cr-free alloys are designed to
optimize g-g’ volume fraction,
size, and morphology to mimic microstructures observed in single crystal
superalloys. The general alloy design strategy and approach are outlined, and the
composition, microstructure, phase transformation temperatures, and mechanical
properties of new Cr-free and Co-containing alloys are reported. A new set of
Cr-free alloys have thus been designed, with modifications of Nb, Ta, and Ti
additions ranging from 3 to 7 at.% to investigate the role of these elements on
the phase transformation strengthening mechanism at elevated temperatures.</p><p></p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/17154368 |
| Date | 18 December 2021 |
| Creators | Sae Matsunaga (11820032) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/DESIGN_AND_PROCESSING_OF_NICO-BASED_SUPERALLOYS_FOR_THE_STUDY_OF_SOLUTE_SEGREGATION_AT_PLANAR_DEFECTS_DURING_HIGH_TEMPERATURE_DEFORMATION/17154368 |
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