Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7880454 | Acta Materialia | 2015 | 15 Pages |
Abstract
Local chemical fluctuations in the vicinity of superlattice intrinsic stacking faults (SISFs) have been observed via high resolution energy dispersive X-ray spectroscopy (EDS) mapping in new single crystal Co- and CoNi-base superalloys containing γâ²-(L12) precipitates. The SISFs were formed during high temperature tensile creep at 900 °C. Chemical fluctuations were found to greatly influence the SISF energy, which was calculated from density functional theory in Co3(Al, Ta, W) compounds at 0 K. The local SISF structure was found to be comprised of four D019 (0001) planes that were enriched in W and Ta, as revealed by high resolution scanning transmission electron microscopy (HRSTEM) imaging and EDS mapping. The precipitates were determined to accommodate up to 22% of the plastic deformation accrued during an interrupted creep test to 0.6% creep strain. The driving forces for segregation are discussed, and new models for shearing of the ordered precipitates are proposed.
Keywords
Related Topics
Physical Sciences and Engineering
Materials Science
Ceramics and Composites
Authors
Michael S. Titus, Alessandro Mottura, G. Babu Viswanathan, Akane Suzuki, Michael J. Mills, Tresa M. Pollock,