Abstract
The microstructural evolution of Ni-20 pct Cr wires was studied during pack cementation where Al and Ti, with and without prior cementation with Mo, are deposited to the surface of the Ni-Cr wires and subsequently homogenized in their volumes. Mo deposition promotes the formation of Kirkendall pores and subsequent co-deposition of Al and Ti creates a triple-layered diffusional coating on the wire surface. Subsequent homogenization drives the alloying element to distribute evenly in the wires which upon further heat treatment exhibit the γ + γ′ superalloy structure. Unexpectedly, formation of cellular structures is observed at some of the boundaries between primary γ′ grains and γ matrix grains. Based on additional features (i.e., ordered but not perfectly periodic structure, confinement at γ + γ′ phase boundaries as a cellular film with ~100 nm width, as well as lack of topologically close-packed phases), and considering that similar, but much larger, microstructures were reported in commercial superalloys, it is concluded that the present cellular structure solidified as a thin film, composed of eutectic γ + γ′ and from which the γ′ phase was subsequently etched, which was created by incipient melting of a region near the phase boundary with high solute segregation.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 2680-2687 |
| Number of pages | 8 |
| Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
| Volume | 46 |
| Issue number | 6 |
| DOIs | |
| State | Published - Jun 1 2015 |
Funding
The authors acknowledge the financial support from the Defense Advanced Research Projects Agency under the Contract Number of W91CRB1010004 monitored by Dr. Judah Goldwasser (Program Manager). They also thank Dr. Dinc Erdeniz and Ms. Ashley Paz y Puente (both of Northwestern University) for useful discussions.
ASJC Scopus subject areas
- Condensed Matter Physics
- Mechanics of Materials
- Metals and Alloys