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Microstructure and phase stability of single crystal nial alloyed with hf and zr
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Noebe, R. D. Darolia, R. Whittenberger, J. D. Garg, A. Dickerson, R. M. Locci, I. E. Nathal, M. V. |
| Copyright Year | 1996 |
| Description | Six near stoichiometric, NiAl single-crystal alloys, with 0.05-1.5 at.% of Hf and Zr additions plus Si impurities, were microstructurally analyzed in the as-cast, homogenized, and aged conditions. Hafnium-rich interdendritic regions, containing the Heusler phase (Ni2AlHf), were found in all the as-cast alloys containing Hf. Homogenization heat treatments partially reduced these interdendritic segregated regions. Transmission electron microscopy (TEM) observations of the as-cast and homogenized microstructures revealed the presence of a high density of fine Hf (or Zr) and Si-rich precipitates. These were identified as G-phase, Nil6X6Si7, or as an orthorhombic NiXSi phase, where X is Hf or Zr. Under these conditions the expected Heusler phase (beta') was almost completely absent. The Si responsible for the formation of the G and NiHfSi phases is the result of molten metal reacting with the Si-containing crucible used during the casting process. Varying the cooling rates after homogenization resulted in the refinement or complete suppression of the G and NiHfSi phases. In some of the alloys studied, long-term aging heat treatments resulted in the formation of Heusler precipitates, which were more stable at the aging temperature and coarsened at the expense of the G-phase. In other alloys, long-term aging resulted in the formation of the NiXSi phase. The stability of the Heusler or NiXSi phases can be traced to the reactive element (Hf or Zr) to silicon ratio. If the ratio is high, then the Heusler phase appears stable after long time aging. If the ratio is low, then the NiHfSi phase appears to be the stable phase. |
| File Size | 1683482 |
| Page Count | 16 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_19970023976 |
| Archival Resource Key | ark:/13960/t0fv3h74v |
| Language | English |
| Publisher Date | 1996-12-01 |
| Access Restriction | Open |
| Subject Keyword | Metallic Materials Phase Stability Materials Phase Diagrams Heat Treatment Directional Solidification Crystals Cooling Hafnium Alloys Chemical Analysis Nickel Alloys Aluminum Alloys Cast Alloys Single Crystals Transmission Electron Microscopy Heat Resistant Alloys Silicon Alloying Chemical Composition Aging Metallurgy Microstructure Zirconium Alloys Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
