Abstract
Precipitation in alloy 718, a Ni-Cr-Fe based superalloy with Nb additions, was studied as a function of heat treatment with specific reference to grain boundary precipitation. Three different heat treatments were studied; a low temperature precipitation treatment (1 h at 650 ° C) typical of age hardening, a high temperature precipitation treatment (1 h at 930 ° C) typical of solution anneal and a homogenization treatment (1 h at 1100 ° C). It was observed that grain boundary precipitation was dependent on the location of the boundary relative to the dendritic solidification pattern of the alloy. The same grain boundary exhibited a change in precipitation behavior as it passed from a dendritic core into the interdendritic region. In general, niobium carbides (NbC) were observed to be located on the grain boundaries in the Nb-depleted core region, while Nb-rich precipitates which included Ni3Nb (δ), Ni3Nb (γ″), laves, and NbC were observed in the Nb-enriched interdendritic region. The grain boundaries in the interdendritic region contained δ precipitated in a discontinuous manner.
| Original language | English |
|---|---|
| Pages (from-to) | 277-283 |
| Number of pages | 7 |
| Journal | Ultramicroscopy |
| Volume | 29 |
| Issue number | 1-4 |
| DOIs | |
| State | Published - May 2 1989 |
| Externally published | Yes |
Funding
The authors wish to acknowledge the support given to this research by the National Science Foundation under grant DMR-8503216. The authors would also like to acknowledge the assistance of T.J. Headley of Sandia National Laboratories in sample preparation and precipitate analysis.