CHAPTER 6
DISCUSSION AND CONCLUSIONS
6.1 Metastable NiyMo Phase Formation:
Effects of Chemistry and
Microstructure
There are clearly differences at all aging
temperatures between the precipitation sequences of the
metastable NixMo phases in the RSR alloys. From the EDS
measurements it is probable that Ta in RSR 197 cannot have
a direct effect on the precipitation of these NixMo phases
in the gamma phase of RSR 197 alloy. This is confirmed by
ternary alloy //17 according to the results discussed in
Section 5.1.7.1. The precipitate and the precipitate
morphologies in alloy //17 are essentially identical to
those in the Ta containing RSR 197. One can conclude that
if it is the presence of an element that allows all three
NixMo precipitates to co-exist, this element must be A1,
not Ta.
The presence of W in the RSR 209 must be a
controlling factor in establishing the precipitation
sequence in this alloy, since this sequence differs from
the ternary alloy //17. The Pt2Mo phase is the predominant
phase, not DO22 and Dla. This is very similar behavior to
170