6.3 Precipitation in RSR 209


 The Ni2Mo and Ni3Mo D022 phases precipitate during

the air quench from the solution heat treatment

temperature. The presence of aluminum in the gamma phase

stabilizes the D022 phase. At the lowest aging

temperature, these phases coarsen and eventually the Dla

phase forms. The Ni2Mo remains the dominant phase for

aging times up to 100 hours.

 The Ni2Mo is also the dominant phase when the RSR 209

is aged at 810 C. It coarsens quickly and is consumed by

equilibrium Mo when aged at the highest temperature.

 The formation of the Pt2Mo phase is not a function of

the gamma prime cube distribution, as was the D022 phase.

It is reasonable to assume that all six Pt2Mo variants can

exist simultaneously in any one region of the gamma

matrix.

 6.4 Mechanical Response to Aging


 The microhardness data shown in Figure 5.32 are now

mostly explicable by considering the aging processes that

take place in these two alloys. In RSR 197 aged at 760 C,

the alloy begins to order immediately following the

quench. The D022 and Dla phases continue to order during

aging, and the gamma matrix becomes essentially fully

ordered after 100 hours at the aging temperature. The

increase in hardness correlates with this ordering trend.