5.1.6.2 Solution Heat Treated. Quenched and Aged
 at 810 C for up to 100 Hours


 The predominant phase at this aging temperature is

the Pt2Mo phase. After one hour at 810 C, Pt2Mo is

densely distributed throughout the gamma matrix. Figures

5.22a and 5.22b are dark field images taken using two of

the six visible Pt2Mo variants. These two variants are

described in Figure 2.21.

 The morphologies of the Pt2Mo precipitates are very

much dependent on their crystallography. The two visible

variants and their relationship to the gamma prime cube

axes are described schematically in Figure 2.21. These

lenticular shaped Pt2Mo precipitates are actually

platelets with [1103 habits (Saburi et al., 1969). Figure

5.23a is a B = [0013, g = 1/3(220) image. If the sample

is rotated 54.7 degrees from this orientation about the

axis described in the figure to the B = [111] orientation

and the 1/3 (220) again used to form the image, an image

like that shown in Figure 5.23b results. The plate-like

nature of the precipitate is very apparent by comparing

these two figures. It is likely that all six Pt2Mo

variants can co-exist simultaneously in any given gamma

region.

 The Pt2Mo Ni2Mo precipitates grow with time, as shown

in Figure 5.24a, a B = [001], g = 1/3(420) dark field

image of the Pt2Mo phase after 100 hours at 810 C. There


_________________ J