172
For RSR 209, the values for the gamma prime phase are
76.8 + .8 at. % Ni, 5.04 + 1.8 at.% Mo, and 18.2 + 1.2 at.%
A1. For the gamma phase, these values are 77.2 + 3.39
at.% Ni, 17.3 + 2.1 at.% Mo, and 5.5 + 2.4 at.% A1. These
averages are similar to those measured by Miracle et al.
(1984) for the equilibrium gamma and gamma prime phase
compositions that were determined in their study of
Ni-Mo-Al ternary alloys.
The EDX data defines the ternary composition of the
gamma phase in which the nonequilibrium precipitation is
observed. This ternary composition is similar in both
alloys and somewhere between the N3M0 stoichiometry and
N4M0 stoichiometry, assuming that the Al enters into the
ordering reactions.
The partitioning of Al to the gamma matrix lends
further credence to the fact that Al influences the
precipitation behavior in RSR. 197, RSR 209, and alloy //17
since DO22 phase was almost never observed in aged Ni-Mo
binaries of any stoichiometry (see Section 2.2.5). The
exception was in the work of Van Tendeloo et al. (1975) in
which DO22 phase precipitated when the alloy was very
rapidly quenched. Under these circumstances, the DO22
phase was only transient, described as a transition phase
between short range order and the more stable N4M0/N2M0
phases. In both RSR alloys and in the ternary alloy //17,
the DO22 is obviously not transient.