A new method for estimating the composition of equilibrium phases has been developed based on the experimentally determined two phase region of the Ni-Al-Cr-Mo-Ti-W system at 850℃. The following general formula is proposed for the method :
$\vec{P}=\vec{A}+\mid{\bec{AP}}\mid·\vec{U}$
where $\vec{P}$ = composition of equilibrium phase expressed as position vector, $\vec{A}$= composition of alloy expressed as position vector, $\mid{\vec{AP}}\mid$ = magnitude of vector connecting the $\vec{A}$ and $\vec{P}$, $\vec{U}$ = unit vector of $\vec{AP}$,$\mid{\vec{AP}}\mid$ and $\vec{U}$ are estimated from composition of the alloy.
In order to check the validity of the two phase boundary reported earier, Ni-base superalloys, of which composition lie near the boundary have been examined. Alloys of eight compositions have been melted under vacuum and heat treated 4-5 h at 1190℃ for homoneization, and it has been aged at 850℃ for 800 h. The alloys have the following compositions in at. pct: Al = 1.5 % and 2.5 %, Cr = 12 % and 16 %, Mo = 0 %, Ti = 1 %, W = 6 % and 10 %.
Microstructures of heat treated specimens and X-ray diffraction patterns of extraction residues have been analyzed qualitatively.
It is found that the present result is in qualitative agreement with the Gamma-Gamma Prime region of the Ni-Al-Cr-Mo-Ti-W system at 850℃ as reported in the literature.
