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National Advisory Committee for Aeronautics, Report - Survey of Portions of the Chromium Cobalt Nickel Molybdenum Quaternary System at 1,200°C

A survey was made of portions of the chromium-cobalt—
nickel—molybdenum quaternary system at 1,200° 0 by means of
microscopic and X-ray difi’raction studies. Since the face-
centered cubic (alpha) solid solutions form the matrix of almost
all practically useful high-temperature alloys, the solid solu-
bility limits of the quaternary alpha phase were determined up
to :20 percent molybdenum. The component cobalt-nickel—
molybdenum, chromium-cobalt—molybdenum, and chromium-
nickel-molybdenum ternary systems were also studied. The
survey of these systems was confined to the detefinination of the
boundaries of the face-centered cubic (alpha) solid solutions and
of the phases coexisting with alpha at 1,200° 0.

In the development of technologically useful alloys it is
usually of considerable help if the phase relationships and
solid solubility limits are known. At the Metallurgy De-
partment of the University of Notre Dame a project has
been in progress for some years to determine the phase
relationships in alloy systems involving chromium, cobalt,
nickel,.iron, and.molybdenum, the transition elements of
greatest importance in high-temperature alloys.

The determination of phase diagrams for systems of four
or more components is an extremely laborious task. The
problem must be approached in a systematic manner in
order to avoid becoming hopelessly lost. The best method
of attack is to begin by establishing the phase relationships
in systems of two or three components and then continue by
adding one new element at a time. The problem of pre—
senting quantitative phase relationships diagrammatically
for systems of three or more components necessitates holding
one or more thermodynamic variables constant.

For example, a ternary phase diagram may be presented as a series of
isothermal sections or as a series of sections in each of which
the amount of one component is held constant. For a qua-
ternary system it is necessary to hold both temperature and
the amount of one component constant in order to obtain
two-dimensional diagrams. The temperature 1,200° C
was chosen as that at which an initial isothermal survey could
be most profitably made. This temperature is of immediate
interest because it lies within the range of solution treat-
ment for most high-temperature alloys now in use and also
because here diffusion rates are fast enough to allow equilib-
rium conditions to be approached in reasonably short
annealing periods.