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The direction of ridge of thermal conductivity contours in a ternary γ′-Ni 3 Al phase agrees with that of solubility lobe of γ′ phase in a ternary phase diagram. The classification of third elements based on the ridge direction does not always agree between ternary Ni 3 Al and NiAl phases.

Thermal conductivities are measured for a series of Ni 3 X and Pt 3 X compounds in which an ordered L1 2 and f.c.c. disordered structures are formed when the constituent X belongs to the first long period in the periodic table. An empirical rule is found for both ordered and disordered structures that the thermal conductivity tends to decrease as the distance of the constituent X increases in the horizontal direction from the location of Ni and Pt in the periodic table. This trend is quite isomorphic with that of dilute solid solutions of Ni-X or Pt-X, although the magnitude is different. For most Ni 3 X and Pt 3 X compounds, thermal conductivity increases with increasing temperature. The temperature coefficient of thermal conductivity is higher in the disordered compounds than in the ordered compounds.