EFFECT OF TERNARY ADDITION ON THE FORMATION OF CU3PT AND CUPT ORDER PHASES IN THE CU-PT SYSTEM

The effect of addition of ternary elements, mainly In and Pd, on the p hase fields of Cu3Pt with the L1(2) type of ordered structure and CuPt with an L1(1) type of ordered structure in the Cu-Pt system has been investigated and the results compared with the substitution behaviour of the added elements and the electron-atom (e/a) ratio of the alloys. Electrical resistivity measurements and structural analysis by X-ray diffraction reveal that the addition of In leads to a shift of the pha se field of the Cu3Pt towards the higher temperature regime and: the P t-rich side, and to a shift of the phase field of the CuPt towards the lower temperature regime and the Pt-rich side in the phase diagram of the Cu-Pt system. In contrast, the addition of Pd leads to a shift of the phase fields of both Cu3Pt and CuPt towards the lower temperature regime and the Cu-rich side. However, by plotting these phase fields on a temperature-e/a diagram, it is seen that the range of e/a ratio f or each phase field is about 0.71-0.97 for the Cu3Pt phase and about 0 .25-0.71 for the CuPt phase irrespective of the kind and amount of the added element.