PHASE-EQUILIBRIA AND MICROSTRUCTURAL CONTROL IN THE NI-CO-AL SYSTEM

This paper is a report of the results of investigations on the phase e quilibria among gamma (Al), and gamma' (L1(2)) and beta(B2) phases, be ta --> beta' (L1(0)) martensitic transformation temperatures, and micr ostructural features of multi-phase alloys fabricated through various thermo-mechanical processes in the Ni-Co-Al system. The isothermal sec tion diagrams and tie line configurations of 900, 1100 and 1300 degree s C was determined by energy dispersion X-ray spectrometry (EDX) analy sis. The Ms temperature was measured by differential scanning calorime try (DSC) analysis and a contour of iso-Ms composition lines was deter mined. On the basis of this information, the various types of microstr ucture of beta + gamma, beta + gamma' and beta + gamma + gamma' phases was obtained through thermo-mechanical treatment. Morphological featu res of the multi-phase alloys with fine blocky, plate, Widmanstatten a nd lamellar structures was discussed in connection with heat-treatment , phase diagram and martensitic transformation. Mechanical properties were also examined and a good combination of strength and ductility wa s obtained in the multi-phase alloys. Copyright (C) 1996 Elsevier Scie nce Ltd.