Spinodal decomposition in Co-3 Ti(wt.%) alloy

Abstract

Spinodal decomposition in Co-3 Ti (wt.%)alloy and its mechanical properties including fracture characteristics as a function of heat-treatment have been studies using experimental techniques such as optical microscopy, TEM, SEM and Instron testing machine. The alloy was quenched from 1473K and aged at 873K and 973K. On ageing at 973K for 15 days, the periodic arrangement of cuboid preci-pitates was seen under transmission electron microscope. This can be taken an indication that this alloy undergoes spinodal decomposition and the coherent spinodal tempe-rature is above 973K. The maximum hardness and yield stress values were obtained from specimens aged at 873K for 24 hours while the maximum ultimate tensile stress was obtained from the specimen aged at 873K for 48 hours. It appears that the hardness and strength are related to coherency strains at shorter times and the precipitate spacing at longer times. The examination of fractured surface by SEM revealed some evidence of dimple charac-teristic of ductile failure but a major portion of the sample showed evidence for intergranular brittle fracture, which account for lower ductility values reported in the present investigation.