Effects of Minor Chemistry Variations on the Structural and Mechanical Behaviour of Alloy 718

Abstract

Three chemistry variants of alloy 718 were prepared a t laboratory scale by vacuum induction melting followed by vacuum arc remelting. The first alloy contained 2% cobalt and iron was reduced by a similar amount. In the second alloy variant 2% cobalt was added a t the expense of nickel and the third alloy was modified by adding 0.02% cerium.. The billets of the modified alloys and also the s tandard alloy were processed to prepare 12.5 m m diameter bars that were subjected to conventional heat treatment. Tensile and stress rupture properties of the four alloys were evaluated under different conditions. Replacement of iron by cobalt did not produce any noticeable effect on the tensile and stress rupture properties and reduction in nickel was also found to produce marginal effect on these properties. The cerium modified alloy, however, showed significant increase in the stress rupture properties. The reasons for this mechanical behaviour have been examined with the help of transmission electron microscopy and a re discussed.