The stability of carbides in Nimonic 80A

The stability of carbides during the commercial heat treatment of Nimonic 80A has been investigated. This involved a detailed study into the kinetics of dissolution and discontinuous precipitation. As a result, stricter controls of solution and ageing treatments have been proposed as a route to enhance the properties of existing nickel-based superalloys. Solution treatment above 1000°C was investigated by weighed extraction of carbide particles using electro-chemical dissolution of the matrix. Subsequent X-ray diffractometry revealed the proportions of the respective phases present in the alloy. This permitted a direct determination of phase stabilities in the form of solubility constants. Also, lightly etched cross-sections of the bulk samples were examined in SEM to compare particle and grain boundary distributions. [Continues.]