Evaluation of Heat Capacity and Resistance to Cyclic Oxidation of Nickel Superalloys

Paper presents the results of evaluation of heat re sistance and specific heat capacity of MAR-M-200, MAR-M-247 and Rene 80 nickel superalloys. Heat resistance was evaluated using cy clic method. Every cycle included heating in 1100°C for 23 hours and cooling for 1 hour in air. Microstructure of the scale was observ ed using electron microscope. Specific heat capacit y was measured using DSC calorimeter. It was found that under conditions of cyclically changing temperature alloy MAR-M-247 exhibits highest heat resistance. Formed oxide scale is heterophasic mixture of alloy ing elements, under which an internal oxidation zon e was present. MAR-M-200 alloy has higher specific heat capacity compared to MAR-M-247. For tested alloys in the temperature range fr om 550°C to 800°C precipitation processes ( γ′ , γ′′ ) are probably occurring, resulting in a sudden inc rease in the observed heat capacity.