Age hardening behaviour of Alloy 693

This paper reports the hardening behaviour of nickel base superalloy Alloy 693. The alloy is designed to derive its strength primarily from the precipitation of coherent γ' phase particles, induced by the addition of Al and Ti, in a face centered cubic matrix of Ni-Cr-Fe solid solution. The alloy possesses excellent combination of mechanical strength, corrosion and oxidation resistance properties at elevated temperatures. In the present work, uni-modal distribution of γ' particles is precipitated out during isothermal annealing of the alloy in the temperatures range 800 °C to 950 °C for time periods ranging from 0.5 h to 100 h. Variations in room temperature hardness and tensile properties of aged alloys have been correlated with precipitation behaviour of the γ' phase. These studies have been carried out in an Instron tensile testing machine in conjunction with microstructural characterization by electron microscopy. Mechanisms responsible for precipitation hardening of the alloy under different microstructural conditions have been identified on the basis of minimum critical resolved shear stress computed theoretically for competing mechanisms.