Characterization of fine, ordered γ' precipitates, precipitation-hardening and softening phenomena in superalloy 693

Superalloy 693 is a Ni-based, austenitic, precipitation-hardenable type alloy that finds applications in aggressive environments at elevated temperatures, At high temperatures, hardening of this alloy is induced by fine, ordered, face centered cubic (fcc), Ni₃AI type precipitates (γ'), whereas softening is caused by coarsening of these γ' precipitates. This presentation highlights results of our earlier work on initial stages of hardening involving characterization of γ' phase with X-ray diffraction (XRD) and transmission electron microscopy (TEM). It also highlights new findings on softening phenomenon. In this presentation, details of analysis involving differentiation of γ' phase and M₆C type phase by deconvolution at initial stages of hardening, modelling of softening phenomenon using the equation H(t)=H₁t^P (where H, t, P are hardness, ageing time and negative exponent of time respectively) showing the hardness to increase to a maximum with time and then drop after 1.5 h at 973 K/1073 K/1173 K will be discussed. (author)