Precipitate evolution in the early stages of ageing in Inconel 718 investigated using small-angle x-ray scattering

Abstract

Microstructural evolution during the early stages of ageing (less than one hour) in a Ni–Cr–Fe based superalloy Inconel 718 (IN718) has been investigated using Small-Angle X-ray Scattering (SAXS). The effects of precipitate kinetics on the precipitate size distribution are compared indirectly with SAXS measurements by using Vickers microhardness data. The microhardness increased after 4min of ageing at a temperature of 760°C, although the recorded SAXS data did not reveal the precipitate size distribution. This indicates that the precipitates had not evolved enough to be detected, but still a small number of precipitates increased the yield strength. After ageing the alloy for the shortest period for which data were available, 8min, clear evidence of precipitates could be found from the SAXS data, showing that the γ″- precipitates are about 6nm in width and 3nm in height.