Characterization of γ′ Precipitation Behavior in Additively Manufactured IN738LC Superalloy via In-Situ Small-Angle Neutron Scattering

In the present study, quantitative evaluation of the size and volume fraction of γ′ particles have been studied by Small-Angle Neutron Scattering (SANS) and FE-SEM in additively manufactured IN738LC Superalloy employing isothermal heat treatment conditions at 850 ℃. The results show that there is no observable γ′ precipitation in the as-deposited alloy, while a large number of small cellular and striated sub-structures can be characterized with widths ranging from 0.5 to 1.5 μm. During the 850 ℃ isothermal heat treatment, the γ′ phase rapidly precipitates in large quantities and shows a unimodal irregular sphere-like shape. The average size of the γ′ particles increases with longer aging times. After 10 min of isothermal heat treatment the average γ′ particle size is 72.5 nm. This average size increase to 137.3 nm after 120 min of ageing. However, the volume fraction (VF) of γ′ precipitates does not change after 10 min of isothermal heat treatment time, at which point the VF % reaches about 40%. This result varies significantly from IN738LC that was prepared by traditional casting processes.