The Effect of Heat Treatment on Tensile Yielding Response of the New Superalloy ABD-900AM for Additive Manufacturing

Abstract

The heat treatment response of the new superalloy ABD-900AM, designed specifically for additive manufacturing (AM), is studied. The as-fabricated microstructure is characterised at multiple length-scales including by X-ray synchrotron diffractometry and transmission Kikuchi diffraction imaging. The very high cooling rates arising during the process suppress γ′ precipitation; thus the details of heat treatment are shown to be important in establishing properties. The yield stress and tensile strength developed are marginally improved by super-solvus rather than sub-solvus heat treatment, but the ductility is then compromised. The tensile behaviour is superior to the heritage alloy IN939 which has a comparable fraction of γ′; this is due to the larger refractory content of ABD-900AM and its finer scale precipitation. The internal strains developed during processing are sufficient to promote recrystallization during super-solvus heat treatment which breaks down microstructural anisotropy and promotes grain growth; however, this effect is absent for the sub-solvus case.