Shearing Mechanisms and Complex Particle Growth in Nickel Superalloy 718

Abstract

Alloy 718 is a -strengthened Ni-base disk superalloy used in the aerospace industry, and it has been used prominently for decades.Though there has been extensive research into the processing/property relationships, there is very little known about the intermediate microstructure and mechanisms that are common in commercial 718 that dictate the yield strength.A variety of analytical techniques, including scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) were employed to investigate the microstructure of alloy 718 after various deformed conditions and heat treatment conditions.The in alloy 718 following a commercial heat treatment was found to have both monolithic particles as well as composite particles in which and share a planar phase boundary.Isothermal heat treatments were applied to solutionized samples, and it was found that low heat treatment temperatures produced a large percentage of composite particles, but high temperatures led to the formation of a primarily monolithic structure.Additionally, these composite particles were shown to have a desirable stabilizing effect at high temperatures, and they were seen to grow much more slowly than their monolithic counterparts.STEM analysis was able easily show the morphology of any edge-on