Oxidation assisted intergranular cracking under loading at dynamic strain aging temperatures in Inconel 718 superalloy

It is well established that 718 superalloy exhibits brittle intergranular cracking when deformed under tension at temperatures above 600 degrees C. This embrittlement effect is related with grain boundary penetration by oxygen (Oxygen Assisted Intergranular Cracking - OAIC). Simultaneously, impacting on its mechanical properties, the precipitation of coherent gamma' and gamma '' phases occur above 650 degrees C and Dynamic Strain Aging (DSA) occurs in the temperature range between 200 and 800 degrees C. Although literature indicates that OAIC is the mechanism that controls mechanical properties at high temperatures, its interactions with DSA and precipitation are still under discussion. The objective of this work is to investigate the interactions between the embrittlement phenomena (OAIC and DSA) and the hardening mechanism of gamma' and gamma '' precipitation on the mechanical properties of an annealed 718 superalloy. Tensile tests were performed at a strain rate of 3.2 x 10(-4) s(-1) under secondary vacuum, in temperatures ranging from 200 to 800 degrees C. Fracture surfaces were observed by scanning electron microscopy (SEM) and precipitation by transmission electron microscopy (TEM). The effect of DSA and precipitation on the strength and of OAIC on the ductility was verified. (C) 2015 Elsevier B.V. All rights reserved.