Serrated yielding in alloy 718

Alloy 718 has been reported to undergo Serrated Yielding (SY) phenomenon over the temperature regime that coincides with its useful service temperature range. The SY is reported to reduce ductility in several alloy systems. The present paper reports the results of detailed investigation carried out on SY phenomenon in Alloy 718 in three different microstructural conditions viz. Solution Annealed (ST), y'' precipitated (STA) and d precipitated (DELTA). Based on the estimated activation energy for appearance and disappearance of serrations as well as the nature of serrations, two regimes of Dynamic Strain Ageing (DSA) have been identified – one below 525°C controlled by diffusion of interstitial carbon and the other above 525°C controlled by diffusion of substitutional niobium atom. The initial microstructure appeared to strongly influence the temperature regime of serrated flow. The mechanism for the delayed disappearance of serrations in ST specimens has been identified from TEM examination of deformed specimens. (AU) © 2010 by The Materials, Metals, & Materials Society. All rights reserved.