High-temperature behavior of additively manufactured Haynes 214: Ductility loss and deformation mechanisms transition

Abstract

This article investigates the evolution of mechanical properties in additively manufactured Haynes 214 alloy across temperatures from ambient to 950 °C, focusing on ductility loss and its relation to mechanical strength. Furthermore, it explores microscopic deformation mechanisms that influence mechanical behavior, such as the Portevin–Le Châtelier (PLC) effect and grain boundary cracking. This study reveals that up to $\approx$650 °C, strain hardening and the PLC effect dominate due to dislocation-solute interactions, while grain boundary cracking becomes prominent above $\approx$ 600 °C, coinciding with negligible slip activity within the grains. Specimens tested at ambient temperature show considerable texture evolution and grain distortion, whereas those tested at 650 °C and 870 °C show no evidence of texture evolution or grain distortion but instead grain boundary cracking. At temperatures above $\approx 900°C$, the activation energy of the slip systems decreases significantly, allowing plastic deformation to be accommodated through a combination of Orowan dislocation bypassing mechanisms and grain boundary deformation and cracking, which partially restores ductility. Experiments with varying sample thicknesses (1 mm–2.5 mm) at ambient, 650 °C, and 870 °C reveal that thinner samples, with smaller grains and larger relative grain boundary areas, show distinct changes in serrated plastic flow, ductility loss, and strength degradation. Enhanced PLC formation in thinner samples compared to thicker ones at the same temperature, combined with reduced ductility, underscores the critical role of grain boundary deformation and cracking in ductility loss at elevated temperatures.