Twinning mediated cryogenic toughness in an additively manufactured high Mn steel by manipulating stacking fault energy

Abstract

The insufficient cryogenic toughness of wire-arc additively manufacturing (WAAM) component hinders their application in cryogenic fields. We report that tungsten is effective in enhancing the impact toughness of WAAM components, increasing it from 42 to 106J at 77K. The outstanding cryogenic toughness depends on the interaction between dislocations and twins, where the thickness of twins plays a pivotal role in determining whether they hinder or facilitate dislocation movement. Twins below 6.1nm hinder dislocations, impeding deformation, while those exceeding 21.7nm coordinate with the matrix orientation, aiding dislocation movement and forming microbands. The W element reduces the critical twinning stress from 112.3 to 83.5MPa by manipulating the stacking fault energy and grain size, thereby altering the twinning structure. However, excessive W content forms large-sized precipitates, serving as crack initiation sites and reducing crack initiation energy.