Spall damage of Invar alloys under shock loading: Interplay between segregation bands, grain boundaries and deformation twins

• Elemental segregation bands influence the spall strength and damage extent of Invar alloys. • Segregation bands constrain the growth of voids, with voids preferentially nucleating in Fe-rich regions. • Deformation twins primarily form at grain boundaries but do not serve as new nucleation sites for voids. The nucleation of voids and the growth of deformation twins are two independent stages, both acting as mechanisms for stress relief. • The coupled effects of segregation bands, grain boundaries, and deformation twins govern the dynamic fracture behavior of the alloy. Segregation bands modulate damage, with voids nucleating at grain boundaries and twinning occurring near voids and cracks. This work investigates the effect of elemental segregation bands on the spallation damage behavior of Invar 36 alloys. Plate impact recovery experiments and postmortem characterizations, as well as molecular dynamics simulations considering anisotropic segregation band structures, are conducted to reveal the underlying mechanisms. Both experimental and simulation results reveal that the orientation of the segregation bands affects the spall strength and the evolution of damage nucleation in Invar 36 alloys. Voids tend to nucleate at both Fe-rich regions and grain boundaries, with the proportion of intragranular voids increasing as the impact velocity rises. The spatial density distribution and morphologies of voids are strongly affected by the segregation bands. Abundant staggered deformation twins are found in the adjacent of the voids. This work presents a comprehensive and in-depth investigation of the coupled effects of various factors including elemental segregation, grain boundaries and deformation twinning, giving us a better understanding of the dynamic spall mechanisms of Invar 36 alloys and directions for design and optimization of new materials.