# Intrinsic Strain Aging, $\Sigma 3$ Boundaries, and Origins of Cellular Substructure in Additively Manufactured 316L

## TL;DR

This paper investigates the formation mechanisms of cellular substructures in additively manufactured 316L stainless steel, revealing a complex interaction of intrinsic strain aging, boundary effects, and diffusion processes that influence mechanical properties.

## Contribution

It provides the first direct evidence of a combined mechanism involving strain aging, Cottrell atmospheres, and boundary diffusion, challenging previous hypotheses about cellular structure formation.

## Key findings

- Cellular features correlate with enhanced mechanical strength.
- Intrinsic strain aging influences substructure formation.
- Multiple phenomena act together to produce cellular features.

## Abstract

The observation of sub-grained cellular features in additively manufactured (AM)/selectively laser melted (SLM) 316L stainless steel components has remained an interesting, though incompletely understood phenomenon. However, the recently observed correlation linking the presence of these features with significantly enhanced mechanical strength in SLM 316L materials has driven a renewed interest and effort toward elucidating the mechanism(s) by which they are formed. To date, the dominant hypothesis, cellular solidification followed by dislocation-solute entanglement, remains incompatible with the ensemble of reported observations from multiple independent studies. This effort offers direct evidence of a previously unrecognized interaction of phenomena, that, when acting in concert, give rise to this commonly observed substructure. These phenomena include SLM-induced intrinsic strain-aging, Cottrell atmosphere formation, and twin-boundary enhanced mass diffusion to structural defects.