Mechanistic modeling of strengthening and stress corrosion cracking in LPBF SS 316L-AL2O3 metal matrix nanocomposites

Abstract

A microstructure-resolved electro-chemo-mechanical framework is developed to investigate strengthening and stress corrosion cracking (SCC) in laser powder bed fusion (LPBF) 316L stainless steel reinforced with Al2O3 ceramic nanoparticles. The framework, implemented in the MOOSE finite element platform, couples three physics: finite-strain crystal plasticity for the austenitic matrix, linear elasticity with a Rankine upper-bound stress limit criterion for ceramic inclusions, and a thermodynamically consistent Allen–Cahn phase-field model for SCC evolution. Electrochemical dissolution is described through Butler–Volmer kinetics, while the interaction between mechanical deformation and corrosion is incorporated through a slip-dependent interfacial mobility that represents passive-film rupture and accelerated local dissolution. Simulations are performed on two-dimensional representative microstructures of pure LPBF 316L and Al2O3 reinforced nanocomposites. Mechanical results show that Al2O3 particles impose kinematic constraints that force crystallographic slip to localize within confined matrix ligaments, increasing kinematic efficiency and accelerating strain hardening through an Orowan strengthening mechanism. SCC simulations demonstrate that reinforcement delays the pit-to-crack transition, reduces degradation depth, and alters crack morphology through particle shielding, crack deflection, and localized branching. These results demonstrate that particle size, content, and spatial distribution play critical roles in governing the balance between mechanical strengthening and SCC resistance in LPBF 316L nanocomposites.