Abstract
Impurities segregated to grain boundaries of a material essentially alter its fracture behavior. A prime example is sulfur segregation-induced embrittlement of nickel, where an observed relation between sulfur-induced amorphization of grain boundaries and embrittlement remains unexplained. Here, 48x10(6)-atom reactive-force-field molecular dynamics simulations provide the missing link. Namely, an order-of-magnitude reduction of grain-boundary shear strength due to amorphization, combined with tensile-strength reduction, allows the crack tip to always find an easy propagation path.
Highlights
In the case of sulfur (S) segregation-induced embrittlement of nickel (Ni), which is important for the development of next-generation nuclear reactors [8], Heuer et al performed tensile tests of notched specimens with varying amount of S segregation to grain boundaries (GBs) [3]. (The maximum range of S segregation was determined to be 0.5 nm on either side of a GB.) They observed a transition from transgranular ductile fracture to intergranular brittle fracture at a critical S concentration of 15:5 Æ 3:4% at GBs
We perform large molecular dynamics (MD) simulations based on reactive force fields (REAXFF) [13,14], which are trained and validated (Supplementary Tables S1 and S2, [10]) by quantum-mechanical calculations based on the density functional theory [15], in order to study the effect of S segregation in nanocrystalline Ni
To study the effect of S-induced GB amorphization on the fracture behavior of Ni, we perform REAXFF MD simulations for two systems: Pure Ni nanocrystal (NC-Ni) and Ni nanocrystal with 20% S-doped GB layers of thickness 0.5 nm (NC-Ni þ 20%S) [17]
Summary
Impurities segregated to grain boundaries of a material essentially alter its fracture behavior. The modification of chemical bonds due to a small amount of impurities segregated to grain boundaries (GBs) controls the mechanical properties of materials [1].
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