Deformation mechanisms of Inconel-718 at the nanoscale by molecular dynamics

A Faiyad and MAM Munshi and MM Islam and S Saha, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 23, 10650-10661 (2021).

DOI: 10.1039/d0cp06614a

Ni-based super alloy Inconel-718 is ubiquitous in metal 3D printing where a high cooling rate and thermal gradient are present. These manufacturing conditions are conducive to high initial dislocation density and porosity or voids in the material. This work proposes a molecular dynamics (MD) analysis method that can examine the role of dislocations, cooling rates, voids, and their interactions governing the material properties and failure mechanisms in Inconel-718 using the Embedded Atom Method (EAM) potential. Throughout this work, three different structures - nanowires (NWs), nanopillars (NPs), and thin- plates - are used. The strain rate is varied from 10(8) s(-1) to 10(10) s(-1) and the temperature is varied from 100 K to 800 K. Different cooling rates ranging from 0.5 x 10(10) K s(-1) to 1 x 10(14) K s(-1) are applied. Our results suggest that the high cooling rates create regular crystalline structures which result in high strength and ductility. In contrast, the lower cooling rates form a non-crystalline structure that exhibits low strength and a brittle nature. This brittle to ductile transition is observed solely due to the cooling rate at the nanoscale. Elimination of voids as a result of heat treatment is reported as well. Shockley dislocation is observed as the key factor during tensile plastic deformation. Increasing strain rates result in strain hardening and a higher dislocation density in tension. Our computational method is successful in capturing extensive sliding on the 111 shear plane due to dislocation, which leads to necking before fracture. Furthermore, notable mechanical properties are revealed by varying the temperature, size and strain rate. Our results detail a pathway to design machine parts with Inconel-718 alloy efficiently in a bottom-up approach.

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