[Paper Review] The effect of the misfit dislocation on the in-plane shear response of the ferrite/cementite interface

Jaemin Kim, Keonwook Kang+1 more|arXiv (Cornell University)|May 4, 2018

Microstructure and Mechanical Properties of Steels30 references3 citations

TL;DR

This study investigates the in-plane shear response of ferrite/cementite interfaces (FCI) in pearlitic steel using atomistic simulations and the extended atomically informed Frank-Bilby (xAIFB) method. It reveals that the misfit dislocation's Burgers vector magnitude and core width govern plasticity, with Isaichev and Near Bagaryatsky orientations showing dislocation-mediated deformation, while Near Pitsch-Petch exhibits shear fracture across all directions.

ABSTRACT

Although the pearlitic steel is one of the most extensively studied materials, there are still questions unanswered about the interface in the lamellar structure. In particular, to deepen the understanding of the mechanical behavior of pearlitic steel with fine lamellar structure, it is essential to reveal the structure-property relationship of the ferrite/cementite interface (FCI). In this study, we analyzed the in-plane shear deformation of the FCI using atomistic simulation combined with extended atomically informed Frank-Bilby (xAIFB) method and disregistry analyses. In the atomistic simulation, we applied in-plane shear stress along twelve different directions to the ferrite/cementite bilayer for Isaichev (IS), Near Bagaryatsky (Near BA) and Near Pitsch-Petch (Near PP) orientation relationship (OR), respectively. The simulation results reveal that IS and Near BA ORs show dislocation-mediated plasticity except two directions, while Near PP OR shows mode II (in-plane shear) fracture at the FCI along all directions. Based on the xAIFB and disregistry analysis results, we conclude that the in-plane shear behavior of the FCI is governed by the magnitude of Burgers vector and core-width of misfit dislocations.

Motivation & Objective

• To understand the mechanical response of ferrite/cementite interfaces (FCI) in fine lamellar pearlitic steel under in-plane shear stress.
• To clarify the role of misfit dislocations in determining the deformation mechanism at FCI.
• To compare the shear behavior across three distinct orientation relationships: Isaichev (IS), Near Bagaryatsky (Near BA), and Near Pitsch-Petch (Near PP).
• To establish a structure-property relationship between misfit dislocation characteristics and interfacial plasticity or fracture.

Proposed method

• Atomistic simulations were performed on ferrite/cementite bilayer structures under in-plane shear stress applied along twelve different crystallographic directions.
• The extended atomically informed Frank-Bilby (xAIFB) method was used to model and analyze the misfit dislocations at the interface.
• Disregistry analysis was applied to characterize the atomic displacement and interfacial structure evolution under shear.
• Simulations were conducted separately for three orientation relationships: IS, Near BA, and Near PP, to compare their mechanical responses.
• The Burgers vector magnitude and core width of misfit dislocations were quantified and correlated with observed deformation modes.
• Stress-strain responses were analyzed to distinguish between dislocation-mediated plasticity and mode II fracture.

Experimental results

Research questions

• RQ1 How does the orientation relationship (IS, Near BA, Near PP) influence the in-plane shear response of the ferrite/cementite interface?
• RQ2 What is the role of misfit dislocation characteristics—specifically Burgers vector magnitude and core width—in determining the deformation mechanism at the FCI?
• RQ3 Why does the Near Pitsch-Petch orientation relationship exhibit mode II fracture across all shear directions, unlike the other two?
• RQ4 To what extent do dislocation-mediated plasticity and interfacial fracture dominate under in-plane shear loading?
• RQ5 How do disregistry patterns correlate with the observed mechanical behavior in different orientation relationships?

Key findings

• The Isaichev (IS) and Near Bagaryatsky (Near BA) orientation relationships exhibit dislocation-mediated plasticity under in-plane shear stress, except for two specific loading directions.
• The Near Pitsch-Petch (Near PP) orientation relationship undergoes mode II (in-plane shear) fracture at the ferrite/cementite interface regardless of the shear direction applied.
• The magnitude of the Burgers vector and the core width of misfit dislocations are critical factors governing the transition between plasticity and fracture at the interface.
• Disregistry analysis confirms that the interfacial structure evolves differently under shear depending on the orientation relationship, with higher disregistry associated with plastic deformation.
• The xAIFB method successfully models the misfit dislocation structure and explains the observed mechanical behavior in terms of dislocation core characteristics.
• The study establishes a direct link between misfit dislocation microstructure and interfacial mechanical response, providing a predictive framework for interface design in pearlitic steels.