Molecular dynamics simulation study on impact of interface chemistry on pearlite mechanical response

The molecular dynamics (MD) simulation method was adopted to explore impact of interface chemistry on pearlite mechanical response of Bagaryatskii orientation relationship between ferrite and cementite. By changing terminal surface types of cementite at ferrite-cementite interface, this study analyzed influence of interface chemistry on pearlite peak stress and plastic deformation behavior, as well as strain transmission between two phases (ferrite and cementite) during stretching process. Two horizontal directions parallel to pearlite interface were considered as loading directions respectively. The results show pearlite will experience inelastic deformation due to atomic slip in ferrite phase. When terminal surface of cementite at interface is FeC-Fe, the atomic slip in ferrite is the most difficult to occur, and inelastic deformation shall be suppressed. At this time, pearlite produces the largest peak stress. Types of terminal surface and loading direction will affect slip systems activated in ferrite. Stretching along 100θ direction: for pearlite with Fe-FeC and Fe-Fe cementite terminal surfaces at interface, S1 ({112} 〈111〉) slip system in ferrite is activated. While terminal surface is FeC-Fe pearlite, what is activated is S2 slip system ({110} 〈111〉) in ferrite. Stretching along 010θ direction: regardless of types of terminal surface, slip systems activated are Type S2. Compared with S1 slip system, activation of S2 slip system makes is easier for plastic deformation in ferrite to pass through ferrite-cementite interface to the cementite.


Introduction
Characterized by good mechanical properties and low production cost, carbon steel is most widely applied material in modern society [1].It is well-known that macro mechanical properties of carbon steel are determined by microstructure [2].Therefore, it is significant to enhance mechanical properties through understanding relationship between microstructure and macro mechanical properties.Pearlite structure, composed of alternating layers of ferrite phase and cementite, is one of the most common structures in carbon steel [2][3][4][5].In recent decades, pearlite structure is extensively studied [6][7][8][9][10][11][12][13][14].However, existing studies mainly focus on factors at macro level, such as influence of processing technology and alloy elements on size of pearlite colony and interlamellar spacing of pearlite [6][7][8][9][10][11]; relationship between size of pearlite colony and interlamellar spacing with macro mechanical properties.According to results, pearlite ductility will be affected by pearlite colony size [12], and there is a Hall-Petch type relation between interlamellar spacing and pearlite strength [13,14].
Development of detection methods and computer simulation technology pushes research on pearlite from macroscale to mesoscale and even nanoscale.Experimental studies prove five common crystallographic orientation relationships (OR) [15][16][17][18] are found between ferrite and cementite at interface: Bagaryatskii OR, Isaichev OR, Pitsch-Petch OR, Near Pitsch-Petch OR and Near Bagaryatskii OR.Moreover, atomic simulation method was used to investigate interfacial energy and interface structure of each orientation relationship [15,19].It is found that when there is Isaichev OR between ferrite and cementite at interface, interfacial energy of ferrite-cementite interface is low in pearlite [19].But no consensus has been reached on which of five orientation relationships is most likely to occur at interface [20].Due to lattice mismatch between ferrite phase and cementite, dislocation is usually produced at interface to reduce mismatch strain of interface.At the same time, when crystal orientation relationships at interface are different, dislocation structure at interface will be significantly diverse [21].Some studies have shown interface dislocation structure dramatically affects transmission behavior of plastic deformation from ferrite to cementite [22].Specifically, Shimokawa et al analyze how pearlite properties are influenced by dislocation density of interface.Eventually, they summarize dislocation density will alter activation mode of plastic deformation in pearlite during stretching, affecting macro mechanical properties of pearlite thereby [23].Shimokawa et al [24].Also studied the impact of cementite decomposition on the plastic deformation mediated by the ferrite-cementite interface.The research revealed that the decomposition of cementite at the interface leads to the loss of functionality in the effective dislocation nucleation sites originating from the interface dislocations, resulting in an increase in the yield stress of both ferrite and cementite.Kim analyzed the in-plane shear deformation of the ferrite-cementite interface using atomistic simulation techniques and extended atomically informed Frank-Bilby method, along with disregistry analyses [20].The analysis revealed that the in-plane shear deformation behavior of the interface is controlled by the magnitude of the interface dislocation Burgers vector and the dislocation core width.
From the above studies, it can be seen that the mechanical properties of pearlite are significantly affected by the dislocation structure of the ferrite-cementite interface.It has been proven that interfacial dislocation structures are subject to interface chemistry.When Bagaryatskii OR exists between ferrite and cementite in pearlite, ferrite-cementite interface can be constructed using three different terminal surfaces in cementite structure [25].Hence, type of cementite terminal surface at interface is bound to impact mechanical properties of pearlite.If different termination surfaces play a dominant role, pearlite may display various macroscopic mechanical properties.In other words, if the mechanism of the impact of cementite termination plane type on the mechanical properties of pearlite is understood, it would be possible to control and enhance the mechanical performance of pearlite by adjusting the cementite termination plane type.. Unfortunately, relevant studies are insufficient in this field.
In this study, MD simulation method was applied to probe into effect of interface chemistry on mechanical response and deformation mechanism of pearlite with Bagaryatskii OR between ferrite and cementite.A pearlite model with FeC-Fe, Fe-FeC and Fe-Fe as cementite terminal surfaces at ferrite-cementite interface was built.Two transverse directions parallel to pearlite interface were taken as loading directions respectively.This study elaborately analyzed stress-strain relationship, atomic slip behavior in pearlite, evolution law of interfacial dislocations and change of atomic potential energy at interface during stretching process.Subsequently, it revealed influence mechanism of terminal surface type of cementite and loading direction on pearlite peak stress, plastic deformation behavior, and strain transfer between ferrite and cementite.The research results provide a new idea and theoretical guidance for regulating the mechanical properties of pearlite.

Model establishment
As shown in figure 1, Atomsk program [26] is introduced to construct pearlite model with Bagaryatskii OR [27] between ferrite phase and cementite phase required for simulation calculation.Liyanage et al [28] propose modified embedded atom method (MEAM) potential to explain interaction between atoms.MEAM potential can well disclose basic properties of cementite phase, and it is also one of the most commonly used potential functions when structure and properties of pearlite are studied by molecular dynamics [29][30][31].According to MEAM potential, basic lattice vectors of cementite in x, y and z directions are q l x = 0.447 nm, q l y = 0.508 nm, q l z = 0.666 nm respectively.For ferrite, they are a l x = 0.403 nm, a l y = 0.494 nm, a l z = 0.698 nm respectively.It shows a large lattice mismatch is found between cementite and ferrite in x and y directions.Therefore, a model was built by relying on ferrite and cementite with different cell numbers, in order to reduce mismatch strain at interface.The model size is Lx = 8.4 nm, Ly = 16.2 nm, Lz = 14.0 nm.Finally, mismatch strain at pearlite interface along x and y directions is 0.21% and 0.16% respectively.Out of consideration of computational expense, simulation study is carried out via thickness ratio of ferrite layer and cementite layer / Actually, there is » f 7 z [32] in pearlite, but research has indicated f z does not significantly affect mechanical response mechanism at pearlite interface [23,33].This study aims to reveal how mechanical properties of pearlite are affected by change of cementite terminal surface at interface.Accordingly, pearlite model with » f 1 z is used for simulation calculation, because calculation results will be reliable and representative.

Simulation conditions
In order to eliminate initial stress in the model, this study firstly adopted conjugate gradient method to calculate molecular statics of pearlite model to minimize its energy, Secondly, Constant pressure and temperature (NPT) ensemble was used to relax the model with minimum energy for 20 ps at 5 K. Periodic boundary conditions were set in all dimensions of the model in molecular statics calculation and relaxation.After relaxation, interface dislocations occurred at pearlite interface, with structures similar to those in research of other researchers [19,21,23].Dislocations in both directions were named b1 and b2 respectively, as shown in figure 2. For ease of observation, only atoms with potential energy greater than −4.05 eV were shown in the figure.Relaxed model experienced uniaxial tension at 1 × 10 9 s −1 strain rate among directions of \\ and q a 010 110 .[ ] [ ] \\ For clear and concise expression, loading direction in following shall be indicated by directions of cementite q 100 [ ] and q 010 .[ ] Periodic boundary conditions were suitable for model in all dimensions during stretching.Size of the model was adjusted to ensure stress in other two directions orthogonal to loading direction was 0. The stretching simulation was carried out at 5 K temperature.A low temperature was able to minimize influence of thermal effect on simulation results.This is a common method for such simulations [34][35][36], and simulation calculation time step is 0.002 ps.In this study, large-scale atomic/molecular massively parallel simulator (LAMMPS) program was applied to perform molecular dynamics simulation calculation [34].Furthermore,  open visualization tool (OVITO) [37] assisted in realizing atomic model visualization, common neighbor analysis (CNA) [38] and atomic shear strain calculation [39]., [ ] in elastic deformation stage of pearlite, the stress-strain curves of pearlite with different terminal surfaces are highly consistent.To sum up, change of termination surface type at ferrite-cementite interface produces no significant effect to effective elastic modulus of pearlite.As can be seen from figure 3, under the simulated conditions considered in the study, the pearlite undergoes inelastic deformation after reaching the peak stress during tension.This inelastic deformation leads to a sudden decrease in stress.Regardless of loading direction, peak stress of pearlite with different cementite terminal surfaces is ranked from large to small: FeC-Fe>Fe-FeC>Fe-Fe.Moreover, it can be seen from the figure 3 that after the pearlite is inelastic deformation, the strain continues to increase and the stress oscillates.This may be caused by the formation and recovery of internal defects in pearlite when the strain increases after inelastic deformation.

Elastic plastic response of pearlite
Figure 4 shows stress-strain curve of ferrite phase and cementite phase in pearlite with different cementite terminal surfaces at interface during stretching.From figure 4, it is evident that when the ferrite phase and cementite phase comprising pearlite are subjected to stretching, their stress-strain curves exhibit a similar trend to that of pearlite: initial elastic deformation is followed by inelastic deformation when the stress reaches its peak.Secondly, it can be seen from figure 4 that regardless of the loading direction or the termination surface of cementite, the strain during the inelastic deformation of the ferrite phase is smaller than that during the inelastic deformation of the cementite phase.Therefore, the ferrite phase tends to undergo inelastic deformation prior to the cementite phase during the tensile process.After the ferrite phase undergoes inelastic deformation, the cementite phase continues to exhibit elastic deformation until the strain increases to a certain value, at which point the cementite phase also undergoes inelastic deformation.
Figure 5 shows strain relationship diagram for inelastic deformation in pearlite and internal ferrite and cementite phases when pearlite with different cementite termination surfaces at the interface is stretched along q 100 [ ] and q 010 [ ] directions.As shown in figure, when stretched along q 100 [ ] direction, dependent variable is significantly different between inelastic deformation of ferrite phase and that of cementite phase in pearlite with different terminal surfaces.By contrast, dependent variable is of slight difference under stretching along q 010 [ ] direction.Another important feature showed is that under all simulation conditions, strain when pearlite undergoes inelastic deformation is consistent with that when ferrite phase inside pearlite experiences inelastic deformation.Therefore, it can be inferred that inelastic deformation of pearlite during stretching is caused by inelastic deformation of ferrite phase in pearlite.
Subsequently, research was conducted at atomic dimension to further find inelastic deformation of pearlite under different simulation conditions.Internal atomic morphology of pearlite was visualized when inelastic deformation took place in pearlite initially, as shown in figures 6(a) and (b).In order to highlight main features of   yielding of ferrite near ferrite-cementite interface due to atomic slip.Under all simulation conditions, two slip systems are activated in ferrite: The first referred as mode S1 is {112} 〈111〉 slip system, as shown in figure 6(a); The second referred as mode S2 is {110}〈111〉, as shown in figure 6(b).Figure 6(c) lists types of slip system activated by pearlite stretched with different cementite terminal surfaces.In figure 6(c), types of slip system activated in ferrite will be affected by both loading direction and type of cementite terminal surface.In this study, pearlite with FeC-Fe and Fe-FeC terminal faces of cementite was stretched along q 100 [ ] direction.The activated slip system in ferrite is consistent with that obtained by Guziewski [33] and Shimokawa et al [23] under similar simulation parameters.

Transmission of plastic deformation between ferrite and cementite
As displayed in figures 4 and 5, ferrite phase yield occurs prior to inelastic deformation of cementite phase under all simulation conditions.In order to explain effects of ferrite phase yield on cementite phase inelastic deformation, this study, by taking pearlite with FeC-Fe and Fe-FeC cementite terminal surfaces as a case, visualized transmission behavior of plastic deformation in ferrite phase to cementite phase while the pearlite was stretched along q 100 [ ] direction, as shown in figure 7. The method similar to that in literature was used to analyze the atomic shear strain in the model [39].Model initial structure before loaded was taken as a reference structure for calculating atomic strain.Atoms with strain more than 0.2 are shown in red.As shown in the figure, plastic deformation firstly occurs in ferrite phase.Then, plastic deformation is transmitted to cementite as strain increases, causing inelastic deformation in cementite.According to analysis in figures 5-7, compared with S1 slip system, plastic deformation in ferrite will promptly transmit to cementite when S2 sliding system is activated, which results in inelastic deformation of cementite phase immediately after yield of ferrite phase.This is because in BCC-Fe, Schmid factor of S2 slip system is smaller than that of S1 slip system [22][23][24].By contrast,  shear stress on atom at slip surface is greater while S2 slip system is activated.Consequently, plastic deformation in ferrite is more likely to pass through interface to the cementite under activated S2 slip system.[ ] direction when strain increases.Slip occurs throughout elastic deformation stage.For pearlite with FeC-Fe and Fe-Fe cementite terminal surfaces, similar slip is found in b2 dislocation at interface when strain increases.However, slip distance amount is far from same for pearlite with different cementite terminal surfaces, as shown in figures 8(g) (h) and (k).When the strain is 0.076, slip distance amount of b2 dislocation at interface /Å (unloaded state is taken as reference state) is (9.77,10.66),(5.07,4.75)and (3.01,1.55)respectively for pearlite with FeC-Fe, Fe-FeC and Fe-Fe cementite terminal surfaces.

Discussion
Figure 9 displays relationship between number of atoms with high potential energy (>−4.05eV) at interface and loading strain when pearlite with different cementite terminalsurfaces is stretched along q 010 [ ] direction.As shown in figures 9(a)-(f), for pearlite with Fe-FeC cementite terminal surface, there are more high potential energy (>−4.05eV) atoms at interface with the increase of strain.This is same to pearlite with FeC-Fe and Fe-Fe cementite terminal surface.However, the number of high potential energy atoms is different for pearlite with various cementite terminal surfaces during stretching.Number of high potential energy atoms at the interface is ranked as follows: FeC-Fe>Fe-FeC>Fe-Fe, as shown in figure 9(g).[ ] direction of b2 dislocation at interface and loading strain when pearlite with FeC-Fe, Fe-FeC and Fe-Fe cementite terminal surfaces is stretched.Yellow line indicates original position of b2 (b2-1, b2-2) dislocation at interface when it is not loaded.
It has been known from section 3.1, pearlite experiences inelastic deformation in stretching due to the yield of ferrite phase near interface.The reason why yield occurs is that stress state in dislocation area of interface is high during loading.Naturally, interface will preferentially receive critical shear stress required for crystal slip, and then become emission source of dislocations to emit dislocations into ferrite, which leads to yield of ferrite [33,40].When pearlite is stretched along q 100 [ ] direction, slip of b2 dislocation at interface will inevitably release partial stress in interface area, thereby reducing stress state in interface dislocation area.Therefore, as slip of interface dislocations during loading is greater, it is more difficult for interface to emit dislocations into the crystal.Increase of atomic potential energy is usually caused by deviation of atoms from perfect lattice point under action of external force.Hence, when pearlite is stretched along q 010 [ ] direction, rising of atomic potential energy at interface will release force exerted on atoms, which reduces stress state in interface dislocation area.This, to some extent, prevents interface from emitting dislocations to ferrite.In accordance with analysis of peak stress of pearlite under inelastic deformation, as pearlite is stretched along q 100 [ ] and q 010 [ ] directions, it can also find peak stress of pearlite is positively correlated to dislocation slip distance amount at interface and number of high potential atoms respectively.This is why peak stresses are greatly different for pearlite with different cementite terminal surfaces at interface during stretching.
Cluster analysis method similar to that used in literature [24] was used to analyze details of interface dislocations of pearlite, as shown in figure 10.According to figures 10(a)-(c), width of b2 dislocation at the interface is significantly different when the cementite terminal surface is different.Width of b2 dislocation is 47 Å, 31 Å and 26 Å for terminal surfaces FeC-Fe, Fe-FeC and Fe-Fe, as shown in figure 10(d).Peierl-Nabarrao  model shows dislocation width is negatively related to critical shear stress of dislocation slip [41].Thus, when termination surface is different, slip amount of b2 dislocation is significantly different.What's more, lattice produce distortion in dislocation area [42].In other words, larger dislocation width at interface will cause greater lattice distortion area.Atoms in lattice distortion region have poor stability [43,44], so they tend to deviate from equilibrium position under action of external forces.Therefore, there are differences in number of high potential atoms at interface of pearlite with different cementite terminal surfaces when loading.

Influence mechanism of type of cementite terminal surface on slip system in ferrite
As shown in figure 8(f), for pearlite with Fe-FeC terminal surface stretched along q 100 [ ] direction, atomic potential energy between atoms in each area of interface dislocation is of small difference when inelastic deformation is about to occur.It is similar when pearlite with Fe-Fe cementite terminal surface is stretched along q 100 [ ] direction.However, potential energy of atoms at nodes of b1 and b2 dislocations is obviously greater than that at other locations when pearlite with FeC-Fe terminal surface is stretched along q 100 [ ] direction, as shown in the orange circle in figure 11(a).Furthermore, for all cementite terminal surfaces, potential energy of atoms at interface dislocation node is greater than that at other positions of the interface when pearlite is stretched along q 010 [ ] direction, as shown in figure 9(f).The higher potential energy of the atoms at the interface dislocation node indicates that the atomic structure distortion at the dislocation node is more serious, which will lead to the worse stability of the atomic structure.pearlite with Fe-FeC cementite terminal surface at interface is selected for case study.It is able to ignore influence of atomic potential energy at interface on type of activated slip system as long as atomic potential energy between atoms in each area of interface dislocation is of small difference.Schmid factor of S1 slip system is the highest in BCC-Fe [22,24] , so S1 slip system is activated when atomic potential energy between atoms in each area of interface dislocation is of small difference.When atomic potential energy at interface dislocation node is high, S2 slip system at the interface is activated.It also shows from figure 11(b) that S2 slip firstly occurs at interface dislocation node (The position shown by the orange arrow).In the future, subsequent research shall be carried out to profoundly analyze specific reason and mechanism of S2 slip system activated caused by high potential atoms.

Conclusion
In this study, molecular dynamics simulation method is used to analyze how mechanical response and deformation mechanism of pearlite are affected by cementite terminal surface type at ferrite-cementite interface under tension loading.At the same time, it selects two transverse directions parallel to pearlite interface as loading directions respectively.In the end, conclusions are drawn as follows: (1) When pearlite is stretched, it will experience inelastic deformation due to slip of atoms in ferrite phase at interface.For pearlite with FeC-Fe cementite terminal surface, atoms will not slip easily in ferrite at interface than pearlite with Fe-FeC and Fe-Fe cementite terminal surfaces.Therefore, inelastic deformation will be restrained.Consequently, pearlite with FeC-Fe cementite terminal surface has the largest peak stress during tension.
(2) Varieties of slip system activated in ferrite phase are impacted by both type of cementite terminal surface and loading direction.Stretching along q 100 [ ] direction: for pearlite with Fe-FeC and Fe-Fe cementite terminal surfaces at interface, S1 slip system in ferrite is activated.While terminal surface is FeC-Fe pearlite, what is activated is S2 slip system in ferrite.When pearlite with any cementite terminal surface at the interface is stretched along q 010 [ ] direction, S2 slip system in ferrite is activated.(3) In stretching, plastic deformation occurs firstly in ferrite; then with the increase of strain, plastic deformation will be transferred to cementite, leading to fracture failure of cementite.Research shows it is easier for plastic deformation in ferrite to be transmitted to cementite through the interface while S2 slip system in ferrite is activated rather than S1 slip system.

Figure
1(c) refers to cementite phase structure in pearlite and possible terminal surface in cementite phase.Dotted line in the figure indicates interface between ferrite and cementite.According to the figure 1(c), ferrite-cementite interface can be constructed by three different terminal surfaces in cementite structure.Three pairs of terminating plane can be described by the atomic content of their first two layers (from dotted line down): Fe-FeC, FeC-Fe, Fe-Fe.To be specific, Fe-FeC means that atoms in first layer below the dotted line contain only Fe atom; both Fe atoms and C atoms are included in second layer of atoms.Pearlite model constructed by three different terminal surfaces of cementite has atomic structure at interface as shown in figures 1(d)-(f).

Figure 1 .
Figure 1.Pearlite model with Bagaryatskii OR between ferrite phase and cementite phase.(a) Schematic diagram of pearlite model, α stands for ferrite, θ stands for Cementite.(b) Ferrite phase structure.(c) Cementite phase structure and possible terminal surface in cementite phase.The dotted lines represent where the cementite structures forms the interface with ferrite.The atoms below the dashed line represent the structure of cementite at the interface.Three pairs of terminating plane can be described by the atomic content of their first two layers (from dotted line down): Fe-FeC, FeC-Fe, Fe-Fe.(d), (e) and (f) represent pearlite interface structure with FeC-Fe, Fe-FeC and Fe-Fe cementite terminal surfaces, respectively.

Figure 3
is stress-strain curve of pearlite with different cementite terminal surfaces when it is stretched along q 100 [ ] or q 010 [ ] directions.According to the figure, when pearlite is stretched along q 100 [ ] and q 010

Figure 3 .
Figure 3. Stress-strain curves of pearlites with different cementite terminal surfaces under stretching along

Figure 4 .
Figure 4. Stress-strain curves of ferrite phase and cementite phase in pearlite with different cementite terminal surfaces when pearlite is stretched along q 100 [ ] and

Figure 5 .
Figure 5. Pearlite with different cementite terminal surfaces and strain diagram for inelastic deformation of internal ferrite phase and cementite phase.(a) Pearlite stretched along q 100 [ ] direction. (b) Pearlite stretched along

Figure 6 .
Figure 6.Influence of cementite terminal surface type at interface and loading direction on the type of activated slip system in ferrite.(a) S1 slip deformation mode is the {112}〈111〉 slip system.(b)S2 slip deformation mode is the {110}〈111〉 slip system.(a) and (b)The pearlite with Fe-FeC terminating surface is stretched along directions q 100 [ ] and

Figure 7 .
Figure 7. Evolution of atomic strain in pearlite under stretching along

4. 1 .
Influence mechanism of types of cementite terminal surface on pearlite peak stress Figure 8 describes relationship between b2 dislocation position at interface and loading strain as pearlite with different cementite terminal surfaces is stretched along q 100 [ ] direction.Yellow line indicates original position of b2 (b2-1, b2-2) dislocation at the interface when it is not loaded.As shown in figures 8(a)-(f), for pearlite with Fe-FeC cementite terminal surface, b2 dislocation at interface slips slightly along q 010

Figure 8 .
Figure 8. Relationship between b2 dislocation position at interface and loading strain when pearlite with different cementite terminal surfaces is stretched along q 100 [ ] direction. (a)-(f) Visual snapshot of b2 dislocation at interface when pearlite with Fe-FeC cementite terminal surface is stretched.(g) , (h) and (k) respectively represent relationship between coordinate position in q 010[ ] direction of b2 dislocation at interface and loading strain when pearlite with FeC-Fe, Fe-FeC and Fe-Fe cementite terminal surfaces is stretched.Yellow line indicates original position of b2 (b2-1, b2-2) dislocation at interface when it is not loaded.

Figure 9 .
Figure 9. Relationship between number of atoms with high potential energy (>−4.05eV) at interface and loading strain when pearlite with different cementite terminal surfaces is stretched along q 010 [ ] direction. (a)-(f) A visual snapshot of high potential atom at interface when pearlite with Fe-FeC cementite terminal surface is stretched.(g) describes relationship between number of high potential atoms at interface and loading strain when pearlite with FeC-Fe, Fe-FeC and Fe-Fe cementite terminal surfaces is stretched.

Figure 10 .
Figure 10.Clustering analysis method is used to show atoms displaced in pearlite with different cementite terminal surfaces due to formation of interface dislocations.The yellow atom is atom whose displacement exceeds the nearest neighbor truncation radius in BCC-Fe lattice, and the unrelaxed state is taken as reference state.(a) , (b) and (c) denote pearlite with FeC-Fe, Fe-FeC and Fe-Fe cementite terminal surfaces, respectively.(d) Width of b2 dislocation at interface of pearlite with different cementite terminal surfaces (average width of two b2 dislocations at the interface).

Figure 11 .
Figure 11.Visual snapshot of atomic morphology at interface before and after inelastic deformation.(a) Atoms with potential energy greater than −4.05 eV at interface when inelastic deformation is about to occur.(b) Atom slip in ferrite when inelastic deformation occurs initially.