Molecular dynamics simulation on (001) interfacial fracture of Fe/Ni and Fe/Pd/Ni and deformation mode analysis by eigenvector of atomic elastic stiffness matrix

Abstract

Tensile fracture simulations are performed on the (001) interfaces of Fe/Ni and Fe/Pd/Ni by molecular dynamics method, in order to discuss the interfacial strength by means of the eigenvalue and eigenvector of atomic elastic stiffness, B^a_ij=Δσ^a_i/Δε_j. Three models are considered, Fe/Ni stacked layers (Bimetal), 2 atomic interlayers of Pd between Fe and Ni phases (Pd 2layer) and same thickness Fe/Pd/Ni/Pd blocks (Trimetal). Before tensile simulation, distribution of η^a(1) < 0 atoms (η^a(1) is the 1st eigenvalue of the solution of B^a_ijΔε_j=η^aΔε_i) and residual atomic stress in each atomic layers are discussed. Then tensile simulations are implemented; the peak strain and stress of Pd2layer are significantly reduced from that of Bimetal. Trimetal shows slightly lower maximum stress at slightly higher strain than Bimetal. Bimetal shows fracture in Ni phase near the interface, while Pd2layer and Trimetal do in Pd phase near the Ni/Pd and Fe/Pd interface, respectively. Void generation process or the initial stage of the fracture is then discussed with the distribution of η^a(1) < 0 atoms and corresponding eigenvector, {Δε₁,Δε₂,・・・,Δε₆} ={Δε_xx,Δε_yy,・・・,Δγ_xy}. In all models the void is formed at the intersection between the interface and slip deformation, so that we can’t find clear mode for atomic plane opening but complicated modes for plastic deformation and inhomogeneous heterometal interface. However, large deformation modes or large negative η^a(1) definitely emerge at the opening void edges.