Atomic-Scale Study On Shock-Induced Plastic Deformation Mechanism Of Nickel-Based Laminate Composites

The ductile layer and the brittle layer of metal matrix laminate composites synergistically have excellent comprehensive performance and strong designability and are widely used.Nickel-based micro-laminated composites replace strategic high-temperature structural materials in key fields such as aerospace,defense,and automotive industries with light weight,high strength,high toughness,high temperature resistance and impact resistance.Important components such as nano-ignition devices and drug-shaped caps play a protective role.In this paper,shock-induced plastic deformation of Ni/Al laminate composites and Ni/Ni₃Al laminate composites is studied by molecular dynamics.Firstly,the characteristic waveform distribution of“reflection unloading”and“reflection loading”caused by interface reflection at the front of shock wave is reasonably explained in combination with impedance matching theory,followed by revealing the intrinsic relationship between component discontinuity and elasto-plastic mismatch of shock wave profile,and finally analyzing the interfacial atomic arrangement of heterogeneous materials,shock-induced plastic deformation behavior,dislocation reaction mechanism and accompanying structural phase transition,to provide a theoretical basis for the design of the impact-resistant structure of nickel-based laminated composites,and the conclusions are as follows:The interface reflection of Ni/Al and Ni/Ni₃Al laminate composites under the impact velocity of 500 m/s causes P_xx“reflection unloading”and“reflection loading”,wherein,Ni-Al reflection unloading,Al-Ni reflection loading;Ni-Ni₃Al Reflective unloading,Ni₃Al-Ni reflective loading.The calculation and simulation results of impedance matching theory(Z_{N i}＞Z_{Ni3 Al}＞Z_Al)are as follows:The calculated and simulated intensities of the Ni-Al reflected wave are 10.26 GPa and 9.33 GPa,respectively,the calculated and simulated intensities of the Al-Ni transmitted wave are 20.66 GPa and 19.64 GPa,respectively;the Ni-Ni₃Al reflected wave intensity is 1.43 GPa,and the simulated result is 1.7 GPa,The transmitted wave intensity of Ni3Al-Ni is 24.25 GPa,and the simulated is 24.02 GPa.The calculation and simulation errors are small,and the impedance matching theory can accurately explain the interface reflection phenomenon.The elastoplastic mismatch leads to the discontinuity of the interface between P_yy and P_zz and the shear stressτ_max.The discontinuity of P_yy and P_zz in the Ni layer,the Al layer and the Ni₃Al layer is determined by the ratio of elastic constants.The shear stressτ_max is discontinuous It is related to shear modulusμand Poisson’s ratioν.The theoretical calculation and simulation results of elastic-plastic mismatch are consistent:the relationship between the transverse stress component profiles P_yy and P_zz of each layer and the shear stressτ_max is as followsp_yy^{Ni3 Al}＞p^N_yy ⁱ＞p_yy^Al,p_zz^{Ni 3 Al}＞p^N_zz ⁱ＞p_zz^Al,t_ma^Ni3 _x^Al（27）t_ma^Ni _x（27）t_m^{A l}_ax.After the Ni/Al and Ni/Ni₃Al laminate composites multi-layer target is relaxed,the atomic stress at the interface is concentrated and the disorder is large,and the Ni/Ni₃Al interface stress is released to the Ni₃Al layer.The dislocation reactions lead to pyramidal dislocations and stacking faults in the Al and Ni₃Al layers,respectively.The mechanism of dislocation formation and slip is explained by tracking atomic motion.The results show that the Perfect dislocation at the Ni/Al interface decomposes one Stair-rod dislocation and two Shockley dislocations,the one Stair-rod dislocation is fixed,and the Shockley dislocation slips.Extension,the orientation is suitable for two Shockley dislocations to generate“Hirth locks”at the intersection,and finally all the edges of the pyramid form“Hirth locks”;the two-step decomposition of Ni/Ni₃Al pyramidal dislocations is[211]and[211].The two-way atoms are not activated at the same time,and the Frank dislocation exists as a transition dislocation.During the process of dislocation merging,due to the change of orientation,a small number of“Hirth locks”are recovered and decomposed,and the formation of pyramidal stacking faults is accompanied by FCC→BCC→HCP continuous phase transition.The impact resistance of Ni/Al and Ni/Ni₃Al laminate composites are comprehensively analyzed.The results show that the shock wave propagates at two adjacent interfaces,0.8457（28）η_Ni-Al×η_Al-Ni（27）η_Ni-Ni3Al×η_Ni3Al-Ni（28）0.9743,Ni/Al has better filtering effect,butt_max^{Ni 3Al}（27）t^Al_max,p_HE^Ni ~3 _L^Al＞p_HE^Al _L,Ni/Ni₃Al has better resistance to yield deformation,and it is known that Ni/Al produces large reflected tensile waves that are easy to cause interface nucleation,growth,and final delamination failure.As mentioned above,Ni/Ni₃Al has better resistance to shock deformation,and the more interfaces,the better the filtering effect.The stress-strain curve of Ni/Ni₃Al coherent interface under compressive load perpendicular to the interface shows that:during the plastic deformation process,the interfacial Pefrect dislocations decompose and Shockley dislocations synthesize,and the Shockley dislocations continue to slip and expand,resulting in interlocking of like pyramid stacking faults and significantly increases the ultimate yield strength.The entire compression process exhibits plastic fracture characteristics.