The Mechanical Properties And Doping Effect Of Ni And Ni₃Al: A Molecular Dynamics Study

Owing to the unique high-temperature mechanical properties, excellent corrosionand oxidation resistance, nickel-based single crystal superalloys are widely used inthe field of aerospace, aviation and other high temperature structural materials.Nickel-based single crystalline superalloys consist of ordered Ni₃Al-based γ’（L12）precipitates and solid solution Ni-based γ （fcc） matrix, where the γ’ precipitates arecoherently embedded in the γ matrix. Precipitation hardening and solid solutionstrengthening are both extremely important method to improve the high temperaturemechanical properties of nickel-base single crystal superalloy materials. It has foundthat the structure of γ andγ’phases and the doping additional elements have obviouslyimpact on the mechanical properties of the superalloy materials. In this paper, themodified analytical embedded atom method and molecular dynamics simulations wereused to study the mechanical properties of the Ni, Ni₃Al, Ni/Ni₃Al nanowires（NWs）and the microstructures of bulk Ni and Ni₃Al doped with Re.We studied the mechanical properties of Ni and Ni₃Al NWs under the effects ofcross sectional sizes and temperatures. It is found that the strain-stress response of theNWs of Ni, Ni₃Al and their core-shell structures consisted of elastic stage and plasticstage. The tensile stress was related linearly to the strain when the tensile strain issmall, while the strain-stress response curves were saw-like in the plastic stage. Theyield stress, Young’s modulus and ductility of Ni and Ni₃Al NWs monotonicallyincreased with the increasing of NW’s diameter. However, the yield stress andYoung’s modulus decreased obviously with the temperature increasing. Comparedwith Ni and Ni₃Al NWs, the yield stresses and Young’s moduli of the core-shell NWschanged slightly. The fracture strains of core-shell NWs were greater than those of Niand Ni₃Al NWs. The ductility of core-shell NWs was improved markedly and had amonotonously variation with the core sizes. The core（Ni₃Al）-shell（Ni） NWs weremore flexible than the core（Ni）-shell（Ni₃Al） ones.Molecular dynamics simulation has also been used to study the effect of Re onthe structure stability of Ni and Ni₃Al. It has been found that the content of Reobviously affected the formation of vacancy both in Ni and Ni₃Al bulks. Doping Re atthe Ni site, the damage on the Ni bulk was weaker than that on Ni₃Al bulk. Thestructure maintained stable when the content of Re was small in Ni bulk, whiledamage became obvious while the content of the doped Re increased. When doping Re at the Ni site in Ni₃Al-Ni, the effect was more obvious. However, the damage onthe Ni₃Al bulk was very weak when Re occupied the Al site in Ni₃Al. The effectbecame obvious as the content of Re was1.0%and the ratio of vacancy to atoms wasabout1.0%. The damage of Re occupying the Al sites in Ni₃Al was weaker than thatoccupying the Ni sites in Ni₃Al, which means that Re atoms prefer the Al sites inNi₃Al to the Ni sites in Ni₃Al.