Abstract
Single-crystalline Ni3Al-based superalloys have been widely used in aviation, aerospace, and military fields because of their excellent mechanical properties, especially at extremely high temperatures. Usually, single-crystalline Ni3Al-based superalloys are welded together by a Ni3Al-based polycrystalline alloy via transient liquid phase (TLP) bonding. In this study, the elastic constants of single-crystalline Ni3Al were calculated via density functional theory (DFT) and the elastic modulus, shear modulus, and Poisson’s ratio of the polycrystalline Ni3Al were evaluated by the Voigt–Reuss approximation method. The results are in good agreement with previously reported experimental values. Based on the calculated mechanical properties of single-crystalline and polycrystalline Ni3Al, three-dimensional finite element analysis (FEA) was used to characterize the mechanical behavior of the TLP bonded joint of single-crystalline Ni3Al. The simulation results reveal obvious stress concentration in the joint because of the different states of crystal orientation between single crystals and polycrystals, which may induce failure in the polycrystalline Ni3Al and weaken the mechanical strength of the TLP bonded joint. Furthermore, results also show that the decrease in the elastic modulus of the intermediate layer (i.e., polycrystalline Ni3Al) can relieve the stress concentration and improve the mechanical strength in the TLP bonded joint.
Highlights
Owing to their extremely high tensile strength, toughness, endurance strength, fatigue strength, corrosion resistance, and oxidation resistance at high temperatures, nickel(Ni)-based superalloys have been widely applied in aviation, aerospace, and military fields [1,2,3]
In addition to increasing strength of the intermediate layer, the simulation result in this study suggests that appropriately reducing the elastic modulus of the intermediate layer can improve the mechanical strength of a transient liquid phase (TLP) bonded joint
Elastic constants of single-crystalline Ni3 Al as well as the elastic modulus, shear modulus, and the Poisson’s ratio of polycrystalline Ni3 Al were calculated via density functional theory (DFT), and the calculation results were subsequently verified against previously reported experimental data
Summary
Owing to their extremely high tensile strength, toughness, endurance strength, fatigue strength, corrosion resistance, and oxidation resistance at high temperatures (such as ≥980 ◦ C), nickel(Ni)-based superalloys have been widely applied in aviation, aerospace, and military fields [1,2,3]. The shortcomings of fusion welding and brazing in the connection of Ni-based superalloys (such as shrinkage stresses induced by rapid precipitation, formation of brittle phases, and the tendency to crack due to local fragility, etc.) limit the industrial application of the process for Ni-based superalloys [4,5]. Paulonis et al proposed a transient liquid phase (TLP) bonding method [4], where in a thin layer of intermediate alloy with a lower melting temperature is employed as the connecting material. During TLP bonding, a low-melting liquid phase is formed between the parent material and the intermediate layer by heating under. Owing to its reasonable welding temperature, low applied pressure requirement, and ability to form a welded joint with excellent mechanical properties, TLP bonding is widely considered as one of the most ideal welding methods for Ni-based superalloys [5,6,7]
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