Suzuki Segregation Of Re And W And Its Impact On Twinning Deformation Of γ′-Ni₃Al Phase

Nickel-based superalloys have many important applications in aerospace,mainly because of their excellent mechanical properties and creep resistance at elevated temperatures.Micro-twinning is a major creep deformation mechanism of the alloy at medium temperature.The formation of micro-twins is accompanied by the generation of stacking faults,and the Suzuki segregation phenomenon has been widely found near the faults.In this paper,the first-principles calculation and simulation software VASP was used to study the Suzuki segregation of Re and W in nickel-based single crystal superalloys and their effects on the twinning deformation ability ofγ′-Ni₃Al phase.The software of VASP is a density functional calculation program based on the pseudopotential plane wave basis set.It is widely used in the research fields of metals and their oxides,crystals,doping systems,molecules,and surface systems.First,the segregation of Re and W near the superlattice intrinsic stacking fault（SISF）and the superlattice extrinsic stacking fault（SESF）in theγ′phase is studied.The calculation results show that the low concentrations of Re and W near the SISF do not show obvious segregation tendency.However,in the case of increasing the doping concentration of Re or W or compound doping them,the Suzuki segregation can be found near the SISF again,which indicates that the Suzuki segregation of elements is a complex behavior affected by many factors,such as the concentration of solute atoms,the interaction between elements and other factors.For SESF,both Re and W show obvious Suzuki segregation tendency and their optimal sites are Ni sites,which are different from their preferred sites in perfect crystals.The analysis of the density of states reveals that it is energetically disadvantageous for Re and W to occupy Al sites near the fault.In addition,further observation found that Re tends to segregate to the twin planes,while W tends to segregate to the interior of the twin regions.Secondly,the effect of Suzuki segregation of Re and W on the twinning deformation ofγ′phase is also explored.In this part,two possible micro-twinning mechanisms are firstly compared,and the results show that the pseudo-twinning mechanism is more likely to occur.The analysis of the changes in the atomic local structure during the defect formation process shows that the hindering effect of the mutual motion between the atomic layers is the main reason why the true-twinning mechanism is more difficult to occur.Since the atomic rearrangement process related to the pseudo-twining mechanism cannot be confirmed,only the true twinning mechanism is investigated in this paper.Using the first-principles calculation method,the effects of Re and W on the twinnabilities of crack tip twinning,grain boundary twinning and intrinsic twinning,and the critical twinning stress_critwere studied.The results show that the Suzuki segregation of Re and W reduces the ideal shear strength_max,unstable twinning energies_UTFand_critof theγ′phase to a certain extent,and improves the three twinning abilities,among which W is more conducive to twinning deformed.