Damage-failure transition in titanium alloy Ti-6Al-4V under dwell fatigue loads

The role of structural mechanisms responsible for the consequent staging of damage-failure transition as the combination and continuity of ductile and creep kinetics of the structure evolution and the modeling in dwell fatigue regime. Damage-failure transition is considered as critical phenomena, the structural-scaling transition, when the damage develops as specific phase with characteristic stages: nucleation of new phase and the phase growth kinetics. In the case of dwell fatigue, the nucleation stage is associated with slip localization, faceting, voids and microcrack initiation; the phase growth kinetics has the relation to specific non-linearity of the free energy release responsible for the staging of damage-failure transition. Statistically based phenomenological model of damage-failure transition specified the links of macroscopic material parameters with structural parameters responsible for the influence of microstructure on the structure sensitive mechanical properties. The developed conception of modeling of Ti alloys based on the duality of damage kinetics in dwell fatigue loads allowed us to propose the strategy of structural study to provide in perspective the links of structural parameters of /phases with phenomenological parameters responsible for different mechanisms of damage accumulation at LCF and stress hold regimes

Effects of Zn and Mg Segregations on the Grain Boundary Sliding and Cohesion in Al: Ab Initio Modeling

The formation of Zn and Mg segregations at a tilt Σ5{013} <100> grain boundary (GB) in Al and the effects of these solutes on deformation behavior of polycrystalline Al were investigated using ab initio total energy calculations. Using a step-by-step modeling of the segregation process, we found that the formation of a thick segregation layer of Zn at the GB is energetically preferable, while the formation of an atomically thin segregation layer is expected in the case of Mg. To reveal the effect of segregation on the cohesive properties of Al GBs, we calculated the energy of cleavage decohesion and the shear resistance for GB sliding. We show that the segregation of Zn results in a substantial decrease in barriers for GB sliding, while the segregation of Mg increases the barriers. The results obtained allow us to explain experimental findings and demonstrate a strong relationship between chemical bonding of solute atoms, their segregation ability, and GB strength

End-member compounds of a 4-sublattice model of multicomponent BCC solid solutions

The article presents ab initio calculated properties (total energies, lattice parameters, and elastic properties) for the complete set of 1540 end-member compounds within a 4-sublattice model of Fe-based solid solutions. The compounds are symmetry-distinct cases of integral site occupancy for superstructure Y (space group #227, type LiMgPdSn) chosen to represent the ordered arrangements of solvent atoms (Fe), solute atoms (Fe, Mg, Al, Si, P, S, Mn, Ni, Cu), and vacancies (Va) on the sites of a body-centered cubic lattice. The model is employed in the research article “Ab-initio based search for late blooming phase compositions in iron alloys” (Hosseinzadeh et al., 2018) [1]