Uncovering the influence of Cu on the thickening and strength of the δ′/θ′/δ′ nano-composite precipitate in Al–Cu–Li alloys

Abstract

Nanoscale d 0 /h 0 /d 0 composite precipitate, as another important strengthening phase in the latest generation of Al-Li alloys, exhibits excellent resistance to coarsening. Here, we propose two thickening models for an anomalous d 0 /h 0 /d 0 that is discovered recently, by analyzing various influencing factors, including the static energy barrier, aging temperature-dependent nucleation conditions, and the elastic distortion suffered during growth. It indicates that the thickness of the d 0 /h 0 /d 0 composite precipitate seems to depend on the nucleation of the d 0. At elevated aging temperatures, h 0 precipitates can grow and thicken rapidly until the d 0 nucleates on them. This is strikingly different from the dislocationinduced growth mechanism. Subsequently, we propose a vacuum-added methodology to accurately extract the interfacial energy. The results show that this nano-composite precipitate can realize supra-nanostructure in thickness at low aging temperatures due to the spontaneous nucleation of the d 0 upon the pre-precipitate h 0. Cu atoms segregated at the interface suppress the nucleation of the d 0 , but release the lattice distortion to some extent. Using Griffith fracture model-assisted ab-initio uniaxial tensile tests, the cohesion strength and fracture process of this composite precipitate with and without Cu segregation have been captured. It indicates that the Cu atoms induced interfacial expansion and the fracture of strong Al-Al covalent bond, resulting in a reduction of fracture strength of this nano-composite precipitate.

Uncovering the Interfacial Strengthening Mechanisms of α-Mg/Mg2Sn/β-Li Interfaces Using First-Principle Calculations and HAADF-STEM

“…Similarly, the interfacial energy calculations of the β-Li/Mg 2 Sn interfacial structure (Figure ) and α-Mg/β-Li interfacial structure (Figure ) were carried out by the same method. Specifically, the interfacial energy calculation can be performed according to the following equation: , γ interface = E slab a / b − E slab a − E slab b + A γ surf a + A γ surf b A where, E slab a/b is the total energy of different laminar interface supercell structures containing vacuum layers, E slab a and E slab b are the total static energies of single-phase layered surface structures containing vacuum layers separated from the interfacial structure, respectively, γ surf a and γ surf b are the surface energies of the a and b phases, and A is the interface area. Subtracting the total energy of the interfacial structures in Figures , , and from the total energy of each phase will subtract more of the surface energy of each phase and therefore needs to be added.…”

Effect of fission defects on tensile strength of U3Si2 Σ5(210) grain boundary from first-principles calculations

“…Last but not least, the ORGS model 48 corresponds to the RGS with subsequent atomistic relaxation, which is named RGS + relaxation or RGSrel in many studies. 28,47,62,63 Following a comprehensive comparison of the various tensile testing methods outlined in the literature, 27,28,48,55,59,61,63 the RGS and RGSrel methods were performed for the GB structure in the current work. The key performance of the RGS approach requires that the investigated GB/bulk region should be split into two free surfaces by inserting an increasing separation distance.…”

Unexpected nucleation mechanism of T1 precipitates by Eshelby inclusion with unstable stacking faults

“…As one of the major strengthening mechanisms in Al‐Li alloys, precipitation strengthening is of great interests to many researchers [8–12] . Among them, the nano T 1 precipitate with high length/diameter ratios is the most important and has been well‐studied in the third and fourth‐generation Al‐Li alloys.…”