Decoupling between Shockley partials and stacking faults strengthens multiprincipal element alloys

Mechanical properties are fundamental to structural materials, where dislocations play a decisive role in describing their mechanical behavior. Although the high-yield stresses of multiprincipal element alloys (MPEAs) have received extensive attention in the last decade, the relation between their mechanistic origins remains elusive. Our multiscale study of density functional theory, atomistic simulations, and high-resolution microscopy shows that the excellent mechanical properties of MPEAs have diverse origins. The strengthening effects through Shockley partials and stacking faults can be decoupled in MPEAs, breaking the conventional wisdom that low stacking fault energies are coupled with wide partial dislocations. This study clarifies the mechanistic origins for the strengthening effects, laying the foundation for physics-informed predictive models for materials design.

Structural study of single Shockley stacking faults terminated near substrate/epilayer interface in 4H-SiC

Structural analysis is carried out of a single Shockley stacking fault (1SSF) that terminates near the substrate/epilayer interface and originally expanded from a basal plane dislocation segment near the epilayer surface of 4H-SiC. The characteristic zigzag structure is found for the partial dislocations (PDs), with microscopic connecting angles of almost 120°. It has been suggested that the microscopic construction of PDs might be limited by the Peierls valley. The termination line near the substrate/epilayer interface was found to have 30° Si-core and 90° Si-core PDs. This combination is the same as that found near the surface of the epilayer in commonly observed 1SSFs. Penetrating BPDs of this kind were also found experimentally for the first time. For the currently proposed charts for the 1SSF expansions, photoluminescence imaging during UV illumination is one of the nondestructive analysis methods that can provide the structural information and expected expansion shapes of the 1SSFs.

Size-induced twinning in InSb semiconductor during room temperature deformation

Room-temperature deformation mechanism of InSb micro-pillars has been investigated via a multi-scale experimental approach, where micro-pillars of 2 µm and 5 µm in diameter were first fabricated by focused ion beam (FIB) milling and in situ deformed in the FIB-SEM by micro-compression using a nano-indenter equipped with a flat tip. Strain rate jumps have been performed to determine the strain rate sensitivity coefficient and the related activation volume. The activation volume is found to be of the order of 3–5 b3, considering that plasticity is mediated by Shockley partial dislocations. Transmission electron microscopy (TEM) thin foils were extracted from deformed micro-pillars via the FIB lift-out technique: TEM analysis reveals the presence of nano-twins as major mechanism of plastic deformation, involving Shockley partial dislocations. The presence of twins was never reported in previous studies on the plasticity of bulk InSb: this deformation mechanism is discussed in the context of the plasticity of small-scale samples.

Formation of Nanolaminated Structure with Enhanced Thermal Stability in Copper

Nanolaminated structure with an average boundary spacing of 67 nm has been fabricated in copper by high-rate shear deformation at ambient temperature. The nanolaminated structure with an increased fraction of low angle grain boundaries exhibits a high microhardness of 2.1 GPa. The structure coarsening temperature is 180 K higher than that of its equiaxial nanograined counterpart. Formation of nanolaminated structure provides an alternative way to relax grain boundaries and to stabilize nanostructured metals with medium to low stacking faults energies besides activation of partial dislocations.

Molecular dynamics study on the relationship between phase transition mechanism and loading direction of AZ31

To develop and design mg-based nanoalloys with excellent properties, it is necessary to explore the forming process. In this paper, to explore the effect of different loading directions on the phase transformation of magnesium alloy, the model of AZ31 magnesium alloy was established, the process of Uniaxial Compression (UC) of magnesium alloy in different directions was simulated, the changes of atomic position and phase structure were observed, and the phase transformation mechanism of AZ31 magnesium alloy under uniaxial compression under different loading directions was summarized. The conclusions are as follows: the stress and strain, potential energy and volume change, void evolution, phase structure change and dislocation evolution of magnesium alloy are consistent, and there is no significant difference. In the process of uniaxial compression, the phase transformation of hexagonal closely packed (HCP) → face-centered cubic (FCC) is the main, and its structure evolves into HCP → Other → FCC. Shockley partial dislocations always precede FCC stacking faults by about 4.5%, and Shockley partial dislocations surround FCC stacking faults. In this paper, the phase transformation mechanism of AZ31 magnesium alloy under uniaxial compression under different loading directions is summarized, which provides a theoretical basis for the processing and development of magnesium-based nanoalloys.