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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.

Materials with low stacking fault energies have been long sought for their many desirable mechanical attributes. Although there have been many successful reports of low stacking fault alloys (for example Cu-based and Mg-based), many have lacked sufficient strength to be relevant for structural applications. The recent discovery and development of multicomponent equiatomic alloys (or high-entropy alloys) that form as simple solid solutions on ideal lattices has opened the door to investigate changes in stacking fault energy in materials that naturally exhibit high mechanical strength. We report in this article our efforts to determine the stacking fault energies of two- to five-component alloys. A range of methods that include ball milling, arc melting, and casting, is used to synthesize the alloys. The resulting structure of the alloys is determined from x-ray diffraction measurements. First-principles electronic structure calculations are employed to determine elastic constants, lattice parameters, and Poisson’s ratios for the same alloys. These values are then used in conjunction with x-ray diffraction measurements to quantify stacking fault energies as a function of the number of components in the equiatomic alloys. We show that the stacking fault energies decrease with the number of components. Nonequiatomic alloys are also explored as a means to further reduce stacking fault energy. We show that this strategy leads to a means to further reduce the stacking fault energy in this class of alloys.

A high-alloy austenitic CrMnNi steel was deformed at temperatures between 213 K and 473 K (−60 °C and 200 °C) and the resulting microstructures were investigated. At low temperatures, the deformation was mainly accompanied by the direct martensitic transformation of γ-austenite to α′-martensite (fcc → bcc), whereas at ambient temperatures, the transformation via ε-martensite (fcc → hcp → bcc) was observed in deformation bands. Deformation twinning of the austenite became the dominant deformation mechanism at 373 K (100 °C), whereas the conventional dislocation glide represented the prevailing deformation mode at 473 K (200 °C). The change of the deformation mechanisms was attributed to the temperature dependence of both the driving force of the martensitic γ → α′ transformation and the stacking fault energy of the austenite. The continuous transition between the ε-martensite formation and the twinning could be explained by different stacking fault arrangements on every second and on each successive {111} austenite lattice plane, respectively, when the stacking fault energy increased. A continuous transition between the transformation-induced plasticity effect and the twinning-induced plasticity effect was observed with increasing deformation temperature. Whereas the formation of α′-martensite was mainly responsible for increased work hardening, the stacking fault configurations forming ε-martensite and twins induced additional elongation during tensile testing.

In this work, the plastic deformation in a model nanocrystalline high entropy alloy (HEA), CoNiCrFeMn, is studied by using molecular dynamics simulations. It is found that the plastic deformation of nanocrystalline CoNiCrFeMn HEAs is dominated by a partially reversible face-centered cubic (FCC) to hexagonal close-packed (HCP) transformation mediated by stacking faults and partial dislocations, which is dramatically different from the full dislocation and deformation twinning-dominated plasticity in conventional FCC metals. This mechanism is strongly associated with the metastable nature of CoNiCrFeMn. Furthermore, although the transformed HCP structures can hinder the migration of the subsequent partial dislocations, they can penetrate each other to form a complicated stacking fault network, which is consistent with the recent experimental observations. Nevertheless, the nanocrystalline CoNiCrFeMn HEAs still show the conventional Hall–Petch breakdown when the grain sizes are reduced below a critical value. It is hoped that this study provides an atomistic insight into the plasticity of metastable HEAs and sheds some light on the design of novel HEAs for ultrahigh strength and plasticity. Graphical abstract

X-ray diffraction analysis is essential in studying stacking faults. Most of the techniques used for this purpose are based on theoretical studies. These studies suggest that the observed diffraction patterns are caused by random stacking faults in crystals. In reality, however, the condition of randomness for stacking faults may be violated. The purpose of the study was to develop a technique that can be used to calculate the diffraction effects of the axis of the thin plates of twin, new phases, as well as other variations in defective structures. Materials and methods. This was achieved through modern X-ray diffraction methods using differential equations (transformations and Fourier transforms) and the construction of the Ewald sphere, mathematical analysis, mathematical logic, and mathematical modeling (complex Markov chain). Conclusion. The study made it possible to develop a technique for the calculation of the diffraction effects of the axis of the thin plates of twin, new phases and other variations in defective structures. The technique makes it possible to solve several complex, urgent problems related to the calculation of X-ray diffraction for crystals with face-centered lattices containing different types of stacking faults. At the same time, special attention was paid to the correlations between the relative positions of faults. The calculations showed that the proposed method can help to determine the nature and structure of stacking faults by identifying the partial and vertex dislocations limiting them in twin crystals with a face-centered cubic structure of silicon carbide based on X-ray diffraction analysis.

The aim of this study is to investigate the main contributing factors to the degradation of the intrinsic body diode in SiC MOSFETs, caused by the expansion of stacking faults (SFs) from the substrate into the epitaxial layer, and how it affects their performance. Additionally, a comparison between DC forward current stress and surge current pulse stress is shown.

The activation of plastic deformation mechanisms determines the mechanical behavior of crystalline materials. However, the complexity of plastic deformation and the lack of a unified theory of plasticity have seriously limited the exploration of the full capacity of metals. Current efforts to design high-strength structural materials in terms of stacking fault energy have not significantly reduced the laborious trial and error works on basic deformation properties. To remedy this situation, here we put forward a comprehensive and transparent theory for plastic deformation of face-centered cubic metals. This is based on a microscopic analysis that, without ambiguity, reveals the various deformation phenomena and elucidates the physical fundaments of the currently used phenomenological correlations. We identify an easily accessible single parameter derived from the intrinsic energy barriers, which fully specifies the potential diversity of metals. Based entirely on this parameter, a simple deformation mode diagram is shown to delineate a series of convenient design criteria, which clarifies a wide area of material functionality by texture control.

The magnetic excitons in diluted magnetic semiconductor (DMS) have varied formats due to the inhomogeneous phases out of doping concentration and/or structural relaxations or defects. Here the high quality cobalt-doped zinc blende ZnSe nanoribbons (NRs) were synthesized, showing bright and color-variable emissions from blue, yellow to a little mixed white colors. Their power and temperature dependent micro-photoluminescence (PL) spectra have been obtained in which two emission bands, one magnetic exciton band near the band-edge and a Co 2+ high-level d – d transition emission band at 550 nm out of their ferromagnetic (FM) coupled aggregates in ZnSe lattice, both bands could also be reflected by a nonlinear optical absorption enhancement. The easy formed stacking fault defects in a chemical vapor deposition (CVD) grown ZnSe zincblende NR took part in the above optical processes out of magnetic polaronic excitons (PXs). The femtosecond (fs) laser pulse pumping on single ZnSe:Co NR produces obvious lasing behavior but with profile of a complicated magnetic exciton interactions with indication of a crossover from collective exciton magnetic polarons (EMP) to bound magnetic polaron (BMP) scattering in Co doped ZnSe NR. These findings indicate the complication of the magnetic coupling natures in varied DMS structures, whose optical properties have been found to be highly nonlinear, due to the involvement of the spin–spin, spin–exciton and spin–phonon interactions, verified by the theoretic calculation in Yang X-T et al (2019 Interstitial Zn-modulated ferromagnetism in Co-doped ZnSe Mater. Res. Express 6 106121).

A triangular single Shockley stacking fault (1SSF) in 4H-SiC, expanding from the surface to the substrate/epilayer interface, was investigated. The triangular 1SSF was observed during electroluminescence examination of PIN diodes that had line-and-space anodes with open windows. The threshold current density of the 1SSF expansion was comparatively intermediate, and differed from that of a 1SSF that expanded from a basal plane dislocation (BPD) that had penetrated from the substrate into the epilayer, and from that of a 1SSF that expanded from a BPD that had converted into threading edge dislocations (TEDs) at the substrate/epilayer interface. No BPDs or surface damage such as cracks were observed by photoluminescence imaging, synchrotron x-ray topography imaging, or scanning electron microscope imaging near the origin of the expansion region. High-resolution observation using cross-sectional transmission electron microscopy showed that a partial dislocation (PD) was present on the basal plane and two inclined TEDs were present on both sides of the PD. A g · b analysis showed that this dislocation had a Burgers vector of ± (1/3) [11 2 ¯ 0], and it was estimated to be a combination of a TED-BPD-TED structure with a short BPD before expansion. Therefore, the triangular 1SSF from the surface side can be explained to have expanded from this BPD. Furthermore, considering the possibility of the BPD-TED conversion at the epitaxial growth process, the TED-BPD-TED dislocation was speculated to have formed after epitaxial growth. The perfect control of the forward voltage degradation of 4H-SiC device is thought to be realized by focusing on this type of BPD.