Co-yield surfaces for {111}〈110〉 slip and {111}〈112〉 twinning in fcc metals

The co-yield surfaces in fcc single crystals for slip on 11111110 and twinning on {111}112 systems have been analyzed and derived systematically for the first time. The results demonstrated that only if the ratio of the critical resolved shear stress (CRSS) for twinning to that for slip is within the range of , slip and twinning can occur together. There are only two types of co-yield surfaces when is within this range. The corresponding analytical expressions of all possible types of yield vertices are also derived and tabulated. One type consists of 259 co-yield stress states when , which can be classified into 21 groups in stress space according to the crystal symmetry. The other type contains 259 co-yield stress states also when , which can be subdivided into 19 groups. Of the two types of the co-yield stress states, 139 ones are common and 120 ones are different.     

Yield Vertices for Symmetric Slip on {110}<111> and Asymmetric Slip on {112}<111> Systems

The single crystal yield surfaces (SCYS) of bcc metals for symmetric slip on {110}＜111＞ and asymmetric slip on {112}＜111＞ systems have been analyzed and deduced. The complete SCYS have been derived when their critical resolved shear stresses (CRSS) are specified in a particular case (such as for Mo metal). The results showed that there are 600 stress states that can be classified into 35 groups according to the crystal symmetry. Each group activates eight, six or five {110}＜111＞ and {112}＜111＞ slip systems depending on crystallographically nonequivalent slip systems groups. Among all these stress states, three groups activate eight systems, there are 24 stress states; four groups activate six systems, there are 48 ones; the remaining twenty-eight groups activate five systems, there are 528 ones. In this case, the fraction of vertices for which there is slip ambiguity (more than five active systems) is reduced considerably compared with pure {110}＜111＞ slip.     

Effects of temperature and alloying content on the phase transformation and{10■1}twinning in Zr during rolling

The effects of temperature and Ti content on the deformation mechanisms of pure Zr and Zr-Ti alloys were investigated by transmission electron microscopy.The results indicate the existence of a relation between deformation-induced phase transformation from a hexagonal close-packed structure to a facecentered cubic structure and{10■1}deformation twinning.That is,when one is suppressed,the other will be promoted.The phase transformation was suppressed while the{10■1}compressive twinning was promoted with increasing the rolling temperature and/or Ti content.This can be attributed to the activation of basaladislocations at high temperature and the increased stacking fault energy with Ti content.     

The microstructure, stability, and elastic properties of 14H long-period stacking-ordered phase in Mg–Zn–Y alloys: a first-principles study

The long-period stacking-ordered (LPSO) phases were demonstrated to be the predominant strengthening phases that can significantly improve the mechanical properties of Mg–Zn–Y alloys. However, the mechanism underlying this improvement has not been satisfyingly understood yet due to unclear characterization of the microstructures of these LPSO phases. We proposed the reliable structural model of Mg₁₄₂Zn₁₂Y₁₆ for 14H LPSO phase formed in Mg–Zn–Y alloys with first-principles calculations in this study. The space group of Mg₁₄₂Zn₁₂Y₁₆ is P6₃/mcm, with lattice dimensions a = b = 11.168 Å, c = 36.408 Å, α = β = 90°, and γ = 120°. And the atomic sites were given in this work. In contrast to other structural models proposed in previous studies, 14H LPSO phase was predicted to be thermodynamically stable on the basis of the present structural model, which can well account for the stability of 14H LPSO phases at higher temperature. Furthermore, the elastic constants and elastic moduli of 14H LPSO phase were also evaluated based on the present structural model. The calculated Young’s modulus of 14H LPSO phase agrees well with the available experimental values. The characteristics of 14H LPSO phase observed in experiments were successfully reproduced using the present structural model. The good match between the calculations and the experiments validates the reliability of the structural model proposed for 14H LPSO phase.     

Formula: see text] ↔ (3 × 3) phase transition in Pb/Ge(111) and Sn/Ge(111): a phenomenological study on the phase transition anomalies and the role of defects

A phenomenological study of the [Formula: see text] phase transitions occurring in the adsorption systems Pb/Ge(111) and Sn/Ge(111) is presented. The starting point of such a study is the Landau theory. The critical behaviour expected theoretically for the two interfaces, and the corresponding influence of defects, are discussed in detail. Symmetry arguments show that, contrary to general belief, the critical behaviours of Pb/Ge(111) and Sn/Ge(111) are essentially different. The Landau-like approach employed to study the influence of defects provides a consistent and general manner to interpret the existing experimental data. Special attention is paid to the influence of hopping defects in Sn/Ge(111).