Revealing texture architecture in a surface gradient nanostructured Al-Cu-Mg alloy

ABSTRACT

A multiscale crystallographic texture architecture in a surface gradient nanostructured Al-Cu-Mg alloy after surface sliding friction treatment (SSFT) has been revealed by a combination of electron backscatter diffraction and precession electron diffraction (PED)-assisted transmission electron microscopy (TEM) orientation mapping. Accompanying a grain structure variation from lamellar coarse grains to equiaxed nanograins, the major texture components evolve from brass {110}<112> in the coarse-grain matrix, Goss {110}<001> at a depth of ～80?μm, E {111}<011> and F {111}<112> at a depth of ～20?μm, to a mixture of rotated cube {001}<110>, E and F in the topmost surface layer. The through-thickness textural development and evolution are attributed to the cyclic loading of concurrent shear and compression during the SSFT processing. The PED-assisted orientation mapping shows good capability in mapping severe plastic-deformation-induced nanostructures with large residual strains and high defect density.     

Approximant phases,phason planes and domain-boundary networks in Al−Ni−Rh alloys

Structurally complicated ξ′- and ξ-phases have been found, for the first time, in as-cast Al₇₃Ni₅Rh₂₂ and Al₇₅Ni₁₅Rh₁₀ alloys. The lattice parameters of these two phases were determined by means of electron diffraction and high-resolution transmission electron microscopy (HREM). These two phases have similar orthorhombic structures but with different lattice parameters of a?=?23.2?Å, b?=?16.4?Å, c?=?12.0?Å for the ξ′-phase and a?=?20.3?Å, b?=?16.4?Å, c?=?14.8?Å for the ξ-phase. A new two-dimensional domain-boundary network has also been observed in these two phases. Domain boundaries with normals closely parallel to the [001] direction are actually phason planes represented by a translation vector of r?=(1/2)a?+(1/2τ)c in the ξ′-phase and r=±(1/2τ²) a?+(τ/2)c in the ξ-phase, whereas the newly-found wide and zigzag boundaries perpendicular to the above set were attributed from the step-like boundary structures of domains related by a translation vector of r?=(1/τ)((1/2)a?+(1/2τ)c). The structural difference between the two types of planar faults is discussed.     

Effects of temperature and electron energy on the electron-irradiation-induced decomposition of sapphire

The effects of temperature and electron energy on the electron-irradiation-induced decomposition of sapphire have been investigated by in situ transmission electron microscopy (TEM). It was found that the decomposition rate of α-Al₂O₃ increased with increasing irradiation temperature and decreased with increasing acceleration voltage. The core-hole Auger decay process (K–F model), rather than knock-on displacement, is responsible for the decomposition of α-Al₂O₃ under electron irradiation.     

Transformation-induced elastic strain effect on the precipitation kinetics of ordered intermetallics

Abstract

A transformation-induced elastic strain effect on the decomposition kinetics of a disordered phase into a mixture of ordered and disordered phases was investigated for a prototype binary alloy in two dimensions (2-D) by using a computer simulation technique. The simulation technique not only described simultaneously different processes, such as atomic ordering, clustering, disordering and coarsening, but also produced automatically ordered structures and alloy morphologies. It was found that irrespective of the degree of the crystal lattice mismatch between precipitates and the matrix, the alloy morphologies, developed during the congruent ordering stage which preceded the decomposition, showed no alignment in any of the crystallographic directions. Alignment developed during subbequent decomposition of the congruently ordered single phase, which resulted in the appearance of an equilibrium disordered phase preferentially along the antiphase domain boundaries. It became increasingly pronounced as the time of alloy aging increased. The aligned morphology finally formed the modulated structure found in many alloys. This mechanism of modulated structure formation is new since almost all previous experimentally observed modulated structures were interpreted as a result of a homogeneous spinodal decomposition. The predicted kinetics was found to be in excellent agreement with recent experimental results in a Fe-Si system and should be expected in most two-phase alloys with an ordered intermetallic precipitate whose stress-free lattice constant is significantly different from that of the disordered matrix.     

Elastic solutions with arbitrary elastic inhomogeneity and anisotropy

An efficient numerical algorithm is proposed to accurately compute the elastic fields in two-dimensional (2D) or three-dimensional (3D) microstructures with arbitrary elastic inhomogeneity and anisotropy. It combines the equivalent inclusion method of Eshelby, the microelasticity theory of Khachaturyan, and the spectral iterative perturbation method of Hu and Chen. Its efficiency is compared with those of existing approaches in the literature. The method can be conveniently implemented in phase-field modeling of stress-dependent microstructure evolution and/or of mass/electrical transport.     

Effects of Si addition on the microstructure evolution of Al–Cu–Mg alloys in the α + S + T phase field

The precipitation behaviour and age-hardening response of Al–1.5Cu–4.0Mg (wt.%) alloys microalloyed with Si have been investigated by means of hardness measurement, TEM and HRTEM. Compared to the ternary alloy, the quaternary alloys exhibit a higher hardness. It is found that the underaged microstructure in the Al–1.5Cu–4.0?Mg alloy contains some fine precipitates, which are identified as the T phase by FFT spectra. The peak-aged microstructures of the ternary alloy is dominated by the T phase, while the peak-aged microstructures of the Si-containing alloys are dominated by the S phase. The volume fraction of the S phase is found to increase as more Si is added.     

Deformation twins induced by multi-mode deformation in nanocrystalline copper

A multi-mode deformation model is used in a molecular dynamics simulation of nanocrystalline copper. Abundant deformation twin lamellae are developed by shearing the following compression to the elastic limit. Deformation twins (DTs) nucleate through two different mechanisms facilitated by Shockley partial slips. Interactions between DTs and Shockley partials are observed in this simulation.     

Multiple identities and career development of GLB immigrants

There has been increasing interest in the study of career development and career counselling for the gay men, lesbian women and bisexual (GLB) people given the clear link between sexual orientation and career development in the past two decades. Yet, there is still a relatively dearth of literature in this area, especially, much is unknown about the career identity and other related identity development experiences of GLB immigrant adults whose acculturation process intersects with cultural identity, race and ethnicity and sexual identity as they rebuild their careers in the host country. This article aims to explore the connections between multiple cultural identities and their affect on career development. It builds upon the current literature, uses some career development theories, and proposes career development and career counselling interventions for the target group.     

Law,Humanity, and Reason: The Chinese Debate,the Habermasian Approach,and a Kantian Outcome

This paper explores the subject-matter of the relationship between law and humanity, filling a significant lacuna in philosophy of law in the West today. Doing so, the paper starts with recasting the traditional Chinese conflict—in particular, the conflict between legalism and Confucianism—over law in a new light of the contemporary call for stopping crimes against humanity. It then explores Habermas’ insight into and illusion of law. Finally, it examines the internal relationship between law and humanity, contending that law must always treat humanity as a purpose, not as a tool to other ends, functioning to build a community of humanity; while a distinction exists between justice and benevolence, law must not be inhumane.     

Uncertainty regulation across cultures: An exploration of individual differences in Chinese and Canadian children in the classroom

This research investigates whether individual differences in uncertainty orientation affect classroom behavior for Chinese and Canadian children. Uncertainty orientation distinguishes between uncertainty-oriented individuals, or those who attempt to attain clarity by finding out for themselves, and certainty-oriented individuals, or those who attempt to maintain clarity by adhering to predictable environments. Although uncertainty orientation is considered an informational variable, uncertainty-oriented children in both countries had higher self-ratings, ratings by other students and ratings by their teachers than certainty-oriented children on a variety of social and achievement behaviours. These results suggest that encouraging a discovery learning style of uncertainty regulation in “UO-centric” cultures may be beneficial.