Results 1 - 10 of 3275
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[en] The deformation behavior of pure copper polycrystals was investigated by in situ X-ray microdiffraction using synchrotron radiation. Tensile axis rotations of several positions of same grain were observed. Tensile axis movement depends on local position of a grain. This phenomenon may originate from the orientation relation between neighboring grains
[en] Aberration-corrected transmission electron microscopy, combined with atomistic simulations, has been used to study the anisotropy profiles of interfaces between metallic Nd (fcc, dhcp), Nd2O3 (hP5, cI80), NdO and the Nd2Fe14B phase. The results show that the dhcp Nd and Nd2O3-hP5 phases have a more detrimental effect on coercivity than fcc Nd, Nd2O3-cI80 and NdO. The coercivity change is rooted in distortions in the Nd2Fe14B crystal lattice; the depth and magnitude of this change is a function of orientation and type of Nd-rich phase
[en] Graphical abstract: -- We report on the shear–bypassing transition of chemically ordered Al3Zr nanoprecipitates. Observation of complex combinations of lattice translations, revealed by scanning transmission electron microscopy, is used as the signature of precipitate shearing during cold deformation. A method is proposed to build a three-dimensional atomic model of sheared particles from a set of three atomic scale projections. An estimation of the antiphase boundary energy of the Al3Zr structure is achieved via the comparison of experimental findings to a model of precipitation hardening
[en] Porous 6H-SiC ceramics were fabricated at a low temperature by an in situ reaction bonding process. After subsequent heat treatment, porous SiC ceramics with elongated 6H-SiC grains and improved strength were obtained. The results indicated that in situ growth of elongated 6H-SiC grains was caused by rare earth elements together with the liquid Ba–Al–Si–O system. The type and content of rare earth oxides had a large influence on the growth of elongated 6H-SiC grains
[en] It is demonstrated that group III atomic species in the mixed III nitrides, differing in their covalent tetrahedral radii, are not distributed at random on their sub-lattice. Two types of deviations from randomness are observed: phase separation and atomic ordering. Phase separation lowers the strain energy of the layer. The absence of phase separation in InGaN quantum wells is attributed to the stress imposed by the GaN barrier layers. Atomic ordering doubles the periodicity along the [0 0 0 1] direction
[en] Graphical abstract: “Nanoweb” formation of highly conductive paths in a composite material as a possible way to overcome the tradeoff between Seebeck coefficient and electrical conductivity. - Abstract: Previously through a combination of doping certain transition-metals into YB_2_2C_2N and heat treatment, Seebeck coefficients were enhanced by up to 220% while simultaneously, electrical conductivity was increased by ∼10,000%. This was a striking result since it overcomes the traditional trade-off between the two; a huge obstacle for enhancing thermoelectric performance. Nano-characterization gives direct proof that this is due to a hybrid/composite effect where highly conductive paths were partially established. At the same time, it is speculated that intrinsic doping modifies the electronic structure of the host material. This hybrid effect may be applicable to a broad spectrum of thermoelectric materials.
[en] Using molecular dynamics simulations, we study the structural properties of body-centered cubic (BCC) and body-centered tetragonal (BCT) phases of U–Mo alloys. The local positions of uranium atoms in the BCC phase correspond to the BCT structure. Thus, the BCC lattice exhibits cubic symmetry only on the scale of several interatomic spacings, and it is therefore more correct to denote the high-temperature state of U–Mo alloys as quasi-BCC. This structural feature occurs for pure uranium as well. This fact is the possible origin of the difficulties encountered in the description of the BCC phase of pure uranium by ab initio methods.
[en] Transmission electron microscopy with in situ ion irradiation has been used to examine the ion-beam-induced amorphisation of crystalline silicon under irradiation with light (He) and heavy (Xe) ions at room temperature. Analysis of the electron diffraction data reveal the heterogeneous amorphisation mechanism to be dominant in both cases. The differences in the amorphisation curves are discussed in terms of intra-cascade dynamic recovery, and the role of electronic and nuclear loss mechanisms.
[en] The redistribution of arsenic in high-k metal gate stacks on fully depleted silicon was investigated. Both gates corresponding to n and p-type devices were analysed by atom probe tomography. Reconstruction shows the presence of arsenic at various interfaces. The most important accumulation is between the silicon and titanium nitride. This is confirmed by energy dispersive X-ray spectroscopy. The maximum concentration is in the order of 10%, with a thickness around 1 nm. Interaction energies between dopants and interface have been estimated to be approximately 0.4 eV. The arsenic is shown by X-ray photo-electron spectroscopy to be bonded to silicon throughout.
[en] In this paper, a new β-metastable titanium alloy, based on the Ti–Cr–Sn system, displaying both an extremely high work hardening rate and a uniform deformation larger than 0.35, was designed and successfully tested. The compositional design was guided through a stability mapping approach based on the “d-electron design method” and using an unexploited region of the Bo/Md map. Detailed analysis of deformation mechanisms shows combined transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects, resulting in a complex network of microstructural features and giving rise to marked kinematic hardening.