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181.
Based on systematic surface observations, experimental measurements on the fatigue limits of differently oriented copper single crystals cyclically deformed at constant plastic strain amplitudes are summarized, and an orientation dependence of the fatigue limit is sketched. It was found that the fatigue limits of crystals depend mainly upon the low-strain-amplitude dislocation structures, which are characteristic of the particular crystal orientations. When multiple-slip deformation is the main mode of deformation and ultimately produces stable lowenergy dislocation structures such as labyrinth and cell structures, the fatigue limit can be improved notably. 相似文献
182.
CeO2-doped diamond-like carbon (DLC) films with thicknesses of 180–200 nm were deposited by unbalanced magnetron sputtering. When the CeO2 concentration is in the range 5–8%, the residual compressive stress of the deposited films is reduced by 90%, e.g. from about 4.1 GPa to 0.5 GPa, whereas their adhesion strength increases. These effects are attributed to the dissolution of CeO2 within the DLC amorphous matrix and a widening interface between the DLC film and the Si substrate, respectively. 相似文献
183.
184.
In spite of many superior high-temperature properties of intermetallics, it has been difficult to understand their intrinsic brittleness. To eliminate or improve the embrittlement, the conventional alloying technique based on the trial-and-error method is still the most effective and practical. However, it remains a main challenge for both physicists and materials scientists to provide either an alloying principle or a deep insight into its toughening mechanism at an atomic or electronic level. This letter reports a simple experimental approach that uses work function (WF) as a sensitive indicator of the role of alloying in changing mechanical behavior. NiAl is chosen as a typical example. It is found that with the addition of Cr and Ce, the ductility of NiAl increases significantly. Such an increase in ductility corresponds to a concomitant decrease in the WF, which is attributed to a change in the nature of the atomic bonding or in the electronic structure induced by the alloying. This fundamental understanding on the embrittlement nature of NiAl could provide some alloying guidelines or principles for other intermetallics. 相似文献
185.
This article proposes a factor, the critical electronegativity difference Δx cri, to correlate alloy composition with thermal stability and glass-forming ability of Al–Ni–RE (RE: Rare Earth element) ternary metallic glasses. The Al-rich metallic glasses with Δx > Δx cri exhibit glassy behavior, whereas alloys with Δx < Δx cri are nanocrystalline. Nanoglassy alloys occur when Δx ≈ Δx cri. The best glass formers are located near Δx cri. Furthermore, an equation has been deduced to calculate Δx cri with varying RE covalent atomic radius. 相似文献
186.
The cyclic strain-hardening behaviour of copper single crystals with various slip orientations is considered systematically. It is shown that the crystallographic orientation has a strong effect on the cyclic hardening behaviours of double- and multiple-slip-oriented copper single crystals. The initial cyclic hardening of differently oriented copper single crystals is mainly dependent on the modes and intensities of dislocation interactions between slip systems operating in the crystal, as well as on the possibility of cross-slip. A distinctive strain burst phenomenon has been frequently observed in the very early stage of cyclic hardening for critical double-slip-oriented crystals. A secondary cyclic hardening stage occurs readily late in cyclic deformation of coplanar doubleslip-oriented crystals. 相似文献
187.
In this article, we propose an efficient atomic packing cluster-based composition protocol to help design Al-based metallic glasses. Its validity is verified by some typical experimental data from the literatures. Furthermore, with this understanding, the Al–Ni–Y alloy system is re-evaluated. As a result, the best glass former Al86Ni9Y5 in this system, with the critical thickness of about 500 µm, is successfully fabricated by wedge casting. 相似文献
188.
Transmission electron microscopy has been used to reveal the microstructure of metastable C40 MoSi 2 thin films produced by annealing amorphous magnetron-sputtered deposits at 700°C. The films contain nanoscale acicular grains elongated parallel to (0001), with extensive basal faulting. The faults are intrinsic with R ´ 1/3[0001] and correspond to thin slabs of the equilibrium C11 b phase. It is proposed that these faults may act as nuclei for the subsequent transformation from C40 to C11 b by a process akin to discontinuous coarsening. 相似文献
189.
H. Li F. Yin T. Sawaguchi K. Ogawa X. Zhao K. Tsuzaki 《Philosophical Magazine Letters》2013,93(5):348-357
A dominant Goss texture component instead of a Brass texture component has been observed in a warm-rolled Fe–28Mn–6Si–5Cr shape memory alloy [H. Li, F. Yin, T. Sawaguchi K. Ogawa, X. Zhao and K. Tsuzaki, Mater. Sci. Eng. A 494 (2008) p.217]. In order to clarify the orientation flow mechanism in these grains of Goss orientation, investigations on microtexture and microstructure were carried out by electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). It is concluded that the Goss–Brass orientation transformation is restrained in the Goss-orientated grains, which were widely observed in both the deformed matrix and shear bands. 相似文献
190.
In this study, bulk nanostructured composite Cu60Fe40 alloy is prepared by a combustion synthesis technique. The prepared Cu60Fe40 alloy consists of Cu(Fe) solid solution and Fe(Cu) solid solution phases. The large-scaled compositional segregation in the Cu-rich and Fe-rich phases is not observed, respectively. A few micron-sized dendrite (Fe(Cu) solid solution) is embedded into the nanostructured matrix (Cu(Fe) solid solution). The grain size of the matrix is in the range 50–300?nm. The yield and fracture strength of the Cu60Fe40 alloy are 540 and 1050?MPa, respectively, and the fracture strain obtained from the compression test is about 20.9%. The Cu60Fe40 alloy displays notable work hardening in the compressive deformation. 相似文献