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231.
232.
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
233.
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
234.
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
235.
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
236.
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
237.
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
238.
Solubility criterion for sequential disordering in metal-metal multilayers upon solid-state reaction
An n-body Ni-Ti potential is derived and applied in a molecular dynamics simulation to study the maximum supersaturated solubility of the terminal solid solutions and solid-state reaction in a Ni/Ti bilayer. It reveals that during interfacial reaction of the Ni/Ti bilayer the Ti lattice reaches its maximum solubility by dissolving Ni earlier than Ni does through dissolution of Ti, which results in a sequential disordering of first Ti and then Ni, although Ti has a higher melting point than Ni. In the Ni-Zr, Ni-Mo and Ni-Ta systems, however, the Ni lattice collapses more rapidly because it reaches a maximum solubility earlier than its partners, which have higher melting points than Ni. A solubility criterion is thus relevant for all the above cases; the lower the maximum solid solubility the less stable is the lattice of the metal upon solid-state reaction. 相似文献
239.
J.J. Wang S. Bhattacharyya Q. Li T.W. Heo X.Q. Ma Long-Qing Chen 《Philosophical Magazine Letters》2013,93(7):327-335
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. 相似文献
240.
X. H. Zhang 《Philosophical Magazine Letters》2013,93(12):797-805
A polymorphous crystallization process in an amorphous FeZr2 alloy has been investigated by means of accurate electrical resistance measurements (ERMs) at elevated temperatures. It was found that, upon crystallization of the amorphous alloy, the electrical resistance increased with increasing temperature, exhibiting three distinct stages. Quantitative microscopy observations revealed that the three stages originated from crystal nucleation, from subsequent growth of crystal nuclei and from coarsening of the crystallites respectively. The activation energies for the crystal nucleation and growth determined from the ERM data agree satisfactorily with the data in the literature. The success in identification of the crystal nucleation and growth processes by means of ERMs may originate from differences in electrical resistance changes due to the crystal formation and the crystalline-amorphous interface formation processes from the amorphous phase. 相似文献