Wang Ren-hui

Plastic Deformation of Fine-Grained Al?Cu?Fe?(B) Icosahedral Poly-Quasicrystals at Elevated Temperature

Fine-grained Al–Cu–Fe–(B) icosahedral poly-quasicrystals (IQCs) as the main materials and fine-grained Al–Pd–Mn IQCs as the supplements, both prepared by powder metallurgy, are uniaxially deformed at various temperatures and strain rates. The systematic study shows the dependences of curves of the true stress versus true strain on several parameters, such as temperature, strain rate and grain size. For Al–Cu–Fe IQCs with grain sizes of about 10–30 μm, QC-specific intra-granular softening drop appears in the deformation curves at lower temperatures and/or faster strain rates, but disappears in those curves at higher temperatures and/or slower strain rates, which suggests that the inter-granular effects such as grain-boundary sliding should be taken into account to interpret the continuous hardening, similarly to conventional poly-crystals. For Al–Cu–Fe-B IQCs with smaller grain sizes of about 1 μm and fine-grained Al–Pd–Mn IQCs with grain sizes of about 10 μm, QC-specific intra-granular softening drop is absent for all the deformation curves at the possible lowest temperature and fastest strain rate. This implies that the smaller the grain size, the more the inter-granular contribution. At the same time, due to the rapid recovery caused by intense diffusion in small-sized grains, the intra-granular quasicrystal lattice reorders rapidly from disordering, which also inhibits the intra-granular softening drop to some extent.

Orientational domains at room temperature in La0.33Ca0.67MnO3 perovskite

Orientational domains at room temperature in orthorhombic perovskite La0.33Ca0.67MnO3 were studied by group-theory and observed systematically using transmission electron microscopy. There are six orientational variants (A, A′, B, B′, C andC′) in orthorhombic perovskite La0.33Ca0.67MnO3. Their orthorhombicbo directions are parallel to theap,bp andcp directions of the cubic prototypic perovskite, respectively. In each case there are two orientational variants (e.g.,A andA′) with theirao andco axes interchanged. Among the possible 15 boundaries between these 6 variants there are only two types of domain boundaries: (1) m<100>boundariesC′/C, A′/A, andB′/B. (2) m<110>boundaryiesC′/A, C′/A′, C′/B, C′/B′, C/A, C/A′, C/B, C/B′, B′/A, B′/A′, B/A, andB/A′.

Generalization of Eshelby's method to the anisotropic elasticity theory of dislocations in quasicrystals

The general expressions of the elastic fields induced by straight dislocations in quasicrystals have been given according to Eshelbys method which was used to treat the anisotropic elasticity of dislocations in crystals. As an example, the elastic displacement vector, the stress tensor and the elastic energy density of a screw dislocation line lying on the quasiperiodic plane of decagonal quasicrystals are calculated.

Rocking curve calculation by means of changing involved diffraction beams

By changing the diffraction beams involved in rocking curve calculation with matrix method, according to the incident beam direction, the required computing time may be considerably reduced.

Three-dimensional size and orientation of the precipitates in AZ91 magnesium alloys measured by TEM techniques

Knowledge of the microscopic structure, including three-dimensional (3-D) size and orientation of the precipitates, is essential to fully understand the mechanical properties of the magnesium alloys and designing the alloys with better performance. Analytical TEM with high spatial resolution offers the simultaneous measurements of 3-D size, structure, orientation, composition of the precipitates from one typical sample along an established crystallographic axis. Besides popular Burgers orientation relationship (OR), other ORs such as Pitsch?Schrader OR, Crawley OR, Potter OR and a new OR with the form of [0001]? 1.0? from [311]? and (110)? 2.0?? from (03)? between the magnesium matrix and the precipitate ?-Mg17Al12 are identified by TEM imaging and diffraction techniques. As a case study, the thicknesses of the individual precipitates with Burgers OR are further measured to be 100?200 nm through both electron energy-loss spectroscopy and x-ray energy dispersive spectroscopy combining differential x-ray absorption and extrapolation, which are in agreement with the overall 3-D size statistic distribution results obtained through analysing various samples along various directions. Furthermore, the fabricated wedge-shape structure provides a platform on which to study the dependence of the interfacial strain on the variation of the thickness.

Temperature-Dependent Structure of Epitaxial (Ba,Sr)TiO3 Films Grown on SrRuO3-Covered SrTiO3 Substrates

Growth dynamics of epitaxial (Ba,Sr)TiO3 thin films deposited at different temperatures on SrRuO3/SrTiO3 substrates by pulsed laser deposition is investigated by transmission electron microscopy. The films exhibit a layered structure comprising sublayers with distinctive features in regard to the remaining strain, density of misfit dislocations and/or lattice defects, and growth habit. We correlate these temperature-dependent features with the predominant misfit-strain relaxation mechanisms for each one of the detected growth regimes. The thickness dependence of the film structure is discussed within the framework of the predictions for a kinetically modified Stranski–Krastanov growth mode.

Fe3O4 Segregation and Transport Properties of La0.67Ca0.33MnO3

Effect of Fe3O4 segregation at grain boundaries on the electrical transport and magnetic properties of La0.67Ca0.33MnO3 is investigated. The experimental results show that the Fe3O4 segregation not only shifts the paramagnetic–ferromagnetic transition temperature of La0.67Ca0.33MnO3 to a lower temperature region but also induces a new transition in a lower temperature region. Meanwhile, the transition processes observed in both the resistivity and magnetization curves are obviously widened. Compared to pure La0.67Ca0.33MnO3, we assume that the Fe3O4 segregation level at the grain boundaries can modify the electrical transport and magnetic properties of La0.67Ca0.33MnO3.

Experimental Observation on Orientation Relationship between Binary Cd5.7Yb Quasicrystal and its Crystalline Approximant Cd6Yb

Similarity in the electron diffraction patterns of the Cd5.7Yb icosahedral quasicrystal and its cubic approximant Cd6Yb crystal is studied in detail by using transmission electron microscopy. The icosahedral twofold axes are parallel to the cubic 1ττ2 (τ = 1.618...) or 0 0 1 directions, the icosahedral pseudo-twofold axes are parallel to the cubic 15 21 25 directions, the icosahedral threefold axes are parallel to the cubic 1 1 1 and the icosahedral fivefold are parallel to the cubic 0 1 τ directions. Based on those observations a general stereographic projection is given to illustrate the exact orientation relationship.

Structure refinement of the icosahedral AIPdMn quasicrystal using quantitative CBED

The atomic structure of the perfect AIPdMn icosahedral phase has been studied on a single crystal specimen by quantitative convergent beam electron diffraction (QCBED) technique in combination with describing the shape of atonic surface by symme try-adapted series of surface harmonics. The spherical model was used as the starting model for the refinement. By fitting the calculated electron diffraction intensities to the experimental line scan profile, the coefficients in the surface harmonics expansion of the boundaries of atomic surface are refined. The refined parameters show that the fluctuations of the external boundary of atomic surface for Pd atn0 can be as large as 0.2 nm. The boundaries of atomic surfaces for Mn show little fluctuation. In the present model. the number of unphysically short interatonic distances is significantly reduced in comparison with the spherical model.

Synthesis of and incommensurate charge and orbital ordering in La1/2Sr3/2MnO4 layered perovskite

Polycrystalline bulky samples of La1/2Sr3/2MnO4 were systhesized by conventional solid-state reaction in air. Composition analysis by energy dispersive X-ray spectrometer indicated that the average composition of the sample is La0.45 Sr1.49 MnO4 with a minor fluctuation. The [001] zone-axis electron diffraction patterns taken at about 100 K revealed the presence of superlattice peaks, due to the incommensurate charge and orbital ordering. The incommensurate modulation wave vector is k = δ[110]T*, with δ = 0. 19. Such an incommensurate modulation may be described as a random distribution of two commensurate modulations with δ= 1/4 and 1/6.