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The influence of annealing on the mechanical properties of high-silicon cast iron for three alloys with distinct chromium levels was investigated. Each alloy was melted either with or without the addition of Ti and Mg. These changes in the chemical composition and heat treatment aimed to improve the material's mechanical properties by inhibiting the formation of large columnar crystals, netlike laminae, precipitation of coarse packs of graphite, changing the length and morphology of graphite, and rounding the extremities of the flakes to minimize the stress concentration. For alloys with 0.07 wt.% Cr, the annealing reduced the impact resistance and tensile strength due to an enhanced precipitation of refined carbides and the formation of interdendritic complex nets. Annealing the alloys containing Ti and Mg led to a decrease in the mechanical strength and an increase in the toughness. Alloys containing approximately 2 wt.% Cr achieved better mechanical properties as compared to the original alloy. However, with the addition of Ti and Mg to alloys containing 2% Cr, the chromium carbide formation was inhibited, impairing the mechanical properties. In the third alloy, with 3.5 wt.% of Cr additions, the mechanical strength improved. The annealing promoted a decrease in both hardness and amount of iron and silicon complex carbides. However, it led to a chromium carbide formation, which influenced the mechanical characteristics of the matrix of the studied material. [ABSTRACT FROM AUTHOR]

The purpose of this work was to experimentally investigate the thermal diffusivity of four different gray cast iron alloys, regularly used to produce brake disks for automotive vehicles. Thermal diffusivity measurements were performed at temperatures ranging from room temperature to 600 °C. The influence of the thermal conductivity on the thermomechanical fatigue life is also briefly presented. The measurements were sensitive to the influence of the carbon equivalent and alloying elements, such as molybdenum, copper and chromium. Molybdenum, unlike copper, lowered the thermal diffusivity of the gray cast iron, and alloy E (without molybdenum), besides presenting a relatively low carbon equivalent content and an increase in the values of the thermal diffusivity, presented the best performance during the thermomechanical fatigue. The molybdenum present in alloys B and C did not fulfill the expectations of providing the best thermomechanical fatigue behavior. Consequently, its elimination in the gray cast iron alloy for this application will result in a significant economy. [ABSTRACT FROM AUTHOR]

We report on a Raman study of the phonon spectrum of La 0.7Sr0.3MnO3 thin films epitaxially grown on LaAlO3. The spectrum, as a function of film thickness d, does not change over the 1000–100 Å range, whereas a strong hardening of the phonon frequencies of both bending and stretching modes is apparent in ultra-thin films (d<100 Å) where substrate-induced effects are remarkable. This behaviour, which appears to be related with the measured d-dependence of the insulator-to-metal transition temperature, is ascribed to co-operative effects of MnO6 octahedra rotation and charge-localization. Raman spectroscopy proves to be a simple and powerful tool to monitor subtle structural modifications hardly detectable with conventional diffraction techniques in ultra-thin films. [ABSTRACT FROM AUTHOR]

The colossal magnetoresistance (CMR) manganese oxides, have been the subject of intense studies. To elucidate the mechanisms at work in the ferromagnetic metallic state is essential for the comprehension of the M–I transition and the associated CMR effect. We present here comparison among resistivities behavior in Ca and Sr-doped manganite films ( x = 0.3) grown by different techniques and on several substrates allowing to analyze samples with different amounts of disorder. At low temperatures, a dominant T 2 term in the resistivity has generally been observed. Our analysis shows that for residual resistivity values larger than a critical one, there is a substantial deviation from the T 2-like behavior and that an unusual T 2.5 one is robust. This behavior supports the theoretical proposal of single magnon scattering in the presence of minority spin states localized by the disorder. In the high temperature insulating paramagnetic phase the resistivity shows the activated behavior characteristic of polaronic carriers. Finally in the whole range of temperatures the experimental data are found to be consistent with a phase separation scenario. [ABSTRACT FROM AUTHOR]

Structural investigation using X-ray synchrotron radiation has been performed on SrRuO3/SrTiO3/SrRuO3 epitaxial heterostructures, with each constituent layer a few unit cell thick grown on (001) SrTiO3 substrate. Detailed information on the evolution of the in-plane lattice structure has been obtained, in these heterostructures, by grazing incidence diffraction measurements. The samples have been grown by low-pressure pulsed laser deposition. Under our deposition conditions, SrRuO3 layers grow with an elongated cell perpendicular to the substrate surface. The in-plane pseudocubic lattice parameters do not match the in-plane square SrTiO3 structure even in the case of very thin SrRuO3 layers. Such a distortion was found to decrease with increasing the thickness of the SrTiO3 barrier layer. [ABSTRACT FROM AUTHOR]

Presents the results of a study on the infrared phonons in the La0.7Sr0.3MnO3 manganite using reflectance measurements on epitaxial films. Relationship between the manganite phonon spectrum and the substrate and film thickness; Role of the thick films measurements in the determination of line profile and the peak-frequency of the bending and stretching of phonons.

In this report we demonstrate that high quality epitaxial heterostructures, based on metallic SrRuO3 and insulating SrTiO3 individual blocks a few unit cells thick, can be grown in a purely 2D, layer-by-layer mode, using pulsed laser deposition with in situ reflection high energy electron diffraction (RHEED) diagnostics. The thickness of each constituent block can be controlled at the level of a single unit cell. A detailed investigation carried out at the synchrotron facility, ESRF, by various X-ray techniques has demonstrated that each intensity oscillation of the RHEED specular spot corresponds strictly to the growth of a single perovskite unit cell, either SrRuO3 or SrTiO3. Furthermore, we show that, in these structures, the interfaces between the different constituent blocks are very sharp with a roughness of only one unit cell. [ABSTRACT FROM AUTHOR]