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2005

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On the use of fractal geometry concepts for evaluating the wear behaviour of ductile materials. Application to Mn Mo sintered steels

The evolution of friction and wear of Fe-2Mn-0.85Mo-0.5C steels sintered under two different conditions was investigated during dry sliding tests. Irregular behaviour of the friction coefficient was observed and analysed by means of fractal geometry methods. It was proven that the friction coefficient traces had the property of fractal curves. In general, the fractal dimension of friction coefficient trace tended to increase with increasing wear rate.

Study of the degradation causes affecting stucco sculptures from the Valentino Castle in Turin

17th century stuccos located in The Valentino Castle in Turin (Northern Italy) have been studied by means of XRD, TG-DTA, Hg porosimetry and SEM coupled with EDX chemical analysis in order to understand their composition and the degradation causes. The investigated un-degraded samples were made of gypsum, hydrated lime and other carbonates phases on the external surface and up to ca. 20 mm in depth but the compositions were highly heterogeneous.

Influence of the dopants on the electrical resistance of hematite-based humidity sensors

Humidity sensing properties of α-Fe2O3 have been studied after doping with alkali and alkaline earth oxides precursors. Sensors were screen-printed and three different firing temperatures were investigated: 850, 900 and 950 °C. Formation of secondary phases has been investigated by means of 57Fe Mössbauer spectroscopy for K-doped hematite samples and by means of TG–DTA and XRD for all the compositions. Alkali and alkaline earth additions to hematite, except sodium ones, increased the opened porosity as evidenced by mercury porosimetry measurements onto pressed pellets.

Influence of the co-precipitation temperature on phase evolution in yttrium-aluminium oxide materials

Yttrium-aluminium garnet (YAG) powders were synthesized using a reverse-strike precipitation, by adding an aqueous solution of yttrium and aluminium chlorides to dilute ammonia while monitoring the pH to a constant value of 9. After precipitation, the gelly product was washed with dilute ammonia and absolute ethanol for avoiding hard agglomeration during drying. Precipitation and washing procedures were performed at three different temperatures, namely at 5, 25 and 60 °C.

Different sintering routes for preparing alumina-yttrium aluminum garnet nanocomposites

Alumina-yttrium aluminum garnet (YAG) 50 vol % nanocomposite powders were prepared by a wet-chemical synthesis and characterized by simultaneous DTA-TG, XRD, and TEM analyses. Amorphous powders were preheated at four different temperatures (namely, 600, 800, 900, and 1215°C) on the basis of the previous characterization, and the influence of this thermal treatment on sintering behavior, final microstructure, and density was investigated.

Study on new ceramic coated metal powders: Microstructure and properties

Metal/ceramic composite materials were produced with core/shell structure by traditional pressing and the influence of the compacting parameters on the material properties has been studied. Different quantities of ceramic have been introduced to coat the base stainless steel powder. The use of a new generation of coated powders gives the opportunity to achieve near net shape massive composite exhibiting a composite microstructure, with a uniform dispersion of ceramic hard particles embedded in the metal matrix.

Fracture of nitrided and nitrocarburized blunt notch three-point bending die steel specimens

Results of studies on impact tested gas and plasma nitrided or nitrocarburized blunt notch die steel samples with varying notch root radii are presented.

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