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Phase composition and morphology as a function of depth for boride coatings grown on Fe-Ni alloys
No full textConsiderable R&D efforts are being carried out in order to produce materials with satisfactory resistance to wear, corrosion or both. In many applications, in fact, the in-service life of components is determined by the surface properties. In the important field of thermochemical treatments of steels, based on diffusion of species such as carbon, nitrogen or boron, boriding is in a peculiar position. Indeed, coatings constituted by iron borides generally display very high hardness, even in excess of 20 GPa, as well as good wear resistance under both sliding and abrasive conditions. Borided steel components display excellent performance in several tribological applications in the mechanical engineering and automotive industries. In spite of several researches performed since many years, some problems remain to be solved as, in particular, the role of alloying elements in the steel on growth and properties of the boride coating.
In the present work the attention has been addressed to the role of Ni, investigated by boronizing binary alloys in order to avoid any interference by other alloying elements. Five Fe-Ni alloys with a Ni contents in the range from 11 to 80 wt.% were borided by a pack-cementation process, using a high boron potential powder mixture constituted by amorphous boron activated with 10 wt.% of potassium fluoborate. The thermochemical treatments were carried out at 850°C for exposure times up to 8 h.
Phase composition and morphology of the boride coatings were characterized as a function of depth by the layer-by-layer removal technique as well as by observations carried out on metallographic cross-sections, using different and complementary techniques: X-ray diffraction (XRD), Mossbauer spectroscopy (MS), micro-Raman spectroscopy, optical (OM) and scanning electron microscopy (SEM), Vickers microhardness measurements (MHV)
Microscale computational simulation and experimental measurement of thermal residual stresses in glass-alumina functionally graded materials
No full textGlass-alumina functionally graded materials are new attractive composite materials, that can achieve peculiar mechanical properties due to their gradual compositional variation. Nevertheless, the difference between the coefficients of thermal expansion of the constituent phases may result in significant thermal residual stresses in service or during fabrication. A proper (glass formulation can minimize the mismatch in thermo-mechanical properties, thus relevantly reducing the mean value of the resultant thermal stresses. However, it is a crucial requirement to evaluate the effect of microstructural discreteness and randomness oil the actual stress distribution in functionally graded materials. With this aim,a computational model which applies the finite element method at the microscale is used. The careful modelling of the real microstructural details enables to accurately predict the local stress values and distribution. In order to verify the reliability of the computational simulations, the residual thermal stresses were also experimentally measured by means of a piezo-spectroscopic technique. The comparison between the numerical and the experimental results validate the microstructure-based model
Resa e composizione di oli essenziali estratti da piante officinali coltivate in agricoltura biodinamica
No full textEffetti allelopatici di Lavandula officinalis L. e Santureja montana L. su Matricaria chamomilla L.
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Effect of Superficial Residual Stresses on Abrasive Wear Resistance of Al2O3/Al2O3 + 3Y-TZP multilayers
No full textMultilayered composite specimens consisting of Al2O3 / Al2O3+ 3Y-TZP (A/AZ) layers with different compositions and thicknesses were prepared starting from ceramic sheets obtained by tape casting. Residual stresses arisen from mismatch in thermal expansion coefficient during sintering were evaluated using luminescence piezo-spectroscopy. The stress in the superficial A layer was found to be compressive, and its value depended on the ratio between thickness of A and AZ layer. The influence of the superficial compressive stress on the abrasive wear resistance was investigated using microscale ball cratering test; results were correlated with the superficial compressive stress and compared with a specimen of pure unstressed Al2O3 prepared both by lamination and by cold isostatic pressing. Experiments show an improvement of performances in the samples containing compressive residual stress in the surfac
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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