1,720,983 research outputs found
Implementation and development of the incremental hole drilling method for the measurement of residual stress in thermal spray coatings
No full textThe experimental measurement of residual stresses originating within thick coatings deposited by thermal spray on solid substrates plays a role of fundamental relevance in the preliminary stages of coating design and process parameters optimization. The hole-drilling method is a versatile and widely used technique for the experimental determination of residual stress in the most superficial layers of a solid body. The consolidated procedure, however, can only be implemented for metallic bulk materials or for homogeneous, linear elastic, and isotropic materials. The main objective of the present investigation was to adapt the experimental method to the measurement of stress fields built up in ceramic coatings/metallic bonding layers structures manufactured by plasma spray deposition. A finite element calculation procedure was implemented to identify the calibration coefficients necessary to take into account the elastic modulus discontinuities that characterize the layered structure through its thickness. Experimental adjustments were then proposed to overcome problems related to the low thermal conductivity of the coatings. The number of calculation steps and experimental drilling steps were finally optimized
Pure thick nickel coating obtained by electroless plating. Surface characterization and wetting properties
No full textPure nickel coatings were directly plated onto steel by using an electroless plating process. The effect of different synthesis strategies on the morphological surface was investigated and the study of growth mechanisms has provided useful information about the surface properties of coating. In this paper, several plating parameters (pH, temperature, solution composition and the ratio between the sample surface area and the volume of solution) were investigated by studying their influence on the plating rate. High thickness (30 μm) coatings were obtained after 2 h of plating at 85 °C. XRD, SEM and AFM analyses were performed to evaluate microstructure morphology and chemical composition of the deposited coatings. Surface analysis has shown the presence of a hierarchical structure with a macro-nano hierarchical structure and a nanostructured roughness; the influence of surface morphology on wetting properties was assessed. Electroless Ni plated samples exhibit wetting properties changing over time: as-coated samples show a super-hydrophilic behavior with a water contact angle 150°. This phenomenon was studied analytically by measuring the water contact angle at different exposure times and by investigating the causes of the surface properties modification. Results confirm that the variation in wettability can be attributed to the presence of airborne hydrocarbon adsorbates on the coating surface
Rapid Solidification of Plasma Sprayed Advanced Materials: nanostructure characterization
No full textRapid solidification of plasma sprayed advanced materials: nanostructure characterisation
No full textComposite ZrB2-SiC materials offer well known resistance to ablation at high temperature. An inert plasma spraying technique was used to manufacture composite ZrB2-SiC as potential thermal protection systems for composite based substrates. Due to the rapid solidification experienced by sprayed droplets, amorphous and/or nanostructured phases can be formed; advanced characterization techniques are therefore required in order to collect all the necessary data for process/product optimisation. In addition, silicon carbide, selected for its contribution to the oxidation resistance of the ceramic coating, is well known to be considered as a non sprayable material, due to the lack of a stable liquid phase. In this paper two issues are investigated: the first is the use of advanced characterization techniques, such as high resolution scanning and transmission electron microscopy, for microstructural analysis of plasma sprayed coatings. The second is the evaluation of possible implications of rapid solidification processes in composite systems for which at least one liquid phase is not stable, but, at the same time, the development of eutectic-like structures results in the formation of nanostructured stable solid phases
A parametric study of an HVOF process for the deposition of nanostructured WC-Co coatings
No full textParametric study of an HVOF process for the deposition of nanostructured WC-Co coatings
No full textNanocrystalline WC-Co coatings were deposited by high velocity oxyfuel from commercial nanostructured composite powders. Processing parameters were optimized for maximal retention of the nanocrystalline size and for minimal decarburation of the ceramic reinforcement. Thermochemical and gas-dynamical properties of gas and particle flows within the combustion flame were identified in various operating conditions by computational fluid-dynamics (CFD) simulation. Significant improvements of the mechanical properties of the coatings were obtained: a decrease of the friction coefficient was measured for the nanostructured coatings, together with an increase of microhardness and fracture toughness
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“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
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