1,720,970 research outputs found
Investigation of solid-liquid interactions in high temperature metal-ceramic systems
No full textStudio delle interazioni solido-liquido in sistemi metallo-ceramico testati ad alta temperatur
Wettability of transparent YAG (Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf>) by molten Ag-Cu-Ti alloys
No full text
Atmospheric-pressure plasma jet texturing of C/C composites for improved joint strength
Full text linkThis study explores the use of air-fed atmospheric pressure plasma jets (APPJs) as a pre-joining treatment for 3D
carbon fiber-reinforced carbon matrix composites (C/C) with the aim of both creating a textured surface that
resembles a brush structure and improving the joint strength.
The effects of various treatment time lengths on the mass loss, etching depth, and surface texture were
investigated using SEM and confocal microscopy. An optimal process time of 30 s was selected, while keeping the
other process parameters fixed (air flow of 1750 l/h and nozzle-sample distance of 5 mm). Wetting tests were
conducted at 1000 ◦C, on both untreated and pre-treated C/C surfaces by means of liquid TiCuNi brazing alloy,
and low contact angles of about 20◦ were measured. C/C–TiCuNi–C/C and C/C–TiCuNi–Cu joints were then
produced, and their interfacial reactivity was evaluated. The apparent shear strength measured for the APPJtreated C/C–Cu joints was 140 % higher than the value recorded for the untreated joints, thus confirming the
effectiveness of the treatment.
Even though a further investigation is needed in which an optimization of the process parameters should be
included, this preliminary study has revealed the viability of APPJ as a promising technique to enhance the
bonding of C/C composites in dissimilar assemblies and to improve the joint qualit
Ag and AgCu as brazing materials for Ti6Al4V-Y 3 Al 5 O 12 joints: Does ennoblement affect the galvanic behaviour in seawater?
No full textTransparent ceramic materials may be used as optical windows, sensors, gas-tight components, etc. in specific marine applications by integration into metallic structures through joining procedures. In such systems the evaluation of galvanic effects between base alloys and compounds obtained during brazing is crucial. In this work, the galvanic behaviour of Ag and AgCu brazes, used to obtain Ti6Al4V-Y3Al5O12 joints, was investigated in natural seawater for the first time. Two test sessions lasting 4 weeks each were performed. During the first, the AgCu brazed joint showed Cu selective depletion from both the interlayer and the diffusion zone, while the Ag brazed one appeared intact. Hence, the second session was devoted to a further study of the Ag brazed joint. Active-passive alloys are well known to undergo important OCP positive shift induced by the biofilm growth, commonly referred as ennoblement. The risk of Ti6Al4V to act as ennobling cathode, with acceleration of the Ag anodic dissolution in the interlayer, was simulated with Ti6Al4V and Ag freely corroding and coupled electrodes. In parallel, a 254 SMO stainless steel/Ag system was used as reference for ennoblement. OCP data were evaluated in the framework of inferential statistic in order to highlight the consistence with galvanic coupling data. The results were: 1) when coupled to Ti6Al4V, Ag showed occasional and reversible anodic inversions with galvanic current z 10-6 A x cm-2, 2) when coupled to 254 SMO, Ag inverted irreversibly as anode with galvanic current up to 10-5 A x cm-2. These differences depended on Ti6Al4V not ennobling, contrary to SS, which ennobled acting as a more powerful cathode. Finally, about dissimilar joints in natural seawater with Ti6Al4V as base alloy, AgCu is confirmed to be unsuitable as brazing material due to early Cu depletion from the interfacial zone. Differently, Ag is promising in relation to generally stable interfaces, even when there is a risk of ennoblement, thanks to Ti6Al4V not ennobling
Brazing transparent YAG to Ti6Al4V: Reactivity and characterization
No full textThe YAG/filler/Ti6Al4V system has been studied for the first time with the aim of producing brazed optical windows. Different fillers (AgCuTi, AgCu, Ag) and temperatures have been taken into account and the interfacial zones of the samples have been evaluated in terms of morphology and compositions. A thin and continuous metal-ceramic layer containing Ti is formed in contact with the YAG ensuring the adhesion between all the joined materials. The best joining results have been obtained at 850. °C, where we have observed the formation of an interfacial CuTi layer when AgCuTi and Ag have been used. No intermetallic compound formation was observed using the pure Ag at 970. °C and 1050. °C. The phase formation was interpreted using the CALPHAD method by means of recalculated Ag-Cu-Ti and Ag-Al-Ti isothermal sections. Microhardness tests have been conducted to evaluate the performances of the joints in terms of mechanical properties
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
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