1,720,958 research outputs found
Relationship between through-thickness residual stress of CrN-PVD coatings and fatigue nucleation sites
No full textA CrN monolithic 5 Am thick was deposited on a substrate of H11 tool steel and was characterised by XRD analysis and nanoindentation measurements. Hardness, elastic modulus, chemical composition, texture and lattice constants were determined along with the throughthickness residual stress distribution. A high level of compressive stress was obtained both at the surface and inside the coating; data always
higher than 2 GPa were measured. Low values of compressive stresses were measured in the steel side near the coating/substrate interface.
Those results, coupled with a good adhesion of the interface, allow, when cycling loads are applied to the coated component, a nucleation of the fatigue crack inside the substrate material. Therefore, the critical microstructural parameter that strongly affects the fatigue resistance of
the CrN coated samples investigated becomes the size of nonmetallic inclusions working as discontinuity inside the steel substrate, close to the location of the coating/substrate interface. Indeed, in such a location the compressive residual stresses induced by the deposition technique are low and, therefore, insufficient to oppose the tensile stress induced by the applied loading condition during four-point bending
fatigue tests
Carburizing and nitriding as surface pre-treatment of PVD coating for gears application
No full textAmong the different treatments that can be carried out to locally improve the mechanical behaviour of gears a combination of case hardening followed by PVD coatings (duplex treatment) seems to give promising results in terms of surface hardness, residual stress profile and fatigue resistance. In particular considering the carburizing and the nitriding treatments they can be both aimed, in the same way than the surface coatings, to introduce a different mechanical behaviour between surface and core in order to improve life, reliability and load capacity of the treated component. This is fundamental for gears whose damage is mainly related to contact fatigue, fatigue at the tooth root and pitting on the tooth flank [1-3]. The need of optimising the surface material in order to delay the progressive deterioration of the components due to wear, fatigue or contact fatigue mechanisms, often worsened by the presence of hostile environments, explains the increasing attention on different coating technologies [5-7], In particular, considering the PVD coatings, chemical composition of the surface deposited film, coating thickness, hardness, adhesion with the substrate material and plastic deformation of the substrate material have an important influence on the damage mechanism affecting the coated component. Although hard PVD coatings are well known for improving friction and resistance to wear and corrosion, their tribological performance is often limited by elastic and plastic deformation of the substrate, which can allow to coating failures [12]. The emergence of the duplex treatments, consisting in the sequential application of two o more established surface technologies, has represented a novel approach to the achievement of enhancing coating properties. Duplex treatments, comprising a nitriding treatment followed by the deposition of a hard PVD coating, have been proven to be successful in increasing wear, thermal fatigue and corrosion resistance and the load carrying capability of different steel substrates [13-16]. By increasing the hardness of the substrate, for instance using a nitriding case, often provides a suitable load support for PVD coatings so that superior wear resistance can be achieved. The high values of hardness related to the thermochemical treatment, further enhanced by the introduction of the ceramic coating characterized by a strong difference in coefficient of thermal expansion with respect to the substrate material, affects the surface level of compression residual stress data [21-23], Therefore the residual stress gradient must be evaluated when a prediction of the gear life is requested: in fact the residual stress distribution affecting the nucleation of the fatigue cracks is a factor able to control the gear performance. Starting from such considerations, this work is focused on the microstructural (fig.2, fig. 4) and mechanical characterization (nanohardness and fatigue behaviour) of a CrN coating, about 5 μm thick, deposed by PVD technique on two different steels: a carburizing 16MnCrS5 steel grade and a nitriding 42CrMo4 steel grade (Table I). CrN films were deposited by means of the standard cathodic. arc using an industrial devices. Before coating the fatigue specimens (Fig. 1) were polished with a 3 μm diamond suspension and then ultrasonically cleaned. On the basis of published works [11] it is known that, in the case of nitrided substrates, the adhesion with the PVD coating is enhanced by the presence of Feα(N) structure while ε-Fe2-3N or γprime;-Fe 4N ones are detrimental. For such a reason a NITREG treatment was executed on the 42NiCrMo4 steel grade with the purpose of producing a low white layer, further reduced, before the coating deposition step, by means of a mechanical samples polishing targeted to remove the superficial brittle and porous layers. A short ion cleaning executed with Ar was carried out before the beginning of the coating deposition phase. The steel temperature was kept constant at 180°C with an initial peak of 210°C acting for about 2 minutes, independently from the type of substrate considered. Microhardness profiles were measured both on uncoated and on coated samples in order to determine both the thickness of the carburized and nitrided layers and the effect of the thin film deposition process (fig. 3). The coating nanohardness data were also measured by the depth sensing technique using a Fisherscope H100 nanoindenter operating by a computer controlled stress limited device and equipped with a Vickers indenter. X-ray diffractometry (XRD) was used to identify the chemical coating composition (fig. 2) and to measure the residual stresses induced from the sample's process route including the coating step. XRD with Bragg Brentano geometry were performed with a Philips PW 1830 instrument with a goniometer PW 3020 and a control unit Philips PW 3710 (Cu K α radiation, scan rate 1° /min). Surface residual stresses were detected using Cu Kα radiation by means of a Italstructure Stress X3000 diffractometer. The stresses (-120±25 MPa after carburizing; -580±40 MPa after nitriding; -1870±87 MPa after carburizing + PVD and -2350±114 MPa after nitriding + PVD) were calculated using the sinj2 method and adapting the elastic modulus value obtained by nanoindentation measurements and assuming a Poisson ratio of 0.2, value usually taken as a reference when ceramic CrN or Cr(C,N) thin films are considered. Using a rotating bending machine fatigue tests were carried out both on case hardened samples and nitrided plus PVD coated specimens (fig. 1). Experiments were executed at room temperature, in air, at a test frequency of 33 Hz using a sinusoidal load wave form and a load ratio (minimum to maximum load) of R=0. The stress level at which specimens can run without occurrence of failure after 3 · 106 stress cycles was chosen as the fatigue limit. Results of the fatigue tests were analysed according to the stair-case up and down method (Table II). The presence of the PVD film is responsible for a light increase in the fatigue resistance both for the carburized samples and for the nitrided ones. Fatigue nucleation sites resulted affected from the presence of PVD coating only in the case of carburized substrate: the high residual stress level characterizing the ceramic coating excludes the surface as nucleation zone and moves it at the interface with the steel material (fig. 5). No change in the nucleation areas were observed in the nitrided specimens or in the nitrided and coated samples (fig. 6) where the weak points resulted the non metallic inclusions inside the substrate material
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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