1,720,986 research outputs found
Hybrid additive manufacturing of an electron beam powder bed fused Ti6Al4V by transient liquid phase bonding
Full text linkHybrid Additive Manufacturing (HAM) is a production strategy enhancing the flexibility of the already versatile Additive Manufacturing (AM) techniques. AM of Ti6Al4V, on the other hand, has been of great interest to numerous research works, thanks to the unique corrosion, biomedical and mechanical properties of the alloy. Hence, this research marks the first report on the HAM of Ti6Al4V by Transient Liquid Phase (TLP) bonding of an Electron Beam Powder Bed Fused (EB-PBF) sample to a conventional one. A copper interlayer was used for bonding, and the TLP process was performed at 890 degrees C and 970 degrees C for 60 min. Shear strength test was carried out and the results showed the highest shear strengths of 579.3 and 662.5 MPa for TLP bonding at 890 degrees C and 970 degrees C, respectively. By increasing the bonding temperature to 970 degrees C, no Cu-rich phases were observed in the microstructure, as opposed to the 890 degrees C samples, and a complete isothermal solidification without intermetallic phases was achieved. Moreover, the 970 degrees C TLP sample was featured with a much better microstructural integrity and homogeneity in both the base metals and the bonded zone. TLP bonding at 970 degrees C resulted in a more ductile fracture surface than that bonded at 890 degrees C. The strong differences between the two TLP bonds were primarily attributed to the faster diffusion rate of elements along the joint and base metal at higher temperatures. (C) 2022 The Author(s). Published by Elsevier B.V
Investigation on the Potential of Laser and Electron Beam Additively Manufactured Ti-6Al-4V Components for Orthopedic Applications
No full textIn the present study, corrosion properties and biocompatibility of as-built and as-polished Ti-6Al-4V samples fabricated by Electron Beam Melting (EBM) and Selective Laser Melting (SLM) were investigated and compared with a conventional sample as a reference. Optical microscope, Scanning Electron Microscope equipped with Energy Dispersive Spectroscopy, and X-ray diffraction analysis were employed for studying the microstructure and composition of the samples. Polarization, electrochemical impedance, and immersion tests were carried out to investigate the corrosion behavior and bioactivity of the samples in the Simulated Body Fluid solution. The results revealed that the EBM samples exhibited a superior corrosion resistance compared to the SLM one, thanks to the absence of low corrosion resistant alpha' martensitic phases and a higher fraction of beta phase in the EBM samples. It was also observed that while the wrought Ti-6Al-4V samples had a higher corrosion current density than the additively manufactured ones, both EBM and SLM processes had a lower corrosion resistance in the as-built state than in the as-polished. The immersion tests in the SBF solution revealed a more significant bioactivity for the EBM samples than the SLM samples. Higher levels of the beta phase in the EBM microstructure stimulated the nucleation and growth of the apatite on the sample surface. Also, higher surface roughness in the as- built samples improved the bioactivity by increasing the metal/ electrolyte interface and thus forming more OH- groups on the Ti alloy surface
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
Microstructure and Corrosion Properties of CP-Ti Processed by Laser Powder Bed Fusion under Similar Energy Densities
No full textIn this work, two types of CP Ti cubes with similar volumetric energy densities (VED) but different process parameters were produced using laser powder bed fusion (LPBF) method. The corrosion behavior of the fabricated specimens was investigated by conducting electrochemical impedance spectroscopy (EIS) and polarization experiments in simulated body fluid (SBF) solution at 37 °C. The results indicated that the microstructure and porosities, which are of great importance for biomedical applications, can be controlled by changing the process parameters even under constant energy densities. The sample produced with a lower laser power (E1) was featured with a higher level of porosity and thinner alpha laths, as compared with the sample fabricated with a higher laser power (E2). Moreover, results obtained from the bioactivity tests revealed that the sample produced with a higher laser power conferred a slight improvement in the bioactivity due to the higher amount of porosity. Lower laser power and hence higher porosity level promoted the formation of bone-like apatite on the surface of the printed specimens. The potentiodynamic polarization tests revealed inferior corrosion resistance for the fabricated sample with higher porosity. Moreover, the EIS results after different immersion times indicated that a stable oxide film was formed on the surface of samples for all immersion times. After 1 and 3 days of immersion, superior passivation behavior was observed for the sample fabricated with lower laser power. However, very similar impedance and phase values were observed for all the samples after 14 days of immersion
The microstructure and wear behaviour of friction stir processed AISI 430 ferritic stainless steel
No full textVariations 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
Friction stir spot welding of TiO2 nanoparticle-reinforced interstitial free steel
No full textThe purpose of the current study was to investigate the effect of different content of TiO2 nanoparticles and FSSW parameter such as tool rotational speed on microstructure and mechanical properties of IF steel FSSW joints. FSSW joints were realized by adding 0.45, 1.14, 2 wt% of TiO2nanoparticles to IF steel. Optical microscopy and scanning electron microscopy and energy dispersive spectroscopy studied along with the results of microhardness measurements and tensile shear analyses. The obtained results showed that the optimal welding conditions were a tool rotational speed of 1120 rpm and a dwell time of 9 s. Microstructural observations demonstrated a good dispersion of TiO2 reinforcements in the steel matrix. TiO2 nanoparticles addition led to a remarkable increase in the mechanical properties of the produced welds. This was attributed to the fine grain size obtained thanks to the ceramic particles addition. The hardness and ultimate load of joints produced by TiO2 amount of 1.14 wt% are optimum welding conditions for fabrication of the best quality of welds which have attributed to the uniform dispersion of TiO2 nanoparticles in the weld regions. For higher than 1.14 wt% content of TiO2, nanoparticles agglomeration occurred, this resulted in the decrease in strength and ductility
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
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