1,720,966 research outputs found
Effect of bias voltage on the erosion performance of TiAlSiN coatings on TC6 substrate by high power impulse magnetron sputtering
No full textTiAlSiN coatings were deposited on TC6 substrates by high power impulse magnetron sputtering at various bias voltages for the improvement of titanium alloy anti-sand erosion performance. The effect of bias voltage on the composition, microstructure and mechanical properties were investigated by X-ray photoelectron spectroscopy, X-ray diffractometer, transmission electron microscopy, scanning electron microscopy, Rockwell-C indentation, scratch testing and nano nanoindentation. The erosion performance was evaluated at the impingent angles of 30 degrees and 90 degrees respectively in a sand blasting tester. With the application and increase in bias voltage, the discharge current increases from -87 A to -210 A. The coatings exhibit face center cubic structure, mainly composed of the (Ti,Al)N nanocrystallites and Si3N4 matrix. The preferred orientation shifts from (200) to (220) in the range of 0--150 V, but goes back to (200) at -200 V. The surface nodular defects and deposition rate are gradually reduced, yet the sectional structure becomes much denser. The residual stress is compressive and continually grows, whereas the adhesion strength, hardness (H), Young's modulus (E) and H/E ratio gradually increase before decreasing, arriving at maximum values of -68 N, -37.53 GPa, -339.9 GPa and 0.11 respectively at -150 V. The erosion resistance of the TiAlSiN coatings is consistent with these mechanical changes at various bias voltages and is also optimal at -150 V, which is -14 times that of TC6 substrate. The failure mechanism comes from coating brittleness nature, fractured chips and microcracks, regardless sand erosion angles, yet the driving forces are different
Plasma potential and ion energy characteristics in BP-HiPIMS discharge with double layer
No full textAbstract
As an emerging ion acceleration plasma source, the bipolar-pulse high power impulse magnetron sputtering (BP-HiPIMS) discharge has been widely studied by academia and industry due to its ability to adjust the ion kinetic energy. Formation of the double layer (DL) potential structure during the BP-HiPIMS positive pulse is vital for accelerating ions, but its structural characteristics are still unclear. In this work, to understand the DL characteristics affected by various discharge parameters, the evolution of plasma potential V
p and ion energy in BP-HiPIMS discharge with copper target has been investigated systematically using an emissive probe and mass spectrometer together. Spatial plasma potential measurements show that the DL is established in front of the target during the positive pulse, whose boundary potential drop U
DL to accelerate ions can be increased to ～60 V at a lower operating gas pressure (p= 0.6 Pa) and a higher applied positive pulse voltage (U
+ = 200 V). The ignition onset time of DL after applying the positive pulse can be shortened to ～25 μs by decreasing the gas pressure and increasing the positive pulse voltage or negative pulse duration. After DL ignition, a group of high-energy copper ions with energy higher than the surrounding plasma potential can be recognized in the ion energy distribution function curves in the downstream plasma. This result illustrates that the copper ions can be ionized in the high-potential plasma region and be accelerated by the DL boundary potential drop. In addition, a global current balance model of the DL in BP-HiPIMS is developed, which suggests that the U
DL can be well adjusted by increasing the positive pulse voltage U
+ especially for U
+ > 200 V as verified by the experimental potential measurements. All results suggest that the copper particles play an important role in the formation of DL and the DL plays an important role in accelerating copper ions
Application of positive pulse to extract ions from HiPIMS ionization region
No full textHigh power impulse magnetron sputtering (HiPIMS) is a promising physical vapor deposition technique with one of the main drawbacks being its relatively low deposition rate. In this article, a method was propose by using a positive ions extraction pulse (Uextract) which would be immediately applied to the sputtering target after the HiPIMS negative pulse to extract out the ions from the ionization region near the HiPIMS target. The Particle-InCell/Monte Carlo Collision (PIC-MCC) simulation, experiments, and theoretical study were conducted to investigate the ions extraction process. It is demonstrated that the higher potential moved from the target area to the substrate direction and the peak ion density was driven to the substrate direction, after applying the positive ions extraction pulse to the target. The measured ion-energy distribution function (IEDF) characteristics verified that the ions extraction method works. The experimental results indicated that the Ti + ion flux dramatically increased when the Uextract was over 50 V. Good agreement between the experimental and simulation results was obtained, validating the simulation conclusion. Finally, the microscopic mechanism of ions extraction is proposed
Effect of geometric position on the film properties for a complex-shaped substrate in HiPIMS discharge: Experiment and simulation
Get PDFThe purpose of this paper is to explore the effect of geometric position on the film properties for a complex shaped substrate in high-power impulse magnetron sputtering (HiPIMS) discharge. The substrate is a trapezoidal prism, whose base has four inner corners of 60?degrees, 120 degrees, 75 degrees, and 105 degrees. A negative bias is added to this trapezoidal prism during the high-density discharge to deposit TiAlSiN films. The chemical compositions, microstructures and mechanical properties of the films at different area of the substrate are analyzed using the energy dispersive spectroscopy, X-ray diffraction, scanning electron microscope, nano-indentor and Vickers indentation tester. Systematic investigations demonstrate that the films properties have prominent differences on various planes of the trapezoidal-prism sample, due to the so-called shadowing effect. Compared with the measurements on the plane perpendicular to the target surface, there is a higher average hardness and stronger toughness on the plane facing to the target surface. However, the values of both the hardness and toughness are the lowest on the plane facing away from the target surface. Moreover, even for the same plane, the enhanced mechanical properties as well as a smoother surface and denser microstructure appear in the edge regions, with respect to that in the planar center regions. To understand these interesting phenomena, a two-dimensional particle-in-cell/Monte Carlo collision simulation (2D PIC-MCC) and Transport of Ions in Matter method (TRIM) are employed to explore the ion dynamics at the different sites of the sample. Simulation results suggest that a higher ion flux density and larger re-sputtering rate may contribute to the improved film properties in the edge regions. These results in this paper are important for broadening the industrial applications of high ion fraction plasma sources in irregular structures, especially for cutting tools
Effect of C2H2/N-2 partial pressure ratio on microstructure and mechanical properties of Ti-Al-Si-C-N coatings
No full textTi-Al-Si-C-N nanocomposite coatings were deposited on cemented carbide (WC-10 wt%, Co) substrates by reactive magnetron sputtering technique. The effect of C2H2/N-2 partial pressure ratio on element concentration, deposition rate, microstructure, cross-sectional morphology, hardness and tribological properties of the coatings were studied. The coatings were found to have a nanocomposite structure consisting of nanocrystallities (Ti,Al) (C,N) and amorphous phase. The coating's columnar crystals structure was restrained with the increase of C2H2/N-2 partial pressure ratio. The deposition rates and nanohardness of coatings firstly increased with the increase of C2H2/N-2 partial pressure ratio and reached their maximum values of 133 nm/min and 35 Gpa, respectively, at C2H2/N-2 partial pressure ratio of 1:2 before decreasing. The friction coefficient and wear rates of Ti-Al-Si-C-N coatings dramatically decreased with the increase of C2H2/N-2 partial pressure ratio and reached the lowest value of 0.17 and 1.1 x 10(-6) mm(3)/Nm, respectively, at C2H2/N-2 partial pressure ratio of 1:1.</p
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
- …
