DJL

Publication date: 15 January 2016
Source:Surface and Coatings Technology, Volume 285
Author(s): Michael Tkadletz, Nina Schalk, Rostislav Daniel, Jozef Keckes, Christoph Czettl, Christian Mitterer
Due to economical demands to further increase the efficiency of production processes, it is essential to exploit the full potential of wear resistant hard coatings. This is, however, possible only if the coating microstructure and properties are well characterized. Thus, in the present work, recently suggested advanced characterization techniques for coatings are reviewed. The application of atom probe tomography, electron backscatter diffraction and synchrotron X-ray nanodiffraction enables previously unrevealed insights in their chemical composition, microstructure and crystallographic structure. For the determination of mechanical and tribological properties at elevated temperatures, high-temperature nanoindentation and high-temperature ball-on-disk tests in combination with in-situ measurement techniques are discussed. Utilization of micromechanical tests for coatings provides information about their fracture toughness and rupture strength. High-temperature X-ray diffraction and biaxial stress temperature measurements for the determination of the coefficient of thermal expansion are compared. The thermal conductivity as well as the specific heat capacity of coatings can be studied using the 3-ω technique, time domain thermoreflectance and differential scanning calorimetry. The introduced portfolio of characterization techniques enables the determination of a complementary microstructural, mechanical and thermo-physical fingerprint of wear resistant hard coatings, which allows to understand the complex structure–property relations in these materials and subsequently to further improve their performance.

Abstract

In the current paper, trilayered films (abridged as APS-GO/PFPE) composed of graphene oxide (GO) and perfluoropolyethers (PFPE) were fabricated successfully on the silicon substrate pre-modified with a self-assembled monolayer of 3-aminopropyl triethoxysilane. The so-prepared films were characterized by a range of complementary techniques including Raman spectroscopy, contact angle measurements, X-ray photoelectron spectroscopy, and atomic force microscopy, to reveal the surface chemical compositions and surface morphologies. Furthermore, the microtribological behavior of the so-prepared films was studied on a ball-on-plate tribometer. The APS-GO/PFPE film showed better friction-reducing and wear-resisting properties as compared with the control samples, which was ascribed to the excellent wear-resisting properties of GO and the excellent lubricating nature and low shear strength of PFPE.

Nature Nanotechnology. doi:10.1038/nnano.2015.247

Authors: Cherie R. Kagan & Christopher B. Murray

Abstract

1-Alkyl-3-methylimidazolium ibuprofen ionic liquids (ILs, L-Ibu104, L-Ibu106 and L-Ibu108) were synthesized from an anti-inflammatory drug, sodium ibuprofen. The physicochemical and tribological properties of these ILs as neat lubricants for steel/steel and steel/copper contacts were measured. The results of hydrolysis stability evaluation and copper strip corrosion test show that these kinds of ILs are hydrolysis stable and have no corrosion to the metal contacts because of stability of anion. The friction and wear test results exhibit that these ibuprofen ILs have more effective friction-reducing and anti-wear properties than poly-alpha-olefin (PAO40) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide (L-F106) at 100 °C. According to the X-ray photoelectron spectrometer analytical results, we speculated that physical adsorption films can easily formed on the metal worn surfaces during the rubbing process because of the high adsorption ability of Ibu⁻ anion, which play an important role in the good lubricating behaviours of ibuprofen ILs.

Graphical Abstract

Abstract

Head wear of thermal flying height control sliders is studied experimentally by (a) comparing the touch-down power before and after a wear test consisting of 300 consecutive touch-down cycles, (b) examining scanning electron microscopy (SEM) images, and (c) investigating atomic force microscopy (AFM) measurements of unworn and worn heads. The effect of bonded lubricant ratio, relative humidity, temperature, and heater power on head wear is investigated. The experiments were carried out on a commercial load/unload tester inside an environmental test chamber. We conclude that (a) head wear increases with increasing bonded lubricant ratio, (b) temperature has a minor effect on head wear for the temperature range of 30–50 °C, (c) head wear increases with decreasing relative humidity, and (d) head wear increases with increasing heater power during the wear test. SEM images show wear of the write shield for changes in touch-down power typically larger than 6 mW. AFM measurements show changes in surface roughness of heads with changes in touch-down power as small as 1.3 mW compared to new, unused head. A wear coefficient on the order of 10⁻¹¹ to 10⁻¹³ was estimated.

Abstract

Materials: Boron made into 2D sheet

Nature 527, 7577 (2015). doi:10.1038/527136c

Researchers have created a 2D form of boron and shown that it behaves as a semiconductor.Materials such as graphene (the atomically thin form of carbon) and others made of silicon and phosphorus have desirable electrical properties that could be useful in electronics, and 2D

Widespread exploitation of the honeybee by early Neolithic farmers

Nature 527, 7577 (2015). doi:10.1038/nature15757

Authors: Mélanie Roffet-Salque, Martine Regert, Richard P. Evershed, Alan K. Outram, Lucy J. E. Cramp, Orestes Decavallas, Julie Dunne, Pascale Gerbault, Simona Mileto, Sigrid Mirabaud, Mirva Pääkkönen, Jessica Smyth, Lucija Šoberl, Helen L. Whelton, Alfonso Alday-Ruiz, Henrik Asplund, Marta Bartkowiak, Eva Bayer-Niemeier, Lotfi Belhouchet, Federico Bernardini, Mihael Budja, Gabriel Cooney, Miriam Cubas, Ed M. Danaher, Mariana Diniz, László Domboróczki, Cristina Fabbri, Jesus E. González-Urquijo, Jean Guilaine, Slimane Hachi, Barrie N. Hartwell, Daniela Hofmann, Isabel Hohle, Juan J. Ibáñez, Necmi Karul, Farid Kherbouche, Jacinta Kiely, Kostas Kotsakis, Friedrich Lueth, James P. Mallory, Claire Manen, Arkadiusz Marciniak, Brigitte Maurice-Chabard, Martin A. Mc Gonigle, Simone Mulazzani, Mehmet Özdoğan, Olga S. Perić, Slaviša R. Perić, Jörg Petrasch, Anne-Marie Pétrequin, Pierre Pétrequin, Ulrike Poensgen, C. Joshua Pollard, François Poplin, Giovanna Radi, Peter Stadler, Harald Stäuble, Nenad Tasić, Dushka Urem-Kotsou, Jasna B. Vuković, Fintan Walsh, Alasdair Whittle, Sabine Wolfram, Lydia Zapata-Peña & Jamel Zoughlami

The pressures on honeybee (Apis mellifera) populations, resulting from threats by modern pesticides, parasites, predators and diseases, have raised awareness of the economic importance and critical role this insect plays in agricultural societies across the globe. However, the association of humans with A. mellifera predates post-industrial-revolution agriculture, as evidenced by the widespread presence of ancient Egyptian bee iconography dating to the Old Kingdom (approximately 2400 bc). There are also indications of Stone Age people harvesting bee products; for example, honey hunting is interpreted from rock art in a prehistoric Holocene context and a beeswax find in a pre-agriculturalist site. However, when and where the regular association of A. mellifera with agriculturalists emerged is unknown. One of the major products of A. mellifera is beeswax, which is composed of a complex suite of lipids including n-alkanes, n-alkanoic acids and fatty acyl wax esters. The composition is highly constant as it is determined genetically through the insect’s biochemistry. Thus, the chemical ‘fingerprint’ of beeswax provides a reliable basis for detecting this commodity in organic residues preserved at archaeological sites, which we now use to trace the exploitation by humans of A. mellifera temporally and spatially. Here we present secure identifications of beeswax in lipid residues preserved in pottery vessels of Neolithic Old World farmers. The geographical range of bee product exploitation is traced in Neolithic Europe, the Near East and North Africa, providing the palaeoecological range of honeybees during prehistory. Temporally, we demonstrate that bee products were exploited continuously, and probably extensively in some regions, at least from the seventh millennium cal bc, likely fulfilling a variety of technological and cultural functions. The close association of A. mellifera with Neolithic farming communities dates to the early onset of agriculture and may provide evidence for the beginnings of a domestication process.

Abstract

Using in situ, high-speed imaging of a hard wedge sliding against pure aluminum, and image analysis by particle image velocimetry, the deformation field in sliding is mapped at high resolution. This model system is representative of asperity contacts on engineered surfaces and die–workpiece contacts in deformation and machining processes. It is shown that large, uniform plastic strains of 1–5 can be imposed at the Al surface, up to depths of 500 μm, under suitable sliding conditions. The spatial strain and strain rate distributions are significantly influenced by the initial deformation state of the Al, e.g., extent of work hardening, and sliding incidence angle. Uniform straining occurs only under conditions of steady laminar flow in the metal. Large pre-strains and higher sliding angles promote breakdown in laminar flow due to surface fold formation or flow localization in the form of shear bands, thus imposing limits on uniform straining by sliding. Avoidance of unsteady sliding conditions, and selection of parameters like sliding angle, thus provides a way to control the deformation field. Key characteristics of the sliding deformation such as strain and strain rate, laminar flow, folding and prow formation are well predicted by finite element simulation. The deformation field provides a quantitative basis for interpreting wear particle formation. Implications for engineering functionally graded surfaces, sliding wear and ductile failure in metals are discussed.

Publication date: 15 December 2015
Source:Surface and Coatings Technology, Volume 283
Author(s): Yasuhiro Miki, Akio Nishimoto, Takumi Sone, Yoshiji Araki
Diamond-like carbon (DLC) films were prepared and their residual stresses were measured nondestructively using Raman microprobe spectroscopy. The plasma-based ion implantation and deposition (PBIID) method was used to coat the DLC films on thin glass substrates using acetylene, a mixture of acetylene and toluene, or only toluene gas at 1.0Pa. Peaks in the Raman spectra of the DLC films were assigned as the D′(disordered) or C–C bonding peaks at 1150cm⁻¹. The phonon deformation potentials (a′) of the films were estimated from data for the phonon deformation potentials for pure graphite and diamond and calculated using the sp³/sp² bonding ratio and the hydrogen content of the films. Thus, a relation was observed between the Raman shift of the G peak (ω G) and the residual stress (σ c) in each film. The Raman shifts (ω 0) of the G peak for the films with no deformation were 1554, 1556, and 1562cm⁻¹ for the films deposited using acetylene, a mixture gas and toluene gas. Moreover, only toluene had stress constants of −0.378, −0.384, and −0.391GPa/cm⁻¹. The residual stresses constant in each film using (8.2×10⁻⁴·a′)⁻¹ ω 0 ⁻¹ were estimated as −0.379, −0.384, and −0.391GPa/cm⁻¹. The Raman shift of the D peak remained stationary as the compressive σ c in the films increased but changed when the deposition gas was varied. The distance the D peak moved from 1420cm⁻¹ corresponded to that of the G peak from 1560cm⁻¹ in the Raman spectra of the films in the stress-free state. In addition, the compressive residual stress in the DLC film had a major impact on the hardness.

Abstract

Publication date: Available online 30 October 2015
Source:Surface and Coatings Technology
Author(s): L. Baiamonte, F. Marra, S. Gazzola, P. Giovanetto, C. Bartuli, T. Valente, G. Pulci
Fuel used in diesel engines for naval propulsion contains high levels of impurities, principally vanadium and sulfates, that can react to form aggressive compounds, responsible for hot corrosion phenomena, leading to severe degradation of engine's components, especially exhaust valves. A protective coating is thus required to increase service life of the valves in the highly corrosive environment. In this work five different thermal-sprayed metal-ceramic coatings are selected as potential candidates and their hot corrosion resistance is investigated and discussed in terms of microstructure evolution and hot corrosion kinetics. Four coatings were deposited by either HVOF or APS processes starting from commercial powders (Cr3C2-CoNiCrAlY, Cr3C2-self fusing alloy, Cr3C2-NiCrAlY, Cr3C2-NiCr), optimizing deposition parameters by DoE technique. The last composite coating was purposely designed including silica nanoparticles and ceramic fillers (mullite) in a NiCr matrix, and was deposited by HVOF. Microstructural characteristics of each coating in the as-sprayed conditions were evaluated by measuring porosity and microhardness. Hot corrosion tests were performed on samples covered with a mixture of Na2SO4 and V2O5 and placed in a furnace at 700°C in air for different times (5, 25, 50, 75 and 100h). Finally, EDS and XRD analyses were carried out on the corroded samples.