Wear Study of a Magnetron-Sputtered TiC/a-C Nanocomposite Coating under Media-Lubricated Oscillating Sliding Conditions

Friction and wear performance of non-reactively magnetron-sputtered hydrogen-free TiC/a-C coatings were characterized under lubricated oscillating sliding conditions against 100Cr6 steel. The friction mediators, isooctane, ethanol and distilled water, were chosen to address the actual trend of environmentally friendly green technologies in mobility and the potential use of carbon-based nanocomposite thin film materials for tribocomponents in contact with gasoline and alternative biofuels. Sliding pairs of the TiC/a-C coatings showed significantly reduced friction and wear compared to the reference materials under both unlubricated and lubricated conditions (when using the aforementioned media isooctane, ethanol and distilled water). Quasi-stationary friction coefficient of the TiC/a-C sliding pairs after running-in was almost independent of test conditions and could be traced back to self-lubrication as a result of the formation of a transfer layer on the steel counter body. Wear of the coatings based on micro-abrasion and tribochemical reaction was significantly influenced by the environmental conditions. Lowest wear was measured after tests in non-polar isooctane whereas highest wear was measured after tests in water

Arc-textured metal surfaces for high thermal emittance space radiators

Carbon arc electrical discharges struck across the surfaces of metals such as Nb-1 percent Zr, alter the morphology to produce a high thermal emittance surface. Metal from the surface and carbon from the arc electrode vaporize during arcing, and then condense on the metal surface to produce a microscopically rough surface having a high thermal emittance. Quantitative spectral reflectance measurements from 0.33 to 15 microns were made on metal surfaces which were carbon arc treated in an inert gas environment. The resulting spectral reflectance data were then used to calculate thermal emittance as a function of temperature for various methods of arc treatment. The results of arc treatment on various metals are presented for both ac and dc arcs. Surface characterization data, including thermal emittance as a function of temperature, scanning electron microscopy, and atomic oxygen durability, are also presented. The ac arc texturing was found to increase the thermal emittance at 800 K from 0.05 to 0.70

Magnetron-sputtered Al-containing MAX phase carbide thin films and their application as oxidation-resistant coatings

Ternary compounds denominated by the structure formula Mn+1AXn (MAX) phases comprise an extended family of layered, hexagonal transition metal carbides and nitrides. Due to their unique crystal chemistries and layered atomic structures, MAX phase materials combine many unique attributes of both ceramics and metals. These include low density, easy machinability, high thermal and electrical conductivities, thermal shock and damage tolerance, and excellent high-temperature resistance to oxidation and corrosion. These remarkable properties attract growing interest on the fabrication, characterization and implementation of MAX phase materials considered for structural and nonstructural applications under extreme conditions in the form of both bulk materials and thin films. Alumina-forming MAX phases, like Ti2AlC and Cr2AlC with self-healing capabilities, have shown great potential in applications as high-temperature oxidation and corrosion resistant coatings. However, deposition of phase-pure polycrystalline MAX phase coatings, either by spraying technology or physical vapor deposition (PVD), often remains a challenge. The retention of stable competing phases, like binary carbides and intermetallics, degrade the performance of the coatings. In this study, a two-step approach has been established, i.e. first magnetron sputtering of nanoscale elemental multilayer stacks and subsequently thermal annealing in argon, for potential growth of three phase-pure MAX phase carbide (Ti2AlC, Cr2AlC and Zr2AlC) coatings. The temperature-dependent phase and microstructural evolutions during annealing were systemically investigated by high-temperature XRD, HRTEM and Raman spectroscopy. Dense and phase-pure Ti2AlC and Cr2AlC coatings were successfully fabricated, while growth of Zr(Al)C carbide rather than Zr2AlC MAX phase was confirmed in the Zr-C-Al system. In addition, the high-temperature oxidation behaviors of the three coatings were examined in steam

Deposition, characterization and high-temperature steam oxidation behavior of single-phase Ti2_{2}AlC-coated Zircaloy-4

Oxidation of single-phase and dense Ti2AlC coatings with or without a 500 nm TiC diffusion barrier deposited on Zircaloy-4 by annealing of nanoscale multilayer stacks between 800 °C and 1200 °C in high-temperature steam was investigated. Coatings without TiC barrier formed a duplex scale: outer θ-Al2O3 rich layer mixed with TiO2 and inner porous TiO2 layer; correspondingly, a triple-layered scale (θ-Al2O3 + TiO2/θ-Al2O3/TiO2) grew on coatings with barrier at 800 °C. The TiC barrier suppresses the rapid diffusion of Al into the substrate, contributing to improved performance and longer life of Ti2AlC/TiC coatings. However, both coatings demonstrated low protection effect from 1000 °C in steam

Impact of Microstructure of Nanoscale Magnetron Sputtered Ru/Al Multilayers on Thermally Induced Phase Formation

In this study, we report on phase formation and microstructure evolution in multiscale magnetron sputtered Ru/Al multilayers upon thermal annealing in vacuum at slow heating rates of 10 K/min. By specifically adjusting the microstructure and design of the as-deposited multilayers, the formation of certain desired phases can be tuned. We demonstrate that the synthesis of single phase RuAl thin films is possible in a very controlled manner in a solid state only via thermal activation without initiating the self-propagating exothermic reactions of Ru/Al multilayers. To investigate phase formation sequences and the resulting microstructures, Ru/Al multilayers were designed via magnetron sputtering with systematic variation of bilayer modulation periods and subsequent vacuum annealing. Thin films samples were characterized by in situ high-temperature XRD, TEM imaging and diffraction. It is shown that different phase sequences appear in strong correlation with the modulation length. Depending on the multilayer design, the phase formation toward single-phase RuAl thin films happens as either a multi-step or single-step event. In particular, below a critical threshold of the modulation period, the multi-step phase formation can be suppressed, and only the desired RuAl target phase is obtained with a pronounced growth in a preferred orientation. This finding may be versatile for the targeted synthesis of intermetallic phases, contributing to further understanding of phase formation in such nanoscale multilayer systems

Impact of Microstructure of Nanoscale Magnetron Sputtered Ru/Al Multilayers on Thermally Induced Phase Formation

In this study, we report on phase formation and microstructure evolution in multiscale magnetron sputtered Ru/Al multilayers upon thermal annealing in vacuum at slow heating rates of 10 K/min. By specifically adjusting the microstructure and design of the as-deposited multilayers, the formation of certain desired phases can be tuned. We demonstrate that the synthesis of single phase RuAl thin films is possible in a very controlled manner in a solid state only via thermal activation without initiating the self-propagating exothermic reactions of Ru/Al multilayers. To investigate phase formation sequences and the resulting microstructures, Ru/Al multilayers were designed via magnetron sputtering with systematic variation of bilayer modulation periods and subsequent vacuum annealing. Thin films samples were characterized by in situ high-temperature XRD, TEM imaging and diffraction. It is shown that different phase sequences appear in strong correlation with the modulation length. Depending on the multilayer design, the phase formation toward single-phase RuAl thin films happens as either a multi-step or single-step event. In particular, below a critical threshold of the modulation period, the multi-step phase formation can be suppressed, and only the desired RuAl target phase is obtained with a pronounced growth in a preferred orientation. This finding may be versatile for the targeted synthesis of intermetallic phases, contributing to further understanding of phase formation in such nanoscale multilayer systems

H₂ permeation behavior of Cr₂AlC and Ti₂AlC max phase coated zircaloy-4 by neutron radiography

Hydrogen uptake by nuclear fuel claddings during normal operation as well as loss of coolant during design basis and severe accidents beyond design basis has a high safety relevance because hydrogen degrade the mechanical properties of the zirconium alloys applied as cladding material. Currently, claddings with enhanced accident tolerance are under development. One group of such accident tolerant fuel (ATF) claddings are zirconium alloys with surface coatings reducing corrosion and high-temperature oxidation rate, as well as the chemical heat and hydrogen release during hypothetical accidents. The hydrogen permeation through the coating is an important parameter ensuring material safety. In this work, the hydrogen permeation of Ti₂AlC and Cr₂AlC MAX phase coatings on Zircaloy-4 is investigated by means of neutron radiography. Both coatings are robust hydrogen diffusion barriers that effectively suppress hydrogen permeation into the matrix

The salmon louse genome: Copepod features and parasitic adaptations

Copepods encompass numerous ecological roles including parasites, detrivores and phytoplankton grazers. Nonetheless, copepod genome assemblies remain scarce. Lepeophtheirus salmonis is an economically and ecologically important ectoparasitic copepod found on salmonid fish. We present the 695.4 Mbp L. salmonis genome assembly containing ≈60% repetitive regions and 13,081 annotated protein-coding genes. The genome comprises 14 autosomes and a ZZ-ZW sex chromosome system. Assembly assessment identified 92.4% of the expected arthropod genes. Transcriptomics supported annotation and indicated a marked shift in gene expression after host attachment, including apparent downregulation of genes related to circadian rhythm coinciding with abandoning diurnal migration. The genome shows evolutionary signatures including loss of genes needed for peroxisome biogenesis, presence of numerous FNII domains, and an incomplete heme homeostasis pathway suggesting heme proteins to be obtained from the host. Despite repeated development of resistance against chemical treatments L. salmonis exhibits low numbers of many genes involved in detoxification.publishedVersio

Cross‐formational flow and salinity sources inferred from a combined study of helium concentrations, isotopic ratios, and major elements in the Marshall aquifer, southern Michigan

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95014/1/ggge741.pd