1,721,103 research outputs found
Fracture toughness determination by repetitive nano-impact testing in Cu/W nanomultilayers with length-scale-dependent films properties
No full textAbstractNanoscale metallic multilayers based on Cu/W have been considered as a potential material for structural applications in nuclear reactors and for the cladding of storage tanks for advanced fuels kept at high temperatures. The understanding of how mechanical properties change in relation to periodicity, λ, is required in order to use Cu/W nano-multilayers as a protective coating against radiation damage. The aim of this work is to demonstrate the feasibility of using the repetitive-nano-impact technique to obtain quantitative fracture toughness, KC, values in nano-multilayers and assess its variation as a function of λ
Structural and mechanical properties of irradiated multilayer nanocomposites
No full textRadiation damage processes in ion-irradiated metals have been thoroughly studied in the last decade revealing complexity and multiscale nature of material damage. Conversely, very little attention has been paid regarding gamma rays damage, which, in reactor pressure vessels, was found to be comparable to that produced by fast neutrons. Nanoscale structural control of nuclear materials through design of interfaces is a promising way of limiting radiation damage. Here we report two case studies regarding: (i) the role of interfaces and of He-ion radiation doses on the structural and mechanical properties of a sputter-deposited Cu/W multilayer, and (ii) the role of interface density distribution on the structural and mechanical properties of gamma-irradiated Zr/Nb multilayers. Transmission electron microscopy and X-ray diffraction were employed to investigate radiation damage, while mechanical properties were explored by nanoindentation. We propose correlations between radiation experiments and materials properties for each case
The role of Ni–Ti–(Cu) interlayers on the mechanical properties and nano-scratch behaviour of solid lubricant W–S–C coatings
No full textA self-lubricant W–S–C coating with different Ni–Ti–(Cu) interlayers was fabricated by magnetron sputtering following a three-step process. It consisted of deposition and annealing of Ni–Ti–(Cu) layers with different Cu contents and subsequent deposition of the transition metal dichalcogenide W–S–C coating bonded to the Ni–Ti–(Cu) layer through a gradient Cr-based thin layer. Doping the Ni–Ti interlayer with Cu led to significant microstructural changes which influenced mechanical properties, such as the H/Er ratio and the resistance against plastic deformation. The response of the bilayers, i.e. W–S–C/Ni–Ti–(Cu) coatings, to indentation was affected by the interlayer material. The resistance to adhesion damage of the W–S–C coating was improved by using Ni–Ti–(Cu) interlayers. It was found that interlayers with lower H/Er ratio showed an improved capability to increase the adhesion of the functional top laye
Ni-Ti-Cu shape memory alloy interlayers supporting low-friction W-S-C coatings
No full textThis work is aimed at assessing the capability of Ni-Ti(-Cu) interlayers, integrated in a bilayer design (tribological top layer/Ni-Ti(-Cu) layer/substrate), to improve the resistance against adhesion damage and the tribological performance of W-S-C self-lubricant coatings, when these bilayers are subjected to different sliding conditions. Interesting differences on adhesion and tribological performance are observed in relation to the grain size of the interlayer materia
Towards frictionless surfaces - ultra-low friction materials for engineering applications
No full textIs it possible to produce frictionless material? Self-adaptive nanostructures could lead to huge friction reduction, say Dr Tomas Polcar from the University of Southampton, UK, and Professor Albano Cavaleiro from the University of Coimbra, Portugal
High temperature behavior of nanolayered CrAlTiN coating: thermal stability, oxidation, and tribological properties
No full textHard protective nitride coatings are often applied to cutting tools operating at high temperature. To further develop and optimize their performance, in-situ investigation of structure, oxidation, mechanical and tribological properties at elevated temperature is required. In this study we focus on the high temperature behavior of a nanolayered CrAlTiN coating deposited on WC substrates by cathodic arc evaporation. The coating's chemical composition and the bonding state were evaluated by electron probe microanalysis and by X-ray photoelectron spectroscopy (XPS). The structure of as-deposited and annealed samples was analyzed using X-ray diffraction. The adhesion was investigated by scratch test and the mechanical properties were studied by depth sensing nanoindentation. The main objective of this work was to have a detailed analysis of friction and wear properties tested by high temperature tribometer (pin-on-disc) with alumina balls as counterparts in the temperature range of 20–800 °C. Selected wear track cross-sections were prepared by focused ion beam and analyzed by transmission electron microscopy; the wear track was investigated as well by XPS (chemical depth profile) and by Raman spectroscopy. The coating showed an excellent thermal stability and wear resistance. The friction reached a maximum at 500 °C and then decreased, whereas the wear rate was negligible up to 600 °C and then increased significantly for higher temperatures. Oxidation of the worn surfaces was surprisingly low even at the highest temperature corroborating results of oxidation tests. The main identified wear mechanism was polishing combined with a nanoscale delamination of thin coating layers; nanoscale multilayer proved to be a vital factor blocking vertical crack propagation
Structure, mechanical properties and tribology of W–N and W–O coatings
No full textThe tribological properties of nitrides and oxides of transition metal thin films deposited by reactive magnetron sputtering have been thoroughly studied for three decades. Nevertheless, there are still several gaps in knowledge. The majority of studies are focused on a limited number of metals, namely Ti, Al and Cr, while other potentially attractive compounds are aside the main attention. Even in case of TiN, probably the most studied hard thin film, the frictional and wear behaviour brings many controversies. Despite significant progress of analytical and computational methods, the analysis of the wear behaviour is still a great challenge.We are presenting here a summary of our recent work on tungsten nitride (nitrogen content 0–58 at.%) and tungsten oxide (oxygen content 0–75 at.%) coatings deposited by reactive magnetron sputtering. Our aim has been the analysis of the connection of fundamental properties of these films, such as chemical composition, structure, hardness, Young’s modulus and residual stress, with their tribological properties – friction coefficient and wear rate. We have been focused mainly on the description of the dominant wear mechanisms influencing the tribological properties. The tribological tests have been carried out both at room and elevated temperature; the temperature was increased in steps until immediate coatings failure.The tungsten nitride coatings with the “worst” parameters generally considered as vital for high wear resistance, such as hardness, were considered to have the best tribological performance
Microstructural evolution of nanometric Ti(NiCu)2 precipitates in annealed Ni–Ti–Cu thin films
No full textTailoring nanoscale friction in MX2 transition metal dichalcogenides
No full textThe lattice dynamics of MX2 transition metal dichalcogenides can be controlled at the atomic scale to improve the frictional behavior. The electro-structural features of the M?X atomic pair are found to determine the lattice frequencies of those phonons affecting the macroscopic friction; the relative contributions are isolated through a new metric, named cophonicity, formulated at the quantum mechanical level. A new protocol to design new tribologic materials is thus propose
Smart surfaces for lubrication: solid lubricants and adaptive texture
No full textModern thin films, although still being developed at laboratory scale, promise revolutionary changes in surface engineering. For automotive industry, we will focus on two classes of thin films with the potential to decrease or even eliminate oil additives, reduce friction, and improve control of tribological process
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