Control of the nanostructure and microtribology of magnetron sputtered surfaces

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Control of the nanostructure and microtribology of magnetron sputtered surfaces

The technological importance of hard thin films is well established. There is growing recognition that nanometre-scale surface structures can be controlled to the benefit of function. In-process structuring brings these ideas together. This study explores how the morphology, especially the surface topography, and microtribological behaviour of Cr-N films can be controlled during unbalanced magnetron (UBM) sputtering. Experiments varying the sputter power, bias voltage, temperature, total pressure and Ar/N2 ratio during UBM sputtering generated different compositions, crystallite orientations and microstructures, and six associated topography types: pyramidal (type P), grain-like (G), crater-like (CR), ribbon-like (R), conical (C) and hillock-like (H). A new empirical zone model consistently relates these topography types to process parameters. The feature dimensions are also controlled by the deposition parameters. The films have closely reproducible topographical and mechanical properties. The microtribological behaviour for three topography types (P, C and CR) is studied under different conditions relevant to unlubricated contacts, lubricated contacts, and humid environments. Nanostructured surfaces show significantly lower friction than smooth ones, with actual reductions depending on the topography type. Friction strongly correlates with summit density (Ssd). Low friction (Ssd ~ 3 #/µm2) was measured on all type CR surfaces, but only by increasing the lateral dimensions of types P and C. Unlubricated friction is attributed principally to solid-solid adhesion, influenced by the density and curvature of summits. Wear is influenced by the density, shape and size of the surface features and by the mechanical properties of the film. Boundary lubrication reduced friction, with slight dependence on lubricant. Alongside the summits parameters, friction correlates with core fluid retention index. Applying hydrophobic and hydrophilic treatments shows that appropriate nanostructuring reduces the dependence of friction on humidity and sliding velocity, principally by controlling the summit density. In-process structuring is clearly very useful for creating nanostructures in order to enhance the microtribological behaviour of surfaces. Further investigations are recommended into friction optimization by nanostructuring

Friction and wear behaviour of pyramidal nanoscaled surface features

This study reports on the friction and wear behaviour of nanoscaled pyramidal surface features of chromium nitride thin films in relation to the dimensions of those features. The pyramidal features were created, and their size controlled, by PVD based in-process structuring. Microtribological tests analysed both the evolution of wear-induced surface alterations and the correlated evolution in the coefficient of friction as functions of normal load and duration of the loading. Results indicate that the severity of wear diminishes tremendously with increasing feature size when tested at the same normal load. So, wear-induced damage similar to that seen on surfaces with small-sized features was observed for the largest surface features tested only after a 100 times longer test duration. The less severe wear of the largest pyramids leads also to friction up to 75% lower compared to surfaces with the smallest features. (C) 2007 Elsevier B.V. All rights reserved

Topographical evolution of sputtered chromium nitride thin films

The modification of the morphology, with special emphasis on the topographical evolution, of chromium nitride thin films has been studied by varying the sputter power, bias voltage, temperature, total pressure and Ar/N-2 ratio in an unbalanced magnetron sputtering process. Six different topography types (here designated pyramid, grain, crater, cone, ribbon and hillock) were identified. The growth conditions for each topography type are specified and summarized in a topography zone model showing the occurrence of each as function of temperature, Ar/N-2 ratio, deposition rate and bias voltage. Furthermore, the relationship between the size of the topographical features and the deposition parameters was investigated and is reported in detail. The control of topographical type and feature size appears sufficient to hold promise of generating topographies designed for specific functions

Ceramic nitride/metal coatings with enhanced fracture toughness and fatigue resistance using a multiscalar laminate architecture

Ceramic coatings can provide benefits such as improved wear resistance, reduced friction, and be chemical and biological corrosion barriers in various biomedical applications. However long-term issues of film cracking, particle generation, or delamination must be addressed, while achieving decades-long coating lifetimes. Instead of brittle, superhard coatings, softer but tougher coatings achieved with multiscalar, laminate architectures may meet these requirements. Layers of Cr and CrN were combined in multi- and nanolayer structures, and compared to monolayer films. The multiscalar coatings had hardness values lying between the pure Cr and CrN, but higher fracture toughness than the monolayer films

Topography-related effects on the lubrication of nanostructured hard surfaces

This study reports the effect of nanoscaled surface structure of some hard coatings on the (micro-) frictional behaviour of systems under minimum lubrication conditions with modest contact pressures and low sliding speeds (below 1 mm/s). For this purpose, Cr-N coatings with a randomly crater-like topography and with varying dimensions of surface features as well as a smooth Cr-N surface were tested with a microtribometer. The friction on the samples was measured as a function of the viscosity of the applied mineral base oil and the sliding velocity. For all tests, the structured surfaces exhibited lower friction than the smooth surface. Furthermore, it was possible to detect variations in the lubrication-promoting effect of the structures depending on the oil viscosity and the sliding speed. Indications for the existence of an optimum topographic scale for this type of surface structure were found. (c) 2005 Elsevier Ltd. All rights reserved

A new Time-of-flight detector for the R 3 B setup

© 2022, The Author(s).We present the design, prototype developments and test results of the new time-of-flight detector (ToFD) which is part of the R3B experimental setup at GSI and FAIR, Darmstadt, Germany. The ToFD detector is able to detect heavy-ion residues of all charges at relativistic energies with a relative energy precision σΔE/ ΔE of up to 1% and a time precision of up to 14 ps (sigma). Together with an elaborate particle-tracking system, the full identification of relativistic ions from hydrogen up to uranium in mass and nuclear charge is possible.11Nsciescopu