Friedrich Franek

Microstructure and mechanical properties of HVOF sprayed nanocrystalline Cr3C2-25(Ni20Cr) coating

The objectives of this work are to deposit nanocrystalline Cr3C2-25(Ni20Cr) powder by thermal spraying and to compare the performance of this coating with that obtained using conventional powder. Towards that purpose, Cr3C2-25(Ni20Cr) powders with nanocrystalline grain size and with conventional grain size were deposited using OSU-SJS high-velocity oxyfuel (HVOF) system. The microstructural features, such as morphology of the coated surface, thickness of the coating, the interface of the coating with the substrate, distribution of various phases, and grain sizes etc, were characterized with the help of optical microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM). The amount of oxide phases and pores were determined by means of image analyzer. The presence of various phases was identified by x-ray diffraction (XRD) technique. Hardness, elastic modulus, and indentation toughness were evaluated employing micro indentation technique. The results indicate the presence of three different zones containing only orthorhombic Cr3C2 phase, FCC NiCr phase, and mixture of Cr3C2 and NiCr phases in, both coatings. The grain sizes in the nanocrystalline coating were in the range of 80 to 100 nm. Nanocrystalline coating exhibits 20% increase in hardness, 40% decrease in surface roughness, and comparable fracture toughness and elastic modulus with respect to conventional coating.

Nanotribology of Mo–Se–C films

Transition metal dichalcogenides with a layered structure are well known for their self-lubricating properties, particularly in a vacuum or dry atmosphere. The macrotribological properties of these films have been studied extensively. However, the tribological behaviour of these films in the nanonewton load range has hardly been reported. Study of tribological properties with load in the nanonewton range is required for applications related to microelectromechanical systems or nanoelectromechanical systems. In view of the above, the hardness, surface force, friction force, etc. of Mo–Se–C films were investigated at an applied load in the nanonewton range using a nanoindenter and atomic force microscopy. The effect of carbon content, applied load and scanning speed on the friction coefficient was determined. Data pertaining to topography, lateral force and pull-off force of various surfaces are illustrated. The observed nanotribological behaviour of these films is analysed in the light of their nanohardness. The results indicate that the friction force of all the films is very low and in general dependent on surface force. However, a film having the highest carbon content exhibits the maximum friction force. With increasing carbon content of the films tested, the hardness increases and wear decreases. The above results pertain to investigations under ambient conditions.

International standardization and organizations in the field of tribology

Wide tribology concept through the knowledge interaction from physics, chemistry and various engineering disciplines, has put tribology in a group with interdisciplinary sciences. This work gives information about the international standardization in the field of tribology, International Tribology Council, whose members consist of 36 national tribology society and associations from 34 countries worldwide and an overview of other international and regional organizations and institutions. Analysis of ISO, IEC and EN standards in various fields related to tribology and a view of the structure of most significant ISO Technical Committees related to standardization in tribology fields are presented.

Biotribological model systems for emerging nanometer scale technologies

Technological devices such as pressure sensors, gyroscopes and accelerometers get smaller and smaller. This increases the necessity for the fundamental understanding of tribological phenomena at the micro- and nanometer scale. Biological systems excel also at this scale. The thesaurus that nature has developed during the last millions of years of evolution comprises self-cleaning surfaces, systems with friction coefficients smaller than any occurring in man-made systems and organisms that produce macromolecules with ice binding properties. Such systems with well adapted biotribological properties shall serve as inspiration for innovation in micro- and nanotechnology.

Scanning Probe Microscopy: From Living Cells to the Subatomic Range

In this review, we have presented scanning probe microscopy across dimensions from large samples like single cells, via single biomolecules and nanometer small ion induced defects on crystal surfaces to subatomic features like electronic orbitals and single electron spins.

Experimental Validation of the Simulated Steady-State Behavior of Porous Journal Bearings

This study deals with a comparison between new experiments on the frictional behavior of porous journal bearings and its prediction by previous numerical simulations. The tests were carried out on bearings lubricated with polyalphaolefin-based oils of distinct viscosities. The theoretical model underlying the simulations includes the effects of cavitation by vaporization and accounts for the sinter flow by virtue of Darcys law. The effective eccentricity ratio corresponding to the experimentally imposed load is estimated by an accurate numerical interpolation scheme. The comparison focuses on the hydrodynamic branches of the Stribeck curve by dimensional analysis, where the variations of the lubricant viscosity with temperature are of main interest. The numerically calculated values of the coefficient of friction are found to reproduce the experimentally obtained ones satisfactorily well in terms of overall trends, yet the former lie predominantly below the measured ones, which results in a low-positive correlation between the two.

Modelling the Doctor Blade-Roller Tribosystem for Improving the Cleaning Performance During Paper Production

Doctor blades are commonly used in paper machines to keep the surface of rollers clean. Due to higher demanding conditions, the requirements for doctor blades have steadily increased. The wear rates must remain low, while simultaneously their cleaning function has to be ensured. For this reason, the paper industry has developed a high degree of empirical knowledge concerning the cleaning of roller surfaces. However, up to now, no systematic approach has been successfully applied to optimize the cleaning performance of the doctor blade-roller tribosystem. This study presents an attempt to model the system based on the force equilibrium conditions at the blade tip between hydrodynamic and contact forces. The change of the blade geometry due to wear is also taken into account. By these means, a non-dimensional group involving the key parameters is obtained. This allows for a systematic improvement of the cleaning efficiency, by targeted changes of the process parameters.

Identification of the mechanisms of wear during sliding of metallic materials at elevated temperature using an optical interferometer

253 MA alloy and PM 1000 alloy are used for application requiring exposure to high temperature. Both alloys form Cr 2 O 3 protective layer on exposure to elevated temperature. As these alloys are designed for elevated temperature applications, it is expected that these alloys will undergo sliding wear at high temperature. Elevated temperature wear behaviour of metallic materials is characterized by formation of several types of layers. These layers determine the friction coefficient, the wearing rate and wear mechanisms. The objectives of the present work is to examine the worn surfaces by means of an optical interferometer and evaluate the surface topography and roughness. On the basis of the observation of optical interferometer it is attempted to correlate the surface roughness with the types of layers formed and the mechanisms of wear. Towards that purpose samples made of 253 MA alloy and PM 1000 alloy are subjected to sliding wear at elevated temperature. The worn surfaces are examined with scanning electron microscope (SEM) and optical interferometer. The results indicated that, using only optical interferometer and without destroying the worn samples, it is possible to identify the wear mechanisms.

Development of a mechanical model of doctor blade-press roll tribosystem with aim to optimise cleaning performance: numerical predictions and first experimental verification

Abstract In the paper production, doctor (scraping) blades are placed in contact with press rolls during wet pressing so as to purge the surface of the rolls from processing water, contamination and stickies. The contact is achieved by mounting the blade on a holder, which is tilted around a rotation axis until the blade tip contacts with the roll. The contact force is determined by the supply pressure of the air forced through the tube that is placed at the bottom of the holder. Owing to contact, the blade wears off and needs to be replaced periodically. Our aim is to optimise the cleaning performance of the system by modelling the tribological contact between the doctor blade and press roll in order to achieve an optimum cleaning performance, thus increasing the blade lifetime and reducing energy consumption. The model is susceptible to an inextensive numerical evaluation as compared to that of a more advanced modelling approach, e.g. in terms of a full finite element analysis of the beam deflection. A first comparison with experimental findings is encouraging.

Tribological properties of lubricated nanocrystalline diamond surfaces for various loads and geometries

Abstract Diamond and diamond-like carbon films are well known for their outstanding properties such as high hardness, low coefficient of friction, good thermal conductivity, excellent biocompatibility and electrical insulation. Diamond films with nanocrystalline grains offer added advantages of higher hardness, improved surface finish (less roughness), very high sp3 content, etc. In view of the above, the present investigation is undertaken to explore the possibility of using nanocrystalline diamond films in advanced tribological applications. In this work, a nanocrystalline diamond film is deposited using a unique chemical vapour deposition (CVD) technique. The microstructural features are characterised using atomic force microscopy (AFM). Tribological behaviour of these films is evaluated by means of a reciprocating model tribometer with various lubricants. The worn surfaces are examined using three-dimensional confocal microscopy. The results show that these films have comparable friction coefficient with and without lubricants. Furthermore, they exhibited negligible wear for the tested range of loads.