Joze Vizintin

Tribochemistry in sliding wear of TiCN-Ni-based cermets

W/Nb/Ta/Hf) at varying loads of 5N, 20N, and 50N against bearingsteel. With these experiments, we attempted to answer some of the pertinent issues:(i) how does the type of secondary carbide (WC/NbC/TaC/HfC) influence friction andwear behavior, and is such influence dependent on load?; and (ii) how does thesecondary carbide addition affect the stability and composition of the tribochemicallayer under the selected sliding conditions? Our experimental results reveal that theadded secondary carbides influence chemical interactions between different oxides andsuch interactions dominate the friction and wear behavior. A higher coefficient offriction (COF) range, varying from 0.75 to 0.64 was recorded at 5N; whereas thereduced COF of 0.46–0.52 was observed at 20N or 50N. The volumetric wear ratedecreased with load and varied on the order of 10

Surface Properties Of Lubricants And Hard Coatings As Predictors Of Frictional Behaviour Under Boundary Lubrication

The surface properties of different lubricants and hard-coated solid surfaces were investigated, in order to analyze their adhesion in the process of boundary lubrication. Firstly, the surface free energies and their dispersive/polar ratio of two hard-coated surfaces-hydrogenated amorphous carbon coating (DLC) and WC doped DLC (WC/C)-were compared with the surface properties of a steel surface and, secondly, the surface free tensions (and their dispersive/polar ratio) of base mineral oil with and without EP/AW additive were compared to ecologically more acceptable sunflower oil. The work of adhesion was calculated in order to describe the interfacial properties of different solid/liquid (hard-coating/lubricant) systems, on the basis of contact angle measurements.

Development of an Intelligent Rotating Machinery Diagnostics Programme

Rotating machines are one of the most wide spread items of equimpnet in the industrial plants; hence the reliable operation is of great practical importance. Analyses show that when a run-to-failure philosophy is adopted in rotating machinery maintenance, their downtime is usually three to four times longer comparing to a periodic or proactive maintenance approach. A successful proactive maintenance program requires an integration of several diagnostic procedures into an intelligent data processing system. Such a system allows detection of a broad range of faults in an early stage. The main aim of this paper is to present current results of our development of an intelligent rotating machinery diagnostics program for detecting a broad range of faults from signals which can be measured non-destructively and on-line. The main motivation is to develop computationally efficient algorithm that can be implemented on a standard (low-cost) platform. In that respect we have developed a test rotating machine equipped with accelerometers, temperature sensors and sensors for lubricating oil characterization. In this paper we focus on gear-box faults and a feature extraction procedure based on non-parametric statistical concepts as suggested and demonstrated on experimental data.Copyright

Characterization and Design of Laser Textured Surfaces

Increased requirements for improved performance and reliability of mechanical systems dictate the use of new advanced materials and surface engineering techniques, which would increase efficiency and reduce energy losses. Already with a small change in surface roughness or topography lubrication mechanism can be change, thus leading to substantial improvement in tribological behaviour of contact surfaces. One of the ways of altering surface topography, known as surface texturing is by introducing small dimples or channels at the contact surface. Surface texturing is already successfully used in different applications, however, they are mainly based on trial and error approach. The aim of this investigation was to identify surface roughness parameters which could be used as a design parameter when preparing textured surfaces and to determine the effect of texturing parameters on roughness and tribological properties of boundary lubricated surfaces. Results of this investigation show that textured surfaces can be treated as an ordered roughness, with skewness and kurtosis parameters showing good correlation with the change in tribological behaviour of contact surfaces. Negative skewness and high kurtosis values, which can be achieved through wedge-shaped dimples, reduced dimple size and increased dimple spacing, were found to result in lower friction.© 2009 ASME

A Viscosity-Based Study of the Tribo-Physical Effects in Boundary-Lubricated DLC Contacts

In about a decade, since interest about boundary lubrication properties of diamond-like carbon (DLC) coatings exists, mainly chemical aspects of the DLC lubrication were investigated, i.e. focusing on interactions between various additives and coatings, while physical aspects of coating-oil interactions were not discussed in a greater extent. To elucidate some of these effects, we have analyzed the friction behaviour of DLC coatings and steel under different boundary lubrication conditions by using polyalphaolefin (PAO) base oils having different viscosity grades. Based on this, we have identified several tribo-physical effects in these contacts and for the purposes of this paper we briefly discuss the physical adsorption between the oils and the DLC surfaces, clearly indicating existence of rather strong physically adsorbed layers, which were able to resist high shear stresses under severe boundary lubrication.Copyright

Modeling of Surface Topography for Reduced Friction

The aim of the present research was to investigate surface topography in terms of different surface roughness parameters and to correlate surface topography change to friction of contact surfaces. For this purpose, different 100Cr6 plate samples with different surface topography were prepared. Using different grades and combinations of grinding and polishing samples with similar Ra values, but different Rku and Rsk values were obtained. To evaluate influence of roughness parameters on friction and wear, dry and lubricated pin-on-disc tests were carried out under different contact conditions. Test results indicate that high Rku and negative Rsk values lead to decrease in friction. To investigate the effect of surface texturing on surface roughness parameters, real roughness profiles were virtually altered to achieve virtually textured surfaces. Using NIST SMATS softgauge for calculation of surface roughness parameters, virtually altered roughness profiles were investigated in terms of texture size, shape and spacing, and their influence on surface roughness parameters, especially on skewness and kurtosis. Lower diameter, higher spacing and wedge-shaped dimples reflect in higher Rku and more negative Rsk parameters.Copyright

Boundary Lubrication of DLC Coatings With Conventional Oils

In this work we present results that show the effect of the type of mating surfaces, the doping elements in the DLC coatings, the type of the base oils and the additives used on the tribological performance of the boundary lubricated DLC coatings. We discuss the results in terms of various physical and chemical effects and we present some recent results of surface analyses under different temperature regimes.Copyright