Andriy Kovalchenko

The Effect of Laser Texturing of Steel Surfaces and Speed-Load Parameters on the Transition of Lubrication Regime from Boundary to Hydrodynamic

Laser surface texturing (LST) is an emerging, effective method for improving the tribological performance of friction units lubricated with oil. In LST technology, a pulsating laser beam is used to create thousands of arranged microdimples on a surface by a material ablation process. These dimples generate hydrodynamic pressure between oil-lubricated parallel sliding surfaces. The impact of LST on lubricating-regime transitions was investigated in this study. Tribological experiments were carried out on pin-on-disk test apparatus at sliding speeds that ranged from 0.15 to 0.75 m/s and nominal contact pressures that ranged from 0.16 to 1.6 MPa. Two types of oil with different viscosities (54.8 cSt and 124.7 cSt at 40°C) were evaluated as lubricants. Electrical resistance between flat-pin and laser-textured disks was used to determine the operating lubrication regime. The test results showed that laser texturing expanded the range of speed-load parameters for hydrodynamic lubrication. LST also reduced the measured friction coefficients of contacts that operated under the hydrodynamic regime. The beneficial effects of laser surface texturing are more pronounced at higher speeds and loads and with higher viscosity oil.

Effect of Humidity on the Tribological Properties of Carbide-Derived Carbon (CDC) Films on Silicon Carbide

The effect of humidity on the tribological behavior of carbide-derived carbon (CDC) films prepared by high-temperature chlorination of silicon carbide was examined. Pin-on-disk tribological tests indicate that CDC, unlike graphite or glassy carbon, performs better in dry nitrogen (less than 0.05 friction coefficient at 0% humidity) than in humid air. This versatility is explained by the onion-like structure of the nanoporous CDC coating.

Phase transformations in silicon under dry and lubricated sliding.

Sliding friction and wear mechanisms of silicon/silicon nitride test pairs were investigated under conditions of both dry and lubricated sliding. High-resolution surface topography mapping and electron microscopy studies revealed that microfracture was the predominant wear mechanism under dry and grease-lubricated sliding conditions. Raman spectroscopy suggested that in certain areas of the sliding contact, silicon underwent phase transformation and reached a metallic state because of high contact pressures. The extent of phase transformation was greater during the very early stages of the run-in period than during steady-state sliding regimes. The use of grease and oil as lubricants led to a substantial reduction in friction and greatly diminished wear due to microfracture. Furthermore, almost all areas on Si surfaces subjected to lubricated sliding contact underwent pressure-induced phase transformation. Both amorphous material and crystalline Si phases were identified by Raman spectroscopy. The experimental observations suggested that the wear process in lubricated sliding contacts was mainly dominated by the formation of a ductile metallic Si phase and subsequent removal of the transformed layers. The results of this study demonstrate that pressure-induced phase transformation must be taken into account when considering possible wear mechanisms of silicon in contact with other hard materials, inasmuch as it contributes notably to the wear of silicon under lubricated sliding. Presented at the 56th Annual Meeting in Orlando, Florida May 20–24, 2001

Tribochemical interactions of boron carbides against steel

Abstract Auger electron spectroscopy and electron microscopy were used to investigate the surface chemistry and tribological properties of boron carbide sliding against steel. It was revealed that the interacting process was accompanied by the diffusion of the ceramic elements into steel and by the oxidation of the steel and ceramic surfaces due to the oxygen presence in the atmosphere. It was established that the oxidation process in air or during friction tests leads to a graphitized layer on the boron carbide surface under the B 2 O 3 film. It was demonstrated that the oxidation caused a decrease in the friction coefficient of boron carbide sliding against steel.

Nano-structured carbide-derived carbon films and their tribology

Carbide-derived carbon (CDC) is a form of carbon produced by reacting metal carbides, such as SiC or TiC, with halogens at temperatures high enough to produce fast kinetics, but too low to permit the rearrangement of the carbon atoms into an equilibrium graphitic structure. The structure of CDC is derivative of the original carbide structure and contains nanoscale porosity and both sp2 and sp3 bonded carbon in a variety of nanoscale structures. CDC can be produced as a thin film on hard carbides to improve their tribological performance. CDC coatings are distinguished by their low friction coefficients and high wear resistance in many important industrial environments and by their resistance to spallation and delamination. The tribology of CDC coatings on SiC surfaces is described in detail.

Tribological Characterization of Carbide-Derived Carbon (CDC) Films in Dry and Humid Environments

The problem of good wear resistance coupled with low friction coefficient has been studied extensively. Carbide-derived carbon (CDC) films have been demonstrated to show excellent friction and wear properties in air. in the present work, we examine the effect of humidity on the tribological behavior of CDC films prepared under various experimental conditions. We produced the films by high temperature chlorination of sintered silicon carbide, characterized them by Raman microspectroscopy and nanoindentation, and carried out pin-ondisk tribological tests in air and dry nitrogen (0% humidity) using silicon nitride counterbodies. Our results indicate that CDC, unlike graphite or glassy carbon, does not fail in dry environments. Moreover, it performs better in dry nitrogen than in humid laboratory air. The CDC coating on SiC can work for hours in dry nitrogen showing the friction coefficient of less than 0.05. Chlorination conditions and the surface condition of the test piece are other important parameters in tribological performance. These coatings may be used in dynamic seals and other tribological applications.

Tribological characterization of carbide-derived carbon layers on silicon carbide for dry friction applications

Carbide-derived carbon (CDC) films prepared on silicon carbide are known to have excellent tribological properties in dry nitrogen. The purpose of this study was both to examine different counterbodies and to study the wear process in more detail. Choice of counterbody appears to have little effect on the tribological performance of the CDC coating, and Raman spectroscopy indicates that the tribological performance is dominated by the formation of a graphitic transfer film on the counterbody. CDC appears to wear in ductile fashion in both air and dry nitrogen.

Friction and wear performance of low-friction carbon coatings under oil lubrication.

Amorphous carbon coatings with very low friction properties were recently developed at Argonne National Laboratory. These coatings have shown good promise in mitigating excessive wear and scuffing problems associated with low-lubricity diesel fuels. To reduce the negative effect of sulfur and other lubricant additives in poisoning the after-treatment catalyst, a lubricant formulation with a low level of sulfur may be needed. Exclusion of proven sulfur-containing extreme pressure (EP) and antiwear additives from oils will require other measures to ensure durability of critical lubricated components. The low-friction carbon coating has the potential for such applications. In the present study, we evaluated the friction and wear attributes of three variations of the coating under a boundary lubrication regime. Tests were conducted with both synthetic and mineral oil lubricants using a ball-on-flat contact configuration in reciprocating sliding. Although the three variations of the coating provided modest reductions in friction coefficient, they all reduced wear substantially compared to an uncoated surface. The degradation mode of oxidative wear on the uncoated surface was replaced by a polishing wear mode on the coated surfaces.

Surface Damage and Wear Mechanisms of Amorphous Carbon Coatings under Boundary Lubrication Conditions

Abstract A class of amorphous carbon coatings with excellent tribological properties under dry conditions was recently developed at Argonne National Laboratory. In the present study, the performance of three variations of such coatings under the boundary lubrication regime was evaluated, with particular focus on the coating surface damage and mechanical aspect of the wear mechanisms of the coated surfaces. The evaluation employed ball on flat contact geometry in reciprocating sliding motion and three different lubricants. Compared with the uncoated steel surface, the three variations of the coatings evaluated significantly reduced the amount of wear. The surface damage in the coatings consisted primarily of localised crack formation at the local asperity points of contact typical of boundary lubrication regime. The cracks propagated over time, resulting in eventual removal of coating material.

Tribological Behavior of Oil-Lubricated Laser Textured Surfaces in Conformal Flat and Point Contacts

The effects of laser surface texturing (LST), which involves the creation of an array of microdimples on the surface with laser, on friction and wear behavior of oil-lubricated steel surfaces were evaluated. Tests were conducted in unidirectional sliding in both the conformal and non-conformal contact configurations with a pin-on-disc test rig using fully formulated synthetic oil lubricant. In conformal contact, LST expanded the operating conditions for mixed and hydrodynamic lubrication regimes to higher loads and slower speeds i.e. the Stribeck curve was shifted to the left. LST was also observed to reduce the magnitude of friction coefficients in the boundary regime. For the non-conformal contact configuration, LST produced more wear on the rubbing counterface compared to untreated surfaces. This also accelerated the run-in process in the tests with LST treated surfaces.Copyright