Fretting study of an impregnated graphite bearing/nitrided stainless steel in a dry contact submitted to severe thermal-vibratory loading

Some industrial applications require the use of self-lubricating materials when fluid lubrication cannot be used. Carbon-based materials and in particular graphites are usually a used solution. However, the application of these materials is limited at high temperature; these materials are exposed to significant degradation and to high friction due to their high sensitivity to the air humidity and to the desorption phenomenon. This study determines the influence of a specific metallic impregnation on the graphite bearing, which is submitted to a severe thermo-vibratory loading by fretting against a stainless steel surface. The stainless steel surface has undergone a nitriding treatment by plasma. During the fretting contact, a strong transfer of the impregnant takes place from the impregnated graphite bearing to the steel conterface by adhesion; this deposit film allows a significant improvement in the tribological properties of the contact surfaces at high temperature.

Characteristics and Crystal Structure of Calcareous Deposit Films Formed by Electrodeposition Process in Artificial and Natural Seawater

In this study, we tried to form the calcareous deposit films by the electrodeposition process. The uniform and compact calcareous deposit films were formed by electrodeposition process and their crystal structure and characteristics were analyzed and evaluated using various surface analytical techniques. The mechanism of formation for the calcareous deposit films could be confirmed and the role of magnesium was verified by experiments in artificial and natural seawater solutions. The highest amount of the calcareous deposit film was obtained at 5 A/m2 while current densities between 1–3 A/m2 facilitated the formation of the most uniform and dense layers. In addition, the adhesion characteristics were found to be the best at 3 A/m2. The excellent characteristics of the calcareous deposit films were obtained when the dense film of brucite-Mg(OH)2 and metastable aragonite-CaCO3 was formed in the appropriate ratio.

Porosity and its Effect on Barrier Performance of Thin Electroless Cobalt Alloy Caps

ABSTRACTPinhole densities of electroless cobalt alloy films on copper substrate are characterized using optical and electrochemical methods. The impact of pits or pinholes on deposit film barrier property is discussed. The improved film barrier property is shown by reduction of pits formation through deposition process optimization.

Effect of Colloidal Silica Addition and Pre-Coating on the Microstructure Change of Cathode Copper Electrodeposited Film

The crystal structure, surface morphology and preferred orientation of copper electro-deposit were investigated by using sulfate bath with SiO2 suspension and the cathode substrate Au-sputtered. By addition of colloidal silica in copper electrolytic bath and Au pre-coating on substrate, the grains of deposits became fined and uniform and the number of grains were increased. Hardness of copper electrodeposits with colloidal silica increased about 15% in comparison with that of pure copper deposit film. The (111), (200) and (311) planes in the X-ray diffraction patterns were almost swept away, so preferred orientation of copper deposits change from (111) to (110) plane by co-deposit SiO2 and pre-coating the substrate.

Preparation of Ni Nanoparticles and Evaluation of Their Tribological Performance as Potential Additives in Oils

The application of nanoparticles in tribology has received considerable attention in recent years. In this paper, we described the preparation of Ni nanoparticles in microemulsions of sodium dodecyl sulphate (SDS)/isopentanol/cyclohexane/water and their tribological performance as additives in oils. The size of these nanoparticles is about 10 nm, and their shape is spherical. The four-ball test results indicate that Ni nanoparticles are potential additives for lubricating oils, and the tribological performance of lubricating oils can be improved significantly by dispersing Ni nanoparticles in oils. The maximum non-seizure load (PB) has been increased by 67 percent as compared with background oil. The wear scar diameter has been reduced from 0.71 mm to 0.49 mm. The relative percentage in friction coefficient has decreased 26 percent. The tribological mechanism is that a deposit film in the contacting regions was formed, which prevented the direct contact of rubbing surfaces and greatly reduced the frictional force between the contacting surfaces.

The importance of NO2 in Bench Tests for Precombustion Deposits in the Spark Ignition Engine Intake System

Most previous laboratory-scale deposit simulator studies have considered mainly fuel or lubricant composition and properties, with no consideration of possible effects of NOx, which may affect initiation of the deposit formation process and the overall rate at which deposition occurs. In this study a laboratory-scale deposit simulator was developed which produced thin deposit films by spraying gasoline on to a heated aluminium sleeve to investigate the effects of temperature, NO2 and possible gasoline blending components, on deposit formation. The amount of deposit collected is indicative of the deposit-forming tendency of the test fuel. The deposit film composition was analysed using Fourier transform infrared (FTIR) spectroscopy. The results of the experiments indicate that deposit formation is indeed sensitive to NO2, in addition to the effects of temperature and the molecular structure of the hydrocarbons. Thus the effect of NOx in deposit-related studies is important and should not be ignored. The FTIR analyses showed that when using NO2 the deposits are of a very similar structure to those produced in a real engine test. The analyses also gave some insight into the role of NO2 in the deposit formation mechanism.