The transition from severe to mild wear in law alloy steel

The wear rates of sliding surfaces are significantly reduced if mild oxidational wear can be encouraged. It is hence of prime importance in the interest of component life and material conservation to understand the factors necessary to promote mild, oxidational wear, The present work investigates the fundamental mechanism of the running-in wear of BS EN 31!EN 8 steel couples. under various conditions of load. speed and test duration. Unidirectional sliding experiments were carried out on a pin-on~disc wear machine where frictional force, wear rate, temperature and contact resistance were continuously monitored during each test. Physical methods of analysis (x-ray, scanning electron microscopy etc.) were used to examine the wear debris and worn samples. The wear rate versus load curves revealed mild wear transitions, which under long duration of running, categorized mild wear into four distinct regions.α-Fe20s. Fe304, FeO and an oxide mixture were the predominant oxides in four regions of oxidational wear which were identified above the Welsh T2 transition. The wear curves were strongly effected by the speed and test duration. A surface model was used to calculate the surface parameters, and the results were found to be comparable with the experimentally observed parameters. Oxidation was responsible for the transition from severe to mild wear at a load corresponding to the Welsh T2 transition. In the running-in period sufficient energy input and surface hardness enabled oxide growth rate to increase and eventually exceeded the rate of removal, where mild wear ensued. A model was developed to predict the wear volume up to the transition. Remarkable agreement was found between the theoretical prediction and the experimentally-measured values. The oxidational mechanjsm responsible for transitjon to mild wear under equilibrium conditions was related to the formation of thick homogenous oxide plateaux on subsurface hardened layers, FeO was the oxide formed initially at the onset of mild wear but oxide type changed.during the total running period to give an equilibrium oxide whose nature depended on the loads applied

Glass-formation region of ternary Sn-Sb-Se-based chalcogenide glasses

Tin-antimony-selenium (TAS)-based system belongs to the ternary chalcogenide compounds of IV-V-VI group owing to their heavy elemental masses, their glass formation region was assumed to be small comparing to their counterpart elements in the same group. However, there were rare published reports on their glass structure, while their glass boundary formation region was not yet reported. It was the aim of this paper to map their glass-forming region experimentally using XRD and validate it theoretically using the average co-ordination number, μ, and the fraction of the bond distributions, f, from chemical order model. Theoretically, it was validated that the glass formation was arrested between μ ≤ 2.4 and the fraction of Sn-Se bonds, f sn-se < 44.5%. XRD analyses of 66-as-prepared samples revealed that the glass formation region was located within the predicted area that mapped in structural triangle

Electrical conductivity measurements in evaporated tin sulphide thin films

Tin sulphide (SnS) has been evaporated on to substrates maintained at fixed temperature in the range 50-300 oC. X-ray diffraction measurements have shown that the films deposited at the lower substrate temperatures are non-stoichiometric, containing higher sulphides of tin, but that those deposited at 300 oC consist essentially only of SnS. Film conductivity increased in the range 0.5-2.0 S m-1 as the substrate temperature during deposition increased from 50 oC to 250 oC, this effect being attributed to the changing film composition. Films deposited at 50 oC and 150 oC showed thermally activated conductivity at temperatures above 220-250K, with activation energies Ea of 0.12 eV and 0.14 eV, respectively. At lower temperatures both conductivity and activation energy were considerably lower, consistent with hoping via localized states. The conductivity is modified after prolonged cooling to 160 K, although the mechanism of this process is not understood

Raman and UV-visible spectrophotometer studies of hydrogenated amorphous carbon thin films

Hydrogenated amorphous carbon (a-C:H) thin films were prepared using a direct-current plasma enhanced chemical vapor deposition (DC-PECVD) over a various range of DC power (w) in range of 0.2989-0.4218 W. Changes in the film properties due to DC-power were systematically studied by Raman spectrometer and UV-Vis spectrophotometer. Based on the results, the films studied in the present research are found to consist of sp2 clusters of which their size increases with increasing power during the deposition, resulting in lower hydrogen, sp3 content and optical band gap. The experimental results revealed that a-C:H properties are highly dependent on DC-power