Papers by Keyword: Surface Structures

Abstract: During of aluminum alloy materials, it is possible to find three surface types which can be distinguish as primary, secondary and tertiary sections. In practice this is a big problem in case of finding the basic parameters of roughness and waviness as described by ISO 4288. According to our research, it is possible to use optical microscopy in the first step and subsequently to scan the surface in 3D in order to distinguish the type of. Another problem is how to determine the boundaries between the individual structures. The article describes methods to distinguish the boundaries in a more precise way by the cumulative functions, leading to more accurate determination of the surface quality parameters.

Abstract: The 4H-SiC(000-1)_C and (0001)_Si surface reconstructed structures and the oxidation processes of these surfaces are investigated using a first-principles calculation method. The most stable reconstructed 4H-SiC(000-1)_C and (0001)_Si surfaces have p-bonded chains. In the topmost SiC bilayer, half of Si and C atoms exchange their positions and C-C or Si-Si bonds formed densely below the surfaces. When we place a SiO₂ layer on the p-bonded chain (000-1)_C surface, C-C bonds are formed more densely below the interface. We simulate a sequence of O₂ molecules arrivals at an interface of tridymite-phase-SiO₂ and 4H-SiC(000-1)_C. Dissociated O atoms at the interface tended to make bonds with Si atoms. The C-C bonds in the SiC substrate break easily and a local C surface occasionally appears. We have examined how the surface structure changes through an O₂ molecule exposure by using a classical molecular dynamics simulation program and confirmed the formation of C-C bonds below the surface and the interface.

Abstract: The tribological behaviors of nitrogen and titanium ion implanted AISI 440C stainless steel were studied by using an oscillating ball-on-disk tribometer under oil lubricated condition. The results showed that the ion implantations would significantly decrease the friction coefficient of the samples. To interpret the effect mechanism of the ion implantation on tribological performance, the surface morphology and oil wettability of the ion implanted samples were investigated by using a three-dimensional white interferometer and a contact angle analyzer, respectively. In addition, the surface structures and components of the samples were analyzed by using XRD and XPS techniques. The results indicated that the low friction coefficients of the ion implanted samples can be attributed to the new phases formed on the sample surfaces. For nitrogen ion implanted sample, the metal nitrides, supersaturated interstitial N and some C-O-N compounds appear on the sample surface. For titanium ion implanted sample, apart from TiO₂ and TiC phases form at the AISI 440C steel surface. Those components increase the surface energy of the AISI 440C steel and are in favor of the formation of the thin oil film.

Abstract: In this work, we studied the surface/water interaction properties of a pure calcium hydroxyapatite (HA) and their modifications as a consequence of the partial Ca2+/Mg2+ (MHA) substitution by means of IR spectroscopy and microcalorimetry of adsorbed water. IR data indicated that water molecules in direct contact with the surface of HA are coordinated to surface cations and experience H-bond significantly stronger than in liquid water. The heats of adsorption associated to such interactions are very high, being twice-triple the heat of liquefaction of water. Interestingly, water experiences H-bond higher than in its bulk liquid state also in the second layer. Finally the entering in the material of Mg2+ ions was shown to significantly affect the affinity of the material toward water and the properties of its hydration layers.

Abstract: The effects of TEA CO2 laser radiation on AISI 420 stainless steel and formed surface structures are studied. The laser energy density of 45.0 J/cm2 has modified the target surface. Qualitatively, the modifications of AISI 420 steel can be summarized as follows: change of color after action of one laser pulse; central zone of interaction in crater like form and periphery zone of interaction (for more than 10 laser pulses); appearance of grainy features and ablation rate of near 4 nm per laser pulse (action of 400 laser pulses); hydrodynamical effects like resolidified rim and droplets.