Structural Changes In Surface Layers Research Articles

Structural Changes in Surface Layers of Vanadium Induced by the Separate and Sequential Impact of Helium Ions and Pulsed Laser Radiation

Structural Changes in Surface Layers of Vanadium Induced by the Separate and Sequential Impact of Helium Ions and Pulsed Laser Radiation

Study of the amorphization of surface silicon layers implanted by low-energy helium ions

The structural changes in surface layers of Si(001) substrates subjected to plasma-immersion implantation by (2–5)-keV helium ions to a dose of D = 6 × 1015–5 × 1017 cm–2 have been studied by highresolution X-ray diffraction, Rutherford backscattering, and spectral ellipsometry. It is found that the joint application of these methods makes it possible to determine the density depth distribution ρ(z) in an implanted layer, its phase state, and elemental composition. Treatment of silicon substrates in helium plasma to doses of 6 × 1016 cm–2 leads to the formation of a 20- to 30-nm-thick amorphized surface layer with a density close to the silicon density. An increase in the helium dose causes the formation of an internal porous layer.

Surface Integrity Evaluation of Brass CW614N after Impact of Acoustically Excited Pulsating Water Jet

Presented article is focused on surface integrity evaluation of brass CW614N form the sight of surface topography, structural changes in surface layers and strengthening character in subsurface layers after impact of acoustically excited pulsating water jet (PWJ). Surface topography was evaluated using optical profilometry. Structural changes in subsurface layer were observed based on mass material removal Δm [mg/s] and maximal depth of penetrance of PWJ hmax [mm]. Nano indentation measurement according to Berkovich were used to examination of strengthening character in subsurface layer. Disintegration of experimental samples was performed under constant technological conditions: hydraulic power of plunger pump Ph = 19kW; round nozzle diameter d = 1.6mm; feed speed rate v = 0.75mm/s; pressure of plunger pump p = 38MPa, stand-off distance of nozzle from target material z = 45mm; ultrasound frequency f = 20.29kHz and as variable factor was set power of ultrasound P on values 340, 360 and 380W. In terms of surface topography experimental investigation proved that PWJ under selected conditions is not suitable for precision machining. Evaluation of the surface characteristics indicates that the chemical composition has a significant effect on material weight loss Δm [mg/s] and a maximum depth of penetration of PWJ hmax [mm]. Evaluation of characteristics of subsurface layer was observed strengthened area with lower elasticity.

Structure, phase composition and mechanical properties of hard alloy treated by intense pulsed electron beams

Phase and structural changes in surface layers of WC–TiC–Co hard alloy treated by intense pulsed electron beams (IPEB) with electron energy of 20kV are studied. IPEB energy density absorbed by surface layer was 10–80J/cm2, pulse duration was 100–200μs. IPEB action with energy density of 30–80J/cm2 results in the formation of tungsten-supersaturated solid solution (Ti,W)C and transformation WC→W2C caused by melting of surface layers and their subsequent rapid quenching from liquid. Electron beam treatment leads to the formation of layered structure. Changes of structure and phase composition result in the increase of surface microhardness in 1.5–3 times and in the reduction of friction coefficient in 2–3.5 times.

Reactivity at the oxygen/titania interface and the related charge transfer

The present paper reports the reactivity between TiO2 and oxygen and the related charge transfer at 298 and 1,073 K. The studies were performed using work function measurements. It was found that oxidation of TiO2 at 1,073 K and p(O2) = 75 kPa, initially standardized at 1,173 K and p(O2) = 10 Pa, results in work function changes that are consistent with the theoretical model of the charge transfer during oxygen chemisorption and oxygen incorporation at the absence of structural transitions. However, oxidation of TiO2 at 298 K, p(O2) = 75 kPa, which has been initially standardized at 1,173 K in extremely reducing conditions at p(O2) = ∼10−10 Pa, results in work function changes that are consistent with low-dimensional structural changes of the surface layer. It is shown that oxidation of strongly reduced TiO2 at 298 K results in a decrease of work function, which cannot be explained without assuming the structural changes of the outermost surface layer.

AlN films grown on diamond and silicon carbide

Abstract Structural changes in surface layers of CVD AlN films were studied by the reflection high-energy electron diffraction technique. Film thickness was varied from 0.2 to 20 μm. Single crystals of diamond, silicon carbide and also bilayered structures of natural diamond/CVD diamond films were used as substrates. On the (111) surfaces of natural diamond, (111) CVD diamond films and (00.1) 6H-SiC at AlN thickness up to 1 μm one can observe the epitaxial correspondence between the growing film and the substrate: (00.1) [11.0] AlN//(111) [110] C α or (00.1) [10.0] AlN//(00.1) [10.0] 6H-SiC. At larger film thickness the epitaxial growth was replaced gradually by the formation of one of axial textures for which the planes (00.1), (10.3) or (11.4) of wurtzite-like aluminum nitride were parallel to the substrate. During the epitaxial growth the twinning structures with the twinning planes of types (10.1) and (11.1) were observed.

Structural Changes of Surface Layer of Vanadyl Pyrophosphate Catalysts by Oxidation−Reduction and Their Relationships with Selective Oxidation of n-Butane

The surface structure of vanadyl pyrophosphate ((VO)2P2O7) and its changes upon controlled oxidation and reduction have been investigated comprehensively by means of Raman spectroscopy, X-ray photo...

Effects of environment on fretting fatigue

Fretting fatigue tests of a carbon steel and an aluminum alloy were carried out in various environments and the effects of oxygen and water vapor were investigated by tangential force measurements, the initiation and propagation of cracks and hardness and structural changes of the damaged surface layer. With carbon steel the effect of water vapor is negligible but oxygen has a deleterious effect on the initiation and propagation of fretting fatigue cracks. However, with an aluminum alloy the effect of oxygen is small but water vapor accelerates the initiation and propagation of cracks. Environmental effects are more dominant than the stress conditions with an aluminum alloy; material softening and structural change of the surface layer occur.