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To investigate the effects of surface chemisorbed hydrogen atoms and hydrogen atoms in the subsurface region of diamond on surface conductivity, models of hydrogen atoms chemisorbed on diamond with (100) orientation and various concentrations of hydrogen atoms in the subsurface layer of the diamond were built. By using the first-principles method based on density functional theory, the equilibrium geometries and densities of states of the models were studied. The results showed that the surface chemisorbed hydrogen alone could not induce high surface conductivity. In addition, isolated hydrogen atoms in the subsurface layer of the diamond prefer to exist at the bond centre site of the C-C bond. However, such a structure would induce deep localized states, which could not improve the surface conductivity. When the hydrogen concentration increases, the C-H-C-H structure and C-3Hbc-C structure in the subsurface region are more stable than other configurations. The former is not beneficial to the increase of the surface conductivity. However, the latter would induce strong surface states near the Fermi level, which would give rise to high surface conductivity. Thus, a high concentration of subsurface hydrogen atoms in diamond would make significant contributions to surface conductivity. [ABSTRACT FROM AUTHOR]

Abstract: The polished quenched-and-tempered 9Cr18Mo steels were implanted with N ions and Ti ions respectively at a fluence of 2×1017 ions/cm2. The mechanical properties of the samples were investigated by using nanoindenter and tribometer. The results showed that the ion implantations would improve the nanohardness and tribological property, especially N ion implantation. The surface analysis of the implanted samples was carried out by using XRD, XPS and AES. It indicated that the surface exhibits graded layers after ion implantation. For N ion implantation, the surface about 20nm thickness is mainly composed of supersaturated interstitial N solid solution, oxynitrides, Cr x C y phase and metal nitrides. In the subsurface region, the metal nitrides dominate and the other phases disappear. For Ti ion implantation, the surface of about 20nm thickness is mainly composed of titanium oxides and carbon amorphous phase, the interstitial solid solution of Ti in Fe is abundant in the subsurface region. The surface components and structures have significant contributions to the improved mechanical properties. [Copyright &y& Elsevier]

Abstract: To clarify the electron transfer behavior of the hydrogen-terminated boron-doped diamond film electrode in an electrolytic solution, its detailed electronic structures were investigated by using scanning probe microscopy and ab initio methods. The interface structure of the hydrogen-terminated diamond electrode and the electrolyte was also studied by means of cyclic voltammetry and AC impedance spectroscopy. The results showed that there exist shallow acceptors in the band gap of the hydrogenated diamond films. Neither the surface hydrogen alone nor the subsurface hydrogen could induce the shallow acceptors, though they interact strongly with the surface carbon atoms or subsurface carbon and boron atoms in the diamond film. It is the interaction of the surface adsorbates and the surface C–H bonding that gives rise to the shallow acceptors in the band gap of the hydrogenated diamond film. The surface shallow acceptors in the band gap of the hydrogenated diamond film could lower the energy barrier of the electron transfer between the diamond electrode and the electrolytic solution. Thus, electrochemical window for the hydrogenated diamond film is narrower and, its film resistance and capacitance are also smaller than those of the oxygenated one. In our work, the experimental data obtained by using scanning probe microscopy are in good agreement with the calculation results. [Copyright &y& Elsevier]

The superhydrophobic behavior of a surface can be generally attributed to the combination of its chemical composition and microscale texture. The surface can be both hydrophobic and rough, and the roughness enhances its hydrophobicity. For a natural or artificial surface, superhydrophobic behavior is generally induced by a structured hydrophobic surface. This paper proposes an alternative; that is the superhydrophobic behavior can be obtained from a structured hydrophilic surface. The superhydrophobic behavior of a T-shape micropillar surface coated with diamond-like carbon has been achieved, which experimentally proved the proposed hypothesis that superhydrophobicity can be created from a hydrophilic surface through surface microstructure modification. [ABSTRACT FROM AUTHOR]

The cavitation erosion-corrosion effect on the metal surface always forms irregular oxide structures. In this study, we reported the formation of regular self-assembled structures of amorphous nanoparticles around the cavitation erosion pits on carbon steel upon the ultrasonic cavitation in methylene blue solution. Each self-assembled structure was composed of linearly aligned nanoparticles of about 100 nm. The formation of self-assembled structures might be due to the combined effect of corrosion, specific sonochemical reaction in methylene blue solution, and the magnetic domain structures on the carbon steel. [ABSTRACT FROM AUTHOR]

In the incubation period of ultrasonic cavitation, due to the impact of microjets on the material surface, the needle-like microjet-pits are formed. Because the formation of microjet-pits relates with the evolution of cavitation erosion on engineering materials, corresponding study will promote the understanding on the mechanism of cavitation erosion. However, little study on the microjet-pits has been carried out, especially in the particles-water mixture. In this study, we firstly demonstrated the microjet-pits on the carbon steel would be significantly inhibited by Al particles in water. Such inhibition effect indicated that particular particles might not only provide growth sites for cavitation bubbles but also affect the collapse of cavitation bubbles near a solid surface. Our study deepened the understanding on the ultrasonic cavitation erosion in the particles-water mixture. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the effect of hydrophobic surface on cavitation damage, hydrogen-terminated diamond film and oxygen-terminated diamond film are prepared for the cavitation damage experiment. Because the film surfaces have the same roughness and hardness, the hydrophobic property effect is focused on. Obvious damage pits appear on the hydrogen-terminated surface after 4h cavitation experiment, while no such pits are found on oxygen-terminated surface. Surface testing results also show that the surface roughness of hydrogen-terminated surface is higher than that of oxygen-terminated surface after the experiment. Such results indicate that the collapse of bubbles growing from the hydrophobic wall to be damaged plays important role in the generation of cavitation damage. [Copyright &y& Elsevier]

The initial characteristics of the surface layer following the quenching and tempering treatment of ultra-high-strength steel play a significant role in determining the subsequent precision machining. This study focus on investigating the influence of machining processes on the quenching and tempering surface layer. The machining processes affect both the oxidation of the quenching and tempering treatment and the development of a distinct preferred grain orientation. Gradual diminishment of surface abrasions leads to the transformation of the needle-like oxidation pattern into a layered oxidation structure. The preferred orientation of the grains prevents the grains from shear sliding, thereby enhancing the Taylor effect. Formation mechanisms of the microhardness and residual stress of the quenching and tempering surface layer induced by machining processes were also discussed and completely revealed. The microhardness is mainly attributed to the dynamic Hall-Petch effect, while plastic strain, dislocation energy storage, and phase transformation contribute to the residual stress changes. • Formation mechanisms of the quenching and tempering surface layer induced by machining processes were revealed. • Machined surface morphology affects preferred grain orientation preference and austenitization characteristics. • Microhardness of the surface layer induced by machining processes is mainly attributed to the dynamic Hall-Petch effect. [ABSTRACT FROM AUTHOR]

• The double influence function method including flattening deformation influence function and deflection deformation influence function are established and combined used to solve the deformations between the rolls. • A model,considering the dispersion distribution characteristics of backing roll,for calculating the contact pressure between the rolls of the Sendzimir 20-high mill based on the double influence function method is established. • The conjugate gradient method is used to solve the contact pressure between the rolls by combining the force balance equation, the moment balance equation and the deformation compatibility equation group of rolls system. • The solving accuracy of the model established is consistent with that obtained by finite element method and the computation time can be greatly reduced. This paper established a model for calculating the contact pressure between the rolls of the Sendzimir 20-high mill based on the influence function method with considering the dispersion distribution characteristics of backup rolls. Stone's and Hirschcock's formula are used to calculate the rolling force between the work rolls and the rolling stock. The force balance equations and the moment balance equations of the roll system are established to determine the relationship between the contact pressure of rolls and the rolling force. The deformation-compatibility equation is established by combining the flattening deformation, deflection deformation, and rigid displacement of the rolls and roll crown. The influence function method is used to solve the flattening deformation and deflection deformation between the rolls. The conjugate gradient method is used to solve the contact pressure between the rolls by combining the force balance equation group, the moment balance equation group, and the deformation compatibility equation group of the roll system. The contact pressure between rolls obtained by the model established is compared to that by the finite element method. The results show that the calculation accuracy of the model established in this paper is consistent with that of the finite element method. Significantly, the contact pressure between the backup roll and the second intermediate roll can be accurately calculated by considering the dispersion distribution characteristics of the backup roll, and the computation time can be greatly reduced. [ABSTRACT FROM AUTHOR]