A quantitative analysis of surface deformation by stick/slip atomic force microscopy

This article presents a quantitative determination of static deformation at a nanometer scale of a surface caused by the tip of an atomic force microscope. An analysis of cantilever displacements while in contact with the surface leads to a directly measurable dimensionless parameter which is well sensitive to surface deformation. The method is specifically aimed at stick/slip friction measurements like on layered compounds, like TiS2 or on a relatively rigid surface of an ionic crystal, in this study NaCl [100]. Stick/slip friction images offer a possibility to investigate details of strain-dependent deformation. The observed deformation in TiS2 could play an important role in the occurrence of strong stick/slip friction in this and other layered materials

Shock wave velocity and shock pressure for low density powders: A novel approach

A novel approach is presented to predict the shock wave velocity as well as the shock wave pressure in powder materials. It is shown that the influence of the specific volume behind the shock wave on shock wave velocity and shock pressure decreases with decreasing initial powder density. The new model is compared with experimental data of various materials: Fe, Cu, Al, C, UO2, Ce2O3, SiO2 (quartz), NaCl, and polystyrene. It is concluded that the model holds in particular for initial powder densities less than 50% and for flyer plate velocities up to 5 km/s.

Effects of self-affine surface roughness on the friction coefficient of rubbers in the presence of a liquid interlayer

In this article, we investigate how the friction coefficient is affected by the presence of a liquid layer in between a self-affine rough surface and a sliding rubber surface. The liquid layer will reduce energy dissipation from the small surface asperities and cavities of lateral sizes smaller than the healing length ζ and, therefore, will reduce the coefficient of friction. Significant coefficients of friction are attained for small healing lengths ζ (≪ξ with ξ the in-plane roughness correlation length). Finally, it is shown that the effect of the substrate roughness exponent H becomes less important especially for large healing lengths (ζ⩾ξ)

Linear growth of thin films under the influence of stress

We have studied the growth of thin films in the presence of stress instability that enhances the roughness and roughening induced by conservative as well as nonconservative noise. It is clearly illustrated that nonconservative noise effects may enhance stress induced roughness. Nevertheless, the incorporation of conservative noise appears to also be substantial in growth processes driven by diffusion. For growth on a rough substrate the dependence of the amplitude of the surface roughness on the film thickness differs from that of a film growing on a flat substrate. The amplitude shows a minimum at a particular substrate thickness, which indicates that the growth up to this thickness is enforced by undulations of the substrate

Correlated roughness effects on electrical conductivity of quantum wires

The influence of electron scattering by rough boundaries on electrical conductivity of quantum wires is studied in the diffuse transport limit within the kinetic Boltzmann equation approach. The considerations are restricted to the wires obtained by lateral confinement of a two-dimensional electron gas. Both intra- and interboundary roughness correlations are taken into account. It is shown that the cross correlations usually increase the conductivity, leaving the shape and phase of the quantum size oscillations almost unaffected

Microstresses and microstructure in thick cobalt-based laser deposited coatings

Microstresses in a thick laser clad Co-based coating on steel substrate were investigated with 3D X-ray microscopy using an intense synchrotron microfocused beam. The microstructure was examined with tight microscopy and field emission scanning electron microscopy equipped with X-ray energy dispersive spectroscopy and Electron Back Scattering Diffraction (orientation imaging microscopy). Microhardness and scratch resistance variations inside the coating are related to the local microstructure influenced by additional heating and by melt convection during the laser track overlapping. The residual microstrains were accessed with a high spatial resolution defined by the size of the synchrotron microbeam. Type 11 residual strains and stresses on the level of individual grains and dendrites were analyzed in terms of tensor invariants, hydrostatic and von Mises shear stress, along the depth of a slightly diluted clad track. The upper part of the coating shows a constant spread of hydrostatic stresses between -500 and 500 MPa; towards the bottom of the track the spread of these stresses increases almost linearly with depth. A correlation between the microstructural features and the spread of the hydrostatic microstresses was found. It is concluded that microstresses in individual neighboring grains are inhomogeneously dispersed. (c) 2007 Elsevier B.V. All rights reserved

Effects of the Alloy Composition on Phase Constitution and Properties of Laser Deposited Ni-Cr-B-Si Coatings

Three Ni-Cr-B-Si hardfacing alloy powders with different Cr contents and Si to B ratios were deposited at cladding speeds of 5-40 mm/s on steel substrate using laser beam and the alloy composition-phase formation-properties relationships in the deposits were studied using several experimental techniques. Two general groups of compositions could be defined in this alloy system; the high-alloy grades characterized by numerous Cr boride precipitates, a low Si/B ratio and substantial Ni-B-Si eutectics, and the low-alloy grades with very little Cr boride precipitates, a high Si/B ratio and limited amounts of interdendritic eutectics. The findings confirmed that phase formation of Ni-Cr-B-Si laser deposited coatings primarily depends on the Cr content and Si/B ratio with the former controlling the amount of Cr-rich precipitates and the latter influencing the nature of the eutectic structures. In addition, it is shown that both Cr-rich precipitates and eutectic structures contribute to the functional properties of the coatings such as hardness and cracking susceptibility. The correlation between phase constitutions produced by different compositions and the hardness/cracking tendency is established and discussed.

Toughening mechanism for Ni-Cr-B-Si-C laser deposited coatings

Laser deposited coatings were made from Colmonoy 69 Ni-Cr-B-Si-C alloy and Nb-modified Colmonoy 69 using laser cladding with powder injection. Addition of Nb was done to decrease the structural scale of Cr boride precipitates by providing Nb-rich nucleation agents. The purpose of the study was to evaluate the viability of microstructural refinement as a toughening mechanism for Ni-Cr-B-Si-C alloys. The results show that although a significant refinement of the Cr-rich precipitates while preserving the original level of hardness could be induced in these alloys by a suitable addition of Nb, cracking susceptibility of the deposits was not decreased. This is attributed to the continuous network of hard eutectics providing an easy route for crack growth. The outcome of this work points out that an effective toughening mechanism for Ni-Cr-B-Si-C alloys should include not only refinement of the hard precipitates, but also modification of the eutectic structure. (C) 2013 Elsevier B.V. All rights reserved.</p