Friction-induced Changes Research Articles

Tribological Performance and In Situ-Generated Oxidative Layer of Cobalt-Based Alloy From 25 °C to 800 °C

AbstractThe friction and wear performances of Haynes 25 alloy sliding against Si3N4 in a ball-on-disk configuration are investigated from room temperature (RT) to 800 °C. The friction-induced changes of morphology and chemical composition in the surface and subsurface regions of the wear tracks were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The results show that the friction coefficient (COF) decreases considerably via temperature, while the wear-rate increases and then decreases with temperature. During dry-sliding contact, the spontaneous formation of multiple metal oxides on the rubbing surface varies as a function of the test temperature, being responsible for either wear loss and/or a change of friction coefficient. The results of this study indicate that the presence of the glazed surface of Haynes 25 helps to lower friction. At 800 °C, a glaze layer with a multilayer structure appears on the rubbing surfaces, leading to the lowest friction coefficient and wear-rate.

Friction-Induced Changes in the Surface Structure of Basalt and Granite

Friction-induced changes in the structure of the surface layer of basalt and granite samples extracted from a well in the triggered seismicity zone in the Koyna–Warna region, India, have been studied by infrared, Raman, and photoluminescence spectroscopy. It has been found that friction leads to a partial degradation of quartz, albite, and clinopyroxenes crystals. Instead of these crystals, a thin layer of a mineral with a low coefficient of friction—kaolinite—is formed on the surface.

Measurement of Friction-induced Changes in Pig Aorta Fibre Organization by Non-invasive Imaging as a Model for Detecting the Tissue Response to Endovascular Catheters

Alterations in quantity or architecture of elastin and collagen fibres are associated with some blood vessel pathologies. Also some medical interventions such as endovascular catheterization have the potential to damage blood vessels. This study reports the use of porcine aorta as a model system for studying the physical impact of catheters on vasculature, in conjunction with non-invasive imaging techniques to analyse collagen and elastin fibre organization and assess load-induced changes. Porcine aorta was exposed to frictional trauma and elastin and collagen fibre orientation evaluated by destructive, histochemical methods and non-invasive imaging. The latter allowed the immediate impact of force on fibre orientation and fibre recovery to be evaluated longitudinally.In normal aorta, elastin fibres are aligned at the surface, but become less aligned with increasing depth, showing no alignment by ~30μm. Collagen fibres meanwhile appear aligned down to a depth of 35μm. Changes in collagen and elastin fibre orientation in healthy pig aorta were detected by conventional destructive histology within 5min of application of a sliding 10N load, while lesser loads had less impact. Good recovery of fibre orientation was observed within 20min. Non-invasive imaging of ex vivo aorta tissue provides a good indication of the extent of fibre re-organization following frictional stress, at loads similar to those encountered during medical interventions such as catheterization. These results indicate that tissue deformation can occur from these procedures, even in healthy tissue, and highlight the potential for the development of an in vivo probe capable of monitoring vascular changes in patients.

Surface modification of diamond-like carbon coatings to control over run-in processes in friction pair

The effect of the nanostructure and chemical composition of thin Mo–Se–C films on the run-in of the diamond-like carbon coating (a-C) and the steel counterbody during ball-on-disk sliding test is studied. At the final stage of the deposition of the a-C coating on the steel substrate, a flow of atoms from the MoSe2 target was added to the flow of atoms being deposited. The influence of the air humidity on the selection of optimum structure and chemical composition of the film, which provide a fairly low (<0.07) coefficient of friction during the entire period of the run-in stage, is considered. In order to explain the effect of the modifying films, analysis of the specific features of the friction-induced changes in the composition of the films during wear debris formation has been carried out using Raman spectroscopy.

Elevated temperature tribology of cobalt and tantalum-based alloys

This paper describes the friction and wear behavior of a Co–Cr alloy sliding on a Ta–W alloy. Measurements were performed in a pin-on-flat configuration with a hemispherically tipped Co-base alloy pin sliding on a Ta–W alloy flat from ambient to 430°C. Focused ion beam-scanning electron microscopy (FIB-SEM) and cross-sectional transmission electron microscopy (TEM) were used to identify the friction-induced changes to the chemistry and crystal structure in the subsurface regions of wear tracks. During sliding contact, transfer of material varied as a function of the test temperature, either from pin-to-flat, flat-to-pin, or both, resulting in either wear loss and/or volume gain. Friction coefficients (μ) and wear rates also varied as a function of test temperature. The lowest friction coefficient (μ=0.25) and wear rate (1×10−4mm3/Nm) were observed at 430°C in argon atmosphere. This was attributed to the formation of a Co-base metal oxide layer (glaze), predominantly (Co, Cr)O with Rocksalt crystal structure, on the pin surface. Part of this oxide film transferred to the wear track on Ta–W, providing a self-mated oxide-on-oxide contact. Once the oxide glaze is formed, it is able to provide friction reduction for the entire temperature range of this study, ambient to 430°C. The results of this study indicate that glazing the surfaces of Haynes alloys with continuous layers of cobalt chrome oxide prior to wear could protect the cladded surfaces from damage.

Synthesis of Au–MoS2 Nanocomposites: Thermal and Friction-Induced Changes to the Structure

The synthesis of Au-MoS2 nanocomposite thin films and the evolution of their structures during film growth, in situ transmission electron microscopy (TEM) heating, and sliding contact were investigated. TEM revealed that the films deposited at ambient (room) temperature (RT) consisted of 2-4 nm size Au particles in a matrix of MoS2. With increasing growth temperatures, the nanocomposite film exhibited structural changes: the Au nanoparticles coarsened by diffusion-driven Ostwald ripening to 5-10 nm size and the MoS2 basal planes encapsulated the Au nanoparticles thereby forming a solid Au-core MoS2 structure. However, when the RT deposited film was heated inside the TEM, the highly ordered MoS2 basal planes did not encapsulate the Au, suggesting that MoS2 surface diffusivity during film growth is different than MoS2 bulk diffusion. Increases in MoS2 crystallinity and coarsening of Au nanoparticles (up to 10 nm at 600 °C) were observed during in situ TEM heating of the RT deposited film. Sliding contact during friction and wear tests resulted in a pressure-induced reorientation of MoS2 basal planes parallel to the sliding direction. The subsurface coarsened Au nanoparticles also provide an underlying load support allowing shear of surface MoS2 basal planes.

Thermal Decomposition Mass-Spectra of Polymer–Fullerene C60 Systems

The various thermal decomposition scenarios of polymer–fullerene C60 systems, as revealed by thermal decomposition spectra registered with the aid of mass spectrometry, are discussed. The examples include polymer–fullerene mixtures and polymer–fullerene C60 covalently bound star-shaped compounds. The friction-induced changes of the thermal decomposition spectra of neat polymers are also discussed.

Friction transitions in nanocrystalline nickel

Nanocrystalline Ni films with 20–100 nm size grains exhibited either of two distinct friction behaviors, μ ∼ 0.30–0.35 or μ ∼ 0.6–0.7, depending upon the contact pressure and sliding speed. Friction-induced changes to grain structure were analyzed by cross-sectional transmission electron microscopy of wear surfaces. Formation of stable ultrafine nanocrystalline layers with 2–10 nm size grains underneath the wear surface may be responsible for the observed friction transitions, possibly due to a transition from traditional dislocation plasticity to deformation controlled by grain boundaries.

Effect of friction-induced hardening on the features of magnetic and eddy-current behavior of an annealed structural steel under cyclic loading conditions

The effect of friction processing on the mechanical properties in uniaxial tension, the magnetic properties, and the electromagnetic characteristics of an annealed Steel 3 (St3) grade structural steel has been studied. It is established that the coercive force, residual magnetic induction, initial magnetic permeability, and eddy-current characteristics can serve as parameters for monitoring the quality of steel hardened by friction processing. Features of friction-induced changes in the strength, magnetic properties, and electromagnetic characteristics of St3 grade steel loaded in the region of low-cycle fatigue are revealed. It is shown that magnetic and eddy-current techniques can be used for monitoring the state of a friction-hardened surface layer of steel samples in the course of their cyclic loading.

Tactile directional sensitivity and postural control

People are good at telling the direction of a moving tactile stimulus and this capacity provides a sensitive clinical test of somatosensory disturbances. Tactile directional sensitivity depends on two different kinds of somatosensory information, i.e. spatiotemporal information and information about friction-induced changes in skin stretch. The objective of this study was to compare the relative contribution to postural control of these two types of information for both glabrous and hairy skin. Postural sway amplitudes and sway paths were recorded, with or without access to tactile and/or visual stabilizing stimuli. Subjects were standing on two types of surface, either solid metal or 50 mm foam plastic. Two types of stimulus were used to generate sway-related tactile information. One was a thin air-stream that was used to assess the contribution by spatiotemporal information, and the second was a narrow steel rod that was glued to the skin to assess the contribution by skin-stretch information. The stimuli were applied to the hairy skin of the forearm and to the glabrous skin of the fingertip. In addition, we studied the ability to tell the direction of movement of an air-stream stimulus on glabrous and hairy skin. The air-stream caused significant sway reductions when applied to glabrous, but not hairy skin. The weak effect on hairy skin reflected the perceptually poor directional sensitivity for the air-stream stimulus in this cutaneous area. In contrast, the glued rod reduced sway when applied to both glabrous and hairy skin reflecting the tactile afferents' high sensitivity to skin stretch in these areas. Both types of tactile stimulus reduced sway amplitudes more than sway paths for both hairy and glabrous skin. The visual cue, on the other hand, tended to reduce sway paths more than amplitudes. The two types of tactile receptive surface seem to influence postural control in the same manner, despite anatomical and physiological differences. The results invite speculation that patients with poor directional sensitivity might have reduced postural stability compared with healthy individuals.

Tactile directional sensibility: peripheral neural mechanisms in man

Tactile directional sensibility, i.e. the ability to tell the direction of an object’s motion across the skin, is an easily observed sensory function that is highly sensitive to disturbances of the somatosensory system. Based on previous psychophysical experiments on healthy subjects it was concluded that directional sensibility depends on two kinds of information from cutaneous mechanoreceptors; spatio-temporal information and information about friction-induced changes in skin stretch. In the present study responses to similar probe movements as in the psychophysical experiments were recorded from human single mechanoreceptors in the forearm skin. All slowly adapting type 2 (SA2) units were spontaneously active, and with increasing force of friction their discharge rates were modified by probe movements at increasing distances from the Ruffini end-organ, reflecting the high stretch-sensitivity of these units. Slowly adapting type 1 (SA1) and field units responded to the moving probe within well-defined skin areas directly overlying the individual receptor terminals, and compared to the SA2 units their response properties were less dependent on the force of friction. The results suggest that SA1 and field units have the capacity to signal spatio-temporal information, whereas a population of SA2 units have the capacity to signal direction-specific information about changes in lateral skin stretch.