Assessment of the surface state behaviour of Al71Cu10Fe9Cr10 and Al3Mg2 complex metallic alloys in sliding contacts

Electrochemical measurements and friction measurements during continuous and intermittent unidirectional sliding tests are used to monitor and to evaluate the surface characteristics of two types of metallic materials characterized by a huge unit cell, namely Al₇₁Cu₁₀Fe₉Cr₁₀ and Al₃Mg₂. The modification of the surface characteristics results from the periodic mechanical removal of a surface film during sliding, and the subsequent (electro)chemical re-growth of a surface film in-between successive sliding contacts. Al₇₁Cu₁₀Fe₉Cr₁₀ and Al₃Mg₂ materials were tested in a phosphate buffer solution pH 7 at 25 °C to compare their depassivation and subsequent repassivation behaviour. The Al₃Mg₂ material was also tested in a 0.1 M KOH solution pH 13 and 25 °C to reveal the role of constituting metallic elements on the surface film formation. The effect of film formation and removal on the coefficient of friction recorded during unidirectional sliding is discussed.     

Surface modification of TiN hard coatings with concentrated solar energy

Physical vapour deposited TiN coatings were partially oxidized by a beam induced heat treatment using concentrated solar radiation, in a search for the tailoring of the functionality of hard ceramic coatings. The TiN coatings were heated in ambient air up to 800°C at a mean heating rate of 1.2°C/s and held at this temperature for periods of 10, 60, and 350 s. The solar treated samples were characterized using techniques as Rutherford backscattering spectrometry, grazing incidence X-ray diffraction, and cross-sectional transmission electron microscopy. At the surface of the heat treated TiN coatings, single oxide layers consisting of the rutile polymorph of TiO₂ were identified. The oxide microstructure was found to be porous and non-uniform across the layer thickness, in particular near the interface between oxide and nitride. The growth of a dense recrystallized oxide layer at the outer surface was observed after a prolonged solar beam treatment of 350 s.     

The use of preoperative fistulography in patients with a second branchial cleft anomaly

The preoperative fistulography used in cases of second branchial cleft anomalies is an effective method of showing the exact anatomy and topography of these fistulas in the neck. This visualisation is very important because the only therapeutic solution is complete surgical resection. This method is easy to perform and is painless. We report two patients with branchiogenic anomalies. The diagnosis was established by fistulography and histological examination.     

Influence of humidity on the friction of diamond and diamond-like carbon materials

The friction of diamond and diamond-like carbon (DLC) materials was evaluated in reciprocating sliding wear testing under controlled relative humidity. The testing conditions were a displacement stroke of 100 μm, an oscillatory frequency of 8 Hz and a normal load of 2 N. The coefficient of friction of diamond and hydrogen-free DLC (a-C) coatings against a corundum sphere in the steady regime decreased with an increase in relative humidity. A water layer physisorbed at the interface between the mating surfaces played two major roles: acting as a lubricant and increasing the true area of contact. However, it was noticed that the friction coefficient of the hydrogenated DLC (a-C:H) coatings first increased and then decreased with increasing relative humidity in the steady state. There appeared to be a critical relative humidity for the a-C:H coatings, at which the steady-state friction reached the maximum value. The frictional behaviour of the a-C:H coatings also showed dependence on the wear test duration. The interaction between hydrogen and oxygen at the interface between the a-C:H coating and water layer was mainly responsible for such behaviour.     

Corrosion-wear behaviour of thermal sprayed nanostructured FeCu/WC-Co coatings

The corrosion and corrosion-wear behaviour of a thermal sprayed nanostructured FeCu/WC-Co coating were investigated in a Hank's solution and compared to stainless steel AISI 304 and nanostructured WC-Co coatings. Electrochemical noise and potentiodynamic polarization measurements were conducted along with an ex situ scanning electron microscopy to unfold the response of these materials under these corrosive and corrosion-wear test conditions. The multiphase structure of the FeCu/WC-Co coating induces a complex corrosion behaviour. Under corrosion-wear conditions, the nanostructured FeCu/WC-Co coating exhibits a depassivation/repassivation behaviour comparable to the behaviour of stainless steel AISI 304 and nanostructured WC-Co coatings.     

Low-Friction MoS x Coatings Resistant to Wear in Ambient Air of Low and High Relative Humidity

The investigation of the tribological performance of MoS₂-based coatings in air of high humidity is critical for the future use of such low-friction and high-wear-resistant coatings in ambient air. Sulfur-deficient MoS _x coatings with a basal plane (x = 1.3) and a random (x = 1.8) crystallographic orientation were produced by planar magnetron sputtering. The coefficient of friction and the wear loss of MoS_x coatings in comparison with TiN and amorphous TiB₂ coatings were investigated in bi-directional sliding fretting tests performed in ambient air of different relative humidity. The wear rate expressed as a volumetric loss per unit of dissipated energy was determined. From these results, the best friction and wear performance was achieved with basal-plane-oriented MoS _x coatings tested at a relative humidity in the range of 10-50%. A coefficent of friction of 0.06-0.08 and a wear rate of 4 × 10³ m³J^-1, at a normal load of 1 N and a fretting frequency of 10 Hz, were recorded for that type of MoS _x coatings.     

Reorientation of Randomly Oriented MoSx Coatings During Fretting Wear Tests

The reorientation of as-deposited randomly oriented sulphur-deficient MoS_x coatings during fretting wear tests has been investigated by X-ray diffraction (XRD), Scanning Electron Microscope and Transmission Electron Microscope. The driving force for the reorientation seems to be the plastic deformation induced by the tangential friction force during fretting tests. The evolution from an as-deposited randomly orientation into a basal one occurs above a threshold normal load and fretting frequency. This reorientation results in a lowering of the coefficient of friction as well as in a high resistance to humidity, but unfortunately a high wear rate is noticed. The effect of normal load and fretting frequency on that reorientation process in MoS_x coatings is discussed.     

The influence of humidity on the fretting behaviour of PVD TiN coatings

The influence of the relative humidity (RH) in ambient air on the friction and wear behaviour of PVD TiN coatings subjected to contact vibrations against corundum and bearing steel (100Cr6) counterbodies has been investigated. The fretting experiments were performed in the gross-slip regime on TiN coatings produced by three different PVD processes. The results indicate two basic friction characteristics. At low relative humidity (RH < 10%), the friction force is in the range of the normal force whereas it is less than one third of the normal force in atmospheres of high relative humidity (RH > 80%). A transition from high to low friction was observed during the course of experiments performed in atmospheres of medium relative humidity. The duration of the high friction phase in such transitions was found to depend on fretting parameters such as the normal force and the vibration frequency. This humidity dependence of the friction force was found for both counterbody materials. The size of the damaged surface area as well as the volumetric wear on the TiN coatings were found to be largest at low relative humidity. Fretting damage occurs over a smaller area but extends more into the depth at high relative humidity. The size of the fretted surface area induced on TiN is larger for Cr-steel than for corundum counterbodies.