The corrosion behaviour of sputter-deposited, Al–W coatings with three different concentrations of tungsten (0.6, 3.5 and 11 at.% W) on AA7075 aluminium alloy substrates was investigated in chloride media. The presence of W reduces the thickness of the oxide layer formed after the EIS test, as proved by the compositional depth profile. From the EIS data of the investigated Al–W coatings, the polarisation resistance (Rp) and the capacitive behaviour as a function of the immersion time were obtained. A small increase in Rp suggested improved corrosion properties over time. However, the extent of the improvement depends on the content of W and the coating-surface morphology (the presence of growth defects on the coating surface). The salt-fog tests to some extent supported the results from the EIS measurements. However, there was a difference between the corrosion EIS and salt-fog test results in the case of the Al89W11 coatings. The thickest oxide layer and the »layering« into the three regions (porous, semi-porous and intact) were observed when the salt-fog corrosion test was performed on the Al89W11 coating. Galvanic corrosion, probably due to the local compositional and structural inhomogeneities, takes place. However, this was not unambiguously observed during the EIS corrosion test.
COBISS.SI-ID: 26541351
Al–WX alloys with the W content ranging from 0.6 to 11 at-% were sputter deposited at a low temperature on AA7075 alloy substrates. The sputtered Al–W alloys exhibit a remarkably broad range of microstructures and were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). For the alloys with a W content from 0.6 to 3.5 at-%, increasing tungsten additions lead to a decrease in the grain size from a few hundred nm to 10 nm. At 11 at-%W, a lamella-like microstructure forms, accompanied by an amorphous phase. Nanoindentation tests revealed that the increasing tungsten additions lead to an increase in the hardness. A polarisation corrosion test in a near neutral 0.1M NaCl solution revealed that increasing the tungsten additions leads to an increasing passive range and, therefore, the pitting potential.
COBISS.SI-ID: 26744615
In biomedical applications, NiTi alloys are used mainly because of their favourable shape memory and superelastic properties. However, in many applications the tribocorrosion properties of these alloys can be of critical concern. For this reason the electrochemical and tribocorrosion properties of superelastic NiTi sheet and orthodontic archwire were studied, taking into account their microstructures and the effect of different surface finishes. Inthe case of the electrochemical tests, samples were tested in artificial saliva, whereas in the tribocorrosion tests the experiments were performed in ambient air, distilled water, and artificial saliva, the latter as a corrosive medium. In these tests, the total wear rate of the alloy samples was determined, together with the corresponding chemical and tribological contributions. It was confirmed that the microstructure of the investigated alloys had a significant effect on the measured electrochemical and tribocorrosion properties.
COBISS.SI-ID: 1982311