In metal-forming processes friction leads to the generation of heat, adhesion and the pick-up of work material, tool wear, inhomogeneous deformations, defects and a poor surface quality. Graphite is a well-known, solid lubricant that is successfully used in the cold and hot forming of aluminium. However, it leaves dark stains on the surface of the formed part. One of the possible substitutes for graphite is hexagonal boron nitride (h-BN), also known as white graphite. In this work the possibility of replacing graphite with h-BN in Al-forming lubricants was investigated, including the influence of h-BN powder size and concentration on its tribological performance and the aluminium's surface quality. The results of the investigation show that h-BN, as a solid lubricant, is capable of successfully replacing graphite in Al-forming processes, while at the same time maintaining a clean surface without staining. The study has shown that the tribological performance, including the friction and wear, the lubrication-film stability and the surface quality, very much depend on the powder size and the concentration. Under the investigated contact conditions, the best performance was obtained for 30-micro m h-BN powder when added to the grease in a concentration between 10 and 20 %.
COBISS.SI-ID: 1076394
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 corrosivemedium. 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
NiTi-alloy archwires are used in dental medicine for tooth positioning. Failures are reported during the mounting and operation. It is supposed that these difficulties are results of a simultaneous presence of corrosion and mechanical wear. First, a corrosive medium was examined in order to simulate the conditions in the mouth. Different simulated body fluids were compared with natural saliva using electrochemical methods. The corrosion properties ofthe NiTi dental wire in the as-received state and without the surface oxide film were studied with electrochemical impedance spectroscopy. Tribo-corrosiontests of NiTi in artificial saliva were performed and a relation between the chemical and mechanical wear was studied. After the experiment, the surface was spectroscopically examined. The relation between the chemical and mechanical wear was determined.
COBISS.SI-ID: 2061671