Sandra Brajčinović

Titanium alloys are among the most important biomaterials due to their good biocompatibility, high corrosion resistance and favourable mechanical properties. Particular interest is directed towards β-Ti alloys, whose properties can be tailored by adding β-stabilisers such as molybdenum and chromium, with the aim of developing materials suitable for biomedical applications. This paper investigates the influence of chemical composition on the phase composition, microstructure, microhardness and corrosion properties of experimental Ti-Mo-Cr alloys produced by casting. Phase composition was determined by X-ray diffraction analysis (XRD), while microstructural characteristics were analysed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results showed that increasing the molybdenum and chromium content contributes to the stabilisation of the β-phase and reduces the proportion of α and α″ martensite. Complete stabilisation of the β-phase was achieved in the Ti-10Mo-30Cr alloy, while the Ti-10Mo-10Cr alloy showed a dominant presence of α″ martensite. EDS analysis confirmed the segregation of alloying elements during solidification. Microhardness measurements showed an increase in hardness with increasing total alloying element content, with the highest hardness measured in the Ti-20Mo-20Cr alloy. Corrosion properties were tested using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and Tafel polarisation methods in 0.9% NaCl (sodium chloride) medium. Among the alloys investigated, Ti-20Mo-20Cr showed a favourable overall balance of electrochemical properties, while Ti-10Mo-30Cr exhibited the lowest corrosion rate. The results suggest that a balanced ratio of molybdenum and chromium plays a key role in optimising the microstructure, mechanical properties, and corrosion performance of Ti-Mo-Cr alloys.

This paper presents the results of a study of the influence of water and the commercial inhibitor VCI 379/611 on the corrosion behaviour of HTCS-130 hot work tool steel. Using the thermodynamic program Thermo-Calc, phase equilibria were determined according to the choice of calculation conditions and the known chemical composition of tool steels. From the obtained projections, it is possible to observe the secretion of individual phases at certain temperatures. To obtain insight into the corrosion resistance of steel, the following electrochemical methods were used: open circuit potential measurement; electrochemical impedance spectroscopy; and Tafel extrapolation. Metallographic tests were performed on a sample previously etched in nital to identify the microstructure of the steel. Using an optical microscope, the sample surface was analysed after each measurement. Images of the sample surface subjected to water without inhibitors indicate the occurrence of pitting corrosion. The presence of tungsten and molybdenum carbides was identified by scanning electron microscopy and energy dispersion spectroscopy. It was found that the corrosion process is more pronounced in the area of the metal base while in the areas of excreted carbides, weaker corrosion activity was observed.