Modyfikacja powierzchni stopu Ti-6Al-7Nb w procesie utleniania izotermicznego

Celem pracy było określenie zmian struktury stopu tytanu podczas izotermicznego utleniania. Badano stop Ti-6Al-7Nb w stanie wyjściowym i po utlenianiu w zakresie temperatury 500-800 °C, w czasie do 72 h. Opisano kinetykę utleniania stopu oraz skład fazowy i morfologię powierzchni tworzącej się zgorzeliny. W temperaturze utleniania 700 i 800 °C proces utleniania miał przebieg paraboliczny. Skład fazowy warstw tlenkowych był złożony i zmieniał się wraz z temperaturą utleniania, przy czym przeważająca fazą był rutyl. Ciągłą i równomierną warstwę zgorzeliny otrzymano w wyniku utleniania w temperaturze 700 i 800 °C.

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Titanium and its alloys are nowadays the most prospective engineering materials and biomedical materials. Despite its advantages,titanium alloys are characterized by low resistance to abrasive wear. One of the most effective methods of the surface engineering for improving the properties of the surface layer on titanium and its alloys is the isothermal oxidation.Changes in the structure and properties of the surface layer can influence in a wide range on processes occurring on the surface of titanium and its alloys. The aim of the study was defining the changes in the structure of titanium alloy during isothermal oxidation. The alloy Ti-6Al-7Nb (before and after oxidation in 500-800 °C for up to 72 hours) was examined.Then, the kinetics of oxidation, phase composition and morphology of the surface were described. At 700 and 800 °C the oxidation process had a parabolic course. The highest weight gain was observed at 800 °C. It was more than twice higher than that obtained at 700 °C in the same time interval. It has been proven that the intensity of the weight gain goes up with temperature and time of oxidation. The morphology of the obtained oxide layer structure was tested in a scanning electron microscope. The layer formed at 600 °C did not cover the whole surface of the sample. Along with the increase of annealing temperature the continuity of the oxide layer also increased. After oxidation at 800 °C the surface of the oxide layer was more developed. For identifying the phases occurring in the obtained oxide layers the phase composition was tested using X-ray diffractometer. The phase analysis revealed that after oxidation at 600 °C four phases were formed: TiO2 as anatase and rutile, NbO, and α-titanium. After oxidation at 700 °C there were detected two phases: TiO2 as rutile and α-titaniu while after oxidation at 800 °C revealed the presence of three phases: TiO2 as rutile, α-Al2O3 and α-Ti. The phase composition of oxide layers was complex and varied with the temperature of the oxidation, but the vast majority of it was dominated by the rutile. It turned out that the oxidation at 700 and 800 °C during 72 h was very effective treatment method because the layer — compact crystalline layer of TiO2 as rutile and a mixture of rutile and stable α-Al2O3 was obtained.