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Role of alloying elements during thermocyclic oxidation of β/γ-TiAl alloys at high temperatures
(2016)
Gamma titanium aluminides are promising alloys known for their good mechanical properties and low densities, but their low oxidation resistance at high temperatures limits their
application. This work discusses the thermocyclic oxidation behavior of newly developed β/γ-TiAl alloys at temperatures between 600 °C and 900 °C. An influence of β-stabilizing alloying elements like Nb and V on the oxidation of these alloys has been investigated here.
The selected alloys are tested in an in-house developed thermocyclic furnace. The oxidation
study is supported by gravimetric measurements along with Scanning Electron Microscopy (SEM) and Electron Diffraction Spectroscopy (EDS) mapping of the oxide layers. Additionally, phase formation after oxidation has been determined using X-Ray Diffraction (XRD). Results show that the Nb containing alloys are more oxidation resistant as compared
to V containing alloys. The formation of a mixture of Al2O3 and TiO2 layers was found for all the alloys. The oxide kinetics controlled oxide growth and formation of
various phases at different testing temperatures.
This research work provides information about the influence of Ti2AlC MAX phase coatings on the
erosion resistance of Ti624 2alloy.Flat specimens were coated witha20 µm Ti2AlC film using an industrial siz emagnetron sputtering coater and annealed at 800 °C for 1h in vacuum for the formation of the MAX phase.The erosion resistance of the specimens was tested using high velocity particles at room
temperature.The results indicate that the erosion resistance of Ti6242 has been significantly enhanced
by the employment of MAX-phase coatings. This demonstrates the capability of using MAX phase
coatings as erosion protective medium for engine components exposed to similar damage conditions.
Additionally,the results show that uncoated Ti6242 samples with duplex microstructure have a better
durability against erosion attack compared to uncoated samples with globular microstructure.
Ti-90Al (in at.%) coatings were deposited on Ti-45Al-8Nb alloy at two different temperatures, 300 and 540 °C. The coatingsputtered at 300 °C consisted of Al and TiAl3 with columnar grain structure. The morphology, chemical composition and microstructureof the coating sputtered at540 °Cwere strongly dependent on the substrate microstructure. The two coating variantsformed oxidation-resistant Al2O3 scales during oxidation. The special morphological features of the coatings make them interestingfor geometrically structuring the surfaces to provoke the lotus effect.