Creep Behavior of Uncoated, Bond-Coated, and Thermal Barrier coated Ti-6Al-4V

Abstract

The Ti-6Al-4V alloy is widely used in aerospace components due to its high strength-to-weight ratio and favorable combination of properties, including low density, mechanical strength, corrosion resistance, and creep resistance. However the alloy loses strength and stability above 500°C due to oxidation. To enhance performance and increase its lifespan or working temperature, thermal barrier coat (TBC) is applied. The TBC consists of a substrate, metallic bond coat (BC), thermally grown oxide layer (TGO), and ceramic top coat (TC). The objective of this work was to study the creep behaviour of Ti-6Al-4V alloy without and with BC (NiCoCrAlY) and TBC (NiCoCrAlY + ZrO2-YO1,5) coatings applied by plasma spraying. Creep tests were performed under constant load conditions at a stress of 125 MPa and temperatures of 500, 600, and 700 °C. The creep parameters were determined, and material characterization by optical microscopy. The results showed that the Ti-6Al-4V alloy with BC and TBC exhibited average increases in creep resistance of 77% and 131%, respectively, compared to the uncoated alloy. These coatings resulted in a reduction in the secondary creep rate and an enhancement in creep lifetime. Microstructural analysis revealed that the delamination of the layers increased with the operating temperature.