Thermal failure of thermal barrier coating with thermal sprayed bond coating on titanium alloy

Abstract

A thermal spray technology high-velocity oxygen fuel (HVOF) was used to deposit NiCoCrAlY as a bond coating between the titanium alloy substrate and top 8 wt% yttria-stabilized zirconia thermal-barrier coating (TBC) deposited by electron beam-physical vapor deposition (EB-PVD). The thermal cycling and isothermal exposure tests were conducted to evaluate the durability of the TBC. Investigations using OM, SEM, EPMA, and XRD revealed that the thermalsprayed BC makes the TBC more durable in isothermal exposure tests but more short-lived in thermal cycling tests, in comparison to our previous study in which the BC was prepared by EB-PVD. This is because the thermal-sprayed imperfections, such as microcracks and voids, elevate the diffusion resistance and degrade the mechanical properties of the BC, simultaneously. To current TBC systems in which the BC is deposited by HVOF, thermal failure behaviors-such as the formation of the Ti/Al mixture oxides at some individual places in the BC, and the Ti 2 Ni gaps formed around the BC/substrate interface-were also discussed.

Thermal shock resistance of yttrium aluminium oxide Y3Al5O12 thermal barrier coating for titanium alloy

“…However, the susceptibility of titanium alloys to oxidation at high temperatures results eventually in degradation of the alloys mechanical performance and limit their operating temperature to around 600 o C. Therefore, several methods have been used to increase the operating temperatures of titanium alloys and protect them from oxidation,these methods are based either on bulk modification using alloying elements or using surface modification methods as coating.The former method may negatively affect the mechanical properties of the alloys, whereas the later method can also be used without affecting the mechanical properties of Ti alloys, such coatings include glass coatings and thermal barrier coatings (TBCs) [7,8]. TBCs are utilized in high temperature parts of gas turbines in order to provide thermal protection of the substrates allowing the possibility of increasing their operating temperature and increasing their efficiency [9,10]. In addition, TBCs can be used to protect the substrate against hot corrosion [11] and attacks by Calcium Magnesium Alumino Silicate (CMAS) attacks [12].…”