Improvement of high-temperature oxidation resistance of γ-TiAl intermetallic alloy by YSZ-NiCoCrAlY coating using APS process

As an important class of high temperature structural materials, γ-TiAl intermetallic alloys have demonstrated unique mechanical characteristics which can be considered as essential payoffs for industrial gas turbines and other applications. In the present investigation, the γ-TiAl alloy with chemical composition of Ti-48Al-2Nb–2Cr (at%) is put to use as the substrate material. Two different coatings are then employed namely as a single-layer coating applied via Ni-based powder of AMDRY 365-2 [NiCoCrAlY] and a two-layered TBC coating consisted of a ceramic top coat of Yttria-stabilized zirconia (YSZ) and a metallic bond coat of NiCoCrAlY using atmospheric plasma spraying (APS) process at $2000{}^{\circ }C.$ A comprehensive microstructural analysis as well as the isothermal oxidation resistance is performed for the both coated intermetallic samples at $1000{}^{\circ }C.$ It is found that for the two-layered thermal barrier coating (TBC) coating, there are the dominant compounds which include ZrO₂ oxide with a little amount of Y₂O₃ oxide. It is indicated that the presence of these oxides has a substantial influence on the high temperature oxidation resistance of the formed TBC coating on the γ-TiAl alloy. Moreover, it is shown that the best high temperature oxidation resistance can be acquired via the two-layered TBC coating on the intermetallic substrate of γ-TiAl. (paper)