Microstructural evolution of mechanically alloyed Ni-based alloys under high temperature oxidation

Microstructural characterization and evolution under high temperature oxidation of CoCrAlYTa-10%Al2O3 coating deposited by high-velocity oxygen fuel thermal spraying

“…Diffraction peaks corresponding to Co, Cr, TaC and Al 2 O 3 are the major peaks clearly seen both in the powders and the assprayed coating patterns. It is noteworthy that the crystal structure of Co in this coating is FCC, and it is consistent with previous reported results [2,13]. The crystalline structure of high-temperature FCC-Co phase is more likely to exist in the MCrAlX coatings than room-temperature HCP-Co phase after HVOF spraying process, which can be attributed to the rapid cooling rates of molten droplets [15].…”

“…Therefore, the crystal structure of Co in the coating depends on their manufacturing processes. Prieto-García E also reported the milling process induced HCP to FCC phase transformation by the reduction on the crystal size which stores a great amount of surface energy as well as the Gibbs free energy [2].…”

“…The crystalline structure of high-temperature FCC-Co phase is more likely to exist in the MCrAlX coatings than room-temperature HCP-Co phase after HVOF spraying process, which can be attributed to the rapid cooling rates of molten droplets [15]. A slight shift to smaller 2θ values is observed in the Co peaks, which is attributed to a doping with alloying elements, causing a growing of the lattice parameters [2]. It can be observed that C phase is existed in the feedstock powders and a new Cr 7 C 3 phase appears in the assprayed coating.…”

“…MCrAlX coatings (where M is Ni and/or Co and/or Fe and X is one or more reactive elements added in minor proportion, which may be Y, Hf, Ta, etc) are known for their superior resistance to high temperature oxidation [1,2]. Generally, these MCrAlX coatings contain high chromium (15-30 wt%) for higher hot corrosion resistance, while the aluminum concentrations are less than 12 wt% to ensure the ductility of the coatings [3].…”

“…Generally, these MCrAlX coatings contain high chromium (15-30 wt%) for higher hot corrosion resistance, while the aluminum concentrations are less than 12 wt% to ensure the ductility of the coatings [3]. When exposed at high temperature, the surface of the MCrAlX coating could form a uniform and dense alumina (α-Al 2 O 3 ) scale, which is desirable to protect the underlying metal from further oxidation [1,2]. Therefore, MCrAlX coatings are widely used in thermal barrier coatings (TBCs), especially applied on the hottest sections of gas turbine engines, allowing the thermal insulation for the turbine engines with additional protection from corrosion and high temperature oxidation.…”