Isothermal oxidation behavior of electrospark deposited NiCrAlY coatings on a Ni-based single-crystal superalloy

Abstract

The isothermal oxidation behavior of a NiCrAlY coating prepared by means of electrospark deposition (ESD) technology on second-generation Ni-based single-crystal DD6 was investigated at 1100°C for 100 h. Surface morphologies, chemical composition, and the phase constitution of the coating were analyzed by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and X-ray diffraction (XRD). The results showed that the as-deposited NiCrAlY coating, with uniform superfine columnar crystals and nanocrystallines, consists of b-NiAl and g-Ni double phases; the oxidation resistance of the DD6 alloy was greatly improved by depositing the NiCrAlY coating, which was covered by two layers of oxides, q-Al2O3 and a-Al2O3, while three layers of oxides, including Ni(Co)O, NiCr2O4, CrTaO4, CoTa2O6 and a-Al2O3, formed on the DD6 superalloy; the interdiffusion zone (IDZ) and secondary reaction zone (SRZ) formed between the NiCrAlY coating and the DD6 superalloy substrate for the interdiffusion; however, no deleterious Kirkendall voids appeared, which may be mainly due to the gradient transition of the elements between the coating and the substrate.

High-temperature oxidation resistance of NiCrAlY columnar microcrystalline coating deposited by EDS

“…1(b) that the coating part is ultra-fine columnar grains. The unique deposition method of ESD makes the cooling rate during deposition reach 10 -5 -10 -6 ℃/s [11]. At the extremely fast cooling rate, the nucleated grains in the coating have no time to grow to form an ultra-fine columnar microcrystalline coating.…”

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“…Thus the sinered Ni-WS 2 composite contains a mass of α-W and Ni 3 S 2 phase. In ESD process, heat is generated in 1 % of one pulse cycle, and then transferred in the rest of 99 % of one pulse cycle due to a short pulse duration and a high frequency, so the cooling speed may reach in the range of 10 5 -10 6 K/s [2,[13][14], and such fast solidification can be utilized to prepared coatings containing nano-sized grains. Combining with the EDS results of point B (Fig.…”

“…Electrospark deposition (ESD) is a surface technique to prepare metallurgical bonded coatings with outstanding properties on metallic substrate materials, and it eliminates distortion or metallurgical changes in substrate due to low heat input. Besides, it is also a simple, cost-effective, easily automated and environment-friendly technique applied in many industrial fields [13][14]. Recently C. Guo, et al [2] studied the performance of friction and wear of the Ni-MoS 2 self-lubricating coatings prepared by ESD, showing that the coating exhibits excellent tribological properties due to the synergistic effect of MoS 2 and MoO 2 in the coating, which indicates that ESD technique has a promising prospect for preparing self-lubricating coatings with transition metal dichalcogenides.…”