Papers by Keyword: Bond Coatings

Abstract: Low pressure plasma spraying (LPPS) is one of the most advanced processes of an MCrAlY bond coat formation. It ensures the forming of metallic coatings free of oxides which can act as an bond coat for thermal barrier coatings used, among others, for protection of turbine blade surface. The paper presents results of tests into microstructure of coatings made from AMDRY 997 powder on the base of type Inconel 617 heat-resistant nickel alloy. The tests were carried out using light and scanning electron microscopy. Evaluated was the influence of spraying conditions on microstructure, porosity and thickness of the obtained coating. Test results show that the LPPS method allows to form coatings of low porosity and free of oxides which can be used as an bond coat in thermal barrier coatings.

Abstract: A diffusion barrier based on a NiW electrolytic coating has been developed to limit interdiffusion between a Ni-base superalloy (MCNG) and a β-NiAl bondcoating. Isothermal oxidation tests of 50h at 1100°C confirmed that W-rich layer formed with NiW coating modifies the oxidation behaviour of the bondcoat and limits interdiffusion. The diffusion barrier reduced β-NiAl  γ’-Ni3Al transformation in the bondcoating and prevented SRZ formation.

Abstract: Bond coatings, CoNiCrAlY, are prepared on Inconel 738 substrate by vacuum plasma spray (VPS). Mechanical properties of VPSed CoNiCrAlY coatings are investigated via Taguchi method and L18(21×37)
orthogonal arrays to determine the optimal setting and the relationship of experimental variables. Seven parameters were considered as follows: (A) arc current; (B) primary gas flow rate; (C) secondary gas flow rate; (D) stand-off distance; (E) working pressure; (F) carrier gas flow rate (Ar); and (G) powder feeding rate.
The effect of carrier gas flow rate on the porosity is determined to be the highest among the parameters investigated. Higher microhardness values are observed for the VPSed coatings as compared to the coatings prepared by conventional high velocity oxygen fuel probably due to low amount of the porosity.

Abstract: Platinum/Palladium modified aluminide coatings prepared by aluminide pack cementation on the nickel base superalloy Inconnel 738. The platinum/palladium modified aluminide coating of cyclic oxidation behavior at 1200°C was investigated by TGA, XRD and SEM/EDS. Platinum/Palladium modified aluminide coatings showed better cyclic oxidation resistance than Platinum modified aluminide coating and palladium modified aluminide coating compared. Pt and Pd alloy played an enough role in alumina stabilization and in delaying the degradation of β-phase.

Abstract: It is well known, that thermally grown oxide (TGO) forms at the interface between the thermal barrier top coating (TBC) and the bond coating during service. In previous work, SEM images showed that the TGO layer contained at least two layers with different oxides. One layer was Al2O3, and the other was a mixed oxide of NiO, CoO, Cr2O3, and their spinels. It was supposed that a reason for macro-crack formation near an interface is due to a decrease in bond strength or to the formation of stress concentration sites caused by the formation of pores in the mixed oxide. In order to improve the bond strength, a modified bond coating material was developed, which is MCrAlY with Ce and Si added. Four- point bending tests were carried out to measure the bond strength of conventional TBC and of the modified TBC with MCrAlYCeSi bond coating. As a result, the TBC with modified bond coating had a bond strength superior to the conventional one. It is likely that the reason for the superior bond strength is due to a notable difference in oxidation behavior.