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Superalloys are crucial in high-temperature applications, particularly in the gas turbine industries. With the development of high-temperature superalloy materials, efforts are still being made to improve the turbine entry temperature (TET), which will ultimately raise the efficiency of gas turbines. In this research, a second-generation single-crystal superalloy CMSX-4 based on nickel was prepared. The surface was coated by thermal barrier coating (TBC) with a bond coat of NiCoCrAlY with vacuum plasma spray (VPS) and a top coat with Yttria Stabilized Zirconia (YSZ) by Electron Beam Physical Vapor Deposition (EB-PVD) with a minimal current of 2.3 A with two sources compared to the conventional high-current that has been currently employed. These CMSX-4 specimens, both the as-cast and TBC coated, were used to test the effects of cyclic oxidation and hot corrosion at 1000 °C, simulating an aircraft engine. Also, a hot corrosion test using salt compositions (Wt%) of 60Na 2 SO 4 - 40NaCl was performed simulating an aviation engine environmental condition. A FE-SEM/EDS analysis was used to examine the surface and cross-section microstructures of oxidized, hot-corroded as-cast, and hot-corroded TBC-coated CMSX-4 and its corrosion products. Using the XRD technique, the phases that were found in the oxidized and hot-corroded samples were identified. The outcome demonstrated that the EB-PVD TBC-coating on CMSX-4 with beam switching technique and a lower electron beam current has adequate protection without any damage to the coatings at 1000 °C. • EBPVD processes with a beam-switching with continuous evaporation of two targets • Beam switching increased the coating window increasing productivity. • Successful coating with a 23 % lower electron beam current, was achieved. • Optimized scanning trajectory increased the aggressiveness of the electron beam. [ABSTRACT FROM AUTHOR]

The effects of different substrates (CMSX-4 and IN738LC) on cyclic oxidation behavior of two thermal barrier coatings (TBCs) were investigated in this study. Cyclic oxidation test was conducted at a peak temperature of 1080 °C with 30 min hold time. The TBC systems tested consisted of two nickel-base superalloy substrates (CMSX-4 and IN738LC), a platinum aluminide bond coat and two types of 8YSZ top coat (vertical cracks (VC) and columnar structure). Samples with CMSX-4 substrate showed greater cyclic oxidation lifetimes than that with IN738LC, and VC YSZ on CMSX-4 offered longer cyclic life than those with columnar structure. After the oxidation test, the samples were analyzed using a scanning electron microscope (SEM) and an X-Ray diffractometer. The failure location of all TBC systems examined was found to be in the vicinity of TGO, consistent with past research of similar coating systems. Alumina and spinels (CS) were detected on all spalled surfaces although the amount of each phase differs from sample to sample. Ta-rich oxide was found on spalled coating surfaces with CMSX-4 substrate while islands of YSZ on the exposed TGO surface of samples with IN738LC substrate. It is believed that alloy composition, TGO rumpling and stresses induced by TGO growth and coefficient of thermal expansion (CTE) mismatch between different layers all contributed to the reduced cycles to failure of TBC systems with IN738LC substrate. [ABSTRACT FROM AUTHOR]

Abstract: The reduction of wall thickness of turbine blades brings coating systems into focus with a high oxidation resistance and mechanical strength at high temperatures. Therefore a multi-layer coating with a nominal composition of 77Pt–12Al–6Cr–5Ni (at.%) was applied to single crystal Ni-based superalloy CMSX-4 substrates by electron beam physical vapor deposition. The multi-layer structures were homogenized at 800–1000°C under continuous argon/2%-hydrogen gas flow for various times. Microstructures were investigated using scanning electron microscopy and transmission electron microscopy. Phase compositions were determined using energy dispersive X-ray spectroscopy in scanning and transmission electron microscopy. The coatings transformed into two phase microstructure with a fcc γ-phase and a L12 ordered γ′-phase during annealing. [Copyright &y& Elsevier]

Abstract: A thermal barrier coating system consisting of the single crystalline Ni-based superalloy CMSX 4, a Pt aluminide bond coat and an EB-PVD processed ceramic top coat was thermally cycled in order to study the influence of three different treatments prior the deposition of the ceramic top coat. Besides the standard treatment, one type of treatment was annealing in vacuum, while the other was annealing in an O containing ArH atmosphere; in both cases for 4 h at 1080 °C. Compared to the standard treatment, annealing in vacuum almost doubled and annealing in ArH atmosphere almost tripled the cyclic life time of the ceramic coating. The improvement was related to the creation of a defined alumina scale before and during TBC deposition. [Copyright &y& Elsevier]

Two commercial Pt modified aluminide coatings (RT22 and MDC150L) on the same single crystal Ni-based superalloy (CMSX-4) were studied by: scanning electron microscopy; transmission electron microscopy; energy dispersive X-ray spectrometry; and gravimetry. The RT22 coating is an inward grown coating (high activity), while MDC150L is produced by outward growth (low activity). Samples were oxidised in still laboratory air at 1050 °C for various times up to 2000 h. It was found that the outward grown coating produced a slower growing oxide that was more spallation resistant. Several possible reasons for this were identified including: coating purity; coating surface topography; and ductile to brittle transition temperature. The microstructural differences between the two coatings in the as-coated condition were investigated and the development of their microstructure during heat treatment was described. A model for coating growth during heat treatment was proposed. [Copyright &y& Elsevier]