Thermal Stability of an EB-PVD thermal arrier coating system on a single Crystal Nickel-Base Superalloy

摘要

The thermal cyclic lifetime of a thermal barrier coating system consisting of an EB-PVD NiCoCrAlY bond coat and an EB-PVD PYSZ top layer deposited onto second generation single crystal alloy CMSX-4 was dound to be half of half of that deposited onto DS alloy In 100. Chemicla factors were considered to be the main cause for the premature failure ofthe TBC system on the SX substrate alloy. In the presetn paper prelimary results of ongoing research are discussed aiming at the assessment of the key factors introducing the failure. Test pins were annealed at 1100 degree in air nd vacuum up to 240h and carefully investigated by scanning electron microscopy and energy dispersive spectroscopy. Interdiffusion between the bond coat and the substrate alloy caused the formatio of an gamma/beta interfiffusio zone which front moved into the gamma/gamma' microstructure where gamma was formed at the expense of gamma'. After a 10h heat treatmetn refractory element-rich topological close packed phases formed beneath the diffusion front which number was increased with increasing exposure time. However, after 240h no TCP phases were detected, suggesting a precipitatio and re-dissolution sequence with inceasing exposure time associated with changing thermodynamic conditios atthe interface.