Characterization of chemical and microstructural evolutions of a NiPtAl bondcoat during high temperature oxidation
Abstract
Bondcoats used to protect turbine blades, such as platinum modified NiAl alloys, are designed to develop a protective alumina scale during exposure conditions at high temperatures. However, during high temperature oxidation, the system is subjected to chemical and microstructural changes that arise from the consumption of aluminium to ensure alumina growth and interdiffusion between the underlying nickel-based superalloy and the bondcoat. The aim of the present work is to report experimental results concerning the chemical and microstructural evolutions of a NiPtAl bondcoat, deposited on a single crystal nickel-based superalloy, during isothermal oxidation tests at 1100 °C, up to 50 h. Analytical STEM studies were carried out, in conjunction with Auger experiments, in order to follow the various changes that occur in the bondcoat and at the Al2O3/bondcoat interface. Efforts were concentrated on the effect of interfacial sulfur segregation (at both intact interface and void surface) as a function of the oxidation time, as well as its dependence on phase transformations in the external layer of the bondcoat. Strong S segregation at some bondcoat NiPtAl/Al2O3 interface, especially at γ′/Al2O3, was found in co-segregation with Cr, which has diffused from the substrate.