Abstract
The most commonly used structural materials for blades and other high temperature components of gas turbines are nickel superalloys such as Inconel 738, MAR M247M or Hastelloy. Thermal barrier coatings (TBCs) are widely used on these substrates as protection against high temperatures and oxidation. A TBC system consists of a top coat of yttria partially stabilized zirconia deposited by air plasma spray and an underlying bond coat (usually MCrAlY, where M is Ni, Co or a combination of both). MCrAlYs are normally deposited by thermal spray processes such as air plasma spray, vacuum plasma spray (VPS/LPPS) or high velocity oxygen fuel (HVOF). In general, the adhesion of the whole thermal barrier system is strongly dependent on the surface preparation of the substrate and it is generally believed that a certain degree of roughness promotes better adhesion. OEM’s (Original equipment manufacturer) procedure for preparation of substrates and analysis have been reviewed and considered as basis of this work. The scope of this work is to set up a new cleaning methodology in order to obtain a completely pollution free surface to be coated afterwards with HVOF or VPS/LPPS. The properties of this new methodology have been compared with standard surface preparation techniques such as blasting with corundum and silicon carbides. The obtained samples have been analysed by means of metallography and chemical composition of the interface in order to measure the interfacial pollution between substrate and coating. Finally adhesion of MCAlY coating have been tested and compared with specification of the main OEMs.
