Studies on the transient stage of oxidation of VPS and HVOF sprayed MCrAlY coatings

• Published in: Surface & coatings technology 1999-11, Vol.120, p.8-15
• Main Authors: Toma, Diana, Brandl, Waltraut, Köster, Uwe
• Format: Article
• Language: English
• Subjects: High-temperature oxidation; HVOF-sprayed coating; MCrAlY; α-Al 2O 3
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/S0257-8972(99)00332-1

Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion. They consist of a MCrAlY bond coating and a ceramic top layer. The oxidation resistance of MCrAlY coating is based on the formation of α-Al 2O 3 in the steady-state stage of oxidation. The α-Al 2O 3 grows very slowly between the metallic bond coating and the ceramic top coating and is thermodynamically stable. High-temperature oxidation experiments with vacuum-plasma-sprayed (VPS) and high-velocity-oxygen-fuel (HVOF)-sprayed MCrAlY coatings showed that the transient stage of oxidation for HVOF coatings is very short. Moreover, in contrast to the VPS coatings, where also Cr 2O 3, NiO or CoO are identified, on HVOF coatings, only metastable modifications of alumina were observed. The transformation of metastable alumina modifications to α-Al 2O 3 is very fast. Oxidation experiments in a high-temperature chamber attached to a X-ray diffractometer were carried out. The morphology and the structure of the formed oxide scale were characterized by X-ray diffraction and scanning electron microscopy (SEM).