MCrAIY coatings deposited on single crystal high temperature alloys by Laser Cladding

Abstract

Despite the improvements brought by the introduction of new alloys and the use of single crystalline materials for turbine blades and vanes, it is impossible to find alloy compositions that allow the required mechanical and corrosion properties to be simultaneously achieved. As a result, turbine blades must be coated with a material with outstanding oxidation and corrosion resistance, like MCrAlY-type alloys, in order to achieve the required component lifetime. The protective action of MCrAlY-type alloys depends on the progressive formation of a uniform and well-adherent oxide layer. The possibility of eliminating high diffusivity paths, such as grain boundaries, from coatings may constitute a major improvement in the oxidation resistance of these materials due to the reduction and uniformization of the growth rate and of the oxide scale. The deposition of single crystalline MCrAlY coatings on single crystalline turbine blade materials is demonstrated by the authors in the present paper. This paper reports on the structure and properties of single crystalline laser cladded coatings. Detailed microstructural characterization and X-ray diffraction experiments were performed in order to establish orientation relationships between the substrate material and the coating material. Experimental results show that the coating structure develops epitaxially from the substrate and inherits its crystal orientation. The single crystalline character is preserved even when several layers of MCrAIY are overlapped.Despite the improvements brought by the introduction of new alloys and the use of single crystalline materials for turbine blades and vanes, it is impossible to find alloy compositions that allow the required mechanical and corrosion properties to be simultaneously achieved. As a result, turbine blades must be coated with a material with outstanding oxidation and corrosion resistance, like MCrAlY-type alloys, in order to achieve the required component lifetime. The protective action of MCrAlY-type alloys depends on the progressive formation of a uniform and well-adherent oxide layer. The possibility of eliminating high diffusivity paths, such as grain boundaries, from coatings may constitute a major improvement in the oxidation resistance of these materials due to the reduction and uniformization of the growth rate and of the oxide scale. The deposition of single crystalline MCrAlY coatings on single crystalline turbine blade materials is demonstrated by the authors in the present paper. This paper report...