Structure of NiCrAlY Coatings Deposited on Oriented Single Crystal Superalloy Substrates by Laser Cladding

Rui Vilar,Edson Costa Santos

doi:10.4028/www.scientific.net/amr.278.503

Abstract

In the present work single and multiple layer NiCrAlY coatings were produced by laser cladding on (100) single-crystalline substrates of SRR99 Ni-based superalloy. Detailed structural characterisation and texture analysis by optical microscopy, scanning electron microscopy, X-ray diffraction and Rutherford backscattering showed that the NiCrAlY coatings consisted essentially of gamma phase with yttrium oxide (Y2O3) and a small proportion of yttrium–aluminium garnet (Al5Y3O12) precipitated in the interdendritic regions. The coatings presented a columnar dendritic structure grown by epitaxial solidification on the substrate and inherited the single-crystalline nature and the orientation of the substrate. The coating material also showed a mosaicity and a defect density similar to those of the substrate. It can be expected that the protective effect of these coatings against oxidation is greatly enhanced compared with polycrystalline coatings because high diffusivity paths, such as grain boundaries, are eliminated in single-crystalline coatings, thus reducing mass transport through the coating.

Highlights

The use of single-crystalline Ni-based superalloys represented a major advance in improving the high-temperature mechanical behaviour and increasing the service life of blades and other components in the hot section of gas turbine engines [1]
These coatings can be applied by a wide range of techniques, such as vacuum plasma spraying [7], high-velocity oxygen-fuel (HVOF), thermal spraying [8], and laser cladding [9]
The coatings produced by laser cladding are typically free of pores and cracks [10] and their oxidation resistance is usually better than the oxidation resistance of similar coatings produced by alternative methods, due to the finer dispersion of the rare-earth-rich phases [11]

Summary

Introduction

The use of single-crystalline Ni-based superalloys represented a major advance in improving the high-temperature mechanical behaviour and increasing the service life of blades and other components in the hot section of gas turbine engines [1]. Gaümann et al [12,13] showed that clad layers of CMSX-4 Ni-based superalloy deposited by laser cladding on a (100) single crystalline substrate of the same material are single crystalline , with a crystallographic orientation similar to that of the substrate. Since a (100) substrate was used, the microstructure of the material consists of parallel dendrites with the same crystallographic orientation as the substrate, forming an imperfect single crystal.

Results

Conclusion