CoNiCrAlY microstructural changes induced during Cold Gas Dynamic Spraying

The present study is part of an ongoing research project that aims to develop high performance bond coats by means of Cold Gas Dynamic Spraying (CGDS) for the manufacturing of thermal barrier coatings (TBC). The objective of this work is to investigate the microstructure of a CGDS coating and compare it to that of the original feedstock powder in order to determine whether any microstructural changes have occurred during the deposition process. CoNiCrAlY coatings were deposited using the CGDS system developed at the University of Ottawa Cold Spray Laboratory. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction techniques were used to assess the phases and microstructure of the original feedstock powder and coatings produced. Contrarily to the generally accepted theory that the CGDS process does not lead to changes in the deposited material's microstructure and phase, results from the analysis performed in this study demonstrate the occurrence of important microstructural and phase changes. Evidence of grain refinement of the γ-phase matrix down to the nanometre scale as well as partial dissolution of β-phase precipitates was observed. It is believed that these changes are attributed to the severe plastic deformation encountered by the deposited particles.