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Three different projection system are used to prepare NiCrAlY bond coats over metallic substrates:
atmospheric plasma spray (APS), high velocity oxyfuel (HVOF) and high frequency pulse detonation
(HFPD). These coatings were tested in hot corrosion experiments with sprayed Na2SO4 at 1000ºC for 20
and 100 hours experiments in air. Coatings surface composition after thermal treatment was
characterised by XRD and SEM. Cross section of coatings were analysed by SEM-EDX. A relationship
between microstructural characteristics of initial coatings and final performance in hot corrosion was
found in terms of porosity percentage: plasma sprayed coatings present higher percentage of porosity
compared to HVOF and HFPD projection systems for the same composition and Al is heavily consumed
in interparticle oxidation. This Al depletion in turn involves intrinsic chemical failure and surface layer
is comprised by a porous spinel of mixed oxides. On the other hand, high energy projection systems
produce dense coatings allowing the Al migration to external alumina layer, particularly in the case of
HVOF coating.
The authors want to express their gratitude to the Spanish Ministry of Education and Science for the
financial support of the work, project MAT2004-02921, and to the Diputación General de Aragón, for
the project PM0252004
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