Plasma-sprayed duplex and graded partially stabilized zirconia thermal barrier coatings: Deposition process and properties

Atmospheric plasma spraying of duplex and graded ZrO2 (8% Y2O3) thermal
barrier coatings (TBCs) on Inconel 617 substrate with a NiCrAIY bond
coat is described in terms of a deposition process of controlled
coating structure, Special attention is devoted to the dominant spray
parameters and the injector configuration for powder feeding, which
play a fundamental role in graded coating deposition with controlled
formation of a graded metal-ceramic (GMC) intermediate zone, The
results of the graded coating spraying allow: (a) suppression of
step-interface effects, (b) suppression of large differences (misfit)
between physical and mechanical constants of the coating and those of
the substrate material, and (c) favorable intergrowth of crystallites
for a microstructurally integrated structure, Sprayed TBCs were
investigated and compared with regard to their thermal cycling,
oxidation behavior, and mechanical properties.
The influence of crystal anisotropy changes on the resulting coating
structure and properties is shown, On the basis of finite element (FE)
calculations, the stress distribution within thermally cycled coating
... mehr
systems was analyzed, It is confirmed that the graded coating structure
relaxes considerably the stresses resulting from the internal
constraint due to thermal expansion difference between both metallic
and ceramic materials, This stress distribution also decreases the
gradient of elastic deformation and/or residual stresses between the
metal bond coat and top ceramic coating, and hence leads to a better
thermal cycling behavior of the graded TBC systems, However, this
advantage is not practical in every case, since the rapid oxidation of
the metallic lamellae causes the ceramic phase in the GMC zone to
undergo tensile stresses within a short thermal exposure time, The
lifetime of duplex TBC systems that are under steady-state thermal load
conditions is much higher than that of graded ones.