The influence of plasma sprayed multilayers of Cr2O3 and Ni10wt%Al on fatigue resistance

• Sequence of Ni10wt%Al and Cr2O3 layers influences the fatigue life.
• Cr2O3 layers increase the fatigue life and block the effect of outer layers.
• Ni10wt%Al layers decrease the fatigue life and transfer the effect of outer layers.
• Explanation by coating damage mode, strain hardening and residual stress is given.

The influence of layering sequence of plasma sprayed composite coatings on the fatigue life was studied. Plain, grit-blasted, and plasma sprayed specimens with one to three coating layers were examined. The layered coatings were composed of alternating sequence of ceramic (Cr2O3) and metallic (Ni10wt%Al) deposits. Deflection controlled resonance symmetrical bending fatigue tests of flat specimens were performed. The deformation amplitude was 1.3 millistrain in the crack initiation site and loading frequency was around 80 Hz. The significance of the effect of surface treatment on fatigue properties was examined statistically using Wilcoxon test. From the obtained data, the effect of individual layers was deduced. In order to explain the observed fatigue behavior, the fractographic analysis was performed and the coating–substrate composite was characterized. Strain hardening profile in the substrate was estimated by microhardness measurement and electron back scatter diffraction (EBSD) analysis. Residual stress depth distribution in the substrate was measured using neutron diffraction. The elemental and phase compositions were analyzed using energy dispersive microanalysis (EDX) and X-ray diffraction (XRD). The explanation of the fatigue behavior of tested specimens consistent with the obtained results was formulated.