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Thermally sprayed coatings have residual stresses due to the processing techniques where the particles go through thermal softening / melting, high velocity impact and rapid solidification. The nature and magnitude of the residual stresses in these coatings determine the coating/substrate bond strength and failure mechanisms. This investigation work presents a non-destructive neutron diffraction residual stress evaluation of suspension high-velocity oxy-fuel (S-HVOF) thermal sprayed YSZ coatings onto 304 stainless steel substrates and CoNiCrAlY bond coat. S-HVOF spray is a high deposition efficiency process to deposit coatings from sub-micron or nanometric feedstock particles. Neutron diffraction measurements were performed at the UK ISIS facility, using ENGIN-X pulsed neutron diffractometer to obtain through thickness residual stress profiles. The Z-scanning method was used to avoid pseudo-strains in the neutron diffraction measurements near the coating surface whereby the incident neutron beam/gauge volume was partially submerged and traversed vertically out of the horizontal coating surface. The elastic modulus of the coatings were also measured by depth sensing indentation on the coatings cross sections. The residual stress changed from tensile to compressive in the YSZ coatings on SS 304 while it remained entirely compressive in the YSZ on CoNiCrAlY bond coat.
Faculty of EngineeringThe University of Nottingham University Park Nottingham, NG7 2RD
email:AdvMaterials@nottingham.ac.uk