Experimental investigations of mechanisms governing residual stress evolution in segmented plasma sprayed coatings

Abstract

This article investigates the equivalent residual stress of the top coat (TC) and thermal grown oxide (TGO) during isothermal cyclic service and experimentally confirms the existence of stress reversal phenomenon in one-surface-coated segmented APS-TBCs for the first time. An in-situ beam curvature measurement equipment is employed to experimentally measure equivalent residual stress, while global curvature is estimated using photographic images. According to the experimental observations, this complex phenomenon is governed by competition between TGO-induced and interlayer-mismatch-induced compressive stresses and substrate oxide (SO)-induced tensile stresses. The discovery of this phenomenon in one-surface-coated APS-TBC samples suggests that traditional laws governing residual stress accumulation are not suitable for describing its evolution during isothermal cyclic service. Therefore, we recommend either using fully-coated samples for long-term isothermal cyclic services or employing one-surface-coated samples for gradient cyclic services (keeping the uncoated substrate surface below 700 °C to prevent SO growth).