Thermal cycling behavior of nanostructured and conventional yttria-stabilized zirconia thermal barrier coatings via air plasma spray

Abstract

Two thermal barrier coating (TBC) systems comprising NiCoCrAlY bond coat onto a second-generation Ni-based single crystal superalloy and nanostructured 4 mol% Y2O3-stabilized ZrO2 (4YSZ) and conventional yttria-stabilized zirconia (YSZ) top coats upwardly were deposited by approaches of arc ion plating (AIP) and air plasma spray (APS). As indicted by the experimental results, the 4YSZ TBCs exhibited superior thermal cycling resistance compared with conventional YSZ TBCs at 1100 °C. The 4YSZ top coat exhibited higher toughness due to its intrinsic property of nanocrystalline structure, homogeneously distributed and diverse directions of pores and preexisted cracks. The cracks and spallation in 4YSZ TBCs occurred at the interface of top coat and thermally grown oxide (TGO) layer. Instead, the crack initiation and propagation started along the lamellar interface in the top coat of conventional YSZ TBCs, leading to the rapid crack bridging and subsequent spalling of top coat. Additionally, before and after oxidation, the 4YSZ top coat showed higher hardness compared to conventional YSZ top coat. Degradation mechanism and distribution of residual stress in TGO for the 4YSZ TBCs were investigated in the current study.