Microstructure and mechanical performance of nanostructured YSZ/NiCoCrAlY thermal barrier coatings via spark plasma sintering: Taguchi L9 optimization

In this investigation, nanostructured thermal barrier coatings (TBCs) comprising a yttria-stabilized zirconia (YSZ) ceramic topcoat and a NiCoCrAlY metallic bond coating were deposited on IN-713LC superalloy substrates via spark plasma sintering (SPS). A Taguchi L9 orthogonal array was utilized to systematically evaluate the influence of key SPS parameters—sintering temperature (900–1060 °C), uniaxial pressure (31.1–44.1 MPa), and dwell time (6–8 min)—on critical coating properties, including tensile adhesion strength, Vickers microhardness, and porosity. The optimal processing conditions (1060 °C, 31.1 MPa, 6 min) yielded coatings with a tensile adhesion strength of 90 MPa (ASTM C633, n = 3), microhardness of 800 HV0.3, and porosity of 2.0–2.5 % (quantified via image analysis, ASTM E2109). X-ray diffraction (XRD) confirmed a phase-pure tetragonal YSZ structure without secondary phases, whereas scanning electron microscopy (SEM) of cross-sections revealed a dense microstructure with excellent interfacial bonding and minimal defects. Statistical analysis, including signal-to-noise ratio (S/N, larger-is-better for adhesion and hardness; smaller-is-better for porosity) and analysis of variance (ANOVA), identified the sintering temperature as the primary factor affecting coating performance, followed by pressure, with dwell time exerting a lesser influence. A confirmation test at the predicted optimal conditions validated the statistical model within a 95 % confidence interval. These results underscore the efficacy of optimized SPS processing in fabricating high-performance TBCs with low porosity, superior adhesion, and enhanced mechanical properties, offering significant advantages over conventional coating techniques for high-temperature applications in gas turbine engines.