This paper investigates the residual stresses and interfacial shear strength of a TiAlN coating on Zr–Nb–Sn–Fe alloy (ZIRLO™) substrate designed to improve corrosion resistance of fuel cladding used in water-cooled nuclear reactors, both during normal and exceptional conditions, e.g. a loss of coolant event (LOCA). The distribution and maximum value of the interfacial shear strength has been estimated using a modified shear-lag model. The parameters critical to this analysis were determined experimentally. From these input parameters the interfacial shear strength between the TiAlN coating and ZIRLO™ substrate was inferred to be around 120 MPa. It is worth noting that the apparent strength of the coating is high (∼3.4 GPa). However, this is predominantly due to the large compressive residuals stress (3 GPa in compression), which must be overcome for the coating to fail in tension, which happens at a load just 150 MPa in excess of this.

•The corrosion resistance of ceramic coatings on ZIRLO™ coupons was tested.•Coating parameters (roughness, thickness) were optimized for best performance.•Best corrosion performance (no spallation or delamination) was for E14.•Boehmite phase formation was observed in TiAlN, but not in TiN.In an attempt to develop a nuclear fuel cladding that is more tolerant to loss-of-coolant-accidents (LOCA), ceramic coatings were deposited onto a ZIRLO™1 substrate by cathodic arc physical vapor deposition (CA-PVD). The coatings consisted of either Ti1 – xAlxN or TiN ceramic monolithic layers with a titanium bond coating layer as the interlayer between the ceramic coating and the ZIRLO™ substrate to improve coating adhesion. Several coating deposition trials were performed investigating the effects of bond coating thickness (200–800 nm), ceramic coating thickness (4, 8 and 12 μm), substrate surface roughness prior to deposition, and select coating deposition processing parameters, such as nitrogen partial pressure and substrate bias, in order to optimize the coating durability in a corrosion environment. Corrosion tests were performed in static pure water at 360 °C and saturation pressure (18.7 MPa) for 3 days. The optimized nitride-based ceramic coatings survived the autoclave test exposure showing very low weight gain of 1–5 mg/dm2 compared to the uncoated ZIRLO™ samples which showed an average weight gain of 14.4 mg/dm2. Post-corrosion exposure analytical characterization showed that aluminum depletion occurred in the TiAlN coated samples during the autoclave corrosion test, which led to the formation of the boehmite phase that degraded the corrosion durability of some of the TiAlN samples. However, by eliminating the aluminum content and depositing TiN, the boehmite phase was prevented from forming. Best results in TiAlN coated samples were obtained with 600 nm Ti bond coating thickness, 12 µm coating thickness and 0.25 µm substrate surface roughness (E14). Results are discussed in terms of the capability of TiN and Ti1 – xAlxN coatings to improve the high temperature corrosion resistance and oxidation resistance of zirconium alloy cladding.

•Monolithic and composite TBCs were fabricated using APS.•Coatings were composed of YSZ, t′ Low-k and cubic Low-k.•Cubic Low-k erosion rate can be reduced via t′ Low-k additions.•t′ Low-k additions have large (nonlinear) beneficial effects on cubic Low-k erosion.To enhance efficiency of gas turbines, new thermal barrier coatings (TBCs) must be designed which improve upon the thermal stability limit of 7 wt.% yttria stabilized zirconia (7YSZ), ~ 1200 °C. This tenant has led to the development of new TBC materials and microstructures capable of improved high temperature performance. This study focused on increasing the erosion durability of cubic zirconia based TBCs, traditionally less durable than the metastable t′ zirconia based TBCs. Composite TBC microstructures composed of a low thermal conductivity/high temperature stable cubic Low-k matrix phase and a durable t′ Low-k secondary phase were deposited via APS. Monolithic coatings composed of cubic Low-k and t′ Low-k were also deposited, in addition to a 7YSZ benchmark. The thermal conductivity and erosion durability were then measured and it was found that both of the Low-k materials have significantly reduced thermal conductivities, with monolithic t′ Low-k and cubic Low-k improving upon 7YSZ by ~ 13% and ~ 25%, respectively. The 40 wt.% t′ Low-k composite (40 wt.% t′ Low-k — 60 wt.% cubic Low-k) showed a ~ 22% reduction in thermal conductivity over 7YSZ, indicating even at high levels, the t′ Low-k secondary phase had a minimal impact on thermal conductivity in the composite coating. It was observed that a mere 20 wt.% t′ Low-k phase addition can reduce the erosion of a cubic Low-k matrix phase composite coating by over 37%. Various mixing rules were then investigated to assess this non-linear composite behavior and suggestions were made to further improve erosion durability.

•Mutlilayer and nanolayer TBCs were fabricated using EB-PVD.•Coatings were composed of alternating layers of t′ low-k and Gd2Zr2O7.•Erosion and thermal conductivity results out-performed baseline materials.•Thermal stability is strongly influenced by layer thickness.To allow for increased gas turbine efficiencies, new insulating thermal barrier coatings (TBCs) must be developed to protect the underlying metallic components from higher operating temperatures. This work focused on using rare earth doped (Yb and Gd) yttria stabilized zirconia (t′ low-k) and Gd2Zr2O7 pyrochlores (GZO) combined with novel nanolayered and thick layered microstructures to enable operation beyond the 1200 °C stability limit of current 7 wt.% yttria stabilized zirconia (7YSZ) coatings. It was observed that the layered system can reduce the thermal conductivity by ~ 45% with respect to YSZ after 20 h of testing at 1316 °C. The erosion rate of GZO is shown to be an order to magnitude higher than YSZ and t′ low-k, but this can be reduced by almost 57% when utilizing a nanolayered structure. Lastly, the thermal instability of the layered system is investigated and thought is given to optimization of layer thickness.

•Mechanical properties in the ZrO2-Gd2O3 fluorite region were explored.•It was found that increasing Gd results in a decrease in toughness.•Properties tend to approach a maxima or asymptote near the pyrochlore composition.•Fluorite phase offers improved toughness and erosion over pyrochlore phase.•Coatings are more sensitive to changes in mechanical properties than bulk specimens.Advanced thermal barrier coating materials are necessary to improve the efficiency of next-generation gas turbine engines. As such, different TBC chemistries must be developed with enhanced temperature stability above that of 7YSZ (~ 1200 °C) while maintaining thermal and mechanical reliability. The present study investigates the effect of rare earth content on the mechanical properties of ZrO2 TBCs. Various cubic compositions in the ZrO2-GdO1.5 system were investigated in the form of monolithic pellets and coatings with stoichiometric GZO serving as reference. The fracture toughness and erosion durability were evaluated, and it was found that fracture toughness decreased with increasing rare-earth content, 15.66 mol% GdO1.5 yielding 1.25 MPa m1/2, compared to 1.04 MPa m1/2 for GZO (50 mol% GdO1.5). It was observed that the erosion performance of the coatings was much more sensitive to the changes in mechanical properties than the bulk specimens and showed a 125% increase through the fluorite region to GZO whereas the dense pellets only exhibited a 33% increase in erosion behavior. These results indicate that cubic ZrO2 phase with reduced rare-earth content show promise as TBC materials with improved durability over GZO as well as temperature stability in this region of the phase diagram.