A novel fully nano-equiaxed-structured thermal insulation Y 2 O 3 -stabilised ZrO 2 (YSZ) coating was first successfully deposited using very-low-pressure plasma spray (VLPPS) and the agglomerates feedstock from nanometer-sized powders. The microstructure of fully nano-equiaxed-structured coating is different from that of a “bimodal microstructure”, which is currently the dominant nanostructured coating. This desirable structure in the new TBCs appears to be responsible for their improved thermal cycling lifetimes and reduced thermal conductivity relative to those of conventional plasma-sprayed TBCs with lamellar structures or bimodal structures. Preliminary results from experiments aimed at understanding the VLPPS deposition mechanisms suggest that the nanometre-scale equiaxed in the coating are formed from original nano-particles, they underwent melted in the low pressure plasma plume and solidification onto the substrate. The VLPPS method, which offers some unique advantages over the conventional plasma-spray process, is generic in nature and can be potentially used to deposit a wide variety of ceramic coatings for diverse applications.

In this paper, the development of surface oxide scale and the evolvement of spallation mechanism of Fe-21Cr-5.6Al super alloy were investigated at 1200°C and 1300°C. The oxidation kinetic curves were obtained by isothermally measuring the weight gain of alloy oxidized with various time durations. The morphologies of oxide scale and grain structures were observed by SEM/EDX, and the phase structure was analyzed by XRD. The results show that the oxidation processes follow the parabolic law and the oxidation rate is higher at 1300°C than 1200°C. Though the FeCrAl alloy shows capabilities against oxidation even at a high temperature of 1300°C, the oxidation behavior and mechanism are distinct from those at moderate temperatures (<1000°C). Different morphologies and phase structure were found in oxide scales generated at different temperatures within the same time duration. Typical buckling was observed in the super alloy when it was subjected to 1200°C. Equiaixed grains with multiple voids were found near the alloy surface. At 1300°C, a flat and thicker oxide layer was formed. The grains were stretched vertically against the alloy and presented as coarse and compact near the interface. The vertically stretching of grain was triggered by fast element transportation inside the alloy. The differences in grain morphologies among the different test temperatures demonstrated that although the super alloy followed parabolic law at both test temperatures, the oxidation processes were different due to the evolvement of grain morphologies and oxide scale structures caused by exposure to high temperature.