Figure 2
Optical microscopy images of the metallographic cross sections. (a) a 300 nm NCD-coated ZIRLO tube sample processed at 1000 °C in hot steam. (1) Outer-surface zirconium dioxide layer, with a thickness of 90.8 μm. (2) Outer-surface oxygen-stabilized zirconium α phase (solid Zr-O solution). (3) Initial Zr β phase (metastable modified hexagonal close-packed structure). (4) Inner-surface oxygen-stabilized Zr α phase. (5) Inner-surface ZrO2 layer, with a thickness of 125.02 μm. (b) an uncoated ZIRLO tube sample subjected to hot steam (1000 °C/1 h). On the outer surface of the tube, the ZrO2 thickness was 195.13 μm; on the inner surface, the ZrO2 thickness was 196.8 μm.
