The microstructure of plasma-sprayed nanostructured yttria-stabilized zirconia (YSZ) coatings may change during high-temperature exposure, which would influence the coating performance and service lifetime. In this study, the phase structure and the microstructural evolution of 3YSZ (zirconia-3 mol% yttria) and 5YSZ (zirconia-5 mol% yttria) nanostructured coatings were investigated by means of sintering at 1400 °C for 50–100 h. The microhardness, elastic moduli, and thermal shock cycles of the 3YSZ and 5YSZ nanostructured coatings were also investigated. The results showed that the redistribution of yttrium ions at 1400 °C caused the continuous increase of monoclinic-phase zirconia, but no obvious inter-splat cracking formed at the cross-sections, even after 100 h. Large voids appeared around the nanoporous zone because of the sintering of nanoscale granules upon high-temperature exposure. The microhardness and elastic moduli of the nanostructured coatings first increased and then decreased with increasing sintering times. The growth rate of the nanograins in the 3YSZ coating was lower than that in 5YSZ, which slowed the changes in 3YSZ coating porosity during sintering. Although the 3YSZ coating was prone to monoclinic phase transition, the experimental results showed that the thermal shock resistance of the 3YSZ coating was better than that of the 5YSZ coating.
Tianquan Liang,Zhihua Huang,Menghao Li,Wantong Xiao,Huan He,Aoping He,Xiyong Chen,Nengneng Luo
The thermochemical reaction behaviors between Y 2 O 3 and calcium-magnesium-aluminosilicate (CMAS) at 1250 °C∼1400 °C were investigated. A continuous-dense reaction layer mainly composed of Y-apatite phase quickly forms within 15 min, and its slow increasing thickness depends on the molten CMAS infiltration along the Y-apatite grain boundaries, the dissolution of the Y-apatite phase into the melt, the inhibiting effect on the CMAS penetration, and the reaction time and temperature. The CMAS crystallization occurs due to the change of chemical composition and the formation of other reaction products. The dense reaction layer shows good resistance to the molten CMAS infiltration.
Lu Zhu,Yousen Zhu,Xuanru Ren,Ping Zhang,Jianghao Qiao,Peizhong Feng
MoSi 2 -MoB-ZrO 2 composite powders are one-step synthesized prepared by self-propagating high-temperature synthesis (SHS), which are further utilized to prepare the oxidation protective coatings by spark plasma sintering (SPS) method on molybdenum substrate. Microstructure and properties of the coatings were investigated and determined. Oxidation behavior of the coatings at high temperature was also studied. The results showed that the composite coating is dense and crack-free due to the addition of ZrO 2 , which is beneficial for the decrease of mismatch in coefficient of thermal expansion, and no void exists in the diffusion layer owing to the diffusion of Si, which is inhibited by adding MoB. Compared with the pure MoSi2 coating, the high hardness of the composite coating is enhanced by about 20% while the fracture toughness of the composite coating is improved by about 25%, which makes the occurrence of intergranular fracture , crack deflection and crack bridging. After oxidation at 1400 °C for 80 h, MoSi 2 coating failed while xMoSi 2 -MoB-3ZrO 2 (x = 3, 4, 5) composite coating still kept its protective effect. Only a little substrate is consumed during oxidation and improved oxidation resistance is gained by MoSi 2 -MoB-ZrO 2 composite coating. 3MoSi 2 -MoB-3ZrO 2 coating shows the relatively best oxidation resistance due to the formation of crack-free oxide film on the surface of the coating.
α-Al 2 O 3 -based coatings have attracted great interest as promising tritium permeation barrier used in the D-T fusion reactor system. However, it is still difficult to fabricate α-Al 2 O 3 coatings at a low temperature that can be endured by the steel substrate. Herein, thermal-chemical reaction method was developed for the fabrication of α-Al 2 O 3 -based coatings. α-Al 2 O 3 /AlPO 4 composite coating was successfully formed on the steel substrate at 500 °C. The resulted coating was uniform and compact without presence of pores and cracks. The binding strength of the coating was tested and the result indicated its good adherence to the substrate. Moreover, the coating thickness could be easily controlled. The low-temperature approach developed is expected to provide a new platform for fabricating α-Al 2 O 3 -based coatings as tritium permeation barrier. This approach is also applicable to the fabrication of other ceramic coatings.
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