湿热环境下 LaCrO₃ 基复合涂层性能演变及机理研究

To reveal the performance evolution and mechanism of La_0.7Ca_0.3Cr_0.95Mn_0.05O₃ composite coating in hygrothermal environments, two distinct coating systems are fabricated via plasma spraying technology: La_0.7Ca_0.3Cr_0.95Mn_0.05O₃ high emissivity layer/YSZ thermal barrier layer/NiCoCrAlY metallic bonding layer/GH4099 substrate (LC/Y/M/G) and La_0.7Ca_0.3Cr_0.95Mn_0.05O₃/metallic bonding layer/TA15 substrate (LC/M/T). Accelerated aging tests are conducted in an environmental chamber under controlled conditions (85 ℃, 85% RH) for 25 days to simulate hygrothermal degradation. Samples are taken at 5, 10, 15, 20, and 25 days to measure the coating bonding strength of the samples. Characterization of coatings is conducted with equipment such as confocal laser microscopy and electrochemical workstations. X-ray diffraction (XRD) analysis indicates no significant changes in the macroscopic morphology or crystal structure of the coatings before and after the 25-day aging test. The La_0.7Ca_0.3Cr_0.95Mn_0.05O₃ phase remains stable, with no detectable phase transitions or new phase formation. Surface roughness measurements reveals that the surface roughness of the LC/Y/M/G coating decreases from 11.03 μm to 9.70 μm, and the Ra value of the LC/M/T coating decreases from 10.52 μm to 9.53 μm. Due to the randomness of the surface roughness of the atmospheric plasma spray coating, it is considered that there is no significant change in the surface roughness Ra. Cross-sectional analysis of bonding strength demonstrates distinct failure modes: LC/Y/M/G system: Fractures occur at the YSZ layer with a bonding strength of (22.75±3.07) MPa, showing negligible degradation during aging; LC/M/T system: Fractures appear in the metallic bond coats with an initial strength of (41.58±3.24) MPa, but exhibit significant exponential decay over time. However, with the extension of accelerated aging test time, there is a significant exponential decay trend in the bonding strength, and the decay function is fitted. Electrochemical tests on the TA15 substrate, and metallic bond coats reveal electrochemical corrosion behaviors. For the self-corrosion current densities: the metallic bond coats (6.950 2 μA/cm²) >TA15 (0.110 8 μA/cm²). After the accelerated aging test, a large number of pitting micro-areas are observed at the cross section of the metallic bonding layer, and more pore defects are found at the interface of the metallic bonding layer, which lead to the stress concentration phenomenon in the bonding strength test, and finally lead to the attenuation of the bond strength. The La_0.7Ca_0.3Cr_0.95Mn_0.05O₃ layers in the LC/Y/M/G and LC/M/T material systems all show good resistance to dampness and heat. However, the metallic bonding layer in LC/M/T is prone to corrosion during the test, which will lead to the exponential attenuation of the bonding strength of the composite coating with the extension of the damp heat test, which will become the weak position of the coating failure. However, when the YSZ layer is added to the coating, the corrosion of the metallic bonding layer is effectively inhibited, which can be attributed to the blocking effect of the YSZ middle layer on corrosive media such as oxygen and water vapor.