作为超高温结构材料,共晶氧化物陶瓷的力学性能和显微组织密切相关.采用高温熔凝法制备Al2O3/ZrO2/YAG共晶陶瓷体,研究熔体温度和结晶种子对凝固组织影响规律,运用经典形核机制和Jackson-Hunt共晶生长模型探讨了凝固组织的演变机理.研究表明,随着熔体温度升高(1750~2000℃),凝固体物相组成从α-Al2 O3,c-ZrO2和YAG转变为α-Al2O3,c-ZrO2和亚稳相YAP.凝固组织依次经历:非共晶Al2O3/ZrO2/YAG、不规则共晶Al2O3/ZrO2/YAG、纳米纤维状共晶Al2O3/ZrO2/YAG和复杂粗大的亚稳复合陶瓷Al2O3/ZrO2/YAP.分析表明,凝固组织的演变源于异质晶核点不断钝化导致形核过冷度和凝固路径改变,所以合理选择熔体温度和结晶种子是共晶组织调控的关键.
As ultra-high-temperature structural materials ,the mechanical properties of eutectic oxide ceramics are closely related with microstructure characteristics .Melt-grown Al2O3/ZrO2/YAG eutec-tic ceramic was prepared by high temperature fused method .Effect of melt temperature and crystal seed on solidification microstructure evolution was investigated ,the structure evolution mechanism was discussed using the classical nucleation mechanism and Jack-hunt mode .Experiment results show the phase composition of solidified samples changes from α-Al2O3/c-ZrO2/YAG to α-Al2O3/c-ZrO2/YAP as the melt temperature increases from 1750℃ to 2000℃ .And the solidification microstructure evolves as follows :non-eutectic ceramic Al2O3/ZrO2/YAG ,irregular eutectic ceramic Al2O3/ZrO2/YAG ,nano-scale regular fibrous pattern eutectic Al2O3/ZrO2/YAG ,and complex coarse metastable composite ceramic Al2O3/ZrO2/YAP .Analysis shows that microstructure evolution is resulted from heterogeneous passivation with elevating temperature followed by variations of nucleation undercoo-ling and solidification path .Therefore ,choosing reasonable melt temperature and crystal seed are the key rules to control the microstructure of Al2O3/ZrO2/YAG eutectic ceramic .
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