采用EB-PVD非连续沉积工艺制备了微叠层结构热障涂层,对涂层结构和晶体形貌进行了SEM观察和分析,采用激光脉冲法测定了涂层的热扩散系数,并采用增重法研究了涂层的氧化动力学特征,分析了氧化后的元素扩散情况.结果表明,非连续EB-PVD沉积工艺制备的涂层具有明显的层状特征,常规EB-PVD热障涂层的柱状晶结构被周期性地打破;但在每一层中,柱状晶结构得以保留,且晶粒更加细化.微叠层热障涂层的热扩散系数比常规热障涂层降低20%~30%,涂层热扩散系数的降低主要与层间界面和晶粒的细化减小了声子的平均自由程有关.微叠层结构热障涂层的氧化增重速率明显低于常规试样,遵循典型的抛物线规律,垂直于元素扩散方向的层间界面和细晶更有效地降低或阻止了O、Al、Ni、Cr等元素的扩散,可能是氧化增重速率较低的主要原因.
Abstract
Thermal barrier coatings(TBCs) with micro laminated structure were fabricated by interrupted electron beam physical vapor deposition(EB-PVD).Using scanning electron microscope(SEM),the structure and crystal morphology of coatings were observed and analyzed.And the thermal diffusivity of coatings was measured by laser flash method.Additionally,the oxidation dynamic characterizations of coatings were investigated via weight gain in isothermal oxidation test and the diffusion of elements in coating systems were analyzed by energy dispersive spectroscopy(EDS) after oxidized.The results show that TBCs prepared by interrupted EB-PVD process presents clear layered characteristic.The columnar crystal structure,which particularly owned to EB-PVD coatings,is periodically disrupted.However,columnar characteristic is still preserved in each layer and the crystal grains become shorter and finer.The inter-layer interface and finer grain of micro laminated TBCs reduce the phonon mean free path,which mainly responsible for the 20% to 30% reduction of thermal diffusivity than that of the conventional deposited value in the temperature range of 25~1200℃.The weight gain rate of micro laminated TBCs is obviously lower than its conventional deposited counterpart.The main reason for this phenomenon is likely that interface and finer grain weaken or prevent the diffusion of O,Al,Ni,Cr,etc.elements.
关键词
热障涂层 /
微叠层 /
电子束物理气相沉积 /
热扩散系数 /
激光脉冲
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Key words
thermal barrier coat /
micro-laminate /
electron beam physic /
thermal diffusivity /
laser flash
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