电泳-预氧化扩散处理法制备NiO/NiFe_2O_4涂层及其形成机制

Preparation of NiO/NiFe_2O_4 coatings by electrophoresis and pre-oxidation diffusion treatment and their formation mechanism

先采用电沉积?电泳方法在Ni基体高温合金上制备电镀Ni/电泳Fe2O3复合涂层,再通过后续空气中进行的高温预氧化处理方法来获得NiO/NiFe2O4复合氧化物涂层。利用DSC、SEM、EDS和XRD等检测手段分析预氧化温度对涂层的结构、微观形貌、元素分布及相组成等影响,并对涂层形成的反应机理及预氧化动力学进行讨论。结果表明:经1 000、1 100和1 200℃下氧化4 h后,氧化膜中均生成NiO和NiFe2O4。氧化温度为1 000℃时涂层表面还存在没有参与反应的Fe2O3,但随氧化温度的升高,Fe2O3层随之消失。温度为1 100和1 200℃时氧化膜中的NiO、NiFe2O4相与镀Ni基体之间形成了冶金结合,并且通过扩散在NiO相内部形成了NiFe2O4析出相。Ni基体以及电镀Ni/电泳Fe2O3复合涂层在1 000℃预氧化时单位面积上的质量增加随时间增加,大体遵循抛物线规律,且电镀Ni/电泳Fe2O3复合涂层单位面积上的质量增加大于镀Ni基体的。涂层的厚度与氧化质量增加随预氧化扩散温度的提高而增加。

Electrodeposition-electrophoretic deposition（EPD） technique was employed for fabricating the ferric oxide（Fe2O3） thick films on the Ni-based superalloy,and then pre-oxidation processing method was used to obtain the NiO/NiFe2O4 composite coating.DSC,SEM,EDS and XRD analysis methods were used to analyze the influence of pre-oxidation temperature on the coating structure,morphology,elemental distribution and composition of the phase,and forming reaction mechanism and kinetics of the coating were also discussed.The results show that by high temperature diffusion processes at 1 000,1 100 and 1 200 ℃ for 4 h,respectively,the oxide film is made up of NiO and NiFe2O4.When the oxidation temperature is 1 000 ℃,there is no reactive Fe2O3 layer on the surface of coating,while with the oxidation temperature increasing,Fe2O3 layer disappears.When the temperature increases to 1 100 and 1 200 ℃,the NiO,NiFe2O4 phase and the Ni plating reach metallurgical combination,and NiFe2O4 spinel precipitates and forms inside NiO matrix phase through diffusion transport.The per unit area mass gain of Ni substrate and electrophoretic Ni/EPD Fe2O3 coating after 1 000 ℃ pre-oxidation diffusion treatment increases with the increase of time,which generally follows the parabolic law,and the per unit area mass gain of Ni/EPD Fe2O3 increases faster than that of the electroplated Ni.The thickness and mass gain of oxide coating obviously increase with the pre-oxidation the increase of temperature.