低红外发射率陶瓷层/金属层/陶瓷层复合薄膜高温性能研究

目的研究热处理工艺对陶瓷层/金属层/陶瓷层复合薄膜低红外发射性能的影响,并分析复合薄膜的有效工作温度。方法采用多弧离子镀方法在Ni基K424合金基底上制备了AlCrN/Cr/AlCrN和AlCrSiN/Cr/AlCrSiN两种复合薄膜,分别在700~800℃和800~900℃大气环境下对样品进行了热处理。利用X射线衍射仪、场发射高分辨率透射电子显微镜、X射线光电子能谱仪、电子探针显微分析仪、辉光放电质谱仪和傅里叶变换红外光谱仪,对样品的微观结构、化学组成和表面辐射特性进行了分析。通过建模计算了两种样品在不同温度下的氧化活化能和扩散系数,对比了其抗氧化性能和抗扩散性能。结果样品中的陶瓷层呈纳米晶-非晶结构特征,AlCrN和AlCrSiN陶瓷层中的纳米晶分别为hcp-Cr2N和hcp-AlN。非晶AlCrN介质会在750℃结晶形成面心立方相的Cr(Al)N,加入Si元素可以将其结晶温度提高至850℃。在氧化初期,由于纳米晶的不同,AlCrN和AlCrSiN陶瓷层的表面分别形成富Cr和富Al的氧化层,而由于fcc-Cr(Al)N的形成,以及氧化铬和氧化铝之间极高的溶解度,最终样品表面会形成铝、铬混合的氧化层。当非晶AlCrN介质结晶后,O元素通过晶界深入样品内部导致样品的红外发射率急剧增大,使其低发射特性失效。同时,结晶后的复合薄膜中陶瓷层的氧化活化能降低,Ni元素的扩散系数增大。结论纳米晶-非晶结构的陶瓷层具有更优异的抗氧化性能和抗扩散性能,加入Si元素可以提高样品的抗氧化性能,AlCrSiN/Cr/AlCrSiN复合薄膜可应用于850℃以下的低红外发射率应用。

Study on Thermal Properties of Ceramic Layer/Metal Layer/Ceramic Layer Composite Coating with Low Infrared Emissivity

This work aims to investigate the effects of annealing duration on low infraed emissivity property of ceramic layer/metallic layer/ceramic layer composite coatings,and analyze its effective operating temperature.The AlCrN/Cr/AlCrN and AlCrSiN/Cr/AlCrSiN compsite coatings were prepared by multi-arc ion plating technology on Ni-based K424 alloy substrate.The microstructure,chemical composition and surface radiation characteristics of the samples were analyzed by X-ray diffractometer,field emission high resolution transmission electron microscope,X-ray photoelectron spectrometer,electron probe microanalyzer,glow discharge mass spectrometer and Fourier transform infrared spectrometer.The oxidation resistance and diffusion resistance of samples were compared by modeling and calculating its oxidation activation energy and diffusion coefficient.The ceramic layer presented a nanocrystalline-amouphous characteristic,and the nanocrystalline in AlCrN and AlCrSiN ceramic layers were hcp-Cr2N and hcp-Al N,respectively.Amorphous AlCrN matrix would crystallize into face-centered cubic phase Cr(Al)N at 750℃.The addition of Si elements could increase the crystallization temperature to 850℃.In the early oxidation stage,Cr rich and Al richoxides was formed on the surface of AlCrN and AlCrSiN ceramic layer,respectively,which was due to the difference of nanocrystals.Then,a mixed oxide layer of aluminum and chromium was observed on the surface of the sample,which resulted from the formation of fcc-Cr(Al)N and the extremely high solubility between chromium oxide and alumina.When amorphous AlCrN media crystallized,the further penetration of O element through crystal boundaries led to a sharp increase in the infrared emissivity,resulting in the failure of its low emissivity property.Meanwhile,after the crystallization of ceramic layer,its oxidation activation energy decreased,and the diffusion coefficient of Ni element increased.Nanocrystalline-amorphous ceramic layer showed more excellent oxidation resistance and diffusion resistance.The addition of Si elements could improve the oxidation resistance of the sample.The AlCrSiN/Cr/AlCrSiN composite coating could be applied for low infrared emissivity applications under the temperature of 850℃.