激光选区熔化成形Kanthal涂层及其微波衰减特性研究

Microstructure and Microwave Attenuation Properties of Kanthal Coating Prepared by Selective Laser Melting

采用2种球形Kanthal合金粉末(颗粒直径45~60μm和50~70μm),通过激光选区熔化(selective laser melting,SLM)技术制备Kanthal涂层。利用光学显微镜、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和谐振腔特性测量系统对Kanthal粉末及涂层的表面形貌、显微组织、相结构和谐振腔品质因子进行检测分析。结果表明:SLM成形Kanthal涂层具有表面粗糙、多孔结构、扁平化的特点,与无氧铜基金属结合牢固,形成了冶金结合界面。其中45~60μm球形合金粉末SLM成形涂层加载谐振腔品质因子(quality factor)Q值整体比50~70μm粉末成形涂层的Q值低,在频率2985 MHz下微波衰减特性更强。涂层成形过程中形成的Al2O3膜和微孔洞使得合金涂层能够散射微波,减少了对微波的反射。涂层厚度对微波有干涉损耗,厚度0.55 mm的Kanthal涂层加载谐振腔Q值最小,达到2280。Kanthal涂层是以磁衰减为主的复合衰减材料。

Kanthal coatings were fabricated by selective laser melting(SLM)with two kinds of powder,45~60μm and 50~70μm in diameter.The surface morphology,microstructure,element distribution,phase structure,and microwave attenuation properties of the coatings were studied by optical microscope,scanning electron microscopy,X-ray diffraction,and cavity characteristic measurement system.The results indicate that Kanthal coatings have the characteristics of rough surface,porous and flaky structure.The quality factor Q of cavity loaded with coatings fabricated by 45~60μm sphere powder is lower than that of coatings by 50~70μm powder,showing better microwave attenuation properties under the frequency of 2985 MHz.Al2 O3 thin films and micro void generated in the structure of coatings have the effect of scattering microwave and thus reduce microwave reflection.It is also shown that flattened shape of Kanthal coatings is a good way to suppress eddy currents in high-frequency electromagnetic field and leads to the formation of easy magnetization planes,which is helpful to enhance the microwave attenuation property.The coating thickness has profound effects on interference loss of microwave.Cavity Q with coating thickness of 0.55 mm reaches the minimum value of 2280.Kanthal coating is composite material whose main mechanism is attributed to magnetic loss.