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采用NaCl∶KCl∶NaF=2∶2∶1(摩尔比)的中性熔融盐作为载体,Na2SiF6∶Si=8∶2粉末做为渗硅剂,以SiO2为助渗剂,800℃下渗硅5h可实现在AISI 304不锈钢表面形成厚约600μm的富含Cr、Ni合金元素的Fe3Si型硅化物渗层,研究了渗层在900℃下的循环氧化行为。采用X射线衍射仪分析了渗层和氧化膜的物相组成,用附带能量色散谱仪附件的扫描电子显微镜研究了渗层和氧化膜截面的形貌和成分。结果表明,渗层为以Fe3Si相为主,Cr在渗层中含量低于其在304不锈钢基体中含量,而Fe和Ni在基体和渗层中的含量大致相当。氧化动力学遵从二次抛物线规律;Cr和Si元素发生上坡扩散形成以SiO2和Cr2O3为主的内层氧化膜,外层氧化膜以Fe2O3为主,这种复合氧化膜是渗层具有优异抗氧化性能的原因。
A neutral molten salt of NaCl: KCl: NaF = 2: 2: 1 (molar ratio) was used as a carrier, and a powder of Na2SiF6: Si = 8: 2 was used as a siliconizing agent. 5h can form a Cr3 + -type Fe3Si-type silicide layer with a thickness of about 600μm on the surface of AISI 304 stainless steel. The cycling oxidation behavior of the diffusion layer at 900 ℃ was studied. The phase composition of the diffusion layer and the oxide film was analyzed by X-ray diffractometer. The morphology and composition of the cross-section of the diffusion layer and the oxide film were studied by scanning electron microscope (SEM) with an attached energy dispersive spectrometer. The results show that the infiltrating layer is dominated by Fe3Si phase, the content of Cr in the infiltrated layer is lower than that in the 304 stainless steel, and the contents of Fe and Ni in the matrix and the infiltrated layer are almost the same. Oxidation kinetics follow the law of the second parabola; Cr and Si elements uphill diffusion to form SiO2 and Cr2O3-based inner oxide film, the outer oxide film to Fe2O3-based, the composite oxide film is the diffusion layer has excellent resistance Oxidation performance reasons.