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采用ω(NaCl)∶ω(KCl)∶ω(NaF)=2∶2∶1(摩尔比,下同)的中性熔融盐作为载体,ω(Na2SiF6)∶ω(Si)=8∶2粉末做为渗硅剂,800℃下渗硅10 h可实现在AISI 304不锈钢表面形成厚度约500μm的富含Cr、Ni合金元素的Fe3Si型硅化物渗层。采用X射线衍射仪(XRD)分析了渗硅层的物相组成,用附带能量色散谱仪(EDS)附件的扫描电子显微镜(SEM)研究了渗层截面的形貌和成分。结果表明,渗层以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。Fe3Si型硅化物渗层在800℃和900℃下的氧化动力学均遵从二次抛物线规律。AISI 304不锈钢渗硅层在800℃下的抗氧化性能略优于不锈钢基体,而在900℃下AISI 304不锈钢发生灾难性破坏,硅化物渗层表现出比其在800℃下更为好的抗氧化性能。900℃下Cr和Si元素发生上坡扩散最终在渗硅层表面形成富含SiO2和Cr3O4的复合氧化膜是其优异抗氧化性能的原因。
A powder of ω (Na2SiF6): ω (Si) = 8: 2 was obtained by using a neutral molten salt of ω (NaCl): ω (KCl): ω (NaF) = 2: 2: 1 (molar ratio, As a siliconizing agent, siliconizing at 800 ℃ for 10 h can form a Fe3Si-type silicide layer rich in Cr and Ni alloying elements with a thickness of about 500 μm on the surface of the AISI 304 stainless steel. The phase composition of the siliconized layer was analyzed by X-ray diffraction (XRD). The morphology and composition of the cross-section of the layer were studied by scanning electron microscopy (SEM) with an attached energy dispersive spectrometer (EDS). The results show that the infiltrated 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. The oxidation kinetics of Fe3Si-type silicide infiltrated layers at 800 ℃ and 900 ℃ both obeyed the quadratic parabola law. The AISI 304 stainless steel infiltrated layer has slightly better oxidation resistance at 800 ° C than the stainless steel substrate, whereas the AISI 304 stainless steel catastrophically disrupts at 900 ° C and the silicide infiltrated layer shows better resistance than its 800 ° C Oxidation performance. Upward slope diffusion of Cr and Si at 900 ℃ finally formed composite oxide film rich in SiO2 and Cr3O4 on the surface of the siliconized layer, which is the reason for its excellent oxidation resistance.