含氯溶液中硫化物对铁基块体非晶合金点蚀萌生与扩展的影响机制

The pitting corrosion resistance of Fe-based bulk metallic glass (Fe-BMG) will be deteriorated since the homogeneity in chemical composition and microstructure is destroyed by in situ formed sulfide in Fe-BMG fabricated using raw industrial materials. Up to now, the researches about pitting corrosion resistance of Fe-BMG are lack, and no one of pitting initiation theories is approved comprehensively, moreover, the behaviors of pitting propagation are not explored extensively.all of those will impede the engineering application of Fe-BMG as anti-corrosive material. In this project, Fe-BMG will be fabricated using pig-iron and another ferralloys in industrial condition. By changing addition of alloying elements Mn and S, the characteristics of sulfide inclusion, such as size, shape and composition, will be varied. By analyzing the effects of sulfide inclusion on pitting corrosion resistance with electrochemical Lab-station in chloride solution, the quantitative analysis model will be established between the characteristics of sulfide inclusion,chlorinic ion concentration, envioremental temperature and pitting potential, so pitting susceptibility will be evaluated for Fe-BMG in chloride solution. With the equipments of AFM, EPMA, SIMS, XPS and so on, the pitting mechanism of Fe-BMG will be explored by analyzing the variation about the characteristics of passive film, the shape of sulfide inclusion, the composition of metallic matrix in interface, and the three-dimension size of pit hole, and exploring the regularity of the pitting initiation and pitting propagation in Fe-BMG, and establishing thermodynamic rule of pit initiation and the kinetic model of pit propagation, which will provides experimental and theoretical principle for promoting the extinsive application of Fe-BMG as anti-corrosive materials in industry.

采用工业原材料制备的铁基块体非晶合金中容易形成硫化物夹杂，破坏其化学成分和显微结构的均匀性，降低非晶合金的耐点蚀性能。目前，鲜有关于铁基块体非晶合金点蚀性能的相关研究，对铁基非晶合金点蚀的萌生机理尚未形成统一认识，且对其扩展规律并不清楚，阻碍铁基块体非晶合金作为耐蚀材料的工程应用。本项目以工业纯铁及其它铁合金为原材料，在工业环境下制备铁基块体非晶合金，改变Mn、S元素含量，控制硫化物特性，如大小、形状及成分，研究含氯溶液中硫化物对其点蚀性能的影响；建立硫化物特性、氯离子溶度、温度与点蚀电位之间的定量分析模型，分析其点蚀敏感性；采用AFM、EPMA、TEM及XPS等，研究钝化膜特征、硫化物形貌、基体界面区成分及蚀孔三维尺寸的变化规律，探索铁基非晶合金点蚀萌生与扩展规律，建立点蚀萌生的热力学准则和扩展的动力学模型，揭示其点蚀机理，为促进铁基块体非晶合金作为耐蚀材料的工程应用提供试验和理论依据

采用工业原材料制备铁基非晶合金中容易形成夹杂,破坏其化学成分和显微结构的均匀性,降低非晶合金的耐点蚀性能。项目采用水冷铜模吸铸法和超音速火焰喷涂技术分别制备块体铁基非晶合金及合金层，通过浸泡、电化学法测试非晶非晶合金的耐点蚀性能，采用SEM、TEM等分析腐蚀产物和腐蚀形貌，揭示硫化物夹杂对铁基非晶合金点蚀性能的影响机制。通过项目研究，获得以下主要结果：.1）铁基非晶合金基体中硫化物为Al2S3，退火后，晶化相包括α-Fe、Fe3C和Fe3B等；铁基非晶涂层中含有少量氧化物FeO和一些晶化相，如α-Fe、Fe3C。.2）非晶铸棒在0.5mol/L的H2SO4、HCl、NaOH、NaCl溶液中均拥有优异的耐腐蚀性能，其腐蚀速率均呈现先升高，之后逐渐趋于稳定的规律；其腐蚀速率大小关系为：在H2SO4溶液中的腐蚀速率最大，HCl次之，而NaOH和NaCl中相对较低，二者的腐蚀速率比较接近。.3）非晶铸棒在不同浓度、不同温度的H2SO4、HCl、NaOH、NaCl溶液中的动电位极化曲线均呈现明显的钝化现象，且均未表现出明显的点蚀现象。.4）采用超音速火焰喷涂技术，制备了铁基非晶涂层，涂层成形良好，涂层厚度达300μm、孔隙率约为1%、非晶含量高达99.6%。.5）铁基非晶涂层具有优异的耐蚀性能，其耐蚀性能于涂层的孔隙率和非晶含量相关；非晶含量越高、孔隙率越低，非晶涂层的耐蚀性能越好。铁基非晶层在氯离子溶液中具有优异的自钝化能力，耐蚀性能优于SUS316不锈钢。.6）在HCl溶液中，在非晶涂层界面两侧出现贫铬现象，导致点蚀发生；建立了点蚀萌生的模型。.7）在FeCl溶液中，硫化物夹杂是点蚀的萌生源；晶化相的析出，加速点蚀的发生。