超音速电弧喷涂FeCoCr涂层组织及性能研究
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摘要
锅炉管道的高温腐蚀与冲蚀一直是困扰电厂安全稳定发电的难题,尤其是近年来随着工业发展用电量的骤增,促使高参数大容量发电机组的投入运行；同时为降低发电成本,劣质煤的使用也加速了管道腐蚀破坏的速度。为提高电厂锅炉管道在高温下的抗腐蚀、抗冲蚀性能,本论文采用超音速电弧喷涂技术在20钢基材表面制备FeCoCr涂层并对涂层进行高温抗氧化、高温抗硫化及耐磨性能的实验；采用金相显微镜、X射线衍射仪、扫描电子显微镜和显微硬度计等仪器对涂层进行检测和表征分析。主要得出以下结论：
(1)超音速电弧喷涂FeCoCr涂层具有明显层状结构,厚度约230μmm,组织致密,涂层孔隙率平均约为5%。涂层主要由金属化合物CoFe, Cr和Fe的化合物(Cr,Fe)及少量的Si02组成。
(2) FeCoCr涂层与基体结合强度约为19MPa。700℃加热、空冷,600次热震实验,涂层没有明显剥落及裂纹,说明涂层的抗热震性好,与基体材料匹配。
(3)700℃加热氧化100小时,20钢基材的增重量约230μg/mm2, FeCoCr涂层材料增重量约60μg/mm2,20钢基材试样氧化增重量是FeCoCr涂层试样的3倍多,说明FeCoCr涂层的抗高温氧化效果明显提高。这是由于涂层表面形成致密的Cr203和CoO氧化膜,氧化方式由最初的界面反应逐渐转化成扩散传质反应,腐蚀减速,而20钢基材一直是单纯的界面反应,所以腐蚀较快。
(4)700℃加热硫化100小时,20钢基材硫化增重量约为1400μg/mm2, FeCoCr涂层材料增重量约400μg/mm2,20钢基材试样硫化增重量是FeCoCr涂层试样的3倍多,说明FeCoCr涂层试样抗硫化腐蚀效果明显。涂层试样的抗硫化性能得益于其硫化后的表面形成具有尖晶石结构的氧化物CoCr2O4和CoFe2O4,它们和Cr203形成致密的保护膜,阻挡了内部金属的快速硫化。
(5)涂层显微硬度约为615N/mm2。在700℃对FeCoCr涂层试样加热100小时,其摩擦系数约为0.33,未加热处理的FeCoCr涂层其摩擦系数略高,约为0.4；20钢基材试样进行同样的加热处理,摩擦系数变化不大,约为0.5。涂层试样加热处理后磨痕由“撕裂”和“犁沟”转变为轻微的损伤,20钢基材试样加热处理磨痕没有明显变化,依然保持“撕裂”和“犁沟”形貌。
High temperature corrosion and erosion of the boiler pipes has been becoming one of major issues which puzzled security and stability of power plant for generations. Especially in recent years, with development of industrial and the increasing of power consumption, the larger capacity generators emerged. At the same time, the low quality coal was used to reduce the cost of power generation, which result the corrosion speed of the pipeline greatly increased. In order to improve the power plant boiler pipe the capability of corrosion-resistant, anti-erosion at high temperature. Preparing FeCoCr coatings on the surface of20steel used the supersonic electric arc thermal spraying technology. The high temperature oxidation, vulcanization and wearing of coatings were tested. Metallographic microscope, X ray diffraction, scanning electron microscope and micro hardness tester etc were used to test and analysis. Draw the following conclusions:
(1)The supersonic electric arc spraying FeCoCr coatings were obvious layer structure, the thickness was about230μ m and the organization was dense. The pore rate of coatings was about5%. The coating is mainly composed of metal compounds of CoFe,(Cr, Fe) and a little of SiO2.
(2) The bond strength of FeCoCr coatings and the substrate is about19MPa. Heated and air-cooled at700℃for600times, there were no significant spalling and cracks in the coatings, indicating that the coatings' roperty of thermal-shock resistance was well and coatings matched with the substrate material well.
(3) Samples oxidized at700℃for100hours, substrate weight gained of20steel was about230μg/mm2and FeCoCr coatings was about60μg/mm2. The weight gained of the20steel as more than3times as the FeCoCr coatings specimen. The high temperature oxidation resistance of20steel was improved obviously by FeCoCr coatings. It benefits from the dense Cr2O3and CoO oxidized film on the surface of coatings. So the way of oxidation gradually transformed into the mass transfer reactions from the initial interface reaction and corrion was decelerated. The substrate of20steel has been interface reaction, so corrosion faster.
(4) Samples vulcanized at700℃for100hours,700℃heat curing100hours, substrate weight gained of20steel was about1400μg/mm2and FeCoCr coatings was about400μg/mm2. The weight gained of the20steel as more than3times as the FeCoCr coatings specimen. The high temperature vulcanization resistance of20steel was improved obviously by FeCoCr coatings. It benefits from the dense CoCr2O4, CoFe2O4and CrO3oxide film on the surface of coatings. They protected the internal metal.
(5)The coating micro-hardness was about615N/mm2. The friction coefficient of FeCoCr coatings was about0.33heated at700℃for100hours. The friction coefficient without heat treatment was about0.4. The friction coefficients of the substrate of20steel always were approximately0.5even heated for100hours. Heat treatment of coatings changed wear morphology from the "tear" and "furrows" into minor injury, but it didn't change the wear morphology of20steel.
(1)超音速电弧喷涂FeCoCr涂层具有明显层状结构,厚度约230μmm,组织致密,涂层孔隙率平均约为5%。涂层主要由金属化合物CoFe, Cr和Fe的化合物(Cr,Fe)及少量的Si02组成。
(2) FeCoCr涂层与基体结合强度约为19MPa。700℃加热、空冷,600次热震实验,涂层没有明显剥落及裂纹,说明涂层的抗热震性好,与基体材料匹配。
(3)700℃加热氧化100小时,20钢基材的增重量约230μg/mm2, FeCoCr涂层材料增重量约60μg/mm2,20钢基材试样氧化增重量是FeCoCr涂层试样的3倍多,说明FeCoCr涂层的抗高温氧化效果明显提高。这是由于涂层表面形成致密的Cr203和CoO氧化膜,氧化方式由最初的界面反应逐渐转化成扩散传质反应,腐蚀减速,而20钢基材一直是单纯的界面反应,所以腐蚀较快。
(4)700℃加热硫化100小时,20钢基材硫化增重量约为1400μg/mm2, FeCoCr涂层材料增重量约400μg/mm2,20钢基材试样硫化增重量是FeCoCr涂层试样的3倍多,说明FeCoCr涂层试样抗硫化腐蚀效果明显。涂层试样的抗硫化性能得益于其硫化后的表面形成具有尖晶石结构的氧化物CoCr2O4和CoFe2O4,它们和Cr203形成致密的保护膜,阻挡了内部金属的快速硫化。
(5)涂层显微硬度约为615N/mm2。在700℃对FeCoCr涂层试样加热100小时,其摩擦系数约为0.33,未加热处理的FeCoCr涂层其摩擦系数略高,约为0.4；20钢基材试样进行同样的加热处理,摩擦系数变化不大,约为0.5。涂层试样加热处理后磨痕由“撕裂”和“犁沟”转变为轻微的损伤,20钢基材试样加热处理磨痕没有明显变化,依然保持“撕裂”和“犁沟”形貌。
High temperature corrosion and erosion of the boiler pipes has been becoming one of major issues which puzzled security and stability of power plant for generations. Especially in recent years, with development of industrial and the increasing of power consumption, the larger capacity generators emerged. At the same time, the low quality coal was used to reduce the cost of power generation, which result the corrosion speed of the pipeline greatly increased. In order to improve the power plant boiler pipe the capability of corrosion-resistant, anti-erosion at high temperature. Preparing FeCoCr coatings on the surface of20steel used the supersonic electric arc thermal spraying technology. The high temperature oxidation, vulcanization and wearing of coatings were tested. Metallographic microscope, X ray diffraction, scanning electron microscope and micro hardness tester etc were used to test and analysis. Draw the following conclusions:
(1)The supersonic electric arc spraying FeCoCr coatings were obvious layer structure, the thickness was about230μ m and the organization was dense. The pore rate of coatings was about5%. The coating is mainly composed of metal compounds of CoFe,(Cr, Fe) and a little of SiO2.
(2) The bond strength of FeCoCr coatings and the substrate is about19MPa. Heated and air-cooled at700℃for600times, there were no significant spalling and cracks in the coatings, indicating that the coatings' roperty of thermal-shock resistance was well and coatings matched with the substrate material well.
(3) Samples oxidized at700℃for100hours, substrate weight gained of20steel was about230μg/mm2and FeCoCr coatings was about60μg/mm2. The weight gained of the20steel as more than3times as the FeCoCr coatings specimen. The high temperature oxidation resistance of20steel was improved obviously by FeCoCr coatings. It benefits from the dense Cr2O3and CoO oxidized film on the surface of coatings. So the way of oxidation gradually transformed into the mass transfer reactions from the initial interface reaction and corrion was decelerated. The substrate of20steel has been interface reaction, so corrosion faster.
(4) Samples vulcanized at700℃for100hours,700℃heat curing100hours, substrate weight gained of20steel was about1400μg/mm2and FeCoCr coatings was about400μg/mm2. The weight gained of the20steel as more than3times as the FeCoCr coatings specimen. The high temperature vulcanization resistance of20steel was improved obviously by FeCoCr coatings. It benefits from the dense CoCr2O4, CoFe2O4and CrO3oxide film on the surface of coatings. They protected the internal metal.
(5)The coating micro-hardness was about615N/mm2. The friction coefficient of FeCoCr coatings was about0.33heated at700℃for100hours. The friction coefficient without heat treatment was about0.4. The friction coefficients of the substrate of20steel always were approximately0.5even heated for100hours. Heat treatment of coatings changed wear morphology from the "tear" and "furrows" into minor injury, but it didn't change the wear morphology of20steel.
引文
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[2]JohnSrtniger, lnaGWrihgt. Oxided Metal [M],1995(44):277
[3]S. Gusatsffna. Proceedings of the ITSC86, Montreal Canada:1996:9-10
[4]蔡向晖.盘山发电厂锅炉高温过热器爆管事故分析[J].华北电力技术,1998：46-47
[5]吴履琛,王晓为.伊敏电厂锅炉过热器爆管事故分析及改进措施[J].锅炉制造,1999：1-8
[6]张羽,王中林.印度海萨电厂锅炉爆管原因分析[J].湖南电力.2001：1-8
[7]徐滨士,李长久.表面工程与热喷涂技术及其发展[J].中国表面工程,1998,11(1)：3-9.
[8]吴和元,阂小兵.热喷涂技术在火电行业的应用[J].湖南电力,2002,4：56
[9]J. H. Zatt. A quarter of a century of plasma spraying [J]. Ann. Rev. Mater.Sci..1983,13: 9-12.
[10]徐滨士等.表面工程的理论与技术[M].北京：国防工业出版社,1999：17-21
[11]F. Kassabji, J. P. Durand,G. Jacq. Thermal spray applications for the next millennium:A business development [J]. Proceedings of the 15 ITSC, Nice, France,1998:1677-1680.
[12]赵守田,吴平,陈森等.含铜超低碳微合金钢冷却过程硼的晶界偏聚[J].钢铁钒钛,2011,32(3)：59-63
[13]李铁藩.金属高温氧化和热腐蚀[M].北京：化学工业出版社,2003：239-250
[14]王越田,盛光敏,孙建春等.镍在自纳米化纯铁表面的扩散系数研究[J].材料导报,2010.24(16)：40-43
[15]周雅,江溢民,周佳.铝合金微弧氧化莫耐蚀性研究现状[J].失效分析与预防,2012,7(1)：57-62
[16]张洋,总广霞,王福会等.微晶化对Ni20Cr合金热生长氧化膜应力的影响[J].腐蚀科学与防护技术,2011,23(5)：434-436
[17]杨世伟,施月杰,张天宇.K4104镍基高温合金A1-S涂层高温氧化过程中的元素中的元素扩散分析[J].材料开发与应用,2010,25(5)：4-8
[18]邓丽红,魏晓伟.铝合金6061在低浓度硫酸中硬质阳极氧化膜的生长方式[J].腐蚀与防护,2011,32(6)：434-437
[19]雷明凯,徐忠成,杨辅军等.高温合金氧化膜破坏的界面断裂力学分析[J].金属学报,2004,10(40)：1104-1108
[20]张青科,邹鹤飞,张哲峰.SnBi/Cu界面Bi偏聚机制与时效脆性抑制[J].中国科学：技术科学,2012,1(42)：13-21
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