【作者】 张俊；

【导师】 张玉文；

【作者基本信息】 上海大学 ， 材料加工工程， 2023， 硕士

【摘要】 贯流式紫铜风口小套是炼铁高炉的关键部件之一,主要作用是向高炉送热风和喷吹煤粉。风口小套的服役环境恶劣、易损坏失效。高温磨损和熔损是小套失效的主要形式。表面熔覆防护层是提高紫铜风口小套耐磨和抗熔损性能、延长其服役寿命的有效途径。本文研究了紫铜表面等离子熔覆高熵合金（FeCoNiCrTi）和FeCoNiCrTi/Ni60A防护层的制备工艺、耐磨性能和抗熔损性能,旨在为进一步改善紫铜风口小套表面覆层的防护性能提供支持。研究的主要结论如下:（1）在紫铜表面直接等离子熔覆FeCoNiCrTi高熵合金,优化参数下制备的FeCoNiCrTi熔覆层表面形成了厚度约891.5 nm的氧化膜（主要为Ti的氧化物）,其物相组成分别为FCC晶格的固溶体相、α-Mn结构的χ相和紧密填充的六方结构的Laves相。由于固溶强化和第二相强化作用,熔覆层的平均硬度是铜基体的13倍左右,不同区域的硬度呈阶梯式下降。但是,由于预热过程中铜表面生成氧化膜,导致高熵合金与之发生界面反应,FeCoNiCrTi熔覆层与铜基体的界面并不是整体连续的良好结合。（2）为了改善FeCoNiCrTi高熵合金与铜基体的界面连接,选择以Ni60A合金为过渡层、FeCoNiCrTi高熵合金为顶层,在紫铜表面等离子熔覆FeCoNiCrTi/Ni60A防护层。优化参数下制备的FeCoNiCrTi/Ni60A熔覆层表面形成了厚度696.1 nm的氧化膜（主要为Ti的氧化物）,界面结合较好,顶部为富含（Ti,Ni）的χ相、富含（Ti,Co）的Laves相和富含（Fe,Cr,Ni）的FCC相固溶体,中间过渡区为富含（Ti,Co）的Laves相、富含（Fe,Ni,Cr）的FCC固溶体、富含（Ti,Ni）的χ相、Cr₂₃C₆和Ti C,下部为γ-（Cu,Fe,Ni）固溶体、Cr B、Cr₂₃C₆和Ni₃Si。由于固溶强化和第二相强化作用,熔覆层顶部的平均硬度是铜基体的11倍左右,约为900 HV,过渡层Ni60A合金的平均硬度约为550 HV,下部由于铜基体的稀释导致硬度逐渐下降。（3）FeCoNiCrTi/Ni60A熔覆层在室温和高温下的耐磨性能都远高于铜基体。在25℃和300℃时FeCoNiCrTi/Ni60A熔覆层的耐磨性分别为铜基体的3.87倍和9.06倍。且随着温度的升高,耐磨性能的优势更加明显,铜基体在300℃即发生严重软化,磨损体积为1.97 mm³,而熔覆层在600℃和700℃时的磨损体积仅为0.15 mm³和0.439 mm³,由于氧化层的润滑,在600℃时熔覆层的耐磨性能达到最佳。在高温氧化与力的相互耦合作用下,FeCoNiCrTi/Ni60A熔覆层的磨损机制从磨粒磨损+黏着磨损转变为了氧化磨损+疲劳磨损。（4）FeCoNiCrTi/Ni60A熔覆层在450℃、550℃和650℃时都表现出较好的抗熔损性能。由于表面氧化膜的保护,表面未处理的熔覆层在450℃、550℃和650℃的预热温度下,仍未和熔融的铁块结合,表现出较强的抗熔损能力;由于熔覆层较高的熔点,表面已处理的熔覆层在450℃、550℃和650℃时被铁块侵蚀的深度仅为1.27μm,3.17μm和5.17μm,因此在外力作用下铁块很容易脱落,熔覆层表现出较好的抗熔损能力。更多还原

【Abstract】 The tubular copper tuyere sleeve is one of the key components of ironmaking blast furnace.Its main function is to supply hot air to blast furnace and inject pulverized coal.The service environment of the tuyere sleeve is harsh and easy to damage and fail.High temperature wear and melting loss are the main forms of sleeve failure.Surface cladding protective layer is an effective way to improve the wear resistance and melting loss resistance of copper tuyere sleeve and prolong its service life.In this paper,the preparation process,wear resistance and melting loss resistance of plasma cladding high-entropy alloy（FeCoNiCrTi）and FeCoNiCrTi/Ni60A protective layer on the surface of copper were studied,in order to provide support for further improving the protective performance of the surface copper tuyere.The main conclusions of the study are as follows:（1）FeCoNiCrTi high-entropy alloy was directly plasma cladded on the surface of copper.A layer of oxide film（mainly Ti oxide）with a thickness of about 891.5nm was formed on the surface of FeCoNiCrTi coating prepared under optimized parameters.The phase composition is the solid solution phase of FCC lattice,theχphase ofα-Mn structure and the Laves phase of hexagonal structure.Due to the solid solution strengthening and the second phase strengthening,the average hardness of the coating is about 13 times that of the copper matrix,and the hardness of different regions decreases step by step.However,due to the formation of an oxide film on the copper surface during the preheating process,resulting in an interfacial reaction between the high-entropy alloy and it,the interface between FeCoNiCrTi coating and the copper substrate is not a good combination of the whole continuous.（2）In order to improve the interface connection between FeCoNiCrTi high-entropy alloy and copper matrix,Ni60A alloy was selected as the transition layer and FeCoNiCrTi high-entropy alloy as the top layer,and FeCoNiCrTi/Ni60A protective layer was plasma clad on the surface of copper.An oxide film with a thickness of 696.1 nm（mainly Ti oxide）was formed on the surface of the FeCoNiCrTi/Ni60A cladding layer prepared under the optimized parameters,and the interface was well bonded.The top wasχphase rich in（Ti,Ni）,Laves phase rich in（Ti,Co）and FCC phase solid solution rich in（Fe,Cr,Ni）.The intermediate transition zone was Laves phase rich in（Ti,Co）,FCC solid solution rich in（Fe,Ni,Cr）,χphase rich in（Ti,Ni）,Cr₂₃C₆and Ti C.The lower part isγ-（Cu,Fe,Ni）solid solution,Cr B,Cr₂₃C₆and Ni₃Si.Due to the solid solution strengthening and the second phase strengthening,the average hardness of the top of the cladding layer is about 11 times that of the copper matrix,which is about 900 HV.The average hardness of the transition layer Ni60A alloy is about 550 HV,and the hardness of the lower part decreases gradually due to the dilution of the copper matrix.（3）The wear resistance of FeCoNiCrTi/Ni60A coating is much higher than that of copper substrate at room temperature and high temperature.At 25°C and 300°C,the wear resistance of FeCoNiCrTi/Ni60A coating is 3.87 times and 9.06 times that of copper matrix,respectively.With the increase of temperature,the advantage of wear resistance is more obvious.The copper matrix is severely softened at 300°C,and the wear volume is 1.97 mm³,while the wear volume of the coating at 600°C and 700°C is only 0.15 mm³and 0.439 mm³.Due to the lubrication of the oxide layer,the wear resistance of the coating is the best at 600°C.Under the coupling effect of high temperature oxidation and force,the wear mechanism of FeCoNiCrTi/Ni60 coating changed from abrasive wear+adhesive wear to oxidation wear+fatigue wear..（4）FeCoNiCrTi/Ni60A coating shows good resistance to melting loss at 450°C,550°C and 650°C.Due to the protection of the surface oxide film,the surface untreated coating is still not combined with the molten iron block at the preheating temperature of 450°C,550°C and 650°C,showing strong resistance to melting loss.Due to the high melting point of the coating,the depth of the surface treated coating eroded by the iron block at 450°C,550°C and 650°C is only 1.27μm,3.17μm and5.17μm.Therefore,the iron block is easy to fall off under the action of external force,and the coating shows good resistance to melting loss.更多还原