离心压缩机叶片变性层对再制造的影响及去除研究

发布时间：2018-08-16 13:38

【摘要】：在西气东输工程中,管线中的离心压缩机叶轮在服役一段时间以后表面层的状态发生了改变,已经完全不同于原始状态,形成变性层,影响压缩机的性能。因为其叶轮尺寸较大更换困难,直接报废又将造成极大资源浪费,因此通常对其进行再制造。然而变性层的存在会对再制造过程产生一定的影响,因此,揭示毛坯变性层对再制造的影响原因和规律以及表面变性层的改善和去除方法对后续的再制造过程是非常必要的。本论文利用高温高压反应釜模拟叶片工作环境,制备了不同厚度的变性层,研究了不同厚度变性层对后续再制造的影响以及弧斑等离子体技术变性层的改善去除的机理及工艺。利用金相、SEM、EDS等手段分析涂层的组织结构变化,利用显微硬度、ansys分析等方法分析涂层的力学性能；最后利用弧斑等离子体设备对表面的变性层进行改善和清理,利用示波器将弧斑等离子体处理过程中的电压电流信号导出并分析,利用SEM、3D形貌仪等设备对处理后的试样表面形貌进行分析,探讨了弧斑等离子体技术去除变性层的机理及实验过程中某些现象的原因。实验结果表明：随着反应时间增长,变性层逐渐增厚并最终分为两层,其对再制造的影响也越来越明显,保温120 h后制得的变性层试样经等离子喷焊后,涂层结合截面处存在大量的硫化物夹杂和尺寸在0.5-1.5mm的孔洞且焊道较窄表面灰暗,用ansys模拟加载叶片所受应力后,这些部位将产生较大的应力集中,在叶片所受的高周循环应力作用下,有很大可能会产生疲劳裂纹。经弧斑等离子体处理后试样表面露出金属光泽,EDS点扫描的结果显示,表面的硫化物已基本去除,达到了实验的目的。利用玻恩-哈伯循环计计算出弧斑范围内硫化物蒸发所需要的能量,比电弧投入弧斑的能量小得多,弧斑的能量足以使表面硫化物蒸发。在处理120 h硫化后的试样表面时,在处理的最后阶段出现了电压的小幅增加,这对应于硫化膜的分层现象,内层的Cr的硫化物的电子逸出功比表面的Fe的硫化物的大。将该电压信号与处理氧化物得到的电压信号对比发现,处理硫化物时的电压高约2V,这是由于氧化物属于n型半导体,具有稍低的电子逸出功。实验时电路电流的增大将导致弧斑数量的增多,处理速率加快。但是电流的增大并不会导致弧斑的电流密度增大,不会对处理后试样的表面形貌产生较大影响。变性层厚度的不同将对处理后的表面形貌产生影响,厚度越大,处理后表面的粗糙度就越大。
[Abstract]:In the West-to-East Gas Transmission Project, the condition of the surface layer of the centrifugal compressor impeller in the pipeline has changed after a period of service, which is completely different from the original state, forming a denatured layer, which affects the performance of the compressor. Because it is difficult to replace the impeller size directly, it will cause great waste of resources, so it is usually remanufactured. However, the existence of denatured layer will have a certain impact on the process of remanufacturing. Therefore, it is necessary to reveal the causes and rules of the influence of the denatured layer on the remanufacturing process and the improvement and removal methods of the surface denatured layer for the subsequent remanufacturing process. In this paper, different thickness denaturation layers were prepared by simulating the blade working environment in a high temperature and high pressure reactor. The effects of different denaturation layers on subsequent remanufacturing and the mechanism and process of improving the removal of the denatured layer by arc spot plasma technology were studied. The microstructure changes of the coatings were analyzed by means of metallographic analysis, SEM EDS, microhardness analysis and so on, and the mechanical properties of the coatings were analyzed by means of microhardness analysis, and the surface denatured layer was improved and cleaned by arc spot plasma equipment. The voltage and current signals during arc spot plasma treatment are derived and analyzed by oscilloscope, and the surface morphology of the treated samples is analyzed by means of SEMN 3D profilometer, etc. The mechanism of removal of denatured layer by arc spot plasma and the causes of some phenomena in the experiment are discussed. The experimental results show that with the increase of reaction time, the denatured layer is gradually thickened and finally divided into two layers, and the effect on the remanufacturing is more and more obvious. The sample of denatured layer prepared after 120 hours of heat preservation is welded by plasma spray welding. There are a large number of sulphide inclusions in the bonding section of the coating, and the size is in the hole of 0.5-1.5mm and the narrow surface of the welding pipe is dark. After the stress of the blade is simulated by ansys, the stress concentration will be greater in these parts. Fatigue cracks are likely to occur under the high cycle cyclic stress of the blade. The results of EDS spot scanning show that the sulfides on the surface have been basically removed and the purpose of the experiment has been achieved. The energy needed for sulphide evaporation in the range of arc spot is calculated by using the Bowen-Hubble cycle, which is much smaller than that put into arc spot by arc spot, and the energy of arc spot is enough to vaporize the surface sulfide. When the sample surface was treated for 120 h, the voltage increased slightly at the last stage of treatment, which corresponds to the delamination of the vulcanization film. The electron escape power of the inner Cr sulfide is larger than that of the Fe sulfide on the surface. By comparing this voltage signal with the voltage signal obtained by processing oxide, it is found that the voltage of sulfide treatment is about 2 V, which is due to the fact that the oxide belongs to n-type semiconductor and has lower electron escape power. The increase of circuit current will lead to the increase of the number of arcs and the speed of processing. However, the increase of current does not lead to an increase in the current density of the arc spot, and will not have a significant effect on the surface morphology of the treated samples. The different thickness of the denatured layer will affect the morphology of the treated surface, and the greater the thickness, the greater the roughness of the treated surface.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TH452

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