【摘要】：在西氣東輸工程中,管線中的離心壓縮機(jī)葉輪在服役一段時間以后表面層的狀態(tài)發(fā)生了改變,已經(jīng)完全不同于原始狀態(tài),形成變性層,影響壓縮機(jī)的性能。因為其葉輪尺寸較大更換困難,直接報廢又將造成極大資源浪費,因此通常對其進(jìn)行再制造。然而變性層的存在會對再制造過程產(chǎn)生一定的影響,因此,揭示毛坯變性層對再制造的影響原因和規(guī)律以及表面變性層的改善和去除方法對后續(xù)的再制造過程是非常必要的。本論文利用高溫高壓反應(yīng)釜模擬葉片工作環(huán)境,制備了不同厚度的變性層,研究了不同厚度變性層對后續(xù)再制造的影響以及弧斑等離子體技術(shù)變性層的改善去除的機(jī)理及工藝。利用金相、SEM、EDS等手段分析涂層的組織結(jié)構(gòu)變化,利用顯微硬度、ansys分析等方法分析涂層的力學(xué)性能；最后利用弧斑等離子體設(shè)備對表面的變性層進(jìn)行改善和清理,利用示波器將弧斑等離子體處理過程中的電壓電流信號導(dǎo)出并分析,利用SEM、3D形貌儀等設(shè)備對處理后的試樣表面形貌進(jìn)行分析,探討了弧斑等離子體技術(shù)去除變性層的機(jī)理及實驗過程中某些現(xiàn)象的原因。實驗結(jié)果表明：隨著反應(yīng)時間增長,變性層逐漸增厚并最終分為兩層,其對再制造的影響也越來越明顯,保溫120 h后制得的變性層試樣經(jīng)等離子噴焊后,涂層結(jié)合截面處存在大量的硫化物夾雜和尺寸在0.5-1.5mm的孔洞且焊道較窄表面灰暗,用ansys模擬加載葉片所受應(yīng)力后,這些部位將產(chǎn)生較大的應(yīng)力集中,在葉片所受的高周循環(huán)應(yīng)力作用下,有很大可能會產(chǎn)生疲勞裂紋。經(jīng)弧斑等離子體處理后試樣表面露出金屬光澤,EDS點掃描的結(jié)果顯示,表面的硫化物已基本去除,達(dá)到了實驗的目的。利用玻恩-哈伯循環(huán)計計算出弧斑范圍內(nèi)硫化物蒸發(fā)所需要的能量,比電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發(fā)。在處理120 h硫化后的試樣表面時,在處理的最后階段出現(xiàn)了電壓的小幅增加,這對應(yīng)于硫化膜的分層現(xiàn)象,內(nèi)層的Cr的硫化物的電子逸出功比表面的Fe的硫化物的大。將該電壓信號與處理氧化物得到的電壓信號對比發(fā)現(xiàn),處理硫化物時的電壓高約2V,這是由于氧化物屬于n型半導(dǎo)體,具有稍低的電子逸出功。實驗時電路電流的增大將導(dǎo)致弧斑數(shù)量的增多,處理速率加快。但是電流的增大并不會導(dǎo)致弧斑的電流密度增大,不會對處理后試樣的表面形貌產(chǎn)生較大影響。變性層厚度的不同將對處理后的表面形貌產(chǎn)生影響,厚度越大,處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.
【學(xué)位授予單位】：合肥工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TH452

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