發(fā)布時間：2018-04-25 03:06

  本文選題：Ti-6Al-4V合金 + 濕噴丸處理�。� 參考：《大連理工大學(xué)》2016年博士論文

【摘要】：Ti-6Al-4V合金因其具有比強(qiáng)度高和耐腐蝕等特點(diǎn),一直是生產(chǎn)航空渦輪發(fā)動機(jī)葉片的重要材料。然而,由于Ti-6Al-4V合金硬度低、抗疲勞性能差等缺點(diǎn)嚴(yán)重影響其航空工件的使用壽命。特別是渦輪葉片與壓氣機(jī)盤的榫頭—榫槽連接部位的微動磨損將大大降低鈦合金葉片的疲勞壽命。同時,這種微小幅度的損傷又具有極強(qiáng)的隱蔽性,常常會造成災(zāi)難的發(fā)生。隨著航空工業(yè)的飛速發(fā)展,微動損傷越來越引起人們的重視,并且航空工業(yè)對微動損傷防護(hù)方面的要求也越來越高。在微動損傷防護(hù)方面,噴丸處理技術(shù)以其成本低、易操作、效率高等優(yōu)點(diǎn)而成為目前航空領(lǐng)域最普遍的表面處理方法。本文利用濕噴丸技術(shù)對Ti-6Al-4V進(jìn)行表面強(qiáng)化處理,并對比分析濕噴丸表面強(qiáng)化對微動損傷及疲勞損傷的影響,綜合濕噴丸強(qiáng)化機(jī)制和微動損傷機(jī)制,系統(tǒng)地研究了濕噴丸強(qiáng)化作用對Ti-6Al-4V合金微動損傷的影響規(guī)律。主要研究內(nèi)容包括：(1)采用濕噴丸技術(shù)對Ti-6Al-4V合金進(jìn)行表面強(qiáng)化處理,利用XRD技術(shù)、納米壓痕技術(shù)、掃描電鏡以及透射電鏡技術(shù)對合金強(qiáng)化層的殘余應(yīng)力、硬度以及微觀組織進(jìn)行測試分析。結(jié)果表明,強(qiáng)化層的殘余壓應(yīng)力和硬度均隨深度增加而減小,影響深度分別為160和80μm。利用修正的硬度與屈服關(guān)系公式對Ti-6Al-4V合金濕噴丸強(qiáng)化層作了定量描述,計算表明,表層屈服強(qiáng)度由820 MPa提高至約1165 MPa并在0-80μm范圍內(nèi)線性降低。通過對強(qiáng)化層的微觀組織觀察探討了濕噴丸晶粒細(xì)化機(jī)制,并根據(jù)晶粒細(xì)化機(jī)制提出了殘余應(yīng)力的形成模型,即噴丸引起的殘余壓應(yīng)力是以晶粒之間未釋放的彈性能形式存在。(2) Ti-6A1-4V合金試樣的常規(guī)疲勞性能試驗(yàn)結(jié)果表明,濕噴丸處理能顯著提高Ti-6Al-4V合金的疲勞壽命。顯微組織觀察發(fā)現(xiàn),濕噴丸強(qiáng)化改變了疲勞裂紋萌生機(jī)制,強(qiáng)化層內(nèi)的細(xì)晶強(qiáng)化和位錯強(qiáng)化導(dǎo)致疲勞裂紋萌生位置由表面轉(zhuǎn)移至試樣內(nèi)部,同時,濕噴丸引入的殘余壓應(yīng)力對裂紋擴(kuò)展起到有效的阻礙作用。(3)通過微動磨損的對比試驗(yàn),研究濕噴丸處理對Ti-6Al-4V合金微動磨損行為的影響規(guī)律。結(jié)果表明,濕噴丸處理對Ti-6Al-4V合金在粘著狀態(tài)和滑移狀態(tài)時的微動磨損行為影響不明顯,但是在部分滑移狀態(tài)時,濕噴丸強(qiáng)化可以對微動磨痕內(nèi)塑性變形積累區(qū)的微裂紋萌生起到有效的阻止作用。通過計算,濕噴丸處理后強(qiáng)化層局部屈服強(qiáng)度的提高是防止局部疲勞損傷的主要因素。(4)利用自主設(shè)計的微動疲勞試驗(yàn)裝置進(jìn)行Ti-6Al-4V合金試樣的微動疲勞試驗(yàn)。與常規(guī)疲勞結(jié)果相比,濕噴丸處理對合金微動疲勞損傷的防護(hù)作用遠(yuǎn)高于常規(guī)疲勞損傷。通過顯微組織觀察,提出了濕噴丸處理前后試樣的微動疲勞失效機(jī)制,即未噴丸試樣微動區(qū)有局部疲勞微裂紋,出現(xiàn)裂紋尖端效應(yīng)；濕噴丸試樣微動區(qū)以磨損為主。濕噴丸強(qiáng)化層對微動區(qū)裂紋萌生的阻礙作用是導(dǎo)致試樣微動疲勞失效機(jī)制不同的主要原因。此外,殘余壓應(yīng)力的引入又能阻礙裂紋的擴(kuò)展。因此,濕噴丸處理對鈦合金微動疲勞抗性的提高是由強(qiáng)化層內(nèi)硬度的增加和殘余壓應(yīng)力的引入共同導(dǎo)致的。
[Abstract]:Because of its high specific strength and corrosion resistance, Ti-6Al-4V alloy has always been an important material for the production of aero turbine engine blades. However, the low hardness of the Ti-6Al-4V alloy and poor fatigue resistance have seriously affected the service life of its aeronautical workpiece. Dynamic wear will greatly reduce the fatigue life of titanium alloy blades. At the same time, this small amplitude damage is very strong concealment and often causes disaster. With the rapid development of the aviation industry, the microdynamic damage has attracted more and more attention, and the aviation industry is becoming more and more demanding on the protection of micro damage. With the advantages of low cost, easy operation and high efficiency, the shot peening technology has become the most common surface treatment method in the field of aviation. This paper uses wet shot peening technology to strengthen the surface of Ti-6Al-4V, and compares and analyzes the influence of the surface hardening of the wet shot peening on the microdynamic damage and fatigue damage. The strengthening mechanism of pellets and the mechanism of microdynamic damage have been studied systematically. The main contents of the study are as follows: (1) the surface hardening of Ti-6Al-4V alloys by wet shot peening technology, XRD technology, nano indentation, scanning electron microscopy and transmission electron microscopy are used to strengthen the alloy strength. The residual stress, hardness and microstructure of the layer are tested and analyzed. The results show that the residual compressive stress and hardness of the reinforced layer decrease with the depth, and the influence depth is 160 and 80 M. respectively. The quantitative description of the wet shot peening layer of Ti-6Al-4V alloy is made by the modified hardness and yield relation formula. The calculation shows that the surface yield can be yielded. The strength is increased from 820 MPa to about 1165 MPa and linearly decreased in the range of 0-80 mu m. The grain refinement mechanism of wet shot peening is discussed by observing the microstructure of the strengthened layer, and the formation model of residual stress is put forward according to the grain refinement mechanism, that is, the residual compressive stress caused by the shot peening is in the form of the unreleased elastic energy between the grains. (2) The normal fatigue test results of Ti-6A1-4V alloy specimens show that the fatigue life of Ti-6Al-4V alloy can be greatly improved by wet shot peening. The microstructure observation shows that wet shot peening has changed the mechanism of fatigue crack initiation, and the fine grain strengthening and dislocation strengthening in the strengthened layer lead to the migration of fatigue crack from the surface to the inside of the specimen. At the same time, the residual compressive stress introduced by the wet shot peening plays an effective hindrance to the crack propagation. (3) the effect of wet shot peening on the fretting wear behavior of Ti-6Al-4V alloy is studied by the contrast test of fretting wear. The results show that the wet shot peening treatment has the microdynamic wear behavior of the Ti-6Al-4V alloy in the adhesion and slip states. It is not obvious that the wet shot peening can effectively prevent the initiation of micro crack initiation in the plastic deformation accumulation area in the fretting wear. By calculation, the improvement of the local yield strength of the reinforced layer after the wet shot peening is the main factor to prevent the local fatigue damage. (4) the self designed micro fatigue test is used. The microdynamic fatigue test of Ti-6Al-4V alloy samples was carried out. Compared with the conventional fatigue results, the protective effect of wet shot peening on the microdynamic fatigue damage of the alloy was much higher than that of the conventional fatigue damage. The microdynamic fatigue failure mechanism of the specimens before and after the wet shot peening was observed. The crack tip effect occurs in the fatigue micro crack, and the fretting zone in the wet shot peening specimen is mainly worn. The hindering effect of the wet shot peening layer on the crack initiation in the microdynamic zone is the main cause of the microfatigue failure mechanism of the specimen. In addition, the introduction of the residual compressive stress can impede the expansion of the crack. The increase of fatigue resistance is caused by the increase of hardness in the strengthened layer and the introduction of residual compressive stress.

【學(xué)位授予單位】：大連理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG146.23;TG668

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