【摘要】：鈦合金是當(dāng)前高性能制造產(chǎn)業(yè)中使用最多的耐高溫合金結(jié)構(gòu)材料。鈦合金常被用來(lái)制作航空發(fā)動(dòng)機(jī)上的葉片、壓氣機(jī)盤、渦輪盤等關(guān)鍵零部件,在發(fā)動(dòng)機(jī)的實(shí)際使用環(huán)境中,葉片等關(guān)鍵部件容易發(fā)生疲勞裂紋、疲勞斷裂以及表面腐蝕,因此改善鈦合金的結(jié)構(gòu)性能和抗腐能力具有重要意義。作為一種表面改性的高新技術(shù),激光沖擊能夠成功地優(yōu)化金屬的綜合力學(xué)特性,增強(qiáng)其耐腐蝕性。本文以TC11鈦合金為研究目標(biāo),通過(guò)激光沖擊、熱腐蝕、性能測(cè)試等實(shí)驗(yàn),證實(shí)了激光沖擊(LSP)增強(qiáng)TC11鈦合金力學(xué)性能以及耐熱腐蝕能力的可行性,分析總結(jié)了強(qiáng)化機(jī)理和耐腐蝕增強(qiáng)的機(jī)理。論文的研究?jī)?nèi)容及結(jié)論如下:(1)分析了激光沖擊波從保護(hù)層、約束層再到金屬表面的能量轉(zhuǎn)化和沖擊作用過(guò)程,通過(guò)理論分析和推導(dǎo),優(yōu)化了強(qiáng)化處理TC11鈦合金的實(shí)驗(yàn)參數(shù)。(2)探究了不同沖擊次數(shù)作用下,TC11鈦合金的表面殘余應(yīng)力、截面殘余應(yīng)力、表面粗糙度、三維形貌及顯微硬度等力學(xué)性能的變化。闡述了沖擊強(qiáng)化改善合金綜合力學(xué)性能的原理。研究結(jié)果表明:經(jīng)過(guò)強(qiáng)化處理后,殘余壓應(yīng)力的最大測(cè)量值出現(xiàn)在材料最上層,強(qiáng)化的次數(shù)越多,影響層越深;強(qiáng)化的次數(shù)達(dá)到某一數(shù)值后,激光沖擊對(duì)顯微硬度的影響削弱;強(qiáng)化次數(shù)增加,合金表面的凹痕加深,導(dǎo)致粗糙度值變大。(3)研究了激光沖擊后TC11鈦合金內(nèi)部位錯(cuò)運(yùn)動(dòng)及晶粒細(xì)化的過(guò)程。結(jié)果表明:激光沖擊后表面發(fā)生塑性變形,分布不均勻的位錯(cuò)會(huì)不斷繁殖,由于位錯(cuò)之間的相互作用就會(huì)形成位錯(cuò)纏結(jié)、位錯(cuò)胞、位錯(cuò)墻等位錯(cuò)結(jié)構(gòu)。位錯(cuò)運(yùn)動(dòng)繼續(xù)發(fā)展,會(huì)繼續(xù)演化為亞晶界,新的組織結(jié)構(gòu)會(huì)切割原始的晶粒組織,使晶粒逐漸被細(xì)化,直到內(nèi)部能量穩(wěn)定后,晶粒細(xì)化完成。(4)討論了腐蝕溫度和持續(xù)時(shí)間對(duì)熱腐蝕性能的影響,并證實(shí)了沖擊處理增強(qiáng)TC11鈦合金的耐熱腐蝕性的有效性。實(shí)驗(yàn)結(jié)果表明:激光沖擊后,TC11鈦合金熱腐蝕過(guò)程的孕育期增長(zhǎng),合金的失重加速度減小;熱腐蝕過(guò)程中會(huì)形成氧化層和腐蝕層。激光沖擊后,表面氧化層更加緊密完整,腐蝕表面的裂紋、凹坑和剝落得到了抑制;隨著持續(xù)時(shí)間或腐蝕溫度的增加,不僅表面腐蝕加劇,而且出現(xiàn)嚴(yán)重的表面裂紋、凹坑和脫落。(5)研究了TC11鈦合金的熱腐蝕形貌變化及激光沖擊增強(qiáng)其耐腐蝕性的機(jī)理。研究結(jié)果表明:熱腐蝕現(xiàn)象是氧化膜從產(chǎn)生到出現(xiàn)裂紋、凹坑,最終脫落的一個(gè)過(guò)程。激光沖擊后,產(chǎn)生的殘余壓應(yīng)力可以減少裂紋的產(chǎn)生,增加氧化物與基體表面的粘附力,減少應(yīng)力腐蝕,防止腐蝕加劇;合金內(nèi)部的位錯(cuò)運(yùn)動(dòng)使內(nèi)部的晶粒組織不斷被分割細(xì)化,生成大量的細(xì)晶組織。位錯(cuò)運(yùn)動(dòng)產(chǎn)生的內(nèi)部缺陷和晶粒細(xì)化提高了合金的力學(xué)性能及表面結(jié)構(gòu)穩(wěn)定性,使腐蝕過(guò)程中生成的氧化物均勻緊密,可塑性增強(qiáng),從而提高抗腐蝕性能。
[Abstract]:Titanium alloy is the most widely used high-temperature alloy structural material in high-performance manufacturing industry. Titanium alloy is often used to make the key parts such as blade, compressor disk, turbine disk and so on the aero-engine. In the actual service environment of the engine, the key parts such as blade are prone to fatigue crack, fatigue fracture and surface corrosion. Therefore, it is of great significance to improve the structural properties and corrosion resistance of titanium alloys. As a new technology of surface modification, laser impact can successfully optimize the comprehensive mechanical properties of metals and enhance their corrosion resistance. In this paper, TC11 titanium alloy is taken as the research object, and the feasibility of enhancing the mechanical properties and thermal corrosion resistance of TC11 titanium alloy by laser shock (LSP) is proved by the experiments of laser shock, hot corrosion and property test, etc. The strengthening mechanism and the mechanism of corrosion resistance enhancement are analyzed and summarized. The research contents and conclusions are as follows: (1) the energy conversion and impact process of laser shock wave from protective layer, confinement layer to metal surface are analyzed. The experimental parameters of strengthening TC11 titanium alloy were optimized. (2) the changes of surface residual stress, cross-section residual stress, surface roughness, 3D morphology and microhardness of TC11 titanium alloy under different impact times were investigated. The principle of improving the comprehensive mechanical properties of the alloy by impact strengthening is described. The results show that the maximum measurement value of residual compressive stress appears at the top of the material after strengthening treatment, the more times of strengthening, the deeper the influence layer is, and the effect of laser impact on microhardness is weakened when the number of strengthening times reaches a certain value. With the increase of strengthening times, the indentation on the surface of the alloy becomes deeper, which leads to the increase of roughness value. (3) the dislocation motion and grain refinement process of TC11 titanium alloy after laser shock are studied. The results show that plastic deformation occurs on the surface after laser shock, and dislocations with uneven distribution will continue to propagate. Dislocation entanglement, dislocation cell, dislocation wall and other dislocation structures will be formed due to the interaction between dislocations. The dislocation motion will continue to evolve into the subcrystalline boundary, and the new structure will cut the original grain structure, so that the grain will be refined gradually until the internal energy is stable. (4) the effects of corrosion temperature and duration on the thermal corrosion properties were discussed, and the effectiveness of impact treatment to enhance the thermal corrosion of TC11 titanium alloy was confirmed. The experimental results show that the incubation period of hot corrosion process of TC11 titanium alloy increases and the acceleration of weight loss decreases after laser shock, and the oxide layer and corrosion layer will be formed during the hot corrosion process. After laser shock, the oxide layer on the surface becomes more compact and complete, and the cracks, pits and spalling of the corroded surface are restrained. With the increase of the duration or the corrosion temperature, not only the surface corrosion intensifies, but also serious surface cracks, pits and shedding occur. (5) the thermal corrosion morphology of TC11 titanium alloy and the mechanism of laser shock strengthening its corrosion resistance are studied. The results show that the hot corrosion is a process from the appearance of oxide film to the appearance of cracks, pits and finally falling off. After laser shock, the residual compressive stress can reduce the occurrence of cracks, increase the adhesion between oxide and matrix surface, reduce stress corrosion and prevent corrosion. The dislocation movement in the alloy makes the grain structure of the alloy continuously divided and refined, resulting in a large number of fine grain structure. The internal defects and grain refinement caused by dislocation movement can improve the mechanical properties and surface structure stability of the alloy, make the oxide formed in the corrosion process uniform and compact, enhance the plasticity and improve the corrosion resistance.
【學(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG146.23;TG665

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