本文關(guān)鍵詞： 激光噴丸 深冷預處理 TC6鈦合金 殘余壓應力 高溫松弛　出處：《江蘇大學》2017年碩士論文　論文類型：學位論文

【摘要】：隨著TC6鈦合金在航空工業(yè)中用量的增加,因其疲勞斷裂引發(fā)的事故也日益突出,表面形變強化是抑制疲勞裂紋擴展,改善零部件使用壽命的有效方法。激光噴丸強化是一種新穎的表面形變強化技術(shù),其可在材料表層誘導產(chǎn)生高幅值殘余壓應力分布,然而在高溫服役條件下,殘余壓應力將產(chǎn)生松弛。為此,本文提出深冷預處理激光噴丸技術(shù),探索深冷處理結(jié)合高應變率形變強化改善殘余壓應力高溫穩(wěn)定性的機理和工藝。主要工作如下:(1)基于位錯強化理論、第二相強化理論、激光與材料相互作用誘導等離子體沖擊波理論和細晶強化理論,闡述深冷處理與激光噴丸過程中材料的強化機制;根據(jù)位錯滑移理論和蠕變理論闡釋殘余應力高溫松弛的宏觀機制,通過晶粒演變、位錯密度演變和析出相演變分析殘余應力高溫松弛的微觀機理。(2)開展深冷預處理激光噴丸的參數(shù)研究,進行不同工藝方法、參數(shù)下TC6試樣的表面完整性和力學性能測試。結(jié)果表明,C-0h-LP試樣和C-12h-LP試樣表面出現(xiàn)了明顯的晶粒細化,且斷口處的韌窩更大更深,但C-12h-LP試樣具有更高的表面硬度、殘余應力及拉伸強度;而C-18h試樣的硬度和強度雖然高于C-0h-LP試樣,但延伸率卻大幅下降,在其斷口中發(fā)現(xiàn)大量微觀組織結(jié)構(gòu)由亞穩(wěn)β相轉(zhuǎn)變成的穩(wěn)定α相,且在拉伸過程中被切割形成準解理面及解理臺階,表明C-18h試樣為脆性斷裂模式。分析確定了C-12h-LP為最佳工藝參數(shù)。(3)對C-12h-LP試樣和C-0h-LP試樣進行不同溫度、不同時間的高溫保持實驗并測量表層殘余應力,觀察表面顯微組織,隨后進行高溫拉伸試驗。研究發(fā)現(xiàn),400℃和600℃下,兩種試樣具有相當?shù)臍堄鄳Ψ�(wěn)定性;而500℃下,C-12h-LP試樣的殘余應力更穩(wěn)定。500℃下C-12h-LP和C-0h-LP試樣的晶粒長大緩慢,斷口中均出現(xiàn)強化相被切割而形成的準解理面,且C-12h-LP試樣中數(shù)量更多、分布更均勻。C-12h-LP工藝能在材料中誘導更高的位錯密度,增加了析出相在位錯線上的形核率,更多的析出相與位錯相互作用導致更大的位錯運動阻力,從而提高了殘余壓應力的穩(wěn)定性。
[Abstract]:With the increase of the amount of TC6 titanium alloy in aviation industry, the accidents caused by fatigue fracture become more and more serious, and the surface deformation strengthening is to restrain the fatigue crack growth. Laser shot peening is a novel surface deformation strengthening technique, which can induce high amplitude residual compressive stress distribution on the surface of the material. However, under the condition of high temperature service, laser shot peening is an effective method to improve the service life of parts. The residual compressive stress will be relaxed. In this paper, a cryogenic pretreatment laser shot peening technique is proposed. To explore the mechanism and process of cryogenic treatment combined with high strain rate deformation strengthening to improve the high temperature stability of residual compressive stress. The main work is as follows: (1) based on dislocation strengthening theory and second phase strengthening theory, The theory of plasma-shock wave induced by laser-material interaction and the theory of fine grain strengthening are discussed, and the strengthening mechanism of materials in the process of cryogenic treatment and laser shot peening is described. According to dislocation slip theory and creep theory, the macroscopic mechanism of residual stress relaxation at high temperature is explained. Microcosmic mechanism of high temperature relaxation of residual stress. (2) study on parameters of cryogenic pretreatment laser shot peening and different processing methods. The surface integrity and mechanical properties of TC6 samples were tested under the parameters. The results showed that the surface of C-0h-LP and C-12h-LP samples had obvious grain refinement, and the dimples at the fracture surface were larger and deeper, but the surface hardness of C-12h-LP specimens was higher than that of C-12h-LP specimens. The hardness and strength of C-18h specimen were higher than that of C-0h-LP sample, but the elongation of C-18h sample decreased significantly. In the fracture surface, a large number of microstructures were transformed from metastable 尾 phase to stable 偽 phase, while the hardness and strength of C-18h specimen were higher than that of C-0h-LP specimen. The quasi cleavage surface and cleavage step were formed during the tensile process, which indicated that the C-18h specimen was brittle fracture mode. C-12h-LP and C-0h-LP samples were analyzed and determined as the optimum process parameters. The temperatures of C-12h-LP and C-0h-LP samples were determined. The residual stress of the surface was measured and the microstructure of the surface was observed at different time, and then the tensile test was carried out at high temperature. It was found that the two samples had considerable residual stress stability at 400 鈩，

本文編號：1509049