【摘要】：激光沉積制造技術(shù)(Laser Deposition Manufacturing,LDM)是以合金粉末為原料,通過高能量密度激光對合金粉末進(jìn)行原位熔化,熔融狀態(tài)的合金粉末快速凝固并逐層沉積來制造實(shí)體零件。該技術(shù)與傳統(tǒng)制造技術(shù)相比具有其獨(dú)特的優(yōu)點(diǎn):由于可實(shí)現(xiàn)近凈成形從而節(jié)約材料,無需模具和專用夾具縮短生產(chǎn)周期而提高生產(chǎn)效率,且所沉積的合金試樣具有優(yōu)異的力學(xué)性能。但在鈦合金零件制造過程中,由于鈦合金粉末在熔融狀態(tài)下具有高氧化和氮化傾向,因此惰性氣體保護(hù)是保證其組織和力學(xué)性能具有至關(guān)重要的關(guān)鍵,為此本文進(jìn)行了激光沉積制造TA15鈦合金惰性氣體保護(hù)研究。本文對惰性氣體保護(hù)下激光沉積制造鈦合金組織和力學(xué)性能進(jìn)行了研究。首先,采用有限元FLUENT軟件數(shù)值模擬了添加縱吹氣簾對同軸送粉激光頭粉末匯聚性的影響,并且搭建了惰性氣體局部保護(hù)裝置,模擬結(jié)果顯示:縱吹氣簾氣壓力為0.5MPa時匯聚性良好,且在焦點(diǎn)到焦點(diǎn)以下10mm的匯聚區(qū)進(jìn)行激光沉積制造成形質(zhì)量較好同時提高了粉末利用率。其次,對成形氣氛中的氧含量對沉積制造的鈦合金試樣組織及力學(xué)性能的影響進(jìn)行了研究,實(shí)驗結(jié)果:在不同氧含量情況下,沉積態(tài)和退火態(tài)顯微組織均呈現(xiàn)出典型的網(wǎng)籃組織。隨著氧含量增加,合金的屈服強(qiáng)度和抗拉強(qiáng)度逐漸提高,而伸長率和斷面收縮率總體呈下降趨勢。氧含量保持在5×10-5以下,合金綜合力學(xué)性能較好。斷口形貌的斷裂機(jī)制也隨著氧含量增加由韌性斷裂變化為半解理半韌性斷裂。退火態(tài)的硬度比沉積態(tài)略低,隨氧含量增加,退火態(tài)和沉積態(tài)硬度均逐漸提高。最后,對惰性氣體局部保護(hù)與整體保護(hù)兩種方式下激光沉積制造TA15鈦合金試樣的組織、拉伸性能和斷口形貌進(jìn)行了對比研究,對比試驗結(jié)果顯示局部保護(hù)方式下抗拉強(qiáng)度高于整體保護(hù)方式,但塑性遠(yuǎn)低于后者。并且對兩種保護(hù)方式下不同取樣方向上沉積態(tài)和退火態(tài)試樣顯微組織和力學(xué)性能的各向異性進(jìn)行了研究。結(jié)果顯示:力學(xué)性能存在方向上的各向異性,原因在于沉積方向和垂直沉積方向上的晶界數(shù)量的不同,不同的晶界數(shù)目造成晶界強(qiáng)化的效果不同。
[Abstract]:Laser deposition technology (Laser Deposition Manufacturing,LDM) is used to fabricate solid parts from alloy powder by in-situ melting of alloy powder with high energy density laser and rapid solidification and layer by layer deposition of alloy powder in molten state. Compared with the traditional manufacturing technology, this technology has its unique advantages: it can realize near-net forming and save materials, and improve the production efficiency without shortening the production cycle of die and special fixture. The deposited alloy samples have excellent mechanical properties. However, due to the high tendency of oxidation and nitridation of titanium alloy powder in melting state, inert gas protection is the key to ensure the microstructure and mechanical properties of titanium alloy parts. In this paper, the inert gas protection of TA15 titanium alloy by laser deposition has been studied. In this paper, the microstructure and mechanical properties of titanium alloy prepared by laser deposition under inert gas protection have been studied. Firstly, the influence of adding longitudinal blowing curtain on the powder convergence of coaxial powder feeding laser head is simulated by finite element FLUENT software, and the local protection device of inert gas is built. The simulation results show that the convergent property is good when the pressure of longitudinal blowing curtain gas is 0.5MPa, and the laser deposition forming quality is better in the convergent region of 10mm from focus to focus, and the utilization ratio of powder is improved at the same time. Secondly, the effect of oxygen content in the forming atmosphere on the microstructure and mechanical properties of titanium alloy samples prepared by deposition was studied. Both deposited and annealed microstructures show typical baskets. With the increase of oxygen content, the yield strength and tensile strength of the alloy increase gradually, while the elongation and the shrinkage of the section decrease as a whole. When oxygen content is kept below 5 脳 10 ~ (- 5), the comprehensive mechanical properties of the alloy are better. The fracture mechanism of fracture morphology changes from ductile fracture to semi-cleavage and semi-ductile fracture with the increase of oxygen content. The hardness of annealed state is slightly lower than that of deposited state, and the hardness of annealed and deposited state increases gradually with the increase of oxygen content. Finally, the microstructure, tensile properties and fracture morphology of TA15 titanium alloy samples fabricated by laser deposition under the two modes of inert gas local protection and integral protection were compared. The results show that the tensile strength of the local protection is higher than that of the whole protection, but the plasticity is much lower than that of the latter. The anisotropy of microstructure and mechanical properties of deposited and annealed samples in different sampling directions were also studied. The results show that anisotropy exists in the direction of mechanical properties because the number of grain boundaries in deposition direction and vertical direction is different and the effect of grain boundary strengthening is different with different number of grain boundaries.
【學(xué)位授予單位】：沈陽航空航天大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG146.23;TG665

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