激光沉积TA15钛合金惰性气体局部保护研究

发布时间：2018-10-09 19:50

【摘要】：激光沉积制造技术(Laser Deposition Manufacturing,LDM)是以合金粉末为原料,通过高能量密度激光对合金粉末进行原位熔化,熔融状态的合金粉末快速凝固并逐层沉积来制造实体零件。该技术与传统制造技术相比具有其独特的优点:由于可实现近净成形从而节约材料,无需模具和专用夹具缩短生产周期而提高生产效率,且所沉积的合金试样具有优异的力学性能。但在钛合金零件制造过程中,由于钛合金粉末在熔融状态下具有高氧化和氮化倾向,因此惰性气体保护是保证其组织和力学性能具有至关重要的关键,为此本文进行了激光沉积制造TA15钛合金惰性气体保护研究。本文对惰性气体保护下激光沉积制造钛合金组织和力学性能进行了研究。首先,采用有限元FLUENT软件数值模拟了添加纵吹气帘对同轴送粉激光头粉末汇聚性的影响,并且搭建了惰性气体局部保护装置,模拟结果显示:纵吹气帘气压力为0.5MPa时汇聚性良好,且在焦点到焦点以下10mm的汇聚区进行激光沉积制造成形质量较好同时提高了粉末利用率。其次,对成形气氛中的氧含量对沉积制造的钛合金试样组织及力学性能的影响进行了研究,实验结果:在不同氧含量情况下,沉积态和退火态显微组织均呈现出典型的网篮组织。随着氧含量增加,合金的屈服强度和抗拉强度逐渐提高,而伸长率和断面收缩率总体呈下降趋势。氧含量保持在5×10-5以下,合金综合力学性能较好。断口形貌的断裂机制也随着氧含量增加由韧性断裂变化为半解理半韧性断裂。退火态的硬度比沉积态略低,随氧含量增加,退火态和沉积态硬度均逐渐提高。最后,对惰性气体局部保护与整体保护两种方式下激光沉积制造TA15钛合金试样的组织、拉伸性能和断口形貌进行了对比研究,对比试验结果显示局部保护方式下抗拉强度高于整体保护方式,但塑性远低于后者。并且对两种保护方式下不同取样方向上沉积态和退火态试样显微组织和力学性能的各向异性进行了研究。结果显示:力学性能存在方向上的各向异性,原因在于沉积方向和垂直沉积方向上的晶界数量的不同,不同的晶界数目造成晶界强化的效果不同。
[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.
【学位授予单位】：沈阳航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.23;TG665

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