低真空激光熔覆沉积系统设计及强制水冷对TC4合金熔覆组织影响的研究

发布时间：2018-05-05 22:36

本文选题：TC4合金粉末 + 激光熔覆沉积　；参考：《石家庄铁道大学》2017年硕士论文

【摘要】：钛合金高的比强度、优异的耐腐蚀性、良好的耐热性使其广泛应用于航空、航天、船舶等领域。但是,钛合金高温下会与氧气剧烈反应,需要为激光熔覆沉积成形过程提供惰性气体保护。本文设计了一套适用于TC4合金粉末激光熔覆成形的真空系统,基于此系统采用数值模拟与实验相结合的方法研究了基板强制水冷对成形件组织的影响。首先,设计了一种低真空成形环境并完成系统搭建,开发了一款LCD成形软件,实现三维平台的自动化控制,为TC4合金粉末的激光熔覆沉积成形提供一套成形平台。然后,分别采用正交实验法、单因素变量成形实验法对TC4合金粉末进行了激光单道、多道成形工艺实验研究,得到优化的工艺参数为:激光功率600 W,扫描速度5 mm/s,送粉速率4.3 g/min,搭接率为30%。利用最优的工艺参数,进行实体零件成形,并对其内部氧含量及拉伸性能进行了检测,检测结果为:真空室内成形件的内部氧含量比惰性气体保护下的成形件下降了48%;随着成形件氧含量的增加,抗拉强度和屈服强度得到提高,而延伸率降低了59.3%;不同气氛保护下的成形件抗拉强度相差不大,但均高出基体(910 MPa)35%左右,屈服强度均高出基体(850MPa)38%左右。说明实验用真空系统对成形件内部氧含量控制有效。最后,使用ANSYS有限元软件模拟了基板不同对流换热系数下TC4合金激光熔覆沉积过程中温度场变化。得出:从熔池底部到熔池顶部,温度梯度不断降低;对基板设置高的对流换热系数会增大熔池凝固时的温度梯度,熔池底部尤为显著,温度梯度方向有向平行于沉积方向转变的趋势,成形件内部的冷却速率也会增大。利用优化的工艺参数在真空系统中进行成形实验,研究基板强制水冷对成形件组织的影响。得出:TC4激光熔覆沉积试样组织为贯穿整个试样呈外延生长的粗大柱状晶。但对基板施加强制水冷后,成形件中沿垂直基板方向的β柱状晶能获得更大竞争优势而持续生长,因受到层间单道熔覆的影响,组织由魏氏组织变为网篮状组织。实验结果与模拟结果较为接近,为后续微观组织“控性”研究打下了良好的基础。
[Abstract]:Titanium alloy has high specific strength, excellent corrosion resistance and good heat resistance, which makes it widely used in aviation, aerospace, ship and other fields. However, titanium alloys react strongly with oxygen at high temperature, so it is necessary to provide inert gas protection for laser cladding deposition. A vacuum system suitable for laser cladding forming of TC4 alloy powder is designed in this paper. Based on this system, the effect of forced water cooling on the microstructure of forming parts is studied by means of numerical simulation and experiment. Firstly, a low vacuum forming environment is designed and the system is built. A LCD forming software is developed to realize the automatic control of 3D platform, which provides a forming platform for laser cladding deposition of TC4 alloy powder. Then, the single pass and multi-pass laser forming experiments of TC4 alloy powder were carried out by orthogonal experiment and single factor variable forming method, respectively. The optimized technological parameters are as follows: laser power 600 W, scanning speed 5 mm / s, powder feeding rate 4.3 g / min, lap ratio 30g / min. The optimum process parameters are used to form the solid parts, and the oxygen content and tensile properties of the parts are tested. The results are as follows: the oxygen content of the forming parts in the vacuum chamber is decreased by 48% than that of the formed parts under the protection of inert gas, and the tensile strength and yield strength are increased with the increase of the oxygen content of the formed parts. The tensile strength of the formed parts under different atmosphere protection is similar, but the tensile strength is about 35% higher than that of the matrix (910 MPA), and the yield strength is about 38% higher than that of the matrix. The results show that the vacuum system used in the experiment is effective in controlling the oxygen content in the forming parts. Finally, the variation of temperature field during laser cladding deposition of TC4 alloy under different convection heat transfer coefficients of substrate was simulated by ANSYS finite element software. From the bottom of the molten pool to the top of the pool, the temperature gradient decreases continuously, and the high convection heat transfer coefficient of the substrate increases the temperature gradient of the molten pool during solidification, especially at the bottom of the molten pool. The temperature gradient direction changes to the direction parallel to the deposition direction, and the cooling rate increases. The effect of forced water cooling on the microstructure of the formed parts was studied by using the optimized process parameters in the vacuum system. It is found that the microstructure of the sample deposited by the laser cladding of the W TC4 is a coarse columnar crystal with epitaxial growth through the whole sample. However, the 尾 columnar crystals along the vertical direction of the substrate can gain greater competitive advantage and continue to grow after forced water cooling on the substrate. Due to the influence of interlaminar single pass cladding, the microstructure changes from Weiss structure to netted structure. The experimental results are close to those of the simulation results, which lays a good foundation for the further study on the "controllability" of microstructures.
【学位授予单位】：石家庄铁道大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG665;TG146.23

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