TZM合金电子束焊接头组织与性能研究

发布时间：2018-06-03 16:01

  本文选题：TZM合金 + 电子束焊接　； 参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：TZM合金作为一种最有前途的钼合金,具有弹性模量高、蒸气压低、抗蚀性强以及高温力学性能良好的特点,因此在航空航天、核电等领域得到了广泛的应用。本文为满足TZM合金高温下的连接需求,研究了不同的焊接工艺对接头组织及性能的影响,揭示了焊接接头的组织转变及接头脆化的机理。分析了焊缝中沉淀相的形成对TZM合金接头力学性能的影响,并提出了焊缝冶金元素调控的新方法。首先进行了TZM合金对接试验的有限元数值模拟,研究了不同的焊接工艺参数对接头温度场及应力场的影响,确定了电子束焊接工艺参数范围。采用该参数范围进行焊接工艺试验,研究了电子束焊接工艺参数对接头表面成形及力学性能的影响。得出了试验条件下优化的工艺参数:聚焦束流为581m A,焊接速度为350mm/min,焊接束流为35m A。该参数下的焊接接头强度为403MPa。由组织分析的结果可知,TZM合金电子束焊缝区晶界容易富集低熔点的Mo O_2及Ti O_2,而沉淀相在晶界上的偏析会造成晶界上共格关系的改变,进而引起晶界处的应力集中,在应力加载过程中造成焊缝区沿晶断裂的产生。而Zr O_2及Mo2C在焊缝晶粒内的弥散强化,使焊缝区硬度高于热影响的硬度。采用Ti作为焊缝冶金调控元素时,接头的抗拉强度无明显提升。向焊缝中添加适量的Zr元素时,Zr元素会优先与O元素发生反应,生成高熔点的Zr O_2弥散分布于焊缝晶粒内部。因此焊缝区晶界得到净化,晶界上应力集中得到缓解。接头的断裂形式由解理与沿晶断裂的混合断裂形式转变为完全的解理断裂,接头的抗拉强度提高到452MPa。进行添加Re中间层的TZM合金电子束焊接试验,焊接接头的抗拉强度随焊缝中Re元素的增加而提高。这主要是由添加Re元素后,富铼相在晶界附近聚集,提高晶界结合能力,抑制了接头沿晶断裂的发生。并且在焊缝区的晶粒内部形成大量的小角度晶界,提高了位错开动的门槛值,阻止焊缝区穿晶裂纹的形成。因此,当焊缝区Re元素的质量分数为48.7%时,接头的抗拉强度达到524MPa,焊接接头在热影响区产生断裂。
[Abstract]:As one of the most promising molybdenum alloys, TZM alloy has been widely used in aerospace, nuclear power and other fields because of its high modulus of elasticity, low vapor pressure, strong corrosion resistance and good mechanical properties at high temperature. In order to meet the requirements of TZM alloy joining at high temperature, the effect of different welding processes on the microstructure and properties of the joint was studied, and the mechanism of microstructure transformation and embrittlement of the welded joint was revealed. The influence of precipitate phase formation on the mechanical properties of TZM alloy joint was analyzed, and a new method for adjusting metallurgical elements of weld metal was proposed. Firstly, the finite element numerical simulation of TZM alloy docking test was carried out. The influence of different welding parameters on the temperature field and stress field of the joint was studied, and the range of electron beam welding parameters was determined. The effects of electron beam welding parameters on the surface forming and mechanical properties of the joints were studied. The optimized process parameters are obtained as follows: the focused beam is 581m A, the welding speed is 350 mm / min, and the welding beam current is 35 Ma. The strength of welded joint under this parameter is 403 MPA. The results of microstructure analysis show that the grain boundary of electron beam weld zone of TZM alloy is easy to enrich Mo / O _ 2 and TIO _ 2 with low melting point, while segregation of precipitated phase at grain boundary will result in the change of coherent relation at grain boundary, which will lead to stress concentration at grain boundary. The intergranular fracture occurred in the weld zone during stress loading. However, the diffusion strengthening of Zr O _ 2 and Mo2C in the weld grain makes the hardness of weld zone higher than that of heat-affected. When Ti is used as the adjusting element of weld metal, the tensile strength of the joint does not increase obviously. When the proper amount of Zr element is added to the weld, the Zr element will react with O element in priority, and the high melting point Zr O _ 2 will be distributed in the weld grain. Therefore, the grain boundary in the weld zone is purified and the stress concentration at the grain boundary is alleviated. The fracture form of the joint changed from the mixed fracture form of cleavage and intergranular fracture to the complete cleavage fracture, and the tensile strength of the joint was increased to 452 MPA. The electron beam welding test of TZM alloy with re interlayer was carried out. The tensile strength of the welded joint increased with the increase of re element in the weld. This is mainly due to the accumulation of rhenium rich phase near grain boundary after the addition of re element, which improves the binding capacity of grain boundary and inhibits the occurrence of intergranular fracture of the joint. In addition, a large number of small angle grain boundaries are formed in the grain interior of the weld zone, which increases the threshold of dislocation starting and prevents the formation of transgranular cracks in the weld zone. Therefore, when the mass fraction of re in the weld zone is 48.7, the tensile strength of the joint reaches 524 MPA, and the welded joint breaks in the heat-affected zone.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407
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本文编号：1973362