锆合金交叉结构脉冲激光点焊特性及焊点氧化膜生长机制

发布时间：2018-03-22 17:30

本文选题：锆合金交叉焊点　切入点：多脉冲激光点焊　出处：《哈尔滨工业大学》2016年博士论文　论文类型：学位论文

【摘要】：锆合金格架是核反应堆芯中的重要组件,其制备技术及服役过程中耐腐蚀性是实现高燃耗的关键因素。锆合金化学性质活泼,焊接过程中对气氛中水氧非常敏感,因此格架焊接需在充氩舱中进行,但是多焊点连续焊接过程中舱室内热量和烟尘排出是保证焊点质量的首要问题。此外,为避免磨损燃料棒及降低冷却介质的压降差,需严格控制格架中交叉焊点的尺寸。更为关键的是,激光焊接后焊点的组织与锆合金母材相比差异较大,焊点的耐腐蚀性成为制约格架服役性能的关键因素。本文针对锆合金格架结构,开展锆合金交叉焊点多脉冲激光点焊工艺及焊点氧化膜生长机制研究,基于数值模拟技术优化充氩舱内保护氩气的流动行为,保证焊接气氛达标;提出多脉冲激光点焊的方法严格控制焊点尺寸,确定控制交叉焊点尺寸的关键激光工艺参数及优化的工艺区间;分析激光作用下快速凝固条件对锆合金材料微观组织的影响;开展锆合金焊点高温高压蒸汽环境下腐蚀后氧化膜特性研究,分析焊点耐腐性较母材降低的原因,揭示激光焊点表面氧化膜的生长机制,并提出可改善其耐腐蚀性的措施。提出采用科恩达空气刀调节舱室内气流行为,设计固定和可旋转两把空气刀结构提升舱室换气量,使一部分射流气附着于工件表面上流动,实现焊接过程中工件表面的可靠保护和快速冷却。设计主排气口与辅助排气口相配合的结构在焊前快速降低舱室中的水氧含量,加速焊接过程中舱室的换气与散热。当可旋转Coanda空气刀角度为30-45°,进气流量为60-120 L/min时,获得了最优的气体流动形态。为实现格架焊点尺寸的精确控制,提出了多脉冲激光点焊的方法,确定了控制交叉焊点尺寸的关键激光工艺参数及优化的工艺区间。为获得熔宽及余高满足要求的焊点,需采用适当较大的脉冲峰值功率和脉冲个数,以及较小的脉冲宽度。得到了优化的工艺参数:脉冲激光的单脉冲能量约为22-27 J,脉冲宽度约为6-9 ms,脉冲个数为4-7个。激光作用于锆合金后,焊点晶粒尺寸增大,原母材中第二相粒子β-Nb和Zr(Nb,Fe)2消失。焊点经过退火处理后,晶粒取向一致性增加,在柱状晶内和晶间析出第二相粒子β-Nb和Zr(Nb,Fe)2,原焊点组织中残留的β-Zr相发生分解,转变为α-Zr相和β-Nb相。进一步,揭示了锆合金激光焊点氧化膜生长机制,发现氧化膜组织相转变和第二相粒子是影响氧化膜生长的主要原因。焊点表面氧化膜/基体金属界面起伏度较小,界面处的应力降低,促进了界面及氧化膜内四方Zr O2相向单斜相ZrO2相转变,加速了腐蚀介质中氧向基体金属的扩散速率,使氧化膜的生长速率加快;另外激光作用后,原母材中耐腐蚀性能高于基体α-Zr相的第二相粒子消失,加速了焊点表面氧化膜的生长。采用650℃保温时间150 min的退火工艺,促进了焊点内耐腐蚀性能更好的第二相粒子析出,抑制焊点表面氧化膜的生长,改善焊点的耐腐蚀性。
[Abstract]:Zirconium alloy frame is an important component of nuclear reactor core, its preparation technology and corrosion resistance of the service process is a key factor to achieve high burnup. Zirconium alloy chemical active, welding process of water and oxygen in atmosphere is very sensitive, so the frame welding to be carried out in the argon chamber, but the continuous multi spot in the process of welding chamber heat and smoke exhaust is the key problem to guarantee welding quality. In addition, in order to avoid wearing the fuel rod and reduce the pressure drop of the cooling medium, the need to strictly control the framework of cross solder joint size. More importantly, after laser welding joint microstructure and zirconium alloy compared differences. Control grid service performance is the key factor of the corrosion resistance of a solder joint. This paper zirconium alloy frame structure, carry out the zirconium alloy cross multi pulse laser spot welding process and solder solder oxide films on the growth mechanism, based on the number of The value simulation technology to optimize the argon argon filled the cabin atmosphere flow behavior, ensure the welding standard; multi pulse laser spot welding method is proposed to strictly control the welding size, determine the key parameters of laser processing and optimization of process control interval cross joint size; analysis of the impact of rapid solidification conditions under the action of laser on the microstructure of zirconium alloy material; development study on the film characteristics of high pressure steam environment zirconium alloy solder joint under high temperature corrosion, corrosion resistance of solder joint due to lower than the parent material, the growth mechanism of oxide film laser welding surface, and proposed can improve the corrosion resistance of the proposed measures. The Coanda air knife regulating cabin airflow behavior, design of fixed and rotating two air cabin ventilation structure lifting knife, a part of gas flow in the attachment on the surface of the work piece, the welding process in the surface of the workpiece can be guaranteed by Support and rapid cooling. The structure of main exhaust port and the exhaust port of the auxiliary design is matched with the rapid decrease of the oxygen content in the water compartment before welding in the welding process, accelerate the cabin ventilation and cooling. When the rotating Coanda air knife angle is 30-45 degrees, the inlet flow rate is 60-120 L/min, the optimal gas flow patterns. To realize accurate control of frame joint size, and puts forward the method of multi pulse laser spot welding, determine the key process parameters of laser and optimization of process control interval size. In order to obtain the cross weld bead width and reinforcement to meet the requirements of the solder joint, and the number of pulses by using appropriate larger pulse peak power, and the smaller the pulse width. The optimized process parameters were obtained: pulse laser pulse energy is about 22-27 J, the pulse width is about 6-9 MS, the pulse number is 4-7. The laser beam on the zirconium alloy solder, the grain size increases Large, original material in the second phase particles of beta -Nb and Zr (Nb, Fe) 2 solder joints disappear. After annealing, the grain orientation consistency increased in columnar grains and intergranular precipitation of second phase particles of beta -Nb and Zr (Nb, Fe) 2, the original residual tissue in beta phase of -Zr solder joint decomposed into a -Zr phase and -Nb phase beta. Further, reveals the laser spot film of zirconium alloy oxide film growth mechanism, found organization and phase transformation of second phase particles is the main factor influencing the growth of oxide film. The oxide / metal interface of solder surface waviness is smaller, at the interface of low stress, and promote the interface in the film Zr O2 tetragonal to monoclinic phase ZrO2 phase transformation, accelerate the diffusion rate of oxygen corrosion medium to the base metal, the film growth rate is accelerated; in addition after laser irradiation, higher than that of the matrix of a -Zr phase corrosion resistance of original material in second phase particles disappear, accelerated The oxide film of solder joint surface growth. The annealing process by 650 DEG C for 150 min, promotes the precipitation of second phase particles and better corrosion resistant solder joint surface oxide film, inhibition of growth, improve the corrosion resistance of the solder joint.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG457.1

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