提高全钽电容器外壳质量的研究

【作者】 张行健；

【导师】 王志法；

【作者基本信息】 中南大学 ， 材料学， 2005， 硕士

【摘要】 钽电容器体积小,容量大,可靠性高,寿命长,是雷达、宇航飞行器、导弹等不可缺少的电子元件之一。用纯钽板冲制液体全钽电容器外壳在国内一直不能生产,主要的原因是:现在国内的钽板在深冲引伸钽外壳时容易产生开裂、起皱、桔皮等现象,成品率低,难以达到高性能,高可靠性的要求。因此,在国内开展高质量的全钽电容器外壳的研制工作就显得格外迫切。本文借用金相、SEM等检测手段对冲制成型和未成型的钽壳进行了研究,探求其未成型的原因,并重新制定深冲前钽板的加工及热处理工艺,探讨了深冲工艺和加工热处理对全钽电容器外壳成型性的影响,以期提高全钽电容器外壳的冲制质量。在此基础上,利用TEM等手段,又开展了钽板加工硬化的研究,探明钽板加工硬化率低的原因,以便为获得高质量的全钽电容器外壳提供实验和理论依据及指导。研究结果表明: 1) 不能深冲成形的钽板存在晶粒粗大的问题,细小均匀的晶粒是保证钽板深冲成合格钽电容器外壳的重要条件。 2) 用粉末冶金工艺生产的锭坯,其开坯后的钽板经90%冷变形后,起始再结晶温度为1100℃,再结晶退火温度定为1150℃～1200℃为宜。用电子束熔炼的锭坯,其开坯后的钽板经90%冷变形后,起始再结晶温度为800℃左右,退火温度在850℃～900℃为宜。 3) 退火温度选择不适当会造成钽板再结晶晶粒粗大,从而对深冲后钽电容器外壳表面质量带来不利的影响。 4) 变形量的增大有利于细化深冲钽板再结晶晶粒。电子束熔炼的钽坯锭经90%变形量,850℃退火40min或在900℃退火10min后获得较细晶粒。适当的高温短时退火可以细化晶粒。粉末冶金工艺生产的钽坯锭经90%变形量,1200℃退火40min可以获得细小均匀的晶粒。 5) 纯钽的宏观加工硬化速率比较低,冷加工时变形量达到90%以上都不需要中间退火。其中电子束熔炼的钽板的加工硬化速率又要低于粉末冶金工艺生产的钽板。电子束熔炼工艺生产的钽板和粉末冶金工艺生产的钽板的应变硬化指数n都较低,反映钽板对加工硬化不是很敏感。 6) 通过TEM观察,发现变形95%后,纯钽的位错密度都不是很高,存在有位错胞亚结构。钽的层错能高,位错容易交滑移,使位错更多还原

【Abstract】 Tantalum capacitor has some advantages, such as small in size, large in capacitivity, high in reliability, long in life and is one of important electronic component in radar, aerospace vehicle, missile etc. The pure tantalum plates can not be deep drawn to cans of wet tantalum capacitor in China because the phenomena such as fissuring, folding or orange peeling appear easily during deep drawing. It is necessary to develop the study on high-quality tantalum cans of tantalum capacitors.By using optical microscope (OM) and scanning electron microscopy (SEM) etc, unshaped and shaped tantalum cans were investigated to find the reason of unshaped problem. To meet the requirement of high-quality tantalum cans, some processing and heat treatment technologies were developed and effect of deep drawing, processing and heat treatment technologies on moldability of tantalum cans was studied. What’s more, the micromechanism about low work hardening rate of pure tantalum was discussed by transmission electron microscope (TEM) in order to provide the experimental and theoretical guide for preparing high-quality tantalum cans. The results showed that:1. The tantalum plates that can not be deep drawn in actual production had great grain size and grain refinement was very important in guaranteeing good surface quality of tantalum cans.2. With a rolling deformation of 90%, the recrystallization temperatures(T_R) of the electron beam melting (EBM) pure tantalum is about 800℃ and proper annealing temperature is 850℃~900℃.The T_R of the powder metallurgy (PM) pure tantalum is 1100℃ and proper annealing temperature is 1150℃~1200℃.3. Improper annealing temperature can make recrystal grain coarse that can bring adverse effect to surface quality of tantalum cans.4. The grains become fine with increasing of reduction rate. With a rolling deformation of 90%, the relatively fine grain of EBM pure tantalum can be obtained after being annealed at 850℃ for 40 min and 900℃ for 10 min. For PM pure tantalum, the proper annealing process is 1200℃ for 40 min. The grain of tantalum can be refinedwith increasing of annealing temperature and decreasing of annealing time.5. Work hardening rate of pure tantalum is low. Pure tantalum didn’t need interannealing when cold rolling reduction was more than 90%.The work hardening rate of EBM pure tantalum was lower than that of PM pure tantalum. Strain hardening exponent n of both EBM and PM pure tantalum was relatively low, which indicate pure tantalum was insensitive to work hardening.6. TEM analysis indicated the dislocation density of pure tantalum was not high and dislocation cells occurred after 95% cold rolling reduction. Because stacking fault energy (SFC) of tantalum is high, dislocation cross slip easily that can lower the dislocation density. On the other hand, according to the tree dislocation theory, it was assumed that when pure tantalum was deformed at room temperature slip system was mainly {110} <111>, while secondary slip systems were seldom activated. So density of tree dislocation penetrating the main slip plane was low and the interaction between dislocations was weak, which led to low work hardening rate of pure tantalum.更多还原