Improve The Quality Of Full-tantalum Capacitors Shell

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.