Study On Mechanical Properties And Microstructures Of Tantalum Foils

Tantalum foil is widely used in electronic industry and other fields.In this paper,the effects of annealing temperature on the microstructures,recrystallization texture and mechanical properties of tantalum foil were studied by unidirectional tensile test,optical microscopy,Vickers micro hardness,scanning electron microscopy(SEM),X-ray diffraction(XRD)and electron backscatter diffraction(EBSD).The size effects of annealed tantalum foils with different thickness were discussed.The main conclusions are as follows:(1)The annealing temperature has a significant effect on the microstructures,recrystallization texture and mechanical properties of tantalum foil.When the annealing temperature is below 900?,tantalum foils only recover and the texture components are mainly ?-fiber represented by strong {001}<110>.When the annealing temperature is900?,the recrystallized nuclei appear in tantalum foils and the texture components are still mainly ?-fiber.When the annealing temperature is above 1000?,tantalum foils recrystallize completely and the grains grow up gradually with the increase of the annealing temperature.In this stage,the ?-fiber gradually disappeared and formed strong?-fiber components represented by {111}<110> and {111}<112>.With the increase of the annealing temperature and the completion of recrystallization,the microstructures of tantalum foils become more homogeneous and the micro hardness decreases gradually until it becomes stable.(2)The annealing temperature has a significant effect on the tensile properties of tantalum foils.In the recovery stage of medium and low temperature,tantalum foils only have elastic deformation and hardly plastic deformation due to the influence of rolling structure.In the recrystallization stage,the microstructures of tantalum foils become homogeneous with the end of the recrystallization,the plastic deformation ability increases gradually and the best annealing temperature is 1100 ?.(3)The tensile properties of tantalum foils with different thickness at room temperature have obvious size effect.As the thickness of tantalum foils decreases from 200?m to30?m,the yield strength and tensile strength increase while the elongation decreases.The constitutive equation of tantalum foil based on Hall-Petch relation considering flow stress and surface layer theory is constructed,and the calculated values are in good agreement with the experimental results.(4)The changes of microstructures and texture before and after tantalum foils deformation were characterized by EBSD.The equiaxed grains are elongated after deformation and the micro texture changes obviously due to the rotation of the grains during deformation.There are lots of low angle boundaries and deformation structures in the grains.The microbands are usually not homogenous distributed in the grains.The morphology of microbands is closely related with the orientations.The density of microbands is largest in the grains with tensile direction // <110>.Most the traces of microbands are inclined 25°-45° with respect with RD,which are usually consistent with slip planes of {110} or {112} which have largest or second largest Schmid factor.