Deep drawing technology for tantalum foil: Tantalum is a refractory metal, but annealed pure tantalum possesses excellent room temperature ductility (elongation after fracture ≥20%～30%) and low strain hardening rate, similar to copper or low-carbon steel, making it very suitable for cold deep drawing.
Raw Material Preparation – Key Requirements for Tantalum Foil for Deep Drawing: It must be in a fully recrystallized annealed state (Annealed/M state) to eliminate residual stress from cold rolling and ensure high plasticity. Hard/semi-hard foil is prone to cracking during deep drawing. Thickness Range: Deep drawing typically uses 0.05～0.5mm tantalum strip/foil; 0.03～0.08mm can be used for microcapacitor casings; extremely thin foils (<0.02mm) are usually not deep drawn independently, but are mostly used for padding or coil welding. Grain control: Fine and uniform recrystallized grains are preferred (powder metallurgy R05400 has better isotropy than electron beam melting R05200). Excessively coarse grains will produce "orange peel" defects, affecting surface quality. Surface quality: The surface must be free of scratches, indentations, and oxide spots—micro-defects can become stress concentration sources during deep drawing and large plastic deformation, leading to cracking. Ra ≤ 0.2–0.5 μm is typically required.
Deep drawing process parameters: Processing method: Single or multiple progressive die deep drawing at room temperature. Tantalum does not work harden as quickly as steel; the initial drawing depth can reach 40%–50% of the billet diameter, and the depth-to-diameter ratio (H/D) can reach 1:1 or even higher (multiple drawing can achieve H/D > 4, such as tantalum capacitor casings).
Die design: The punch-die clearance is generally 6%–8% of the material thickness per side (slightly larger than steel) to prevent scratches and excessive thinning. The fillet radius of the die should be large (to prevent cracking), and the blank holder force needs to be precisely controlled to prevent wrinkling. Tool steel is commonly used for the punch, while aluminum bronze, beryllium copper, or DLC (diamond-like carbon)/silicon nitride ceramic coating is recommended for the die to reduce tantalum seizing/galling—tantalum is soft and easily adheres to and wears against the steel die.
Lubrication: A critical and challenging aspect. Chlorinated paraffin oil, sulfurized tallow, special deep-drawing wax, polyethylene film, or DLC coating are commonly used for isolation and lubrication to prevent sticking and surface scratches. Intermediate annealing: If further deformation is required between multiple deep-drawing passes, annealing can be performed at 800–1100℃ under vacuum or high-purity inert gas protection to restore plasticity (care should be taken to prevent oxygen absorption and embrittlement).
