Nano-laminated Structure Pure Tantalum And Its Thermal Stability

In this work nano-laminated structured pure tantalum was processed by equal channel angular press(ECAP)followed by liquid-nitrogen rolling(LNR).The microstructure evolution of nano-laminated structure pure tantalum processed in different rolling reductions was characterized by electron backscatter diffraction(EBSD)?transmission kikuchi diffraction(TKD)and transmission electron microscope(TEM).Mechanical properties were characterized by microhardness and tensile tests.The result shows that with the increase of rolling reduction,the lamella spacing of nano-laminated structure tantalum reduced constantly and decreased to a refinement limit of about 40 nm.The tensile strength and microhardness increased with decrease of the lamella spacing,exhibiting maximum tensile strength of ?1.3 GPa.However,the elongation and ductility reduced at the same time.When the lamella spacing reduced below100 nm,the relation between yield strength and lamella spacing deviated from the Hall-Petch relationship.The fracture model changed from ductile fracture to brittle fracture and the elongation decreased obviously.Relatively stronger ? fiber texture and relatively weaker ? fiber texture are formed during the rolling of ECAPed tantalum.When the rolling reduction is greater than 60%,the strongest texture component becomes {111}<110>.The fraction of low angle grain boundaries(LAGBs)of nano-laminated structure tantalum increased obviously during annealing at 1100?.? fiber texture are strengthened while ? fiber texture weakens after annealing.For the nano-laminated structure tantalum with large rolling reduction before annealing(>60%),it is almost completely {111}<112> single texture component after recrystallization.