Hardness and microstructure changes in severely deformed and recrystallized tantalum

Vacuum arc remelted (VAR) pure tantalum was deformed at room temperature to a strain of 4.6 by multipass equal channel angular extrusion through a tool containing an abrupt 90 degree angle. The as-worked microstructure shows a progression from dense dislocation tangles containing primitive dislocation cells at a strain of 1.2, to the development of well defined subgrains with dimensions on the order of hundreds of nanometers at a strain of 4.6. The recrystallization temperature decreases from about 1100C to 900C as the strain increases from 1.2 to 4.6. The recrystallized grain size for the material strained to 4.6 is under 15 microns. The Hall-Petch relationship is found to reasonably predict subgrain size from microhardness measurements in the most severely deformed material.

Hardness and microstructure changes in severely deformed and recrystallized tantalum Conference Paper