Two kinds of body centered cubic (bcc) structure refractory metals, pure Cr and Nb, were subjected to severe plastic deformation through high-pressure torsion (HPT) under applied pressures of 2 and 6 GPa for 2, 3, 4 and 5 revolutions at room temperature. Vickers microhardness is plotted as a function of the distance from the disk center and equivalent strain. It is shown that all hardness values fall on a single curve when they are plotted against equivalent strain for both metals. Vickers microhardness increases with increasing equivalent strain at an early stage of straining and then reaches steady state with the grain size of 200250nm in Cr and 240270nm in Nb irrespective of the applied pressures. In the steady state, there is no changing in hardness even in applying further straining. Tensile and bending tests show that brittle fracture occurs in Cr but in Nb, the strength significantly increases with some ductility after HPT processing.
All Science Journal Classification (ASJC) codes
- General Materials Science
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering