Structural refinement of chromium by severe plastic deformation

In the present study, pure chromium (99.97%) has been deformed by high pressure torsion (HPT). The deformation has been performed clearly above the ductile to brittle transition temperature (320–390 °C) of the material in its recrystallized condition and at room temperature. Specimens with different degrees of deformation have been produced. A reduction of grain size from ≈80 μm to the submicrometer region with typical structural sizes between 50 and ≈500 nm has been found by examinations in the scanning electron microscope (SEM) by means of back scattered electrons (BSE) images and by electron back scatter diffraction (EBSD) measurements. The thermal stability of the microstructures has been investigated after annealing the samples in vacuum for 10 h at 500, 600 and 700 °C. Furthermore, micro hardness measurements have been carried out. The hardness after an applied degree of deformation of 25.8 (von Mises) at room temperature of the deformed sample has been about four times higher than the hardness of the undeformed material. After the heat treatment at 700 °C, the hardness remains about two times higher.