Plastic deformation of chromium single crystals at 77 K

Chromium (Cr) is an antiferromagnetic body-centered cubic (bcc) metal with longitudinally polarized spin density waves below 123 K. Virtually nothing is known about the plastic deformation its single crystals and the changes of internal magnetic order around extended defects such as dislocations. The present study provides for the first time a detailed analysis of deformation mechanisms operative in macroscopic single crystals of Cr with 99.999% purity. Samples with different orientations are compressed at 77 K to 2-4% of plastic strain at strain rates around 10^-5 s^-1. The slip trace analysis is made by light microscopy using the Normarski differential interference contrast, more detailed investigations of slip morphology is made by the scanning electron microscopy in conjunction with the electron backscatter diffraction technique to determine sample orientation before/after deformation. The experimental results are reconciled using the theoretical predictions made by an effective yield criterion for Cr that was developed recently using molecular statics studies of an isolated 1/2[111] screw dislocation under stress.