Effect of magnetic-lattice transformations on low-temperature plasticity and fracture of chromium single crystals
V.I. Sokolenko and V.M. Gorbatenko
National Science Center “Kharkov Institute of Physics and Technology” 1 Akademicheskaya Str., Kharkov 61108, Ukrain
Received March 23, 2018, published online July 26, 2018
Analysis of the literature data indicates the interconnection of the lattice and magnetic subsystems of chromium, which predetermined the study of changes in low-temperature plasticity and fracture of chromium as a result of magneto-lattice transformations during thermal cycling in the 373↔77 K regime. For the initial microalloyed Eu single crystals of Cr (the content of impurities Ci = 10–3 wt.%) with orientations  and  along the compression axe, a monotonous growth of the yield point was observed in the temperature range from room temperature to T = Tx ≈ 170 K (Tx is the temperature of cold-brittleness or the temperature of viscous-brittle transition). When temperature was lowered in the interval Tx–4.2 K, the samples broke brittle, with a decrease in the fracture stress, which is due to the growth of local stresses at the concentrators. As a result of thermal cycling ac-companied by multiple phase transformations from the paramagnetic to the antiferromagnetic AF1 and AF2 states and vice versa, a decrease in Tx value of chromium was observed by ≈ 20 K. The effect is related to the occurrence of relaxation processes near stress concentrators due to the displacement of the walls of domain structures and also cyclic striction deformations that compensate for the volume change caused by overheating and supercooling of the sample when a rapid change in temperature.
Key words: chromium single crystals, thermocycling, magnetic-lattice transformations, low-temperature mechanical properties.