E. G. Zakharova

Orientational dependence of shape memory effects and superelasticity in CoNiGa, NiMnGa, CoNiAl, FeNiCoTi, and TiNi single crystals

The dependence of deforming stresses, shape memory effect (SME), and superelasticity (SE) on the orientation of the single crystal axis, test temperature, and disperse particle size is examined for CoNiGa, NiMnGa, CoNiAl, FeNiCoTi, and TiNi single crystals. The orientational dependence of SME, SE, and temperature interval of the development of martensitic transformations (MT) under loading and SE is established. The influence of disperse particles on magnitudes of SME, SE, and mechanical hysteresis is discussed.

Strain hardening and fracture of austenitic steel single crystals with high concentration of interstitial atoms

Stages in the flow curves, mechanisms of deformation (slip or twinning), evolution of the dislocation structure and fracture are studied in austenitic stainless steel single crystals alloyed with nitrogen (CN = 0–0.7 wt. %) and Hadfield steel in relation to the orientation of the crystal axis of tension, test temperature, and atomic concentrations of nitrogen and carbon. The dislocation-structure pattern (cellular or planar) and deformation mechanisms (slip or twinning) are shown to depend on the matrix stacking-fault energy γsf, friction forces due to solid-solution hardening by interstitial atoms, and crystal orientation. An interrelation between the stages in the flow curves and the type of dislocation structure is found. The contribution of mechanical twinning to the plastic flow of steel crystals is shown to increase with increase in nitrogen and carbon concentrations. The mechanical twinning develops in the early stages of deformation and determines the strain-hardening coefficient and fracture of crystals in high-strength states for interstitial atomic concentration C ≥ 0.5–0.7 wt. %. High deforming stresses due to solid-solution strain hardening by interstitial atoms of nitrogen and carbon in combination with low γsf are found to result in twinning in the <001> orientations. The values of γsf in Hadfield steel single crystals and in austenitic stainless steel single crystals are found experimentally depending on the concentration of nitrogen atoms and test temperature.