The Influence of Hydrogen on Shape Memory Effect and Superelasticity in [001]-Oriented FeNiCoAlTi Single Crystals

Abstract

Using [001]-oriented single crystals of an iron-based alloy (Fe – 28% Ni – 17% Co – 11.5% Al – 2.5% Ti at.%), which were aged at 973 K for 7 h, the influence of hydrogen on the axial-stress temperature response σ0.1(Т), the values of shape-memory effect (SME) and superelasticity (SE) is investigated during thermoelastic γ–α'-martensitic transformation (MT) (γ-FCC – face centered lattice, α'-BCT – body centered tetragonal lattice) under tensile conditions. It is found that saturation of [001]-oriented single crystals of the Fe – 28% Ni – 17% Co – 11.5% Al – 2.5% Ti alloy with hydrogen within 2 h at Т = 300 K and current density j = 50 mA/cm2 results in lower starting temperature, Ms, of a forward MT during cooling and Md temperature, increased strength properties of the high-temperature phase at Md temperature and wider temperature range of SE observation compared to hydrogen-free crystals. It is shown that hydrogen affects but only slightly the SME and SE values, the temperature and stress hysteresis under the above saturation mode. In [001]-oriented crystals aged at 973 K for 7 h, which are saturated with hydrogen and hydrogen-free, the SME and SE values are found to be equal to 7.8–8 and 6.5–6.9%, respectively.