Role of Nickel Content in One-Way and Two-Way Shape Recovery in Binary Ti-Ni Alloys

The shape recovery characteristics of titanium nickelide with an Ni content of 50.0 at % and 50.7 at % were studied in a wide range of structures obtained as a result of cold drawing with an accumulated true strain of e = 0.52 and subsequent annealing in the 250 to 700 °C temperature range. Shape memory effect (SME) inducing was carried out by bending using a non-isothermal loading mode, which made it possible to reveal implementing elastic strain in the equiatomic alloy up to 12% and thereby increase the total shape recovery by a factor of 1.5. The obtained results prove that the Ni content strongly affects the value and specific features of changes of the shape recovery characteristics with loading strain as well as grain/subgrain size. In equiatomic alloy, the total recovery strain manifests its maximum of 13.5–15% and the recovery strain of 9% at a loading strain range of 12 to 14%. In Ni-rich alloy, the total recovery strain manifests its maximum of 20% and the recovery strain of 14% at a loading strain range of 15 to 21%. The maximum two-way SME value correlates with the residual strain in both alloys and reaches its maximum of 3.0% in a material with a recrystallized structure. Varying the loading strain value under bending in the 11 to 21% range allows regulation of the temperature of shape recovery in Ni-rich alloy in the 45 to 80 °C range.

Структурные особенности наноструктурного эквиатомного сплава TiNi при многократных мартенситных превращениях

The paper describes in detail a study dealing with the influence of multiple martensite transformations on the equiatomic alloy of the TiNi system microstructure. Thermocyclic treatment of the equiatomic alloy in the nanocrystalline state obtained by the intensive torsional plastic deformation method was carried out.

Microstructure and Mechanical Properties of Precipitate Strengthened High Entropy Alloy Al10Co25Cr8Fe15Ni36Ti6 with Additions of Hafnium and Molybdenum

High entropy or compositionally complex alloys provide opportunities for optimization towards new high-temperature materials. Improvements in the equiatomic alloy Al17Co17Cr17Cu17Fe17Ni17 (at.%) led to the base alloy for this work with the chemical composition Al10Co25Cr8Fe15Ni36Ti6 (at.%). Characterization of the beneficial particle-strengthened microstructure by scanning electron microscopy (SEM) and observation of good mechanical properties at elevated temperatures arose the need of accomplishing further optimization steps. For this purpose, the refractory metals hafnium and molybdenum were added in small amounts (0.5 and 1.0 at.% respectively) because of their well-known positive effects on mechanical properties of Ni-based superalloys. By correlation of microstructural examinations using SEM with tensile tests in the temperature range of room temperature up to 900 °C, conclusions could be drawn for further optimization steps.