“the Alloying Effect, Martensitic Transformations and Properties of the Melt-Spun Shape-Memory TiNi- and Ni2mnga-Based Alloys”

The results of comparative study of the structural and phase transformations and properties of the binary and multicomponent shape-memory TiNi- and Ni₂MnGa-based alloys in the initial as-cast state, after rapid quenching of the melt, and after subsequent annealing are presented. The melt-spun ribbons were produced by the technique of the planar flow casting of molten alloys onto a cold copper spinning wheel, which yields a cooling rate up to 10⁶ K/s.

The as-cast and melt-spun alloys of the binary Ti-Ni and quasi-binary ternary Ti₅₀Ni_50-xFe_x, Ti₅₀Ni_50-yCo_y, Ti₅₀Ni_25-zCu_z systems were investigated. Specially, the melt-spun shape-memory alloys of chemical composition with deviation from stoichiometric Ti₅₀Ni₂₅Cu_z5 within ± 1 at.% have been produced and analysed. Among the Ni₂MnGa-based as-cast and melt-spun alloys the Ni₅₄Mn₂₁Ga₂₅, Ni₅₄Mn₂₀Fe₁Ga₂₅, Ni₅₀Mn_28.5Ga_21.5, Ni₄₈Mn_28.5Co₂Ga_21.5 and Ni₄₈Mn_28.5Cu₂Ga_21.5 alloys were studied systematically.

The electron-microscopic investigations in situ were performed using HRTEM Tecnai G²30, CM30, JEM 200CX, SEM Quanta 200 Genesis. The θ/2θ X-ray diffraction measurements in situ were carried out using monochromatized copper radiation. Also the electrical resistivity and magnetic susceptibility were measured in wide temperature range (4.2 K – 770 K). The sequence and characteristic temperatures of the onset and finish of the forward and reverse thermoelastic martensitic transformations have been determined for as-cast and melt-spun alloys. It was established that the variation of the chemical composition of alloys permits to regulate the values of the critical temperatures and sequence of martensitic transformations. The tension and bending mechanical tests were performed for determination of the strength and plastic properties and shape-memory characteristics.