Crystallization Kinetics of Ti<SUB>50</SUB>Ni<SUB>25</SUB>Cu<SUB>25</SUB> Melt-Spun Amorphous Ribbons

Abstract

The Avrami exponent n of Ti 50 Ni 25 Cu 25 amorphous ribbons during isothermal annealing derived from the Johnson-Mehl-Avrami equation is about 3.0 and shows good agreement with that obtained by Schloßmacher et al. This indicates that the main crystallization mechanism of Ti 50 Ni 25 Cu 25 ribbons is interface-controlled three-dimensional isotropic growth with early nucleation-site saturation. According to the Arrhenius relation, the activation energy for crystallization is 314 kJ/mol. This value is similar to that obtained using the Kissinger method, which implies that the crystallization during continuous heating or isothermal annealing follows a similar crystallization mechanism.

Shape memory characteristics of as-spun and annealed Ti51Ni49 crystalline ribbons

“…Several literatures have reported the annealing effect on the microstructures, textures, martensitic transformations, shape memory properties and crystallization kinetics of melt-spun Ti 50 Ni 25 Cu 25 ribbon [13][14][15][16]. Nevertheless, it is very difficult to control the appropriate annealing conditions for Ti 50 Ni 25 Cu 25 ribbon [17,18].…”

“…Recently, melt-spinning technique has been utilized to fabricate amorphous or crystalline Ti-Ni binary and Ti-Ni-Cu ternary SMA ribbons for various applications. Among them, Ti 50 Ni 25 Cu 25 ribbon was widely studied because of its unique properties, such as small transformation hysteresis, low flow stress level in the martensite state, low sensitivity of the martensitic transformation start (Ms) temperature and easy fabrication for fully amorphous melt-spun ribbons [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. These advantages make Ti 50 Ni 25 Cu 25 ribbon a good candidate for applications, such as actuator and sensor that require short response time at thermal cycle.…”

Effect of milling time on the structure, micro-hardness, and thermal behavior of amorphous/nanocrystalline TiNiCu shape memory alloys developed by mechanical alloying

“…However, the possibility of amorphization during MA can be detrimental to the shape recovery, since SME is attributed to the transformation of crystalline phases. Therefore, to show SME, the crystallization of the amorphous phase by a heating cycle is required after MA [21].…”

Pseudoelasticity response of aged Ti50Ni25Cu25 shape memory ribbon under nanoindentation tests

“…Because amorphous Ti 50 Ni 25 Cu 25 ribbon can be obtained at the as-spun condition, the crystallization behavior of the ribbon has been investigated [20,22]. Many researchers have also carefully investigated the effects of heat-treatment/crystallization temperatures on the properties of the ribbon, including transformation behavior [17,23], microstructure [18,24] and two-way SME [25,26].…”