Thermodynamic study of the low-temperature phase B19′ and the martensitic transformation in near-equiatomic Ti-Ni shape memory alloys

Abstract

Experimental information on the transformation temperatures and the thermodynamic properties of the near-equiatomic TiNi alloys is analyzed. Special attention is paid to the estimation of T 0 temperature from experimental M s and A f temperatures. The properties of the TiNi low-temperature phase (B19') are evaluated from selected experimental data by using a two-sublattice model. The Ti-Ni phase diagram including the B19' phase is then calculated. It reveals that the equiatomic TiNi parent phase (B2) remains stable from high temperatures until 370 K, and then the B19' phase becomes thermodynamically stable as a linear compound under 370 K. Thermodynamic quantities such as the T 0 temperature and transformation enthalpy are also calculated and compared with experimental data. Further, the M s temperature is predicted and compared with data from different sources.

Effect of Mechanical Alloying and Sintering on Ni–Ti Powders

“…[10,11] The SME is a thermoelastic process that can be induced by cooling of the B2 phase to a temperature below Ms or by application of an externally applied stress. [12,13] During cooling, the so-called parent phase undergoes a diffusionless transformation to a martensitic product with a triclinic distortion of the B19 type [14] lattice or a monoclinic type [15,16] crystal structure. In Ni-rich alloys, the Ni 4 Ti 3 precipitate is the closest phase that can induce memory effect.…”

Challenges of Using Elemental Nickel and Titanium Powders for the Fabrication of Monolithic NiTi Parts

“…One of the most important aspects of NiTi alloy is its martensitic transformation. Previous researches [4,16] (Fig. 5) have shown that the temperature at which martensitic transformation starts (M s ) is extremely sensitive to chemical composition of NiTi (Ni/Ti ratio).…”

“…The magnitude of this latent heat shows the amount of NiTi which can participate in martensitic transformation. [4,16] …”

Influence of Heat Treatment on Phase Transformation of Ni-rich TiNi Foils Produced <i>via</i> Ultrafine Laminates

“…The transformation heat of this sample is 24.6 J/g which is comparable with those of bulk TiNi alloys. 17) A practical demonstration of foil usability for a three dimensional (3D) actuator was done by constraining a foil into a flower-shape and apply the aging treatment at 773 K for 36 ks. The results of this experiment are shown in Fig.…”