Fabrication of Ti-Ni-Zr Shape Memory Alloy by P/M Process

Abstract

This work focuses on the fabrication of Ti-Ni-Zr high-temperature shape memory alloy by powder metallurgy (P/M) process. The effects of fabrication conditions on the microstructure and shape memory characteristics of Ti-50.2 mol%Ni-5 mol%Zr alloy were investigated. In this research, elemental Ti, Ni and Zr powders were used. These powders were mixed by a planetary ball mill at a rotational speed of 500 rpm for milling times of 0.6 ks (mixed powder) and 720 ks (MAed powder). The mixtures were sintered by a pulse-current pressure sintering equipment at 1153 K for sintering times of 1.8 ks and 1.2 ks. The solution treatment was carried out at various temperatures between 1073 K and 1273 K to homogenize the microstructure of the as-sintered alloy. The microstructure of the alloy became more homogeneous with an increase in solutiontreatment temperature. In the case of the mixed powder, however, Zr-rich phases were observed in the microstructure of the solution-treated alloy. The alloy solution-treated at 1173 K showed a yielding behavior in the stress-strain curve, and the tensile strength and elongation of the alloy were more than 350 MPa and 2.5%, respectively. On the other hand, in the case of the MAed powder, the microstructure of the as-sintered alloy was homogeneous. The P/M alloy showed higher transformation temperatures than those of the wrought alloy. But, the alloy showed no shape memory effect and poor tensile property due to contamination of the MAed powder.

Influence of Zirconium Percentage on Microhardness and Corrosion Resistance of Ti50 Ni50-xZrx Shape Memory Alloys

“…While Ti atoms migrate to form TiO 2 and TiO particles, residual Ni atoms diffuse into the TiNi matrix to form Ni-rich regions, and then the Ni 4 Ti 3 (223) and Ni 10 Zr 7 (422) phases appear 18,19 . Also in the N5 and N10 alloys, other phases appear, e.g., λ1 and NiZr phases and the coexistence of the austenite and martensite phases, which was also found by other authors 19,20 . Table 2 shows the transformation temperatures of these alloys.…”

Stimulation of Electro-oxidation Catalysis by Bulk-Structural Transformation in Intermetallic ZrPt3 Nanoparticles

“…We have synthesized NPs of an ordered alloy (intermetallic compound) of an early d -metal and Pt, ZrPt 3 (ZrPt 3 NPs), and tailored their bulk structure by controlled annealing. It is known that the bulk structure of Zr-based alloys is sensitive to external stimuli such as pressure or temperature, often exhibiting shape-memory effects . We have demonstrated that a temperature-induced structural transformation in the ZrPt 3 NPs from cubic to hexagonal structures lowers the bulk free energy and, in turn, elevates the surface energy.…”

“…It is known that the bulk structure of Zrbased alloys is sensitive to external stimuli such as pressure or temperature, often exhibiting shape-memory effects. 28 We have demonstrated that a temperature-induced structural transformation in the ZrPt 3 NPs from cubic to hexagonal structures lowers the bulk free energy and, in turn, elevates the surface energy. The catalytic activity and stability of the ZrPt 3 NPs are significantly enhanced through the structural transformation, as the result of the elevated surface energy and the lowered bulk free energy.…”

Structure and shape memory effect in a Ni54Mn25Ga20Gd1 alloy with a high transformation temperature

“…Current HTSMAs systems include Cu-based alloys, NiAl, NiTi-based alloys (NiTiHf, NiTiZr, NiTiPd, etc.) [1][2][3][4][5][6][7], but until now some problems have remain unresolved. The brittleness of NiTiZr and NiTiHf limits their practical use [1,2].…”

“…[1][2][3][4][5][6][7], but until now some problems have remain unresolved. The brittleness of NiTiZr and NiTiHf limits their practical use [1,2]. NiAl and Cu-based HTSMAs are considered unstable [4,5] because of precipitate phase formed at high temperature, which are detrimental to the shape memory effect.…”