Training Effect on Microstructure and Shape Recovery in Ti-Pd-Zr Alloys

Abstract

The training effect of microstructure and shape recovery on Ti-50Pd-xZr (x = 7 and 10) at% and Ti-50Pd-xZr-(5-x)V (x = 1, 2.5, and 4) high-temperature shape memory alloys were investigated. Zr was selected as an alloying element as it is known to improve the shape recovery of TiPd. As a further alloying element, V was selected because it is effective in strengthening TiPd. The dependence of Zr content and V addition on the martensitic transformation (MT) temperature, shape recovery, and training effect were investigated. For example, M f , decreased with increasing Zr from 480 C in Ti-50Pd to 302 C in Ti-50Pd-10Zr. In Ti-50Pd-xZr-(5-x)V, when the total amount of Zr and V was 5 at%, the MT temperatures did not change drastically. The MT temperatures ranged between 350 and 550 C. Shape recovery was investigated using the thermal cyclic test under a constant applied stress in the range of 15 to 200 MPa. Perfect recovery was obtained at low stresses, while irrecoverable strain was observed at high stresses. For Ti-50Pd-2.5Zr-2.5V and Ti-50Pd-1Zr-4V, creep deformation was observed above 150 MPa. To obtain perfect recovery, training (repeated thermal cyclic tests under a constant applied stress) was performed. Perfect recovery was obtained for the alloys by training, except for Ti-50Pd-4Zr-1V. Ti-50Pd-10Zr achieved perfect recovery up to 200 MPa, while Ti-50Pd-1Zr-4V achieved perfect recovery up to 150 MPa. Other alloys achieved perfect recovery at lower stresses of 65 or 50 MPa. The microstructure changed from a random martensite variant to a speci c orientation during training, to accommodate the large strain during deformation. It was found that a strong texture led to perfect shape recovery.

Thermal Cyclic Properties of Ti-Pd-Pt-Zr High-Temperature Shape Memory Alloys

“…Similar behavior was also observed in Ti-50Pd-(7,10) Zr and Ti-50Pd-Zr-V [37]. The lattice parameter b remained the smallest, even after adding Zr or V. The transformation strain was calculated using the orientation relationship between martensite and austenite.…”

Shape Change and Crystal Orientation of B19 Martensite in Equiatomic TiPd Alloy by Isobaric Test

“…From these results, it was found that the shape of the crystal grains in the old parent phases was the long columnar crystal according to the solidification from the hearth side by arc-melting, and the crystal orientations of martensitic variants were different for each cut surface of the button ingot. The transformation strain associated with the martensitic transformation was calculated using the method reported in Sato et al [6] and Kim et al [17] on the basis of the above EBSD results and HTXRD measurements. HTXRD measurements were performed to identify constituent phases and accurate lattice constants before and after the martensitic transformation of the equiatomic TiPd alloy.…”

“…This tendency is in disagreement with the TMA measurement of Figure 1b. Thus, The transformation strain associated with the martensitic transformation was calculated using the method reported in Sato et al [6] and Kim et al [17] on the basis of the above EBSD results and HTXRD measurements. HTXRD measurements were performed to identify constituent phases and accurate lattice constants before and after the martensitic transformation of the equiatomic TiPd alloy.…”

“…In the A1 direction of Figure 5(a-1,2) and the A3 direction of Figure 5(b-1,2), it can be seen that plate-shaped martensitic variants are strongly oriented to (010). This originated from the rearrangement of martensitic variants due to stress-loading [6]. Although the micrographs are not included here, it was Based on the HTXRD measurements and compression tests, the isobaric test was as follows: the compressive specimens with the longitudinal direction between the center side and the edge side of button ingot were heated from room temperature to 923 K (Af or more), cooled to 723 K (Mf or less), heated again to 923 K, and returned to room temperature.…”

“…Moreover, the shape recovery ratio improves with the addition of a third element [4,5]. In addition, Sato et al reported that a complete shape recovery was achieved by the effect of a training process, that is, a repeated isobaric test on the Ti-Pd-Zr alloy [6]. The isobaric test is a process of changing the temperature while applying a load, that is, a process of repeating martensitic transformation with loading.…”