The effect of Ti-B on stabilization of Cu-Zn-Al martensite

doi:10.1016/S1359-6462(98)00305-4

Scripta Materialia

Volume 39, Issue 9, 5 October 1998, Pages 1199-1204

https://doi.org/10.1016/S1359-6462(98)00305-4 Get rights and content

Introduction

The application of shape memory effect in devices requires, in many cases, stable and reliable transformation temperatures. However, as a consequence of diffusional processes, in Cu-based shape memory alloys, reverse transformation temperature significantly rises after aging at temperatures above room temperature. This generally unwanted behavior is usually referred to as the stabilization of martensite. Numerous investigations have been carried out on this subject as reviewed by Ahlers (1) and Chandrasekaran et al (2). Within the Cu-based alloys the Cu-Zn-Al are claimed to be more prone to stabilization than Cu-Al-Ni on aging. It has been proposed (3) that in the Cu-Zn-Al the stabilization is due to the interchange of Cu and Zn atoms assisted by vacancies, changing, consequently, the long range order inherited from the β phase. Several methods have been used to inhibit the stabilization of Cu-Zn-Al martensite, namely: reduction of vacancy concentration (4); hot rolled in the parent phase (5) and alloying additions. In the latter case, it has been recently reported that Ti addition at Cu-Zn-Al resulted in lowering the mobility of the vacancies and retarding the stabilization of martensite 6, 7.

Besides the shift of the reverse transformation temperature to higher values, other way to manifest the stabilization is when, after suitable thermal treatment, martensite is induced by stressing at temperatures above the temperature M_s for spontaneous transformation and then aging at constant strain, in this case it is found that the reverse transformation stress is shifted to lower values. This stress shift also depends on stabilization temperature, stabilization time and thermal treatment in the matrix β phase before stabilization.

In the present work we investigate the stabilization behavior of polycrystalline samples of stress induced Cu-Zn-Al and Cu-Zn-Al-Ti-B martensite.

Section snippets

Experimental procedures

Commercial purity copper, zinc and aluminum (with and without Ti-B addition) were melted in sealed quartz tubes in a resistive furnace to obtain ingots whose nominal compositions are shown in Table 1. The melt was vigorously shaken in order to obtain a homogeneous solution. After solidification, the alloy was homogenized at 1073 K for about four days.

From each ingot, slices were cut and were repeatedly hot rolled at 1123 K, the total deformation was 60%. After rolling, the slices remained at

Results

A typical stress-strain curve for Cu-Zn-Al without stabilization is shown in Figure 1 (a). As can be seen, when the sample is unloaded the stress induced martensite disappears completely and the original shape is restored. The point of deviation from linearity in the tensile curve prior and post to plateau region are taken as the critical stress σ_m and σ_β for transformation and reverse transformation processes respectively.

To make comparable stress results originated from different samples it

Discussion

We studied the influence of the aging process in the martensite phase on the stress induced martensite transformation for Cu-Zn-Al and Cu-Zn-Al-Ti-B alloys. However, this type of study is equivalent to an investigation of the changes in the spontaneous transformation temperature M_s by using the Clausius-Clapeyron equation. Consequently, the present findings may be of general application.

The results presented above establish that the addition of Ti-B has a considerable influence on the

Acknowledgements

This research was supported partially by the Comisión de Investigaciones Cientı́ficas de la Provincia de Buenos Aires, by CONICET/FONCYT (PMT–PICT0373) and by the Secretarı́a de Ciencia y Técnica de la UNCentro.

First page preview

Click to open first page preview

View PDF

References (13)

A.Abu Arab et al.
Acta Metall.
(1988)
J Van Humbeeck et al.
Scripta Metall.
(1984)
X Duan et al.
Scripta Metall.
(1989)
Z.G Wei et al.
Mater. Lett.
(1996)
D Segers et al.
Scripta Metall.
(1988)
M. Ahlers, in Proceedings of the International Conference on Martensitic Transformation, p. 786, JIM, Nara...

There are more references available in the full text version of this article.

Cited by (5)

Effect of grain size on the stress-temperature relationship in a β CuAlBe shape memory alloy
2011, Intermetallics
The grain size dependence of the DO₃-18R martensitic transformation start temperature (M_s) and start stress (σ_s) was investigated in a Cu–22.66Al–2.98Be (at.%) alloy. M_s decreases and σ_s increases with the grain size decrease. The σ_s–T relationship is linear, however the slope depends on the grain size. Moreover, the zero stress extrapolated temperature decreases with the grain size decrease and remains lower than M_s. Results are analyzed in a thermodynamical framework.
Phase decomposition in a β Cu-Zn-Al-Ti-B shape memory alloy
2005, Materials Science and Engineering: A
A β Cu–Zn–Al, with and without TiB addition as grain refining, shape memory alloy has been investigated with detail in order to evaluate the influence of this grain refiner on some alloy properties. For Cu–Zn–Al–Ti–B, on isothermal aging in the range of 523–773 K, the β phase was found to decompose by the precipitation of γ phase followed by α phase and eutectoid decomposition. The γ precipitate volume fraction evolution as a function of aging time has been determined and the TTT diagram for the precipitation of both γ and α phases has been constructed. Besides, nonisothermal aging behavior has been investigated by means of differential scanning calorimetry for Cu–Zn–Al and Cu–Zn–Al–Ti–B alloys.
The effect of post-quench aging on stabilization of martensite in Cu-Zn-Al and Cu-Zn-Al-Ti-B shape memory alloys
1999, Materials Science and Engineering: A
The effect of post-quench aging in polycrystalline β Cu–Zn–Al and Cu–Zn–Al–Ti–B on the martensite stabilization has been studied. The samples were heat treated at 1073 K and subsequently quenched into water at 373 K. After the quench, the samples were aged in the β phase, 373 K≤T≤ 403 K, during 300 s ≤t_β≤10⁵ s. The stabilization tests were performed by applying compressive stresses at temperatures above the reverse transformation temperature, A_f followed by martensite aging under constant strain. When unloading the sample, it recovers its original shape but the reverse transformation stress is shifted to lower values. The magnitude of the stress shift, a measure of martensite stabilization, is a function of the thermal treatment and aging time. The process continues until a saturation is reached. It was found that the stress shift saturation value depends on the temperature and the aging time in the β phase. The results show that the stabilization depends on the vacancy concentration and that dislocations can not be the dominating type of vacancy sinks in martensite.
Grain size evolution in Cu-based shape memory alloys
2015, Journal of Materials Science
The stabilization of martensite in Cu-Zn-Al-Ti-B shape memory alloys
2001, Journal De Physique. IV : JP

View full text

Original ArticlesThe effect of Ti-B on stabilization of Cu-Zn-Al martensite

Introduction

Section snippets

Experimental procedures

Results

Discussion

Acknowledgements

First page preview

Acta Metall.

Scripta Metall.

Scripta Metall.

Mater. Lett.

Scripta Metall.

Original Articles
The effect of Ti-B on stabilization of Cu-Zn-Al martensite