Pseudoelastic cycling in Cu-Al-Be single crystals: Interaction with diffusive phenomena

Abstract

Abstract. CuAlBe alloys exhibit martensitic transformations and several properties related to this transformation such as the shape memory effect, pseudoelasticity and the two way shape memory effect. In this work results concerning pseudoelastic cycling of CuAlBe single crystals are presented and discussed. Particularly noticeable is the strong effect of diffusive phenomena on the stress strain curves obtained at test temperatures between 333 K and 373 K. In effect, a stronger stabilization of the martensite is observed during cycling as compared with the stabilization effect upon static conditions, which was found to be negligible at the same test temperatures. Results also indicate that the recovery of the austenitic phase plays a significant role during cycling. The generation of vacancies and the increase in their mobility have been considered in order to explain the observed behavior.

Shape memory alloys as an effective tool to damp oscillations

“…Furthermore, the kinetics of the diffusive phenomena is controlled by the martensite stabilization and by changes in parent material recovery, such as pseudo-elastic cycling [149,150]. For the CuAlBe system, the pseudo-elastic fatigue of single crystals exhibits a nonhomogeneous decrease in the critical stresses and mechanical hysteresis during cycling [150,156]. In the following section, a brief revision of the basic characteristics of the pseudo-elastic behavior of CuAlBe single crystals is presented.…”

“…Pseudo-elastic cycling of CuAlBe single crystals causes a strong mechanical evolution after a few hundred cycles [149,156]. Figure 46 shows the main features that characterize pseudo-elastic cycling in the samples; several r-e curves obtained from sample ''cabsc1m4'' at 353 K with a crosshead speed of 0.1 mm min -1 are shown [156].…”

“…Figure 46 shows the main features that characterize pseudo-elastic cycling in the samples; several r-e curves obtained from sample ''cabsc1m4'' at 353 K with a crosshead speed of 0.1 mm min -1 are shown [156]. An obtained reference cycle was found to deform the sample up to 10.5 % for a crosshead speed of 0.1 mm min -1 ; pseudoelastic cycling was then performed at 10 mm min -1 until a deformation of 8.3 % was reached.…”

“…A more detailed example concerning the evolution of the cycling and recovery of the b phase [156] obtained for sample ''cab2m1'' is presented in Fig. 47a.…”

“…The behavior can be fitted to an exponential growth curve with a time constant larger than the one obtained for the martensite dynamic stabilization (time constants of 780 min and 150 min, respectively). The strong difference in time constants can be explained considering that the recovery of the austenitic structure takes place under quasistatic conditions, while the time constant which describes the martensitic stabilization corresponds to an enhanced dynamic effect [149,156].…”