Orthorhombic lattice deformation of CuAlBe shape-memory single crystals under cyclic strain

Abstract

X-ray diffraction experiments were carried out to prove that X-ray methods can be used to assess strain-induced fatigue in CuAlBe shape-memory alloys. The pseudoelastic fatigue behaviour of CuAlBe single crystals presents a strong decrease of the critical stress of the martensitic transformation. During the fatigue test, the austenitic lattice exhibits a lattice distortion. This lattice distortion evolves during the fatigue test: the austenitic cubic lattice ( 1 ) tends to transform gradually towards an orthorhombic one. Various hypotheses concerning this lattice distortion are proposed.

Shape memory alloys as an effective tool to damp oscillations

“…Moreover, considering that the initial amount of vacancies should be close to the equilibrium concentration, differing from the start conditions usually used to explore the behavior associated with the stabilization of martensite in these alloys. This point will not be further analyzed here, and in fact, it is still unknown which structure should be the final one after the stabilization of the martensite [165]. A last point we would like to emphasize is the noticeable difference in the kinetics constants if static and dynamic stabilization are compared.…”

“…A last point we would like to emphasize is the noticeable difference in the kinetics constants if static and dynamic stabilization are compared. Tidu et al [165] explain the strong stabilization as a consequence of the structural change of martensite, which is not complete in each cycle and an inherited disorder in the b phase. However, it is still an open question why this does not occur under static conditions.…”

Development of a stress-induced martensitic transformation criterion for a Cu–Al–Be polycrystalline shape memory alloy undergoing uniaxial tension

“…The EBSD measurements were performed in a JEOL model JSM 6300 scanning electron microscope with INCA software. In this software, the crystallographic parameters of Cu-Al-Be must be input as follows: DO 3 bcc, a o = 5.82 Å and special group Fm 3m (225) [32]. The uniaxial tensile tests were then conducted on a Deben-Gatan Microtest tensile device (Gatan, Inc., Pleasanton, California, United States), which was coupled to an optical microscope from Leica MZ APO.…”

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

“…The experiments presented so far do not allow to precisely assessing the physical mechanism behind the dynamic stabilization, moreover considering that the initial amount of vacancies should be close to the equilibrium concentration, differing from the start conditions mentioned above. Tidu et al, have shown that CuAlBe single crystals with the equilibrium concentration of vacancies, and pseudoelastically cycled, show in the phase a change in the deformation state corresponding to a tendency to form an othorrombic cell [8]. This change should be inherited from the martensite which is indeed altered due to cycling.…”

“…Additionally, the changes in the Ms temperatures which are obtained after quenching the phase have been explained considering the retained vacancies and their evolution to equilibrium [7].These authors considered that the variation in the amount of vacancies induce a change in the concentration of Be with a corresponding change in Ms. An interesting point here is that the reported experiments concerning pseudoelastic cycling performed by Siredey et al [6] started with a concentration of vacancies equal or close to the equilibrium one, which leave it open the questions about the physical mechanisms responsible for the variations obtained after cycling. Tidu et al have reported a change in the deformation of the phase just after pseudoelastic cycling [8]. This lattice distortion was considered by the authors as a consequence of a structural change of martensite which might take place during pseudoelastic cycling.…”