JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS Vol. 16, No. 3-4, March - April 2014, p. 394 - 400 Variation tendencies of shape memory alloys surface relief as a function of training-cycling parameters M.-G. SURU a , C. MOROŞANU b , L.-G. BUJOREANU a,* a Faculty of Materials Science and Engineering, The “Gheorghe Asachi” Technical University of Iaşi, Bd. D. Mangeron 67, 700050 Iaşi, Romania b Department of Mathematics, Alexandru Ioan Cuza University, Bd. Carol I-11, 700506 Iasi, Romania Lamellar specimens of Cu-Zn-Al Shape Memory Alloy (SMA) were trained in bending under as much as 500 cycles, until two-way shape memory effect (2WE) was obtained. Trained specimens were further tested by means of a hydraulic installation where, heating-cooling cycles were performed in oil conditions. Considering that the lower concave surface of the specimens was kept in compressed state while the upper convex surface was kept in elongated state, this study reveals the variation tendencies of the width and height of martensite plates as a function of training-cycling parameters, while considering the effects of different loading modes, namely compression and elongation. The convex and concave regions, of the Cu-Zn-Al specimens in air-trained or oil-cycled conditions after being subjected to large number of cycles, were metallographically prepared and analysed by atomic force microscopy (AFM). The study comprised comparative investigations of 2D and 3D representative profiles corroborated with numerical analysis of large number of recorded data, in order to reveal the effects of the number of cycles, loading mode and environmental conditions, on the general variation tendency of the surface relief of martensite plates. (Received February 5, 2014; accepted March 13, 2014) Keywords: Shape memory alloys, Training-cycling, Surface relief, Martensite plates, Statistical evaluation 1. Introduction Shape memory alloys (SMAs) belong to a class of shape memory materials (SMMs), which have the ability to ‘‘memorise” a previous form, from their thermomechanical history, when subjected to certain stimulus [1]. ‘‘Shape memory” is the term used to describe the main property of SMMs [2]. SMAs have been used in industrial fields [3] for their one-way shape memory effect (1WE) [4], pseudoelasticity (PE) [5] and two-way shape memory effect 2WE [6]. Any SMA with 1WE can revert to its original shape once the low temperature stress- induced martensite phase is heated to A f (austenite transformation finish temperature). Any SMA with 2WE [7] has the potential to change its shape once the low temperature martensite phase is heated to the high- temperature austenite phase, and to revert to its original shape while being cooled back to martensite. Many alloys exhibit shape memory effect, but Ni–Ti- based shape memory alloys, have to date, provided the best combination of materials properties for most commercial applications [8]. On the other hand, Cu–Zn– Al alloys provide a more economical alternative to Ni –Ti. Shape memory properties in copper-base alloys [9] are associated with the thermoelastic martensitic transformation taking place from hard austenite phase (β 2 ) to soft martensite (β’ 2 ) [10]. The transformation occurs without diffusion [11], and, consequently, martensite inherits a part of long-range order of the β phase [12]. The β 2 CuZnAl phase, at high temperatures, displays a body centred cubic (bcc) disordered structure [13]. However, in the interest range of temperatures it exhibits a long-range ordered structure called B2 [14]. The martensitic product phase has a 9R structure [15], which can be well described as an face centred tetragonal (fct) lattice with stacking faults every three planes. Martensitic transformation can be induced by cooling [16], spontaneous transformation, or by applying mechanical stress [17]. During cooling, transformation starts at a critical temperature Ms and completes at M f [18], below which, theoretically, the crystal is purely martensitic. On heating, the reverse martensitic transformation starts at A s temperature and ends at A f . When applying a mechanical stress, such as tension or compression, at temperature above A f , stress induced martensitic transformation starts at a critical stress level, and ends at almost constant stress, when a critical deformation is reached [19]. However, this stress-induced martensite is unstable at temperatures above A f , and therefore reverse phase transformation to austenite occurs, at a lower stress level, during unloading [20]. Thus, a hysteretic loop is formed, in cooling/heating cycles [21] as well as in isothermal loading/unloading cycles [22]. The aim of the present paper is to determine the general variation tendencies of SMA surface relief as a function of number of cycles, heating-cooling environment and loading mode (elongation and compression).