Loading Mode and Alloy System Effects On Surface Relief Characteristics of Martensite Plates in Cu-Based Shape Memory Alloys

The present work reports the influence of the loading mode developed during training under constant stress, in bending, applied to lamellar specimens of a Cu-Zn-Al and Cu-Al-Ni Shape Memory Alloys (SMAs), respectively. During training, the specimens were bent by a load fastened at their free end, while being martensitic at room temperature and they lifted the load by One Way Effect (1-WE), during heating up to austenitic field. On cooling to martensite field, the lower concave surface of bent specimens was compressed, and during heating it was elongated, being subjected to a series of tension-compression cycles, during heating-cooling, respectively. Conversely, the upper convex surface of bent specimens was elongated during cooling and compressed during heating, being subjected to compression-tension cycles. Considering that the lower concave surface of the specimens was kept in compressed state while the upper convex surface was kept in elongated state, the study reveals the influence of the two loading modes on the width and heights of martensite plates within specimens of the two alloy systems, which were trained under various numbers of cycles. In this purpose, Cu-Zn-Al and Cu-Al-Ni specimens, trained under various numbers of cycles, were prepared and analyzed by atomic force microscopy (AFM) as well as optical and scanning electron microscopy (OM and SEM, respectively). The analysis also included 2D and 3D micrographs corroborated with statistical evaluations in order to reveal the effects of loading mode and initial state (tension or compression) of the specimens on the surface relief characteristics of martensite plates.