Laser surface remelting of the Cu-11.85Al-3.2Ni-3Mn (% WT) shape memory alloy

Abstract

Shape memory alloys (SMA) are alloys which undergo martensitic transformation due to an external solicitation (temperature, stress, strain or magnetic field) and are capable of recovering permanent deformation when heated above a critical temperature. The most used shape memory alloys are Ti-Ni- and Cu-based. Cu-based alloys have some advantages when compared with Ti-Ni-based as better thermal and electrical conductivity, a relatively lower cost and are easier to process (Ti-Ni-based alloys show high reactivity with oxygen). The main disadvantage of Cu-based SMAs is the low ductility. This property is improved by decreasing the grain size and by a reduction of microstructural segregations. This can be achieved at the surface of structural components after laser remelting, through which the surface of the material is re-melted by a laser beam and solidifies under extremely high cooling rates (on the order of 1010 K/s) depending on the parameters used. The microstructural refinement at the surface improves the mechanical properties and also affects the martensitic transformation and the shape memory behavior, since the martensitic transformation temperature is inversely proportional to the grain size. In this context, the aim of the present work is to investigate the influence of laser surface remelting in the microstructure, thermal stability, and mechanical properties of plates of a Cu-11.5Al-3.2-Ni-3Mn (wt. %) SMA obtained by suction casting. The samples were characterized by optical and scanning electron microscopy, electron backscattered diffraction, differential scanning calorimetry, X-ray diffraction, X-ray tomography, microhardness and tensile tests. (AU)