Microstructural Characterization of a Laser Surface Remelted Cu-Based Shape Memory Alloy

Murillo Romero Da Silva,Simon Pauly,Tobias Gustmann,Witor Wolf,Piter Gargarella,Claudemiro Bolfarini,Jürgen Eckert,Claudio Shyinti Kiminami

doi:10.1590/1980-5373-mr-2017-1044

Abstract

Cu-based shape memory alloys (SMAs) present some advantages as higher transformation temperatures, lower costs and are easier to process than traditional Ti-based SMAs but they also show some disadvantages as low ductility and higher tendency for intergranular cracking. Several studies have sought for a way to improve the mechanical properties of these alloys and microstructural refinement has been frequently used. It can be obtained by laser remelting treatments. The aim of the present work was to investigate the influence of the laser surface remelting on the microstructure of a Cu-11.85Al-3.2Ni-3Mn (wt%) SMA. Plates were remelted using three different laser scanning speeds, i.e. 100, 300 and 500 mm/s. The remelted regions showed a T-shape morphology with a mean thickness of 52, 29 and 23 µm and an average grain size of 30, 29 and 23µm for plates remelted using scanning speed of 100, 300 and 500 mm/s, respectively. In the plates remelted with 100 and 300 mm/s some pores were found at the root of the keyhole due to the keyhole instability. We find that the instability of keyholes becomes more pronounced for lower scanning speeds. It was not observed any preferential orientation introduced by the laser treatment.

Highlights

Shape memory alloys (SMAs) are a class of smart materials that exhibit a property known as shape memory effect (SME)[1,2]
In our previous work[10], we have studied the effect of laser surface remelting on the mechanical properties and thermal behavior of a Cu-11.85Al-3.2Ni-3Mn SMA
The microstructural characterization was carried out using optical (OM), scanning (SEM) and transmission electron microscopy (TEM), employing a Nikon EPIPHOT-300 optical microscope, a Hitachi Tabletop Microscope TM-1000 SEM and a Philips CM-120 transmission electron microscope, respectively

Summary

Introduction

Shape memory alloys (SMAs) are a class of smart materials that exhibit a property known as shape memory effect (SME)[1,2]. The SME can be defined as the ability to recover the original shape and size of a specimen after plastic deformation by heating the alloy above a critical temperature[1,2]. This effect is related to a thermoelastic martensitic transformation and a crystallographic subgroup relation between austenitic and martensitic phases[1]. SMAs have attracted significant attention and interest in recent years for a wide range of commercial applications, due to the outstanding properties that they present. The application of SMAs in the electronic industry is in good progress as well due to the growing interest in the use of shape memory based actuators[3,6]

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