Local electrochemical investigation of single grains of polycrystalline Cu-16%Zn-8%Al alloy

Abstract

Estudos eletroquímicos localizados de grãos individuais de uma liga policristalina Cu-16%Zn-8%Al foram realizados em solução de tampão borato (pH 8,4) por meio da técnica eletroquímica com microcapilar. As orientações dos grãos, determinadas pelo método de retro-reflexão de Laue, foram predominantemente próximas à direção [110], sugerindo uma texturização da amostra. As medidas de potencial em circuito aberto mostraram que o menor potencial de estado estacionário foi observado para o grão que possui o maior número de degraus na superfície da liga. Os experimentos de voltametria cíclica sugeriram que a orientação do Cu 2 O segue a orientação do substrato na liga Cu-Zn-Al, enquanto que CuO cresce independentemente.Local electrochemical studies of single grains of a polycrystalline Cu-16%Zn-8%Al alloy were investigated in borate buffer solution (pH 8.4) by means of microelectrochemical technique. The grain orientations, which were determined by the Laue back-reflection method, were predominantly close to [110] direction, suggesting that the sample was texturized. The open circuit potential measurements showed that the lower steady state potential was observed for the grain which has the highest number of steps on the alloy surface. The cyclic voltammetry experiments suggested that the orientation of Cu 2 O follows the substrate one in the Cu-Zn-Al alloy, while CuO grows independently.Keywords: Cu-Zn-Al alloys, shape memory alloys, single grains, borate buffer, microelectrochemical cell IntroductionSince the discovery of shape memory effect (first in Au-Cd alloys and later in Ni-Ti ones) 1,2 great effort and funds have been spent on the study of shape memory alloys (SMAs) by virtue of their attractive properties such as low cost, pseudoelasticity and two-way shape memory effect (TWSME). [3][4][5][6][7] Cu-based and Ni-Ti alloys fill up these requisites, for instance. Owing to these unique properties, SMAs have been classified as "smart" or "intelligent" materials along with ferroelectric and piezoelectric ones. 8,9 These materials exhibit a reversible transformation in macroscopic size which is controlled by changes of external conditions such as temperature, pressure or magnetic field.In this context, SMAs have a myriad of applications in the engineering and medical fields including couplings, sensors, actuators, antennas for mobile phones, 10 air conditioning systems, 11 active endoscopes and artificial muscle components for robotics. 12 In this work, we report on the local electrochemical investigation of single grains of a polycrystalline Cu-16(wt.%)Zn-8(wt.%)Al alloy. Many studies have only described the fabrication, mechanical properties and physical characterization of SMAs, but electrochemical studies concerning Cu-Zn-Al alloys are hitherto scarce. Celis et al. 13 focused on the corrosion behavior of austenite (β) and martensitic (β') Cu-Zn-Al alloys in different media. They observed that alloys containing more than 15 wt.% Zn may undergo a process called dezincification where Zn is leached out. According t...